| 1. |
- Ahangar Zonouzi, S., et al.
(author)
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Experimental investigation of the flow and heat transfer of magnetic nanofluid in a vertical tube in the presence of magnetic quadrupole field
- 2018
-
In: Experimental Thermal and Fluid Science. - : Elsevier. - 0894-1777 .- 1879-2286. ; 91, s. 155-165
-
Journal article (peer-reviewed)abstract
- In this paper, the effects of applying magnetic field on hydrodynamics and heat transfer of Fe3O4/water magnetic nanofluid flowing inside a vertical tube have been studied experimentally. The applied magnetic field was resulted from quadrupole magnets located at different axial positions along the tube length. The variations of the local heat transfer coefficient and also the pressure drop of the ferrofluid flow along the length of the tube by applying the magnetic quadrupole field have been investigated for different Reynolds numbers. The obtained experimental results show maximum enhancements of 23.4%, 37.9% and 48.9% in the local heat transfer coefficient for the magnetic nanofluid with 2 vol% Fe3O4 in the presence of the quadrupole magnets located at three different axial installation positions for the Reynolds number of 580 and the relative increase in total pressure drop by applying the magnetic field is about 1% for Re = 580. The increase of the heat transfer coefficient is due to the radial magnetic force toward the heated wall generated by magnetic quadrupole field acting over the ferrofluid flowing inside the tube so that the velocity of the ferrofluid in the vicinity of the heated wall is increased. It is also observed that the enhancement of heat transfer coefficient by applying magnetic quadrupole is decreased with increasing the Reynolds number.
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| 2. |
- Ahangar Zonouzi, S., et al.
(author)
-
Experimental study of the subcooled flow boiling heat transfer of magnetic nanofluid in a vertical tube under magnetic field
- 2020
-
In: Journal of thermal analysis and calorimetry (Print). - : Springer. - 1388-6150 .- 1588-2926. ; 140:6, s. 2805-2816
-
Journal article (peer-reviewed)abstract
- In this study, the subcooled boiling heat transfer of a Fe3O4/water magnetic nanofluid flowing through a vertical tube has been investigated experimentally in the presence and absence of a magnetic field. The magnetic field has been generated by quadrupole magnets. The subcooled boiling heat transfer coefficient and the boiling curves of the ferrofluid flow under the action of the magnetic field have been compared with those in the absence of magnetic field. The results showed that magnetic actuation contributes to have higher heat fluxes at the same wall superheat in comparison with heat fluxes achieved in the no magnetic field case. Therefore, the local subcooled boiling heat transfer coefficients are increased by the magnetic field. The maximum measured enhancement in local subcooled boiling heat transfer coefficient along the length of the tube by applying magnetic field is 46.58% at applied heat flux of 77,000 W m−2 and mass flux of 270 kg m−2 s−1. Furthermore, the enhancement of local heat transfer coefficient by applying magnetic field decreases as the applied heat flux in the subcooled boiling region is increased.
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| 3. |
- Anwar, Z., et al.
(author)
-
Dryout characteristics of natural and synthetic refrigerants in single vertical mini-channels
- 2015
-
In: Experimental Thermal and Fluid Science. - : Elsevier. - 0894-1777 .- 1879-2286. ; 68, s. 257-267
-
Journal article (peer-reviewed)abstract
- Experimental results on dryout of seven refrigerants (R134a, R1234yf, R152a, R22, R245fa, R290 and R600a) in small, single vertical tubes under upward flow conditions are reported in this study. The experiments were conducted under a wide range of operating conditions in stainless steel tubes (0.64-1.70. mm and 213-245. mm heated length). The effects of operating parameters like mass flux, vapor quality, saturation pressure and channel size are discussed in detail. In general, dryout heat flux increased with increasing mass flux, and with increasing tube diameter. No effect of varying saturation temperature was observed. The experimental findings were compared with well-known macro and micro-scale correlations from the literature and it was found that Wu's correlation (in modified form) quite satisfactorily predicted the whole database. A new correlation for prediction of heat flux at dryout conditions is also proposed.
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| 4. |
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| 5. |
- Anwar, Zahid, et al.
(author)
-
Dryout characteristics of R1234yf in a uniformly heated vertical mini-channel
- 2013
-
In: UK Heat Transfer Conference.
-
Conference paper (peer-reviewed)abstract
- Two phase heat transfer in small channels has many practical applications like, miniature heatexchangers, high powered electronics, miniature refrigeration system. Flow boiling in these compactchannels offers many potential advantages like, cope with high heat flux, less fluid inventory,compactness in size. It is well known that two phase heat transfer is drastically reduced when theheater surface becomes partially dry, for any reason. Moving beyond the point where this happensresults in a sharp increase in the temperature of the heated surface and eventually leads towardsburnout. So the upper operational limit (from safety and efficiency point of view) is extremelyimportant to be able to predict.Experimental findings on dryout of Isobutane in a uniformly heated, vertical, stainless steel testsection (1.6 mm inside diameter and 245mm heated length) are reported in this article. Experimentswere conducted at two saturation pressures corresponding to temperatures of 27 and 32 oC, with fivemass fluxes in the range 50-350 kg/m2s and with vapor fractions at the outlet up till dryout conditions.Analysis showed that the dryout heat flux increased with increasing mass flux, while no effect ofvarying the operating pressure was observed. Experimental results were compared with differentcorrelations from the literature, Wu [5], Mikielewicz [6], Callizo [3] and Katto-Ohno [4] correlationsquite satisfactorily predicted the data.
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| 6. |
- Anwar, Zahid, et al.
(author)
-
Dryout characteristics of R1234yf in a vertical mini-channel
- 2013
-
In: Eurotherm seminar on convective heat transfer.
-
Conference paper (peer-reviewed)abstract
- This article reports dryout characteristics of R1234yf in a single, uniformly heated vertical stainless steel channel (d=1.6mm, Lh=245mm). Tests were conducted at 27 and 32 oC saturation temperature with 100-500 kg/m2s. Results of various operating parameters (mass flux, vapor quality, saturation temperature) were discussed in detail. Comparison with R134a revealed lower (about 18%) critical heat flux values with R1234yf. Experimental findings were compared with various macro & micro scale correlations from the literature. Katto- Ohno and Wu’s correlations [7,8] accurately predicted the data from macro and micro scale models respectively.
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| 7. |
- Anwar, Z., et al.
(author)
-
Flow boiling heat transfer and dryout characteristics of R152a in a vertical mini-channel
- 2014
-
In: Experimental Thermal and Fluid Science. - : Elsevier BV. - 0894-1777 .- 1879-2286. ; 53, s. 207-217
-
Journal article (peer-reviewed)abstract
- This article reports on flow boiling heat transfer and dryout characteristics of R152a in a vertical mini-channel. The experiments were carried out with a resistively heated stainless steel tube (1.60mm in diameter and 245mm heated length) at 27 and 32°C saturation temperature. Five mass fluxes in the range 100-500kg/m2s with heat fluxes from 5 to 245kW/m2 were tested. Under similar operating conditions experiments were repeated with R134a in the same setup to compare thermal performance of R152a. The results showed that the heat transfer was strongly influenced by the applied heat flux with insignificant convective contributions. The dryout heat flux increased with increasing mass flux but no effect of varying operating pressure was noticed. The experimental results for heat transfer and dryout heat flux were compared with well-known macro and micro-scale correlations from the literature.
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| 8. |
- Anwar, Zahid, et al.
(author)
-
Flow Boiling Heat Transfer and Dryout Characteristics of R600a in a Vertical Minichannel
- 2015
-
In: Heat Transfer Engineering. - : Informa UK Limited. - 0145-7632 .- 1521-0537. ; 36:14-15, s. 1230-1240
-
Journal article (peer-reviewed)abstract
- Refrigerant-related environmental concerns forced legislative bodies to phase out some types of refrigerants, namely, chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs) and in the near future European legislation will be affecting hydrofluorocarbons (HFCs) as well. Natural refrigerants such as hydrocarbons can thus be expected to be more common as refrigerants in the future. Experimental findings on flow boiling heat transfer and dryout characteristics of isobutane (R600a) in a uniformly heated, vertical, stainless-steel test section (1.60mm inside diameter and 245mm heated length) are reported in this article. The experiments were conducted at two saturation pressures corresponding to the temperatures of 27 and 32 degrees C, with five mass fluxes in the range 50-350kg/m(2)-s and at outlet vapor qualities up to dryout conditions. Analysis showed that heat transfer was primarily controlled by the applied heat flux with insignificant effect of mass flux and vapor quality. The dryout heat flux increased with increasing mass flux; however, no significant effect of varying saturation temperature was observed. The experimental results (for heat transfer and dryout) were compared with different macro and microscale correlations from the literature.
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| 9. |
- Anwar, Zahid, et al.
(author)
-
Flow boiling heat transfer of R600a in a uniformly heated smooth vertical minichannel
- 2013
-
In: Proceedings of the 13th UK Heat Transfer Conference Sept. 2-3, 2013, UKHTC2013. - 9780957229853
-
Conference paper (peer-reviewed)abstract
- Refrigerant related environmental concerns forced legislative bodies to phase out some types of refrigerants namely CFC’s and HCFC’s and in the near future European legislation will be affecting HFCs as well. Natural refrigerants such as hydrocarbons can thus be expected to be more common as refrigerants in the future. Experimental studies with these fluids are important in understanding their performance and potential. Experimental findings on flow boiling of Isobutane in a uniformly heated, vertical, stainless steel test section (1.6 mm inside diameter and 245mm heated length) are reported in this article. Experiments were conducted at two saturation pressures corresponding to the temperature of 27 and 32 oC, with five mass fluxes in the range 50-350 kg/m2s and at outlet vapour qualities up till dryout conditions. Analysis showed that heat transfer was primarily controlled by the applied heat flux with insignificant effect of mass flux and vapor quality. The experimental results were compared with different macro and micro-scale correlations from the literature, and Owhaib, Liu & Winterton and Mikielewicz correlations quite accurately predicted the heat transfer data.
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| 10. |
- Anwar, Zahid, 1981-
(author)
-
Flow boiling heat transfer, pressure drop and dryout characteristics of low GWP refrigerants in a vertical mini-channel
- 2014
-
Doctoral thesis (other academic/artistic)abstract
- Two-phase heat transfer in mini/micro-channels is capable of meeting the high cooling demands of modern high heat flux applications. The phase change process ensures better temperature uniformity and control for local hot spots. Furthermore, these compact channels could be helpful in reducing the required charge and material inventories.Environmental concerns—mainly ozone depletion and global warming—have instigated a search for new alternatives in refrigeration industry. While new compounds are being developed to address stringent legislative demands, natural alternatives are also coming into prominence. A limited number of investigators have reported on thermal performance of such alternatives. The current study is therefore focused on saturated flow boiling heat transfer, pressure drop and dryout characteristics for three low global warming potential (GWP) refrigerants (R152a, R600a and R1234yf) in a vertical mini-channel.In this study experiments were carried out by uniformly heating a test section (stainless steel tube with 1.60 mm inside diameter and 245 mm heated length) at 27 and 32 oC saturation temperature with 50-500 kg/m2s mass velocities. The effects of various parameters of interest (like heat flux, mass flux, system pressure, vapor quality, operating media) on flow boiling heat transfer, frictional pressure drop and dryout characteristics were recorded. R134a, which has been widely used in several applications, is utilized as a reference case for comparison of thermal performance in this study.Experimental results for saturated boiling heat transfer showed strong influence of heat flux and system pressure with insignificant contributions from mass flux and vapor quality. Two phase frictional pressure drop increased with mass flux, vapor quality and with reduced operating pressure. The dryout heat flux remained unaffected with variation in saturation temperature, critical vapor quality in most cases was about 85%. The experimental results (boiling heat transfer, two-phase pressure drop and dryout heat flux) were compared with well-known macro and micro-scale correlations from the literature.
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| 11. |
- Anwar, Zahid, et al.
(author)
-
Flow boiling heat transfer, pressure drop and dryout characteristics of R1234yf : Experimental results and predictions
- 2015
-
In: Experimental Thermal and Fluid Science. - : Elsevier BV. - 0894-1777 .- 1879-2286. ; 66, s. 137-149
-
Journal article (peer-reviewed)abstract
- Flow boiling heat transfer, pressure drop and dryout characteristics of R1234yf in a vertical stainless steel test section (1.60mm inside diameter and 245mm heated length) under upward flow conditions are reported in this article. The experiments were carried out at 27 and 32°C saturation temperatures with five mass fluxes in the range of 100-500kg/m2s while the applied heat flux was in the range of 5-130kW/m2. The experiments were carried out with gradual increase of the applied heat flux til completion of dryout. Under similar conditions, tests were repeated with R134a in the same test setup to compare thermal performance of these two refrigerants. The results showed that boiling heat transfer was strongly controlled by the applied heat flux and operating pressure with insignificant dependence on mass flux and vapor quality. The frictional pressure drop increased with mass flux and vapor quality and decreased with increasing saturation temperature as expected. Signs of dryout first appeared at vapor qualities of 85%, with the values generally increasing with increasing mass flux. The effect of varying system pressure was insignificant. The experimental results (boiling heat transfer, pressure drop and dryout heat flux) were compared with the predictions from well-known correlations (for macro and micro-scale channels) from the literature.
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| 12. |
- Anwar, Zahid, et al.
(author)
-
Flow boiling of R1234yf in a uniform smooth vertical minichannel
- 2013
-
In: Science et Technique du Froid. Comptes Rendus/Refrigeration Science and Technology. Proceedings, 2013, Vol. 3. - : Institut International du Froid. - 9782913149991 ; , s. 1-11
-
Conference paper (peer-reviewed)abstract
- This study describes experimental findings on flow boiling heat transfer with R1234yf in a smooth, vertical stainless steel tube of 1.6 mm inner diameter and 245 mm heated length. Tests were conducted at two saturation pressures corresponding to saturation temperatures of 27 and 32 °C. Other operating parameters were: mass flux 100-500 kg/m²s with heat flux 3-65 kW/m² while quality change was up to 60%. The heat transfer coefficient appeared to be a strong function of the applied heat flux and insignificant effect of mass flux and quality was observed. Increase in saturation temperature/pressure increased the heat transfer performance. Experiments were repeated with R134a in the same test section to compare the two fluids, almost similar results were duplicated with R134a. Experimental results were compared with different correlations, Tran et al. (1996), Gungor and Winterton (1986) and Martín-Callizo et al. (2007) correlations accurately predicted the data.
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| 13. |
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| 14. |
- Badran, Bassam E., et al.
(author)
-
Theoretical Study of a Multilevel Heat Pump for Multi-Source Heating
- 2021
-
In: 6Th Iir Conference On Thermophysical Properties And Transfer Processes Of Refrigerants (Tptpr2021). - : INT INST REFRIGERATION. ; , s. 243-250
-
Conference paper (peer-reviewed)abstract
- Industry and other sectors are currently looking for solutions to decarbonize their processes, including heating, which is mainly based on fossil fuel boilers. Heat pumps can provide heating with higher performance based on their high coefficient of performance (COP). This work considers a multilevel heat pump (MTHP) for multi-source heating, based on a three-stage cascade in which excess heat in the condenser is used for external flows, that can be connected in series or parallel. Several available low GWP refrigerants have been considered, and a multi-parameter selection analysis has been carried out. For low, medium, and high-temperature stages, R1243zf, R-1224yd(Z), and R-1233zd(E) are the best refrigerants, respectively, selected. This system is able to operate between 0 and 160 degrees C, with three heating levels at 60, 110, 160 degrees C (31.75, 21.59, and 29.92 kW, respectively) at a COP of 2.181. The total cooling capacity of the system is 45.08 kW and the total heating capacity is 83.26 kW. The MTHP concept can provide a significant carbon footprint reduction compared to natural gas boilers used in European countries.
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| 15. |
- Bitaraf Haghighi, Ehsan, et al.
(author)
-
Combined effect of physical properties and convective heat transfer coefficient of nanofluids on their cooling efficiency
- 2015
-
In: International Communications in Heat and Mass Transfer. - : Elsevier BV. - 0735-1933 .- 1879-0178. ; 68, s. 32-42
-
Journal article (peer-reviewed)abstract
- The advantages of using Al2O3, TiO2, SiO2 and CeO2 nanofluids as coolants have been investigated by analysing the combined effect of nanoparticles on thermophysical properties and heat transfer coefficient. The thermal conductivity and viscosity of these nanofluids were measured at two leading European universities to ensure the accuracy of the results. The thermal conductivity of nanofluids agreed with the prediction of the Maxwell model within +/- 10% even at elevated temperature of 50 oC indicating that the Brownian motion of nanoparticles does not affect thermal conductivity of nanofluids. The viscosity of nanofluids is well correlated by modified Krieger-Dougherty model providing that the effect of nanoparticles aggregation is taken into account. It was found that at the same Reynolds number the advantage of using a nanofluid increases with increasing nanofluid viscosity which is counterintuitive. At the same pumping power nanofluids do not offer any advantage in terms of cooling efficiency over base fluids since the increase in viscosity outweighs the enhancement of thermal conductivity.
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| 16. |
- Bitaraf Haghighi, Ehsan, et al.
(author)
-
Cooling performance of nanofluids in a small diameter tube
- 2013
-
In: Experimental Thermal and Fluid Science. - : Elsevier. - 0894-1777 .- 1879-2286. ; 49, s. 114-122
-
Journal article (peer-reviewed)abstract
- This article reports convective single-phase heat transfer performance in laminar flow for some selected nanofluids (NFs) in an open small diameter test section. A 0.50 mm inner diameter, 30 cm long stainless steel test section was used for screening single phase laminar convective heat transfer with water and five different water based NFs. Tested NFs were; Al2O3 (two types), TiO2 (two types) and CeO2 (one type), all 9 wt.% particle concentration. The effective thermal conductivity of the NFs were measured with Transient Plane Source (TPS) method and viscosity were measured with a rotating coaxial cylindrical viscometer. The obtained experimental results for thermal conductivity were in good agreement with the predicted values from Maxwell equation. The local Shah correlation, which is conventionally used for predicting convective heat transfer in laminar flow in Newtonian fluids with constant heat flux boundary condition, was shown to be valid for NFs. Moreover, the Darcy correlation was used to predict the friction factor for the NFs as well as for water. Enhancement in heat transfer for NFs was observed, when compared at equal Reynolds number, as a result of higher velocity or mass flow rate of the NFs at any given Reynolds number due to higher viscosity for NFs. However, when compared at equal pumping power no or only minor enhancement was observed.
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| 17. |
- Bitaraf Haghighi, Ehsan, et al.
(author)
-
Experimental study on convective heat transfer of nanofluids in turbulent flow : Methods of comparison of their performance
- 2014
-
In: Experimental Thermal and Fluid Science. - : Elsevier BV. - 0894-1777 .- 1879-2286. ; 57, s. 378-387
-
Journal article (peer-reviewed)abstract
- Turbulent convective heat transfer coefficients of 9 wt% Al2O3/water and TiO2/water nanofluids inside a circular tube were investigated independently at the Royal Institute of Technology, KTH (Sweden) and at University of Birmingham (UK). The experimental data from both laboratories agreed very well and clearly show that Nusselt numbers are well correlated by the equations developed for single phase fluids with the thermophysical properties of nanofluid. The heat transfer coefficients of nanofluids can be compared with those of the base fluids at the same Reynolds number or at the same pumping power. As the same Reynolds number requires higher flow rate of nanofluids therefore such comparison shows up to 15% increase in heat transfer coefficient. However, at equal pumping power, the heat transfer coefficient of Al2O3 nanofluid was practically the same as that of water while that of TiO2 was about 10% lower. Comparing performance at equal Reynolds number is clearly misleading since the heat transfer coefficient can always be increased by increased pumping power, accordingly, the comparison between the fluids should be done at equal pumping power.
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| 18. |
- Bitaraf Haghighi, Ehsan, 1980-, et al.
(author)
-
Measurement of temperature–dependent viscosity of nanofluids and its effect on pumping power in cooling systems
- 2013
-
Conference paper (peer-reviewed)abstract
- Nanofluids are engineered colloids of nanoparticlesdispersed homogenously in a base fluid, which theirthermophysical properties are changed by adding solidnanoparticles. Among the characteristic parameters,viscosity is one of the most important, as it directly affectsthe pumping power in cooling systems. In this study, theviscosity of water based Al2O3, ZrO2, and TiO2 (with 9wt%for all) nanofluids was measured and its impact on pressuredrop in a simple tubular pipe was estimated for bothlaminar and turbulent flow by classical correlations. Theeffect of temperature on the viscosity of these nanofluidswas also studied in the temperature range of 5˚C - 30˚C. Toassess the applicability of the classical correlations, pressuredrops across an open 30cm long, 0.50mm diameterstainless steel test section was measured for water andnanofluids by a differential pressure transducer. Theaverage viscosity increments compared to water in thetemperature range of 5˚C - 30˚C are 105%, 98% and 31% forAl2O3, ZrO2, and TiO2 nanofluids respectively. Moreover, theresults show that the viscosity of nanofluids decreases withthe increase of temperature; however the relative viscosity,which is defined as the viscosity ratio between a nanofluidand its base fluid is constant in 5˚C - 30˚C temperaturerange.
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| 19. |
- Bitaraf Haghighi, Ehsan, et al.
(author)
-
Shelf stability of nanofluids and its effect on thermal conductivity and viscosity
- 2013
-
In: Measurement science and technology. - : IOP Publishing. - 0957-0233 .- 1361-6501. ; 24:10, s. 105301-
-
Journal article (peer-reviewed)abstract
- This study proposes a method and apparatus to estimate shelf stability of nanofluids. Nanofluids are fabricated by dispersion of solid nanoparticles in base fluids, and shelf stability is a key issue for many practical applications of these fluids. In this study, shelf stability is evaluated by measuring the weight of settled solid particles on a suspended tray in a colloid versus time and correlated with the performance change of some nanofluid systems. The effects of solid particle concentration and bath sonication time were investigated for selected nanofluids. The results show the applicability of this simple method and the apparatus to evaluate nanofluid shelf stability. Furthermore, it shows that Stokes' law is not valid for determining the settling time of the tested nanoparticles probably due to their complicated shape and presence of surface modifiers. The effect of shelf stability on thermal conductivity and viscosity was illustrated for some nanofluids. Experimental results show that water-based Al2O3 nanofluids have quite good shelf stability and can be good candidates for industrial applications.
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| 20. |
- Chiu, Justin NingWei, et al.
(author)
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Advanced Thermosyphon Cooling with Nanoporous Structured Mini Channel Evaporators
- 2010
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In: PROCEEDINGS OF THE ASME MICRO/NANOSCALE HEAT AND MASS TRANSFER INTERNATIONAL CONFERENCE, VOL 3. - NEW YORK : AMER SOC MECHANICAL ENGINEERS. - 9780791843918 ; , s. 183-189
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Conference paper (peer-reviewed)abstract
- Attention has been given to enhance boiling surfaces in order to decrease the temperature difference and to increase heat transfer coefficient. Structured surfaces may provide both surface enlargement and artificial nucleation sites, thus ameliorate the heat transfer coefficient. The goal of the present experimental work is to analyze the influence on heat transfer coefficient (HTC) of enhanced surface structures coated on mini channel heat exchanger working in a closed loop thermosyphon system. Experimental tests were carried out with three types of surface enhanced mini channel evaporators: smooth surface, threaded structure and nanoporous coating. The evaporators are single channel half circularly shaped, adapted for filming purpose, measuring 30mm in length and 3mm in diameter. Surface areas of channels are 1.41cm(2). Experiments were conducted in refrigerant 134a at 4.87bar (reduced pressure pr=0.12) and at heat fluxes ranging from 0.7W/cm(2) to 63.8W/cm(2). A high speed video camera was used for visualization of the two-phase flow in the evaporator channel. It is shown that threaded surface provides the highest heat transfer coefficient (HTC) from no load to heat flux of 7.1W/cm(2), the nanoporous structure shows the highest performance between 7.1W/cm(2) and 49.6W/cm(2), and the smooth surface channel exhibits the best HTC from 49.6W/cm(2) and higher. In this paper, the influences of heat flux and surface structures on HTC are discussed, and the impact of refrigerant flow regimes on heat transfer performance is also highlighted.
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| 21. |
- Furberg, Richard, et al.
(author)
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Experimental investigation of an evaporator enhanced with a micro-porous structure in a two-phase thermosyphon loop
- 2009
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In: HT2008. - NEW YORK : AMER SOC MECHANICAL ENGINEERS. - 9780791848487 ; , s. 327-334
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Conference paper (peer-reviewed)abstract
- Following is an experimental study of six different evaporators in a closed two-phase thermosyphon loop system, where the influence of various evaporator dimensions and surfaces was investigated. The evaporators featured a 30 mm long rectangular channel with hydraulic diameters ranging from 1.2-2.7 mm. The heat transfer surface of one of the tested evaporators was enhanced with copper nano-particles, dendritically connected into an ordered micro-porous three dimensional network structure. To facilitate high speed video visualization of the two-phase flow in the evaporator channel, a transparent polycarbonate window was attached to the front of the evaporators. Refrigerant 134A was used as a working fluid and the tests were conducted at 6.5 bar. The tests showed that increasing channel diameters generally performed better. The three largest evaporator channels exhibited comparable performance, with a maximum heat transfer coefficient of about 2.2 W/(cm(2)K) at a heat flux of 30-35 W/cm(2) and a critical heat flux of around 50 W/cm(2). Isolated bubbles characterized the flow regime at peak performance for the large diameter channels, while confined bubbles and chaotic churn flow typified the evaporators with small diameters. In line with previous pool boiling experiments, the nucleate boiling mechanism was significantly enhanced, tip to 4 times, by the nano- and micro-porous enhancement structure.
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| 22. |
- Ghanbarpour, Morteza, et al.
(author)
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An investigation of thermal performance improvement of a cylindrical heat pipe using Al2O3 nanofluid
- 2016
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In: Heat and Mass Transfer. - : Springer. - 0947-7411 .- 1432-1181. ; , s. 1-11
-
Journal article (peer-reviewed)abstract
- In this study, effect of Al2O3 nanofluid on thermal performance of cylindrical heat pipe is investigated. An analytical model is employed to study the thermal performance of the heat pipe utilizing nanofluid and the predicted results are compared with the experimental results. A substantial change in the heat pipe thermal resistance, effective thermal conductivity and entropy generation of the heat pipe is observed when using Al2O3 nanofluid as a working fluid. It is found that entropy generation in the heat pipe system decreases when using a nanofluid due to the lower thermal resistance of the heat pipe which results in an improved thermal performance. It is shown that the proposed model is in reasonably good agreement with the experimental results and can be used as a fast technique to explore various features of thermal characteristics of the nanofluid based heat pipe.
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| 23. |
- Ghanbarpour, Morteza, et al.
(author)
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ANN Modeling to Analyze the R404A Replacement with the Low GWP Alternative R449A in an Indirect Supermarket Refrigeration System
- 2021
-
In: Applied Sciences. - : MDPI. - 2076-3417. ; 11:23
-
Journal article (peer-reviewed)abstract
- Artificial neural networks (ANNs) have been considered for assessing the potential of low GWP refrigerants in experimental setups. In this study, the capability of using R449A as a lower GWP replacement of R404A in different temperature levels of a supermarket refrigeration system is investigated through an ANN model trained using field measurements as input. The supermarket refrigeration was composed of two indirect expansion circuits operated at low and medium temperatures and external subcooling. The results predicted that R449A provides, on average, a higher 10% and 5% COP than R404A at low and medium temperatures, respectively. Moreover, the cooling capacity was almost similar with both refrigerants in both circuits. This study also revealed that the ANN model could be employed to accurately predict the energy performance of a commercial refrigeration system and provide a reasonable judgment about the capability of the alternative refrigerant to be retrofitted in the system. This is very important, especially when the measurement data comes from field measurements, in which values are obtained under variable operating conditions. Finally, the ANN results were used to compare the carbon footprint for both refrigerants. It was confirmed that this refrigerant replacement could reduce the emissions of supermarket refrigeration systems.
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| 24. |
- Ghanbarpour, Morteza, et al.
(author)
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Energy, Exergy, and Environmental (3E) Analysis of Hydrocarbons as Low GWP Alternatives to R134a in Vapor Compression Refrigeration Configurations
- 2021
-
In: Applied Sciences. - : MDPI AG. - 2076-3417. ; 11:13, s. 6226-
-
Journal article (peer-reviewed)abstract
- The phase-down of hydrofluorocarbons and substitution with low global warming potential values are consequences of the awareness about the environmental impacts of greenhouse gases. This theoretical study evaluated the energy and exergy performances and the environmental impact of three vapor compression system configurations operating with the hydrocarbons R290, R600a, and R1270 as alternatives to R134a. The refrigeration cycle configurations investigated in this study include a single-stage cycle, a cycle equipped with an internal heat exchanger, and a two-stage cycle with vapor injection. According to the results, the alternative hydrocarbon refrigerants could provide comparable system performance to R134a. The analysis results also revealed that using an internal heat exchanger or a flash tank vapor injection could improve the system's efficiency while decreasing the heating capacity. The most efficient configuration was the two-stage refrigeration cycle with vapor injection, as revealed by the exergy analysis. The environmental impact analysis indicated that the utilization of environmentally-friendly refrigerants and improving the refrigeration system's efficiency could mitigate equivalent CO2 emissions significantly. The utilization of hydrocarbons reduced the carbon footprint by 50%, while a 1% to 8% reduction could be achieved using the internal heat exchanger and flash tank vapor injection.
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| 25. |
- Ghanbarpour, Morteza, et al.
(author)
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Entropy generation analysis of cylindrical heat pipe using nanofluid
- 2015
-
In: Thermochimica Acta. - : Elsevier BV. - 0040-6031 .- 1872-762X. ; 610, s. 37-46
-
Journal article (peer-reviewed)abstract
- Thermal performance of cylindrical heat pipe with nanofluid is studied based on the laws of thermodynamics. The objective of the present work is to investigate nanofluids effect on different sources of entropy generation in heat pipe caused by heat transfer between hot and cold reservoirs and also frictional losses and pressure drop in the liquid and vapor flow along heat pipe. An analytical study was performed to formulate all sources of entropy generation and the predicted results are compared with experimental ones. Cylindrical miniature grooved heat pipes of 250 mm length and 6.35 mm outer diameter were fabricated and tested with distilled water and water based TiO2 and Al2O3 nanofluids at different concentrations as working fluids. Analytical and experimental results revealed that the entropy generation in heat pipes decreases when nanofluids are used as working fluids instead of basefluid which results in improved thermal performance of the heat pipes with nanofluids.
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| 26. |
- Ghanbarpour, Morteza, et al.
(author)
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Improvement of heat transfer characteristics of cylindrical heat pipe by using SiC nanofluids
- 2015
-
In: Applied Thermal Engineering. - : Elsevier. - 1359-4311 .- 1873-5606. ; 90, s. 127-135
-
Journal article (peer-reviewed)abstract
- An experimental study was performed to investigate the thermal performance of heat pipes using SiC/water nanofluid as the working fluid. Four cylindrical copper heat pipes containing two layers of screen mesh were fabricated and tested with water and water based SiC nanofluids with nanoparticle mass concentrations of 0.35%, 0.7% and 1.0% as working fluids. SiC nanofluids properties and characteristics are evaluated and its effects on thermal performance improvement of screen mesh heat pipes at different concentrations and inclination angles are investigated. Experimental results show that nanofluid improves the performance of the heat pipes and the thermal resistance of the heat pipe with SiC nanofluid decreases with increasing nanoparticle concentration. Thermal resistance reduction of heat pipes by 11%, 21% and 30% was observed with SiC nanofluids containing 0.35 wt.%, 0.7 wt.% and 1.0 wt.% SiC nanoparticles as compared with water. In addition, it is revealed that the inclination angle has remarkable influence on the thermal performance of the heat pipes and the lowest thermal resistance belongs to the inclination angle of 60 in all concentrations. The present investigation indicates that the maximum heat removal capacity of the heat pipe increases by 29% with SiC nanofluids at nanoparticle mass concentration of 1.0 wt.%.
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| 27. |
- Ghanbarpour, Morteza, et al.
(author)
-
Theoretical Global Warming Impact Evaluation of Medium and High Temperature Heat Pumps Using Low GWP Refrigerants
- 2021
-
In: Applied Sciences. - : MDPI AG. - 2076-3417. ; 11:15
-
Journal article (peer-reviewed)abstract
- This study provides a global warming impact analysis of environmentally friendly refrigerants used as replacements for R134a and R245fa. R290, R1234yf, R1234ze(E), R513A and R450A are considered as refrigerants to replace R134a in medium temperature applications. For R245fa, there are five alternative refrigerants, R1224yd(Z), R600, R1336mzz(Z), R1233zd(E) and R1234ze(Z), which are selected for high-temperature applications. The analysis is done considering the emission factors in Brazil, Sweden, Canada and Poland. In Sweden and Brazil, the total equivalent warming impact per heating capacity of R134a is higher than its alternative refrigerants in medium temperature application, although R134a exhibits a higher coefficient of performance than its alternatives. In high-temperature applications, R1336mzz(Z) has the lowest total equivalent warming impact per heating capacity due to its higher coefficient of performance than other tested refrigerants. The highest total equivalent warming impact per heating capacity belongs to R245fa in all countries except in Poland, where R600 exhibits a higher value due to its lower coefficient of performance and the relatively higher emission factor in Poland compared to other selected countries. These results revealed that in addition to the global warming potential, the emission factor associated with the sources of electricity generation has a crucial impact on indirect emissions.
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| 28. |
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| 29. |
- Ghanbarpour, Morteza, et al.
(author)
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Thermal properties and rheological behavior of water based Al2O3 nanofluid as a heat transfer fluid
- 2014
-
In: Experimental Thermal and Fluid Science. - : Elsevier BV. - 0894-1777 .- 1879-2286. ; 53, s. 227-235
-
Journal article (peer-reviewed)abstract
- An experimental investigation and theoretical study of thermal conductivity and viscosity of Al2O3/water nanofluids are presented in this article. Various suspensions containing Al2O3 nanoparticles were tested in concentration ranging from 3% to 50% in mass and temperature ranging from 293K to 323K. The results reveal that both the thermal conductivity and viscosity of nanofluids increase with temperature and particle concentration accordingly while the increase in viscosity is much higher than the increase in thermal conductivity. The thermal conductivity and viscosity enhancement are in the range of 1.1-87% and 18.1-300%, respectively. Moreover, the results indicate that the thermal conductivity increases nonlinearly with concentration, but, linearly with the increase in temperature. In addition, the experimental results are compared with some existing correlations from literature and some modifications are suggested. Finally, the average heat transfer coefficient at different basis of comparisons including equal Reynolds number, fluid velocity and pumping power is studied based on the experimental thermal conductivity and viscosity in fully developed laminar and turbulent flow regimes. It is found that equal Reynolds number as a basis of comparison is highly misleading and equal pumping power can be used to study the advantage of using nanofluid instead of the base fluid.
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| 30. |
- Ghanbarpourgeravi, Morteza, 1985-
(author)
-
Investigation of Thermal Performance of Cylindrical Heatpipes Operated with Nanofluids
- 2017
-
Doctoral thesis (other academic/artistic)abstract
- Nanofluids as an innovative class of heat transfer fluids created by dispersing nanometre-sizedmetallic or non-metallic particles in conventional heat transfer fluids displayed the potential toimprove the thermophysical properties of the heat transfer fluids. The main purpose of this study is toinvestigate the influence of the use of nanofluids on two-phase heat transfer, particularly on thethermal performance of the heat pipes. In the first stage, the properties of the nanofluids were studied,then, these nanofluids were used as the working fluids of the heat pipes. The thermal performance ofthe heat pipes when using different nanofluids was investigated under different operating conditionsexperimentally and analytically. The influences of the concentration of the nanofluids, inclinationangles and heat loads on the thermal performance and maximum heat flux of the heat pipes wereinvestigated.This study shows that the thermal performance of the heat pipes depends not only on thermophysicalproperties of the nanofluids but also on the characteristics of the wick structure through forming aporous coated layer on the heated surface. Forming the porous layer on the surface of the wick at theevaporator section increases the wettability and capillarity and also the heat transfer area at theevaporator of the heat pipes.The thermal performance of the heat pipes increases with increasing particle concentration in all cases,except for the heat pipe using 10 wt.% water/Al2O3 nanofluid. For the inclined heat pipe, irrespectiveof the type of the fluid used as the working fluid, the thermal resistance of the inclined heat pipes waslower than that of the heat pipes in a horizontal state, and the best performance was observed at theinclination angle of 60o, which is in agreement with the results reported in the literature. Otheradvantages of the use of nanofluids as the working fluids of the heat pipes which were investigated inthis study were the increase of the maximum heat flux and also the reduction of the entropy generationof the heat pipes when using a nanofluid.These findings revealed the potential for nanofluids to be used instead of conventional fluids as theworking fluid of the heat pipes, but the commercialization of the heat pipes using nanofluids for largescale industrial applications is still a challenging question, as there are many parameters related to thenanofluids which are not well understood.
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| 31. |
- Grozdek, Marino, et al.
(author)
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Experimental investigation of ice slurry flow pressure drop in horizontal tubes
- 2009
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In: Experimental Thermal and Fluid Science. - : Elsevier BV. - 0894-1777 .- 1879-2286. ; 33:2, s. 357-370
-
Journal article (peer-reviewed)abstract
- Pressure drop behaviour of ice slurry based on ethanol-water mixture in circular horizontal tubes has been experimentally investigated. The secondary fluid was prepared by mixing ethyl alcohol and water to obtain initial alcohol concentration of 10.3% (initial freezing temperature -4.4 degrees C). The pressure drop tests were conducted to cover laminar and slightly turbulent flow with ice mass fraction varying from 0% to 30% depending on test conditions. Results from flow tests reveal much higher pressure drop for higher ice concentrations and higher velocities in comparison to the single phase flow. However for ice concentrations of 15% and higher, certain velocity exists at which ice slurry pressure drop is same or even lower than for single phase flow. It seems that higher ice concentration delay flow pattern transition moment (from laminar to turbulent) toward higher velocities. In addition experimental results for pressure drop were compared to the analytical results, based on Poiseulle and Buckingham-Reiner models for laminar flow, Blasius. Darby and Melson, Dodge and Metzner, Steffe and Tomita for turbulent region and general correlation of Kitanovski which is valid for both flow regimes. For laminar flow and low buoyancy numbers Buckingham-Reiner method gives good agreement with experimental results while for turbulent flow best fit is provided with Dodge-Metzner and Tomita methods. Furthermore, for transport purposes it has been shown that ice mass fraction of 20% offers best ratio of ice slurry transport capability and required pumping power.
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| 32. |
- Grozdek, Marino, et al.
(author)
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Experimental investigation of ice slurry heat transfer in horizontal tube
- 2009
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In: International journal of refrigeration. - : Elsevier BV. - 0140-7007 .- 1879-2081. ; 32:6, s. 1310-1322
-
Journal article (peer-reviewed)abstract
- Heat transfer of ice slurry flow based on ethanol-water mixture in a circular horizontal tube has been experimentally investigated. The secondary fluid was prepared by mixing ethanol and water to obtain initial alcohol concentration of 10.3% (initial freezing temperature -4.4 degrees C). The heat transfer tests were conducted to cover laminar and slightly turbulent flow with ice mass fraction varying from 0% to 22% depending on test performed. Measured heat transfer coefficients of ice slurry are found to be higher than those for single phase fluid, especially for laminar flow conditions and high ice mass fractions where the heat transfer is increased with a factor 2 in comparison to the single phase flow. In addition, experimentally determined heat transfer coefficients of ice slurry flow were compared to the analytical results, based on the correlation by Sieder and Tate for laminar single phase regime, by Dittus-Boelter for turbulent single phase regime and empirical correlation by Christensen and Kauffeld derived for laminar/turbulent ice slurry flow in circular horizontal tubes. it was found that the classical correlation proposed by Sieder and Tate for laminar forced convection in smooth straight circular ducts cannot be used for heat transfer prediction of ice slurry flow since it strongly underestimates measured values, while, for the turbulent flow regime the simple Dittus-Boelter relation predicts the heat transfer coefficient of ice slurry flow with high accuracy but only up to an ice mass fraction of 10% and Re-cf > 2300 regardless of imposed heat flux. For higher ice mass fractions and regardless of the flow regime, the correlation proposed by Christensen and Kauffeld gives good agreement with experimental results. (C) 2009 Elsevier Ltd and IIR. All rights reserved.
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| 33. |
- Grozdek, Marino, et al.
(author)
-
Performance comparison of a static ice-bank and dynamic ice slurry cool thermal energy storage systems
- 2010
-
In: 9th IIR Gustav Lorentzen Conference on Natural Working Fluids (GL2010) Paris, France. - 9782913149748
-
Conference paper (peer-reviewed)abstract
- In this study theoretical evaluation of performance of a three ice based cool thermal energy storage systems is conducted ; (a) static, indirect, external melt ice-on-coil ; (b) dynamic ice slurry type storage with a water and (c) ice slurry distribution system. In order to investigate and assess possible economic and energy saving potential of an ice slurry storage system over conventional static type a computer simulation models were used. The systems were compared for high temperature application, for the purpose of milk cooling in the dairy industry. The product temperature that has to be achieved is +3 °C which requires a secondary coolant temperature to be less than +1 °C. Calculations have been performed on basis of specific user supplied load data for a design day, acquired as an actual case for dairy plant Prehrambeno industrijski kombinat (PIK) in the city of Rijeka, Croatia, and local electricity billing rate structure. The comparison shows that the dynamic cool thermal energy storage system (CTES) is favourable as to energy consumption in all studied cases.
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| 34. |
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| 35. |
- Gustafsson, Marcus, 1987-
(author)
-
Energy efficient and economic renovation of residential buildings with low-temperature heating and air heat recovery
- 2015
-
Licentiate thesis (other academic/artistic)abstract
- With the building sector accounting for around 40% of the total energy consumption in the EU, energy efficiency in buildings is and continues to be an important issue. Great progress has been made in reducing the energy consumption in new buildings, but the large stock of existing buildings with poor energy performance is probably an even more crucial area of focus. This thesis deals with energy efficiency measures that can be suitable for renovation of existing houses, particularly low-temperature heating systems and ventilation systems with heat recovery. The energy performance, environmental impact and costs are evaluated for a range of system combinations, for small and large houses with various heating demands and for different climates in Europe. The results were derived through simulation with energy calculation tools.Low-temperature heating and air heat recovery were both found to be promising with regard to increasing energy efficiency in European houses. These solutions proved particularly effective in Northern Europe as low-temperature heating and air heat recovery have a greater impact in cold climates and on houses with high heating demands. The performance of heat pumps, both with outdoor air and exhaust air, was seen to improve with low-temperature heating. The choice between an exhaust air heat pump and a ventilation system with heat recovery is likely to depend on case specific conditions, but both choices are more cost-effective and have a lower environmental impact than systems without heat recovery. The advantage of the heat pump is that it can be used all year round, given that it produces DHW.Economic and environmental aspects of energy efficiency measures do not always harmonize. On the one hand, lower costs can sometimes mean larger environmental impact; on the other hand there can be divergence between different environmental aspects. This makes it difficult to define financial subsidies to promote energy efficiency measures.
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| 36. |
- Haghighi, Ehsan Bitaraf, et al.
(author)
-
Accurate basis of comparison for convective heat transfer in nanofluids
- 2014
-
In: International Communications in Heat and Mass Transfer. - : Elsevier BV. - 0735-1933 .- 1879-0178. ; 52, s. 1-7
-
Journal article (peer-reviewed)abstract
- Thermal conductivity and viscosity of alumina (Al2O3), zirconia (ZrO2), and titania (TiO2) nanofluids (NFs) were measured at 20°C. All the NF systems were water based and contained 9wt.% solid particles. Additionally, the heat transfer coefficients for these NFs were measured in a straight tube of 1.5m length and 3.7mm inner diameter. Based on the results, it can be stated that classical correlations, such as Shah and Gnielinski, for laminar and turbulent flow respectively, can be employed to predict convective heat transfer coefficients in NFs, if the accurate thermophysical properties are used in the calculations. Convective heat transfer coefficients for NFs were also compared with those of the base fluids using two different bases for the comparison, with contradictory results: while compared at equal Reynolds number, the heat transfer coefficients increased by 8-51%, whereas compared at equal pumping power the heat transfer coefficients decreased by 17-63%. As NFs have higher viscosity than the base fluids, equal Reynolds number requires higher volumetric flow, hence higher pumping power for the NFs. It is therefore strongly suggested that heat transfer results should be compared at equal pumping power and not at equal Reynolds number.
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| 37. |
- Haghighi, Ehsan Bitaraf, et al.
(author)
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Screening Single Phase Laminar Convective Heat Transfer of Nanofluids in a Micro-tube
- 2012
-
In: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 395
-
Journal article (peer-reviewed)abstract
- Nano scale solid particles dispersed in base fluids are a new class of engineered colloidal solutions called nanofluids. Several studies reported enhancement of heat transfer by using nanofluids. This article reports convective single-phase heat transfer coefficients in an open 30 cm long, 0.50 mm internal diameter stainless steel test section. The setup is used for screening single phase laminar convective heat transfer with water and three different nanofluids: water based Al2O3, ZrO2, and TiO2 (all with 9 wt% of particles). A syringe pump with adjustable pumping speed is used to inject fluids into the test section. Thirteen T-type thermocouples are attached on the outer surface of the test section to record the local wall temperatures. Furthermore, two T-type thermocouples are used to measure inlet and outlet fluid temperatures. A DC power supply is used to heat up the test section and a differential pressure transducer is used to measure the pressure drop across the tube. Furthermore, the effective thermal conductivities of these nanofluids are measured using the Transient Plane Source (TPS) method at a temperature range of 20 - 50 degrees C. The experimental average values of heat transfer coefficients for nanofluids are compared with water. Enhancement in heat transfer of nanofluids is observed only when compared at constant Reynolds number (Due to higher viscosity for nanofluids, higher velocity or mass flow rate is required for nanofluids to reach the same Reynolds number). The other methods of comparison: equal mass flow rate, volume flow rate, pressure drop and pumping power did not show any augmentation of the heat transfer coefficient for the tested nanofluids compared to water.
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| 38. |
- Jahedi, Mohammad, 1984-
(author)
-
Experimental and Numerical Investigation of the Quenching Process on Rotary Hollow Cylinder by Multiple Impinging Jets
- 2021
-
Doctoral thesis (other academic/artistic)abstract
- The worldwide competitive market on metal products with higher quality in industry has increased the need to implement more advanced and controllable quenching techniques in the hardening stage of the heat treatment process. Moreover, sustainability and energy efficiency are key factors to consider in the development of advanced quenching techniques. Among various cooling methods that are used in industry, a water impinging jet quenching system is one of the few that offers wide flexibility to adjust cooling rate based on the chemical composition and proper phase transformation in the continuous cooling transformation diagram (CCT) to achieve desired material properties. On an industrial scale, a large number of water impinging jets are placed in the cooling configuration introducing multiple array of jets in the quenching system. In the literature study by the author, there has been interest to study the quenching heat transfer by single water jet in various applications. Even so, little scientific attention has been paid to the multiple array of water impinging jets and the importance of various quenching parameters on the quenching heat transfer with multiple array of jets. This thesis deals with a study of quenching rotary hot hollow cylinder with multiple configurations of water impinging jets. The aim of this investigation is to obtain better understanding of boiling heat transfer phenomena in application of multiple array of water impinging jets and quenching parameters. An experimental test rig was designed to control most influential parameters in quenching experiments. The results of experimental study contained recorded temperature data beneath the quenching surface of a hollow cylinder. A heat conduction inverse solution based on the GMRES method was developed for application of quenching hollow cylinder. This model used the recorded temperature data of quenching experiments to predict surface temperature and heat flux. A thorough parametric study investigated the effect of various quenching parameters and multiple configuration of jets in terms of local and area-averaged heat transfer over surface as well as in the solid material.The local surface boiling curve captured clear effect of multiple array and cyclic variation of heat transfer caused by rotation of hollow cylinder. The delay in onset of wetting front flow growth over the surface, collision of adjacent wetting front flows and creation of upwash flow were captured on the surface heat flux contour plot. Higher heat flux was obtained around stagnation and upwash flow zones over the quenching surface. The relation between jet flow rate and multiple array configuration revealed a trade-off between these two parameters in terms of optimizing the water resource usage and desired cooling rate with this cooling technique.Comprehensive parametric study revealed effect of various quenching parameters in the local heat transfer in the boiling regimes. The results show improvement of heat flux in the film and nucleate boiling is more difficult than transition boiling regime. In the study of area-averaged heat transfer in 1-row array, higher subcooling and jet flow rate enhance the surface heat flux. In contrast, smaller rotation speed, jet-to-jet spacing and initial wall-superheat temperature increase the area-averaged surface heat flux of hollow cylinder. An extra row of nozzles in the array (2-row) also enhanced the area-averaged surface heat flux significantly. The results from comprehensive parametric study of 4-row in-line and staggered configurations have been used to propose correlation for surface area-averaged Nusselt number. In the local heat transfer, two correlations of average and maximum local heat flux at stagnation point of water impinging jet were proposed.The result of this study and the proposed correlations may provide a road map for engineers to design hollow cylinder quenching system with multiple array of water impinging jets based on cooling rate for proper phase transformation and optimized water resource and energy usage in the quenching process.
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| 39. |
- Jarahnejad, Mariam, et al.
(author)
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Experimental investigation on viscosity of water-based Al2O3 and TiO2 nanofluids
- 2015
-
In: Rheologica Acta. - : Springer Science and Business Media LLC. - 0035-4511 .- 1435-1528. ; 54:5, s. 411-422
-
Journal article (peer-reviewed)abstract
- This article investigates the influence of temperature, concentration, and size of nanoparticles, and addition of surfactants on dynamic viscosity of water-based nanofluids containing alumina (Al2O3) and titania (TiO2) nanoparticles. Two viscometers, a capillary and a falling ball, were used for the measurements in the temperature range of 20-50 A degrees C and the particle concentration of 3-14.3 wt.%. The results indicate that the viscosity of nanofluids is reduced by increasing the temperature, similar to their base fluids. Moreover, surfactants, which are used to improve the shelf stability of nanofluids, most likely increase their viscosity. The correlations derived from the linear fluid theory such as Einstein and Batchelor, especially for solid concentration above 1.5 wt.% are not accurate to predict viscosity of nanofluids, while the modified Krieger-Dougherty equation estimates viscosity of nanofluids with acceptable accuracy in a specific range of solid particle size to aggregate size.
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| 40. |
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| 41. |
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| 42. |
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| 43. |
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| 44. |
- Khodabandeh, Rahmatollah, et al.
(author)
-
An experimental investigation of the influence of threaded surface on the boiling heat transfer coefficients in vertical narrow channels
- 2002
-
In: Microscale thermophysical engineering (Print). - : Informa UK Limited. - 1089-3954 .- 1091-7640. ; 6:2, s. 131-139
-
Journal article (peer-reviewed)abstract
- One efficient method of cooling electronics is to use a closed-loop two-phase thermosyphon system. The setup tested here utilizes three small evaporators connected in parallel, each made from a small block of copper in which five vertical channels with diameter 1.5 mm and length 15 mm were drilled. The article presents the experimental results in terms of heat transfer coefficients of smooth surfaces as well as for threaded surfaces. Tests were done at different heat fluxes while maintaining constant system pressure. Tests were performed with heat loads of 30-450 W dissipated through the system. Two different refrigerants, R134a and R600a, were tested. The experimental two-phase flow heat transfer coefficients were compared to correlations from the literature.
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| 45. |
- Khodabandeh, Rahmatollah, et al.
(author)
-
COOLING OF CPU WITH A THERMOSYPHON
- 2008
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In: 2008 SECOND INTERNATIONAL CONFERENCE ON THERMAL ISSUES IN EMERGING TECHNOLOGIES - THEORY AND APPLICATION (THETA). - NEW YORK : IEEE. ; , s. 239-243
-
Conference paper (peer-reviewed)abstract
- In this study the tested evaporator is made from small blocks of copper with I I vertical channels with a diameter of 2.5 mm and length of 30 mm. The riser and downcomer connected the evaporator to the condenser, which is cooled by air in free or forced convection. The condenser is made from 10 mm aluminium heat sink profile of the size of 365x365 mm with a fin length of 20 mm at a distance of 8 mm. In the top part of the heat sink a condenser channel system with 2x2 mm cross section is milled. The CPU used in this study is an Intel Pentium 4 with 3.2 GHz. The maximum heat load to the processor is 104W, and the highest temperature allowed on the processor is 65 degrees C Temperatures are measured for idle, 50% and maximum heat load of the processor at the CPU, evaporator wall, condenser wall and in the ambient. Temperature differences in the thermosyphon system, between the CPU and the evaporator wall, the condenser wall and ambient are presented. Isobutane has been used as the working fluid, due to the fact that it has low saturation pressure and that this refrigerant is friendly to the environment.
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| 46. |
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| 47. |
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| 48. |
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| 49. |
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| 50. |
- Khodabandeh, Rahmatollah, et al.
(author)
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Heat transfer, flow regime and instability of a nano- and micro-porous structure evaporator in a two-phase thermosyphon loop
- 2010
-
In: International journal of thermal sciences. - : Elsevier BV. - 1290-0729 .- 1778-4166. ; 49:7, s. 1183-1192
-
Journal article (peer-reviewed)abstract
- Two-phase flow instabilities which may occur at low and high heat loads were studied for a thermosyphon loop with R134a as refrigerant. The heat transfer surface of the evaporator was enhanced with a copper nano- and micro-porous structure. The heat transfer of the enhanced evaporator was compared to a smooth surface evaporator. Finally, the influence of the liquid level and the inside diameter of the riser on the instability of the system have been investigated. It was found that the enhanced structure surface decreased the oscillations at the entire range of heat fluxes and enhanced the heat transfer coefficient. Three flow regimes were observed: Bubbly flow with nucleate boiling heat transfer mechanism, confined bubbly/churn flow with backflow and finally churn flow at high heat fluxes.
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