| 1. |
- Ahangar Zonouzi, S., et al.
(författare)
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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
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Ingår i: Experimental Thermal and Fluid Science. - : Elsevier. - 0894-1777 .- 1879-2286. ; 91, s. 155-165
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Experimental study of the subcooled flow boiling heat transfer of magnetic nanofluid in a vertical tube under magnetic field
- 2020
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Ingår i: Journal of thermal analysis and calorimetry (Print). - : Springer. - 1388-6150 .- 1588-2926. ; 140:6, s. 2805-2816
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Dryout characteristics of natural and synthetic refrigerants in single vertical mini-channels
- 2015
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Ingår i: Experimental Thermal and Fluid Science. - : Elsevier. - 0894-1777 .- 1879-2286. ; 68, s. 257-267
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Dryout characteristics of R1234yf in a uniformly heated vertical mini-channel
- 2013
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Ingår i: UK Heat Transfer Conference.
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Konferensbidrag (refereegranskat)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.
(författare)
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Dryout characteristics of R1234yf in a vertical mini-channel
- 2013
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Ingår i: Eurotherm seminar on convective heat transfer.
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Konferensbidrag (refereegranskat)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.
(författare)
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Flow boiling heat transfer and dryout characteristics of R152a in a vertical mini-channel
- 2014
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Ingår i: Experimental Thermal and Fluid Science. - : Elsevier BV. - 0894-1777 .- 1879-2286. ; 53, s. 207-217
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Flow Boiling Heat Transfer and Dryout Characteristics of R600a in a Vertical Minichannel
- 2015
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Ingår i: Heat Transfer Engineering. - : Informa UK Limited. - 0145-7632 .- 1521-0537. ; 36:14-15, s. 1230-1240
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Flow boiling heat transfer of R600a in a uniformly heated smooth vertical minichannel
- 2013
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Ingår i: Proceedings of the 13th UK Heat Transfer Conference Sept. 2-3, 2013, UKHTC2013. - 9780957229853
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Konferensbidrag (refereegranskat)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-
(författare)
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Flow boiling heat transfer, pressure drop and dryout characteristics of low GWP refrigerants in a vertical mini-channel
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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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