| 1. |
- Johansson, Bert, et al.
(författare)
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Application of wedge-shaped hot-film probes in a gas-particle flow
- 2003
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Ingår i: Experimental Thermal and Fluid Science. - 0894-1777. ; 27:2, s. 187-191
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Tidskriftsartikel (refereegranskat)abstract
- A wedge-shaped hot-film probe is used to perform measurements of turbulence intensity and an estimate of the turbulent kinetic energy as well as the Eulerian spectra, macro- and micro-scales of the gas phase in a horizontal pipe flow carrying pulp fibres or spherical particles. In addition, the paper gives a summary of a method for handling the poor frequency response of the probe and discusses how to sort out "bad samples", occurring when the probe is hit by particles.
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| 2. |
- Jørgensen, F.E., et al.
(författare)
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A multi-sensor hot-wire anemometer system for investigation of wall-bounded flow structures
- 2003
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Ingår i: Experimental Thermal and Fluid Science. - 0894-1777. ; 27:2, s. 207-214
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Tidskriftsartikel (refereegranskat)abstract
- This work describes a hot-wire anemometer system and an experimental procedure designed for mapping of the flow structure in disturbed boundary layers. It also briefly presents results from periodically disturbed wing boundary layers. The hot-wire system consists of a number of individual anemometer units, which can be combined to operate multi-sensor probes for simultaneous measurement of velocities in many points. In the present paper, however, only a single probe was used mounted in a dedicated traverse system in order to demonstrate how ensemble averaging can provide knowledge about the growth and decay of organised flow structures, as long as they are periodic in both time and space. The information from this flow structure can then be used in the design of multi-array hot-wire probes for further studies of the non-deterministic stages of the boundary layer transition.
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| 3. |
- Owhaib, Wahib Suleiman, et al.
(författare)
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Experimental investigation of single-phase convective heat transfer in circular microchannels
- 2004
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Ingår i: Experimental Thermal and Fluid Science. - 0894-1777 .- 1879-2286. ; 28:2-3, s. 105-110
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the heat transfer characteristics of single-phase forced convection of R134a through single circular micro-channels with 1.7, 1.2, and 0.8 mm. as inner diameters were investigated experimentally. The results were compared both to correlations for the heat transfer in macroscale channels and to correlations suggested for microscale geometries. The results show good agreement between the classical correlations and the experimentally measured data in the turbulent region. Contrary, none of the suggested correlations for microchannels, agreed with the test data. In the laminar regime, the heat transfer coefficients were almost identical for all three diameters.
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| 4. |
- Theofanous, T. G., et al.
(författare)
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The boiling crisis phenomenon - Part I : nucleation and nucleate boiling heat transfer
- 2002
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Ingår i: Experimental Thermal and Fluid Science. - 0894-1777 .- 1879-2286. ; 26:6-7, s. 775-792
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Tidskriftsartikel (refereegranskat)abstract
- This paper (Part I) and the companion paper (Part II, Exp. Therm. Fluid. Sci. 26 (6-7) (2002) 793- 810) present results of an experimental study on nucleate pool boiling. The experiments were conducted under highly-controlled conditions, using electrically heated, vapor-deposited sub-micron metallic films. A high-speed. high-resolution infrared camera was used to visualize dynamic thermal patterns on the heater's surface over a broad range of heat fluxes, starting from the onset of nucleation and up to boiling crisis. Both fresh heaters and aged heaters were experimented with. The heaters' surface nanomorphology and chemistry were characterized with atomic force microscopy, scanning electron microscopy, and X-ray diffraction spectroscopy. First-of-a-kind experimental data on nucleation and boiling heat transfer at high heat fluxes are presented, and a stark difference between fresh and aged heaters is revealed. Remarkable are the origin, evolution and dynamics of the heater dryout process (leading to burnout), identified quantitatively and captured in action for the first time.
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| 5. |
- Theofanous, T. G., et al.
(författare)
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The boiling crisis phenomenon - Part II : dryout dynamics and burnout
- 2002
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Ingår i: Experimental Thermal and Fluid Science. - 0894-1777 .- 1879-2286. ; 26:6-7, s. 793-810
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Tidskriftsartikel (refereegranskat)abstract
- This is Part II of a two-part paper on the boiling crisis phenomenon. Here we report on burnout experiments conducted on fresh and aged heaters in pool boiling. Critical heat fluxes (CHFs) were found to vary from 50% to 140% of the hydrodynamic limit, previously thought to exist at well-wetting conditions. The burnout events were captured in action (for the first time), using highspeed, high-resolution infrared thermometry. Based on these observations and in conjunction with the levels of CHF reached, we are led to conclude that the phenomenon cannot be (macro)hydrodynamically limited, at east at normal pressure and gravity conditions. Based on infrared thermometry, and aided by X-ray radiography data on void fraction, the case for a scale separation phenomenon in high heat flux pool boiling is argued. This indicates that boiling crisis is controlled by the microhydrodynamics and rupture of an extended liquid microlayer, sitting and vaporizing autonomously on the heater surface. Further. the detailed dynamics of this microlayer, as revealed by our experiments. demonstrates that all previous thermally based models of boiling crisis are inappropriate.
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| 6. |
- 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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| 7. |
- Andersson, Klas, 1977, et al.
(författare)
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Radiation intensity of lignite-fired oxy-fuel flames
- 2008
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Ingår i: Experimental Thermal and Fluid Science. - : Elsevier BV. - 0894-1777. ; 33:1, s. 67-76
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Tidskriftsartikel (refereegranskat)abstract
- The radiative heat transfer in oxy-fuel flames is compared to corresponding conditions in air-fuel flames during combustion of lignite in the Chalmers 100 kW oxy-fuel test facility. In the oxy-fuel cases the flue-gas recycle rate was varied, so that, in principle, the same stoichiometry was kept in all cases, whereas the oxygen fraction in the recycled flue-gas mixture ranged from 25 to 29 vol.%. Radial profiles of gas concentration, temperature and total radiation intensity were measured in the furnace. The temperature, and thereby the total radiation intensity of the oxy-fuel flames, increases with decreasing flue-gas recycle rate. The ratio of gas and total radiation intensities increases under oxy-fuel conditions compared to air-firing. However, when radiation overlap between gas and particles is considered the ratios for air-firing and oxy-fuel conditions become more similar, since the gas-particle overlap is increased in the CO2-rich atmosphere. A large fraction of the radiation in these lignite flames is emitted by particles whose radiation was not significantly influenced by oxy-fuel operation. Therefore, an increment of gas radiation due to higher CO2 concentration is not evident because of the background of particle radiation, and, the total radiation intensities are similar during oxy-fuel and air-fuel operation as long as the temperature distributions are similar.
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| 8. |
- 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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| 9. |
- 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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| 10. |
- Anwar, Zahid, et al.
(författare)
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Flow boiling heat transfer, pressure drop and dryout characteristics of R1234yf : Experimental results and predictions
- 2015
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Ingår i: Experimental Thermal and Fluid Science. - : Elsevier BV. - 0894-1777 .- 1879-2286. ; 66, s. 137-149
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Tidskriftsartikel (refereegranskat)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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