| 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. |
- Gao, Xiufang, et al.
(författare)
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PIV measurement of the flow field in rectangular ducts with 60 circle parallel, crossed and V-shaped ribs
- 2004
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Ingår i: Experimental Thermal and Fluid Science. - : Elsevier BV. - 1879-2286 .- 0894-1777. ; 28:6, s. 639-653
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Tidskriftsartikel (refereegranskat)abstract
- The flow characteristics in rectangular ducts with aspect ratio of 1:8 were investigated experimentally using particle image velocimetry to reveal the function of the inclined ribs as turbulators or generators of favorable flows. Circular ribs were attached on the wide walls and the rib height-to-hydraulic diameter ratio was kept as 0.06 with an attack angle of 60degrees. The obtained results showed strong effects of the inclined ribs on the flow behavior by the development of secondary flows. The magnitude of the streamwise velocity component was detected to have spanwise variation. The flow characteristics were correlated with the previous corresponding heat transfer results obtained by the same authors. (C) 2003 Elsevier Inc. All rights reserved.
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| 7. |
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| 8. |
- Omrane, Alaa, et al.
(författare)
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Temperature measurements of combustible and non-combustible surfaces using laser induced phosphorescence
- 2004
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Ingår i: Experimental Thermal and Fluid Science. - : Elsevier BV. - 1879-2286 .- 0894-1777. ; 28:7, s. 669-676
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Tidskriftsartikel (refereegranskat)abstract
- In recent years, thermographic phosphors used for surface temperature measurements have been developed to suit combustion applications. Pulsed ultraviolet laser radiation at 266 nm and 7 ns duration was used to excite a thermographic phosphor, Mg4FGeO6:Mn, which was adapted to the surface of the investigated material. The laser-induced emission from the phosphor was recorded. A calibration of the phosphorescence lifetime and spectral properties against temperature allowed surface temperature measurements between 298 and 873 K. The techniques were successfully used in a flame spread scenario for two-dimensional measurements of surface temperature on a low-density fiber board. The phosphorescence images were obtained with eight consecutively gated CCD detectors enable pixel by pixel-lifetime evaluation of the phosphorescence by interpolating an exponentialdecay curve to the counts of the corresponding pixel positions of the sequential CCD images. The best precision, better than +/-5 K, was obtained at these temperatures. The technique was also applied to temperature measurements of decomposing materials in a pyrolysis oven. The material investigated was birch particles. Recent development of the technique has allowed other applications, e.g., to such as engine valve and droplets temperature measurements. (C) 2004 Elsevier Inc. All rights reserved.
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| 9. |
- Toffolo, Andrea, et al.
(författare)
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An experimental investigation of the flow field pattern within the impeller of a cross-flow fan
- 2004
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Ingår i: Experimental Thermal and Fluid Science. - : Elsevier BV. - 0894-1777 .- 1879-2286. ; 29:1, s. 53-64
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Tidskriftsartikel (refereegranskat)abstract
- Cross-flow fan performance is strongly influenced by the geometry of the casing, as the latter, in turn, affects the position and the strength of the eccentric vortex that characterizes the operation of this category of fans. The paper presents a systematic experimental investigation of the flow field within the impeller at different throttling conditions and for different geometries of the fan casing. Both pressures and velocities are measured using a three-dimensional five-hole probe that is inserted in the flow. This study helps determine the relationship between the design parameters of the casing and the flow field pattern, and it is part of an extensive work, by the same research group, aimed at establishing a general theory on cross-flow fan operation and at outlining the design guidelines for this particular type of turbomachines
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