Heat Transfer Experiments in a Confined Jet Impingement Configuration Using Transient Techniques

2011 ◽  
Vol 133 (9) ◽  
Author(s):  
Florian Hoefler ◽  
Nils Dietrich ◽  
Jens Wolfersdorf
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Jet Impingement ◽  
Fast Response ◽  
Heat Fluxes ◽  
Thermochromic Liquid Crystal ◽  
Turbine Blade Cooling ◽  
Transient Techniques

A confined jet impingement configuration has been investigated in which the matter of interest is the convective heat transfer from the air flow to the passage walls. The geometry is similar to gas turbine blade cooling applications. The setup is distinct from usual cooling passages by the fact that no crossflow and no bulk flow directions are present. The flow exhausts through two staggered rows of holes opposing the impingement wall. Hence, a complex 3-D vortex system arises, which entails a complex heat transfer situation. The transient thermochromic liquid crystal (TLC) method was used in previous studies to measure the heat transfer on the passage walls. Due to the nature of these experiments, the fluid as well as the wall temperature vary with location and time. As a prerequisite of the transient TLC technique, the heat transfer coefficient is assumed to be constant over the transient experiment. Therefore, it is the scope of this article to qualify this assumption and to validate the results at discrete locations. For this purpose, fast response surface thermocouples and heat flux sensors were applied, in order to gain information on the temporal evolution of the wall heat fluxes. The linear relation between heat flux and temperature difference could be verified for all measurement sites. This validates the assumption of a constant heat transfer coefficient. Nusselt number evaluations from independent techniques show a good agreement, considering the respective uncertainty ranges. For all investigated sites, the Nusselt numbers range within ±9% of the values gained from the TLC measurement.

Heat Transfer Experiments in a Confined Jet Impingement Configuration Using Transient Techniques

2010 ◽  
Author(s):  
Florian Hoefler ◽  
Nils Dietrich ◽  
Jens von Wolfersdorf
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Direction ◽  
Jet Impingement ◽  
Thermochromic Liquid Crystal ◽  
Transient Techniques ◽  
Nusselt Numbers ◽  
The Heat Transfer Coefficient ◽  
Good Agreement

A confined jet impingement configuration has been investigated in which the matter of interest is the convective heat transfer from the airflow to the passage walls. The geometry is similar to gas turbine applications. The setup is distinct from usual cooling passages by the fact that no crossflow and no bulk flow direction are present. The flow exhausts through two staggered rows of holes opposing the impingement wall. Hence, a complex 3-D vortex system arises, which entails a complex heat transfer situation. The transient Thermochromic Liquid Crystal (TLC) method was used to measure the heat transfer on the passage walls. Due to the nature of the experiment, the fluid as well as the wall temperature vary with location and time. As a prerequisite of the transient TLC technique, the heat transfer coefficient is assumed to be constant over the transient experiment. Therefore, additional measures were taken to qualify this assumption. The linear relation between heat flux and temperature difference could be verified for all measurement sites. This validates the assumption of a constant heat transfer coefficient which was made for the transient TLC experiments. Nusselt number evaluations from all techniques show a good agreement, considering the respective uncertainty ranges. For all sites the Nusselt numbers range within ±9% of the values gained from the TLC measurement.

scholarly journals Deterioration in Heat Transfer to Fluids at Supercritical Pressure and High Heat Fluxes

1969 ◽  
Vol 91 (1) ◽  
pp. 27-36 ◽  
Author(s):  
B. S. Shiralkar ◽  
Peter Griffith
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
High Heat ◽  
Supercritical Pressure ◽  
Heat Fluxes ◽  
Bulk Temperature ◽  
Operating Pressure ◽  
The Heat Transfer Coefficient

At slightly supercritical pressure and in the neighborhood of the pseudocritical temperature (which corresponds to the peak in the specific heat at the operating pressure), the heat transfer coefficient between fluid and tube wall is strongly dependent on the heat flux. For large heat fluxes, a marked deterioration takes place in the heat transfer coefficient in the region where the bulk temperature is below the pseudocritical temperature and the wall temperature above the pseudocritical temperature. Equations have been developed to predict the deterioration in heat transfer at high heat fluxes and the results compared with previously available results for steam. Experiments have been performed with carbon dioxide for additional comparison. Limits of safe operation for a supercritical pressure heat exchanger in terms of the allowable heat flux for a particular flow rate have been determined theoretically and experimentally.

The Effect of Swirl, Inlet Conditions, Flow Direction, and Tube Diameter on the Heat Transfer to Fluids at Supercritical Pressure

1970 ◽  
Vol 92 (3) ◽  
pp. 465-471 ◽  
Author(s):  
B. Shiralkar ◽  
P. Griffith
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Supercritical Pressure ◽  
Heat Fluxes ◽  
Operating Conditions ◽  
Tube Diameter ◽  
Inlet Temperature ◽  
The Heat Transfer Coefficient

An investigation has been made of the factors governing the heat transfer coefficient to supercritical pressure fluids, particularly at high heat fluxes. The deterioration in heat transfer to supercritical carbon dioxide has been experimentally studied with reference to the operating conditions of mass velocity and heat flux, tube diameter, orientation, tape induced swirl, inlet temperature, and pressure. A detailed comparison has been made with the apparently contradictory results of other investigators, and operating regions, in which the heat transfer coefficient behaves differently, have been defined. The terms used to describe these regions are the Reynolds number, a heat-flux parameter, and a free-convection parameter.

Nucleate Boiling Characteristics of R-113 in a Small Tube Bundle

1992 ◽  
Vol 114 (2) ◽  
pp. 425-433 ◽  
Author(s):  
P. J. Marto ◽  
C. L. Anderson
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Tube Bundle ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Average Heat Transfer Coefficient ◽  
Average Heat

Heat transfer measurements were made during nucleate boiling of R-113 from a bundle of 15 electrically heated, smooth copper tubes arranged in an equilateral triangular pitch. The bundle was designed to simulate a portion of a refrigeration system flooded-tube evaporator. The outside diameter of the tubes was 15.9 mm, and the tube pitch was 19.1 mm. Five of the tubes that were oriented in a vertical array on the centerline of the bundle were each instrumented with six wall thermocouples to obtain an average wall temperature and a resultant average heat transfer coefficient. All tests were performed at atmospheric pressure. The majority of the data were obtained with increasing heat flux to study the onset of nucleate boiling and the influence of surface “history” upon boiling heat transfer. Data taken during increasing heat flux showed that incipient boiling was dependent upon the number of tubes in operation. The operation of lower tubes in the bundle decreased the incipient boiling heat flux and wall superheat of the upper tubes, and generally increased the boiling heat transfer coefficients of the upper tubes at low heat fluxes where natural convection effects are important. The boiling data confirmed that the average heat transfer coefficient for a smooth-tube bundle is larger than obtained for a single tube.

Inverse Estimation of Heat Transfer Coefficient and Reference Temperature in Jet Impingement

2020 ◽  
Vol 142 (9) ◽  
Author(s):  
Anil Ramkishanrao Kadam ◽  
Vijaykumar Hindasageri ◽  
G. N. Kumar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Steady State ◽  
Transfer Coefficient ◽  
Jet Impingement ◽  
Impinging Jets ◽  
Reference Temperature ◽  
Present Technique ◽  
Transient Heat Flux

Abstract Applications of impinging jets are wide-ranging from cooling to heating in industrial as well as domestic field. Most of the reported heat transfer distribution data to and from impinging jets have been found from steady-state measurements. This study utilizes the solution to three-dimensional (3D) inverse heat conduction problem to estimate transient temperatures on the impingement side. Then, the temperature gradient is determined near the impingement wall (∼0.01 mm inside) with which transient heat flux is estimated on the impingement side. Instead of steady-state values, transient heat flux and corresponding wall temperatures are utilized in a thin foil technique to find out heat transfer coefficient and reference temperature simultaneously. The scope of the present technique is examined through its application to impinging jets with various configurations such as laminar jet, turbulent jet, hot jet, cold jet, and multiple jets. In all cases, estimations are reasonably close. The application of this inverse technique can be extended to any configuration of jet impingement irrespective of geometry of nozzle (circular/rectangular), the orientation of nozzle (orthogonal/inclined), the temperature of a jet (hot/cold), Reynolds numbers (laminar/turbulent), the nozzle-to-plate spacing (any Z/d), and roughness of the plate surface. The effect of plate thickness on the accuracy of the present technique is also studied. Up to 5 mm thick plates can be used in impinging jet applications without worrying much on accuracy. The use of the present technique significantly reduces the experimental cost and time since it works on transient data of just a few seconds.

3D Thermal Stress Model for SiC Power Modules

2008 ◽  
Vol 600-603 ◽  
pp. 1227-1230
Author(s):  
Bang Hung Tsao ◽  
Jacob Lawson ◽  
James D. Scofield ◽  
Clinton Laing ◽  
Jeffery Brown
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Thermal Stress ◽  
Transfer Coefficient ◽  
Maximum Shear Stress ◽  
Cvd Diamond ◽  
Heat Fluxes ◽  
Von Mises Stress ◽  
Device Placement

Three dimensional models of both single-chip and multiple-chip power sub-modules were generated using ANSYS in order to simulate the effects of various substrate materials, heat fluxes, heat transfer coefficients, and device placement configurations on temperature and thermal stress contours. Alumina, aluminum-nitride, and CVD diamond were compared as substrates. Heat fluxes of 100 to 500 watts/cm2 resulted in SiC device junction temperatures in the range of 350 to 650 K. The predicted maximum operating temperature for a chip, to which 300 watts/cm2 of heat flux was applied, would be 239°C (512 K). In the applied heat flux range, the minimum and maximum Von Mises stress of a simulated single SiC device sub-module was between 1.2 MPa to 2.4 GPa. The maximum shear stress at 300 watts/cm2 was predicted to be 243 MPa. Both the maximum and minimum chip temperature decreased with increasing heat transfer coefficient from 25 to 2500 watts/m2 K. With modest cooling, represented by a heat transfer coefficient (hconv) of 250 watts/m2 K, SiC chips operated at 300 watts/cm2 power density maintained junction temperatures Tj < 400 K. If consistent with simulation results, CVD diamond integrated substrates should be superior to those comprised of AlN or Al2O3. Asymmetric device placement in the multi-chip module proved more effective at avoiding potential hot spots than the symmetric configuration.

Performance of a Flexible Evaporator for Loop Heat Pipe Applications

2008 ◽  
Author(s):  
Mukta S. Limaye ◽  
James F. Klausner
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Pipe ◽  
Heat Fluxes ◽  
Loop Heat Pipe ◽  
Maximum Heat ◽  
Maximum Heat Transfer ◽  
Maximum Heat Flux

A flat and flexible evaporator, which conforms to contoured surfaces, has been developed for loop heat pipe applications. A loop heat pipe (LHP) is a passive, two phase heat transfer device that uses a porous membrane in the evaporator to circulate fluid. A number of flexible membranes have been tested as evaporator wicks that have a length of 12.7 cm and heated area of 50.6 cm2. For cellulose, polyethylene, and blotting paper membranes, maximum heat fluxes of 0.43, 1.5 and 2.9 W/cm2 have been observed, respectively. The maximum heat transfer coefficients measured for these membranes are 551, 876, and 2100 W/m2-K, respectively. The best performance was observed by a membrane made of a fibrous cotton matrix, typically used as gauze. This material has a large pore size and high wettability with water. When tested in a rigid, brass evaporator, the maximum heat flux observed is 5.95 W/cm2, and the maximum heat transfer coefficient is 2865 W/m2-K. A flexible evaporator is fabricated using a heat sealable, flexible barrier pouch, and the cotton matrix membrane is sealed inside. The maximum measured heat flux for the flexible evaporator is 3.2 W/cm2 and maximum measured heat transfer coefficient is 1165 W/m2-K. The observed reduction in heat transfer as compared to the rigid evaporator is due to the poor contact between the evaporator and membrane. It is concluded that for the flexible evaporator membranes considered, the heat transfer mechanism is boiling and the maximum heat flux is limited by the wicking rate of the membrane. For a given membrane, the wicking rate increases with a reduction in the wicking length and decreases with an increasing rate of evaporation. To further improve the performance of the flexible evaporator, it is necessary to ensure efficient vapor removal from the evaporator as well as maintaining good contact between the membrane and the evaporator surface.

Concerning the Effect of Surface Material on Nucleate Boiling Heat Transfer of R-113

2011 ◽  
Author(s):  
R. Hosseini ◽  
A. Gholaminejad ◽  
Mahdi Nabil ◽  
Mohammad Hossein Samadinia
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Nucleate Boiling ◽  
High Heat ◽  
Heat Fluxes ◽  
Surface Material ◽  
Effect Of Surface

This paper presents results of an experimental investigation carried out to determine the effects of surface material on nucleate pool boiling heat transfer of refrigerant R113. Experiments were performed on horizontal circular plates of brass, copper and aluminum. The heat transfer coefficient was evaluated by measuring wall superheat and effective heat flux removed by boiling. The experiments were carried out in the heat flux range of 8 to 200kW/m2. The obtained results have shown significant effect of surface material, with copper providing the highest heat transfer coefficient among the samples, and aluminum the least. There was negligible difference at low heat fluxes, but copper showed 23% better performance at high heat fluxes than aluminum and 18% better than brass.

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