Development of a General Dynamic Pressure Based Single-Phase Spray Cooling Heat Transfer Correlation

2011 ◽  
Vol 133 (5) ◽  
Author(s):  
Bahman Abbasi ◽  
Jungho Kim
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Single Phase ◽  
Dynamic Pressure ◽  
Local Heat ◽  
Spray Cooling ◽  
Maximum Deviation ◽  
Transfer Coefficients

One of the main challenges of spray cooling technology is the prediction of local and average heat transfer coefficients on the heater surface. It is hypothesized that the local heat transfer coefficient can be predicted from the local normal pressure produced by the spray. In this study, hollow cone, full cone, and flat fan sprays, operated at three standoff distances, five spray pressures, and two nozzle orientations, were used to identify the relation between the impingement pressure and the heat transfer coefficient in the single-phase regime. PF-5060, PAO-2, and PSF-3 were used as test fluids, resulting in Prandtl number variation between 12 and 76. A microheater array operated at constant temperature was used to measure the local heat flux. A separate test rig was used to make impingement pressure measurements for the same geometry and spray pressure. The heat flux data were then compared with the corresponding impingement pressure data to develop a pressure-based correlation for spray cooling heat transfer. The maximum deviation between the experimental data and prediction was within ±25%.

Pressure-Based Prediction of Single Phase Spray Cooling Heat Transfer Coefficient for Low Prandtl Number Liquids

2010 ◽  
Author(s):  
Bahman Abbasi ◽  
Jungho Kim
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Prandtl Number ◽  
Transfer Coefficient ◽  
Single Phase ◽  
Local Heat ◽  
Spray Cooling ◽  
Maximum Deviation ◽  
Transfer Coefficients

One of the main challenges of spray cooling technology is the prediction of local and average heat transfer coefficients on the heater surface. It is hypothesized that the local heat transfer coefficient can be predicted from the local normal pressure produced by the spray. In this study, hollow cone, full cone, and flat fan sprays operated at three standoff distances, five spray pressures, and two nozzle orientations were used to identify the relation between impingement pressure and heat transfer coefficient in the single phase regime. PF-5060, PAO-2, and PSF-3 were used as test fluids, resulting in Prandtl number variation between 12 to 75. A micro-heater array operated at constant temperature was used to measure the local heat flux. A separate test rig was used to make impingement pressure measurements for the same geometry and spray pressure. The heat flux data were then compared with the corresponding impingement pressure data to develop a pressure-based correlation for spray cooling heat transfer. The maximum deviation between the experimental data and prediction was within ±25%.

Experimental Measurement of the Effect of Heat Flux on Local Heat Transfer Coefficient and Friction Coefficient in an Annulus

1965 ◽  
Vol 7 (3) ◽  
pp. 300-305 ◽  
Author(s):  
B. S. Larkin
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Friction Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Number Range ◽  
Temperature Method

This paper describes a closed-circuit apparatus for the measurement of local heat transfer coefficients from the inner surface and overall friction coefficients for air flowing through an annulus (radius ratio 1.7). Results were obtained for Reynolds numbers from 35 000 to 170 000 for temperature ratios Ti/Tb up to 1.74. A novel type of heater bar was used in order to avoid some of the disadvantages of the more usual designs. The results were very consistent. It was found that the effect of heat flux on the heat transfer coefficient could be eliminated either by the film temperature method using a film temperature coefficient of 0.25 or by including a temperature ratio term ( TiTb)-0.2 in the Nu-Re relationship. Over most of the Reynolds number range the overall friction coefficient did not vary with heat flux.

Modeling Bubble Growth in Micro-Channel Cooling Systems

2007 ◽  
Author(s):  
Joshua L. Nickerson ◽  
Martin Cerza ◽  
Sonia M. F. Garcia
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Conduction Equation ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Local Heat Transfer Coefficient ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

The solution of the heat conduction equation in the liquid layer beneath a moving bubble’s base and the resulting local heat transfer coefficient are presented. An analytical model was constructed using separation of variables to solve the heat conduction equation for the thermal profile in the liquid film beneath the base of a bubble moving through a microchannel at a given velocity. Differentiating the resulting liquid thermal profile and applying the standard definition for the local heat transfer coefficient resulted in a solution for local heat transfer coefficient as a function of bubble length. Analysis included varying pertinent parameters such as film thickness beneath the bubble base, wall heat flux, and superheated temperature in the microchannel. Water and FC-72 were analyzed as prospective coolant fluids. Analytical data revealed that as the superheated temperature in the microchannel increases, local heat transfer coefficients increase and arrive at a higher steady-state value. Increasing wall heat flux achieved the same result, while increasing film thickness resulted in lower heat transfer coefficients. The model indicated that water had superior performance as a coolant, provided the dielectric fluid (FC-72) is not mandated.

Pressure Based Prediction of Spray Cooling Heat Transfer Coefficients

2007 ◽  
Author(s):  
Thierry Some ◽  
Eckhard Lehmann ◽  
Hitoshi Sakamoto ◽  
Jungho Kim ◽  
Jin Taek Chung ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Spray Cooling ◽  
Local Heat Transfer Coefficient ◽  
Transfer Coefficients ◽  
Local Pressure ◽  
Heat Transfer Coefficients

An important goal of spray cooling research is the ability to predict local heat transfer coefficient from the spray hydrodynamics. It is postulated in this work that the local pressure is the controlling parameter for local heat transfer coefficient. To test this hypothesis, local pressure and heat transfer data were obtained for a 1×1, 1×2, and 2×2 arrays of hollow cone sprays at two pressures and three standoff distances. A correlation between the pressure and heat transfer coefficient was determined, then used to “predict” the heat transfer coefficient from the pressure data. The local variations in heat transfer coefficient were captured well using this technique, and the area-averaged heat transfer coefficient could be predicted within 12.6%. The technique needs to be verified with different nozzles and fluids over a wider range of conditions.

Effect of Water Temperature on Spray Cooling Heat Transfer on Hot Steel Plate

2010 ◽  
Author(s):  
Jungho Lee ◽  
Cheong-Hwan Yu ◽  
Sang-Jin Park
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Water Temperature ◽  
Steel Plate ◽  
Cooling Water ◽  
Local Heat ◽  
Spray Cooling ◽  
Transfer Coefficients ◽  
Cooling Water Temperature ◽  
Local Heat Flux

Water spray cooling is an important technology which has been used in a variety of engineering applications for cooling of materials from high-temperature nominally up to 900°C, especially in steelmaking processes and heat treatment in hot metals. The effects of cooling water temperature on spray cooling are significant for hot steel plate cooling applications. The local heat flux measurements are introduced by a novel experimental technique in which test block assemblies with cartridge heaters and thermocouples are used to measure the heat flux distribution on the surface of hot steel plate as a function of heat flux gauge. The spray is produced from a fullcone nozzle and experiments are performed at fixed water impact density of G and fixed nozzle-to-target spacing. The results show that effects of water temperature on forced boiling heat transfer characteristics are presented for five different water temperatures between 5 to 45°C. The local heat flux curves and heat transfer coefficients are also provided to a benchmark data for the actual spray cooling of hot steel plate cooling applications.

Heat Transfer Enhancement by Turbulent Impinging Jets

2000 ◽  
Author(s):  
M. Kumagai ◽  
R. S. Amano ◽  
M. K. Jensen
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Stokes Equations ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Impinging Jets ◽  
Transfer Model ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

Abstract A numerical and experimental investigation on cooling of a solid surface was performed by studying the behavior of an impinging jet onto a fixed flat target. The local heat transfer coefficient distributions on a plate with a constant heat flux were computationally investigated with a normally impinging axisymmetric jet for nozzle diameter of 4.6mm at H/d = 4 and 10, with the Reynolds numbers of 10,000 and 40,000. The two-dimensional cylindrical Navier-Stokes equations were solved using a two-equation k-ε turbulence model. The finite-volume differencing scheme was used to solve the thermal and flow fields. The predicted heat transfer coefficients were compared with experimental measurements. A universal function based on the wave equation was developed and applied to the heat transfer model to improve calculated local heat transfer coefficients for short nozzle-to-plate distance (H/d = 4). The differences between H/d = 4 and 10 due to the correlation among heat transfer coefficient, kinetic energy and pressure were investigated for the impingement region. Predictions by the present model show good agreement with the experimental data.

scholarly journals A Statistical Evaluation of the Influence of Different Material and Process Parameters on the Heat Transfer Coefficient in Gravity Die Casting

Metals ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 1367
Author(s):  
Nino Wolff ◽  
Golo Zimmermann ◽  
Uwe Vroomen ◽  
Andreas Bührig-Polaczek
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Die Casting ◽  
Local Heat Transfer ◽  
Mold Temperature ◽  
Local Heat ◽  
Mold Material ◽  
Transfer Coefficients ◽  
The Heat Transfer Coefficient

Local heat transfer in gravity die casting is of great importance for precision in terms of distortion, mechanical properties, and the quality of the castings due to its effect on solidification. Depending on contact conditions such as liquid melt to solid mold, a gap between mold and component, or contact pressure between casting and mold as a result of shrinkage, there are very large differences in heat transfer. The influences of mold material, mold coating and its influence of aging, mold temperature control, and layout on the heat transfer coefficient (HTC) were investigated experimentally for different contact cases. The experiments were carried out on a rotationally symmetrical experimental setup with modular exchangeable die inserts and cores using an AlSi7Mg0.3 alloy. From the results of the individual test series, the quantitative shares of the above-mentioned influencing variables in the respective effective heat transfer coefficients were determined by means of analysis of variance. From this, the parameters having the most significant influence on the local heat balance were derived.

Single Phase and Flow Boiling Heat Transfer of Water and Ethanol in a Mini-Channel Array

2010 ◽  
Author(s):  
M. W. Alnaser ◽  
K. Spindler ◽  
H. Mu¨ller-Steinhagen
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
High Speed ◽  
Single Phase ◽  
Flow Boiling ◽  
Video Camera ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
High Speed Video Camera

A test rig was constructed to investigate flow boiling in an electrically heated horizontal mini-channel array. The test section is made of copper and consists of twelve parallel mini-channels. The channels are 1 mm deep, 1 mm wide and 250 mm long. The test section is heated from underneath with six cartridge heaters. The channels are covered with a glass plate to allow visual observations of the flow patterns using a high-speed video-camera. The wall temperatures are measured at five positions along the channel axis with two resistance thermometers in a specified distance in heat flow direction. Local heat transfer coefficients are obtained by calculating the local heat flux. The working fluids are deionised water and ethanol. The experiments were performed under near atmospheric pressure (0.94 bar to 1.2 bar absolute). The inlet temperature was kept constant at 20°C. The measurements were taken for three mass fluxes (120; 150; 185 kg/m2s) at heat fluxes from 7 to 375 kW/m2. Heat transfer coefficients are presented for single phase forced convection, subcooled and saturated flow boiling conditions. The heat transfer coefficient increases slightly with rising heat flux for single phase flow. A strong increase is observed in subcooled flow boiling. At high heat flux the heat transfer coefficient decreases slightly with increasing heat flux. The application of ethanol instead of water leads to an increase of the surface temperature. At the same low heat flux flow boiling heat transfer occurs with ethanol, but in the experiments with water single phase heat transfer is still dominant. It is because of the lower specific heat capacity of ethanol compared to water. There is a slight influence of the mass flux in the investigated parameter range. The pictures of a high-speed video-camera are analysed for the two-phase flow-pattern identification.

Local Heat Transfer Coefficient of Flow Boiling in Microchannels With Artificial Reentrant Cavities

2007 ◽  
Author(s):  
Chih-Jung Kuo ◽  
Yoav Peles
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Flow Boiling ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Bubble Generation ◽  
Parallel Microchannels

Flow boiling in parallel microchannels with structured reentrant cavities was experimental studied. Flow patterns, boiling inceptions and heat transfer coefficients were obtained and studied for G = 83 kg/m2-s to G = 303 kg/m2-s and heat fluxes up to 643 W/cm2. The heat transfer coefficient-mass velocity and quality relations had been analyzed to identify boiling mechanism. Comparisons of the performance of the enhanced and plain-wall microchannels had also been made. The microchannels with reentrant cavities were shown to promote nucleation of bubbles and to support significantly better reproducibility and uniformity of bubble generation.

Three-Dimensional Transient Heat Conduction Equation Solution for Accurate Quantification of Heat Transfer Coefficient in Transient Liquid Crystal Experiments

2019 ◽  
Author(s):  
Shoaib Ahmed ◽  
Prashant Singh ◽  
Srinath V. Ekkad
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Liquid Crystal ◽  
Transfer Coefficient ◽  
Three Dimensional ◽  
Jet Impingement ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Coefficients ◽  
Conduction Model

Abstract Liquid crystal thermography and infrared thermography techniques are typically employed to measure detailed surface temperatures, where local heat transfer coefficient (HTC) values are calculated by employing suitable conduction models. One such practice, which is very popular and easy to use, is the transient liquid crystal thermography using one-dimensional semi-infinite conduction model. In these experiments, a test surface with low thermal conductivity and low thermal diffusivity (e.g. acrylic) is used where a step-change in coolant air temperature is induced and surface temperature response is recorded. An error minimization routine is then employed to guess heat transfer coefficients of each pixel, where wall temperature evolution is known through an analytical expression. The assumption that heat flow in the solid is essentially in one-dimension, often leads to errors in HTC determination and this error depends on true HTC, wall temperature evolution and HTC gradient. A representative case of array jet impingement under maximum crossflow condition has been considered here. This heat transfer enhancement concept is widely used in gas turbine leading edge and electronics cooling. Jet impingement is a popular cooling technique which results in high convective heat rates and has steep gradients in heat transfer coefficient distribution. In this paper, we have presented a procedure for solution of three-dimensional transient conduction equation using alternating direction implicit method and an error minimization routine to find accurate heat transfer coefficients at relatively lower computational cost. The HTC results obtained using 1D semi-infinite conduction model and 3D conduction model were compared and it was found that the heat transfer coefficient obtained using the 3D model was consistently higher than the conventional 1D model by 3–16%. Significant deviations, as high as 8–20% in local heat transfer at the stagnation points of the jets were observed between h1D and h3D.

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