Film Thickness and Heat Transfer Measurements in a Spray Cooling System With R134a

2011 ◽  
Vol 133 (1) ◽  
Author(s):  
Eduardo Martínez-Galván ◽  
Juan Carlos Ramos ◽  
Raúl Antón ◽  
Rahmatollah Khodabandeh
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Film Thickness ◽  
High Speed ◽  
Average Nusselt Number ◽  
Cooling System ◽  
Spray Cooling ◽  
Heat Fluxes ◽  
Long Distance ◽  
Thickness Measurements

Experimental measurements in a spray cooling test rig have been carried out for several heat fluxes in the heater and different spray volumetric fluxes with the dielectric refrigerant R134a. Results of the heat transfer and the sprayed refrigerant film thickness measurements are presented. The film thickness measurements have been made with a high speed camera equipped with a long distance microscope. It has been found that there is a relation between the variation in the average Nusselt number and the film thickness along the spray cooling boiling curve. The heat transfer regimes along that curve are related not only with a variation in the average Nusselt number but also with changes in the film thickness. The qualitative analysis of those variations has served to understand better the heat transfer mechanisms occurring during the spray cooling.

Enhancement of Heat Transfer to an Air Jet Impinging on a Flat Plate

Volume 1 ◽  
2004 ◽  
Author(s):  
D. P. Mishra ◽  
D. Mishra
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Flat Plate ◽  
Average Nusselt Number ◽  
Cooling System ◽  
Reynolds Numbers ◽  
Heated Plate ◽  
Maximum Heat ◽  
Air Jet ◽  
Maximum Heat Transfer

An experimental investigation of the impinging jet cooling from a heated flat plate has been carried out for several Reynolds numbers (Re) and nozzle to plate distances. The present results indicate that the maximum heat transfer occurs from the heated plate at stagnation point and decreases with radial distances for all cases. The maximum value of the stagnation as well as average Nusselt number is found to occur at separation distance, H/D = 6.0 for Re = 55000. An attempt is also made to study effects of nozzle exit configuration on the heat transfer using a sharp edged orifice for same set of Reynolds numbers and nozzle to plate distance. The stagnation Nusselt numbers of sharp orifice jets are found to be enhanced by around 16–21.4% in comparison to that of square edged orifice. However, the enhancement in the average Nusselt number of sharp orifice is found to be in the range of 7–18.9% as compared to the square edged orifice. The maximum enhancement of 18.9% in average Nu is achieved for Re = 55 000 at H/D = 6. Two separate correlations in terms of Nuo, Re, H/D for both square and sharp edged orifice are obtained which will be useful for designing impinging cooling system.

scholarly journals The Simultaneous Analysis of Droplets’ Impacts and Heat Transfer during Water Spray Cooling Using a Transparent Heater

Water ◽  
2021 ◽  
Vol 13 (19) ◽  
pp. 2730
Author(s):  
Vladimir Serdyukov ◽  
Nikolay Miskiv ◽  
Anton Surtaev
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Heating Surface ◽  
Nucleate Boiling ◽  
Spray Cooling ◽  
Capillary Waves ◽  
Heat Fluxes ◽  
Small Scale ◽  
Unsteady Temperature ◽  
The Impact

This paper demonstrates the advantages and prospects of transparent design of the heating surface for the simultaneous study of the hydrodynamic and thermal characteristics of spray cooling. It was shown that the high-speed recording from the reverse side of such heater allows to identify individual droplets before their impact on the forming liquid film, which makes it possible to measure their sizes with high spatial resolution. In addition, such format enables one to estimate the number of droplets falling onto the impact surface and to study the features of the interface evolution during the droplets’ impacts. In particular, the experiments showed various possible scenarios for this interaction, such as the formation of small-scale capillary waves during impacts of small droplets, as well as the appearance of “craters” and splashing crowns in the case of large ones. Moreover, the unsteady temperature field during spray cooling in regimes without boiling was investigated using high-speed infrared thermography. Based on the obtained data, the intensity of heat transfer during spray cooling for various liquid flow rates and heat fluxes was analyzed. It was shown that, for the studied regimes, the heat transfer coefficient weakly depends on the heat flux density and is primarily determined by the flow rate. In addition, the comparison of the processes of spray cooling and nucleate boiling was made, and an analogy was shown in the mechanisms that determine their intensity of heat transfer.

Influence of surface roughness on a spray cooling system with R134a. Part II: Film thickness measurements

2013 ◽  
Vol 48 ◽  
pp. 73-80 ◽  
Author(s):  
Eduardo Martínez-Galván ◽  
Juan Carlos Ramos ◽  
Raúl Antón ◽  
Rahmatollah Khodabandeh
Keyword(s):  
Surface Roughness ◽  
Film Thickness ◽  
Cooling System ◽  
Spray Cooling ◽  
Thickness Measurements

Alumina Nanofluid for Spray Cooling Enhancement

2007 ◽  
Author(s):  
Aditya Bansal ◽  
Frank Pyrtle
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Heat Dissipation ◽  
Cooling System ◽  
Spray Cooling ◽  
Open Loop ◽  
Heat Fluxes ◽  
Alumina Nanoparticles ◽  
Transfer Enhancement ◽  
Thermal Conductivities

Nanofluids have been demonstrated as promising for heat transfer enhancement in forced convection and boiling applications. The addition of carbon, copper, and other high-thermal-conductivity nanoparticles to water, oil, ethylene glycol, and other fluids has been determined to increase the thermal conductivities of these fluids. The increased effective thermal conductivities of these fluids enhance their abilities to dissipate heat in such applications. The use of nanofluids for spray cooling is an extension of the application of nanofluids for enhancement of heat dissipation. In this investigation, experiments were performed to determine the level of heat transfer enhancement with the addition of alumina nanoparticles to the fluid. Using mass percentages of up to 0.5% alumina nanoparticles suspended in water, heat fluxes and surface temperatures were measured and compared. Compressed nitrogen was used to provide constant spray nozzle pressures to produce full-cone sprays in an open loop spray cooling system. Heat fluxes were measured for single-phase and evaporative spray cooling regimes.

scholarly journals Nanofluids Characterization for Spray Cooling Applications

Symmetry ◽  
2021 ◽  
Vol 13 (5) ◽  
pp. 788
Author(s):  
Miguel Sanches ◽  
Guido Marseglia ◽  
Ana P. C. Ribeiro ◽  
António L. N. Moreira ◽  
Ana S. Moita
Keyword(s):  
Heat Transfer ◽  
Thermophysical Properties ◽  
High Speed ◽  
Lower Surface ◽  
Spray Cooling ◽  
Heat Fluxes ◽  
Structure Evolution ◽  
Transfer Coefficients ◽  
Systematic Analysis ◽  
Nanoparticles Concentration

In this paper the mathematical and physical correlation between fundamental thermophysical properties of materials, with their structure, for nanofluid thermal performance in spray cooling applications is presented. The present work aims at clarifying the nanofluid characteristics, especially the geometry of their nanoparticles, leading to heat transfer enhancement at low particle concentration. The base fluid considered is distilled water with the surfactant cetyltrimethylammonium bromide (CTAB). Alumina and silver are used as nanoparticles. A systematic analysis addresses the effect of nanoparticles concentration and shape in spray hydrodynamics and heat transfer. Spray dynamics is mainly characterized using phase Doppler interferometry. Then, an extensive processing procedure is performed to thermal and spacetime symmetry images obtained with a high-speed thermographic camera to analyze the spray impact on a heated, smooth stainless-steel foil. There is some effect on the nanoparticles’ shape, which is nevertheless minor when compared to the effect of the nanoparticles concentration and to the change in the fluid properties caused by the addition of the surfactant. Hence, increasing the nanoparticles concentration results in lower surface temperatures and high removed heat fluxes. In terms of the effect of the resulting thermophysical properties, increasing the nanofluids concentration resulted in the increase in the thermal conductivity and dynamic viscosity of the nanofluids, which in turn led to a decrease in the heat transfer coefficients. On the other hand, nanofluids specific heat capacity is increased which correlates positively with the spray cooling capacity. The analysis of the parameters that determine the structure, evolution, physics and both spatial and temporal symmetry of the spray is interesting and fundamental to shed light to the fact that only knowledge based in experimental data can guarantee a correct setting of the model numbers.

Heat Transfer Characteristics of a Train of Droplets Impinging Over a Hot Surface: From Film Evaporation to Leidenfrost Point

2021 ◽  
Author(s):  
Ganesh Guggilla ◽  
Ramesh Narayanaswamy ◽  
Peter Stephan ◽  
Arvind Pattamatta
Keyword(s):  
Heat Transfer ◽  
High Speed ◽  
Heated Surface ◽  
Contact Angle Hysteresis ◽  
Electronics Cooling ◽  
Spray Cooling ◽  
Heat Fluxes ◽  
High Speed Photography ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics

Abstract High-performance computing systems are needed in advanced computing services such as machine learning and artificial intelligence. Consequently, the increase in electron chip density results in high heat fluxes and requires good thermal management to maintain the servers. Spray cooling using liquid offers higher heat transfer rates and is efficient when implemented in electronics cooling. Detailed studies of fundamental mechanisms involved in spray cooling, such as single droplet and multiple droplet interactions, are required to enhance the process's knowledge. The present work focuses on studying a train of two FC-72 droplets impinging over a heated surface. Experimental investigation using high-speed photography and infrared thermography is conducted. Simultaneously, numerical simulations using opensource CFD package, OpenFOAM are carried out, emphasizing the significance of contact angle hysteresis. The surface temperature is chosen as a parameter, and different boiling regimes along with Dynamic Leidenfrost point (DLP) for the present impact conditions are identified. Spreading hydrodynamics and heat transfer characteristics of these consecutively impinging droplets till the Leidenfrost temperature, are studied and compared.

Correlation of Heat Transfer Data to Film Thickness Data of the Thin Film Found in Spray Cooling

2004 ◽  
Author(s):  
Adam G. Pautsch ◽  
Timothy A. Shedd
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Film Thickness ◽  
Heated Surface ◽  
Spray Cooling ◽  
Heat Fluxes ◽  
Experimental Measurements ◽  
Transfer Coefficients ◽  
Two Phase ◽  
Heat Transfer Coefficients

As electronic circuit design and packaging technology progresses, the density and power levels of electronic components is increasing at a nearly exponential rate. The higher heat loads dissipated by these devices are nearing the limits of traditional cooling techniques. One method capable of removing heat fluxes as high as 100 W/cm2 is spray cooling. This process involves the impingement of liquid droplets onto a heated surface, forming a thin two-phase film. In order to create reliable models of the heat transfer during spray cooling, the behavior of the film must be understood. This paper presents an investigation into the behavior of the thin film found in spray cooling. A study was performed to relate experimental measurements of the heat transfer coefficients to experimental measurements of film thickness as they vary spatially over a die surface. Both a single nozzle and a multi-nozzle array were investigated. Measured heat transfer coefficients ranged from 0.2 to 1.2 W/m2K and film thicknesses ranged from 90 to 300 μm.

Forced convection heat transfer study of a blunt-headed cylinder in non-Newtonian power-law fluids

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Jaspinder Kaur ◽  
Roderick Melnik ◽  
Anurag Kumar Tiwari
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Drag Coefficient ◽  
Power Law ◽  
Average Nusselt Number ◽  
Convection Heat Transfer ◽  
Convection Heat ◽  
Total Drag ◽  
Shear Thinning Fluids ◽  
Power Law Fluids

Abstract In this present work, forced convection heat transfer from a heated blunt-headed cylinder in power-law fluids has been investigated numerically over the range of parameters, namely, Reynolds number (Re): 1–40, Prandtl number (Pr): 10–100 and power-law index (n): 0.3–1.8. The results are expressed in terms of local parameters, like streamline, isotherm, pressure coefficient, and local Nusselt number and global parameters, like wake length, drag coefficient, and average Nusselt number. The length of the recirculation zone on the rear side of the cylinder increases with the increasing value of Re and n. The effect of the total drag coefficient acting on the cylinder is seen to be higher at the low value of Re and its effect significant in shear-thinning fluids (n < 1). On the heat transfer aspect, the rate of heat transfer in fluids is increased by increasing the value of Re and Pr. The effect of heat transfer is enhanced in shear-thinning fluids up to ∼ 40% and it impedes it’s to ∼20% shear-thickening fluids. In the end, the numerical results of the total drag coefficient and average Nusselt number (in terms of J H −factor) have been correlated by simple expression to estimate the intermediate value for the new application.

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