Investigation of Enhanced Surface Spray Cooling

Abstract

Phase change technology is a science that is continually finding new applications, from passive refrigeration cycles to semiconductor cooling. The primary heat transfer techniques associated with phase change heat transfer are pool boiling, flow boiling, and spray cooling. Of these techniques, spray cooling is the least studied and the most recent to receive attention in the scientific community. Spray cooling is capable of removing large amounts of heat between the cooled surface and the liquid, with reported heat flux capabilities of up to 1000 W/cm 2 for water. Many previous studies have emphasized heat flux as a function of spray parameters and test conditions.Enhanced spray cooling investigations to date have been limited to surface roughness studies. These studies concluded that surface tolerance (i.e. variations in machined surface finish) had an impact upon heat flux when using pressure atomized sprays.Analogous pool boiling studies with enhanced surfaces have shown heat flux enhancement. A spray cooling study using enhanced surfaces beyond the surface roughness range may display heat flux enhancement as well.In the present study, a group of extended and embedded surfaces (straight fins, cubic pin fins, pyramids, dimples and porous tunnels) have been investigated to determine the effects of enhanced surface structure on heat flux. The surface enhancements were machined on the top surface of copper heater blocks with a crosssectional area of 2.0 cm 2 . Measurements were also obtained on a flat surface for baseline comparison purposes. Thermal performance data was obtained under saturated (pure fluid at 101 kPa), nominally degassed (chamber pressure of 41.4 kPa) and gassy conditions (chamber with N 2 gas at 101 kPa). The study shows that both extended and embedded structures (beyond the surface roughness range) promote heat flux enhancement for both degassed and gassy spray cooling conditions. The study also shows that straight fins provide the best utilization of surface area added for heat transfer. An Energy conservation based CHF correlation for flat surface spray cooling was also developed. CHF predictions were compared against published and non-published studies by several researchers. Results for the correlations performanceshow an average mean error of ±17.6% with an accuracy of ±30% for 88% of the data set compared against.

Impact of Cubic Pin Finned Surface Structure Geometry Upon Spray Cooling Heat Transfer

“…Other topics researched to date include the effect of surfactant addition [12,13], and secondary nucleation [ 1, 14,15]. This work is a continuation of the enhanced surface study by Silk et al [16], with an emphasis on cubic pin fins as the basic geometric feature of the surface enhancement, The objective of the current work is to examine the effects of these geometries and their arrangement on heat flux when using spray Most previous studies that have examined enhanced surfaces have done so primarily from the perspective of surface roughness. Sehmbey et al [l] gives an overview of spray cooling and provides a comparison of its effectiveness when using liquid and secondary gas atomizers (air used as the secondary gas).…”

“…The initial work by Silk et al [16] showed that spray cooling of enhanced structure surfaces results in a corresponding heat flux enhancement. The present work investigates spray cooling heat flux as a hnction of cubic pin fin geometry and structure arrangement.…”

Hybrid Solid- and Liquid-Cooling Solution for Isothermalization of Insulated Gate Bipolar Transistor Power Electronic Devices

“…Lee and Mudawar [7]- [9] designed an R134a-cooled two-phase microchannel heat sink capable of providing a heat transfer coefficient up to 50 000 W/m 2 -K. Fabbri et al [10] developed a single-phase spray-cooling system showing that a heat transfer coefficient of 15 000 W/m 2 -K can be obtained with the water as the working fluid. Silk et al [11] demonstrated that a two-phase spray cooling with PF-5060 as the working fluid can achieve a heat transfer coefficient of 24 000 W/m 2 -K. Compared to microchannel cooling and spray cooling, jet impingement cooling can offer much higher heat transfer capability. For example, Natarajan and Bezama [12] demonstrated that a single-phase water submerged jet can reach a heat transfer coefficient as high as 52 000 W/m 2 However, these high heat flux cooling solutions, when applied on the back side of the direct-bonded copper (DBC) substrate and designed for thermal management of the entire IGBT module, cannot remove the nonuniform temperature distribution on the individual IGBT chips.…”

Spray Cooling of High Aspect Ratio Open Microchannels

“…The very high spray efficiencies observed in this study are likely due to the small scale of the microchannels along with the relative sparseness of the spray. It may likely be confirmed that given a greater flow rate, the heat transfer could be improved at the expense of a decreased spray efficiency as shown by Pautsch and Shedd (2005) with flat surfaces and Silk et al (2004Silk et al ( , 2005 with enhanced surfaces. However, spraying microchannels with a sparse spray may be one way of improving thermal performance without merely increasing the mass flow rate, which can be expensive in terms of pump power, cost, and weight.…”

“…However, recent studies have indicated that enhanced surfaces with large-scale roughness elements (greater than the liquid film thickness) have the potential to transfer as much as 50% more heat than comparable flat surfaces. Most recently, Silk et al (2004Silk et al ( , 2005 investigated spraying gassy (1 atm) PF-5060 on a flat surface and enhanced surfaces including straight fins, square pin fins, and pyramidal fins. They used a 2×2 Parker Hannefin nozzle array with a volumetric flux of 0.016 m 3 /(m 2 ·s).…”