Session: 10-01 Interactive Presentations

Paper Number: 100297

100297 - An Experimental Study on Two-Phase Flow Boiling in Compressed Metallic Foams for Advanced Thermal Management of High Heat Flux Electronics 

Porous and cellular structured materials, including open-cell metallic foams, have been previously studied as enhanced surfaces for heat sinks used in cooling of modern electronics. Several studies exist for foam heat sinks with single-phase flow but there are few investigations on two-phase foam evaporators. Due to the latent heat of vaporization and higher heat transfer coefficients, flow boiling is more efficient for cooling of high heat fluxes, as compared to single-phase flow. This work focuses on an experimental study on the thermohydraulic performance of copper foam evaporators using R134a refrigerant. Two foam samples, one compressed four times (4X) and other uncompressed, were tested, each with a heated footprint area of 1x1 in, height of 0.1 in and pore size of 40 PPI, and with porosities of 0.62 and 0.91, respectively. Compressing the foam by up to 4X proportionally reduced the effective pore hydraulic diameter and increased both the surface area per unit volume and bulk thermal conductivity. Experiments were conducted for heat flux ranging from 7 to 216 W/cm², mass flux varied from 150 to 375 kg/m².s, inlet saturation temperatures (T_sat,in) of 31 to 40 ^oC, and with subcooling of 1 to 3^oC. Results show that 4X foam demonstrated up to three-times lower unit thermal resistance with a penalty on pressure drop. The apparent heat transfer coefficient in 4X foam evaporator maximizes at exit vapor qualities of about 70 to 75 %. The pressure drop increases linearly with exit quality, which is similar to what is commonly observed in microchannels. Results show that 4X foam CHF is a strong function of mass flux, and the boiling curves reveal that 4X foam delayed CHF up to as high as 201 W/cm² at a moderate mass flux of 200 kg/m².s (8 g/s), T_sat,in.of 40 ^oC and subcooling of 3 ^oC. Generally, current results show that compressed metallic foams appear to be a powerful alternative to microchannels in indirect two-phase electronic cooling applications.

Presenting Author: Deogratius Kisitu Villanova University