Heat removal using microjet arrays and microdroplets in open and closed systems for electronic cooling

The objective of this work is to develop an efficient and economical heat removal technique that will meet the present and future integrated circuit (IC) chip cooling requirements. The impingement of liquid droplets/jets on a hot surface is an effective way of dissipating high heat fluxes from the surface. The proposed method is to deposit a thin liquid film on the hot surface using impingement of liquid microdroplets/microjets, and heat will be removed from the surface mainly through forced convection and evaporation of the liquid.; In this study, three types of cooling arrangements were experimentally studied and compared; (i) microjet arrays, (ii) HAGO nozzle, (iii) airbrush. The heated surface was the flat surface of a copper cylinder of 2 cm diameter. The heat flux at the surface was varied by controlling power to the cartridge heaters placed in the lower portion of the copper block. Experiments were conducted in both open and closed systems. In the closed system, the system pressure and partial pressure of air inside the system were varied systematically. Effect of non-condensibles on evaporation and over all heat transfer coefficient was studied.; Arrays of microjets were produced with different orifice plates having orifice sizes of 50 μm, 100 μm, and 150 μm and orifice spacing of 1 mm, 2 mm and 3 mm.; Effect of non-condensibles in the closed system on total heat transfer coefficient was further investigated using HAGO nozzle. Maintaining an air partial pressure of 3.1 kPa, while varying the vapor partial pressure from 7.3 kPa to 97.9 kPa, the total system pressure varied from 10.4 kPa to 101 kPa. As such, partial pressure of air to total system pressure ratio was varied from 3% to 29.8%. Experiments were also conducted by keeping the system pressure constant at 101 kPa and by varying the air pressure inside the chamber from 2.75 kPa to 93.7 kPa.; Experiments were also conducted using an air-atomized spray impinging normal to the heated surface. In the experiments, the water flow rate was varied from 1.57 ml/min/cm2 to 15.8 ml/min/cm2 and the air flow rate was varied from 4.7 l/min/cm2 to 9.171/min/cm 2.; For the studied flow rates, it was found that heat fluxes as high as 130 W/cm2 could be accommodated at a surface temperature of just 100°C. Critical heat flux as high as 300 W/cm2 was obtained at surface temperature of 120°C.; Best technique of impingement cooling was found to be the orifice plates with 150 μm orifice diameter, and 2 mm orifice spacing by comparing the single phase heat transfer coefficient, CHF and ratio of pumping power over total power removed for all the three techniques used in this study. (Abstract shortened by UMI.)...