The use of impinging liquid jets in electronics thermal management is attracting some consideration due to their very high heat transfer coefficients, hot spot targeting capabilities and moderate hydraulic power requirements. In this investigation an experimental study of the cooling capabilities of impinging water jet arrays is presented. Of particular interest here is the influence that the inlet and outlet geometries have on the thermal-hydraulics of jet impingement heat transfer with the aim of determining practical configurations in which heat transfer to the impinging jets is increased and/or the hydraulic pumping power is decreased. For a square array of 45 jets of fixed 1.0 mm diameter and fixed interjet spacing of 5 mm, six different nozzle geometries were investigated. The arrays impinged normally upon a heated circular copper surface of 31.5 mm diameter for a nominal heat flux of 25.66 W/cm2. Each array was tested under confined-submerged flow conditions with a constant jet-to-target spacing of 2.0 mm as well as free-surface conditions with a constant jet-to-target spacing of 20 mm. All nozzles were tested for a Reynolds number range of approximately 800 ≤ Redn ≤ 10000. It has been found that the confined-submerged tests yield greater heat transfer coefficients compared with their free jet counterparts. Chamfering and contouring the nozzle inlets showed significant decrease in the pressure drop across the nozzle plate whilst chamfering and contouring the exit showed moderate gains in the surface averaged heat transfer coefficient. Nozzles that provide the highest heat transfer for a given hydraulic pumping power are identified for each free-surface and confined-submerged scenarios. Chamfering and contouring the nozzle inlets showed significant decrease in the pressure drop across the nozzle plate whilst chamfering and contouring the exit showed moderate gains in the surface averaged heat transfer coefficient. Nozzles that provide the highest heat transfer for a given hydraulic pumping power are identified for each free-surface and confined-submerged scenarios. Nozzle Geometry Effects in Liquid Jet

A liquid CPU cooler has been designed and tested with the aim to achieve a cooling capacity of 200 W for a surface area of 8.24 cm 2 , commensurate with the integrated heat spreader dimensions of an Intel® Pentium® 4 Processor. The primary aim of the design was to develop thermal hardware components that can be manufactured simply and cost effectively. To this end, a miniature jet array waterblock and a tube bundle remote heat exchanger were employed since the bulk of their housings could be manufactured using low cost injection molding techniques which could significantly reduce the total system cost compared with conventional units. The system was capable of dissipating the required heat load and exhibited an overall thermal resistance of 0.18 K/W requiring approximately 1.5 W of hydraulic power. At maximum power the chip-to-air temperature difference was 45°C which is adequately close to typical design thresholds. The influences of power loading and liquid volumetric flow rate are also discussed.

A model is presented to simulate the power cycle and gas exchange process in a crankcase-compression two-stroke spark-ignition engine which includes intake and exhaust systems. Chemical equilibrium and a two-zone combustion model with a spherical flame front are assumed for the power cycle and generalized non-steady gas dynamic expressions. including variable composition. variable specific heats. friction and heat transfer, are assumed for the gas exchange process in the intake and exhaust systems. For the scavenge process in the cylinder. a thermal mixing model is used to calculate the pressure changes. Experiments with a small high-speed engine showed that the model gave good predictions of the pressure changes during the gas exchange process and the air flow rate. The power predictions followed the experimental trend, but the quantitative results were not so good as the air flow predictions. Despite the limitations of the power predictions. the method offers the designer a tool for improving the performance of the crankcase-compression engine.

Due to the current trend of miniaturization of electronic components, higher heat fluxes are encountered. Current fan cooling methods are approaching their maximum cooling capabilities leading to the investigation of liquid cooling techniques. An experimental study of the cooling capabilities of liquid water impinging jet arrays, with a view for use in the cooling of electronic chips, is presented. The 3.0 mm thick jet nozzle plate contained 45 individual jets of 1mm diameter with 5 mm spacing between each jet. The arrays impinged onto a copper surface of 31.5 mm diameter, which dissipated approximately 200 W of heat. The inlet and outlet geometries of the jets were varied with a view of determining an optimal configuration with regards to maximum heat transfer to the impinging jets for the minimal pressure drop across the nozzle plate. Each array was tested under free-surface flow conditions, with a constant jet-to-target spacing of H/d = 20 for a Reynold’s number range of approximately 300–10,000. The results indicate that chamfering of the inlet decreased the pressure drop for a given average heat transfer coefficient, whilst chamfering of the outlet provided a greater heat transfer for a given Reynold’s number.