Charles L. Tilton

LIQUID NITROGEN SPRAY COOLING OF A SIMULATED ELECTRONIC CHIP

Evaporative spray cooling with liquid nitrogen is investigated as a candidate method for thermal management of electronic assemblies utilizing High Temperature Super-Conducting (HTSC) materials. A heated copper surface simulating an electronic chip is cooled in two configurations: spraying vertically upwards onto the heated surface (normal impingement), and spraying across the heated surface in a confined channel (narrow gap). For both cases, heat transfer is characterized for a range of supply pressures and liquid inlet temperatures. For the normal impingement study, three full cone nozzles were tested at variable spacing from the heated surface. For the narrow gap study, one fan-spray atomizer was tested with a fixed gap height of 1 mm. The results indicated that heat transfer rates do not vary considerably over a wide range of operating conditions. Heat flux up to 75 W/cm2 was obtained at a surface temperature below 83 K. Two distinct regions of heat transfer are observed: a forced-convection dominated region at low superheat, followed by a thin film evaporation region where heat transfer coefficients rise sharply with increasing surface temperature. In general, heat transfer is roughly an order of magnitude improved over pool boiling. The results have favorable implications for thermal management of advanced cryoelectronic packages.

A Low Profile Thermal Management Device for High Power Processors Using Enhanced Flow Boiling Techniques and Perfluorocarbon Fluids

It is advantageous to the electronic industry to remove in excess of 150W from a processor die with a case-to-ambient thermal resistance < 0.2 ° C/W. Although this is achievable with air cooled thermal solutions, the form factor is unwieldy and as the ambient temperature rises, the processor throttles the performance. Alternatively, thermal solutions containing water are trivial to implement but potential leaks can pose a threat to the electronic suite. The present solution is non-trivial; it utilizes a dielectric perfluorocarbon fluid (PF5050) and a combination of spray cooling and mini-channel flow boiling techniques with a particular focus on superficial quality at the onset of the channels. The idea behind mixing the two techniques is to augment the heat transfer coefficient by driving the fluid into an annular state upon entry of the mini-channels while retaining a low profile package. A macro-channel boiling heat transfer correlation was used and results show that it predicts the average surface temperature to within 10% of the experimental data. Quasi-one-dimensional numerical models were developed to predict vapor entrainment and two-phase pressure drop. Experimental results show that in excess of 250W can be removed from a 1.24cm × 1.24cm die without removing the integrated heat sink (IHS), with a case-to-ambient thermal resistance of <0.2° C/W at 150W. The packaged size is 5.6cm long by 3.1cm wide by 1.6cm tall, thus allowing the end user to adapt the technology into blade style or 1U style servers with low risk.Copyright