Thermal management issues in cryo-electronics

The maximum drain current of power MOSFETs shows a great improvement under cryogenic temperature operation due to the reduced on-resistance and thermal resistance. However, the thermal management of superconductor/semiconductor hybrid circuits at cryogenic temperatures poses a challenge due to the high levels of heat dissipation at the semiconductor devices when they are operated near their current carrying capacities. In this study, heat dissipation levels of power MOSFETs are examined against their current carrying capacities at low temperatures. It is seen that significant improvement in current carrying capacity can be realized if a high heat flux removal thermal management technique is used. The maximum drain current can be increased significantly when a high heat flux removal technique like spray cooling is used as compared to immersion cooling

Critical Heat Flux In Spray Cooling

Similar to other processes involving boiling/evaporation, spray cooling is also characterized by a critical heat flux. Due to the nature of liquid supply in spray cooling, the critical heat flux could be an order of magnitude higher than in pool boiling even for very low liquid flow rates. Hence, spray cooling is one of the best candidates for applications requiring high heat flux removal, e.g., thermal management of high power electronics and electro-optic systems. However, the critical heat flux phenomenon in spray cooling is not well understood. This paper presents a discussion on this topic. A semi-empirical correlation was derived recently for sprays produced by pressure atomizing nozzles based on the macrolayer dry-out theory. With modifications to this correlation, a unified correlation is obtained for critical heat flux in spray cooling with both air atomizing and pressure atomizing nozzles. The data of various past researchers compare very well with the correlation. The effects of some important factors, not included in the correlation, are also discussed