An Enhanced Vapor Chamber using Dielectric Organic Refrigerant

Abstract

General purpose computing on GPU (Graphics Processing Units) is gaining momentum, however, GPU is reaching air cooling limit at the same time. As thermal resistance of GPU’s heat sink is already minimized, thermal resistance between GPU and heat sink is required to be reduced in order to overcome the air cooling limit. The present study investigates an enhanced vapor chamber using dielectric organic refrigerant in place of water as working fluid. It is important to increase evaporative heat transfer coefficient in order to reduce thermal resistance of a vapor chamber, and it is confirmed that evaporative heat transfer coefficient at the heat flux of GPU can be increased by utilizing refrigerant, because bubble generation frequency becomes significantly higher due to weaker surface tension although heat transfer quantity by generating a vapor bubble becomes smaller due to smaller thermal conductivity and specific heat. In addition, the presented vapor chamber can be applied to immersion cooling as refrigerant is dielectric, and thermal resistance of grease between GPU and vapor chamber can be eliminated. On the other hand, wick redesign is necessary because thermal diffusion performance of the vapor chamber is greatly degraded due to the weaker surface tension. It is also revealed that evaporative heat transfer coefficient is decreased by making effective capillary diameter of wick smaller, therefore, the vapor chamber (and the wick) should be made thicker contrary to the conventional design. The air cooling limit is estimated to be increased by 5%, and for future work, is aimed to be doubled by applying to immersion cooling.