Effect of the thermostatic expansion valve characteristics on the stability of a refrigeration system-Part I

The combination of increased power dissipation and increased packaging density has led to substantial increases in chip and module heat flux in high-end computers. The challenge has been to limit the rise in chip temperature. In the past virtually all-commercial computers were designed to operate at temperatures above the ambient. However researchers have identified the advantages of operating electronics at low temperatures. The current research focuses on IBM´s S/390 mainframe, which uses a conventional refrigeration system to maintain chip temperatures below that of comparable air-cooled systems, but well above cryogenic temperatures. Attention will be to investigate the characteristics of the thermostatic expansion valve, specifically, the effect of variation of evaporator outlet superheat on the flow through the TXV at varying evaporator temperature, and the effect of sudden changes in evaporator heat load and condenser pressure variation on the temperature oscillations at the evaporator. The paper also discusses the effect of changes in the thermostatic bulb location and bulb time constant on the hunting phenomena at the evaporator.