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 mainframe, which uses a conventional refrigeration system to maintain chip temperatures below that of comparable air-cooled systems, but well above cryogenic temperatures. An experimental bench was built to study the effect of variation of evaporator outlet superheat on system performance. Three different types of thermostatic expansion valves were tested in order to verify that the bulb size and bulb location have significant effect on the transient behavior of the system. Bulbs of each of the three thermostatic expansion valves were mounted at five different locations on the suction line. It was observed that the overall system stability increases as we move closer to the evaporator exit. It was also observed that there exists a region in the suction line at which the superheat variation is the least and placing the bulb at this region gives maximum stable operation of the system. This region can be defined as the minimum stable superheat point. Tests were conducted at five different load conditions 1000W, 750W, 500W, 250W and no load condition. It was observed that the system was the most stable at full load condition for all three types of valves and system stability consistently decreased as the load was decreased.

This content is only available via PDF.
You do not currently have access to this content.