Impact of area contact between sensor bulb and evaporator return line on MRU-Part 2, Experimental work

In the past, virtually all-commercial computers were designed to operate at temperatures above the ambient and were primarily air-cooled. However, researchers have always known the advantages of operating electronics at low temperatures. This facilitates faster switching time of semiconductor devices, increased circuit speeds due to lower electrical resistance of interconnecting materials and reduction in thermally induced failures of devices and components. Depending on the doping characteristics of the chip, performance improvement ranges from 1 to 3% for every 10/spl deg/ C lower transistor temperature can be realized. The IBM S/390 high-end server system is the first IBM design which uses a conventional refrigeration system to maintain the chip temperatures below that of comparable air-cooled systems, but well above cryogenic temperature. In previous work, the focus was to study the effect of variation of evaporator outlet superheat on the flow through thermostatic expansion valve at varying evaporator temperature. The effect of change in bulb location and effect of bulb time constant on the hunting at the evaporator has been reported. Also the effect of area contact on the stability of the system has been predicted theoretically. Mechanical analysis was performed in order to check the stresses induced. The evaporator return line and the sensor bulb are simply attached. In the present study, the effect of the area contact will be studied in detail by performing experiments on an experimental bench and the results will be compared with the theory reported.