Impact of TXV and Compressor in the Stability of a High-End Computer Refrigeration System

Abstract

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 is to limit the rise in chip temperature above the ambient. 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. Until recently, large-scale scientific computers used direct immersion cooling of single-chip modules. The current research focuses on mainframes (computer system), which uses a conventional refrigeration system to maintain chip temperatures below that of comparable air-cooled systems, but well above cryogenic temperatures. Multivariable control of compressor speed along with thermostatic expansion valve (TXV) opening can give better stability and performance. TXV is a mechanical controlling device used in the refrigeration system. The compressor is the only mechanical-working component in the refrigeration cycle that circulates refrigerant through the system continuously. Hence, controlling the compressor is an important aspect. The control objective is defined as improving the transient behavior of the vapor compression cycle for the refrigeration system operating around an evaporator set-point temperature. The system behavior is studied in two cases, TXV being the only control element in the first case, while TXV and a compressor both act as control elements in the other case.