Hot water cooled electronics for high exergetic utility

Abstract

Cooling poses as a major challenge in the IT industry because recent trends have led to more compact and energy intensive microprocessors. Typically microprocessors in current consumer devices and state-of-the-art data centers are cooled using relatively bulky air cooled heat sinks. The large size heat sinks are required due to the poor thermophysical properties of air. In order to compensate for the poor thermal properties of air, it is typical to use chillers to pre-cool the air below the ambient temperature before feeding it to the heat sinks. Operating the chillers requires additional power input thereby making the cooling process more expensive. The growing cooling demand of electronic components will, however, render these cooling techniques insufficient. Direct application of liquid-cooling on chip level using directly attached manifold microchannel heat sinks reduces conductive and convective resistances, resulting in the reduction of the thermal gradient needed to remove heat. Water is an inexpensive, nontoxic and widely available liquid coolant. Therefore, switching from air to water as coolant enables a much higher coolant inlet temperature without in any way compromising the cooling performance. In addition, it eliminates the need for chillers and allows the thermal energy to be reused. All these improvements lead to higher thermal efficiency and open up the possibility to perform electronic cooling with higher exergetic efficiency. The current work explores this concept using measurements and exergetic analyses of a manifold microchannel heat sink and a small scale, first of its kind, hot water cooled data center prototype. Through the measurements on the heat sink, it is demonstrated that the heat load in the state-of-the-art microprocessor chips can be removed using hot water with inlet temperature of 60°C. Using hot water as coolant results in high coolant exergy content at the heat sink outlet. This facilitates recovering the energy typically wasted as heat in data centers, and can therefore result in data centers with minimal carbon footprint. The measurements on both the heat sink and the data center prototype strongly attest to this concept. Reuse strategies such as space heating and adsorption based refrigeration were tested as potential means to use the waste heat from data centers in different climates. Application-specific definitions of the value of waste heat were formulated as economic measures to evaluate potential benefits of various reuse strategies. Copyright © 2012 by ASME.