Compact/micro-heat exchangers - Their role in heat pumping equipment

Compact and micro-heat exchangers have many advantages over their larger counterparts, particularly when used to handle clean fluid streams, either single- or two-phase. Probably the most exciting feature of such heat exchangers is their ability to operate with close approach temperatures, leading to high effectiveness. This can be particularly beneficial when the exchangers are used in power-producing or power-consuming systems, where the improved heat exchanger effectiveness can be immediately realised in higher power outputs or reduced power consumption. In the case of heat pumping equipment - the most common examples being air-water or air-air vapour compression cycle heat pumps for domestic heating - this manifests itself in an increased Coefficient of Performance (COP) that reduces CO2 emissions due to a lower energy input needed to drive the compressor. This paper gives a snapshot of some of the work carried out in five countries, Austria, Japan, Sweden, USA and the UK, within the IEA Heat Pump Implementing Agreement Annex 33 to identify the heat exchangers that can most benefit heat pump cycles, with a strong emphasis on micro-channel heat transfer. It also presents data on other research relevant to the subject, highlighting the 'micro' size range - the theme of the MNF 2009 Conference.