Heat transfer efficiency of metal honeycombs

The efficiency of micro-cell aluminium honeycombs in augmenting heat transf er in compact heat exchangers is evaluated using analytical models. For con vective cooling, the overall heat transfer rate is found to be elevated by about two order of magnitudes when an open channel is designed with an alum inium honeycomb core. The performance is comparable to that achieved by usi ng open-celled aluminium foams, but attributed to different mechanisms. At low Reynolds numbers (< 2000), the flow is essentially laminar in honeycomb s, in contrast to the largely turbulent flow in metal foams; this deficienc y in fluid dynamics is compensated for by the superior surface area density offered by honeycombs over foams. Another advantage of designing heat sink s with honeycombs is the relatively small pressure drop experienced and min imal noise generated by the laminar flow. The overall heat transfer rate of the heat sink is maximised when the cell morphology of the honeycomb is op timised. However, the optimal cell morphology is not constant but dependent upon the geometry and heat transfer condition of the heat sink as well as the type of convective cooling medium used. For air cooling, the optimal re lative density of the honeycomb is about 0.1. Other related effects, such a s cell orientation and double cell wall thickness, are discussed. (C) 1998 Elsevier Science Ltd. All rights reserved.