Thermal performance of Gas-to-gas Micro Heat Exchangers

In this paper an experimental investigation of the thermal performances of gas-to-gas micro heat exchangers operating under different flow configurations (co-current, counter-current, cross flow) is presented and the results are compared with the predictions of the conventional correlations developed for the design of the conventional-sized heat exchangers. A double-layered microchannel heat exchanger has been designed in order to be able to reproduce co-current, counter-current and cross flow gas arrangements. The core is housed in a shell made of polymer; on the contrary, the foil between the hot and cold flow is exchangeable; several foils made with different materials (copper, peek, stainless steel,aluminum) and with different thickness have been investigated in order to put in evidence the effect due to the axial wall-fluid conjugate heat transfer on the thermal efficiency of the micro heat exchanger. The results show that the conjugate heat transfer tends to reduce the effectiveness of counter-current micro heat exchangers and to increase the effectiveness of cross flow micro heat exchangers. In the case of a co-current arrangement the role of the wall axial conduction is negligible.