Microchannel counter-current heat exchanger analysis highlighting equitability of conventional heat transfer theory in both macro and micro domains

Abstract

• The axial conduction effect has been identified as a critical scaling factor. • Applicability of macro-models in micro domain depends on axial conduction intensity. • Kroeger’s model with conventional correlations can analyse micro heat exchanger. • Heat exchanger performance prediction is validated against 3D computational model. Some of the early experimental investigations on microchannel surfaces could not be explained using the macroscale heat transfer theory, creating doubts regarding its applicability. However, the data analysis in those studies has often been done neglecting performance deteriorating effects like axial heat conduction. The axial conduction effect is often overlooked in macroscale applications depending on the operating conditions. Nevertheless, recent studies have proved that the axial conduction effect becomes significantly dominant when the fluid free-flow area and solid cross-sectional area are comparable with the scaling down channel dimensions. Anticipating that the axial conduction effect overshadows the actual information of the microscale heat transfer characteristics, an approach taking care of the latter should be adopted. Kroeger’s analysis, an established macroscale method, has been used to analyze microchannels heat exchangers. The results are compared against those obtained from a three-dimensional conjugate computational model of a miniaturized exchanger. A good agreement between them indicates that the macro-scale exchanger analysis (including axial conduction) with the conventional correlations usually recommended for macro channels can also predict the thermal performance of the heat exchanger in the micro-realm. If axial conduction is neglected, performance deterioration in microscale heat exchanger effectiveness can be as high as 43%.