Conjugated Heat Transfer in Microchannels

Abstract

Energy conservation and sustainable development demands have been driving research efforts, within the scope of thermal engineering, towards more energy efficient equipments and processes. In this context, the scale reduction in mechanical fabrication has been permitting the miniaturization of thermal devices, such as in the case of micro-heat exchangers [1]. More recently, heat exchangers employing micro-channels with characteristic dimensions below 500 μm have been calling the attention of researchers and practitioners, towards applications that require high heat removal demands and/or space and weight limitations [2]. Recent review works [2, 3] have pointed out discrepancies between experimental results and classical cor-relation predictions of heat transfer coefficients in micro-channels. Such deviations have been stimulating theoretical research efforts towards a better agreement between experiments and simulations, through the incorporation of different effects that are either typically present in micro-scale heat transfer or are effects that are normally disregarded at the macro-scale and might have been erroneously not accounted for in micro-channels. Our own research effort was first related to the fundamental analysis of forced convection within micro-channels with and without slip flow, as required for the design of micro-heat exchangers in steady, periodic and transient regimen [4, 5]. Also recently in Refs. [6–11], the analytical contributions were directed towards more general problem formulations, including viscous dissipation, axial diffusion in the fluid and three-dimensional flow geometries. Then, this fundamental research was extended to include the effects of axial fluid heat conduction and wall corrugation or roughness on heat transfer enhancement [12]. The work of Maranzana et al. [13] further motivated the present analysis, dealing with longitudinal wall heat conduction effects in symmetric micro-channels.