Axial Heat Conduction in the Context of Developing Flows in Microchannels

For practical microchannel applications involving convective heat transfer, the flows are usually, not only laminar, they are also simultaneously developing in nature. Moreover, flat plate substrates with microchannels engraved/ machined or etched on them are emerging as one of the most popular flow geometries. Not analyzing such situations as conjugate heat transfer problems with multi-dimensional effects, often leads to erroneous estimation of heat transfer coefficients. In this context, we report three dimensional numerical simulations of simultaneously developing internal convective flow through a square microchannel (side = 400 μm), treating the substrate thickness, flow Reynolds number and the thermal conductivity of the substrate and the fluid, in the conjugate formulation. Constant heat flux is applied at the bottom of the substrate, away from the fluid-solid interface, as in real-time situations. The parametric study reveals that depending on geometry considerations, flow parameters and thermo-physical properties of fluid-solid combination, conjugate heat transfer effects must be accounted for, to correctly estimate the local Nusselt number.