Heat transfer in micro-channels: Comparison of experiments with theory and numerical results

Single-phase heat transfer in microchannels: The importance of scaling effects

“…The review carried out above has highlighted, consistently with Hetsroni et al [14], that there are no new phenomena in heat transfer in microchannels, but the scaling effects and the measurement uncertainties can have a strong influence. Therefore, great care has to be used to estimate their influence when analysing the experimental results; otherwise, an incorrect representation of the physical reality may lead to wrong conclusions in the interpretation of experimental results.…”

“…All of the cited reviews about microchannels [9,12,[14][15][16][17] agreed that one possible explanation of the discrepancies between experimental and theoretical results, other than the above listed scaling effects, is the experimental uncertainty which may significantly reduce the reliability of the measurements. Morini [12], in particular, concluded that, because of experimental uncertainties, much of the earlier published results may be unreliable and not useful for comparisons.…”

“…Hetsroni et al [14] observed that, when comparing the experimental published data with simple 1D models that assume, for example, constant thermophysical properties, constant heat transfer coefficients and uniform wall temperature or heat flux, there are significant discrepancies between the measurements and the theoretical predictions and some "new effects" are often called for to adjust the models and make them match the experiments. On the other hand, numerical solutions based on the Navier-Stokes and  the experimental heat transfer coefficient calculated numerically, using the exact model with regard to the heat transferred through the solid substrate, represents the correct variation of the Nusselt number with respect to the Reynolds number;…”

Numerical Analysis About the Influence of Inappropriate Shape of the Cross-Section of Microchannels in Laminar Flow

“…However, other researchers have indicated that differences in rates and coefficients of heat transfer, as well as in Nusselt number, can be related to the flow velocity and fluid temperature [16,[34][35][36], the Reynolds number [9], the heat transfer conjugated [2,[37][38][39], the viscous dissipation [16,20,26,40,41], the surface roughness [42], the aspect ratio of microchannels [5,43] and the conductivity of the material that compose them [2,[37][38][39], besides experimental uncertainties [4,[30][31][32][33]44]. Some numerical studies [45,46] showed that the Nusselt number is more sensitive to the shape of the cross-section of the microchannels in comparison to other parameters, such as surface roughness, for example.…”

“…Some numerical studies [45,46] showed that the Nusselt number is more sensitive to the shape of the cross-section of the microchannels in comparison to other parameters, such as surface roughness, for example. Furthermore, there are numerical and theoretical studies that consider simplifications which differ a lot from what actually should occur experimentally as, for example, the negligence of viscous dissipation in numerical model [28,47], the true boundary condition at the limits [44] and the consideration of the fluid with constant thermophysical properties, in general.…”