Numerical Study On Heat Conduction Effect In Mini Crossflow Heat Exchanger

In a traditional heat exchanger, the heat conduction within the wall materialdriven by the temperature gradient in axial direction of the fluid flow is usually verylimited and its effects can be neglected because the cross-section area of the wall ismuch smaller than that of the heat exchanger channel. However, in amini/micro-scale heat exchanger, the cross-section area of the wall material is of thesame order of magnitude as that of the channel, and the heat conduction in the wallmaterial in the direction of the fluid flow has a significant effect on the performanceof the heat exchanger.In this paper, the fluid velocity and temperature fields in mini cross-flow heatexchanger (MCHE) was numerically simulated to investigate the longitudinal heatconduction and its effect on the heat exchange in MCHE.In the present study, the global heat transfer coefficient and the equivalentthermal resistance were employed as the criteria to evaluate the performance ofMCHE. MCHEs were numerically studied with water and helium as the heat transfermedium respectively. The effects of the design parameters including thecenter-to-center distance of adjacent tubes in the same layer, the distance of adjacentlayers, solid materials, and tube diameter on the longitudinal heat conduction wasanalyzed, and the correlations of the global heat transfer coefficient and theequivalent thermal resistance with the design parameters were presented in this paper.The simulation results indicate that under low Reynolds number at the fluid inlet,increasing the center-to-center distance of adjacent tubes in the same layer, reducingthe distance of adjacent layers, selecting the solid materials with low thermalconductivity, increasing the cross-sectional area ratio of the fluid channel and thesolid wall could weaken the effect of the longitudinal heat conduction, and thusimprove the global heat transfer coefficient to achieve heat transfer enhancement. Inaddition,, the influence of the geometric parameters on the irreversibility of the heattransfer process in MCHE was studied based on the analysis on equivalent thermalresistance. The present study also proposed a method to estimate the global heat transfercoefficient of MCHE based on its operating and geometric parameters, and alsodefined a factor M concerning the effects of heat conduction in both fluids and solidmaterial to quantitatively determine whether the heat conduction of MCHE could beignored.