Numerical Investigation In Heat Conduction Effect On Heat Transfer For Mini Cross-flow Heat Exchanger (mche)

Mini heat exchanger is a kind of high efficient heat-exchange equipment and has found applications in many highly specialized areas. Compared with the traditional heat exchangers, mini heat exchanger has smaller size but much higher heat transfer coefficient. Due to the difficulties in the experimental study of mini heat exchanger, the numerical simulation is an important approach to research of mini heat exchangers. In this paper, a solution procedure for simulation of the mini cross-flow heat exchanger (MCHE) has been implemented into a commercial CFD package (FLUENT).Different from the traditional heat exchanger, in a mini heat exchanger, the heat conduction in the material in the direction of the fluid flow may have a significant effect on the performance of the heat exchanger. However, limited research has been done on the heat conduction effect for MCHE.In this work, numerical simulation of heat conduction effect on heat transfer for mini cross-flow heat exchanger is performed. Three kinds of simplified models for MCHE are used in the numerical simulation: the plate simplified model, the square-section-channel simplified model and the circle-section-channel simplified model. The influences of the partition material thickness and its heat conductivity as well as velocities of the fluid on the heat transfer coefficient and heat transfer effectiveness are studied. The distribution of temperature and local Nu is also investigated.The simulation results indicate that the axial heat conduction in the partition material between the streams degrades effectively the performance of the heat exchanger by decreasing the heat transfer coefficient. The axial heat conduction has less influence when the velocity of fluid is larger. Longitudinal heat conduction in the partition material between the cool channels in the same layer (or the hot channels in the same layer) and axial heat conduction in the material between the adjacent hot and cold channels both have negative impact on overall heat transfer. It is demonstrated that the axial heat conduction effect can be weakened by optimizing the wall material conductivity, diameter of channels and partition thickness.