Prediction of Heat Transfer for Compact Tube Heat Exchanger Based on Porous Models

A prediction method for temperature distributions in compact heat exchangers was developed by modeling the microchannel as porous medium. The study is focused on the mathematical formulas and solution methods for convective heat transfer of heat core. The governing parameters include Reynolds number, longitudinal pitch, transverse pitch, Nusselt number, inertial resistance factor, and effective heat transfer coefficient. First, the correlation mechanisms and laws between the key parameters' effects and heat transfer were revealed and explained. The results show that the temperature/pressure/velocity contours obtained from the porous-media model are consistent with those of the tube-matrix. When the longitudinal pitch has little effect on flow characteristics and Reynolds number, porous-media model and Zukauskas-correlation are consistent. Transverse pitch has significant effects on the flow characteristics and the Reynolds number. The heat transfer performance and Nusselt numbers obtained from tube-matrix, porous-media model, and Zukauskas-correlation decrease as the transverse pitch increases. Under different pitch conditions, the Nusselt number obtained by Zukauskas-correlation is larger than that of the porous-media model, which is larger than that of the tube-matrix. Second, the simplified model and fast calculation method were developed. Tube bundles of the heat exchanger core were modeled as micro-channels and theoretically as fluid-saturated porous structures. Results show the heat transfer performance predicted by the micro-channels, tube-matrix, and porous-media model is consistent under the same boundary conditions. These results are consistent with the experiment. In addition, the computing cost and time required for the porous-media and micro-channels model is relatively reduced. Especially for the micro-channels model, the calculating time is less than one-tenth of the original. Compared with the time-consuming numerical method, the new analytical solution has the advantages of cost and speed.