서강대학교

초록/요약

The main objective of the present study is to analyze flow and heat transfer characteristics of a heat exchanger in an industrial application using high-fidelity simulation techniques. We performed large-eddy simulations (LES) of turbulent flows around a fin-tube heat exchanger enclosed by a compartment. The complex geometry of the compartment poses a difficulty in a simulation as the local Reynolds number ranges two-orders of magnitude and generates various scales of the 3-D vortices and complex flow patterns. A careful test with the grid resolution and inflow condition was performed in order to compare our results with the measured data from a MRV experiment as well as the results from RANS simulations. It was observed that the results of the present study show a significantly improved agreement with the MRV experiment compared to the RANS simulations and enable realistic prediction of complex flow structures. From interaction of the flow structures such as the 3-D vortices, we observed a few interesting flow phenomena different from a plain fin-tube heat exchanger such as helical flows and a jet stream observed behind the fin-tube region. It was found that these flow phenomena and spatial pressure imbalance result in fluctuation of the jet stream, which can compensate for the loss of heat transfer in the regions with a relatively small flow rate affected by the compartment. Also, performance of the heat exchanger was analyzed using the data from plain fin-tube heat exchangers. Based on this analysis, a numerical technique was devised and tested to show a possibility of reducing the computational cost significantly using a porous media model. In spite of the reduction of the computational cost almost 40%, the difference of the heat trasnfer rate from LES with detailed geometry and the porus media model was about 2%.