Numerical Investigation on the Conjugate Heat Transfer in Double-Pipe Heat Exchangers With Propane Flow Boiling

This investigation is part of the composite fuel project in the University of Oklahoma [1]. The composite fuel is a mixture resulted from natural gas resolving in liquid propane, which has a relatively lower storage pressure compared with that of compressed natural gas. Here in this paper, a numerical investigation of conjugate heat transfer among convection, wall conduction and flow boiling in a double-pipe heat exchanger is presented. The heat exchanger has hot fluid flowing in the annular section and propane boiling in the inside tube. A computer program is developed to calculate the conjugate heat transfer of convection, conduction and boiling. In computing the convection and conduction, control volume method and SIMPLE algorithm are used to solve momentum equations and the energy equation of conjugate heat transfer. The contribution of this work is to combine the third kind (Neuman) of boundary condition with the boiling correlations for flow boiling in horizontal tubes in order to calculate the conjugate heat transfer of the whole problem. Two boiling correlations have been selected to give inside tube boiling heat transfer coefficient. Because the boiling coefficient depends on the wall temperature and local propane quality, so we have to solve the boiling correlation, the conduction and the convection governing equations simultaneously. The iteration method and TDMA are used to solve these coupled equations. The two boiling correlations are Chen’s (1966) correlation [2] and Kandlikar’s (1990) correlation [3]. Finally the results are compared with the experiment data. It has been found in low quality range, Kandlikar’s result is close to the experiment data. Because very few data of propane flow boiling can be found in literature, we use propane pool boiling data by Shen, Spindler and Hahne (1997) [4] to estimate parameter F_fl in Kandlikar’s correlation. The influence of simultaneously developing velocity and temperature field at entrance length in annular passage is considered and discussed in detail. The wall conduction resistance is also compared with convection and boiling resistance in the whole length of the heat exchanger. The completed computer program can be used to the design of shell and tube heat exchangers.