Numerical Study On Flow And Heat Transfer Characteristics For Supercritical Pressure Carbon Dioxide In Horizontal Tubes

The heat transfer performance of supercritical fluid is different from that of subcritical fluid because of their distinctive thermophysical properties.Recent years more and more engineering applications of supercritical fluid have been put forward,which requires accurate understanding of heat transfer characteristics of supercritical fluid.In this paper,the the accuracy of ten turbulence models for calculating supercritical heat transfer is systematically evaluated by using supercritical pressure carbon dioxide as the object of study.The flow and heat transfer characteristics of supercritical carbon dioxide in horizontal smooth tube and internal rifled tube are investigated by using the recommended model.The influence factors of heat transfer such as flow condition parameters,the diameter of pipe,the buoyancy force,the flow acceleration are systemic studied.The accuracy of buoyancy criteria in predicting flow pattern and heat transfer performance in the tube was evaluated and the threshold of buoyancy criterion is modified.Finally the performance of smooth tube and internal rifled tube was compared and analyzed.The main work of this paper is as follows:1.Based on the published experimental data,the accuracy of ten turbulence models for predicting supercritical heat transfer is systematically evaluated.The results show that the low Reynolds number LB model is the best one.2.The effects of flow parameters such as heat flux,mass flow rate,inlet pressure and pipe diameter on the heat transfer performance of supercritical pressure carbon dioxide are investigated,the mechanisms for the influence of the above factors on the heat transfer performance are summarized.3.The effects of buoyancy and flow acceleration on heat transfer performances are investigated.The influence of buoyancy on heat transfer performance is analyzed from the aspects of flow field distribution,thermophysical parameters distribution,turbulent kinetic energy distribution and so on.The accuracy of commonly used buoyancy criteria in predicting the influence of buoyancy on flow pattern and heat transfer performance are evaluated and the threshold of buoyancy criterion is modified according to the calculation results.4.The flow and heat transfer characteristics of supercritical pressure carbon dioxide in internal rifled tube are studied in this paper.The results show that the inherent structure of internal ribbed tube obviously inhibits the influence of buoyancy and enhances the heat transfer,the heat transfer performance between the upper and lower wall of the tube tends to be the same,the circumferential wall temperature distribution is more uniform,but the pressure drop is slightly higher than that in smooth tube.