Study On Heat Transfer Characteristics Of Supercritical Carbon Dioxide Tube-in-tube Gas Cooler

Casing heat exchanger is widely used in power,energy,petrochemical and food industries due to its compact structure,high pressure resistance and high heat transfer efficiency.Based on the excellent physical properties of carbon dioxide and its good thermal performance in the trans critical state,the research on supercritical carbon dioxide fluid is increasing in recent years,but most of the research focuses on the flow characteristics and flow field analysis of supercritical fluid in a single tube.This paper takes the tube-in-tube gas cooler with supercritical carbon dioxide as the research object,and intends to carry out the numerical simulation research on the flow and heat transfer characteristics of supercritical carbon dioxide fluid in the tube-in-tube gas cooler,so as to provide reference for the application and design of carbon dioxide heat pump air cooler in the future.The internal heat transfer process of the gas cooler is an irreversible process,and the irreversible loss has a great influence on its heat transfer performance,based on the entropy production theory and the theory of entransy dissipation,this paper uses the CFD numerical simulation technology to establish the model of the straight tube tube-in-tube cooler.Through the numerical simulation method,the heat transfer process between carbon dioxide and cooling water in the supercritical carbon dioxide tube-in-tube gas cooler is numerically simulated,the influence of different operating parameters on the distribution of irreversible loss in the gas cooler is analyzed,and the structure of the air cooler is improved.It is found that the entropy production increases with the increase of carbon dioxide inlet temperature,and the entransy dissipation increases,while the entropy production decreases with the increase of cooling water temperature,but the change of cooling water temperature has little effect on the entransy dissipation,which can be ignored;With the increase of cooling water mass flow rate,the entransy dissipation decreases,and the entransy dissipation at the inlet of carbon dioxide is the largest relative to that at other locations of the tube-in-tube gas cooler.Compared with the cooling water mass flow rate of 0.03kg/s,when the cooling water mass flow rate is 0.04kg/s,the entransy dissipation is reduced by 2.6%,and when the cooling water mass flow rate is 0.05kg/s,the entransy dissipation is reduced by 3.2%;With the increase of carbon dioxide mass flow rate,the entropy production decreases and the entransy dissipation increases.And with the increase of pressure,entropy production increases and entransy dissipation decreases Finally,on the basis of the straight tube-in-tube gas cooler,the structure of the tube-in-tube gas cooler is optimized,and the spiral tube-in-tube air cooler is designed based on the entropy production theory and the theory of entransy dissipation.Compared with the straight tube-in-tube gas cooler,the average temperature difference of spiral tube gas cooler is reduced by 8.1%,the entropy generation of 60% tube length is reduced,the entropy generation is reduced by 7.31%,and the entransy dissipation is reduced by75.87%,the energy loss of the spiral tube-in-tube gas cooler is greatly reduced,the irreversible degree is reduced,and the heat transfer efficiency of the air cooler is improved.For the engineering application of carbon dioxide heat pump air cooler has laid a good theoretical basis.