The Research On Entransy Degeneration Theorem And Optimization Of Heat Exchanger

High consumption and high pollution are the main characteristics of industrial development in our country.One of the keys to solve the problem is the development and application of the technology relevant to energy conservation and emissions reduction,one of which is the development of the heat transfer technology.The research on the entransy theory and the combination between the entransy theorem and the optimozaion of heat exchanger has important theoretical value and practical significance.In this study,entransy theorem and the optimozaion of heat exchanger were studied systematically under the support of the National Natural Science Foundation of China(Project Contract No.21576245).The achievements are as follows:(1)The exergy theory and the entransy theory were employed to investigate the characteristics of the generalized irreversible Carnot engine system(GICES),which is based on the generalized irreversible Carnot engine model with the generalized heat transfer law.A novel physical variable named "Entransy degeneration" was proposed,which is the mathematical expression of the exergy loss with entransy theory.Two types of entransy descriptions,the entransy loss and entransy dissipation,were used to express the GICES and the heat transfer process,respectively.Thus,the "Entransy degeneration" was applied on the analysis of the entransy loss balance equation of the GICES,and the entransy dissipation for heat transfer process.In addition,a novel dimensionless number named "entransy number" was defined to synthesize the entransy loss for the GICES and the entransy dissipation for the heat transfer system.Then,the synthetic expression of the entransy equations was obtained,which is the mathematical expression of the relationship between the entransy loss and the entransy dissipation.(2)The "Entransy degeneration" was applied on the research for the generalized heat transfer system(GHTS)and the heat exchanger,in which another novel dimensionless number named "Entransy degeneration number" was defined to express the characteristics of "Entransy degeneration".In addition,the comparative study on the characteristics among "Entransy dissipation",the "Entransy degeneration",and the exergy loss was conducted.The result showed that,there was the equivalent physical meaning among them to express the energy loss in the GHTS and the heat exchanger.(3)The experimental platform of heat exchanger was built for testing the multiple coiled-tubes heat exchanger(MCTHE).The Wilson plot method was employed to obtain the enhanced heat transfer coefficient of the MCTHE.In addition,the study on the characteristics among the "Entransy dissipation",the "Entransy degeneration",the exergy loss,and the effectiveness of heat exchanger in the MCTHE was investigated.There is phase change in the hot working fluid of the heat exchanger(steam),thus,a new equivalent average temperature to express the phase change process of the steam was proposed.The results showed that,the "Entransy degeneration" could effectively express the irreversible loss in the MCTHE,which proved the validity of the "Entransy degeneration".(4)The numerical investigation on the multiple objectives optimization of the MCTHE was carried out,in which the "Entransy dissipation",the "Entransy degeneration",the Nu,and the pressure drop were adopted as the optimization objectives,and the pitch of the inner level tube(P1)and the pitch of the outer level tube(P2)were adopted as the parameters.The Multi-Objective Genetic Algorithm(MOGA)was taken as the optimization algorithm.Through the software ANSYS workbench,the whole process of the numerical optimization of the MCTHE was carried out.The results showed that,the validity of the equivalent average temperature was confirmed with the "Entransy degeneration".Through the analysis on the effect of the optimization parameters to the optimization objectives,the optimized values of the PI and P2 were obtained.(5)The topology optimization method of heat exchanger was preliminary explored.The N-S equations of the fluid in the porous medium was utilized as the governing equations of design domain,the SIMP(Solid Isotropic Microstructures with Penalization)method was applied to control the difference between the solid domain and the fluid domain.The MMA(Method of Moving Asymptotes)was taken as the optimization algorithm,Through the software COMSOL Multiphysics,the whole process of the topology optimization of heat exchanger was carried out.The results showed that,both the input power and the heat source had greatly effect on the final structure of the optimized results.Under the constant heat generation,the structure of the optimized results become more and more complex,that is,Re increases with the number of the branches.While under the constant input power,the structure of the optimized results become more and more complex as the heat generation of the solid domain increases.