Optimal Design Method For Sub-sections Of Shell And Tube Condenser For Vapor Compression Refrigeration

The main feature of a shell and tube condenser is that one or more sets of horizontal condenser tube bundles are installed in the housing.The cooling water goes through the tube side,and the refrigerant vapor goes through the shell side.The cooling water takes away the heat condensed by the working medium vapor outside the shell side tube bundle.Due to its advantages of adaptability to high temperature and high pressure,easy cleaning,easy manufacturing,and low production cost,it is widely used in petrochemical industry,energy power,refrigeration and air conditioning and other fields.However,the shell-and-tube condenser is still not satisfactory in terms of compact structure,heat exchange performance per unit of metal and metal consumption,etc.,so that its material saving efficiency has a significant impact on the quality improvement of the related fields.Imperfect design methods and inaccurate（or even missing）core thermal parameters are the main factors that cause the design redundancy of this type of heat exchanger.This article aims to correctly understand the heat exchange mechanism of different sections in the actual horizontal shell and tube condenser,and proposes a new design method that can effectively improve the compactness of the shell and tube condenser,and demonstrates it by combining experiments and theoretical analysis.The specific research work and results of this article are as follows:Firstly,the sensitivity analysis of each calculation parameter that affects the heat exchange area of the shell and tube condenser.Starting from the influence of the heat exchange area of the three heat exchange areas（superheat area,two-phase area and supercooling area）in the refrigeration and heat pump field on the total heat exchange area,the impact factors on the heat exchange area of each heat exchange area are analyzed separately.The results show that under most operating conditions,the heat exchange area of the two-phase zone has the greatest influence on the overall heat exchange area,and the area required for the unit heat exchange in the superheat zone and the supercool zone is large.Secondly,combined with the results of sensitivity analysis and the ideas and experimental work proposed by the research team to eliminate the tube bundle effect based on the drainage fluid,a new design method for the shell-and-tube condenser in this paper is proposed.The thermal design calculation process is improved.The thermal design calculation process is improved.Aiming at the sensitivity analysis results,the idea of separation of superheated zone and supercooled zone was put forward,combined with the original theoretical results of tube bundle effect,using the law of condensate flow pattern evolution and heat transfer,a new method of optimal design for the change law of tube bundle effect in two-phase zone The three main heat exchange tubes（smooth tube,2D tube and 3D tube）’s thermal calculation process are improved,and a specific application example was given by using smooth tubes as an example.Thirdly,based on the needs of the two-phase zone optimization idea,a falling film flow pattern control method based on the influence of liquid uniformity on the flow pattern evolution is proposed.An observation test bed for falling film flow patterns between horizontal tubes was established.Four types of liquid distributor structures were designed to create liquid distribution conditions with different degrees of uniformity.Experiments were conducted to study the evolution of falling film flow patterns between horizontal tubes with non-uniform liquid distribution conditions.The test results confirmed that the uniformity of the incoming flow can change the evolution law of the falling film flow pattern between the horizontal tubes.With the different degree of non-uniform liquid distribution,the difference of the falling film Reynolds number at the transition point of the flow pattern is higher than 90%.The uniformity of the incoming flow can be controlled by the structural parameters D_i,A/d_h and l_h/d_h of the liquid distributor.The falling film Reynolds number Re_tr at the transition point of the flow pattern has a certain functional relationship with the value of l_h/d_h that characterizes the uniformity of the incoming flow.Finally,combined with technical and economic analysis,the benefits that can be obtained by applying a new method of designing shell and tube condensers are evaluated.Using the new optimization design method proposed in this paper,combined with the precise tube bundle effect test results of HFC134a in smooth tubes and Turbo-CSL tubes,it is compared with the design results of the traditional tube bundle effect semi-empirical model and the improved semi-empirical model.The results show that for condensers that use smooth tubes and Turbo-CSL tubes as heat exchange tubes,under the same heat exchange capacity（at the same heat exchange amount）,after optimizing the structure of the superheating zone and supercooling zone,the material saving rate（heat exchange metal consumption）can reach98/7%,97.5%and 93.4%,94.4%.The amount of condensation heat exchange tubes in the new method in the two-phase zone can be reduced to 69.3%and 50.6%of the traditional method at most.Under investment,the heat exchange performance of the shell-and-tube condenser designed under the new method is increased to 2.37 times and 3.41 times that of the traditional design method.Through economic analysis,it is confirmed that the new method of optimal design using the test results of the high-precision tube bundle effect model can significantly reduce the design redundancy compared with the traditional design method.Based on the sensitivity analysis results of conventional shell-and-tube condensers,this paper proposes a reverse design method for the shell-and-tube condenser superheat,two-phase and supercooled three-section heat exchange surface structure and the overall heat exchanger.The key scientific issues involved in the reverse design of the heat exchange tube bundles in the phase zone were to conduct an experimental study on the effect of the uniformity of the liquid distribution on the falling film flow pattern of the single row of horizontal tubes,and to further improve the new design method.This article opens up new ideas for the independent research and development of China’s future development of large-scale shell and tube condensers,and provides an effective way to achieve sustainable energy development and promote energy conservation and emission reduction.