Experimental Study Of The Film Condensation Row Effect On An Array Of Tubes With Large Tube Row

Horizontal shell and tube condensers are widely used in refrigeration system,chemical process and other areas.For the refrigeration system,the condenser is an important part of chiller,heat pump unit and central air conditioner.The heat exchange efficiency of the condenser directly affects the cooling and heating performance of the entire unit.In the design of the horizontal shell and tube condenser,the heat exchange tubes as its core component has gradually developed from a smooth tube to a two or three-dimensional finned tube with a stronger heat exchange performance.For the tube bundle composed of the tubes in the shell,the film condensation heat transfer occurring in the shell is a key link in the design process,in which the row effect is an important parameter of the film condensation heat transfer characteristics,and is also an indispensable primary parameter to measure the heat transfer efficiency.However,due to high experimental cost,complicated experimental system construction,difficult experimental operation,and uncontrollable experimental error,the row effect is still problematic for further research at the experimental and theoretical levels.(a)In the field of film condensation heat transfer of large tube row,there is no uniform validation of experiment and inspection standard.For the single tube experiment,the experimental results of the plain tube can be compared with the Nusselt single tube prediction model to verify the reliability of the single tube experimental system.However,for the experiment and research of tube bundles,there is no standard tube bundle model for comparative analysis to verify the reliability of the tube bundle experimental system.(b)In the process of modeling the tube bundle effect of two and three-dimensional tubes,there is still a lack of universal falling film mode correlation that considers the influence of fin structure.This is the premise and basis for further research on the row effect of two and three-dimensional tubes.(c)At present,there is a lack of high-precision and easy-to-operate row effect instruments in engineering applications.In order to solve the above problems,this thesis carried out systematic experiments and theoretical work,the specific contents are as follows.First of all,in order to study the validation of experiment and inspection standard of tube bundle film condensation of large tube row,this thesis designs a test section and contains two arrays of 17 horizontal plain tubes,and the test section is applied to construct experimental system of film condensation on an array of horizontal plain tubes.Commissioning and inspection of the experimental system are completed.The result shows that the thermal balance rate of the experimental system is within ±4.9%,and the deviations from the Nusselt analytical solution of single tube were within ±3.9%,all of which meet the internationally recognized thermal balance rate±5.0%and validation of single tube experiment±10.0%.This research work provides test conditions and data analysis methods for obtaining high-precision row effect data.Secondly,in this thesis,using an experimental system of plain tube bundles and R134a as the refrigerant,the experimental study of film condensation on an array of horizontal plain tubes is carried out.Within the range of test conditions,accurately obtained the variation of the row effect of the plain tube(the error of the row effect is controlled within ±2.0%)with the Reynolds number of the condensate falling film.According to the experimental results,a standard semiempirical model of the tube bundle considering the judgment of the falling film mode between tubes is obtained by regression.The result shows that the tube bundle model obtained in this thesis can accurately describe variation of row effect,and the result of row effect and the model provide high-precision validation of experiment and data inspection standard for the field of tube bundle film condensation heat transfer.The research method of the plain tube bundle also provides a reference for the subsequent research on the row effect of the three-dimensional tube.Thirdly,in order to obtain universality and consider the influence of fin structure,the falling film mode correlation between two and three-dimensional tubes is to further study the row effect of these two types of high-efficiency tubes,this thesis designs and establishes an experimental system of falling film flow between tubes.Commissioning and inspection of the experimental system are completed.The experimental system uses water as the falling film working fluid.This system is used to study the effect of hysteresis,tube spacing and fin structure on the falling film transitional Reynolds number.According to the experimental results,the correlation of the falling film mode determination criteria for two-dimensional tubes and some three-dimensional tubes are established respectively,which further standardized the determination of falling film mode between two-dimensional and three-dimensional tubes.The two and three-dimensional tube bundle heat transfer model provide a more widely applicable falling film mode determination formula.Fourthly,in order to apply the research methods of the tube bundle validation of experiment and inspection standard in this article to the actual project,and solve the problem of the lack of high-precision and easy-to-operate tube bundle effect instruments in the project.This thesis designs,develops and processes a three-dimensional row effect test equipment with two arrays of 8 horizontal tubes.Commissioning and inspection of the test equipment are completed.The result shows that the thermal balance rate of the test equipment is within ± 4.8%,and the deviations from the Nusselt analytical solution of single tube were within ±3.1%,all of which meet the internationally recognized thermal balance rate±5.0%and validation of single tube experiment ± 10.0%.Provides test conditions and data analysis methods for studying the tube bundle film condensation row effect of the three-dimensional tube.Finally,using the test equipment of row effect,using R134a as the refrigerant,the film condensation row effect of three-dimensional tube bundles is studied within the set test conditions.Accurately obtained the variation of the row effect of the three-dimensional tube(the error of the row effect is controlled within±2.0%)with the Reynolds number of the condensate falling film.According to the test results,a semi-empirical model of threedimensional tube bundle is obtained by using the correlation for judging the falling film mode between tubes and the modeling method of plain tube bundle.The result shows that validation of experiment for plain tube bundle and the research on the falling film mode between tubes can be applied to the film condensation study of the three-dimensional tube bundle.The research results provide high-precision reference data and tube bundle modeling methods for the subsequent experimental and theoretical studies of enhanced tube bundles.The research work in this paper will have important academic value to reveal the variation of tube bundle film condensation heat transfer and to promote the development of tube bundle heat transfer model,to further improve the heat exchange efficiency of air conditioning and refrigeration units.It has the value of promotion and application for saving tube materials and reducing equipment cost,designing and developing high-efficiency horizontal shell and tube condensers,optimizing and developing the air-conditioning and refrigeration equipment industry.