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Numerical Simulation Of Enhanced Heat Transfer And Structure Optimum For High Temperature Heat Pipe Heat Exchanger

Posted on:2005-12-20Degree:DoctorType:Dissertation
Country:ChinaCandidate:S M SunFull Text:PDF
GTID:1102360125964490Subject:Chemical Process Equipment
Abstract/Summary:PDF Full Text Request
High temperature heat pipe heat exchanger (HTHPHE) is a type of high efficiency heat transfer equipment in the field of high temperature technology. The complicated structure and changing working conditions demand a highly complicated knowledge system for the HTHPHE, and this has resulted in large-size structure, high cost and unstable operation of the heat pipes in the transition zone in HTHPHE. In face of intensive market competition, to realize more reasonable design for HTHPHE, make it more economic and accelerate the process of its industrial application has become an urgent subject for study nowadays.In this article, study on enhanced heat transfer has been conducted for the HTHPHE on the basis of the research result on enhanced heat transfer performance of single heat pipe with respect to the structural features of HTHPHE, and the synergetic function of temperature fields inside and outside the heat pipe performed using the numerical simulation analysis method. On the basis of this research, structure optimization simulation study has been conducted using the parameter design method of computable items with the shortest period of initial investment recovery as the objective, for the purpose to minimize the investment cost and lower the operation expenses.The following has been mainly studied in this article:The following conclusion has been obtained from the research on enhanced heat transfer performance of single heat pipe: the theoretical and experimental studies have shown that, inserting a coaxial perforated pipe (referred to as diverting pipe in this article) into a thermal siphon pipe has been proved as a highly effective method to enhance the heat transfer performance of single heat pipes. The research results show that, the structural dimension of the diverting pipe has a significant bearing on the boiling heat transfer in the evaporating section; with the same transmission power, a diverting pipe with a perforation rate of about 33% and an annular gap of about 4.5mm provides the optimum boiling heat transfer, with the boiling heat transfer coefficient increasing by 2~3 times and the steam temperature in the pipe lowering by about 15~30C. By multi-parameter linear regression analysis of a large number of experimentaldata, the criterion equation for enhanced boiling heat transfer of diverting pipe has been obtained, and the regression calculation value of heat transfer coefficient basically agrees with the test results, and this has provided the theoretical basis for the study on local enhanced heat transfer for HTHPHE.HTHPHE's consist of heat pipes with different working media depending on their working temperature. This has added many difficulties on the simulation optimization study of the overall performance of heat exchangers. On one hand, the steam temperature inside the heat pipe is influenced by the temperature field of fluid outside the pipe and the heat transfer performance of the pipe itself, and on the other hand, the heat transfer performance of the heat pipe itself in turn influences the fluid temperature distribution outside the pipe. To coordinate the temperature distribution inside and outside the pipe, the author conducted study on local enhanced heat transfer for HTHPHE by means of the computation software of THERMAL ANALYSIS. For an ordinary carbon steel - water heat pipe, with an evaporating segment of 390mm and a condensing segment of 270mm in length, to ensure safe operation of the heat pipe, the fluid temperature outside the pipe must not exceed 300C, and the temperature of the fluid outside the pipe can reach 320 C when the enhanced pipe with optimized diverting pipe structure is used. In the mean time, the simulation result has well predicted the structure of optimum enhanced heat transfer elements, providing a reliable basis for widening the temperature range of application of heat pipe heat exchanger, and for safe connection of heat pipe heat exchangers with different temperature zones.On the basis of the above study results, optimization simulation study was...
Keywords/Search Tags:high temperature heat pipe heat exchanger, structure optimization, numerical simulation, enhanced heat transfer, parameter design
PDF Full Text Request
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