Numerical Simulation Research On Heat Transfer Characteristic Of Natural Circulation Heat Exchanger

The natural circulation heat exchanger of passive residual heat removal system was putinto use in the nuclear plant non-loss-of-coolant accident. It can discharge the waste heat inthe reactor core timely, and prevent the reactor accident. The passive means such as densitydifference, temperature difference and the gravity are as driving force in natural circulationheat exchanger, so that the fluid within the heat exchanger can produce natural circulation.The passive means reduce the dependence of the facilities which need power such as pumps,fans, etc. It can also reduce the influence of people factors to power plant safety. The use ofnatural circulation in the nuclear power plants can effectively increase the reactor safetyperformance of the power plant in the event of an accident.In this paper, FLUENT hydrodynamics analysis software is used to simulate the heattransfer characteristics of natural circulation heat exchanger. The main content of the study isthe following:1. Analysis physical model of the heat exchanger, then appropriate simplified thisphysical model, and application Pro/E software to establish the study physical model of thenatural circulation heat exchanger. Assisted by the mathematical model, the establishing of theentire heat exchanger modeling is completed.2. Analysis the tube side and shell side temperature field of the heat exchangerrespectively，then research the heat transfer process of the heat transfer tubes, and analysisdifferent position heat transfer of the heat exchangers shell side. Analysis the averagetemperature of the outlet of the heat exchanger and the error between the outlet averagetemperature and design temperature，then evaluate the heat transfer performance of the heatexchanger.3. Analysis velocity field of the heat exchanger shell side, from the analysis theinfluence of the heat exchanger structure to the natural circulation can be known, and thenmake relevant comments to optimize the design of the heat exchanger.4. Analysis the work performance of the heat exchanger in different operation condition;and compiling boiling UDF model of the heat exchanger, and then embedded the model in theFLUENT software. Simulation and analysis the internal steam flow under the boilingconditions of the heat exchanger，and improvements of the heat exchanger according to the simulation results.Through the analysis to simulation results, it can know that natural circulation heatexchanger can discharge the waste heat in the reactor core timely. Although some errors areexist between the analog value and the design value, but the errors are so small that theycannot influence the analysis to the heat exchanger. Through the analysis we can also knowthat because of the complex structure of the heat exchanger makes the locally part generate“heat transfer dead zone” and “flow dead zone”. The presence of these dead zones affectedthe formation of the natural circulation in the heat exchanger. When the heat transfer for aperiod of time, the fluid temperature in the shell side of the heat exchanger reaches thesaturated and the fluid appears boiling, then the large amount of steam generated andaggregated the “cusp” of the heat exchanger, it can affect the flow and heat transfer of thefluid in the heat exchanger. In this paper the results of this study can provide some referencefor the construction of nuclear power plant facilities passive.