Research On The Condensation Heat Transfer Characteristics Of C-Shaped Passive Residual Heat Removal Heat Exchanger

The passive residual heat removal heat exchanger is one of the most important passive safety equipment used in the new generation nuclear power stations AP1000 and CAP1400.Passive residual heat removal heat exchanger consists of a large number of C-tubes.The heat capacity of C-tube directly determines the performance of the heat exchanger,so it is necessary to study the transfer mechanism of C-tube bundles.For severe accident conditions,an experimental study is performed for the steam condensation in C-tube.This paper mainly includes the design and construction of principles of the experimental platform of C-tube bundles,and the tube steam condensation heat transfer tests at full level and low-level conditions.The major experimental work and results are showed as follows:1.Adoption of single-tube and tube bundles tests at the full level,the results show that: the condensation heat transfer coefficient of C-tube increases with the promotion of steam pressure,which is similar to that in the horizontal tube;The heat transfer capabilities of each tube is different due to the effect of the bundle;Affected bundle effects,when the vapor pressure is lower(less than 0.3MPa),the heat capacity of B pipe of tube bundle is stronger than B pipe of single tube;When the vapor pressure is higher(greater than 0.4MPa),the heat capacity of B pipe of tube bundle is lower than the B pipe of single tube;2.The traditional relationships of calculating condensation heat transfer coefficient were used for straight tubes,not for C-tubes.This paper based on a large number of experimental data,consulting Shah empirical formula and D-B formula,considering the specific structural features of C-tube,proposes respectively new condensation relationships for single-tube and tube bundles.With this relationship,the maximum deviation of calculated values and the experimental value are maintained within ±9% and ±18% severally.Therefore it has good predictive ability;3.By reducing the level of saturated water tank,this paper implemented four low-level tests,including the elbow level,the vertical tube 4/5 level,the vertical tube 2/3 level and the vertical tube 1/2 level.The results show that: under low level conditions,in order to simplify the calculation,the heat transfer tube is divided into the vapor space region and liquid immersion region.The calculated results show that the condensation heat transfer occurs mainly in the liquid immersion region;The condensation heat power of C-tube increases with the promotion of steam pressure and continuously drops with the decrease of level.However,the reduction rate of heat transfer power for C-tube is basically consistent with the reduced rate of heat transfer area;Furthermore,the condensation heat transfer coefficient of low level tests are lower than that of full level test at same pressure condition,but the condensation heat transfer coefficient of the various low-level changes little.