Research On Heat Transfer Exchanger Of Long-term Filter Venting System

As the last barrio to prevent the radioactive materials releasing into the environment under the serious accident,the integrity of containment is important for the safety of the nuclear power plant. To ensure the long-term emission of the containment, this paper designed a long-term filter venting system. The horizontal layout air-cooler is most critical equipment of this system. It's used to condense the water evaporated from the venture scrubber. The condensate draw back to the scrubber,thereby maintaining the chemical solution level in the scrubber. In the steam condensation process inside the horizontal tube, the presence of large amounts of non-condensable gases will lead to the serious deterioration of heat transfer coefficient, further research on steam condensation in the presence of air must be conducted.So an experimental device was built to study this problem. Furthermore, a program using Fortran language was built to verify the operating characteristics of heat exchangers and the overall system. The main work and results are given as:(1) The local condensation heat transfer characteristics of pure steam inside horizontal tube were experimentally investigated and the influence of wall subcooling, steam pressure and steam velocity on condensation heat transfer coefficient was analyzed. What's more, the two-phase flow patterns along the heat transfer tube were identified using Mandhane, Taitel and Dukler, Breber and Tandon flow map. On this basis, the heat transfer coefficient calculated by current correlations was compared with the experimental results and the disadvantages were pointed out. At last, a new correlation was put forwarded by fitting experimental data.(2) The local heat transfer characteristics of steam condensation with noncondensable gas inside horizontal tube were experimentally investigated and the influence of noncondensable gas mass fraction, wall subcooling, pressure and velocity on condensation heat transfer coefficient was analyzed. And by fitting the experimental data, a correlation which is suitable for calculating the condensation heat transfer coefficient of steam condensation with noncondensable gas is obtained. On the basis of experimental studies, a RELAP5/MOD4.0 simulation model was established, and the calculated resutls were compared with experimental results, and the applicability and accuracy of the model were analyzed.(3) The operating characteristics of condensate recovery system and passive air cooling system of long term filter venting system were analyzed. The results showed that it just needs to ensure that the diameter between outlet of venture scrubber and inlet of air cooler is greater than 0.2m and the relative height between venture scrubber and air cooler is greater than 2.5m,then the condensate can return to the venture scrubber just depending on gravity; The pipe length and number of elbows of the air side have significant impacts on the amount of condensate of the air cooler, and the amount of condensate decreases with the pipe length and the number of elbows increasing; Compared with smooth tube, it required less length and number of tubes if air cooler used finned tubes under the same condition and condensate of air cooler, and air cooler become more compact. The performance of air cooler is greatly improved when using finned tube.