| The passive containment cooling system is an advanced safety facility that uses passive technology,which has great significance for ensuring the integrity of the containment under accident conditions.However,due to the existence of non-condensable gases such as air and hydrogen in the containment under accident conditions,it will seriously deteriorate the condensation heat transfer efficiency of steam.Therefore,further research on heat transfer enhancement technology of steam condensation with non-condensable gas has far-reaching significance for improving reactor safety and optimizing passive safety cooling systems.In response to this problem,this paper has carried out and completed the following experimental and numerical simulation research work:(1)The steam condensation experiments with air on the exterior surface of the tube were carried out on the smooth tube,chrome-plated tube,and polished tube using the steam condensation test device,the influence of air mass fraction,condensation surface characteristics,total pressure and wall sub-cooling on the condensation heat transfer characteristics were analyzed.By combining the characteristics of the condensation surface(scanning electron microscope image and droplet contact angle)and the experiment results,it is found that the heat transfer capacity of the smooth tube is always better than the chrome–plated tube and the polished tube within the scope of the experiment conditions.It can better produce dropwise condensation on the surface of the smooth tube,the surface of the chrome-plated tube can be partially dripped,but the overall condensation mode is still close to film condensation,filmwise condensation can occur on the surface of the polished tube.The deep cavities on the surface of the chrome-plated tube tend to trap air,which inhibits its condensation capacity.(2)The condensing experiments of the steam containing air outside the heat transfer tube with the inclined arrangement were carried out to explore the effect of inclined arrangement tube on the air-contained steam condensation heat transfer characteristics.The experiments adopted three kinds of heat transfer tube inclination angles,and compared the results with the heat transfer tube vertical arrangement experiments.It is found that the inclined arrangement will cause the condensate on the surface of the chrome-plated tube and the polished tube to gather in the lower part of the heat transfer tube and cause falling off.It can effectively disturb the air boundary layer to enhance heat transfer,so the inclined arrangement has a significant effect on the condensation heat transfer enhancement of chrome-plated tubes and polished tubes.However,for the smooth tube,the droplet shedding radius is reduced due to the inclination and the washing time on the surface is reduced.This makes the condensation heat transfer capacity of the smooth tube not improved compared with the vertical arrangement,and it will even decrease in the medium wall subcooling range.(3)Combined with the comprehensive experiment of the containment,the CFD study of the directional induced flow method to strengthen the air-contained steam condensation in the Passive Containment cooling System internal heat exchanger was carried out.The main method is to induce flow in the flow field near the internal heat exchanger by designing some diversion structures to improve the gas flow and physical field distribution nearby to enhance heat transfer.In the numerical simulation,the geometric structure was made according to the actual test device,and the reliability and accuracy of the condensation heat transfer model used in the numerical simulation were verified by combining the relevant experiment data.The simulation results show that the calculation case with three diversion structures designed in this paper has significantly improved condensation heat transfer coefficient and total power compared with the case without diversion baffle,and the strengthening effect is between 5.83% and 10.76%. |
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