Font Size: a A A

Study Of Heat Transfer Enhancement On Steam Condensation In The Presence Of Air Outside The Single-tube

Posted on:2024-06-21Degree:MasterType:Thesis
Country:ChinaCandidate:W T LiFull Text:PDF
GTID:2531306941999079Subject:Nuclear Science and Technology
Abstract/Summary:PDF Full Text Request
When serious accidents occur in nuclear power plants,such as Loss-of-Coolant Accidents,a large amount of steam is released into the containment vessel.To prevent the containment from breaking and releasing radioactive materials into the environment,new generation nuclear power plants have installed a Passive Containment Cooling System(PCS).The PCS is designed to transfer the heat inside the containment vessel to the outside world without using any external energy sources.However,the efficiency of the PCS heat exchangers is affected by the presence of non-condensable gases,such as air,outside the tube steam condensation.This deterioration in heat transfer efficiency can be significant,and structures that are effective at enhancing heat transfer in pure steam condensation may not work well when air is present.To improve the heat transfer efficiency of PCS heat exchangers and enhance the safety margin of the containment,it is important to study methods for enhancing steam condensation heat transfer in the presence of air outside the tube.In this paper,the enhanced heat transfer by condensing air-containing vapor outside the tube is investigated by numerical simulation and experiment.A diffusion boundary layer model was developed using CFD software to simulate the condensation of air-containing vapor outside the tube,and the distribution of each parameter outside the tube was analyzed to find out the factors affecting heat transfer,and new enhanced heat transfer tubes were designed accordingly.In order to study the heat transfer performance of the designed enhanced heat exchanger tubes,the condensation and species transport facility was built,and experimental studies were conducted for each enhanced heat exchanger tube containing air vapor condensation outside the tube in the range of 0.2 MPa ~ 1.3 MPa,10% ~ 90% air mass share,and 20 ℃ ~ 80 ℃ wall subcooling.Through numerical simulation studies,it has been discovered that the high concentration air layer is an important factor affecting heat transfer,and its appearance can significantly reduce the local heat transfer coefficient.The study on tube length and inclination angle found that tubes with a length of less than 0.3 m have higher heat transfer coefficients,and the shorter the tube length,the higher the heat transfer coefficient.The high concentration air layer outside the inclined tube will fall downward,which will result in a larger increase in the heat transfer coefficient compared to a vertical tube.Based on the above influencing factors,two types of enhanced heat transfer tubes have been designed: spoiler heat transfer tube,which divide the heat transfer tube into short tubes and guide the air layer,and heterotypic tubes that combine the advantages of short tubes and inclined tubes.The results of the spoiler heat transfer tube experiment show that the air layer above the spoiler still affects the bottom.The heat transfer effect of the heat transfer tube with a 5 cm radius of thespoiler is poor.The horizontal spoiler only has about a 10% strengthening effect at high pressures above 1.0 MPa,but it inhibits heat transfer at low and medium pressures.The heat transfer coefficient of the tilted spoiler heat transfer tube is lower than that of the vertical light tube under different working conditions.Moreover,the heat transfer coefficient of the staggered spoiler heat transfer tube is only about 5% higher than that of the vertical light tube under various working conditions.The results of the heterotypic tubes(microwave tubes and serpentine tubes)show that heterotypic tubes can cause the air layer to detach and create scouring in some areas of the heat transfer tube,resulting in better enhanced heat transfer.The higher the arch of the microwave tube and the larger the radius of the semicircular section and the length of the horizontal section of the serpentine tube,the better the enhanced heat transfer effect.In the experimental components,the microwave tube with a higher arch(150 mm)can enhance the heat transfer by about 20% compared to the vertical light tube under the experimental conditions,with a maximum enhancement of 35%.The serpentine tube with a larger semicircular section radius and horizontal section length(semicircular section radius of 250 mm and horizontal section length of 200 mm)can enhance the heat transfer by more than 20% compared to the vertical light tube under the experimental conditions,with a maximum enhancement of 51%.
Keywords/Search Tags:steam condensation, noncondensable gas, smooth tube, enhanced tube
PDF Full Text Request
Related items