Investigation Of Steam Condensation Heat Transfer Characteristics In The Presence Of Noncondensable Gases In A Horizontal Tube

To ensure the integrity of the containment in nuclear power plant under some serious accidents,the new generation nuclear reactors has applied the passive containment cooling system(PCCS)to condensate the steam by using the inner heat exchanger and finally accomplish the cooling and decompression to the containment.When the system is running,due to the influences of air and other noncondensable gases produced by the chemical reaction,such as hydrogen,the condensation heat transfer of steam will be strongly restained which will finally weaken the capacity of the whole system.To have a better understanding on the physical process of condensation,develop the current related researches and optimize the design of PCCS,the present paper conducted the experimental and theoretical study on the characteristics of condensation in the presence of noncondensable gases inside a horizontal tube.The major contents of the current research can be summarized as follows:1.By the experimental investigation on pure steam condensation,a general empirical correlation is proposed which is suitable for different flow regimes.The results has shown that the local heat transfer coefficient always increases with the increasing quality and pressure while the increase of gas velocity plays an active role on promoting condensation for annular flow but a negative role for wavy flow.Considering all the above effects on local heat transfer,the correlation gotten by multiple linear regression is proven applicable to annular,wavy and stratified regimes.Besides,the present correlation has an excellent accuracy and a more concise form.2.The condensation of steam with monocomponent and multi-component noncondensable gases is studied in the present research.The trends of the local heat transfer coefficient changing with noncondensable gases mass fraction and component,mixture gases pressure and velocity have been explored.During the experiments,hydrogen is replaced by helium due to the similarity of their physical properties and the influence of helium on condensation heat transfer was determined.According to the analysis,the diffusion of steam and the thermal diffusion of the noncondensable gases layer are both enhanced with the increasing volume ration of helium against air which eventually strengthen the local condensation heat transfer coefficient.3.Based on the experiments using water-cooling and air-cooling facilities,the effect of wall sub-cooling on condensation was comprehensively investigated for the first time.It is shown that this influence varies with the transition of flow regimes: for annular and wavy flow,the increase of wall sub-cooling promotes the condensation process;for stratified flow,it performs an opposite trend.Moreover,the increase of noncondensable gases mass fraction,mixture gases velocity and pressure can all boost expression of wall sub-cooling.On the basic of the analysis,the empirical correlations for condensation in the presence of monocomponent and multi-component noncondensable gases are brought out and have been proven to own a bigger applicable range and higher accuracy which compensates the shortage of the present researches in the world-side.4.A theoretical heat transfer model using the diffusion layer method for predicting the local heat transfer coefficient of condensation with monocomponent and multi-component noncondensable gases are built in the current work.By considering influence of the suction effect,interface roughness and the inhomogeneous distribute of condensate film,the prediction precision of the modified model is improved to a great extent.In addition,in the process of deriving the inhomogeneous factor,the model for calculating the thickness of the film is proven to predict the void fraction quite well whose calculated results show a little difference with the classical correlations.The axial distribute of the temperature and the thermal resistance is analyzed which shows that with the condensation of steam,the convective heat transfer of the bulk gases can be neglected when compared with the heat transfer for the film and gaseous boundary which causing the liquid-gas interface temperature gradually getting close to the inner wall temperature instead of the bulk mixture gases temperature.