Experimental Study On The Pool Vaporization Process Of Cryogenic Liquid Leakage On Land

Cryogenic liquids,such as liquid hydrogen,liquid ammonia,liquid chlorine and liquid nitrogen,as liquid fuels,refrigerants and industrial chemicals,are flammable,explosive,low temperature and toxic.Once leakage occurs,it will cause serious consequence.Relevant research work mainly focused on the analysis of heat transfer process of concrete base after the leakage of cryogenic liquid.The cryogenic pool above the concrete surface was assumed to be an ideal low temperature condition,without considering the boiling heat transfer process of the cryogenic pool above.In this paper,the heat transfer and vaporization process of cryogenic pool under the combined action of heat conduction of concrete and boiling convective heat transfer of cryogenic pool is studied experimentally.A coupled calculation method of heat transfer and vaporization process of cryogenic pool is proposed.On this basis,the influence of different leakage base conditions on the heat transfer and vaporization process of cryogenic pool is explored.The specific work and conclusions are as follows:Firstly,a visualized experimental platform for cryogenic liquid leakage heat transfer and vaporization was built,including temperature measurement system,weight measurement system,high-speed image and data acquisition system and visual device of pool boiling.It can realize high-speed recording of liquid nitrogen boiling bubble morphology during liquid nitrogen heat transfer and vaporization process,and high-frequency acquisition of concrete temperature and liquid nitrogen pool mass.Secondly,using liquid nitrogen as cryogenic medium,the heat transfer and vaporization of cryogenic pool on concrete were studied.The heat transfer and vaporization process of liquid nitrogen pool under the combined action of heat conduction of concrete and boiling convective heat transfer of liquid nitrogen pool were investigated.The experimental results show that the vaporization rate of the cryogenic pool is approximately linear with the reverse of the square root of time,which is consistent with the unsteady semi-infinite one-dimensional heat conduction theory.The bubble morphology of the cryogenic pool during the transition from film boiling to transition boiling and nucleate boiling was observed experimentally.The experimental results show that the temperature difference of critical heat flux point is 20 K,and the temperature difference of minimum heat flux point is 40 K.Thirdly,according to the experimental results,the coefficients of Kutateladze correlation and Berenson correlation for nucleate boiling and film boiling were corrected,and the empirical boiling correlations for liquid nitrogen-concrete were obtained.Combining with the unsteady semi-infinite one-dimensional heat conduction temperature calculation formula,a coupling calculation method for pool vaporization process of liquid nitrogen leakage on concrete was proposed.The prediction error of vaporization mass of pool is within 5%,and the prediction accuracy is 37.4% higher than that of the heat conduction theory.Finally,on the basis of the above work,experimental study on heat transfer and vaporization process of liquid nitrogen leakage on different kinds of surfaces was carried out.The surface conditions were wet concrete,water,sand and soil.It is found that the vaporization mass of concrete,wet concrete,sand and soil is approximately linear with the square root of time.The vaporization characteristic parameter F shows the phenomena of wet concrete > soil > concrete > sand.The change of the temperature below water surface is less affected by the depth.The water temperature at different depths below 25 mm of water surface decreases with the increase of time and the decrease is similar;the ice layer distributes near the water surface,and the ice layer thickness distribution is not uniform;the boiling process of liquid nitrogen on the water is mainly in the stage of film boiling.