Experimental Study And Analysis On Heat Transfer Performance Of LNG Cylinders

According to Safety of Special Equipment Law and other related regulations, the LNG cylinder as a kind of storing inflammable pressure vessel should be inspected regularly. Because of thermal insulation and security is the guarantee of the use of LNG cylinders high efficiently and reliably, the research about the mechanism of thermal insulation structure, the lossless stored pressure, the heat leakage of each part and the effective structural optimization has important theoretical significance and practical value.With liquid nitrogen as the working medium in this paper, experiment platform based on liquid nitrogen rate of evaporation, the pressure in the cylinder and the bottle wall temperature measurement has been established.Based on the heat transfer theory, the theoretical analysis, and finite element theory, and the lossless storage time of gas cylinders was calculated and of rising pressure in the cylinder. Under steady heat conduction of the cylinder, the heat leakage of various parts and the structure of the neck was calculated and optimized in use the software of ANSYS.The followings are the specific work includes several aspects:(1) Summarized of the domestic and overseas scholars’ research about the high vacuum multilayer insulation heat transfer calculation model, and established multi-layer insulation structure model. In view of the application in the experiment of container glass fiber materials in different layers at different vacuum degree calculation, and the equivalent thermal conductivity of each component are analyzed and comprised. The equivalent thermal conductivity which was calculated of cylinders has provided boundary conditions in finite element research at all parts of heat leakage.(2) According to the test platform, use the measurement of natural pressure booster and steam flow rate method combined with method of surface temperature, firstly, put forward a criterion of the pressure rise rate(MPa/24 h or kPa/h) based on measured the pressure inside the cylinder with enough test data of different specifications of LNG vehicle bottle; Secondly, through contrast experiment of the same type of LNG cylinders, under the same conditions of steam flow measuring method and surface temperature, has evaluated the performance of heat insulation in the method of surface temperature measurement.(3) Avoided long time lossless storage and natural pressure booster for experiment, choose a suitable calculation model of lossless storage of cylinders and predicted the time of lossless storage and the pressure change inside the cylinder, which all meet the economy,and improve the manufacture efficiency, and provides reference for the practical application of LNG cylinders.(4) The research shows that, heat leak has directly impact on pressure variation in the container in the process of lossless storage. So, according to the structure characteristics of the gas cylinder, steady state heat conduction model of gas cylinders is established with ANSYS software. Compared with the experiment, the maximum error of 8.7%, and in this model on neck of heat transfer at ratio of height todiameter on 2.36, 2.02, and 1.72 is analyzed.