Modeling And Experimental Study Of No-Vent Fills For Cryogenic Liquid

An increasing demand for cryogenic liquid has been grown in the fields of science explorations, industrial applications and daily lives. The expansion of the market of cryogenic insulated vessels boosts the development of filling technology for cryogens. To maintain low tank pressure and steady inflow rate during a fill in a normal gravity environment, a top vent is kept open to vent the vapor generated during the filling process, which is called as the vented fill. However, the disadvantages of cryogenic liquid, such as scarcity, toxicity, explosiveness and volatility, should be clearly realized. The no-vent fill becomes a promising technique for charging vessels with dangerous cryogens (such as LH2 and LNG) and precious resources (such as LHe) to ensure the safety of our environment and build a friendly and economical society, since the characteristic of no venting helps to stop vapor from escaping and minimize mass loss.In this paper, the characteristic parameters such as pressure, final filling by volume and filling time, the main influencing factors such as incoming liquid temperature, inflow rate and initial wall temperature, and the thermodynamic process have been systematically studied in a cryogenic thermal-insulated cylinder with a volume of 180 liters. A new general model of the no-vent fill for cryogenic liquid is put forward based on the combination of the experimental results, the theoretical analysis and experience of former researches. Based on the new model, parameters which is difficult to be measured, such as the mass, volume and internal energy change of cryogens and the heat transfer rate are also studied. The purposes of this paper are to maturate the technique of no-vent fill and to provide practical evidence of the thermodynamic state changed in the process of no-vent fills. The work has been performed from the following aspects and some conclusions have been obtained:(1) The criterions used to judge the achievement of no-vent fills and study of these characteristic criterionsThe criterions used to judge the achievement of no-vent fills are performance parameters such as pressure in the receiver vessels, the final filling by volume and the filling time, based on the feasibility of observation or measurement and considerations of economic efficiency. Firstly, pressure in the receiver vessels is the most important criterion. According to the experimental study of the pressure tendency in the receiver vessels, pressure history goes through three distinguishable stages: rapid rise, gradual balance and sharp increase in no-vent fills. The second sharp increase of pressure in the receiver vessels can be regarded as a signal of ending the no-vent fill. Secondly, the final filling by volume should be consistent with the designed value which is usually larger than 90% but less than 100%. Thirdly, the less time spent on achieving a given final filling by volume, the more successful the no-vent fill is.(2) The systematical analysis of main influencing factors and their influencing rule in no-vent fillsMany variables should be considered into the establishment of a good model of the no-vent fill. Their tendency and degree of influence are important for proper assumptions and simplification of the model. After huge amounts of experiments, the incoming liquid temperature, the inflow rate, the initial wall temperature, the initial pressure in the receiver vessels, the filling configurations and the properties of both the receiver vessels and cryogenic liquid are regarded as the main influencing factors of no-vent fills. The incoming liquid temperature is regarded as the most important influencing factor.(3) The systematical study of the thermodynamic process of no-vent fills Within the existing literature, the radial temperature distribution in the receiver tank was not typically reported, and most of the models assumed a uniform temperature in radial direction. Former experiments laid emphasis on the pressure history in the receiver tanks and showed less attention to temperature distribution which is another key thermodynamic parameter for the establishment of models. In this paper, temperature tests of no-vent fills have been systematically conducted. The inner wall temperature and temperature distribution at different directions in the receiver tanks are analyzed in detail to help to estimate heat transfer mechanism or thermodynamic state. To investigate the effects of different fill configurations on the performance of no-vent fills, test results of three fill configurations (a top spray, a top nozzle and a bottom nozzle) are involved into the discussion. (4) The establishment of a new model of no-vent fillsThe new model of no-vent fills put forward in this paper is different from those established by other researchers. The most of the former models are limited to some given filling configurations such as the upward bottom filling configuration. In the new model of this paper, several improvements has been conducted as follows: (1) new lump nodes are defined; (2) new method of dealing with heat transfer between the tank wall and the cryogen is introduced; (3) the immersed theory is introduced to explain the condensation occurring at the liquid-vapor interface after the filling outlets are submerged; (4) a simple and straightforward TSE (thermodynamic saturated equilibrium) model is established to predict the performance of top filling configurations in no-vent fills; (5) assumptions are modified to improve the reliability of the simulation.(5) The application of the new model and study of the effects of vertical and horizontal placement on no-vent fills.The new model is used to preset the incoming liquid temperature, the supply pressure or the initial wall temperature, to achieve the no-vent fills. The study of the effects of vertical and horizontal placement on no-vent fills shows that the horizontal placement performs better than the vertical one in the process of no-vented fills.