| In recent years,with the emergence of problems such as global warming and environment pollution,energy saving and emission decreasing,environment protection and other issues have been paid more attention,and some relevant laws and regulations also arise at this historic moment.With its green and efficient features,the trade of natural gas has increased year by year,which makes the small and medium sized LNG ships become a research hotspot.The small and medium sized LNG ships mainly adopt type C independent tank.The evaporation property of type C independent cryogenic tank is not only the research hotspot and difficulty at this time but also influences the operation capacity and economy of LNG ships.In this paper,both experiment and numerical simulation method are used to analyze the evaporation property of type C independent cryogenic tank and appropriate method has been established.The content of this paper mainly includes the following aspects:1).Introduce the experiment on evaporation property of 1.5 m3 type C independent cryogenic tank with liquidfied nitrogen.The results show that the temperature of gas phase is higher than that of the gas-liquid interface,and the temperature of gas-liquid interface is higher than that of liquid phase in the cryogenic tank.In addition,the results also prove that evaporation of cryogenic liquid is an unstable and irregular dynamic process.2).A method to predict the evaporation rate of cryogenic tank is presented in this paper,which couples the insulation maintenance system with cryogenic fluid together.And the method is used to analyze the evaporation property of 1.5 m3 type C independent cryogenic tank.Results indicate that: the temperature inside the tank increase gradually from the bottom to the top,and the temperature of fluid near the wall is higher than that in the inner region;the pipe and the saddle will affect the temperature distribution in its vicinity;cryogenic liquid realizes mass transfer process in the form of evaporation and it is significant at the gas-liquid interface;under the state of free evaporation(standard atmosphere),the pressure increases gradually from the top to the bottom;the result of flow field shows that velocity of gas phase is higher than that of liquid phase,and the fluid velocity near the wall is higher than that in inner region.3).The differences of the evaporation properties between the sloshing state and static state of the cryogenic tank are compared and analyzed by means of numerical simulation.It turns out that: compared with the static state,the heat transfer between the gas and liquid,fluid and wall will increase under sloshing state,which will further aggravate the evaporation of the cryogenic liquid;at the same filling rate,the free surface is more disordered and the heat transfer as well as evaporation phenomenon is more significant with greater amplitude and closer to the natural frequency of the tank;as for the temperature field inside the tank,the temperature of gas at the sloshing state is lower than that in static state,while the temperature of liquid in the sloshing state is higher than that in static state;in addition,the temperature of inner heads in the sloshing state is significantly lower than that in static state.4).In this paper,four filling rates in sloshing and static state are analyzed with three dimensional model,and the heat leakage between fluid and wall is extracted.The results prove that heat leakage of wall under sloshing condition is about 20% higher than that in static condition.Sloshing mothion has a significant effect on the evaporation rate.In this paper,a method of forecasting the evaporation rate of type C independent cryogenic tank has been presented,and the influence of sloshing on the cryogenic tank has been researched,the results of which provide guidance for the design of the type C independent tank. |
PDF Full Text Request