Global demand of LNG is expected to increase continuously because of the limited resource of fossil fuels. Also various reasons such as the steep rise of fuel costs, environment friendly requirements etc. lead to use low-emission and green energy sources. Hence, the thermal performance of LNG vapori...
Global demand of LNG is expected to increase continuously because of the limited resource of fossil fuels. Also various reasons such as the steep rise of fuel costs, environment friendly requirements etc. lead to use low-emission and green energy sources. Hence, the thermal performance of LNG vaporizer is one of the main issue in LNG production industry. In the present study, the ambient air LNG vaporizer(AAV) was investigated. It does not need any mechanical components and has compact structure, and it can be easily modulated depending on production rate. Although it has many advantages, the frost growth on the surface of LNG vaporizer is a serious problem that can reduce the heat transfer efficiency and LNG production rate of LNG system. In the present study, effects of various parameters on the thermal performance of LNG vaporizer were investigated numerically. The influence of the frost formation around the vaporizer's outer surface for environmental conditions was analyzed numerically using ANSYS CFX 13.0 and the optimum structure was proposed. There are various environmental variables such as the existence of fin, material of pipe, LNG flow velocity, air temperatures, air flow velocity and air humidity. But, in this study, numerical study was focused on the effects of LNG flux, air temperature, air humidity and air velocity on the heat transfer characteristics of LNG vaporizer because these variables can be main influencing parameters for frost growth on the vaporizer surface. The numerical analysis was performed with assumptions that the flow state is incompressible-steady state in order to exchange heat at cryogenic temperature and the method to solve the solution domain is standard k-ε turbulence model. The finite volume methods for solution were applied by the Navier-Stokes equation. The grid was constructed with the hexa-structure and total number of grid is approximately 390,000. Basic boundary conditions were LNG of 0.4 m/s velocity, LNG of 110K temperature, air velocity of 6m/s , air temperature of 293.15K and air relative humidity of 60%. Based on numerical simulation, the outside air is generally required to provide the warm air to increase the thermal vaporization performance and efficiency of a vaporizer. It was investigated at the low temperatures such as 273K, the frost was the thickest in the air velocity of 1 m/s, but the frost thickness is significantly reduced in the air velocity of 1m/s and 2m/s at higher temperatures. Relatively, it was appeared to be thicker at the velocity of 6m/s and 10m/s. Also, the velocity of LNG is a important parameter for frost growth, the thickness of the frost at 0.7m/s is observed to be thicker but the difference is very slight between 0.4m/s and 0.7m/s cases. Air humidity is the most sensitive variable for frost growth. It was observed with numerical simulation that increasing moist air humidity leads to grow the frost thickness.
Global demand of LNG is expected to increase continuously because of the limited resource of fossil fuels. Also various reasons such as the steep rise of fuel costs, environment friendly requirements etc. lead to use low-emission and green energy sources. Hence, the thermal performance of LNG vaporizer is one of the main issue in LNG production industry. In the present study, the ambient air LNG vaporizer(AAV) was investigated. It does not need any mechanical components and has compact structure, and it can be easily modulated depending on production rate. Although it has many advantages, the frost growth on the surface of LNG vaporizer is a serious problem that can reduce the heat transfer efficiency and LNG production rate of LNG system. In the present study, effects of various parameters on the thermal performance of LNG vaporizer were investigated numerically. The influence of the frost formation around the vaporizer's outer surface for environmental conditions was analyzed numerically using ANSYS CFX 13.0 and the optimum structure was proposed. There are various environmental variables such as the existence of fin, material of pipe, LNG flow velocity, air temperatures, air flow velocity and air humidity. But, in this study, numerical study was focused on the effects of LNG flux, air temperature, air humidity and air velocity on the heat transfer characteristics of LNG vaporizer because these variables can be main influencing parameters for frost growth on the vaporizer surface. The numerical analysis was performed with assumptions that the flow state is incompressible-steady state in order to exchange heat at cryogenic temperature and the method to solve the solution domain is standard k-ε turbulence model. The finite volume methods for solution were applied by the Navier-Stokes equation. The grid was constructed with the hexa-structure and total number of grid is approximately 390,000. Basic boundary conditions were LNG of 0.4 m/s velocity, LNG of 110K temperature, air velocity of 6m/s , air temperature of 293.15K and air relative humidity of 60%. Based on numerical simulation, the outside air is generally required to provide the warm air to increase the thermal vaporization performance and efficiency of a vaporizer. It was investigated at the low temperatures such as 273K, the frost was the thickest in the air velocity of 1 m/s, but the frost thickness is significantly reduced in the air velocity of 1m/s and 2m/s at higher temperatures. Relatively, it was appeared to be thicker at the velocity of 6m/s and 10m/s. Also, the velocity of LNG is a important parameter for frost growth, the thickness of the frost at 0.7m/s is observed to be thicker but the difference is very slight between 0.4m/s and 0.7m/s cases. Air humidity is the most sensitive variable for frost growth. It was observed with numerical simulation that increasing moist air humidity leads to grow the frost thickness.
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