Transient thermal analysis on pre-cooling process of LNG cryogenic corrugated hose

Abstract

The pre-cooling mechanism of LNG (liquefied natural gas) cryogenic corrugated hoses is complicated due to the structural complexity of the hose and the rapid temperature changes during the process. Conventional predicting temperature drop methods for pre-cooling heat transfer mostly simplify it to a steady heat transfer analysis, which results in the transient heat transfer process under pre-cooling conditions cannot be well reflected, and the calculation results are inaccurate. Considering the turbulent flow effect caused by the corrugated contour, a mathematic model is built to capture the temperature distribution in hoses. The numerical integration method is used to calculate the average temperature of the section which varies with time and space position under the condition of pre-cooling and stable operation. Meanwhile, a numerical model is established and its results are in good agreement with the mathematic model results. Case studies show how those factors like the thickness of the cold insulation layer, the nitrogen inflow rate and the radius of the hose affect the pre-cooling process. It is concluded that there is a certain non-linear relationship between the internal temperature of the hose and the pre-cooling time, axial and radial position. In addition, the thickness of the insulation layer and the nitrogen inflow rate dominate the pre-cooling process. Some suggestions can be put forward for the optimization of the pre-cooling process. The theoretical formulas not only provide an efficient tool for quick and reliable calculations of the temperature of LNG cryogenic corrugated hose during the pre-colling process but also apply to cryogenic pipe systems under other conditions.