Flow characterization of slush hydrogen in transfer lines

摘要

This work presents a thorough investigation of flow characterization and heat transfer performance of SLUSH hydrogen in transfer lines with various types of insulation and flow conditions. Slush is used as a fuel for the National Aerospace Plane (NASP). NASP is a horizontal take off and landing, single stage-to-orbit vehicle using hydrogen as fuel. The high heating value, cooling capacity, and combustion properties make hydrogen the fuel of choice, but the low density of hydrogen results in a large vehicle tank. Both the fuel cooling capacity and density are increased with the use of slush hydrogen and results in significant reduction in vehicle size. This computational work includes the effects of interfacial dynamics to the flow field. Thus, a numerical model is developed using PHOENICS, a general CFD program, as a tool to model the flow of solid particles in a liquid and to study the heat transfer characteristics of the slush. This model is applied to vacuum-jacketed and standard insulation pipe systems. The author obtained permission from NASA, Lewis Research Center, Cleveland, to compare his model's prediction with experimental data. The comparison shows good agreement, which provides confidence in the numerical model and theoretical analyses. At low flow rates, the data show that the heat loss effects dominate the solid volume fraction loss, while at higher flow rates, friction heating causes most of the solid hydrogen degradation. These two effects are the basis of a model for the minimum slush solid volume fraction loss for each pipe size. Furthermore, as the pipe diameter increases, this minimum slush solid volume fraction loss decreases owing to the decreasing friction losses. The interfacial mass and heat transfer fluxes are predicted and exhibit a larger value at the boundary due to wall friction effect and surface heat flux into the pipe. Comparison of the results is made with previous studies. The comparisons show good agreement in slush loss and pressure drop, which provides confidence in the numerical model and theoretical analyses.