Three-Dimensional Numerical Studies Of Conjugate Heat Transfer Of Cryogenic Methane At Supercritical Pressures

In this thesis, intended to study the regenerative cooling processes in aeronautic and astronautic flight vehicles and their engines, a computational software has been developed based on the user coding capabilities in commercial CFD package, FLUENT. It is capable of accurately calculating the thermophysical properties and appropriately treating the fluid/solid interactions and heat transfer at supercritical pressures. Three-dimensional numerical studies of heat transfer of cryogenic methane flowing inside a rectangular engine cooling channel under supercritical pressures has been conducted with consideration of the coupled thermal conduction in the solid channel region. The effects of wall heat fluxes, operation pressures, inlet flow velocities, and cooling channel geometries on fluid flow and heat transfer processes under supercritical pressures are carefully examined. Variations of the fluid velocity, channel surface temperature, wall heat flux, thermophysical properties, and Nusselt number are obtained and discussed. Results indicate that with consideration of the coupled heat transfer in both solid and fluid regions, a fraction of the heat flux imposed on the top channel surface is transferred into the cryogenic methane through the side walls. As the imposed wall heat flux increases, more heat can be thermally conducted into the side channel walls. An increased operation pressure can result in a higher Nusselt number in the heat transfer process, indicating that the increased pressure can enhance heat transfer of the cryogenic methane at supercritical pressures. At a given mass flow rate, decreasing the cooling channel height/width aspect ratio leads to the enhanced heat transfer, but the pressure loss is also increased significantly. Therefore, the combined effects of the channel aspect ratio on both heat transfer and pressure loss has to be taken into account to obtain an optimum cooling channel design. The thermal performance parameter can be used as a reference in this regard. The modified Jackson&Hall coefficient is applicable to heat transfer predictions under supercritical pressures with acceptable accuracy under all tested conditions in this thesis, but the predictive error could be increased to more than20%as the heat flux increases and the inlet flow velocity decreases.