Numerical Study Of Heat Transfer Enhancement Of Crvogenic Methane Flowing In Ribbed Cooling Tubes At Supercritical Pressures

Regenerative cooling technology plays a very important role in maintaining engine operating reliability and durability in many propulsion and power-generation systems, including the rocket, scramjet, and advanced gas turbine engines. In a regenerative cooling process, it is very important to apply certain surface modifications to the cooling tube to achieve effective heat transfer enhancement. In this thesis, numerical studies of the turbulent fluid flows and heat transfer phenomena of the cryogenic methane in ribbed circular tubes at a supercritical pressure were conducted. The conservation equations of mass, momentum, and energy are properly solved, with accurate calculations of the thermodynamic and transport properties, which undergo drastic variations at supercritical pressures. The present studies focus on effects of several key influential parameters on both heat transfer enhancement and pressure loss, including the rib geometry, both square and triangle shapes, rib height, ranging from0.01to0.05mm, wall thermal conductivity, varing between20and400W/mK, wall heat flux, ranging from1to4MW/m2, and inlet velocity, from10to20m/s. The operating pressure is8MPa, which is higher than the critical pressure of methane at4.6MPa. Numerical results reveal that the ribbed roughness in the cooling tube can significantly improve the heat transfer performance, but the pressure loss is also dramatically increased. A proper thermal performance factor is thus chosen to assess the combined effects. Under the tested conditions, the rectangular rib generally performs better than the triangular one, in terms of both heat transfer enhancement and pressure loss; there exists an optimum rib height. The role of the rib becomes more important at an increased thermal conductivity of the tube wall and under a higher wall heat flux. The convective heat transfer capability of the fluid turns better in a higher inlet velocity, but the pressure loss also increases; under the tested conditions, the overall thermal performance of the ribbed cooling tube improves as the inlet velocity increases. The present studies have practical implications for effective applications of heat transfer enhancement technique in the propulsion and power-generation systems.