Liquid propellants, which are typically used for regenerative cooling of rocket thrust chambers, can flow in channels at supercritical pressures and in the neighborhood of pseudo-critical temperature (near-critical fluid). This could be for instance the case for the envisioned liquid-oxygen/liquid-methane engines with chamber pressures larger than about 50 bar. When the fluid is in such a near-critical condition, deterioration in heat transfer can occur if the heat transfer level is higher than a threshold value. In this study detailed three-dimensional numerical analyses are performed to study the coupled wall/coolant environment of an electrically-heated test article designed in order to investigate the thermo-fluid dynamic behavior of methane inside a rectangular cooling channel which can be representative of a regenerative system. Different coolant pressure and surface roughness levels are considered in order to understand their influence on the heat transfer capability of the cooling system. Results evidence that the heat transfer deterioration can be mitigated either by increasing the coolant pressure or by increasing the surface roughness. In the latter case, a penalty in terms of coolant pressure drop is expected.

A trade-off analysis is performed on a cooling channel system representative of liquid rocket engine cooling systems. This analysis requires multiple cooling channel flow calculations which are performed by means of a proper numerical approach, referred to as quasi-2D model. This model, which is suited to high-aspect-ratio cooling channels, permits to have a fast prediction of both the coolant flow evolution and the temperature distribution along the whole cooling channel structure. Before using the quasi-2D model for the trade-off analysis, its validation by comparison with CFD results is presented and discussed. Results show that the pump power required to overcome losses in the cooling circuit can be minimized selecting a channel shaped with a suitably high aspect ratio. Nomenclaturė m mass flow rate, kg s −1 A area of the channel cross section, m 2 b channel width, m D h channel hydraulic diameter, m f w skin friction factor G mass flow rate per unit area, kg m −2 s −1 h channel height, m h w heat transfer coefficient, W m −2 K −1 k thermal conductivity, W m −1 K −1 L channel length, m N number of cooling channels N u Nusselt number P channel perimeter, m p pressure, Pa P r Prandtl number q heat flux, W m −2 r chamber radius, m Re Reynolds number s w internal wall thickness, m T temperature, K t w rib thickness, m x, y, z length, height, and width coordinates, m Subscripts 0 total value aw adiabatic wall