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.
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