Heat transfer of supercritical endothermic fuel in 3-mm diameter channels: Comparison between asymmetric and uniform heating

Abstract

In the study, a novel conductive and asymmetric heating (AH)1AH: Asymmetric heating.1 test section was built to simulate a regenerative cooling passage in the scramjet combustor wall. A test channel with an external diameter of 4.0 mm and a wall thickness of 0.5 mm was conductively heated by a semicircle heating element, and this was electrically heated with zirconia coating as an electrical insulator. Heat transfer characteristics of endothermic fuel in the AH test section were compared with those in the uniform heating (UH)2UH: Uniform heating.2 test section at a supercritical pressure of 3.0 MPa, fluid temperatures of up to 600 °C, and mass flow rates of 0.5, 1.0, and 1.5 g/s (71, 142, and 212 kg/m2s). The results indicated that the absorbed heat flux reached a maximum value of 272 kW/m2 with a surface temperature of asymmetric heating element approaching 800 °C, and it significantly decreased when the fluid temperature increased. When compared with UH, the AH exhibited a lower heating efficiency of always less than 50% owing to the higher heat loss caused by higher surface temperature of the heating element. However, the heating efficiency in AH exceeded that in the UH at fluid temperature exceeding pseudo-critical point. The heat transfer characteristics of endothermic fuel were barely affected by the elevated different mass flow rates due to the mitigation of the refractory coating in the AH test section. However, the general heat transfer trends of endothermic fuel were obtained between AH and UH including a decrease in the heat transfer approximately at the pseudo-critical point, heat transfer enhancement at sub-cooled boiling conditions, and surface temperature profile of test channel at different mass flow rates.