Numerical and entropy studies of hydrogen-fuelled micro-combustors with different geometric shaped ribs

Abstract

Micro-combustor design plays an important role in determining the performances of Micro Thermo-Photovoltaic (MTPV) systems. In this work, 3D numerical simulations are conducted on a hydrogen-fuelled micro-combustor with two ribs to achieve a more uniform but higher wall temperature. The effects of: 1) the shape of the ribs, 2) the axial location, 3) the height, 4) the inlet velocity and 5) the equivalence ratio are evaluated. The numerical model is built with a standard k-ε turbulence model and EDC chemical reaction model (eddy dissipation concept). These models are validated before being applied to study 3 different ribs with a cross-sectional view of: 1) rectangular, 2) Ո-shaped and 3) Ս-shaped (defined basing on the bottom rib). It is found that the combustor with 2 ribs performs generally better than that of a single-rib one under the same flow conditions. The optimum design is found to be the Ս-shaped ribs, since the mean temperature of the outer wall is increased by 25.4 K in comparison with other designs. In addition, the mean temperature is observed to increase with increased inlet velocity. However, it decreases slightly with increased rib height. Further analysis is conducted on entropy production due to chemical reactions and heat transfer processes. It is found that the chemical reaction and the conduction heat transfer contribute 70% and 15% of the total entropy generation respectively. Furthermore, the thermodynamic 2nd-law efficiency remains in the range of 46%–51%, as the equivalence ratio varies from 0.8 to 1.2. This study provides physical insights on the optimum design of a hydrogen-fuelled micro-combustor.