2D Trefftz method in identification of flow boiling heat transfer coefficient in horizontal minichannel

This study investigates heat transfer coefficients during two-phase flow boiling of distilled water within a horizontal, rectangular mini-channel with asymmetric heating. The microchannel dimensions are 180 mm × 4 mm × 1.5 mm. Experimental observations of flow structures were made through a transparent channel wall. Experiments were conducted under low Reynolds number conditions (281 ≤ Re ≤ 499), with measurements of inlet pressure, pressure drop, volumetric flow rate, heater power supply parameters, and temperatures at various points. The employed model assumed negligible influence of material properties on temperature and time-independent heat transfer. The flow resistance based on the two-phase separated flow Lockhart-Martinelli model was used to determine the water velocity profile in the mini-channel. The velocity profile satisfied the Poisson equation. The copper block and working fluid temperature distributions were assumed to adhere to appropriate energy equations with suitable boundary conditions. The Trefftz method was applied to solve these equations, providing the water velocity profile and 2D temperature distributions. Based on the calculated temperature distributions, the Nusselt number at the heating surface-water interface was determined. The experimental results were subsequently compared with theoretical correlations.