Trefftz-Type Functions Applied for Subcooled Flow Boiling Heat Transfer Calculations in a Minichannel of Different Spatial Orientation

Abstract

ABSTRACT The paper describes the results of subcooled flow boiling heat transfer in an asymmetrically heated group of five minichannels 1 mm deep. The heated element for the cooling fluid (FC-72) flowing in the minichannels was a foil made of Haynes-230 alloy. The time-dependent temperature distribution of the outer heated foil surface was recorded as a result of infrared thermography. The test section was oriented in several spatial orientations, that is, 30°, 45°, 60° and 75° inclinations to the horizontal plane. The objective of the numerical calculations, referring to the experimental results, was to determine the time–dependent heat transfer coefficient on the wall-fluid contact surface from the Robin boundary condition. Both the foil and the fluid temperatures were the result of solving the inverse and direct two-dimensional heat transfer problem in two neighboring domains: the heated foil and flowing fluid. The problem was solved using the Trefftz method and the FEM with Trefftz type basis functions. The heat transfer coefficient obtained by two numerical methods appears to be similar. During subcooled flow boiling, at higher minichannel inclination angles, higher values of the heated foil temperature were obtained, as well as higher values of the heat transfer coefficient.