Metodologia de análise numérica do processo de ebulição em piscina no evaporador de um termossifão fechado

Abstract

Thermosyphons are devices with great potential in industrial and residential sustainable applications, due to their high heat transfer efficiency. For a thermosyphon’s design, one of the parameters to be determined is the multiphase heat transfer coefficient of the flow in the evaporator section, which involves high complexity since it is a phase change flow and can operate in different regimes and, therefore, exists a lack of correlations in literature. The goal of this present thesis is to develop a methodology of numerical analysis of the pool boiling process in an evaporator section of a thermosyphon. The continuity equations were solved using the software ANSYS FLUENT through the finite volume method. In order to capture the evaporation process, the Volume of Fluid (VOF) method was used, such as a user-defined function (UDF) for the pool boiling regime process, where it was defined the condensationevaporation Lee Model applied for mass transfer between phases. To determine the multiphase heat transfer coefficient in the thermosyphon evaporator, the local convective coefficients for several points were calculated through Newton's Law, and the average convective coefficient was calculated by obtaining the average temperature at the evaporator surface. Those values were compared with correlation available in the literature. The results obtained in this work show that the methodology developed is adequate for the proposed problem. The numerical data obtained in this work, as well as the proposed methodology, can feed further studies to obtain correlations to estimate the coefficient of heat transfer by convection inside the evaporator of the thermosyphon.