Pool boiling heat transfer augmentation by using metal foam

Author(s)

Leonardo Lachi Manetti

• Document type: Doctoral Thesis
• Press: Ilha Solteira. 2022-03-09.
• Institution: Universidade Estadual Paulista (Unesp). Faculdade de Engenharia. Ilha Solteira
• Defense date: 2021-12-10
• Advisor: Elaine Maria Cardoso

Abstract

The growth of electronic technology has resulted in components with high perfor-mance and high heat generation. The pool boiling technique with direct contact of the fluid and the component - immersion cooling - is a solution for the industry of electronics. Dielec-tric fluids have been chosen in boiling research because they allow the components to be im-mersed without short-circuiting damage and have a low saturation temperature - which keeps the system below the critical temperature. The use of techniques to treat/modify the heating surface has been proposed to increase boiling performance. An appropriate technique for the industry is using metal foams with an open structure – open-cell metal foam. In this work, metal foams of different materials, Copper and Nickel, with different characteristics and thicknesses were first characterized to determine their porosity, pore and fiber diameters, pore density, surface area, permeability, and wickability. Then, they were used as a heating surface during the boiling of two dielectric fluids, HFE-7100 and Ethanol, under conditions of satura-tion at atmospheric pressure in two different laboratories. In general, the metal foams provid-ed a higher heat transfer coefficient when compared to the flat surface and prevented initial overheating, with an early nucleation onset. For identical thicknesses, the copper foam showed better performance because there is a balance between the thermal conductivity of the material and the metal foam area. For thickness variation, it was noted that the optimum thickness de-pends on the heat flux: the thicker foam has a better performance at low fluxes while the thin-ner one is better at high heat fluxes because there is a balance between the area and the re-sistance to the vapor bubble escape and the consequent liquid flow into the foam. When com-paring the different fluids, Ethanol performed better than HFE-7100 due to its better thermo-physical properties, mainly the latent heat of vaporization, thermal conductivity, and satura-tion temperature. Finally, a predictive model was developed to predict the heat transfer coef-ficient and the maximum heat flux according to the characteristics of the metal foam and the working fluid. The model predicts with a good agreement our experimental data as well as the literature data, being a good guide for use in the industry. (AU)

• FAPESP's process: 17/13813-0 - Pool boiling heat transfer enhancement by using metal foam enhanced surfaces
• Grantee: Leonardo Lachi Manetti
• Support Opportunities: Scholarships in Brazil - Doctorate