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Evaluation of transient aspects of flow boiling inside microchannels using infrared thermography

Grant number: 20/02062-7
Support type:Scholarships in Brazil - Doctorate (Direct)
Effective date (Start): June 01, 2020
Effective date (End): June 30, 2022
Field of knowledge:Engineering - Mechanical Engineering - Transport Phenomena
Principal Investigator:Gherhardt Ribatski
Grantee:Maurício Mani Marinheiro
Home Institution: Escola de Engenharia de São Carlos (EESC). Universidade de São Paulo (USP). São Carlos , SP, Brazil
Associated research grant:16/09509-1 - Phase change heat transfer processes of high performance applied to solar energy recovery, AP.TEM

Abstract

A better understanding of the heat transfer mechanisms during micro-scale flow boiling is fundamental for the development of disruptive technologies which require the dissipation of high heat fluxes (values up to 3MW/m2 are expected in a close future). The combination of microchannels and phase change processes allows high heat transfer rates, minimizing the need of space and reducing costs of material and working fluid. The gains from such benefits are necessary for the development of technologies in the areas of microelectronics, nuclear microreactors, lasers, super capacitors, super batteries, solar thermal and photovoltaic energy and so on. However, the application of such technology is not yet feasible due to aspects associated to boiling under confined conditions, which implies on fluid maldistribution, thermal instabilities and premature surface dryout. In this context, the use of infrared thermography and high-speed filming are promising instruments to evaluate the transient processes associated to bubbles nucleation, growth and detachment. In this context, the present proposal deals with the study of the heat transfer mechanisms during subcooled convective boiling in microchannels, using thermography techniques along with high speed videos in order to simultaneously characterize the temperature distribution on the heated surface and the two-phase flow topology. Firstly, its execution involves (i) critical analysis of the literature concerning infrared thermography applied to the investigation of boiling processes; (ii) development and implementation of an IR calibration method considering the optical properties of the involved materials; (iii) design and manufacture of the test section, consisting of a single microchannel, considering transparent materials to infrared and visible light radiations. Experimental results will be obtained aiming to characterize the preponderant heat transfer mechanisms during nucleation, growth and detachment of bubbles under boiling conditions (ONB). Investigating the main heat transfer mechanisms for elongated bubbles is also the focus of this work. Based on the experimental results, mechanistic models will be developed. These models are expected to become tools to investigate flow boiling under confined conditions and to be used for the development of high performance heatsinks. This doctoral proposal also includes a Research Internship abroad under the supervision of Professor Jungho Kim from the University of Maryland. Professor Kim is one of the pioneers in the use of infrared thermography to investigate boiling heat transfer. (AU)