O estudante Andrés Paul Sarmiento Cajamarca, orientado pela Prof.ª Márcia Barbosa Henriques Mantelli, Ph.D. e coorientado pelo Prof. Fernando Henrique Milanese, Dr.Eng. , defenderá sua tese na próxima terça-feira (17/11), às 14h, por videconferência. A defesa é vinculada ao Programa de Pós-Graduação em Engenharia Mecânica.
Banca:
Prof.ª Márcia Barbosa Henriques Mantelli, Ph.D. (Presidente)
Prof. José Maria Sáiz Jabardo, Ph.D. (Relator/Universidad de La Coruña, Espanha)
Prof. Alexandre Kupka da Silva, Ph.D.
Prof. Jader Riso Barbosa Jr., Ph.D.
Título: “Thermal and hydraulic modeling of diffusion-bonded compact heat exchangers”
Resumo:
The increasing demand for energy consumption has pushed the pursuit of more efficient thermal systems and devices. This effort has led to the development of heat transfer intensification techniques, aimed to meet both energy conservation and improved global efficiencies. Heat exchangers are one of the critical devices that need improvement, as they should combine excellent thermal-hydraulic behavior with high structural reliability in a reduced volume. In this sense, diffusion-bonded heat exchangers (DBHE) appear as strong candidates to meet these requirements, since they combine high thermal effectiveness and robustness, for fluid streams under high pressure and temperature environments. Based on a literature review regarding DBHE, several research gaps were detected, including the thermal-hydraulic behavior of compact heat exchangers and its relationship with channel topology and working fluids. This doctoral thesis is focused on the development of general models for the thermal rating and designing of DBHE. To fulfill the objective, fundamental heat transfer and fluid flow models were developed and global heat exchangers models were formulated. Therefore, theoretical models for calculating the Nusselt and Fanning friction numbers for most common circular and non-circular channels were developed. It was shown that asymptotic results for both laminar and turbulent flows along with an appropriate characteristic length resulted in Nusselt number models that provides good predictions for a large range of literature experimental data for both uniform heat flux and uniform wall temperature boundary conditions. This model shown an overall root mean square error (RMSE) of 10.0%, smaller than other literature correlations. A numerical analysis was developed to understand the hydrodynamic development length of square and rectangular minichannels, which results were used to pick the most appropriate literature correlation. Also, the literature correlation for the Fanning friction factor was rewritten in terms of the square root of the cross-section area, which proved to be convenient to estimate the Fanning friction values in most common channels, from laminar to fully turbulent flows. Besides, robust models for rating DBHE considering its thermal and hydraulic characteristics, for both rectangular and semicircular straight channels were developed. This model combines the well-known ? – NUT method, the Nusselt and Fanning friction models, axial conduction effects, and heat loss models, aiming the estimation of both the overall thermal conductance and pressure drop of the heat exchanger. Comparisons between the proposed theoretical model and literature experimental data have shown excellent agreement.
Palavras-chave: Diffusion-bonded heat exchangers, Nusselt number, Fanning friction factors.