Investigating natural convection heat transfer from a horizontal cylinder buried in saturated porous medium using local thermal equilibrium model

نوع: Type: thesis

مقطع: Segment: PHD

عنوان: Title: Investigating natural convection heat transfer from a horizontal cylinder buried in saturated porous medium using local thermal equilibrium model

ارائه دهنده: Provider: Behnam Keshavarzian

اساتید راهنما: Supervisors: Dr. Sayehvand

اساتید مشاور: Advisory Professors:

اساتید ممتحن یا داور: Examining professors or referees: Dr. Vesy- Dr. Ahmadikia

زمان و تاریخ ارائه: Time and date of presentation: 2024

مکان ارائه: Place of presentation: Faculty of Engineering

چکیده: Abstract: In this thesis, two common models used to study the natural convection heat transfer of a horizontal cylinder embedded in a saturated porous medium have been investigated. In the first case, boundary layer for the natural convection of a horizontal cylinder buried in an infinite porous medium saturated with Newtonian fluid have been investigated. For this purpose, first, by using boundary layer assumptions, the governing equations of the problem have been simplified, and these boundary layer equations, which are parabolic in nature, have been transferred to a rectangular computational area using variable change. Then, they were solved using the Keler box numerical method, which is an implicit finite difference method. In the following, the natural displacement heat transfer of the horizontal cylinder buried in the saturated infinite porous medium has been simulated by using Comsol software and using the complete equations of momentom and energy. Then, the results obtained from these two solution models have been compared with each other and the difference between the results of these two models has been investigated. In this regard, the effect of different parameters of flow and solid matrix such as Rayleigh number, conductivity ratio, diameter ratio, porosity and Bio number on the difference between two models has been studied. The comparison of the results indicates that in high values of conduction ratio and diameter ratio and small values of porosity and Bio number, the difference between the results of the two used models increases and it is better to use the complete equations to check the heat transfer. In fact, any parameter that increases the effect of the solid matrix on conduction heat transfer increases the difference between the results of the boundary layer equations and the complete equations. In the second case, the local thermal equilibrium model (isothermal fluid and solid matrix) has been investigated for the natural displacement heat transfer of a horizontal cylinder buried in a saturated infinite porous medium. For this purpose, the assumption of local thermal equilibrium (two separate energy equations for the fluid and the solid matrix) has been used for the energy equation, and by solving the equations governing the problem, the temperature of the fluid and the solid matrix have been calculated. Then, by calculating the average local temperature difference of the fluid and the solid matrix, the correctness of the isothermal assumption of the fluid and the solid matrix has been investigated. In this study, the effect of different parameters of fluid flow and solid matrix on the temperature difference between fluid and solid phase has been investigated. Then, the correctness of the local heat balance model for the energy equation has been checked. In the continuation of this thesis, the effect of different parameters on the velocity field, temperature and local Nusselt have been investigated. The effect of parameters such as Rayleigh number, porosity, diameter ratio, conduction ratio, magnetic forces and mass transfer on fluid temperature field, solid matrix temperature and velocity field have been investigated. Also, variable porosity, which causes the phenomenon of channeling near the borders, has been investigated separately.

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