Investigating the effect of heat source location on natural convection inside the enclosure

نوع: Type: Thesis

مقطع: Segment: masters

عنوان: Title: Investigating the effect of heat source location on natural convection inside the enclosure

ارائه دهنده: Provider: Mohammad Mehdi Khoshzare

اساتید راهنما: Supervisors: Dr Mohammad Saeed Aghighi

اساتید مشاور: Advisory Professors:

اساتید ممتحن یا داور: Examining professors or referees: Dr Mohsen Goodarzi - Dr Amire Nourbakhsh

زمان و تاریخ ارائه: Time and date of presentation: 2025

مکان ارائه: Place of presentation: 52

چکیده: Abstract: In this research, natural convection heat transfer inside a square enclosure filled with a casson model viscoplastic fluid along with a rectangular heat source placed vertically inside the enclosure has been investigated. The governing differential equations on the flow field and the temperature field, along with the boundary conditions of this problem, have been coded in MATLAB software. These equations have been discretized and solved numerically using the finite element method with the Galerkin weighted residue technique. The results are presented in a wide range of influential parameters such as heat source height (y= -0.25 , 0 , +0.25), dimensionless Rayleigh number (〖10〗^4≤Ra≤〖10〗^6), dimensionless Bingham number (0≤Bn≤〖Bn〗_max) at a fixed value of Prandtl number (Pr=100), in the form of contours of streamlines, shear rates and isothermal lines, as well as plots of the average Nusselt number (¯("Nu" )). It was found that factors such as increasing the Rayleigh number, decreasing the Bingham number, and decreasing the height of the thermal heat source increased the strength of the streamlines and increased the fluid circulation speed. It was also observed that any factor that increases the strength of the convection flow inside the enclosure causes an increase in velocity gradients, especially in the boundary regions, and an expansion of the regions with shear rates and an increase in the maximum shear rate. On the other hand, it was found that in regions with low shear rates, such as the corners of the enclosure, the fluid is prone to becoming solid-like, and as the flow strength decreases, the solid-like regions expand. Regarding the effect of parameters on heat transfer, it was also observed that with increasing Rayleigh number, the distortion of isothermal lines increases. Therefore, due to the increase in temperature gradient, the average Nusselt number, in other words, the heat transfer rate inside the enclosure, increased. It was also shown that with increasing Bingham number, the average Nusselt number decreases until at the maximum Bingham number (〖Bn〗_max), heat transfer reaches its minimum value. In this condition, the solid-like regions cover most of the areas inside the enclosure and conductive heat transfer is the dominant heat transfer inside the enclosure. Also, in Rayleigh 〖10〗^4, where conduction in the enclosure still dominates, the position y=0 has the highest heat transfer rate due to the symmetry of the geometry and boundary conditions of the problem. But at Rayleigh numbers of 〖10〗^5 and 〖10〗^6, as the height of the heat source decreases, the average Nusselt number increases, of course, as long as convective heat transfer is the dominant heat transfer in the enclosure. For all cases, the heat transfer rate of the Newtonian fluid is higher than that of the Casson fluid.