Natural convection heat transfer of the Casson fluid within a circular cylinder

نوع: Type: thesis

مقطع: Segment: masters

عنوان: Title: Natural convection heat transfer of the Casson fluid within a circular cylinder

ارائه دهنده: Provider: Amirreza Sadeghi

اساتید راهنما: Supervisors: Amireh Nourbakhsh Ph.d

اساتید مشاور: Advisory Professors: Mohammad saeid aghighi Phd

اساتید ممتحن یا داور: Examining professors or referees: mohsen goodarzi Ph.d- Habibolah saievand Ph.d

زمان و تاریخ ارائه: Time and date of presentation: 1October 2022

مکان ارائه: Place of presentation: seminar 3

چکیده: Abstract: In this study, the flow and heat transfer of the slow natural movement of a viscoplastic fluid of the casson type has been numerically investigated inside a horizontal tube in a two-dimensional mode. The boundary conditions of the problem are considered as the non-uniform temperature of the left and right walls of the cylinder and the principle of non-slip walls. The governing partial differential equations describing fluid flow and heat transfer (using the finite element method based on coding in MATLAB environment) have been solved on a wide range of dimensionless parameters. In this research, the effect of different numbers: Rayleigh, Bingham, and yield number corresponding to the related Bingham, as well as the impact of cylinder rotation with different α rotation angles compared to the initial state in both clockwise and counterclockwise directions on the value of the average Nusselt number on the wall of the heated cylinder and velocity distribution, temperature, yielded/unyielded areas and flow lines, isothermal lines and also velocity gradient distribution in flow geometry are discussed. The details of temperature and flow fields inside the cylinder are shown by the shapes of the temperature, and flow lines, respectively. Also, the yielded and unyielded areas of different parts of the flow range are specified. In addition, more explanations have been provided by the graphs showing the distribution of the local Nusselt number on the lower temperature surface of the cylinder, along with its average value and velocity and temperature graphs in the cross section between the cylinders at the angle (∅ = 0). It was found that the average Nusselt number decreases with the increase of the Bingham number until the limiting value of the Bingham number (Bnmax), which due to the unyielding nature of the flow, the average Nusselt number reaches an approximate value, close to the pure conductivity limit. As the angle α increases more and more in both counterclockwise and clockwise directions, the average Nusselt maximum value decreases, and this decrease is greater for the clockwise direction, so the maximum heat transfer between the cylinder and the fluid occurs at an angle of zero degrees. Also, another point that was obtained is that the gradual loss of convection heat transfer and the dominance of conduction heat transfer occurs in the values of the yield number or, in other words, Bingham numbers lower than the zero degrees state, which shows the earlier stopping of the current movement compared to the mentioned state. In addition, it was found that the maximum Bingham number (Bnmax) and the average Nusselt number ((Nu) ̅) rise with the increase of the Rayleigh number. In addition, due to the presence of fluid yield stress, quasi-fluid (yielded) and quasi-solid (unyielded) regions coexist in the flow domain depending on the amount of dominant flow stress versus fluid yield stress. It was found that naturally, in quasi-solid regions, heat transfer occurs as conduction and convection heat transfer is limited to yielded (quasi-fluid) regions. In addition, it became clear that the extent of yielded regions decreases with increasing Bingham number and/or decreasing Rayleigh number due to the deterioration of the flow caused by buoyancy. Finally, at the maximum Bingham number (Bnmax), the entire flow becomes quasi-solid, and as a result, heat transfer occurs as pure conduction

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