نوع مقاله : مقاله پژوهشی
نویسندگان
دانشکده مهندسی مکانیک- دانشگاه صنعتی شریف
چکیده
کلیدواژهها
عنوان مقاله [English]
نویسندگان [English]
Concentric annular pipe flow with rotation of the inner wall is often used in engineering applications, such as chemical mixing devices, turbo machinery, bearings, rotating tube heat exchangers and the drilling of oil wells. In addition to the practical implications of achieving a better understanding of this type of flow, the study of turbulent rotating flows in concentric cylinders provides insight into the general problem of three dimensional turbulent boundary layers. Several experimental and numerical investigations hae examined rotating flows in concentric cylinders.In this paper, velocity and temperature fields of concentric cylinders with rotation of the inner wall have been investigated numerically. Air enters the gap between the cylinders and attains full development in both velocity and temperature fields after certain lengths. Adiabatic and constant heat flux boundary conditions have been applied and the Nusselt number was calculated. In order to analyze the variations of velocity and temperature fields, different angular velocities at constant axial Reynolds number and different axial velocities at constant angular velocity have been investigated. The turbulent stresses were approximated with the model. Results show that for high values of angular velocity, Nusselt number increases at the outer wall and, also, by increasing the axial Reynolds number, the temperature decreases on the inner and outer wall. In the present study, it is assumed that the fluid is incompressible and Newtonian with temperature-independent fluid properties. Results show that the inner wall rotation in turbulent annular flow produces significant effects on velocity and temperature fields, as well as on heat transfer rate. The results also indicate that if the rotational speed of the inner cylinder increases, the outer cylinder heat transfer coefficient will increase, due to a decrease in the boundary layer thickness at the outer wall.
کلیدواژهها [English]
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