Non-isothermal flow with convective heat transfer through a curved duct for various aspect ratios

2021 ◽  
Author(s):  
Shamsun Naher Dolon ◽  
Mohammad Sanjeed Hasan ◽  
Rabindra Nath Mondal
1982 ◽  
Vol 104 (1) ◽  
pp. 111-117 ◽  
Author(s):  
B. A. Meyer ◽  
J. W. Mitchell ◽  
M. M. El-Wakil

The effects of cell wall thickness and thermal conductivity on natural convective heat transfer within inclined rectangular cells was studied. The cell walls are thin, and the hot and cold surfaces are isothermal. The two-dimensional natural convection problem was solved using finite difference techniques. The parameters studied were cell aspect ratios (A) of 0.5 and 1, Rayleigh numbers (Ra) up to 105, a Prandtl number (Pr) of 0.72 and a tilt angle (φ) of 60 deg. These parameters are of interest in solar collectors. The numerical results are substantiated by experimental results. It was found that convection coefficients for cells with adiabatic walls are substantially higher than those for cells with conducting walls. Correlations are given for estimating the convective heat transfer across the cell and the conductive heat transfer across the cell wall. These correlations are compared with available experimental and numerical work of other authors.


1991 ◽  
Vol 113 (3) ◽  
pp. 604-611 ◽  
Author(s):  
C. Y. Soong ◽  
S. T. Lin ◽  
G. J. Hwang

The paper presents an experimental study of convective heat transfer in radially rotating isothermal rectangular ducts with various height and width aspect ratios. The convective heat transfer is affected by secondary flows resulting from Coriolis force and the buoyancy flow, which is in turn due to the centrifugal force in the duct. The growth and strength of the secondary flow depend on the rotational Reynolds number; the effect of the buoyancy flow is characterized by the rotational Rayleigh number. The aspect ratio of the duct may affect the secondary flow and the buoyancy flow, and therefore is also a critical parameter in the heat transfer mechanism. In the present work the effects of the main flow, the rotational speed, and the aspect ratio γ on heat transfer are subjects of major interest. Ducts of aspect ratios γ=5, 2, 1, 0.5, and 0.2 at rotational speed up to 3000 rpm are studied. The main flow Reynolds number ranges from 700 to 20,000 to cover the laminar, transitional, and turbulent flow regimes in the duct flow. Test data and discussion are presented.


2013 ◽  
Vol 56 ◽  
pp. 141-148 ◽  
Author(s):  
Rabindra Nath Mondal ◽  
Md. Saidul Islam ◽  
Md. Kutub Uddin

Author(s):  
F. Kowsary ◽  
N. Noroozi ◽  
M. Rezaei Barmi

The increased power dissipation and reduced dimensions of microelectronics devices have emphasized the need for highly efficient compact cooling technologies. Microchannel heat sinks are of particular interest due to the very high rates of heat transfer they enable in conjunction with greatly reduced heat sink length scales and coolant mass flow rate. Therefore, in the present work, optimization of laminar convective heat transfer in the microchannel heat sinks is investigated for uniform heat flux and different cross sectional areas of different aspect ratios. Three-dimensional numerical simulations of general form of energy equation were performed to predict Nusselt number in the laminar flow regime. Using these results, an optimum forced convective heat transfer coefficient was computed for several cross sectional areas and Reynolds numbers, utilizing the univariable search method. Different aspect ratios have different influences on Nusselt number in thermally developing and fully developed regions for different cross sectional areas and Reynolds numbers. There exists an optimum Nusselt number for each Reynolds number and cross sectional area by varying aspect ratio. Thus, optimized state is computed and related graphs are presented.


Author(s):  
Patrick H. Oosthuizen

Natural convective heat transfer from isothermal rectangular cylinders which have an exposed upper surface has been numerically studied. The cylinders considered have high aspect ratios, i.e., have high width-to-depth ratios, and are relatively short, i.e., have a “height” that is of the same order of magnitude as their width. The cylinders considered are mounted on a plane adiabatic base, the cylinders being normal to the plane base with the cylinders pointing either vertically upwards or vertically downwards. One of the main aims of the present work was to numerically determine how the depth-to-width ratio of the rectangular cylinder influences the mean heat transfer rate from the cylinder when this depth-to-width ratio is large. The flow has also been assumed to be steady and laminar and it has been assumed that the fluid properties are constant except for the density change with temperature which gives rise to the buoyancy forces, this having been treated by using the Boussinesq approach. The solution has been obtained by numerically solving the governing equations using the commercial CFD solver, ANSYS FLUENT©. The solution is dependent on the Rayleigh number, the ratio of the width to the height of the heated cylinder, the ratio of the width to the depth of the heated cylinder, the Prandtl number, Pr, and on whether the cylinder is pointing vertically upwards or vertically downwards. Because of the applications that motivated this study, results have only been obtained for a Prandtl number of 0.74, i.e., effectively the value for air. A range of the other governing parameters has been considered and the effects of these governing parameters on the Nusselt number variation have been examined.


Author(s):  
V. A. Afanasiev ◽  
L. N. Frolova ◽  
K. A. Sizikov ◽  
A. N. Ostrikov ◽  
S. N. Zobova

The equations of motion, the equation of continuity, the equation of energy (heat balance), the rheological equation were chosen to describe the non-isothermal flow of the cereals melt in the extruder as the initial equations. The following assumptions were made to solve the model: the flow of a moving viscous medium is assumed to be laminar and steady; the forces of inertia and gravity are so small compared to the forces of friction and pressure that they can be neglected; a viscous medium (melt) is an incompressible liquid characterized by constant thermal conductivity and thermal diffusivity; the change in thermal conductivity in the longitudinal direction was neglected due to the fact that convective heat transfer in the flow direction is higher than the heat transfer by thermal conductivity; heat transfer in the direction perpendicular to the flow of the melt occurs only due to thermal conductivity. The numerical finite difference method was used to solve a system of equations taking into account convective heat transfer. Its essence of use lies in the fact that the considered area (extruder channel) is divided into calculated cells using a grid. The grid consisted of rectangular cells with a constant step between nodes, which exactly lie on the boundaries of the integration region. In this case, the differential equations were transformed into difference equations by replacing the derivatives at a point with finite differences along the cell boundaries. The mathematical model of non-isothermal melt flow in the extruder channel was obtained as a result of the solution. To solve a mathematical model of the process of grain crops extrusion with a non-isothermal flow of their melts, a program in the algorithmic language C ++ was compiled. A non-isothermal mathematical model of the process of extrusion of grain crops at temperatures of the beginning of the Maillard reaction, i.e., up to 120–125 ?, was obtained. It allows us to identify the nature of the temperature change along the length of the extruder. Comparative analysis of the results of the numerical solution and experimental data showed good convergence: the standard deviation did not exceed 12.7%.


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