Numerical Study of Turbulent Flow and Convective Heat Transfer Characteristics in Helical Rectangular Ducts

2014 ◽  
Vol 136 (12) ◽  
Author(s):  
Yunfei Xing ◽  
Fengquan Zhong ◽  
Xinyu Zhang
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Numerical Study ◽  
Rectangular Cross Section ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Axial Direction ◽  
Outer Wall ◽  
Centrifugal Effect

Three-dimensional turbulent forced convective heat transfer and its flow characteristics in helical rectangular ducts are simulated using SST k–ω turbulence model. The velocity field and temperature field at different axial locations along the axial direction are analyzed for different inlet Reynolds numbers, different curvatures, and torsions. The causes of heat transfer differences between the inner and outer wall of the helical rectangular ducts are discussed as well as the differences between helical and straight duct. A secondary flow is generated due to the centrifugal effect between the inner and outer walls. For the present study, the flow and thermal field become periodic after the first turn. It is found that Reynolds number can enhance the overall heat transfer. Instead, torsion and curvature change the overall heat transfer slightly. But the aspect ratio of the rectangular cross section can significantly affect heat transfer coefficient.

A Numerical Study of Assisting and Opposing Mixed Convective Heat Transfer From a Horizontal Isothermal High Aspect Ratio Rectangular Cylinder

2012 ◽  
Author(s):  
Patrick H. Oosthuizen
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Numerical Study ◽  
Rectangular Cross Section ◽  
Boussinesq Approximation ◽  
Forced Flow ◽  
Width Ratio ◽  
Flow Conditions ◽  
Rectangular Cylinder

Mixed convective heat transfer from an isothermal cylinder with a rectangular cross-section and a relatively large height-to-width ratio has been numerically studied. The axis of the cylinder is horizontal with the longer sides of the rectangular cylinder being vertical. There is a vertical forced flow over the cylinder. The flow conditions considered are such that in general mixed forced and natural convective flow exists. Both the case where the buoyancy forces act in the same direction as the forced flow (assisting flow) and the case where they act in the opposite direction to the forced flow (opposing flow) have been considered. The flow has been assumed to be two-dimensional and the Boussinesq approximation has been adopted. Attention has been restricted to the flow of air and results have therefore been obtained for a Prandtl number of 0.74. The flow conditions considered are such that laminar or turbulent flow can exist. The main attention is this work has been directed at determining the effect of the flow parameters on the mean heat transfer rate from the cylinder and on determining the conditions under which the flow can be assumed to be forced convective and under which it can be assumed to be natural convective.

Experimental and Numerical Study of Convective Heat Transfer in an Array of Slot Jets

2002 ◽  
Author(s):  
Jean-Marie Buchlin ◽  
Jean-Baptiste Gouriet ◽  
Philipe Planquart ◽  
Jeroen van Beeck ◽  
Michel Renard
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Cooling System ◽  
Numerical Study ◽  
Three Dimensional ◽  
Small Width ◽  
Moving Strip ◽  
Experimental Findings

The paper describes a study of convective heat transfer in a multiple-jet systems composed of straight and inclined slot nozzles. The application concerned is the fast cooling of moving strip. The experimental approach involves the application of infrared thermography associated with the steady-state heated foil technique. Three-dimensional numerical simulations performed with the code FLUENT compare agreeably with the IR data. The study aims to determine the effect on the average heat transfer coefficient of the slot Reynolds number up to the value of 100000, the nozzle spacing normalised by the slot hydraulic diameter in the range 6 ≤ W/S ≤ 18, the normalised nozzle emergence length, E/S, from 5 to 17 and the normalised nozzle to strip standoff distance Z/S from 3 to 10. The geometrical arrangements tested include perpendicular (90°) and tilted (60°) nozzles. A thermal entrainment phenomenon is found for cooling system of small width. A corrective factor is derived to account for this effect. The experimental findings are compared with existing correlation; deviations, which are observed at high values of the Reynolds number may reach 25%. The numerical simulation emphasises the benefit to use H2/N2 gas mixture to enhance significantly the cooling rate.

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