Spatially Resolved Heat Transfer Coefficient in a Rib-Roughened Channel Under Coriolis Effects

2013 ◽  
Author(s):  
Ignacio Mayo ◽  
Tony Arts ◽  
Julien Clinckemaillie ◽  
Aude Lahalle
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Shear Layer ◽  
Rotation Number ◽  
Rectangular Cross Section ◽  
Flow Direction ◽  
Secondary Flows ◽  
Uniform Heat Flux ◽  
Flux Boundary Condition ◽  
Coriolis Forces

Heat transfer in a magnified rotating ribbed channel is studied by means of liquid crystal thermometry. The test section consists of four Plexiglas walls, forming a rectangular cross section, mounted on a large rotating disk together with the complete necessary measurement chain. The investigated wall is equipped with ribs perpendicular to the main flow direction, it is heated in such a way to achieve a uniform heat flux boundary condition. Facing the need of two-dimensional experimental heat transfer data, tets were carried out in order to quantify the convective heat transfer distribution on the wall between two consecutive ribs under rotating conditions. Different Rotation numbers (0, 0.06, 0.11 and 0.17) were tested at a Reynolds number of 15,000. For the selected heat flux and rotation rates, and based on previous aerodynamic and thermal investigations presented in open literature, no effect of buoyancy is expected, while the Coriolis forces play an important role in the determination of heat transfer. The rotating cases were performed in both senses of rotation in order to allow the studied wall to act as both a trailing and a leading side. At the highest Rotation number, the results confirm that heat transfer is enhanced up to 17% along the trailing side compared with the non-rotating case. This is due to the secondary flows and shear layer instability instigated by the Coriolis forces. On the other hand, heat transfer on the leading side is reduced up to 19% at the highest rotation number; this is caused by the stabilization of the shear layer and the contribution of the secondary flows.

Two-Dimensional Heat Transfer Distribution of a Rotating Ribbed Channel at Different Reynolds Numbers

2014 ◽  
Vol 137 (3) ◽  
Author(s):  
Ignacio Mayo ◽  
Tony Arts ◽  
Ahmed El-Habib ◽  
Benjamin Parres
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Rotation Number ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Operating Conditions ◽  
Flux Boundary Condition

The convective heat transfer distribution in a rib-roughened rotating internal cooling channel was measured for different rotation and Reynolds numbers, representative of engine operating conditions. The test section consisted of a channel of aspect ratio equal to 0.9 with one wall equipped with eight ribs perpendicular to the main flow direction. The pitch to rib height ratio was 10 and the rib blockage was 10%. The test rig was designed to provide a uniform heat flux boundary condition over the ribbed wall, minimizing the heat transfer losses and allowing temperature measurements at significant rotation rates. Steady-state liquid crystal thermography (LCT) was employed to quantify a detailed 2D distribution of the wall temperature, allowing the determination of the convective heat transfer coefficient along the area between the sixth and eighth rib. The channel and all the required instrumentation were mounted on a large rotating disk, providing the same spatial resolution and measurement accuracy as in a stationary rig. The assembly was able to rotate both in clockwise and counterclockwise directions, so that the investigated wall was acting either as leading or trailing side, respectively. The tested Reynolds number values (based on the hydraulic diameter of the channel) were 15,000, 20,000, 30,000, and 40,000. The maximum rotation number values were ranging between 0.12 (Re = 40,000) and 0.30 (Re = 15,000). Turbulence profiles and secondary flows modified by rotation have shown their impact not only on the average value of the heat transfer coefficient but also on its distribution. On the trailing side, the heat transfer distribution flattens as the rotation number increases, while its averaged value increases due to the turbulence enhancement and secondary flows induced by the rotation. On the leading side, the secondary flows counteract the turbulence reduction and the overall heat transfer coefficient exhibits a limited decrease. In the latter case, the secondary flows are responsible for high heat transfer gradients on the investigated area.

Three Dimensional Numerical Simulation of Gas Heat Transfer in Rectangular Microchannels

2010 ◽  
Author(s):  
Xiaohong Yan ◽  
Qiuwang Wang
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Heat Flux ◽  
Aspect Ratio ◽  
Wall Temperature ◽  
Three Dimensional ◽  
Uniform Heat Flux ◽  
Flux Boundary Condition ◽  
Uniform Heat ◽  
Heat Flux Boundary Condition

Rectangular microchannel is the typical component of the micro heat exchangers and micro heat sinks. Three-dimensional compressible Navier-Stokes equations are solved for gas flow and heat transfer in microchannels under uniform heat flux boundary condition. The numerical methodology is based on the control volume SIMPLE scheme. It is found that the heat removal characteristic for compressible flow is better than the incompressible flow and it is not suitable to use conventionally defined Nu to measure the heat transfer characteristic for compressible heat transfer. The effect of the aspect ratio (width to height) on the cross-sectional averaged wall temperature and the Nu is negligible under the uniform heat flux boundary condition. However, the local uniformity of the wall temperature is significantly influenced by the aspect ratio. The square cross-section exhibits the best local uniformity of the wall temperature.

scholarly journals Laminar convective heat transfer for in-plane spiral coils of noncircular cross sections ducts: A computational fluid dynamics study

2012 ◽  
Vol 16 (1) ◽  
pp. 109-118 ◽  
Author(s):  
Jundika Kurnia ◽  
Agus Sasmito ◽  
Arun Mujumdar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Cross Sections ◽  
Wall Temperature ◽  
Heat Transfer Performance ◽  
Constant Heat Flux ◽  
Uniform Heat Flux ◽  
Transfer Performance ◽  
Constant Wall Temperature ◽  
Flux Boundary Condition

The objective of this study was to carry out a parametric study of laminar flow and heat transfer characteristics of coils made of tubes of several different cross-sections e.g. square, rectangular, half-circle, rectangular and trapezoidal. For the purpose of ease of comparison, numerical experiments were carried out base on a square-tube Reynolds number of 1000 and a fixed fluid flow rate while length of the tube used to make coils of different diameter and pitch was held constant. A figure of merit was defined to compare the heat transfer performance of different geometry coils; essentially it is defined as total heat transferred from the wall to the surroundings per unit pumping power required. Simulations were carried out for the case of constant wall temperature as well as constant heat flux. In order to allow reasonable comparison between the two different boundary conditions - constant wall temperature and constant wall heat flux - are tested; the uniform heat flux boundary condition was computed by averaging the heat transferred per unit area of the tube for the corresponding constant wall temperature case. Results are presented and discussed in the light of the geometric effects which have a significant effect on heat transfer performance of coils.

Computation of Laminar Heat Transfer in Rotating Rectangular Ducts

1985 ◽  
Vol 107 (3) ◽  
pp. 575-582 ◽  
Author(s):  
S. Neti ◽  
A. S. Warnock ◽  
E. K. Levy ◽  
K. S. Kannan
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Heated Wall ◽  
Uniform Heat Flux ◽  
Rectangular Duct ◽  
Temperature Variations ◽  
Axis Parallel ◽  
Axis Of Symmetry

Cooling passages are often used in the rotor windings of large electrical generators, where the flow channel rotates about an axis parallel to but displaced from its axis of symmetry. In such a rotating passage, Coriolis accelerations and density gradients caused by the heated wall lead to the development of secondary flows which can have strong effects on heat transfer and pressure drop characteristics. Finite difference solutions were obtained for laminar flow of air in a rotating rectangular duct with aspect ratio 2/1, where the duct wall is subjected to a uniform heat flux. The solutions show the effect of rotation on the development of the flow patterns and velocity and temperature variations. Results for Nusselt number and friction factor are presented in both the inlet and fully developed regions over a range of Grashof and Reynolds numbers.

Rotation Effects on the Heat Transfer Distribution in a Two-Pass Rotating Internal Cooling Channel Equipped With Triangular Ribs

2017 ◽  
Author(s):  
Ignacio Mayo ◽  
Tony Arts ◽  
Nicolas Van de Wyer
Keyword(s):  
Heat Transfer ◽  
Rotation Number ◽  
Channel Model ◽  
Flow Direction ◽  
Secondary Flows ◽  
Internal Cooling ◽  
Cooling Channel ◽  
Experimental Conditions ◽  
Cfd Validation ◽  
The Impact

The present paper addresses the detailed heat transfer pattern in a two-pass rotating internal cooling channel model, with a square cross section and equipped with triangular ribs on one of its walls. The turn region consists of a smooth high curvature U-bend that generates a complex flow field and wall heat transfer. The investigation is based on Liquid Crystal Thermography (LCT) measurements in a rotating facility at Reynolds numbers varying from 20,000 to 60,000, and a maximum rotation number equal to 0.20. For these experimental conditions, the centripetal buoyancy effects are negligible. The channel is rotated around an axis perpendicular to the main flow direction in clockwise and counter-clockwise senses, in order to observe the impact of cyclonic and anti-cyclonic behavior on the heat transfer in both legs. The objective of the present study is two-fold: firstly, it aims to understand the flow physics and heat transfer phenomena at different regimes. Secondly, the detailed heat transfer measurements are intended to be a reference set for Computational Fluid Dynamics (CFD) validation. The measurements obtained in the first leg have been compared with previous experimental data in channels with square ribs and radially outward flow, showing a similar behavior in terms of heat transfer distribution and overall dependency on the rotation number. In the second leg, the heat transfer distribution is more complex. The heat transfer distribution is not symmetric, and high gradients are present in the span-wise direction. Nevertheless, the dependency of the heat transfer to increasing rotation shows a trend similar to the one observed in the first pass. The combined effects of rib-induced secondary flows stabilization/destabilization by rotation, Coriolis-induced stream-wise vortices and high streamline curvature on the heat transfer distribution are analyzed in the paper.

Turbulent Heat Transfer in Concentric Annuli With Constant Wall Temperatures

1970 ◽  
Vol 92 (1) ◽  
pp. 33-45 ◽  
Author(s):  
Alan Quarmby ◽  
R. K. Anand
Keyword(s):  
Heat Transfer ◽  
Boundary Condition ◽  
Heat Flux ◽  
Reynolds Number ◽  
Velocity Profile ◽  
Turbulent Heat Transfer ◽  
Uniform Heat Flux ◽  
Turbulent Heat ◽  
Flux Boundary Condition ◽  
Heat Flux Boundary Condition

The problem of turbulent heat transfer in concentric annuli is analyzed for the case in which one wall has a constant temperature while the other is insulated. The solution is given for both, the thermal entrance region and the fully developed situation with heating at either one of the annular surfaces. The description of the velocity profile properly takes into account the Reynolds number and radius ratio dependence of the nondimensional turbulent velocity profile in concentric annuli. Results are presented for radius ratios 2.88, 5.625, and 9.37 with the Reynolds number range from 20,000 to 240,000 and for Prandtl numbers 0.01, 0.7, and 1000. The calculated Nusselt numbers for the constant wall temperature boundary condition are smaller than the corresponding result for a uniform heat-flux boundary condition. The available experimental evidence for concentric annuli is insufficient to provide a direct test of the analysis. However some calculated results for the radius ratios 1.05 and 50 are in agreement with available theory and experiments for the parallel plate channel and circular tube, respectively. There is also good agreement, between the calculated results for the extension of the analysis to the case of a linear rise in wall temperature and experiments for a uniform heat-flux boundary condition for the annuli considered.

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