Experimental Investigation of Mixed Laminar Convection in the Entrance Region of Inclined Rectangular Channels

1986 ◽  
Vol 108 (3) ◽  
pp. 574-579 ◽  
Author(s):  
S. M. Morcos ◽  
M. M. Hilal ◽  
M. M. Kamel ◽  
M. S. Soliman
Keyword(s):  
Nusselt Number ◽  
Experimental Results ◽  
Entrance Region ◽  
Test Facility ◽  
Working Fluid ◽  
Aspect Ratios ◽  
Rectangular Channels ◽  
Axial Variation ◽  
Uniform Wall ◽  
Laminar Convection

The present experimental study considers the effect of combined forced and free laminar convection on the heat transfer in the entrance region of horizontal and inclined rectangular channels under uniform wall heat flux. The test facility includes electrically heated aluminum rectangular channels having aspect ratios AR = 2.667 and 0.375, with water as the working fluid. The experimental results included the circumferential wall temperature distribution and the axial variation of Nusselt number. Correlations of the experimental results of Nusselt number in the fully developed region were obtained in terms of Rayleigh number, Reynolds number, and inclination angle.

Numerical Solution for Combined Free and Forced Laminar Convection in Horizontal Rectangular Channels

1969 ◽  
Vol 91 (1) ◽  
pp. 59-66 ◽  
Author(s):  
K. C. Cheng ◽  
Guang-Jyh Hwang
Keyword(s):  
Numerical Solution ◽  
Axial Position ◽  
Uniform Wall Temperature ◽  
Thermal Boundary Conditions ◽  
Aspect Ratios ◽  
Rectangular Channels ◽  
Free And Forced Convection ◽  
Uniform Wall ◽  
Laminar Convection ◽  
Uniform Wall Heat Flux

Combined free and forced convection for steady fully developed laminar flow in horizontal rectangular channels under the thermal boundary conditions of axially uniform wall heat flux and peripherally uniform wall temperature at any axial position is approached by the method of successive overrelaxation. The convergence of the numerical solution is ascertained. Graphical results are presented for streamlines, isotherms, w/w0 versus Re Ra, f Re/(f Re)0 versus Re Ra, and Nu/Nu0 versus Re Ra for the aspect ratios γ = 0.2, 0.5, 1, 2, and 5 and Pr = 0.73. For square channels, velocity and temperature distributions for Pr = 0.73 and heat transfer results for Pr = 7.2 are also presented.

Effect of Wall Conduction on Combined Free and Forced Laminar Convection in Horizontal Rectangular Channels

1987 ◽  
Vol 109 (4) ◽  
pp. 936-942 ◽  
Author(s):  
G. J. Hwang ◽  
F. C. Chou
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Temperature Distribution ◽  
Finite Difference ◽  
Aspect Ratio ◽  
Finite Difference Method ◽  
Numerical Study ◽  
Fully Developed Flow ◽  
Rectangular Channels ◽  
Laminar Convection

This paper presents a numerical study of the effect of peripheral wall conduction on combined free and forced laminar convection in hydrodynamically and thermally fully developed flow in horizontal rectangular channels with uniform heat input axially, In addition to the Prandtl number, the Grashof number Gr+, and the aspect ratio γ, a parameter Kp indicating the significance of wall conduction plays an important role in heat transfer. A finite-difference method utilizing a power-law scheme is employed to solve the system of governing partial differential equations coupled with the equation for wall conduction. The numerical solution covers the parameters: Pr = 7.2 and 0.73, γ = 0.5, 1, and 2, Kp = 10−4–104, and Gr+ = 0–1.37×105. The flow patterns and isotherms, the wall temperature distribution, the friction factor, and the Nusselt number are presented. The results show a significant effect of the conduction parameter Kp.

Experimental Investigation of the Maximum Heat Transport in Triangular Grooves

1996 ◽  
Vol 118 (3) ◽  
pp. 740-746 ◽  
Author(s):  
H. B. Ma ◽  
G. P. Peterson
Keyword(s):  
Experimental Investigation ◽  
Heat Transport ◽  
Heat Pipes ◽  
Effective Area ◽  
Experimental Results ◽  
Test Facility ◽  
Working Fluid ◽  
Maximum Heat ◽  
Pressure Losses ◽  
Micro Heat Pipes

An experimental investigation was conducted and a test facility constructed to measure the capillary heat transport limit in small triangular grooves, similar to those used in micro heat pipes. Using methanol as the working fluid, the maximum heat transport and unit effective area heat transport were experimentally determined for ten grooved plates with varying groove widths, but identical apex angles. The experimental results indicate that there exists an optimum groove configuration, which maximizes the capillary pumping capacity while minimizing the combined effects of the capillary pumping pressure and the liquid viscous pressure losses. When compared with a previously developed analytical model, the experimental results indicate that the model can be used accurately to predict the heat transport capacity and maximum unit area heat transport when given the physical characteristics of the working fluid and the groove geometry, provided the proper heat flux distribution is known. The results of this investigation will assist in the development of micro heat pipes capable of operating at increased power levels with greater reliability.

scholarly journals Flow Characteristics of the Entrance Region with Roughness Effect within Rectangular Microchannels

Micromachines ◽  
2019 ◽  
Vol 11 (1) ◽  
pp. 30
Author(s):  
Haiwang Li ◽  
Yujia Li ◽  
Binghuan Huang ◽  
Tiantong Xu
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Stokes Equations ◽  
Critical Role ◽  
Flow Characteristics ◽  
Entrance Region ◽  
Working Fluid ◽  
Asymmetric Distribution ◽  
Rectangular Microchannels ◽  
Aspect Ratios

We conducted systematic numerical investigations of the flow characteristics within the entrance region of rectangular microchannels. The effects of the geometrical aspect ratio and roughness on entrance lengths were analyzed. The incompressible laminar Navier–Stokes equations were solved using finite volume method (FVM). In the simulation, hydraulic diameters ( D h ) ranging from 50 to 200 µm were studied, and aspect ratios of 1, 1.25, 1.5, 1.75, and 2 were considered as well. The working fluid was set as water, and the Reynolds number ranged from 0.5 to 100. The results showed a good agreement with the conducted experiment. Correlations are proposed to predict the entrance lengths of microchannels with respect to different aspect ratios. Compared with other correlations, these new correlations are more reliable because a more practical inlet condition was considered in our investigations. Instead of considering the influence of the width and height of the microchannels, in our investigation we proved that the critical role is played by the aspect ratio, representing the combination of the aforementioned parameters. Furthermore, the existence of rough elements obviously shortens the entrance region, and this effect became more pronounced with increasing relative roughness and Reynolds number. A similar effect could be seen by shortening the roughness spacing. An asymmetric distribution of rough elements decreased the entrance length compared with a symmetric distribution, which can be extrapolated to other irregularly distributed forms.

Nusselt Number as Composite Functions of Aspect Ratio and Wall Inclination in Parallelogram Microchannels with Three Types of Thermal Boundary Conditions

2016 ◽  
Vol 33 (4) ◽  
pp. 521-533 ◽  
Author(s):  
T.-M. Liou ◽  
H. Wang ◽  
S.-P. Chan
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Boundary Conditions ◽  
Simple Algorithm ◽  
Working Fluid ◽  
Constant Wall Temperature ◽  
Time Saving ◽  
Thermal Boundary Conditions ◽  
Aspect Ratios ◽  
New Findings

AbstractIn this study, attention is focused on the numerical simulations of laminar fluid flow and heat transfer in straight smooth-walled parallelogram channels with various aspect ratios (α) and inclined angles (θ). The Reynolds number (Re), characterized by the channel hydraulic diameter and the working fluid of water, is fixed at 100. The examinedαandθrange from 1 to 10 and 45° to 90°, respectively. Their effects on the thermal fluid features are explored under three thermal boundary conditions: constant wall temperature (TBC), constant axial heat transfer rate with constant peripheral temperature (H1BC), and constant wall heat flux (H2BC). The SIMPLE algorithm is employed for velocity–pressure coupling with the algebraic multigrid method, while the second-order upwind scheme is utilized for spatial discretization in pressure term; the momentum and energy equations are solved with a QUICK scheme; Least Squares Cell-Based Gradient Evaluation is applied for predicting scalar values at the cell faces and for computing secondary diffusion terms and velocity derivatives. One of the new findings is that there exists a critical value ofθ= 70° below which the Nusselt number under H2BC increases with increasingαwhereas beyond which the trend reverses, a result distinct from those computed with TBC and H1BC. Moreover, TBC is found to be a time-saving alternative to H1BC. Furthermore, both Nusselt numbers under the three thermal boundary conditions and friction factor timesReare successfully and compactly correlated with α andθto offer useful reference for designing micro-cooling channels.

Combined Forced and Free Convection in the Entrance Region of an Isothermally Heated Horizontal Pipe

1982 ◽  
Vol 104 (1) ◽  
pp. 153-159 ◽  
Author(s):  
Mikio Hishida ◽  
Yasutaka Nagano ◽  
M. S. Montesclaros
Keyword(s):  
Numerical Solutions ◽  
Entrance Region ◽  
Temperature Fields ◽  
Horizontal Pipe ◽  
Uniform Wall Temperature ◽  
Nusselt Numbers ◽  
Developing Flow ◽  
Uniform Wall ◽  
Secondary Velocity ◽  
Laminar Convection

Numerical solutions are given without the aid of a large Prandtl number assumption for combined forced and free laminar convection in the entrance region of a horizontal pipe with uniform wall temperature. The steady-state solutions have been obtained from the asymptotic time solutions of the time-dependent equations of momentum and energy with the Poisson equation for pressure. Results are presented for the developing primary and secondary velocity profiles, developing temperature fields, local wall shear stress, and local and average Nusselt numbers, which reveal how the developing flow and heat transfer in the entrance region are affected by the secondary flow due to buoyancy forces.

Buoyancy Effects on Heat Transfer in Five Different Aspect-Ratio Rectangular Channels With Smooth Walls and 45-Degree Ribbed Walls

2005 ◽  
Author(s):  
Wen-Lung Fu ◽  
Lesley M. Wright ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Aspect Ratio ◽  
Thermal Performance ◽  
Flow Direction ◽  
Aspect Ratios ◽  
Number Ratio ◽  
Buoyancy Parameter ◽  
Rectangular Channels ◽  
Channel Aspect Ratio

This paper experimentally studies the effects of the buoyancy force and channel aspect ratio on heat transfer in two-pass rotating rectangular channels with smooth walls and 45° ribbed walls. The channel aspect ratios include 4:1, 2:1, 1:1, 1:2 and 1:4. Four Reynolds numbers are studied: 5000, 10000, 25000 and 40000. The rotation speed is fixed at 550 rpm for all tests, and for each channel, two channel orientations are studied: 90° and 45° or 135°, with respect to the plane of rotation. Rib turbulators are placed on the leading and trailing walls of the channels at an angle of 45° to the flow direction. The ribs have a 1.59 by 1.59 mm square cross section, and the rib pitch-to-height ratio (P/e) is 10 for all tests. The effects of the local buoyancy parameter and channel aspect ratio on the regional Nusselt number ratio are presented. The results show that increasing the local buoyancy parameter increases the Nusselt number ratio on the trailing surface and decreases the Nusselt number ratio on the leading surface in the first pass for all channels. However, the trend of the Nusselt number ratio in the second pass is more complicated due to the strong effect of the 180° turn. Results are also presented for this critical turn region of the two-pass channels. In addition to these regions, the channel averaged heat transfer, friction factor, and thermal performance are determined for each channel. With the channels having comparable Nusselt number ratios, the 1:4 channel has the superior thermal performance because it incurs the least pressure penalty.

Vorticity-Velocity Method for the Graetz Problem and the Effect of Natural Convection in a Horizontal Rectangular Channel With Uniform Wall Heat Flux

1987 ◽  
Vol 109 (3) ◽  
pp. 704-710 ◽  
Author(s):  
F. C. Chou ◽  
G. J. Hwang
Keyword(s):  
Heat Flux ◽  
Prandtl Number ◽  
Numerical Solutions ◽  
Rectangular Channel ◽  
Wall Heat Flux ◽  
Entrance Region ◽  
Grashof Number ◽  
Uniform Wall ◽  
Laminar Convection ◽  
Uniform Wall Heat Flux

Numerical solutions given by a vorticity-velocity method are presented for combined free and forced laminar convection in the thermal entrance region of a horizontal rectangular channel without the assumptions of large Prandtl number and small Grashof number. The channel wall is heated with a uniform wall heat flux. Typical developments of temperature profile, secondary flow, and axial velocity at various axial positions in the entrance region are presented. Local friction factor and Nusselt number variations are shown for Rayleigh numbers Ra = 104, 3×104, 6×104, and 105 with the Prandtl number as a parameter. The solution for the limiting case of large Prandtl number and small Grashof number obtained from the present study confirms the data of existing literature. It is observed that the large Prandtl number assumption is valid for Pr = 10 when Ra ≤ 3×104 but for a larger Prandtl number when the Rayleigh number is higher.

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