Experimental and Numerical Study of Heat Transfer and Flow Friction in Channels With Dimples of Different Shapes

2015 ◽  
Vol 137 (3) ◽  
Author(s):  
Yu Rao ◽  
Yan Feng ◽  
Bo Li ◽  
Bernhard Weigand
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Flow Structure ◽  
Channel Flow ◽  
Numerical Study ◽  
Rectangular Channel ◽  
Transfer Enhancement ◽  
Number Range ◽  
Flow Friction ◽  
Different Shapes

An experimental and numerical study was conducted to investigate the effects of dimple shapes on the heat transfer and flow friction of a turbulent flow over dimpled surfaces with different dimple shapes: spherical, teardrop, elliptical, and inclined elliptical. These dimples all have the same depth. The heat transfer, friction factor, and flow structure characteristics in the cooling channels with dimples of different shapes have been obtained and compared with each other for a Reynolds number range of 8500–60,000. The study showed that the dimple shape can have distinctive effects on the heat transfer and flow structure in the dimpled channels. The teardrop dimples show the highest heat transfer, which is about 18% higher than the conventional spherical dimples; and the elliptical dimples have the lowest heat transfer, which is about 10% lower than the spherical dimples; and however the inclined elliptical dimples have comparable heat transfer and pressure loss performance with the spherical dimples. The experiments still showed the realistic heat transfer enhancement capabilities of the dimpled channels relative to a smooth rectangular channel flow under the same flow and thermal boundary conditions, even after considering the thermal entrance effects in the channel flow and the enlarged heat transfer (wetted) area due to the dimpled surface. The three-dimensional numerical computations showed different vortex flow structures and detailed heat transfer characteristics of the dimples with different shapes, which revealed the influential mechanisms of differently shaped dimples on the convective heat transfer enhancement.

An Experimental and Numerical Study of Heat Transfer and Pressure Loss in a Rectangular Channel With V-Shaped Ribs

2006 ◽  
Author(s):  
Michael Maurer ◽  
Jens von Wolfersdorf ◽  
Michael Gritsch
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Thermal Performance ◽  
Pressure Loss ◽  
Numerical Study ◽  
Rectangular Channel ◽  
Reynolds Numbers ◽  
Transfer Enhancement ◽  
High Reynolds Numbers ◽  
High Reynolds

An experimental and numerical study was conducted to determine the thermal performance of V-shaped ribs in a rectangular channel with an aspect ratio of 2:1. Local heat transfer coefficients were measured using the steady state thermochromic liquid crystal technique. Periodic pressure losses were obtained with pressure taps along the smooth channel sidewall. Reynolds numbers from 95,000 to 500,000 were investigated with V-shaped ribs located on one side or on both sides of the test channel. The rib height-to-hydraulic diameter ratios (e/Dh) were 0.0625 and 0.02, and the rib pitch-to-height ratio (P/e) was 10. In addition, all test cases were investigated numerically. The commercial software FLUENT™ was used with a two-layer k-ε turbulence model. Numerically and experimentally obtained data were compared. It was determined that the heat transfer enhancement based on the heat transfer of a smooth wall levels off for Reynolds numbers over 200,000. The introduction of a second ribbed sidewall slightly increased the heat transfer enhancement whereas the pressure penalty was approximately doubled. Diminishing the rib height at high Reynolds numbers had the disadvantage of a slightly decreased heat transfer enhancement, but benefits in a significantly reduced pressure loss. At high Reynolds numbers small-scale ribs in a one-sided ribbed channel were shown to have the best thermal performance.

Numerical Investigation of Heat Transfer Enhancement on a Small Scale Vortex Generator

2009 ◽  
Author(s):  
Jiansheng Wang ◽  
Zhiqin Yang
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Flow Structure ◽  
Rectangular Channel ◽  
Vortex Generator ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Vortex Generators ◽  
Small Scale ◽  
Transfer Enhancement

The heat transfer characteristic and flow structure of fluid in the rectangular channel with different height vortex generators in small scale are investigated with numerical simulation. Meantime, the properties of heat transfer and flow of fluid in the rectangular channel are compared with the channel which located small scale vortex generator. The variation law of local heat transfer and flow structure in channel is obtained. The mechanism of heat transfer enhancement of small scale vortex generators is discussed in detail. It is found that the influence of vortex generator on heat transfer is not in proportion to the size of vortex generator. What is more, turbulent flow structure near the wall, which influences the temperature distribution near the wall, induces the variety of local heat transfer. The fluid movement towards to the wall causes the heat transfer enhanced. On the contrary, the fluid movement away from the wall decreases the local heat transfer.

Optimization and Development for Fin-and-Tube Heat Exchangers With Vortex Generators

2010 ◽  
Author(s):  
Ya-Ling He ◽  
Pan Chu ◽  
Wen-Quan Tao
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Flow Structure ◽  
Heat Exchangers ◽  
Pressure Loss ◽  
Numerical Study ◽  
Moderate Pressure ◽  
Computational Domain ◽  
Transfer Enhancement ◽  
Local Flow

In this paper, heat transfer enhancement and pressure loss penalty for fin-and-tube heat exchangers with rectangular winglet pairs (RWPs) were numerically investigated in a relatively low Reynolds number flow. The purpose of this study was to explore the fundamental mechanism between the local flow structure and the heat transfer augmentation. The RWPs were placed with a special orientation for the purpose of enhancement of heat transfer. The numerical study involved three-dimensional flow and conjugate heat transfer in the computational domain, which was set up to model the entire flow channel in the air flow direction. The effects of attack-angle of RWPs, row-number of RWPs and placement of RWPs on the heat transfer characteristics and flow structure were examined in detail. It was observed that the longitudinal vortices caused by RWPs and the impingement of RWPs-directed flow on the downstream tube were important reasons of heat transfer enhancement for fin-and-tube heat exchangers with RWPs. It was interesting to find that the pressure loss penalty of the fin-and-tube heat exchangers with RWPs could be reduced by altering the placement of the same number of RWPs from inline array to staggered array and simultaneously maintain the heat transfer enhancement level. The results showed that the rectangular winglet pairs (RWPs) can significantly improve the heat transfer performance of the fin-and-tube heat exchangers with a moderate pressure loss penalty.

Heat Transfer Enhancement in a Rectangular Channel With the Combination of Ribs, Dimples and Protrusions

2011 ◽  
Author(s):  
Jibing Lan ◽  
Yonghui Xie ◽  
Di Zhang
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Thermal Performance ◽  
Rectangular Channel ◽  
Low Pressure ◽  
Internal Cooling ◽  
Transfer Enhancement ◽  
Number Range ◽  
Baseline Case ◽  
The One

Rib turbulators can enhance the heat transfer successfully, but in most cases this is associated with large pressure loss penalties. Recently, dimple techniques become an attractive method for gas turbine blade internal cooling because dimples enhance heat transfer with low pressure penalty. In the present paper, a compound heat transfer enhancement technique, heat transfer enhancement in rectangular channel (Aspect ratio = 4) with the combination of ribs, dimples and protrusions, are investigated. The calculations are conducted on five different channel configurations. Case 1 which is the baseline configuration is a rectangular channel with rectangular ribs (e/Dh = 0.078, P/e = 10). In case 2, one row of dimples are placed between two ribs. In case 3, instead of dimples, one row of protrusions are placed between two ribs. In case 4, three rows of dimples are place between two ribs. Case 5 places three rows of protrusions between two ribs instead of dimples. The present paper focuses on Reynolds numbers (based on the channel hydraulic diameter) ranging from 10000 to 60000. In all configurations, the non-dimensional dimple/protrusion depths are 0.2. The results show that the rib+dimple cases provide minor increase in Nu/Nu0, f/f0 and thermal performance. Within the Reynolds number range studied, the Nu/Nu0 values of the three row rib+protrusion case is 17% ∼ 7% higher than that of the baseline case, and the decrease in f/f0 is about 10%. The thermal performance of the three row rib+protrusion case is about 16% higher than that of the baseline case. The Nu/Nu0 values of the one row rib+protrusion case is about 9% higher than that of the baseline case, and the decrease in f/f0 is about 12%. The thermal performance of the one row rib+protrusion case is about 14% higher than that of the baseline case. It can be concluded that rib+protrusion technique in rectangular channel has the potential to provide heat transfer enhancement with low pressure penalty.

scholarly journals 2D Numerical Study of Heat Transfer Enhancement Using Fish-Tail Locomotion Vortex Generators

2021 ◽  
Vol 8 (3) ◽  
pp. 386-392
Author(s):  
Ahmed Hashim Yousif ◽  
Hakim T. Kadhim ◽  
Kadhim K. Idan Al-Chlaihawi
Keyword(s):  
Heat Transfer ◽  
Friction Factor ◽  
Numerical Study ◽  
Rectangular Channel ◽  
Flow Characteristics ◽  
Vortex Generators ◽  
Transfer Enhancement ◽  
Number Range ◽  
Maximum Value ◽  
Fluid Flow Characteristics

In this paper, a numerical simulation is performed to study the effect of two types of concave vortex generators (VGs), arranged as fish-tail locomotion in a rectangular channel. The heat transfer and fluid flow characteristics with and without VGs are examined over the Reynolds number range 200≤Re≤2200.The two proposed types of the VGs are selected based on the speed of the fish movement which is arranged in different distances between them (d/H=0.6, 1, 1.3). The results show that the use of VGs can significantly enhance the heat transfer rate, but also increases the friction factor. The heat transfer performance is enhanced by (4-21.1%) reaching the maximum value by using the first type of the VGs at (d/H=1.3) due to better mixing of secondary flow and the new arrangement of the VGs which lead to decreasing the friction factor with an easy flow of fluid.

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