Flow Characteristics of a Narrow Rectangular Channel Equipped With a Flapping Flag

2017 ◽  
Author(s):  
Ralph Kristoffer B. Gallegos ◽  
Rajnish N. Sharma
Keyword(s):  
Heat Transfer ◽  
Rectangular Channel ◽  
Spectral Characteristics ◽  
Flow Characteristics ◽  
Vortex Generators ◽  
Streamwise Location ◽  
Flow Parameters ◽  
Flow Reynolds Number ◽  
Channel Aspect Ratio ◽  
Four Levels

Recently, the use of flapping plates or ‘flags’ as vortex generators has gained attention for its potential application in heat transfer enhancement in channels. The motion of the flag generates additional turbulence which leads to enhanced heat transfer. However, very few reports deal with the turbulence characteristics inside a channel with flag vortex generators. This paper presents some flow turbulence properties experimentally measured behind a flapping flag. Using multi-hole pressure (cobra) probes, the flow properties behind a flag (M* = 0.42) were measured in a rectangular channel (aspect ratio, α = 1/3) at four levels of flow Reynolds number (Redh = 11.5k–19.7k). Results show that the spectral properties of the flow parameters are closely dependent on the flag oscillation properties. Depending on streamwise location and Redh, measurements reveal that the flag can generate as high as 20% turbulence intensity in the channel centerline, almost six times that of a bare channel at the same Redh. In addition, a streamwise location has been identified where the flag’s oscillation no longer influences the spectral characteristics of the flow. The insights gained from this study may serve as a basis for the design and analysis of systems using flags as turbulence enhancers.

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.

scholarly journals Numerical Investigation of Heat Transfer and Fluid Flow Characteristics in a Rectangular Channel with Presence of Perforated Concave Rectangular Winglet Vortex Generators

2021 ◽  
Author(s):  
Syaiful ◽  
M. Kurnia Lutfi
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Rectangular Channel ◽  
Convection Heat Transfer ◽  
Flow Characteristics ◽  
Vortex Generator ◽  
Vortex Generators ◽  
Heated Plate ◽  
Convection Heat ◽  
Fluid Flow Characteristics

The high thermal resistance of the airside of the compact heat exchanger results in a low heat transfer rate. Vortex generator (VG) is one of the effective passive methods to increase convection heat transfer by generating longitudinal vortex (LV), which results in an increase in fluid mixing. Therefore, this study aims to analyze the convection heat transfer characteristics and the pressure drop of airflow in a rectangular channel in the presence of a concave rectangular winglet VG on a heated plate. Numerical calculations were performed on rectangular winglet pairs vortex generators (RWP VGs) and concave rectangular winglet pairs vortex generators (CRWP VGs) with a 45° angle of attack and one, two, and three pairs of VGs with and without holes. The simulation results show that the decrease in the value of convection heat transfer coefficient and pressure drop on CRWP with three perforated VG configuration is 4.63% and 3.28%, respectively, of the three pairs of CRWP VG without holes at an airflow velocity of 2 m/s.

Heat Transfer in Rotating Rectangular Cooling Channels AR=4 With Dimples

2003 ◽  
Vol 125 (3) ◽  
pp. 555-563 ◽  
Author(s):  
Todd S. Griffith ◽  
Luai Al-Hadhrami ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Rectangular Channel ◽  
Density Ratio ◽  
Orientation Effect ◽  
Internal Cooling ◽  
Cooling Channels ◽  
Flow Parameters ◽  
Dimple Surface ◽  
Channel Aspect Ratio ◽  
Channel Orientation

As the world of research seeks ways of improving the efficiency of turbomachinery, attention has recently focused on a relatively new type of internal cooling channel geometry, the dimple. Preliminary investigations have shown that the dimple enhances heat transfer with minimal pressure loss. An investigation into determining the effect of rotation on heat transfer in a rectangular channel (aspect ratio=4:1) with dimples is detailed in this paper. The range of flow parameters includes Reynolds number Re=5000-40000, rotation number Ro=0.04-0.3 and inlet coolant-to-wall density ratio Δρ/ρ=0.122. Two different surface configurations are explored, including a smooth duct and dimpled duct with dimple depth-to-print diameter δ/Dp ratio of 0.3. A dimple surface density of 10.9 dimples/in2 was used for each of the principal surfaces (leading and trailing) with a total of 131 equally spaced hemispherical dimples per surface; the side surfaces are smooth. Two channel orientations of β=90 and 135 deg with respect to the plane of rotation are explored to determine channel orientation effect. Results show a definite channel orientation effect, with the trailing-edge channel enhancing heat transfer more than the orthogonal channel. Also, the dimpled channel behaves somewhat like a 45 deg angled rib channel, but with less spanwise variations in heat transfer.

scholarly journals Heat Transfer and Friction in a Low-Aspect-Ratio Rectangular Channel with Staggered Slit-Ribbed Walls

1998 ◽  
Vol 4 (4) ◽  
pp. 283-291 ◽  
Author(s):  
Jenn-Jiang Hwang ◽  
Tong-Miin Liou
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Rectangular Channel ◽  
Area Ratio ◽  
Open Area ◽  
Ribbed Channel ◽  
Flow Parameters ◽  
Constant Friction ◽  
Flow Reynolds Number ◽  
The Heat Transfer Coefficient

Fully developed heat transfer and friction in a rectangular channel with slit-ribbed walls are examined experimentally. The slit ribs are transversely arranged on the bottom and top channel walls in a staggered manner. Effects of rib open-area ratio (β= 24%, 37%, and 46%), rib pitch-to-height ratio(Pi/H=10,15and20), and Reynolds number(10,000≤Re≤50,000)are examined. The rib height-to-channel hydraulic diameter ratio is fixed atH/De=0.081. It is disclosed that the heat transfer coefficient for the slit-ribbed channel is higher than that for the solid-ribbed channel, and increases with rib open-area ratio. Results also show that the friction factor for the slit-ribbed channel is significantly lower than that for the solid-ribbed one. Moreover, the ribs with larger open-area ratios in a higher flow Reynolds number condition could give the better thermal performance under the constant friction power constraint. Roughness functions for friction and heat transfer are further developed in terms of rib and flow parameters.

Heat Transfer in Rotating Rectangular Cooling Channels (AR=4) With Dimples

2002 ◽  
Author(s):  
Todd S. Griffith ◽  
Luai Al-Hadhrami ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Rectangular Channel ◽  
Density Ratio ◽  
Orientation Effect ◽  
Internal Cooling ◽  
Cooling Channels ◽  
Flow Parameters ◽  
Dimple Surface ◽  
Channel Aspect Ratio ◽  
Channel Orientation

As the world of research seeks ways of improving the efficiency of turbomachinery, attention has recently focused on a relatively new type of internal cooling channel geometry, the dimple. Preliminary investigations have shown that the dimple enhances heat transfer with minimal pressure loss. An investigation into determining the effect of rotation on heat transfer in a rectangular channel (aspect ratio = 4:1) with dimples is detailed in this paper. The range of flow parameters includes Reynolds number (Re = 5000–40000), rotation number (Ro = 0.04–0.3) and inlet coolant-to-wall density ratio (Δρ/ρ = 0.122). Two different surface configurations are explored, including a smooth duct and dimpled duct with dimple depth-to-print diameter (δ/Dp) ratio of 0.3. A dimple surface density of 10.9 dimples/in2 was used for each of the principal surfaces (leading and trailing) with a total of 131 equally spaced hemispherical dimples per surface; the side surfaces are smooth. Two channel orientations of β = 90° and 135° with respect to the plane of rotation are explored to determine channel orientation effect. Results show a definite channel orientation effect, with the trailing-edge channel enhancing heat transfer more than the orthogonal channel. Also, the dimpled channel behaves somewhat like a 45° angled rib channel, but with less spanwise variations in heat transfer.

scholarly journals A Numerical Study on Heat Transfer in the Channel with Delta Winglet Pair Vortex Generators

2021 ◽  
Vol 39 (4) ◽  
pp. 1305-1312
Author(s):  
Mohammad Mazidi Sharfabadi ◽  
Parham Mobadersani ◽  
Leila Nourpour
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Numerical Study ◽  
Rectangular Channel ◽  
Flow Characteristics ◽  
Vortex Generators ◽  
Hydrodynamic Performance ◽  
Hydrodynamic Characteristics ◽  
Quick Scheme ◽  
Volume Method

In this study, the effect of the vortex generators on the heat transfer and flow characteristics in a rectangular channel is investigated numerically by finite volume method. The governing equations are discretized using QUICK scheme. The numerical results are validated against published experimental data. In this paper, the effects of the winglet aspect ratio and the distance between the vertices of the winglets on the heat transfer and hydrodynamic characteristics of the flow are surveyed. In addition, to achieve the optimum amount of heat transfer, it is important to know the proper arrangement of the triangular winglet pairs as well as their suitable position. Therefore, the appropriate values of the longitudinal and transverse pitch are presented in this paper. The results show that the winglet with the aspect ratio of 1.75 has the best thermal and hydrodynamic performance. Furthermore, the transverse pitch of 1.24 causes 6.5% growth in the average Nusselt number.

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