scholarly journals Influence of Narrow Rectangular Channel ( AR = 1 : 4 ) on Heat Transfer and Friction for V- and W-Shaped Ribs in Turbine Blade Applications

2021 ◽  
Vol 2021 ◽  
pp. 1-13
Author(s):  
Karthik Krishnaswamy ◽  
Suresh Sivan ◽  
Hafiz Muhammad Ali
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Secondary Flow ◽  
Gas Turbines ◽  
Rectangular Channel ◽  
Hydraulic Diameter ◽  
Transfer Enhancement ◽  
Maximum Enhancement ◽  
Heat Transfer Augmentation ◽  
Nominal Pressure

Effective cooling of blades with a nominal pressure drop is essential for performance augmentation and thermal management of gas turbines. Hence, present work is aimed at determining the heat transfer enhancement and friction for W- and V-shaped ribs inside a rectangular cooling channel having hydraulic diameter ( D h ) of 0.048 m and aspect ratio ( AR ) 1 : 4. Ribs are fixed facing downstream with angle of attack ( α ) 45° on opposite walls. Pitch ( P ) between two successive ribs is 25 mm for both cases. Continuous V- and W-shaped ribs with height to channel hydraulic diameter ratio ( e / D h ) 0.052 and 0.0416 and pitch to height ratio ( P / e ) 10 and 12.5, respectively, have been examined for Reynolds number ( Re ) range 20000-80000. Heat transfer augmentation achieved at Re 80000 is 1.94 and 1.8 times higher than Re 20000 for V- and W-shaped ribs, respectively. Streamwise and spanwise variations in local Nusselt number ratio are highest for V-shaped ribs, which are estimated to be 31% and 12%. For W-shaped ribs, variations are 17.5% and 3.5%. Nusselt number ( Nu ) is highest along span length 0.5 w for V-shaped ribs due to dominance of apex induced secondary flow. For W-shaped ribs, Nusselt number along the span lengths is found to be nearly same view uniformity in secondary flow. Maximum enhancement ( Nu / N u o ) estimated for both the rib shapes is 3.9 at Re 20000. Due to increased rib height, friction losses for V-shaped ribs are higher than W-shaped ribs. Maximum friction loss increment is estimated to be 85% for V-shaped ribs and 42% for W-shaped ribs between Re 20000 and 40000. For both rib shapes, impact of ribs is found to be greatest at Re 40000. Thermohydraulic performance ( THP ) for W-shaped ribs is superior to V-shaped ribs. Best THP achieved for W- and V-shaped ribs are 3.7 and 3.4 at Re 20000.

FORCED CONVECTION BASED HEAT TRANSFER ANALYSIS OF SPHERICAL DIMPLE AND PROTRUSION SURFACE IN TURBULENT FLOW

2017 ◽  
Vol 41 (5) ◽  
pp. 771-786 ◽  
Author(s):  
Ashif Perwez ◽  
Shreyak Shende ◽  
Rakesh Kumar
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Friction Factor ◽  
Vortex Flow ◽  
Rectangular Channel ◽  
Heat Transfer Analysis ◽  
Flow Structures ◽  
Transfer Enhancement ◽  
Heat Transfer Augmentation ◽  
Thermal Boundary Conditions

An experimental and numerical investigation is performed to study the effect of dimple and protrusion geometry on the heat transfer enhancement and the friction factor of surfaces with dimples and protrusions subjected to turbulent flow. The parameters used to compare the spherical dimples and protrusions are Nusselt Number, friction factor, and flow pattern. These parameters are obtained for a Reynolds number of 10500-60900. The spherical dimple results showed the greater heat transfer, which is about 6.97% higher and pressure loss which is 5.07% lower than the spherical protrusion. The realistic heat transfer augmentation capabilities of channels with dimples and protrusions can be studied from the experimental results. The comparison is made with respect to the smooth rectangular channel under the same flow and thermal boundary conditions. The numerical analysis is performed which shows the different vortex flow structures of the spherical dimples and protrusions channel.

Heat Transfer and Pressure Loss in Rectangular One-Side-Ribbed Channels With Different Aspect Ratios

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Sébastien Kunstmann ◽  
Jens von Wolfersdorf ◽  
Uwe Ruedel
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Heat Transfer Enhancement ◽  
Gas Turbines ◽  
Pressure Loss ◽  
Rectangular Channel ◽  
Channel Height ◽  
Transfer Enhancement ◽  
Height Ratio ◽  
Aspect Ratios

An investigation was conducted to assess the thermal performance of W-shaped, 2W-shaped and 4W-shaped ribs in a rectangular channel. The aspect ratios (W/H) were 2:1, 4:1, and 8:1. The ribs were located on one channel wall. The rib height (e) was kept constant with a rib height-to-hydraulic diameter ratio (e/Dh) of 0.02, 0.03, and 0.06. The rib pitch-to-height ratio (P/e) was 10. The Reynolds numbers investigated (Re > 90 000) are typical for combustor liner cooling configurations of gas turbines. Local heat transfer coefficients using the transient thermochromic liquid crystal technique and overall pressure losses were measured. The rib configurations were investigated numerically to visualize the flow pattern in the channel and to support the understanding of the experimental data. The results show that the highest heat transfer enhancement is obtained by rib configurations with a rib section-to-channel height ratio (Wr/H) of 1:1. W-shaped ribs achieve the highest heat transfer enhancement levels in channels with an aspect ratio of 2:1, 2W-shaped ribs in channels with an aspect ratio of 4:1 and 4W-shaped ribs in channels with an aspect ratio of 8:1. Furthermore, the pressure loss increases with increasing complexity of the rib geometry and blockage ratio.

Convective Heat Transfer Enhancement in a Circular Tube Using Twisted Tape

2009 ◽  
Vol 131 (8) ◽  
Author(s):  
Zhi-Min Lin ◽  
Liang-Bi Wang
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Convective Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Secondary Flow ◽  
Convective Heat ◽  
Tube Wall ◽  
Twisted Tape ◽  
Transfer Enhancement ◽  
Thermal Boundary Conditions

The secondary flow has been used frequently to enhance the convective heat transfer, and at the same flow condition, the intensity of convective heat transfer closely depends on the thermal boundary conditions. Thus far, there is less reported information about the sensitivity of heat transfer enhancement to thermal boundary conditions by using secondary flow. To account for this sensitivity, the laminar convective heat transfer in a circular tube fitted with twisted tape was investigated numerically. The effects of conduction in the tape on the Nusselt number, the relationship between the absolute vorticity flux and the Nusselt number, the sensitivity of heat transfer enhancement to the thermal boundary conditions by using secondary flow, and the effects of secondary flow on the flow boundary layer were discussed. The results reveal that (1) for fully developed laminar heat convective transfer, different tube wall thermal boundaries lead to different effects of conduction in the tape on heat transfer characteristics; (2) the Nusselt number is closely dependent on the absolute vorticity flux; (3) the efficiency of heat transfer enhancement is dependent on both the tube wall thermal boundaries and the intensity of secondary flow, and the ratio of Nusselt number with twisted tape to its counterpart with straight tape decreases with increasing twist ratio while it increases with increasing Reynolds number for both uniform wall temperature (UWT) and uniform heat flux (UHF) conditions; (4) the difference in the ratio between UWT and UHF conditions is also strongly dependent on the conduction in the tape and the intensity of the secondary flow; and (5) the twist ratio ranging from 4.0 to 6.0 does not necessarily change the main flow velocity boundary layer near tube wall, while Reynolds number has effects on the shape of the main flow velocity boundary layer near tube wall only in small regions.

Heat Transfer Enhancement of Jet Impingement on a Flat Plate Attached by a Porous Medium with a Center Cavity

2010 ◽  
Vol 297-301 ◽  
pp. 427-432 ◽  
Author(s):  
Pey Shey Wu ◽  
Chia Yu Hsieh ◽  
Shen Ta Tsai
Keyword(s):  
Heat Transfer ◽  
Porous Medium ◽  
Nusselt Number ◽  
Flat Plate ◽  
Porous Layer ◽  
Jet Impingement ◽  
Stagnation Zone ◽  
Transfer Enhancement ◽  
Maximum Enhancement ◽  
Impingement Heat Transfer

Jet impingement heat transfer on a target plate covered with a thick porous layer with or without a cylindrical center cavity is experimentally investigated using the transient liquid crystal technique. Based on the results of jet impingement on a bare flat plate, heat transfer enhancement due to the attachment of porous medium is assessed. The varying parameters in the experiments include the nozzle-to-plate distance, jet Reynolds number, jet-to-cavity diameter ratio, and the cavity depth. Results of Nusselt number distribution, stagnation-zone Nusselt number, and averaged Nusselt number over a region of 3 times the hole diameter are documented. Experimental results show that the attachment of the porous layer with a center cavity can either hamper, or effectively enhance the jet impingement heat transfer over a flat plate. The maximum enhancement occurs at jet Reynolds number of 12400 when the cavity is a through hole and the cavity has the same diameter as the jet. The stagnation-zone Nusselt number increases 58.3% and the averaged Nusselt number increases 77.5% at the maximum enhancement condition. On the other hand, the addition of the thick porous layer without a center cavity gave rise to severe adverse effect on jet impingement heat transfer.

scholarly journals Heat Transfer and Fluid Flow in a Square Duct With 12 Different Shaped Vortex Generators

1999 ◽  
Author(s):  
Tong-Miin Liou ◽  
Chung-Chu Chen ◽  
Tzi-Wei Tsai
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Fluid Flow ◽  
Secondary Flow ◽  
Fluid Dynamic ◽  
Vortex Generator ◽  
Flow Patterns ◽  
Hydraulic Diameter ◽  
Longitudinal Vortex ◽  
Mean Velocity

Detailed local Nusselt number distributions, streamwise mean flow patterns and cross-sectional secondary flow patterns, and friction factors in the first pass of a sharp turn two-pass square channel with various configurations of longitudinal vortex generator arranged on one wall were measured using transient liquid crystal thermography, laser-Doppler velocimetry, and pressure transducer probing, respectively. The Reynolds number, based on channel hydraulic diameter and bulk mean velocity, was fixed at 1.2 × 104. The vortex generator height-to-hydraulic diameter ratio and pitch-to-height ratio were 0.12 and 10, respectively. Comparisons in terms of heat transfer augmentation and uniformity and friction loss are first performed on 12 configurations of longitudinal vortex generator. The fluid dynamic mechanisms and wall confinement relevant to heat transfer enhancement are then documented for three-selected vortex generator models. In addition, the differences in fluid flow and heat transfer characteristics between a single vortex generator and a vortex generator array are addressed for the delta wing 1 U and 45° V U models which provide better thermal performance. The direction and strength of the secondary flow with respect to the heat transfer wall are found to be the most important fluid dynamic factors affecting the heat transfer promotion through the channel wall, followed by the convective mean velocity, and then the turbulent kinetic energy. Furthermore, the effects of the two-dimensional heat conduction near the vortex generator edge and unseen heat transfer areas on the Nusselt number estimation are documented in detail.

Heat Transfer and Pressure Loss in Rectangular One-Side-Ribbed Channels With Different Aspect Ratios

2009 ◽  
Author(s):  
Se´bastien Kunstmann ◽  
Jens von Wolfersdorf ◽  
Uwe Ruedel
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Heat Transfer Enhancement ◽  
Gas Turbines ◽  
Pressure Loss ◽  
Rectangular Channel ◽  
Channel Height ◽  
Transfer Enhancement ◽  
Height Ratio ◽  
Aspect Ratios

An investigation was conducted to assess the thermal performance of W-shaped, 2W-shaped and 4W-shaped ribs in a rectangular channel. The aspect ratios (W/H) were 2:1, 4:1 and 8:1. The ribs were located on one channel wall. The rib height (e) was kept constant with a rib height-to-hydraulic diameter ratio (e/Dh) of 0.02, 0.03 and 0.06. The rib pitch-to-height ratio (P/e) was 10. The Reynolds numbers investigated (Re>90,000) are typical for combustor liner cooling configurations of gas turbines. Local heat transfer coefficients using the transient thermochromic liquid crystal technique and overall pressure losses were measured. The rib configurations were investigated numerically to visualize the flow pattern in the channel and to support the understanding of the experimental data. The results show that the highest heat transfer enhancement is obtained by rib configurations with a rib section-to-channel height ratio (Wr/H) of 1:1. W-shaped ribs achieve the highest heat transfer enhancement levels in channels with an aspect ratio of 2:1, 2W-shaped ribs in channels with an aspect ratio of 4:1 and 4W-shaped ribs in channels with an aspect ratio of 8:1. Furthermore, the pressure loss increases with increasing complexity of the rib geometry and blockage ratio.

Numerical Simulation of Laminar Flow Heat Transfer Enhancement Using Surface Modification

2014 ◽  
Author(s):  
Abhijit S. Paranjape ◽  
Ninad C. Maniar ◽  
Deval A. Pandya ◽  
Brian H. Dennis
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Surface Modification ◽  
Laminar Flow ◽  
Heat Transfer Enhancement ◽  
Rectangular Channel ◽  
Longitudinal Vortex ◽  
Bottom Wall ◽  
Transfer Enhancement ◽  
Smooth Channel

Heat transfer augmentation techniques have gained great importance in different engineering applications to deal with thermal management issues. In this work, a numerical investigation was carried out to see the effects of a modified surface on the heat transfer enhancement compared to a smooth surface. In the first case, spherical dimple arrays were applied to the surface. The effects were observed for dimples on the bottom wall of a channel for a laminar airflow. The effects of a 21×7 staggered array and a 19×4 inline array on the bottom wall were investigated. In the second case, the heat exchange enhancement in a rectangular channel using longitudinal vortex generators (LVG) for a laminar flow was considered. In both cases, a 3D steady viscous computational fluid dynamics package with an unstructured grid was used to compute the flow and temperature field. The heat transfer characteristics were studied as a function of the Reynolds number based on the hydraulic diameter of the channel. The heat transfer was quantified by computing the surface averaged Nusselt number. The pressure drop and flow characteristics were also calculated. The Nusselt number was compared with that of a smooth channel without surface modification to assess the level of heat transfer enhancement.

Fluid Flow and Heat Transfer in a Rotating Two-Pass Square Duct With In-Line 90-deg Ribs

2002 ◽  
Vol 124 (2) ◽  
pp. 260-268 ◽  
Author(s):  
Tong-Miin Liou ◽  
Meng-Yu Chen ◽  
Meng-Hsiun Tsai
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Fluid Flow ◽  
Secondary Flow ◽  
Separation Bubble ◽  
Hydraulic Diameter ◽  
Duct Flow ◽  
Mean Velocity ◽  
Number Ratio ◽  
Sharp Turn

Laser-doppler velocimetry and transient thermochromic liquid crystal measurements are presented to understand local fluid flow and surface heat transfer distributions in a rotating ribbed duct with a 180 deg sharp turn. The in-line 90-deg ribs were arranged on the leading and trailing walls with rib height-to-hydraulic diameter ratio and pitch-to-height ratio of 0.136 and 10, respectively. The Reynolds number, based on duct hydraulic diameter and bulk mean velocity, was fixed at 1.0×104 whereas the rotational number varied from 0 to 0.2. Results are compared with those of the rotating smooth duct flow in terms of maximum streamwise mean velocities Umax/Ub and turbulence intensities u′max/Ub, skewness of mean velocity profiles, secondary flow pattern, turn-induced separation bubble, and turbulence anisotropy. Nusselt number ratio mappings are also provided on the leading and trailing walls. The relationships between the fluid flow and local heat transfer enhancement are also documented. It is found that the rotating ribbed duct flow provides higher Umax/Ub,u′max/Ub, and stronger total averaged secondary flow and, hence heat transfer is enhanced. Comparisons with heat transfer data published by other research groups are also made. Furthermore, simple linear correlations between regional averaged Nusselt number ratio and rotation number are developed.

Fluid Flow and Heat Transfer in a Rotating Two-Pass Square Duct With In-Line 90° Ribs

2001 ◽  
Author(s):  
Tong-Miin Liou ◽  
Meng-Yu Chen ◽  
Meng-Hsiun Tsai
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Fluid Flow ◽  
Secondary Flow ◽  
Separation Bubble ◽  
Hydraulic Diameter ◽  
Duct Flow ◽  
Mean Velocity ◽  
Number Ratio ◽  
Sharp Turn

Laser-Doppler velocimetry and transient thermochromic liquid crystal measurements are presented to understand local fluid flow and surface heat transfer distributions in a rotating ribbed duct with a 180° sharp turn. The in-line 90° ribs were arranged on the leading and trailing walls with rib height-to-hydraulic diameter ratio and pitch-to-height ratio of 0.136 and 10, respectively. The Reynolds number, based on duct hydraulic diameter and bulk mean velocity, was fixed at 1.0×104 whereas the rotational number varied from 0 to 0.2. Results are compared with those of the rotating smooth duct flow in terms of maximum streamwise mean velocities (Umax/Ub) and turbulence intensities (u′max/Ub), skewness of mean velocity profiles, secondary flow pattern, turn-induced separation bubble, and turbulence anisotropy. Nusselt number ratio mappings are also provided on the leading and trailing walls. The relationships between the fluid flow and local heat transfer enhancement are also documented. It is found that the rotating ribbed duct flow provides higher Umax/Ub, u′max/Ub, and stronger total averaged secondary flow and, hence heat transfer is enhanced. Comparisons with heat transfer data published by other research groups are also made. Furthermore, simple linear correlations between regional averaged Nusselt number ratio and rotation number are developed.

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