Heat Transfer Enhancement in a Rectangular (AR=3:1) Channel With V-Shaped Dimples

2011 ◽  
Author(s):  
C. Neil Jordan ◽  
Lesley M. Wright
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Liquid Crystal ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Thermal Performance ◽  
Secondary Flows ◽  
Transfer Enhancement ◽  
Reduced Pressure

An alternative to ribs for internal heat transfer enhancement of gas turbine airfoils is dimpled depressions. Relative to ribs, dimples incur a reduced pressure drop, which can increase the overall thermal performance of the channel. This experimental investigation measures detailed Nusselt number ratio distributions obtained from an array of V-shaped dimples (δ / D = 0.30). Although the V-shaped dimple array is derived from a traditional hemispherical dimple array, the V-shaped dimples are arranged in an in-line pattern. The resulting spacing of the V-shaped dimples is 3.2D in both the streamwise and spanwise directions. A single wide wall of a rectangular channel (AR = 3:1) is lined with V-shaped dimples. The channel Reynolds number ranges from 10,000–40,000. Detailed Nusselt number ratios are obtained using both a transient liquid crystal technique and a newly developed transient temperature sensitive paint (TSP) technique. Therefore, the TSP technique is not only validated against a baseline geometry (smooth channel), but it is also validated against a more established technique. Measurements indicate that the proposed V-shaped dimple design is a promising alternative to traditional ribs or hemispherical dimples. At lower Reynolds numbers, the V-shaped dimples display heat transfer and friction behavior similar to traditional dimples. However as the Reynolds number increases to 30,000 and 40,000, secondary flows developed in the V-shaped concavities further enhance the heat transfer from the dimpled surface (similar to angled and V-shaped rib induced secondary flows). This additional enhancement is obtained with only a marginal increase in the pressure drop. Therefore, as the Reynolds number within the channel increases, the thermal performance also increases. While this trend has been confirmed with both the transient TSP and liquid crystal techniques, TSP is shown to have limited capabilities when acquiring highly resolved detailed heat transfer coefficient distributions.

Heat Transfer Enhancement in a Rectangular (AR = 3:1) Channel With V-Shaped Dimples

2012 ◽  
Vol 135 (1) ◽  
Author(s):  
C. Neil Jordan ◽  
Lesley M. Wright
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Liquid Crystal ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Thermal Performance ◽  
Secondary Flows ◽  
Transfer Enhancement ◽  
Reduced Pressure

An alternative to ribs for internal heat transfer enhancement of gas turbine airfoils is dimpled depressions. Relative to ribs, dimples incur a reduced pressure drop, which can increase the overall thermal performance of the channel. This experimental investigation measures detailed Nusselt number ratio distributions obtained from an array of V-shaped dimples (δ/D = 0.30). Although the V-shaped dimple array is derived from a traditional hemispherical dimple array, the V-shaped dimples are arranged in an in-line pattern. The resulting spacing of the V-shaped dimples is 3.2D in both the streamwise and spanwise directions. A single wide wall of a rectangular channel (AR = 3:1) is lined with V-shaped dimples. The channel Reynolds number ranges from 10,000–40,000. Detailed Nusselt number ratios are obtained using both a transient liquid crystal technique and a newly developed transient temperature sensitive paint (TSP) technique. Therefore, the TSP technique is not only validated against a baseline geometry (smooth channel), but it is also validated against a more established technique. Measurements indicate that the proposed V-shaped dimple design is a promising alternative to traditional ribs or hemispherical dimples. At lower Reynolds numbers, the V-shaped dimples display heat transfer and friction behavior similar to traditional dimples. However, as the Reynolds number increases to 30,000 and 40,000, secondary flows developed in the V-shaped concavities further enhance the heat transfer from the dimpled surface (similar to angled and V-shaped rib induced secondary flows). This additional enhancement is obtained with only a marginal increase in the pressure drop. Therefore, as the Reynolds number within the channel increases, the thermal performance also increases. While this trend has been confirmed with both the transient TSP and liquid crystal techniques, TSP is shown to have limited capabilities when acquiring highly resolved detailed heat transfer coefficient distributions.

Numerical investigation of fluid flow structure and heat transfer in a passage with continuous and truncated V-shaped ribs

2015 ◽  
Vol 25 (1) ◽  
pp. 171-189 ◽  
Author(s):  
Shian Li ◽  
Gongnan Xie ◽  
Bengt Sunden
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Fluid Flow ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Thermal Performance ◽  
Internal Cooling ◽  
Transfer Enhancement ◽  
Content Type ◽  
Flow And Heat Transfer

Purpose – The employment of continuous ribs in a passage involves a noticeable pressure drop penalty, while other studies have shown that truncated ribs may provide a potential to reduce the pressure drop while keeping a significant heat transfer enhancement. The purpose of this paper is to perform computer-aided simulations of turbulent flow and heat transfer of a rectangular cooling passage with continuous or truncated 45-deg V-shaped ribs on opposite walls. Design/methodology/approach – Computational fluid dynamics technique is used to study the fluid flow and heat transfer characteristics in a three-dimensional rectangular passage with continuous and truncated V-shaped ribs. Findings – The inlet Reynolds number, based on the hydraulic diameter, is ranged from 12,000 to 60,000 and a low-Re k-e model is selected for the turbulent computations. The local flow structure and heat transfer in the internal cooling passages are presented and the thermal performances of the ribbed passages are compared. It is found that the passage with truncated V-shaped ribs on opposite walls provides nearly equivalent heat transfer enhancement with a lower (about 17 percent at high Reynolds number of 60,000) pressure loss compared to a passage with continuous V-shaped ribs or continuous transversal ribs. Research limitations/implications – The fluid is incompressible with constant thermophysical properties and the flow is steady. The passage is stationary. Practical implications – New and additional data will be helpful in the design of ribbed passages to achieve a good thermal performance. Originality/value – The results imply that truncated V-shaped ribs are very effective in improving the thermal performance and thus are suggested to be applied in gas turbine blade internal cooling, especially at high velocity or Reynolds number.

Comparison of Staggered and In-Line V-Shaped Dimple Arrays Using S-PIV

2015 ◽  
Author(s):  
Charles P. Brown ◽  
Lesley M. Wright ◽  
Stephen T. McClain
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Thermal Performance ◽  
Rectangular Channel ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Spanwise Direction ◽  
Reduced Pressure ◽  
Line Array

As a result of the reduced pressure loss relative to ribs, recessed dimples have the potential to increase the thermal performance of internal cooling passages. In this experimental investigation, a Stereo-Particle Image Velocimetry (S-PIV) technique is used to characterize the three-dimensional, internal flow field over V-shaped dimple arrays. These flowfield measurements are combined with surface heat transfer measurements to fully characterize the performance of the proposed V-shaped dimples. This study compares the performance of two arrays. Both a staggered array and an in-line array of V-shaped dimples are considered. The layout of these V-shaped dimples is derived from a traditional, staggered hemispherical dimple array. The individual V-shaped dimples follow the same geometry, with depths of δ / D = 0.30. In the case of the in-line pattern, the spacing between the V-shaped dimples is 3.2D in both the streamwise and spanwise directions. For the staggered pattern, a spacing of 3.2D in the spanwise direction and 1.6D in the streamwise direction is examined. Each of these patterns was tested on one wide wall of a 3:1 rectangular channel. The Reynolds numbers examined range from 10000 to 37000. S-PIV results show that as the Reynolds numbers increase, the strength of the secondary flows induced by the in-line array increases, enhancing the heat transfer from the surface, without dramatically increasing the measured pressure drop. As a result of a minimal increase in pressure drop, the overall thermal performance of the channel increases as the Reynolds number increases (up to the maximum Reynolds number of 37000).

Experimental Study on Flow Behavior and Heat Transfer Enhancement with Distinct Dimpled Gas Turbine Blade Internal Cooling Channel

2021 ◽  
pp. 1-28
Author(s):  
Farah Nazifa Nourin ◽  
Ryoichi S. Amano
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Gas Turbine ◽  
Turbine Blade ◽  
Thermal Performance ◽  
Diameter Ratio ◽  
Internal Cooling ◽  
Cooling Channel ◽  
Transfer Enhancement

Abstract The study presents the investigation on heat transfer distribution along a gas turbine blade internal cooling channel. Six different cases were considered in this study, using the smooth surface channel as a baseline. Three different dimples depth-to-diameter ratios with 0.1, 0.25, and 0.50 were considered. Different combinations of partial spherical and leaf dimples were also studied with the Reynolds numbers of 6,000, 20,000, 30,000, 40,000, and 50,000. In addition to the experimental investigation, the numerical study was conducted using Large Eddy Simulation (LES) to validate the data. It was found that the highest depth-to-diameter ratio showed the highest heat transfer rate. However, there is a penalty for increased pressure drop. The highest pressure drop affects the overall thermal performance of the cooling channel. The results showed that the leaf dimpled surface is the best cooling channel based on the highest Reynolds number's heat transfer enhancement and friction factor. However, at the lowest Reynolds number, partial spherical dimples with a 0.25 depth to diameter ratio showed the highest thermal performance.

A Numerical Study of the Thermal Performance of Two Stationary Insert Designs in Internal Compressible Flows

2009 ◽  
Author(s):  
Emad Y. Tanbour ◽  
Ramin K. Rahmani
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Forced Convection ◽  
Thermal Performance ◽  
Compressible Flows ◽  
Convection Heat Transfer ◽  
Convection Heat ◽  
Transfer Enhancement ◽  
Stationary Heat Transfer

Enhancement of the natural and forced convection heat transfer has been the subject of numerous academic and industrial studies. Air blenders, mechanical agitators, and static mixers have been developed to increase the forced convection heat transfer rate in compressible and incompressible flows. Stationary inserts can be efficiently employed as heat transfer enhancement devices in the natural convection systems. Generally, a stationary heat transfer enhancement insert consists of a number of equal motionless segments, placed inside of a pipe in order to control flowing fluid streams. These devices have low maintenance and operating costs, low space requirements and no moving parts. A range of designs exists for a wide range of specific applications. The shape of the elements determines the character of the fluid motion and thus determines thermal effectiveness of the insert. There are several key parameters that may be considered in the design procedure of a heat transfer enhancement insert, which lead to significant differences in the performance of various designs. An ideal insert, for natural conventional heat transfer in compressible flow applications, provides a higher rate of heat transfer and a thermally homogenous fluid with minimized pressure drop and required space. To choose an insert for a given application or in order to design a new insert, besides experimentation, it is possible to use Computational Fluid Dynamics to study the insert performance. This paper presents the outcomes of the numerical studies on industrial stationary heat transfer enhancement inserts and illustrates how a heat transfer enhancement insert can improve the heat transfer in buoyancy driven compressible flows. Using different measuring tools, thermal performance of two different inserts (twisted and helix) are studied. It is shown that the helix design leads to a higher rate of heat transfer, while causes a lower pressure drop in the flowfield, suggesting the insert effectiveness is higher for the helix design, compared to a twisted plate.

A Comparative Study of Performance of Low Reynolds Number Turbulence Models for Various Heat Transfer Enhancement Simulations

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
Ankit Tiwari ◽  
Savas Yavuzkurt
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Nusselt Number ◽  
Heat Transfer Enhancement ◽  
Friction Factor ◽  
Fluid Dynamic ◽  
Low Reynolds Number ◽  
Turbulence Models ◽  
Transfer Enhancement ◽  
Low Reynolds

The goal of this study is to evaluate the computational fluid dynamic (CFD) predictions of friction factor and Nusselt number from six different low Reynolds number k–ε (LRKE) models namely Chang–Hsieh–Chen (CHC), Launder–Sharma (LS), Abid, Lam–Bremhorst (LB), Yang–Shih (YS), and Abe–Kondoh–Nagano (AKN) for various heat transfer enhancement applications. Standard and realizable k–ε (RKE) models with enhanced wall treatment (EWT) were also studied. CFD predictions of Nusselt number, Stanton number, and friction factor were compared with experimental data from literature. Various parameters such as effect of type of mesh element and grid resolution were also studied. It is recommended that a model, which predicts reasonably accurate values for both friction factor and Nusselt number, should be chosen over disparate models, which may predict either of these quantities more accurately. This is based on the performance evaluation criterion developed by Webb and Kim (2006, Principles of Enhanced Heat Transfer, 2nd ed., Taylor and Francis Group, pp. 1–72) for heat transfer enhancement. It was found that all LRKE models failed to predict friction factor and Nusselt number accurately (within 30%) for transverse rectangular ribs, whereas standard and RKE with EWT predicted friction factor and Nusselt number within 25%. Conversely, for transverse grooves, AKN, AKN/CHC, and LS (with modified constants) models accurately predicted (within 30%) both friction factor and Nusselt number for rectangular, circular, and trapezoidal grooves, respectively. In these cases, standard and RKE predictions were inaccurate and inconsistent. For longitudinal fins, Standard/RKE model, AKN, LS and Abid LRKE models gave the friction factor and Nusselt number predictions within 25%, with the AKN model being the most accurate.

scholarly journals Heat Transfer Enhancement from Microprocessor

2020 ◽  
Vol 8 (4S4) ◽  
pp. 174-178
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Thermal Performance ◽  
Hydraulic Diameter ◽  
Constant Speed ◽  
Heat Sinks ◽  
Experimental Investigations ◽  
Transfer Enhancement ◽  
Pass Through

Experiments were conducted to investigate the cooling of processor to increase the thermal performance by employing a mini channel instead of conventional heat sinks. Now a day’s aluminium fin with fans is used for cooling the processor. Constant speed of the fans is found to be not enough to remove the heat generated by the processor. The experimental investigations were carried out in the channels with the hydraulic diameter of about 1.5x10-3m for the Reynolds number varying from 80 to 1150. The water is allowed to pass through the channel by virtue of which heat is rejected from the processor. The influence of Reynolds number on heat transfer enhancement from the microprocessor is discussed in details. Comparison between heat transfer by air and by water is presented. From the experiment it is disclosed that further increase in heat transfer was observed when compared to air.

Heat Transfer Enhancement in Square Ducts With V-Shaped Ribs of Various Angles

2002 ◽  
Author(s):  
Rongguang Jia ◽  
Arash Saidi ◽  
Bengt Sunde´n
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Experimental Studies ◽  
Eddy Diffusivity ◽  
Heat Fluxes ◽  
Secondary Flows ◽  
Turbulent Heat ◽  
Transfer Enhancement ◽  
Transfer Coefficients

Experimental studies have revealed that both downstream and upstream pointing V-shaped ribs result in better heat transfer enhancement than transverse straight ribs of the same geometry. Secondary flows induced by the angled ribs are believed to be responsible for this higher heat transfer enhancement. Further investigations are needed to understand this. In the present study, the heat and fluid flow in V-shaped-ribbed ducts is numerically simulated by a multi-block 3D solver, which is based on solving the Navier-Stokes and energy equations in conjunction with a low-Reynolds number k-ε turbulence model. The Reynolds turbulent stresses are computed with an explicit algebraic stress model (EASM), while turbulent heat fluxes are calculated with a simple eddy diffusivity model (SED). Firstly, the simulation results of transverse straight ribs are validated against the experimental data, for both velocity and heat transfer coefficients. Then, the results of different rib angles (45° and 90°) and Reynolds number (15,000–30,000) are compared to determine the goodness of different rib orientations. Detailed velocity and thermal field results have been used to explain the effects of the inclined ribs and the mechanisms of heat transfer enhancement.

Regional Heat Transfer and Pressure Drop in Two-Pass and Three-Pass Flow Passages With 180-Degree Sharp Turns

1989 ◽  
Author(s):  
M. K. Chyu
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Pressure Loss ◽  
Secondary Flows ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Pressure Loss Coefficient ◽  
Single Turn

The heat transfer distributions for flow passing through a two-pass (one-turn) and a three-pass (two-turn) passages with 180-degree sharp turns are studied by using the analogous naphthalene mass transfer technique. Both passages have square cross-section and length-to-height ratio of 8. The passage surface, including top wall, side walls and partition walls, is divided into 26 segments for the two-pass passage and 40 segments for the three-pass passage. Mass transfer results are presented for each segment along with regional and overall averages. The very non-uniform mass transfer coefficients measured around a sharp 180-degree turn exhibit the effects of flow separation, reattachment and impingement, in addition to secondary flows. Results of the three-pass passage indicate that heat transfer characteristics around the second turn is virtually the same as that around the first turn. This may imply that, in a multiple-pass passage, heat transfer at the first turn has already reached the thermally developed (periodic) condition. Over the entire two-pass passage, the heat transfer enhancement induced by the single-turn is about 45% to 65% of the fully developed values in a straight channel. Such a heat transfer enhancement decreases with an increase in Reynolds number. In addition, overall heat transfer of the three-pass passage is approximately 15% higher than that of the two-pass one. This 15% increase appears to be Reynolds number independent. The pressure loss induced by the sharp turns is found to be very significant. Within the present testing range, the pressure loss coefficient for both passages varies significantly with the Reynolds number.

Experimental Investigations on Heat Transfer Enhancement in a Horizontal Tube Using Converging and Diverging Conical Strip Inserts

2014 ◽  
Vol 592-594 ◽  
pp. 1590-1595 ◽  
Author(s):  
Naga Sarada Somanchi ◽  
Sri Rama R. Devi ◽  
Ravi Gugulothu
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Pressure Drop ◽  
Turbulent Flow ◽  
Heat Transfer Enhancement ◽  
Friction Factor ◽  
Working Fluid ◽  
Experimental Investigations ◽  
Transfer Enhancement ◽  
Enhancement Of Heat Transfer

The present work deals with the results of the experimental investigations carried out on augmentation of turbulent flow heat transfer in a horizontal circular tube by means of tube inserts, with air as working fluid. Experiments were carried out initially for the plain tube (without tube inserts). The Nusselt number and friction factor obtained experimentally were validated against those obtained from theoretical correlations. Secondly experimental investigations using three kinds of tube inserts namely Rectangular bar with diverging conical strips, Rectangular bar with converging conical strips, Rectangular bar with alternate converging diverging conical strips were carried out to estimate the enhancement of heat transfer rate for air in the presence of inserts. The Reynolds number ranged from 8000 to 19000. In the presence of inserts, Nusselt number and pressure drop increased, overall enhancement ratio is calculated to determine the optimum geometry of the tube insert. Based on experimental investigations, it is observed that, the enhancement of heat transfer using Rectangular bar with converging and diverging conical strips is more effective compared to other inserts. Key words: Heat transfer, enhancement, turbulent flow, conical strip inserts, friction factor, pressure drop.

Sign in / Sign up

Export Citation Format

Share Document