A numerical investigation of dimple effects on internal heat transfer enhancement of a double wall cooling structure with jet impingement

2016 ◽  
Vol 26 (7) ◽  
pp. 2175-2197 ◽  
Author(s):  
Lei Luo ◽  
Chenglong Wang ◽  
Lei Wang ◽  
Bengt Ake Sunden ◽  
Sangtao Wang
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Friction Factor ◽  
Flow Behavior ◽  
Target Surface ◽  
Surface Heat ◽  
Transfer Enhancement ◽  
Content Type ◽  
Surface Heat Transfer ◽  
Double Wall

Purpose The dimple is adopted into a double wall cooling structure which is widely used in hot gas components to increase the heat transfer effects with relatively low pressure drop penalty. The purpose of this paper is to study the effect of dimple depth and dimple diameter on the target surface heat transfer and the inlet to outlet friction factor. Design/methodology/approach The study is carried out by using the numerical simulations. The impingement flow is directly impinging on the dimple and released from the film holes after passing the double wall chamber. The ratio between dimple depth and dimple diameter is varied from 0 to 0.4 and the ratio between dimple diameter and impingement hole diameter is ranging from 0.5 to 3. The Reynolds number is between 10,000 and 70,000. Results of the target surface Nusselt number, friction factor and flow structures are included. For convenience of comparison, the double wall cooling structure without the dimple is considered as the baseline. Findings It is found that the dimple can effectively enhance the target surface heat transfer due to thinning of the flow boundary layer and flow reattachment as well as flow recirculation outside the dimple near the dimple rim especially for the large Re number condition. However, the stagnation point heat transfer is reduced. It is also found that for a large dimple depth or large dimple diameter, a salient heat transfer reduction occurs for the toroidal vortex. The thermal performance indicates that the intensity of the heat transfer enhancement depends upon the dimple depth and dimple diameter Originality/value This is the first time to adopt a dimple into a double wall cooling structure. It suggests that the target surface heat transfer in a double wall cooling structure can be increased by the use of the dimple. However, the heat transfer characteristic is sensitive for the different dimple diameter and dimple depth which may result in a different flow behavior

Full Surface Heat Transfer Measurement of a Turbine Internal Cooling System Using a Large Scaled Model

2018 ◽  
Author(s):  
Nojin Park ◽  
Changmin Son ◽  
Jangsik Yang ◽  
Changyong Lee ◽  
Kidon Lee
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Pressure Loss ◽  
Cooling System ◽  
Surface Heat ◽  
Internal Cooling ◽  
Transfer Enhancement ◽  
Scaled Model ◽  
Surface Heat Transfer

A series of experiments were conducted to investigate the detailed heat transfer characteristics of a large scaled model of a turbine blade internal cooling system. The cooling system has one passage in the leading edge and a triple passage for the remained region with two U-bends. A large scaled model (2 times) is designed to acquire high resolution measurement. The similarity of the test model was conducted with Reynolds number at the inlet of the internal cooling system. The model is designed to simulate the flow at engine condition including film extractions to match the changes in flowrates through the internal cooling system. Also, 45 deg ribs were installed for heat transfer enhancement. The experiments were performed varying Reynolds number in the range of 20,000 to 100,000 with and without ribs under stationary condition. This study employs transient heat transfer technique using thermochromic liquid crystal (TLC) to obtain full surface heat transfer distributions. The results show the detailed heat transfer distributions and pressure loss. The characteristics of pressure loss is largely dependent on the changes in cross-sectional area along the passages, the presence of U-bends and the extraction of coolant flow through film holes. The local and area averaged Nusselt number were compared to available correlations. Finally, the thermal performance counting the heat transfer enhancement as well as pressure penalty is presented.

scholarly journals Heat Transfer Enhancement for Finned-Tube Heat Exchangers With Winglets

2000 ◽  
Author(s):  
James E. O’Brien ◽  
Manohar S. Sohal
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Circular Tube ◽  
Reynolds Numbers ◽  
Surface Heat ◽  
Operating Conditions ◽  
Transfer Enhancement ◽  
Height Ratio ◽  
Surface Heat Transfer ◽  
Delta Winglet

Abstract This paper presents the results of an experimental study of forced convection heat transfer in a narrow rectangular duct fitted with a circular tube and/or a delta-winglet pair. The duct was designed to simulate a single passage in a fin-tube heat exchanger. Heat transfer measurements were obtained using a transient technique in which a heated airflow is suddenly introduced to the test section. High-resolution local fin-surface temperature distributions were obtained at several times after initiation of the transient using an imaging infrared camera. Corresponding local fin-surface heat transfer coefficient distributions were then calculated from a locally applied one-dimensional semi-infinite inverse heat conduction model. Heat transfer results were obtained over an airflow rate ranging from 1.51 × 10−3 to 14.0 × 10−3 kg/s. These flow rates correspond to a duct-height Reynolds number range of 670–6300 with a duct height of 1.106 cm and a duct width-to-height ratio, W/H, of 11.25. The test cylinder was sized such that the diameter-to-duct height ratio, D/H is 5. Results presented in this paper reveal visual and quantitative details of local fin-surface heat transfer distributions in the vicinity of a circular tube, a delta-winglet pair, and a combination of a circular tube and a delta-winglet pair. Comparisons of local and average heat transfer distributions for the circular tube with and without winglets are provided. Overall mean fin-surface Nusselt-number results indicate a significant level of heat transfer enhancement associated with the deployment of the winglets with the circular cylinder. At the lowest Reynolds numbers (which correspond to the laminar operating conditions of existing geothermal aircooled condensers), the enhancement level is nearly a factor of two. At higher Reynolds numbers, the enhancement level is close to 50%.

scholarly journals Heat Transfer Enhancement for Finned-Tube Heat Exchangers With Winglets

2005 ◽  
Vol 127 (2) ◽  
pp. 171-178 ◽  
Author(s):  
James E. O’Brien ◽  
Manohar S. Sohal
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Circular Tube ◽  
Reynolds Numbers ◽  
Surface Heat ◽  
Operating Conditions ◽  
Transfer Enhancement ◽  
Height Ratio ◽  
Surface Heat Transfer ◽  
Delta Winglet

This paper presents the results of an experimental study of forced convection heat transfer in a narrow rectangular duct fitted with a circular tube and/or a delta-winglet pair. The duct was designed to simulate a single passage in a fin-tube heat exchanger. Heat transfer measurements were obtained using a transient technique in which a heated airflow is suddenly introduced to the test section. High-resolution local fin-surface temperature distributions were obtained at several times after initiation of the transient using an imaging infrared camera. Corresponding local fin-surface heat transfer coefficient distributions were then calculated from a locally applied one-dimensional semi-infinite inverse heat conduction model. Heat transfer results were obtained over an airflow rate ranging from 1.51×10−3 to 14.0×10−3kg/s. These flow rates correspond to a duct-height Reynolds number range of 670–6300 with a duct height of 1.106 cm and a duct width-to-height ratio, W/H, of 11.25. The test cylinder was sized such that the diameter-to-duct height ratio, D/H is 5. Results presented in this paper reveal visual and quantitative details of local fin-surface heat transfer distributions in the vicinity of a circular tube, a delta-winglet pair, and a combination of a circular tube and a delta-winglet pair. Comparisons of local and average heat transfer distributions for the circular tube with and without winglets are provided. Overall mean fin-surface Nusselt-number results indicate a significant level of heat transfer enhancement associated with the deployment of the winglets with the circular cylinder. At the lowest Reynolds numbers (which correspond to the laminar operating conditions of existing geothermal air-cooled condensers), the enhancement level is nearly a factor of 2. At higher Reynolds numbers, the enhancement level is close to 50%.

Numerical Study on the Heat Transfer Characteristics of Supercritical Water in Enhanced Sub-Channels in Reactors

2010 ◽  
Vol 156-157 ◽  
pp. 426-431
Author(s):  
Wei Shu Wang ◽  
Hong Sheng Zhang ◽  
Qin Cheng Bi ◽  
Jun Liu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Supercritical Water ◽  
Surface Heat ◽  
Inlet Temperature ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Surface Heat Transfer ◽  
Heat Transfer Coefficients ◽  
Equal Distance

The characteristics of heat transfer enhancement and deterioration in supercritical water reactor core is essential to the reactor efficiency and security. At present, there exists deficiency in the study of core enhanced channels. Two different fins arrangements of the enhanced channels are designed in present paper, which are long-strip fins and equal-distance short fins. At the conditions of the supercritical pressure of 25MPa, the inlet temperature of 350°C and different inlet velocities, the heat transfer enhancement and deterioration characteristics of water flowing in the two different fins arrangements of the enhanced channels were studied and comparatively analyzed. The results show that the heat transfer is enhanced in the channels with fins. The heat transfer enhancement is better in the channel with equal-distance short fins when lower input velocity, better in the channel with long-strip fins when high input velocity. The surface heat transfer coefficients increase with the velocity increases; the surface heat transfer coefficients in equal-distance short fins is two to three times than that in the channel without fins. There exists heat transfer deterioration when the input velocity is lower in the channel without fins and with long-strip fins, no deterioration occurs in the channel with equal-distance short fins. The channel with equal-distance short fins is a relatively reasonable of the three channels.

Non-similar solutions for mixed convection along a wedge embedded in a porous medium saturated by a non-Newtonian nanofluid

2014 ◽  
Vol 24 (7) ◽  
pp. 1471-1486 ◽  
Author(s):  
Ali J. Chamkha ◽  
M. Rashad ◽  
Rama Subba Reddy Gorla
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Friction Factor ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Mass Transfer Rate ◽  
Surface Heat ◽  
Content Type ◽  
Transfer Rates ◽  
Surface Heat Transfer

Purpose – The purpose of this paper is to present a boundary layer analysis for the mixed convection past a vertical wedge in a porous medium saturated with a power law type non-Newtonian nanofluid. Numerical results for friction factor, surface heat transfer rate and mass transfer rate have been presented for parametric variations of the buoyancy ratio parameter Nr, Brownian motion parameter Nb, thermophoresis parameter Nt, Lewis number Le and the power law exponent n. The dependency of the friction factor, surface heat transfer rate (Nusselt number) and mass transfer rate on these parameters has been discussed. Design/methodology/approach – This general non-linear problem cannot be solved in closed form and, therefore, a numerical solution is necessary to describe the physics of the problem. An implicit, tri-diagonal finite-difference method has proven to be adequate and sufficiently accurate for the solution of this kind of problems. Therefore, it is adopted in the present study. Variable step sizes were used. The convergence criterion employed in this study is based on the difference between the current and the previous iterations. When this difference reached 10−5 for all the points in the η directions, the solution was assumed to be converged, and the iteration process was terminated. Findings – The results indicate that as the buoyancy ratio parameter (Nr) and thermophoresis parameter (Nt) increase, the friction factor increases whereas the heat transfer rate (Nusselt number) and mass transfer rate (Sherwood number) decrease. As the Brownian motion parameter (Nb) increases, the friction factor and surface mass transfer rates increase whereas the surface heat transfer rate decreases. As Le increases, mass transfer rates increase. As the power law exponent n increases, the heat and mass transfer rates increase. Research limitations/implications – The analysis is valid for natural convection dominated regime. The combined forced and natural convection dominated regimes will be reported in a future work. Practical implications – The approach used is useful in optimizing the porous media heat transfer problems in geothermal energy recovery, crude oil extraction, ground water pollution, thermal energy storage and flow through filtering media. Originality/value – The results of the study may be of some interest to the researchers of the field of porous media heat transfer. Porous foam and microchannel heat sinks used for electronic cooling are optimized utilizing the porous medium. The utilization of nanofluids for cooling of microchannel heat sinks requires understanding of fundamentals of nanofluid convection in porous media.

Heat transfer and friction factor in a dimple-pin fin wedge duct with various dimple depth and converging angle

2016 ◽  
Vol 26 (6) ◽  
pp. 1954-1974 ◽  
Author(s):  
Lei Luo ◽  
Chenglong Wang ◽  
Lei Wang ◽  
Bengt Ake Sunden ◽  
Songtao Wang
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Friction Factor ◽  
Leading Edge ◽  
Relative Depth ◽  
Transfer Enhancement ◽  
Content Type ◽  
Pin Fin ◽  
High Heat Transfer ◽  
Converging Angle

Purpose – The dimple is adopted into a pin fin wedge duct which is widely used in modern gas turbine vane cooling structure trailing edge region. The purpose of this paper is to study the effects of dimple depth and duct converging angle on the endwall heat transfer and friction factor in this pin fin wedge duct. Design/methodology/approach – The study is carried out by using the numerical simulations. The diameter of dimples is the same as the pin fin diameter with an inline manner arrangement in relation to the pin fin. The ratio between dimple depth and dimple diameter is varied from 0 to 0.3 and the converging angle is ranging from 0° to 12.7°. The Reynolds number is between 10,000 and 50,000. Results of the endwall Nusselt number, friction factor, and flow structures are included. For convenience of comparison, the pin fin wedge duct with a converging angle of 12.7° without dimples is considered as the baseline. Findings – It is found that the dimples can effectively enhance the endwall heat transfer due to the impingement on the dimple surface, reattachment downstream the dimple and recirculation in front of the pin fin leading edge. By increasing the converging angle, the heat transfer is also increased but with a large friction factor penalty. In addition, the heat transfer enhancement for deep depth cases is 1.57 times higher than that of the low depth case. The thermal performance indicates that the intensity of heat transfer enhancement depends upon the dimple depth and converging angle. Originality/value – It suggests that the endwall heat transfer in a pin fin wedge duct can be increase by the adoption of dimples. The optimal dimple relative depth is 0.2 with low friction factor and high heat transfer performance.

Multi-objective optimization of the dimple/protrusion channel with pin fins for heat transfer enhancement

2019 ◽  
Vol 29 (2) ◽  
pp. 790-813 ◽  
Author(s):  
Lei Luo ◽  
Wei Du ◽  
Songtao Wang ◽  
Weilong Wu ◽  
Xinghong Zhang
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Heat Transfer Enhancement ◽  
Friction Factor ◽  
Dissipative Function ◽  
Transfer Enhancement ◽  
Nsga Ii ◽  
Content Type ◽  
Pin Fin ◽  
Geometry Model

PurposeThe purpose of this paper is to investigate the optimal geometry parameters in a dimple/protrusion-pin finned channel with high thermal performance.Design/methodology/approachThe BSL turbulence model is used to calculate the flow structure and heat transfer in a dimple/protrusion-pin finned channel. The optimization algorithm is set as Non-dominated Sorting Genetic Algorithm II (NSGA-II). The high Nusselt number and low friction factor are chosen as the optimization objectives. The pin fin diameter, dimple/protrusion diameter, dimple/protrusion location and dimple/protrusion depth are applied as the optimization variables. An in-house code is used to generate the geometry model and mesh. The commercial software Isight is used to perform the optimization process.FindingsThe results show that the Nusselt number and friction factor are sensitive to the geometry parameters. In a pin finned channel with a dimple, the Nusselt number is high at the rear part of the dimple, while it is low at the upstream of the dimple. A high dissipative function is found near the pin fin. In the protrusion channel, the Nusselt number is high at the leading edge of the protrusion. In addition, the protrusion induces a high pressure drop compared to the dimpled channel.Originality/valueThe originality of this paper is to optimize the geometry parameters in a pin finned channel with dimple/protrusion. This is good application for the heat transfer enhancement at the trailing side for the gas turbine.

Heat transfer enhancement in microchannels using ribs and secondary flows

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Karthikeyan Paramanandam ◽  
Venkatachalapathy S. ◽  
Balamurugan Srinivasan
Keyword(s):  
Heat Transfer ◽  
Temperature Distribution ◽  
Heat Transfer Enhancement ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Secondary Flows ◽  
Transfer Enhancement ◽  
Heat Transfer Characteristics ◽  
Content Type ◽  
Flow And Heat Transfer

Purpose The purpose of this paper is to study the flow and heat transfer characteristics of microchannel heatsinks with ribs, cavities and secondary channels. The influence of length and width of the ribs on heat transfer enhancement, secondary flows, flow distribution and temperature distribution are examined at different Reynolds numbers. The effectiveness of each heatsink is evaluated using the performance factor. Design/methodology/approach A three-dimensional solid-fluid conjugate heat transfer numerical model is used to study the flow and heat transfer characteristics in microchannels. One symmetrical channel is adopted for the simulation to reduce the computational cost and time. Flow inside the channels is assumed to be single-phase and laminar. The governing equations are solved using finite volume method. Findings The numerical results are analyzed in terms of average Nusselt number ratio, average base temperature, friction factor ratio, pressure variation inside the channel, temperature distribution, velocity distribution inside the channel, mass flow rate distribution inside the secondary channels and performance factor of each microchannels. Results indicate that impact of rib width is higher in enhancing the heat transfer when compared with its length but with a penalty on the pressure drop. The combined effects of secondary channels, ribs and cavities helps to lower the temperature of the microchannel heat sink and enhances the heat transfer rate. Practical implications The fabrication of microchannels are complex, but recent advancements in the additive manufacturing techniques makes the fabrication of the design considered in this numerical study feasible. Originality/value The proposed microchannel heatsink can be used in practical applications to reduce the thermal resistance, and it augments the heat transfer rate when compared with the baseline design.

Convective heat transfer enhancement: effect of multi-frequency heating

2019 ◽  
Vol 29 (10) ◽  
pp. 3822-3856 ◽  
Author(s):  
Nirmal Kumar Manna ◽  
Nirmalendu Biswas ◽  
Pallab Sinha Mahapatra
Keyword(s):  
Heat Transfer ◽  
Natural Convection ◽  
Heat Transfer Enhancement ◽  
Convection Heat Transfer ◽  
Enhancement Effect ◽  
Natural Convection Heat Transfer ◽  
Convection Heat ◽  
Transfer Enhancement ◽  
Content Type ◽  
Frequency Heating

Purpose This study aims to enhance natural convection heat transfer for a porous thermal cavity. Multi-frequency sinusoidal heating is applied at the bottom of a porous square cavity, considering top wall adiabatic and cooling through the sidewalls. The different frequencies, amplitudes and phase angles of sinusoidal heating are investigated to understand their major impacts on the heat transfer characteristics. Design/methodology/approach The finite volume method is used to solve the governing equations in a two-dimensional cavity, considering incompressible laminar flow, Boussinesq approximation and Brinkman–Forchheimer–Darcy model. The mean-temperature constraint is applied for enhancement analysis. Findings The multi-frequency heating can markedly enhance natural convection heat transfer even in the presence of porous medium (enhancement up to ∼74 per cent). Only the positive phase angle offers heat transfer enhancement consistently in all frequencies (studied). Research limitations/implications The present research idea can usefully be extended to other multi-physical areas (nanofluids, magneto-hydrodynamics, etc.). Practical implications The findings are useful for devices working on natural convection. Originality/value The enhancement using multi-frequency heating is estimated under different parametric conditions. The effect of different frequencies of sinusoidal heating, along with the uniform heating, is collectively discussed from the fundamental point of view using the average and local Nusselt number, thermal and hydrodynamic boundary layers and heatlines.

Sign in / Sign up

Export Citation Format

Share Document