scholarly journals Vortex heat transfer enhancement by energy-efficient structured plates with zigzag grooves for micro- and macro-scale energy and electronic devices

2022 ◽  
Vol 2150 (1) ◽  
pp. 012004
Author(s):  
S A Isaev ◽  
A I Leontiev ◽  
D V Nikushchenko ◽  
D Kong ◽  
K M Chung ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Energy Efficient ◽  
Flat Surface ◽  
Electronic Devices ◽  
Cross Flow ◽  
Separation Flow ◽  
Transfer Enhancement ◽  
Flow And Heat Transfer ◽  
Macro Scale ◽  
Wall Flow

Abstract An energy-efficient flat surface is formed when applying single-row cross-flow zigzag grooves (VVVVVV) in a dense arrangement. Convective heat transfer is considered in turbulent flow around a longitudinal fragment of a plate with a length of 40 and a width of 4 with a package of 14 singlerow inclined backslash(\)-shaped grooves with symmetry conditions at the lateral boundaries. The width of the grooves is 1, the depth is 0.25, the edge rounding radius is 0.2, the angles of inclination are 30°, 45°, 50° and 60°, the pitch is 2.4, the Reynolds number is 104, and the thickness of the incoming boundary layer is 0.175. The phenomenon of anomalous enhancement of the separation flow and heat transfer in zigzag grooves and acceleration of the wall flow discovered in inclined oval-trench dimples has been confirmed.

Fluid Flow and Heat Transfer Features at a Cross-Flow of Dimpled Tubes in a Confined Space

2003 ◽  
Author(s):  
G. V. Kovalenko ◽  
A. A. Khalatov
Keyword(s):  
Heat Transfer ◽  
Reverse Flow ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
Smooth Tube ◽  
Confined Space ◽  
Transfer Enhancement ◽  
Flow And Heat Transfer ◽  
Heat Exchange Surface ◽  
Exchange Surface

This paper provides the primary results of an experimental study into the fluid flow and heat transfer features at a cross-flow of a dimpled tube in a rectangular-shaped duct between two adjacent dimpled tubes. The cylindrical dimples were engraved on each tube surface both in the staggered and in-line mode; altogether nine dimpled tubes were tested in the range of the Reynolds number Re from 8,000 to 115,000. The first group (four samples) represents tubes structured with symmetrical dimples drilled in the radial direction, while the second group (five samples) is tubes with asymmetrical dimples. In the latter case each dimple was made in such a way that its axis is parallel to the tube diameter with a certain clearance between axes. For comparisons a row of smooth tubes of the same configuration was tested under identical fluid boundary conditions. Three factors primarily influencing heat transfer are under consideration in this paper: a) increase in a heat exchange surface due to a tube dimpling, b) variations in the flow pattern, c) interaction between boundary layer and main flow. Behind a smooth tube in confined space the reverse flow zone grows initially to Re = 37,000 however decreases at larger Reynolds numbers. Unlike this, behind a dimpled tube in confined space the reverse flow zone reduces at low Reynolds numbers to reach minimum magnitude at Re = 10,000–28,000, and increases afterwards to become approximately constant at Reynolds numbers over 45,000. It has been found, the reverse flow length depends on the Reynolds number, dimple parameters and configuration. The frequency spectrum of the dimpled tube is different from that occurring for a smooth tube. A few frequency ‘picks’ with corresponding the Strouhal numbers were registered including those typical to a single dimple on a flat plate. The heat transfer enhancement rates of around 45%–55% compared with a smooth tube in confined space were obtained depending on dimple parameters and flow regimes. Increase in the heat transfer enhancement rate for tubes with shallow dimples exceeds growth of heat exchange surface due to a dimpling. Increases in a pressure drop at the tube bundle caused by dimpling do not exceed 14%.

Effects of alternating elliptical chamber on jet impingement heat transfer in vane leading edge under different cross-flow conditions

2021 ◽  
pp. 1-17
Author(s):  
K. Xiao ◽  
J. He ◽  
Z. Feng
Keyword(s):  
Heat Transfer ◽  
Velocity Ratio ◽  
Cross Flow ◽  
Leading Edge ◽  
Longitudinal Vortices ◽  
Impingement Jet ◽  
Flow And Heat Transfer ◽  
Impingement Heat Transfer ◽  
Cross Flow Velocity ◽  
The Cross

ABSTRACT This paper proposes an alternating elliptical impingement chamber in the leading edge of a gas turbine to restrain the cross flow and enhance the heat transfer, and investigates the detailed flow and heat transfer characteristics. The chamber consists of straight sections and transition sections. Numerical simulations are performed by solving the three-dimensional (3D) steady Reynolds-Averaged Navier–Stokes (RANS) equations with the Shear Stress Transport (SST) k– $\omega$ turbulence model. The influences of alternating the cross section on the impingement flow and heat transfer of the chamber are studied by comparison with a smooth semi-elliptical impingement chamber at a cross-flow Velocity Ratio (VR) of 0.2 and Temperature Ratio (TR) of 1.00 in the primary study. Then, the effects of the cross-flow VR and TR are further investigated. The results reveal that, in the semi-elliptical impingement chamber, the impingement jet is deflected by the cross flow and the heat transfer performance is degraded. However, in the alternating elliptical chamber, the cross flow is transformed to a pair of longitudinal vortices, and the flow direction at the centre of the cross section is parallel to the impingement jet, thus improving the jet penetration ability and enhancing the impingement heat transfer. In addition, the heat transfer in the semi-elliptical chamber degrades rapidly away from the stagnation region, while the longitudinal vortices enhance the heat transfer further, making the heat transfer coefficient distribution more uniform. The Nusselt number decreases with increase of VR and TR for both the semi-elliptical chamber and the alternating elliptical chamber. The alternating elliptical chamber enhances the heat transfer and moves the stagnation point up for all VR and TR, and the heat transfer enhancement is more obvious at high cross-flow velocity ratio.

A Numerical Study of Heat Transfer and Flow Structure in Channels With Miniature V Rib-Dimple Hybrid Structure on One Wall

2018 ◽  
Author(s):  
Peng Zhang ◽  
Yu Rao ◽  
Yanlin Li
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Numerical Simulations ◽  
Numerical Study ◽  
Reynolds Numbers ◽  
Hybrid Structure ◽  
Transfer Enhancement ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer ◽  
Flow Mixing

This paper presents a numerical study on turbulent flow and heat transfer in the channels with a novel hybrid cooling structure with miniature V-shaped ribs and dimples on one wall. The heat transfer characteristics, pressure loss and turbulent flow structures in the channels with the rib-dimples with three different rib heights of 0.6 mm, 1.0 mm and 1.5 mm are obtained for the Reynolds numbers ranging from 18,700 to 60,000 by numerical simulations, which are also compared with counterpart of a pure dimpled and pure V ribbed channel. The results show that the overall Nusselt numbers of the V rib-dimple channel with the rib height of 1.5 mm is up to 70% higher than that of the channels with pure dimples. The numerical simulations show that the arrangement of the miniature V rib upstream each dimple induces complex secondary flow near the wall and generates downwashing vortices, which intensifies the flow mixing and turbulent kinetic energy in the dimple, resulting in significant improvement in heat transfer enhancement and uniformness.

scholarly journals Two-Phase Flow and Heat Transfer Enhancement

2013 ◽  
Vol 5 ◽  
pp. 256839
Author(s):  
Somchai Wongwises ◽  
Afshin J. Ghajar ◽  
Kwok-wing Chau ◽  
Octavio García Valladares ◽  
Balaram Kundu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Two Phase Flow ◽  
Phase Flow ◽  
Transfer Enhancement ◽  
Two Phase ◽  
Flow And Heat Transfer

Investigations on the Heat Transfer and Flow Characteristics in a Trapezoid Duct for Turbine Blade Leading Edge

2018 ◽  
Author(s):  
Hai-yong Liu ◽  
Cun-liang Liu ◽  
Lin Ye
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Cross Flow ◽  
Side Wall ◽  
Swirl Flow ◽  
Transfer Enhancement ◽  
Impingement Cooling ◽  
Exit Side ◽  
Target Wall ◽  
The Cross

To evaluate the application of the impingement cooling in a trapezoidal duct, particularly the influence on internal cooling of the cross flow and swirl flow. Experimental and numerical studies have been performed. The experiment focuses on the heat transfer characteristics in the duct, when the numerical simulation focuses on the flow characteristics. Four Reynolds numbers (10000, 20000, 30000 and 40000), six cross flow mass flow ratios (0, 0.1, 0.2, 0.3, 0.4 and 0.5) and two impingement angle (35° and 45°) are considered in both the experiment and the numerical simulation. The temperature on the target wall and the exit side wall is measured by the thermocouples, when the realizable k-ε turbulence model and enhanced wall treatment are performed using a commercial code Fluent. The results show that only part of the jets contribute in the heat transfer enhancement on the target wall, the other jets improve a large anticlockwise vortex occupied the upper part of the duct and drive strong swirl flow. The heat transfer on the exit side wall is enhanced by the swirl flow. The cross flow is induced in the duct by the outflow of the end exit hole. It deflects the jets and abates the impingement cooling on the target wall in the downstream region but has no evidently effect on the heat transfer on the exit side wall. Higher impingement angle helps to augment the impingement cooling on the target wall and improves the resistance ability of the jets against the effect of the cross flow. The heat transfer enhancement ability on the target wall and exit side wall in the present duct is compared to that of a smooth duct. The Nusselt number of the former is about 3 times higher than that of the latter. It indicates that the impingement and swirl play equally important roles in the heat transfer enhancement in the present duct. Empirical dimensionless correlations based on the present experiment data are presented in the paper.

Effects of Guide Vanes on the Tip Heat Transfer Enhancement of a Turbine Blade

2011 ◽  
Author(s):  
Gongnan Xie ◽  
Bengt Sunde´n
Keyword(s):  
Heat Transfer ◽  
Fluid Flow ◽  
Heat Transfer Enhancement ◽  
Turbine Blade ◽  
Pressure Loss ◽  
Transfer Enhancement ◽  
Guide Vanes ◽  
Flow And Heat Transfer ◽  
Numerical Predictions ◽  
Blade Tip

Gas turbine blade tips encounter large heat load as they are exposed to the high temperature gas. A common way to cool the blade and its tip is to design serpentine passages with 180-deg turns under the blade tip-cap inside the turbine blade. Improved internal convective cooling is therefore required to increase the blade tip life time. This paper presents numerical predictions of turbulent fluid flow and heat transfer through two-pass channels with and without guide vanes placed in the turn regions using RANS turbulence modeling. The effects of adding guide vanes on the tip-wall heat transfer enhancement and the channel pressure loss were analyzed. The guide vanes have a height identical to that of the channel. The inlet Reynolds numbers are ranging from 100,000 to 600,000. The detailed three-dimensional fluid flow and heat transfer over the tip-walls are presented. The overall performances of several two-pass channels are also evaluated and compared. It is found that the tip heat transfer coefficients of the channels with guide vanes are 10∼60% higher than that of a channel without guide vanes, while the pressure loss might be reduced when the guide vanes are properly designed and located, otherwise the pressure loss is expected to be increased severely. It is suggested that the usage of proper guide vanes is a suitable way to augment the blade tip heat transfer and improve the flow structure, but is not the most effective way compared to the augmentation by surface modifications imposed on the tip-wall directly.

scholarly journals Convective Heat Transfer of Ethanol/Polyalphaolefin Nanoemulsion in Mini- and Microchannel Heat Exchangers for High Heat Flux Electronics Cooling

2021 ◽  
Author(s):  
Jaime Rios ◽  
Mehdi Kabirnajafi ◽  
Takele Gameda ◽  
Raid Mohammed ◽  
Jiajun Xu
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Convective Heat ◽  
Phase Flow ◽  
Transfer Performance ◽  
Transfer Enhancement ◽  
Heat Transfer Characteristics ◽  
Two Phase ◽  
Flow And Heat Transfer

The present study experimentally and numerically investigates the flow and heat transfer characteristics of a novel nanostructured heat transfer fluid, namely, ethanol/polyalphaolefin nanoemulsion, inside a conventionally manufactured minichannel of circular cross section and a microchannel heat exchanger of rectangular cross section manufactured additively using the Direct Metal Laser Sintering (DMLS) process. The experiments were conducted for single-phase flow of pure polyalphaolefin (PAO) and ethanol/PAO nanoemulsion fluids with two ethanol concentrations of 4 wt% and 8 wt% as well as for two-phase flow boiling of nanoemulsion fluids to study the effect of ethanol nanodroplets on the convective flow and heat transfer characteristics. Furthermore, the effects of flow regime of the working fluids on the heat transfer performance for both the minichannel and microchannel heat exchangers were examined within the laminar and transitional flow regimes. It was found that the ethanol/PAO nanoemulsion fluids can improve convective heat transfer compared to that of the pure PAO base fluid under both single- and two-phase flow regimes. While the concentration of nanoemulsion fluids did not reflect a remarkable distinction in single-phase heat transfer performance within the laminar regime, a significant heat transfer enhancement was observed using the nanoemulsion fluids upon entering the transitional flow regime. The heat transfer enhancement at higher concentrations of nanoemulsion within the transitional regime is mainly attributed to the enhanced interaction and interfacial thermal transport between ethanol nanodroplets and PAO base fluid. For two-phase flow boiling, heat transfer coefficients of ethanol/PAO nanoemulsion fluids were further enhanced when the ethanol nanodroplets underwent phase change. A comparative study on the flow and heat transfer characteristics was also implemented between the traditionally fabricated minichannel and additively manufactured microchannel of similar dimensions using the same working fluid of pure PAO and the same operating conditions. The results revealed that although the DMLS fabricated microchannel posed a higher pressure loss, a substantial heat transfer enhancement was achieved as compared to the minichannel heat exchanger tested under the same conditions. The non-post processed surface of the DMLS manufactured microchannel is likely to be the main contributor to the augmented heat transfer performance. Further studies are required to fully appreciate the possible mechanisms behind this phenomenon as well as the convective heat transfer properties of nanoemulsion fluids.

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