Experiments on heat transfer enhancement from a heated square cylinder in a pulsating channel flow

2008 ◽  
Vol 51 (5-6) ◽  
pp. 1130-1138 ◽  
Author(s):  
Tae Ho Ji ◽  
Seo Young Kim ◽  
Jae Min Hyun
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Channel Flow ◽  
Square Cylinder ◽  
Transfer Enhancement

Heat Transfer Enhancement in Channel Flow Using an Inclined Square Cylinder

2009 ◽  
Vol 131 (7) ◽  
Author(s):  
Dong-Hyeog Yoon ◽  
Kyung-Soo Yang ◽  
Choon-Bum Choi
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Channel Flow ◽  
Large Scale ◽  
Channel Wall ◽  
Flow Direction ◽  
Flow Characteristics ◽  
Vortex Generator ◽  
Square Cylinder ◽  
Transfer Enhancement

Heat transfer enhancement in channel flow by using an inclined vortex generator has been numerically investigated. A square cylinder is located on the centerline of laminar channel flow, which is subject to a constant heat flux on the lower channel wall. As the cylinder is inclined with some angle of attack with respect to the main flow direction, flow characteristics change downstream of the cylinder, and significantly affect heat transfer on the channel wall. A parametric study has been conducted to identify the cause, and to possibly find the optimal inclination angle. It turns out that the increased periodic fluctuation of the vertical velocity component in the vicinity of the channel walls is responsible for the heat transfer enhancement. The large fluctuation is believed to be induced by the large-scale vortices shed from the inclined square cylinder, as well as by the secondary vortices formed near the channel walls.

Heat transfer enhancement of turbulent channel flow using tandem self-oscillating inverted flags

2018 ◽  
Vol 30 (7) ◽  
pp. 075108 ◽  
Author(s):  
Yujia Chen ◽  
Yuelong Yu ◽  
Wenwu Zhou ◽  
Di Peng ◽  
Yingzheng Liu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Channel Flow ◽  
Turbulent Channel Flow ◽  
Transfer Enhancement

Numerical Investigation of Heat Transfer in the Wake of a Single Highly Confined Bubble in a Horizontal Minichannel

2018 ◽  
Author(s):  
John R. Willard ◽  
D. Keith Hollingsworth
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Numerical Investigation ◽  
Channel Flow ◽  
Heat Generation ◽  
Reduced Order Model ◽  
Two Dimensional ◽  
Transfer Enhancement ◽  
Order Model ◽  
Reduced Order

Confined bubbly flows in millimeter-scale channels produce significant heat transfer enhancement when compared to single-phase flows. Experimental studies support the hypothesis that the enhancement is driven by a convective phenomenon in the liquid phase as opposed to sourcing from microlayer evaporation or active nucleation. A numerical investigation of flow structure and heat transfer produced by a single bubble moving through a millimeter-scale channel was performed in order to document the details of this convective mechanism. The simulation includes thermal boundary conditions emulating those of the experiments, and phase change was omitted in order to focus only on the convective mechanism. The channel is horizontal with a uniform-heat-generation upper wall and an adiabatic lower surface. A Lagrangian framework was adopted such that the computational domain surrounds the bubble and moves at the nominal bubble speed. The liquid around the bubble moves as a low-Reynolds-number unsteady laminar flow. The volume-of-fluid method was used to track the liquid/gas interface. This paper reviews the central results of this simulation regarding wake heat transfer. It then compares the findings regarding Nusselt number enhancement to a reduced-order model on a two-dimensional domain in the wake of the bubble. The model solves the advective-diffusion equation assuming a velocity field consistent with fully developed channel flow in the absence of the bubble. The response of the uniform-heat-generation upper wall is included. The model assumes a temperature profile directly behind the bubble which represents a well-mixed region produced by the passage of the bubble. The significant wake heat transfer enhancement and its decay with distance from the bubble documented by the simulation were captured by the reduced-order model. However, the channel surface temperature recovered in a much shorter distance in the simulation compared to the reduced-order model. This difference is attributed to the omission of transverse conduction within the heated surface in the two-dimensional model. Beyond approximately one bubble diameter into the bubble wake, the complex flow structures are replaced by the momentum field of the precursor channel flow. However, the properties and thickness of the heated upper channel wall govern the heat transfer for many bubble diameters behind the bubble.

1518 Dissimilar heat transfer enhancement using permeable walls in turbulent channel flow

2015 ◽  
Vol 2015 (0) ◽  
pp. _1518-1_-_1518-3_
Author(s):  
Hisaaki HASEGAWA ◽  
Yuuki AOKI ◽  
Kousuke ISHIKAWA ◽  
Genta KAWAHARA ◽  
Markus UHLMANN ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Channel Flow ◽  
Turbulent Channel Flow ◽  
Transfer Enhancement ◽  
Permeable Walls

scholarly journals Heat transfer enhancement of a channel flow by rotation circular cylinder

2015 ◽  
Vol 81 (823) ◽  
pp. 14-00440-14-00440
Author(s):  
Norihiro TAKAHASHI ◽  
Eisaku MORITA ◽  
Yuhei INOUE ◽  
Guannan XI ◽  
Kyoji INAOKA ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Circular Cylinder ◽  
Heat Transfer Enhancement ◽  
Channel Flow ◽  
Transfer Enhancement

Heat Transfer Enhancement by Synthetic Jet Arrays in Air-Cooled Heat Sinks for Use in Electronics Cooling

2012 ◽  
Author(s):  
Longzhong Huang ◽  
Terrence Simon ◽  
Min Zhang ◽  
Youmin Yu ◽  
Mark North ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Channel Flow ◽  
Heat Sink ◽  
Jet Flow ◽  
Synthetic Jet ◽  
Synthetic Jets ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

A synthetic jet is an intermittent jet which issues through an orifice from a closed cavity over half of an oscillation cycle. Over the other half, the flow is drawn back through the same orifice into the cavity as a sink flow. The flow is driven by an oscillating diaphragm, which is one wall of the cavity. Synthetic jets are widely used for heat transfer enhancement since they are effective in disturbing and thinning thermal boundary layers on surfaces being cooled. They do so by creating an intermittently-impinging flow and by carrying to the hot surface turbulence generated by breakdown of the shear layer at the jet edge. The present study documents experimentally and computationally heat transfer performance of an array of synthetic jets used in a heat sink designed for cooling of electronics. This heat sink is comprised of a series of longitudinal fins which constitute walls of parallel channels. In the present design, the synthetic jet flow impinges on the tips of the fins. In the experiment, one channel of a 20-channel heat sink is tested. A second flow, perpendicular to the jet flow, passes through the channel, drawn by a vacuum system. Surface- and time-averaged heat transfer coefficients for the channel are measured, first with just the channel flow active then with the synthetic jets added. The purpose is to assess heat transfer enhancement realized by the synthetic jets. The multiple synthetic jets are driven by a single diaphragm which, in turn, is activated by a piezoelectrically-driven mechanism. The operating frequency of the jets is 1250 Hz with a cycle-maximum jet velocity of 50 m/s, as measured with a miniature hot-film anemometer probe. In the computational portion of the present paper, diaphragm movement is driven by a piston, simulating the experimental conditions. The flow is computed with a dynamic mesh using the commercial software package ANSYS FLUENT. Computed heat transfer coefficients show a good match with experimental values giving a maximum difference of less than 10%. The effects of amplitude and frequency of the diaphragm motion are documented. Changes in heat transfer due to interactions between the synthetic jet flow and the channel flow are documented in cases of differing channel flow velocities as well as differing jet operating conditions. Heat transfer enhancement obtained by activating the synthetic jets can be as large as 300% when the channel flow is of a low velocity compared to the synthetic jet peak velocity (as low as 4 m/s in the present study).

scholarly journals An Experimental Investigation on the Flow Characteristics Over Dimple Arrays Pertinent to Internal Cooling of Turbine Blades

2014 ◽  
Author(s):  
Wenwu Zhou ◽  
Hui Hu ◽  
Yu Rao
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Heat Transfer Enhancement ◽  
Channel Flow ◽  
Flat Surface ◽  
Reynolds Shear Stress ◽  
Turbine Blades ◽  
Flow Characteristics ◽  
Internal Cooling ◽  
Transfer Enhancement

Due to the dimple’s unique characteristics of comparatively low pressure loss penalty and good heat transfer enhancement performance, dimple provides a very desirable alternative internal cooling technique for gas turbine blades. In the present study, an experimental investigation was conducted to quantify the flow characteristics over staggered dimple arrays and to examine the vortex structures inside the dimples. In addition to the surface pressure measurements, a high-resolution digital Particle Image Velocimetry (PIV) system was also utilized to achieve detailed flow field measurements to quantify the characteristics of the turbulent channel flow over the dimple arrays in terms of the ensemble-averaged velocity, Reynolds shear stress and turbulence kinetic energy (TKE) distributions. The experimental measurement results show that the friction factor of the dimpled surface is much higher than that of a flat surface. The measured pressure distribution within a dimple reveals clearly that flow separation and attachment would occur inside each dimple. In comparison with those of a conventional channel flow with flat surface, the channel flow over the dimpled arrays was found to have much stronger Reynolds stress and higher TKE level. Such unique flow characteristics are believed to be the reasons why a dimpled surface would have a better heat transfer enhancement performance for internal cooling of turbine blades as reported in those previous studies.

Heat and Mass Transfer Caused by a Laminar Channel Flow Equipped With a Synthetic Jet Array

2010 ◽  
Author(s):  
Zdeneˇk Tra´vni´cˇek ◽  
Petra Dancˇova´ ◽  
Jozef Kordik ◽  
Toma´sˇ Vit ◽  
Miroslav Pavelka
Keyword(s):  
Heat Transfer ◽  
Mass Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Channel Flow ◽  
Heat Mass Transfer ◽  
Low Reynolds Number ◽  
Transfer Enhancement ◽  
Laminar Channel Flow ◽  
Low Reynolds

Low-Reynolds-number laminar channel flow is used in various heat/mass transfer applications, such as cooling and mixing. A low Reynolds number implies a low intensity of heat/mass transfer processes, since they rely only on the gradient diffusion. To enhance these processes, an active flow control by means of synthetic (zero-net-mass-flux) jets is proposed. This arrangement can be promising foremost in microscale. The present study is experimental in which a Reynolds number range of 200–500 is investigated. Measurement was performed mainly in air as the working fluid by means of hot-wire anemometry and the naphthalene sublimation technique. PIV experiments in water are also discussed. The experiments were performed in macroscale at the channel cross-section (20×100)mm and (40×200)mm in air and water, respectively. The results show that the low Reynolds number channel flow can be actuated by an array of synthetic jets, operating near the resonance frequency. The control effect of actuation and the heat transfer enhancement was quantified. The stagnation Nusselt number was enhanced by 10–30 times in comparison with the non-actuated channel flow. The results indicate that the present arrangement can be a useful tool for heat transfer enhancement in various applications, e.g., cooling and mixing.

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