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 in Channel Flow Using an Inclined Square Cylinder

2008 ◽  
Author(s):  
Dong-Hyeog Yoon ◽  
Kyung-Soo Yang ◽  
Choon-Bum Choi
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Heat Transfer Enhancement ◽  
Large Scale ◽  
Vortex Generator ◽  
Square Cylinder ◽  
Transfer Enhancement ◽  
Enhance Heat Transfer ◽  
Positive Role ◽  
Secondary Vortices

The large-scale vortices shed from a cylindrical object as a vortex generator can be used to enhance heat transfer in a heat exchanger [1]. Furthermore, the large-scale vortices induce secondary vortices on the walls of a heat exchanger, which also play a positive role in heat transfer enhancement.

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.

scholarly journals A Numerical Investigation of Turbulent Flow and Heat Transfer in Rectangular Channels With Elliptic Scale-Roughened Walls

2013 ◽  
Vol 135 (8) ◽  
Author(s):  
Feng Zhou ◽  
Ivan Catton
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Flow Direction ◽  
Flow Characteristics ◽  
Volume Averaging ◽  
Spanwise Direction ◽  
Transfer Enhancement ◽  
Pressure Drops ◽  
Flow Mixing ◽  
Rectangular Channels

In the present paper, rectangular channels with six types of elliptic scale-roughened walls for heat transfer enhancement are numerically studied. Heat transfer and fluid flow characteristics for sixteen different scale-roughened models (with the scale height varying in the range from 1 mm to 2.5 mm) are numerically predicted using commercial computational fluid dynamics (CFD) code, Ansys cfx. The turbulent model employed is the k–ω based shear–stress transport (SST) model with automatic wall function treatment. In the performance evaluation, we use a “universal” porous media length scale based on volume averaging theory (VAT) to define the Reynolds number, Nusselt number, and friction factor. It is found that heat transfer performance is most favorable when the elliptic scales are oriented with their long axis perpendicular to the flow direction, while the scales elongated in the flow direction have lower Nusselt numbers and pressure drops compared with the circular scale-roughened channels. Results indicate that the scale-shaped roughness strongly spins the flow in the spanwise direction, which disrupts the near-wall boundary layers continuously and enhances the bulk flow mixing. With the flow marching in a more intense spiral pattern, a 40% improvement of heat transfer enhancement over the circular scale-roughened channels is observed.

A Critical Review of the Prominent Method of Heat Transfer Enhancement for the Fin-and-Tube Heat Exchanger by Interrupted Fin Surface: The Vortex Generators Approach

2018 ◽  
Vol 26 (03) ◽  
pp. 1830001 ◽  
Author(s):  
Nares Chimres ◽  
Somchai Wongwises
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Heat Transfer Enhancement ◽  
Flow Characteristics ◽  
Vortex Generator ◽  
Vortex Generators ◽  
Experimental Investigations ◽  
Transfer Enhancement ◽  
Tube Heat Exchanger ◽  
Performance Indexes

The performance of heat exchangers impacts industry investment, energy consumption, and pollution because the heat exchanger has been used in many industries. The use of vortex generators on the fin is the prominent method of heat transfer enhancement because the performance indexes of fins with vortex generators are greater than those of the fins without vortex generators. However, this method faces obstacles because the concepts and design instructions are still obscure. Therefore, this paper provides a summary of the publications about the use of vortex generators. The publications on the effects of traditional and alternative vortex generators that are combined with plain, wavy, and louver fins are summarized. The aim of this paper is to aggregate the publications concerned with the thermal performance and flow characteristics of the fin-and-tube heat exchanger with vortex generator using numerical and experimental investigations as the guideline for future studies.

scholarly journals Heat-Transfer and Mixing Enhancement by Vortex Generators Used in Heat Exchanger-Reactors

2003 ◽  
Author(s):  
S. Ferrouillat ◽  
P. Tochon ◽  
C. Garnier ◽  
H. Peerhossaini
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Heat Transfer Enhancement ◽  
Flow Direction ◽  
Vortex Generator ◽  
Chemical Reactor ◽  
Vortex Generators ◽  
Mixing Enhancement ◽  
Transfer Enhancement ◽  
Longitudinal Vortices

Compact heat exchangers are well known for their ability to transfer a large amount of heat while retaining low volume and weight. The purpose of this paper is to study the potential of using this device as a chemical reactor, generally called a heat exchanger-reactor (HEX reactor). Indeed, the question arises: can these geometries combine heat transfer and mixing in the same device? Such a technology would offer many potential advantages, such as better reaction control (through the thermal aspect), improved selectivity (through intensified mixing, more isothermal operation and shorter residence time, and sharper RTDs), byproduct reduction, and enhanced safety. Several geometries of compact heat exchanger based on turbulence generation are available. This paper focuses on one type: vortex generators. The main objective is to contribute to the determination of turbulent flow inside various geometries by computational fluid dynamics methods. These enhanced industrial geometries are studied in terms of their thermal-hydraulic performance and macro-/micro-mixing ability. The longitudinal vortices they generate in a channel flow turn the flow perpendicular to the main flow direction and enhance mixing between the fluid close to the fin and that in the middle of the channel. Two kinds of vortex generators are considered: a delta winglet pair and a rectangular winglet pair. For both, good agreement is obtained between numerical results and data in the literature. The vortex generator concept is found to be very efficient in terms of heat-transfer enhancement and macro-mixing. Nevertheless, the micro-mixing level is poor due to strong inhomogeneities: the vortex generator must be used as a heat-transfer enhancement device or as a static mixer for macro- and meso-mixing.

Heat Transfer Characteristics of Baffled Channel Flow

2011 ◽  
Vol 133 (9) ◽  
Author(s):  
Changwoo Kang ◽  
Kyung-Soo Yang
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Channel Flow ◽  
Large Scale ◽  
Heat Removal ◽  
Channel Height ◽  
Transfer Enhancement ◽  
Heat Transfer Characteristics ◽  
Physical Reason ◽  
Transfer Characteristics

Heat transfer characteristics of baffled channel flow, where thin baffles are mounted on both channel walls periodically in the direction of the main flow, have been numerically investigated in a laminar range. The main objectives of the present study are to find the physical reason responsible for the heat transfer enhancement in finned heat exchangers, and to identify the optimal configurations of the baffles to achieve the most efficient heat removal from the channel walls. Two key parameters are considered, namely ratio of baffle interval to channel height (RB) and Reynolds number (Re). We performed a parametric study and found that the large-scale vortices travelling along the channel walls between the neighboring baffles, which are generated by flow separation at the tips of the baffles and become unsteady due to a Hopf bifurcation from steady to a time-periodic flow, play the key role in the heat transfer enhancement by inducing strong vertical velocity fluctuation in the vicinity of the channel walls. We also propose a contour diagram (“map”) of averaged Nusselt number on the channel walls as a function of the two parameters. The results shed light on understanding and controlling heat transfer mechanism in a finned heat exchanger, being quite beneficial to its design.

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