Vortex Heat Transfer Enhancement in Narrow Channel by Oval Dimples Arrangement

2013 ◽  
Author(s):  
Sergey Isaev ◽  
Yaroslav Chudnovsky ◽  
Alexander Leontiev ◽  
Nikolai Kornev ◽  
Egon Hassel
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Numerical Study ◽  
Heated Surface ◽  
Spherical Shape ◽  
Narrow Channel ◽  
Constant Heat Flux ◽  
Hydraulic Performance ◽  
Equivalent Diameter ◽  
Transfer Enhancement

There are many passive techniques of heat transfer enhancement ranging from surface (2D) to volumetric (3D) vortex generators, however only a few of them are capable to provide a reliable increase in a heat transfer rate overrunning the increase in pressure losses. One of such successful techniques is the profiling of a heat transfer surface with the regulated arrangement of 3D cavities (dimples). The authors explored that the deviation of the dimple geometry from the spherical shape affects the flow structure and thermal and hydraulic performance of the dimpled wall. Detailed numerical simulation of fluid flow and heat transfer has been performed in the narrow channel with the 2.5 × 0.33 cross section normalized by the equivalent diameter of the dimple footprint at the constant Reynolds number Re = 10,000 and the constant heat flux through the dimpled wall. The oval dimple geometry was varied by changing the aspect ratio of the dimple footprint from 1 to 4.5 keeping the same footprint area. In the course of the numerical study, the optimal geometry, the arrangement and the orientation of oval dimples on the heated surface to achieve the superior thermal and hydraulic performance over the spherical cavities are established. Numerical results of local and integral heat transfer characteristics enhanced with the visual representation of the generated vortices clearly illustrated the flow restructuring and an increase in the thermal and hydraulic performance.

Thermal-Hydraulic Performance Enhancement by the Combination of Rectangular Winglet Pair and V-Shaped Dimples

2019 ◽  
Vol 12 (2) ◽  
Author(s):  
Inderjot Kaur ◽  
Prashant Singh ◽  
Srinath V. Ekkad
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Performance Enhancement ◽  
Numerical Study ◽  
Hydraulic Performance ◽  
Channel Height ◽  
Transfer Enhancement ◽  
Spacing Variation ◽  
Lower Heat

Abstract This paper presents numerical study on heat transfer enhancement due to the combination of rectangular winglet pair with V-dimples in an array-type arrangement. Array of rectangular winglet pairs results in heat transfer enhancement, however, at a cost of significant pressure drop, resulting in reduced thermal-hydraulic performance (THP). On the other hand, dimples are associated with lower heat transfer enhancement levels at relatively lower pumping power penalty. To this end, a combination of rectangular winglet pair and V-shaped dimples has been studied in this paper, where the arrangements were intended to achieve enhanced thermal-hydraulic performance. Three different configurations, namely, rectangular winglet pair, rectangular winglet pair with one V-dimple between two consecutive winglets, and rectangular winglet pair with two V-dimples packed in a pitch, are studied here. The variation of heat transfer enhancement, pressure drop gain, and THP with respect to winglet-to-winglet (S) spacing variation for rectangular winglet pair and rectangular winglet pair with one V-dimple configuration is presented at a Reynolds number of 25,000. The THP of the rectangular winglet pair configuration decreases up to S/H equal to 2.5 and then increases (H: channel height). For rectangular winglet pair with one V-dimple, three values of winglet-to-dimple (P) spacings are analyzed. For fixed S/H, the highest P/H configuration provided highest heat transfer enhancement and THP. Among the three configurations studied, rectangular winglet pair with two V-dimples resulted in the highest thermal-hydraulic performance.

Numerical Study of Convective Heat Transfer Enhancement in a Pipe Rotating Around a Parallel Axis

2014 ◽  
Vol 136 (5) ◽  
Author(s):  
Aurélie Fasquelle ◽  
Julien Pellé ◽  
Souad Harmand ◽  
Igor V. Shevchuk
Keyword(s):  
Heat Transfer ◽  
Convective Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Convective Heat ◽  
Numerical Study ◽  
Electrical Machines ◽  
Equivalent Diameter ◽  
Transfer Enhancement ◽  
Circular Pipes ◽  
Electrical Motors

Cooling of electrical machines is nowadays of high interest in order to improve their efficiency. In railway applications, electrical motors can be shrouded in order to avoid particles to be deposited inside. To ensure a satisfactory cooling, pipes are placed inside the rotor and are thus rotating. Improvements in convective heat transfer inside the rotating pipes were numerically investigated. Model was first validated against experimental data and after that several geometry modifications were tested. Influence of the angle of attack of the fluid at the inlet to the pipe was discussed and it was shown that heat transfer can be significantly increased near the pipe inlet. In addition to that changing a circular pipe with an elliptical pipe was investigated in two ways: fixing the same hydraulic diameter or the same equivalent diameter. It was shown that the cooling efficiency can be significantly increased. The best overall heat transfer enhancement of about 45% exhibited elliptic pipes located orthogonal to the rotation radius and having the same cross-section as the reference circular pipes. Results can be used by designers of electrical machines in order to choose the best cooling strategy.

An Experimental and Numerical Study of Heat Transfer and Pressure Loss in a Rectangular Channel With V-Shaped Ribs

2006 ◽  
Author(s):  
Michael Maurer ◽  
Jens von Wolfersdorf ◽  
Michael Gritsch
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Thermal Performance ◽  
Pressure Loss ◽  
Numerical Study ◽  
Rectangular Channel ◽  
Reynolds Numbers ◽  
Transfer Enhancement ◽  
High Reynolds Numbers ◽  
High Reynolds

An experimental and numerical study was conducted to determine the thermal performance of V-shaped ribs in a rectangular channel with an aspect ratio of 2:1. Local heat transfer coefficients were measured using the steady state thermochromic liquid crystal technique. Periodic pressure losses were obtained with pressure taps along the smooth channel sidewall. Reynolds numbers from 95,000 to 500,000 were investigated with V-shaped ribs located on one side or on both sides of the test channel. The rib height-to-hydraulic diameter ratios (e/Dh) were 0.0625 and 0.02, and the rib pitch-to-height ratio (P/e) was 10. In addition, all test cases were investigated numerically. The commercial software FLUENT™ was used with a two-layer k-ε turbulence model. Numerically and experimentally obtained data were compared. It was determined that the heat transfer enhancement based on the heat transfer of a smooth wall levels off for Reynolds numbers over 200,000. The introduction of a second ribbed sidewall slightly increased the heat transfer enhancement whereas the pressure penalty was approximately doubled. Diminishing the rib height at high Reynolds numbers had the disadvantage of a slightly decreased heat transfer enhancement, but benefits in a significantly reduced pressure loss. At high Reynolds numbers small-scale ribs in a one-sided ribbed channel were shown to have the best thermal performance.

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