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%.

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.

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.

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

An Experimental and Numerical Study of Heat Transfer and Pressure Losses of V- and W-Shaped Ribs at High Reynolds Numbers

2007 ◽  
Author(s):  
Michael Maurer ◽  
Jens von Wolfersdorf ◽  
Michael Gritsch
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Thermal Performance ◽  
Pressure Loss ◽  
Numerical Study ◽  
Reynolds Numbers ◽  
Transfer Enhancement ◽  
Height Ratio ◽  
Reduced Pressure ◽  
Pressure Losses

An experimental and numerical investigation was conducted to assess the thermal performance of V- and W-shaped ribs in a rectangular channel. The ribs were located on one channel sidewall in order to simulate a typical combustor liner cooling. The cross section of the channel had an aspect ratio of 2:1. Local heat transfer coefficients were measured using the transient thermochromic liquid crystal technique. Pressure taps along the channel sidewall were used to obtain the periodic pressure losses. The rib height-to-hydraulic diameter ratio (e/Dh) was set to 0.02, and the rib pitch-to-height ratios (P/e) were 5 and 10. The Reynolds numbers investigated varied from 80,000 to 500,000. All rib configurations were additionally investigated numerically and the obtained computational results were compared with experimental data. For all computations the commercial software FLUENT™ was used with a two-layer k-ε turbulence model. It could be demonstrated that applying W-shaped ribs instead of V-shaped ribs has the advantage of an increased heat transfer enhancement, but is accompanied by a rise in pressure loss. Reducing the rib pitch-to-height ratio from 10 to 5 decreases the heat transfer enhancement, but results in a significantly reduced pressure loss. Finally, the best thermal performance was found for W-shaped ribs with a pitch-to-height ratio of 10, having a slightly increased pressure loss but with considerable rise in heat transfer enhancement compared to V-shaped ribs.

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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