Channel Height Effect on Heat Transfer and Friction in a Dimpled Passage

2000 ◽  
Vol 122 (2) ◽  
pp. 307-313 ◽  
Author(s):  
H. K. Moon ◽  
T. O’Connell ◽  
B. Glezer
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Channel Height ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Entry Length ◽  
Heat Transfer Coefficients ◽  
Friction Factors ◽  
Smooth Channel

The heat transfer enhancement in cooling passages with dimpled (concavity imprinted) surface can be effective for use in heat exchangers and various hot section components (nozzle, blade, combustor liner, etc.), as it provides comparable heat transfer coefficients with considerably less pressure loss relative to protruding ribs. Heat transfer coefficients and friction factors were experimentally investigated in rectangular channels which had concavities (dimples) on one wall. The heat transfer coefficients were measured using a transient thermochromic liquid crystal technique. Relative channel heights H/d of 0.37, 0.74, 1.11, and 1.49 were investigated in a Reynolds number range from 12,000 to 60,000. The heat transfer enhancement NuHD on the dimpled wall was approximately constant at a value of 2.1 times that Nusm of a smooth channel over 0.37⩽H/d/⩽1.49 in the thermally developed region. The heat transfer enhancement ratio Nu¯HD/Nusm was invariant with Reynolds number. The friction factors (f) in the aerodynamically fully developed region were consistently measured to be around 0.0412 (only 1.6 to 2.0 times that of a smooth channel). The aerodynamic entry length was comparable to that of a typical turbulent flow xo/Dh=20, unlike the thermal entry length on dimpled surface which was much shorter xo/Dh<9.8. The thermal performance Nu¯HD/Nusm/f/fsm1/3≅1.75 of dimpled surface was superior to that 1.16<NuHD/Nusm/f/fsm1/3<1.60 of continuous ribs, demonstrating that the heat transfer enhancement with concavities can be achieved with a relatively low-pressure penalty. Neither the heat transfer coefficient distribution nor the friction factor exhibited a detectable effect of the channel height within the studied relative height range 0.37⩽H/d⩽1.49.[S0742-4795(00)02802-7]

Channel Height Effect on Heat Transfer and Friction in a Dimpled Passage

1999 ◽  
Author(s):  
H. K. Moon ◽  
T. O’Connell ◽  
B. Glezer
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Channel Height ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Entry Length ◽  
Heat Transfer Coefficients ◽  
Friction Factors ◽  
Smooth Channel

The heat transfer enhancement in cooling passages with dimpled (concavity imprinted) surface can be effective for use in heat exchangers and various hot section components (nozzle, blade, combustor liner, etc.), as it provides comparable heat transfer coefficients with considerably less pressure loss relative to protruding ribs. Heat transfer coefficients and friction factors were experimentally investigated in rectangular channels which had concavities (dimples) on one wall. The heat transfer coefficients were measured using a transient thermochromic liquid crystal technique. Relative channel heights (H/d) of 0.37, 0.74, 1.11 and 1.49 were investigated in a Reynolds number range from 12000 to 60000. The heat transfer enhancement (NuHD) on the dimpled wall was approximately constant at a value of 2.1 times that (Nusm) of a smooth channel over 0.37≤H/d≤1.49 in the thermally developed region. The heat transfer enhancement ratio Nu¯HD/Nusm was invariant with Reynolds number. The friction factors (f) in the aerodynamically fully developed region were consistently measured to be around 0.0412 (only 1.6 to 2.0 times that of a smooth channel). The aerodynamic entry length was comparable to that of a typical turbulent flow (Xo/Dh = 20), unlike the thermal entry length on dimpled surface which was much shorter (xo /Dh<9.8). The thermal performance Nu¯HD/Nusm/f/fsm1/3≅1.75 of dimpled surface was superior to that 1.16<Nu¯HD/Nusm/f/fsm1/3<1.60 of continuous ribs, demonstrating that the heat transfer enhancement with concavities can be achieved with a relatively low-pressure penalty. Neither the heat transfer coefficient distribution nor the friction factor exhibited a detectable effect of the channel height within the studied relative height range (0.37≤H/d≤1.49).

scholarly journals Effect of Integrating Metal Wire Mesh with Spray Injection for Liquid Piston Gas Compression

Energies ◽  
2021 ◽  
Vol 14 (13) ◽  
pp. 3723
Author(s):  
Barah Ahn ◽  
Vikram C. Patil ◽  
Paul I. Ro
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Metal Wire ◽  
Wire Mesh ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Gas Compression ◽  
Liquid Piston

Heat transfer enhancement techniques used in liquid piston gas compression can contribute to improving the efficiency of compressed air energy storage systems by achieving a near-isothermal compression process. This work examines the effectiveness of a simultaneous use of two proven heat transfer enhancement techniques, metal wire mesh inserts and spray injection methods, in liquid piston gas compression. By varying the dimension of the inserts and the pressure of the spray, a comparative study was performed to explore the plausibility of additional improvement. The addition of an insert can help abating the temperature rise when the insert does not take much space or when the spray flowrate is low. At higher pressure, however, the addition of spacious inserts can lead to less efficient temperature abatement. This is because inserts can distract the free-fall of droplets and hinder their speed. In order to analytically account for the compromised cooling effects of droplets, Reynolds number, Nusselt number, and heat transfer coefficients of droplets are estimated under the test conditions. Reynolds number of a free-falling droplet can be more than 1000 times that of a stationary droplet, which results in 3.95 to 4.22 times differences in heat transfer coefficients.

Heat Transfer Enhancement Using a Convex-Patterned Surface

2003 ◽  
Vol 125 (2) ◽  
pp. 274-280 ◽  
Author(s):  
H. K. Moon ◽  
T. O’Connell ◽  
R. Sharma
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Reynolds Numbers ◽  
Smooth Wall ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Patterned Surface ◽  
Nusselt Numbers ◽  
Friction Factors ◽  
Smooth Channel

The heat transfer rate from a smooth wall in an internal cooling passage can be significantly enhanced by using a convex patterned surface on the opposite wall of the passage. This design is particularly effective for a design that requires the heat transfer surface to be free of any augmenting features (smooth). Heat transfer coefficients on the smooth wall in a rectangular channel, which had convexities on the opposite wall were experimentally investigated. Friction factors were also measured to assess the thermal performance. Relative clearances δ/d between the convexities and the smooth wall of 0, 0.024, and 0.055 were investigated in a Reynolds number ReHD range from 15,000 to 35,000. The heat transfer coefficients were measured in the thermally developed region using a transient thermochromic liquid crystal technique. The clearance gap between the convexities and the smooth wall adversely affected the heat transfer enhancement NuHD. The friction factors (f ), measured in the aerodynamically developed region, were largest for the cases of no clearance δ/d=0). The average heat transfer enhancement Nu¯HD was also largest for the cases of no clearance δ/d=0, as high as 3.08 times at a Reynolds number of 11,456 in relative to that Nuo of an entirely smooth channel. The normalized Nusselt numbers Nu¯HD/Nuo, as well as the normalized friction factors f/fo, for all three cases, decreased with Reynolds numbers. However, the decay rate of the friction factor ratios f/fo with Reynolds numbers was lower than that of the normalized Nusselt numbers. For all three cases investigated, the thermal performance Nu¯HD/Nuo/f/fo1/3 values were within 5% to each other. The heat transfer enhancement using a convex patterned surface was thermally more effective at a relative low Reynolds numbers (less than 20,000 for δ/d=0) than that of a smooth channel.

Heat Transfer Enhancement Using a Convex-Patterned Surface

2002 ◽  
Author(s):  
H. K. Moon ◽  
T. O’Connell ◽  
R. Sharma
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Reynolds Numbers ◽  
Smooth Wall ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Patterned Surface ◽  
Nusselt Numbers ◽  
Friction Factors ◽  
Smooth Channel

The heat transfer rate from a smooth wall in an internal cooling passage can be significantly enhanced by using a convex patterned surface on the opposite wall of the passage. This design is particularly effective for a design that requires the heat transfer surface to be free of any augmenting features (smooth). Heat transfer coefficients on the smooth wall in a rectangular channel, which had convexities on the opposite wall were experimentally investigated. Friction factors were also measured to assess the thermal performance. Relative clearances (δ/d) between the convexities and the smooth wall of 0, 0.024, and 0.055 were investigated in a Reynolds number (ReHD) range from 15,000 to 35,000. The heat transfer coefficients were measured in the thermally developed region using a transient thermochromic liquid crystal technique. The clearance gap between the convexities and the smooth wall adversely affected the heat transfer enhancement (NuHD). The friction factors (f), measured in the aerodynamically developed region, were largest for the cases of no clearance (δ/d = 0). The average heat transfer enhancement (NuHD) was also largest for the cases of no clearance (δ/d = 0), as high as 3.08 times at a Reynolds number of 11,456 in relative to that (Nuo) of an entirely smooth channel. The normalized Nusselt numbers (NuHD/Nuo), as well as the normalized friction factors (f/fo), for all three cases, decreased with Reynolds numbers. However, the decay rate of the friction factor ratios (f/fo) with Reynolds numbers was lower than that of the normalized Nusselt numbers. For all three cases investigated, the thermal performance ((NuHD/Nuo) /(f/fo)1/3) values were within 5% to each other. The heat transfer enhancement using a convex patterned surface was thermally more effective at a relatively low Reynolds numbers (less than 20,000 for δ/d = 0) than that of a smooth channel.

Effect of Partial 3-Dimensional Pin Fin Geometry for Heat Transfer Enhancement in High Aspect Ratio Channels

2012 ◽  
Author(s):  
Jaideep Pandit ◽  
Megan Dove ◽  
Srinath V. Ekkad ◽  
Scott Huxtable
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Test Surface ◽  
Channel Height ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
3 Dimensional ◽  
Pin Fin ◽  
Heat Transfer Coefficients ◽  
The Difference

The efficiency of a TEG (Thermoelectric Generator) may be thought of as the ratio of the power output to the heat input at the hot junction. This ratio is governed by the laws of thermodynamics and cannot thus exceed the Carnot efficiency. It follows that the greater the difference between the hot and cold side temperatures, the greater the efficiency of the TEG. Heat transfer enhancement measurements with 3-Dimensional partial pin-fin arrays of varying shapes on a flat plate are presented. The fin height is fixed at 15% of channel height. The hydraulic diameter and configuration of the fins are chosen based on existing literature. The study is carried out at various Reynolds numbers based on full channel height. The shapes studied are circular, semi-circular, triangular, hexagonal and diamond shaped. These shapes are compared against a baseline case without fins. The experiment uses the transient liquid crystal (TLC) method to calculate the heat transfer coefficient on the test surface. The data shows that diamond shaped fins provide the highest turbulent mixing downstream of the pins leading to the highest heat transfer coefficients.

Heat Transfer Enhancement in Triangular Ducts With an Array of Side-Entry Wall/Impinged Jets

1999 ◽  
Author(s):  
J.-J. Hwang ◽  
C.-S. Cheng ◽  
Y.-P. Tsia
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Leading Edge ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Pressure Drops ◽  
Heat Transfer Coefficients ◽  
Inclined Angle

An experimental study has been performed to measure local heat transfer coefficients and static well pressure drops in leading-edge triangular ducts cooled by wall/impinged jets. Coolant provided by an array of equally spaced wall jets is aimed at the leading-edge apex and exits from the radial outlet. Detailed heat transfer coefficients are measured for the two walls forming the apex using transient liquid crystal technique. Secondary-flow structures are visualized to realize the mechanism of heat transfer enhancement by wall/impinged jets. Three right-triangular ducts of the same altitude and different apex angles of β = 30 deg (Duct A), 45 deg (Duct B) and 60 deg (Duct C) are tested for various jet Reynolds numbers (3000≦Rej≦12600) and jet spacings (s/d = 3.0 and 6.0). Results show that an increase in Rej increases the heat transfer on both walls. Local heat transfer on both walls gradually decreases downstream due to the crossflow effect. At the same Rej, the Duct C has the highest wall-averaged heat transfer because of the highest jet center velocity as well as the smallest jet inclined angle. Moreover, the distribution of static pressure drop based on the local through flow rate in the present triangular duct is similar to that that of developing straight pipe flows. Average jet Nusselt numbers on the both walls have been correlated with jet Reynolds number for three different duct shapes.

Falling Film Evaporation of Water on Horizontal Configured Tube Bundles

2010 ◽  
Author(s):  
Wei Li ◽  
Xiaoyu Wu ◽  
Zhong Luo
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Transfer Enhancement ◽  
Inlet Temperature ◽  
Falling Film ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Film Evaporation ◽  
Tube Bundles ◽  
Falling Film Evaporation

This paper reports an experimental study on falling film evaporation of water on 6-row horizontal configured tube bundles in a vacuum. Three types of configured tubes, Turbo-CAB-19fpi and −26fpi, Korodense, including smooth tubes for reference, were tested in a range of film Reynolds number from about 10 to 110. Results show that as the falling film Reynolds number increases, falling film evaporation goes from tubes partial dryout regime to fully wet regime; the mean heat transfer coefficients reach peak values in the transition point. Turbo-CAB tubes have the best heat transfer enhancement of falling film evaporation in both regimes, but Korodense tubes’ overall performances are better when tubes are fully wet. The inlet temperature of heating water has hardly any effects on the heat transfer, but the evaporation pressure has controversial effects. A correlation with errors within 10% was also developed to predict the heat transfer enhancement capacity.

Heat Transfer Enhancement Induced by Cube- and Diamond-Shaped Block Arrays in Two-Pass High-Aspect Ratio Channels With a 180-Degree Turn

2010 ◽  
Author(s):  
Pavin Ganmol ◽  
Minking K. Chyu
Keyword(s):  
Heat Transfer ◽  
Aspect Ratio ◽  
Heat Transfer Enhancement ◽  
High Aspect Ratio ◽  
Local Heat Transfer ◽  
Channel Height ◽  
Transfer Enhancement ◽  
Smooth Channel ◽  
Sharp Turn ◽  
First Pass

Described in this paper is an experimental investigation of the heat transfer and pressure characteristics in a high aspect ratio, (4.5:1 width-to-height), two-pass channel, with cube-shaped and diamond-shaped block arrays placed in both passes before and after a 180-degree sharp turn. Transient liquid crystal technique was applied to acquire detailed local heat transfer data on both the channel surfaces and the block elements. Reynolds number tested varies between 13000 and 28000. To further explore potential design alternatives for enhancement cooling, the effects of block height, ranging from 1/4, 1/2, 3/4 and full span of the channel height were also evaluated. Present results suggest that a staggered cube-array can enhance heat transfer rate up to 3.5 fold in the first pass and about 1.9 fold in the second pass, relative to the fully-developed smooth channel counterpart. For the corresponding diamond-shaped block array, the enhancement is 3.4 and 1.9 fold respectively. Even though the post-turn turbulence transport in the second pass is generally higher than that in the first pass, the effects of surface-block induced heat transfer enhancement in fact are less prominent in the post-turn region of the second pass. Pressure loss for diamond block arrays is generally higher than that of the corresponding cube-block arrays.

Heat Transfer in Rotating Multi-Pass Rectangular Smooth Channel With and Without a Turning Vane in Hub Region

2013 ◽  
Author(s):  
Jiang Lei ◽  
Shiou-Jiuan Li ◽  
Je-Chin Han ◽  
Luzeng Zhang ◽  
Hee-Koo Moon
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Reynolds Number ◽  
Density Ratio ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
The Third ◽  
Rotation Numbers ◽  
Smooth Channel ◽  
Turn Region

This paper experimentally investigates the effect of a turning vane on hub region heat transfer in a multi-pass rectangular smooth channel at high rotation numbers. The experimental data were taken in the second and the third passages (Aspect Ratio = 2:1) connected by an 180° U-bend. The flow was radial inward in the second passage and was radial outward after the 180° U-bend in the third passage. The Reynolds number ranged 10,000 to 40,000 while the rotation number ranged 0 to 0.42. The density ratio was a constant of 0.12. Results showed that rotation increases heat transfer on leading surface but decreases it on the trailing surface in the second passage. In the third passage, the effect of rotation is reversed. Without a turning vane, rotation reduces heat transfer substantially on all surfaces in the hub 180° turn region. After adding a half-circle-shaped turning vane, heat transfer coefficients do not change in the second passage (before turn) while they are quite different in the turn region and the third passage (after turn). Regional heat transfer coefficients are correlated with rotation numbers for multi-pass rectangular smooth channel with and without a turning vane.

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).

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