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.

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).

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]

Latticework (Vortex) Cooling Effectiveness: Part 2 — Rotating Channel Experiments

2004 ◽  
Author(s):  
S. Acharya ◽  
Fuguo Zhou ◽  
Jonathan Lagrone ◽  
Gazi Mahmood ◽  
Ronald S. Bunker
Keyword(s):  
Heat Transfer ◽  
Thermal Performance ◽  
Density Ratio ◽  
Transfer Coefficients ◽  
Performance Factors ◽  
Nusselt Numbers ◽  
Friction Factors ◽  
Smooth Channel ◽  
Rib Turbulators ◽  
Density Ratios

The heat transfer and pressure drop characteristics of latticework coolant blade passages have been investigated experimentally under conditions of rotation. Stationary studies with the latticework configuration have shown potential advantages including spatially-uniform streamwise distributions of the heat transfer coefficient, greater blade strength, and enhancement levels comparable to conventional rib turbulators. In the present study, a latticework coolant passage, with orthogonal-ribs, is studied in a rotating heat transfer test-rig for a range of Reynolds numbers (Res), Rotation numbers (Ros), and density ratios. Measurements indicate that for Res≥20,000, the latticework coolant passage provides very uniform streamwise distributions of the Nusselt number (Nus) with enhancement levels (relative to smooth-channel values) in the range of 2.0 to 2.5. No significant dependence of Nus on Ros and density ratio is observed except at lower Res values (≤10,000). Nusselt numbers are highest immediately downstream of a turn indicating that bend-effects play a major role in enhancing heat transfer. Friction factors are relatively insensitive to Ros, and thermal performance factors at higher Res values appear to be comparable to those obtained with conventional rib-turbulators. The present study indicates that latticework cooling geometry can provide comparable heat transfer enhancements and thermal performance factors as conventional rib-turbulators, with potential benefits of streamwise uniformity in the heat transfer coefficients and added blade strength.

Dimple Enhanced Heat Transfer in High Aspect Ratio Channels

2001 ◽  
Author(s):  
Srinath V. Ekkad ◽  
Hasan Nasir
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Rectangular Cross Section ◽  
Rectangular Channel ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
High Heat Transfer ◽  
Smooth Channel ◽  
Wide Range

Abstract Detailed heat transfer measurements are presented for a rectangular channel with dimples on one wall. Dimpled surfaces provide high heat transfer enhancement comparable to ribbed surfaces with reduced overall pressure drop. The heat transfer coefficients were measured using a transient liquid crystal technique. The effect of channel flow Reynolds number was investigated for a wide range from 10000 to 65000. The channel is a 25.4 mm × 101.6 mm (1” × 4”) rectangular cross-section with the dimples on one of the 101.6 mm wall. Heat transfer enhancement around three times that of a smooth channel were achieved for all flow conditions. The overall pressure drop through the dimpled section of the passage was also measured. The resulting thermal performance of the dimples surfaces is significantly higher compared to channels with protruding ribs.

Experimental Investigation on Heat Transfer and Pressure Drop of Nanodiamond-Engine Oil Nanofluid in a Microfin Tube

2010 ◽  
Author(s):  
M. A. Akhavan-Behabadi ◽  
M. Ghazvini ◽  
E. Rasouli
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Convection Heat Transfer ◽  
Heat Fluxes ◽  
Engine Oil ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers

In this study, the effect of adding nanodiamond powder as an additive to engine oil on laminar flow heat transfer enhancement and pressure drop increasing is experimentally investigated. The plain and microfin tubes were used as the test sections and were heated by an electrical coil heater to produce constant heat fluxes. Thermal conductivity and heat capacity of nanofluids were measured for different volume fractions and temperatures. Convection heat transfer coefficients and Nusselt numbers of nanofluids were obtained for different nanoparticle concentrations as well as various Peclet and Reynolds numbers. Experimental results show the enhancement of heat transfer due to the nanoparticles presence. Furthermore, the effect of particle concentration on pressure drop was studied for different heat fluxes. Finally, the performance evaluation of both nanofluid and microfin tube from the point view of heat transfer enhancement and pressure drop increasing is done.

Heat Transfer Enhancement for Turbulent Flows in Corrugated Tubes

2014 ◽  
Author(s):  
Zhi-Min Yao ◽  
Zhi-Gang Feng ◽  
Zuo-Qin Qian ◽  
Zhi-Zhe Chen
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Turbulent Flows ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Reynolds Numbers ◽  
Smooth Wall ◽  
Transfer Enhancement ◽  
Corrugated Tube

Heat transfer rate and pressure drop of turbulent flows of water in a smooth-wall tube and five corrugated tubes at Reynolds numbers between 7,500 and 50,000 are studied using the commercial software FLUENT. The corrugated tube is constructed by placing protruded ridges evenly along a tube. Depending on the different design of corrugated tubes, our numerical simulation results show that the use of corrugated tubes can improve heat transfer rate by a factor of 1.5 to 2 at Reynolds numbers between 7,500 and 12,000 when compared to a smooth-wall tube. However, the rate of enhancement gradually decreases to a factor of 1.1 to 1.5 as flow Reynolds number increases to 50,000. We further studied the pressure drop and friction factors of the corrugated tube. For the corrugated tube with the highest heat transfer enhancement, we found the pressure drop increases by a factor of 3 to 4 compared to a smooth-wall tube, while the friction factor increases by a factor of 3.5 to 4.4. These findings can be very useful in the design of more efficient heat exchangers.

Influence of Crossflow-Induced Swirl and Impingement on Heat Transfer in an Internal Coolant Passage of a Turbine Airfoil

2000 ◽  
Vol 122 (3) ◽  
pp. 587-597 ◽  
Author(s):  
S. V. Ekkad ◽  
G. Pamula ◽  
S. Acharya
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Transfer Enhancement ◽  
Feed System ◽  
Nusselt Numbers ◽  
Flow Through ◽  
Transient Liquid Crystal Technique ◽  
Measured Pressure

Detailed heat transfer distributions are presented inside a two-pass coolant channel with crossflow-induced swirl and impingement. The impingement and passage crossflow are generated from one coolant passage to the adjoining coolant passage through a series of straight or angled holes along the dividing wall. The holes provide for the flow turning from one passage to another typically achieved in a conventional design by a 180-deg U-bend. The holes direct the flow laterally from one passage to another and generate different secondary flow patterns in the second pass. These secondary flows produce impingement and swirl and lead to higher heat transfer enhancement. Three different lateral hole configurations are tested for three Reynolds numbers (Re=10,000, 25,000, 50,000). The configurations were varied by angle of delivery and location on the divider wall. A transient liquid crystal technique is used to measure the detailed heat transfer coefficient distributions inside the passages. Results with the new crossflow feed system are compared with the results from the traditional 180-deg turn passage. Results show that the crossflow feed configurations produce significantly higher Nusselt numbers on the second pass walls without affecting the first pass heat transfer levels. The heat transfer enhancement is as high as seven to eight times greater than obtained in the second pass for a channel with a 180-deg turn. The increased measured pressure drop (rise in friction factor) caused by flow through the crossflow holes are compensated by the significant heat transfer enhancement obtained by the new configuration. [S0022-1481(00)03103-0]

An Experimental and Numerical Investigation on the Thermal-Hydraulic Performance of Double Notched Plate

2012 ◽  
Vol 134 (9) ◽  
Author(s):  
Lei Zhang ◽  
Defu Che
Keyword(s):  
Heat Transfer ◽  
Swirling Flow ◽  
Reynolds Numbers ◽  
Velocity Fields ◽  
Local Information ◽  
Transfer Coefficients ◽  
Enhanced Heat Transfer ◽  
Heat Transfer Coefficients ◽  
Nusselt Numbers ◽  
Friction Factors

The double notched (DN) plate is commonly used in rotary air preheaters, but relevant investigations are rare. Thus, thermal-hydraulic performances of the DN plate are investigated in this paper. A single-blow, transient technique is refined and then used to measure the overall mean heat transfer coefficients and friction factors. A validated numerical method is also utilized to provide local information. The measured results show that the performance of the DN plate approaches that of the double undulated (DU) plate and lies between that of the cross corrugated (CC) plate and the parallel plate. No swirling flow pattern is identified in the predicted velocity fields. Basically, two types of flow are observed: wavy channel flow and pipe flow. High or low Nusselt numbers, Nu, are obtained at the luff or lee side of undulations and notches, respectively. Nu values increase and Nu distributions become more homogenous with increasing Reynolds numbers, Re. A recommendation is made that the DN plate be operated under moderate Re to achieve homogenous and enhanced heat transfer, given the allowable pressure drop.

Influence of Cross-Flow Induced Swirl and Impingement on Heat Transfer in an Internal Coolant Passage of a Turbine Airfoil

1999 ◽  
Author(s):  
Srinath V. Ekkad ◽  
Gautam Pamula ◽  
Sumanta Acharya
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Cross Flow ◽  
Reynolds Numbers ◽  
Transfer Enhancement ◽  
Feed System ◽  
Injection Angle ◽  
Nusselt Numbers ◽  
Flow Through ◽  
Transient Liquid Crystal Technique

Abstract Detailed heat transfer distributions are presented inside a two-pass coolant channel with crossflow-induced swirl and impingement. The crossflow is generated from one coolant passage to the adjoining coolant passage through a series of straight or angled holes along the dividing wall. The communicating holes provide for the flow turning from one passage to another typically achieved in a conventional design by a 180° U-bend. The holes direct the flow laterally from one passage to another, and depending on the injection angle, cause impingement and generate swirl. The heat transfer enhancement in the second pass is achieved by the combination of impingement and crossflow-induced swirl. Heat transfer distributions are presented on the sidewalls of the passages. Three different hole configurations are tested for three flow channel Reynolds numbers (Re = 10000–50000). The hole configurations were varied by angle of delivery and location on the divider wall. A transient liquid crystal technique is applied to measure the detailed heat transfer coefficient distributions inside the passages. Results for the three hole supply cases are compared with the results from the traditional 180° turn passage. Results show that the new feed system, from first pass to second pass using crossflow injection holes, produces significantly higher Nusselt numbers on the second pass walls. The enhancement is as high as 7–8 times greater than obtained in the second pass for a channel with a 180° turn. The additional pressure drop (rise in friction factor) caused by flow through the crossflow holes is compensated by the significant heat transfer enhancement obtained by the new configuration.

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