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.

Heat Transfer Enhancement in Narrow Diverging Channels

2013 ◽  
Vol 135 (4) ◽  
Author(s):  
Justin Lamont ◽  
Sridharan Ramesh ◽  
Srinath V. Ekkad ◽  
Anil Tolpadi ◽  
Christopher Kaminski ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Heat Transfer Enhancement ◽  
Color Change ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer

Detailed heat transfer coefficient distributions have been obtained for narrow diverging channels with and without enhancement features. The cooling configurations considered include rib turbulators and concavities (or dimples) on the main heat transfer surfaces. All of the measurements are presented at a representative Reynolds number of 28,000. Pressure drop measurements for the overall channel are also presented to evaluate the heat transfer enhancement geometry with respect to the pumping power requirements. The test models were studied for wall heat transfer coefficient measurements using the transient liquid crystal technique. The model wall inner surfaces were sprayed with thermochromic liquid crystals and a transient test was used to obtain the local heat transfer coefficients from the measured color change. An analysis of the results shows that the choice of designs is limited by the available pressure drop, even if the design provides significantly higher heat transfer coefficients. Dimpled surfaces provide appreciably high heat transfer coefficients and a reasonable pressure drop, whereas ribbed ducts provide significantly higher heat transfer coefficients and a higher overall pressure drop.

Heat Transfer Enhancement in Narrow Diverging Channels

2012 ◽  
Author(s):  
Justin Lamont ◽  
Sridharan Ramesh ◽  
Srinath V. Ekkad ◽  
Anil Tolpadi ◽  
Christopher Kaminski ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Heat Transfer Enhancement ◽  
Color Change ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients ◽  
High Heat Transfer

Detailed heat transfer coefficient distributions have been obtained for narrow diverging channels with and without enhancement features. The cooling configurations considered include rib turbulators and concavities (or dimples) on the main heat transfer surfaces. All the measurements are presented at a representative Reynolds number of 28,000. Pressure drop measurements for the overall channel are also presented to evaluate the heat transfer enhancement geometry with respect to pumping power requirements. The test models were studied for wall heat transfer coefficient measurements using the transient liquid crystal technique. The model wall inner surfaces were sprayed with thermochromic liquid crystals, and a transient test was used to obtain the local heat transfer coefficients from the measured color change. Analysis of results shows that choice of designs is limited by available pressure drop even if the design provides significantly higher heat transfer coefficients. Dimpled surfaces provide appreciably high heat transfer coefficients and reasonable pressure drop whereas ribbed ducts provide significantly higher heat transfer coefficients and higher overall pressure drop.

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 Between Blockages With Holes in a Rectangular Channel

2003 ◽  
Vol 125 (4) ◽  
pp. 587-594 ◽  
Author(s):  
S. W. Moon ◽  
S. C. Lau
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Transfer Enhancement ◽  
Rectangular Channel ◽  
Local Heat Transfer ◽  
Reynolds Numbers ◽  
Local Heat ◽  
Hole Array ◽  
Transfer Enhancement ◽  
Large Pressure

Experiments have been conducted to study steady heat transfer between two blockages with holes and pressure drop across the blockages, for turbulent flow in a rectangular channel. Average heat transfer coefficient and local heat transfer distribution on one of the channel walls between two blockages, and overall pressure drop across the blockages were obtained, for nine different staggered arrays of holes in the blockages and Reynolds numbers of 10,000 and 30,000. For the hole configurations studied, the blockages enhanced heat transfer by 4.6 to 8.1 times, but significantly increased the pressure drop. Smaller holes in the blockages caused higher heat transfer enhancement, but larger increase of the pressure drop than larger holes. The heat transfer enhancement was lower in the higher Reynolds number cases. Because of the large pressure drop, the heat transfer per unit pumping power was lower with the blockages than without the blockages. The local heat transfer was lower nearer the upstream blockage, the highest near the downstream blockage, and also relatively high in regions of reattachment of the jets leaving the upstream holes. The local heat transfer distribution was strongly dependent on the configuration of the hole array in the blockages. A third upstream blockage lowered both the heat transfer and the pressure drop, and significantly changed the local heat transfer distribution.

Heat Transfer and Pressure Drop Measurements in a High Aspect Ratio Channel With Circular Pins and Strip Fins

2019 ◽  
Vol 12 (3) ◽  
Author(s):  
Metapun Nuntakulamarat ◽  
Chao-Cheng Shiau ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Aspect Ratio ◽  
Heat Transfer Enhancement ◽  
High Aspect Ratio ◽  
Thickness Effect ◽  
Internal Cooling ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Pin Fin

Abstract This paper focuses on the measurements of heat transfer enhancement and pressure drop of different pin or fin configurations in a high aspect ratio (AR = 9.57/1.2) channel. Two different pin-fin shapes including circular pins and strip fins were studied. Different pin-fin spacings for circular pins (S/D = 2, 4) and strip fins (S/W = 8, 16) were investigated, respectively. In addition, the thickness effect of the strip fin was included in this study. The regionally averaged heat transfer measurement method was used to acquire the heat transfer coefficients on two opposite featured surfaces within the test channel. For each configuration, the tested Reynolds number was ranging from 20,000 to 80,000. The results indicate that the channel with circular pins has better heat transfer enhancement and higher pressure loss than their strip fins counterparts. However, the strip fins are considered better designs in terms of thermal performance. For the gas turbine designers aim at developing an improved internal cooling feature, this work demonstrates the great potential of the strip fins as a novel and effective cooling design compared with the conventional circular pins.

Numerical Simulation of Laminar Flow Heat Transfer Enhancement Using Surface Modification

2014 ◽  
Author(s):  
Abhijit S. Paranjape ◽  
Ninad C. Maniar ◽  
Deval A. Pandya ◽  
Brian H. Dennis
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Surface Modification ◽  
Laminar Flow ◽  
Heat Transfer Enhancement ◽  
Rectangular Channel ◽  
Longitudinal Vortex ◽  
Bottom Wall ◽  
Transfer Enhancement ◽  
Smooth Channel

Heat transfer augmentation techniques have gained great importance in different engineering applications to deal with thermal management issues. In this work, a numerical investigation was carried out to see the effects of a modified surface on the heat transfer enhancement compared to a smooth surface. In the first case, spherical dimple arrays were applied to the surface. The effects were observed for dimples on the bottom wall of a channel for a laminar airflow. The effects of a 21×7 staggered array and a 19×4 inline array on the bottom wall were investigated. In the second case, the heat exchange enhancement in a rectangular channel using longitudinal vortex generators (LVG) for a laminar flow was considered. In both cases, a 3D steady viscous computational fluid dynamics package with an unstructured grid was used to compute the flow and temperature field. The heat transfer characteristics were studied as a function of the Reynolds number based on the hydraulic diameter of the channel. The heat transfer was quantified by computing the surface averaged Nusselt number. The pressure drop and flow characteristics were also calculated. The Nusselt number was compared with that of a smooth channel without surface modification to assess the level of heat transfer enhancement.

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 by Delta-Wing-Generated Tip Vortices in Flat-Plate and Developing Channel Flows

2002 ◽  
Vol 124 (6) ◽  
pp. 1158-1168 ◽  
Author(s):  
M. C. Gentry ◽  
A. M. Jacobi
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Flat Plate ◽  
Heat Transfer Enhancement ◽  
Channel Flow ◽  
Delta Wing ◽  
Leading Edge ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Vortex Strength

Using delta wings placed at the leading edge of a flat plate, streamwise vortices are generated that modify the flow; the same wings are also used to modify a developing channel flow. Local and average measurements of convection coefficients are obtained using naphthalene sublimation, and the structure of the vortices is studied using flow visualization and vortex strength measurements. The pressure drop penalty associated with the heat transfer enhancement of the channel flow is also investigated. In regions where a vortex induces a surface-normal inflow, the local heat transfer coefficients are found to increase by as much as 300 percent over the baseline flow, depending on vortex strength and location relative to the boundary layer. Vortex strength increases with Reynolds number, wing aspect ratio, and wing attack angle, and the vortex strength decays as the vortex is carried downstream. Considering the complete channel surface, the largest spatially averaged heat average heat transfer enhancement is 55 percent; it is accompanied by a 100 percent increase in the pressure drop relative to the same channel flow with no delta-wing vortex generator.

Rib Spacing Effect on Heat Transfer and Pressure Loss in a Rotating Two-Pass Rectangular Channel (AR=1:2) With 45-Degree Angled Ribs

2006 ◽  
Author(s):  
Yao-Hsien Liu ◽  
Lesley M. Wright ◽  
Wen-Lung Fu ◽  
Je-Chin Han
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Thermal Performance ◽  
Rectangular Channel ◽  
Spacing Effect ◽  
Turbine Blades ◽  
Internal Cooling ◽  
Transfer Enhancement ◽  
Cooling Channels ◽  
Smooth Channel

Rib turbulators are commonly used to enhance the heat transfer within internal cooling passages of advanced gas turbine blades. Many factors affect the thermal performance of a cooling channel with ribs. This study experimentally investigates the effect of rib spacing on the heat transfer enhancement, pressure penalty, and thus the overall thermal performance in both rotating and non-rotating rectangular, cooling channels. In the 1:2 rectangular channels, 45° angled ribs are placed on the leading and trailing surfaces. The pitch of the ribs varies, so rib pitch-to-height (P/e) ratios of 10, 7.5, 5, and 3 are considered. Square ribs with a 1.59 mm × 1.59 mm cross-section are used for all spacings, so the height-to-hydraulic diameter (e/Dh) ratio remains constant at 0.094. With a constant rotational speed of 550 rpm and the Reynolds number ranging from 5000 to 40000, the rotation number in turn varies from 0.2 to 0.02. Because the skewed turbulators induce secondary flow along the length of the rib, the very close rib spacing of P/e = 3, has the best thermal performance in both rotating and non-rotating channels. This close spacing yields the greatest heat transfer enhancement, while the P/e = 5 spacing has the greatest pressure penalty. In addition, the effect of rotation is more pronounced in the channel with the rib spacing of 3. As more ribs are added, the channel is approaching a smooth channel, and the strength of the rotation induced vortices increases.

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