Enhanced Heat Transfer in Single-Phase Forced Convection in Tubes due to Helical Swirl Generated by Twisted-Tape Inserts

2012 ◽  
Author(s):  
Arthur E. Bergles ◽  
Raj M. Manglik
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Single Phase ◽  
Fluid Motion ◽  
High Heat ◽  
Twisted Tape ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Heat Exchanger Design ◽  
High Heat Transfer

Very high heat transfer enhancement can be achieved in single-phase flows by using twisted-tape inserts in circular tubes. The primary convection mechanism is the generation of helical swirl or secondary fluid motion that is induced by the helical curvature of the tape insert. This promotes cross-stream mixing and sharper wall gradients, which are further aided by the increased flow velocity due to the tube partitioning and blockage along with an effectively longer helical flow length. These phenomena are scaled for both laminar and turbulent flow regimes, and an evaluation of the transition is also given to highlight the damping effects of tape-generated swirl. The nature of swirl and its dimensionless scaling, and concomitant development of predictive correlations for heat transfer coefficients and friction factors are discussed. Finally, a brief discussion of the quantification of heat transfer enhancement by means of twisted tapes is given so as to extend their application in heat exchanger design.

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.

Boiling Heat Transfer Enhancement by Controllable Tailoring of the TPL

2010 ◽  
Author(s):  
Alexander Ustinov ◽  
Jovan Mitrovic
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Boiling Heat Transfer ◽  
Heat Fluxes ◽  
Thermal Engineering ◽  
Metallic Ions ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Treatment Technology ◽  
High Heat Transfer

Novel surface treatment technology was developed in the University of Paderborn in partnership with MiCryon Technik GmbH, Quedlinburg, Germany. The technology allows creation of micro-pin structures, which enhance the boiling heat transfer up to 18 times in comparison with a smooth surface, and provide an independency of the surface superheat on the applied heat flux [1–6]. The micro pins as basic structure elements can be created with the diameters of 0.1 μm to 25 μm at pins density ranging up to 109 pins/cm2. Such pin structures are created by electro-deposition of metallic ions on the basic surface. The microstructure provides for the very first time in thermal engineering a possibility to adjust the available length of the three phase line (TPL) on demand, correspondingly tailoring the shape of a boiling curve. The TPL, formed by the micro pins piercing the vapor-liquid interface, acts as an extremely efficient heat sink, providing high heat transfer coefficients and the constancy of the wall superheat at heat fluxes up to 125 kW/m2. Present article delivers the summary on boiling experiments performed with the novel microstructure, and reveals the quantitative dependencies of the heat transfer enhancement rate on the TPL length, having the pressure and the liquid type as further parameters. A newly discovered phenomenon of the vapor bubble chains formation on microstructured surfaces is discussed as well. Experiments were conducted with the refrigerants R134a, R141b and the fluorocarbon liquid FC-3284 at pressures, ranging between 0.5 bar and 9 bar.

Numerical Studies on Heat Transfer and Friction Factor Characteristics of a Tube Fitted With Helical Twisted Tape Without Core-Rod Inserts

2010 ◽  
Author(s):  
Zhichun Liu ◽  
Xiaoyu Zhang ◽  
Wei Liu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Friction Factor ◽  
High Efficiency ◽  
Three Dimensional ◽  
Twisted Tape ◽  
Transfer Enhancement ◽  
Transfer Coefficients ◽  
Turbulence Analysis ◽  
Core Rod

The principles of heat transfer enhancement in the core flow of tube have been proposed to improve the temperature uniformity and reduce flow resistance, which is different from that of heat transfer enhancement in the boundary flow of tube. Helical twisted tape inserts with four different widths (w = 7.5mm, 12mm, 15mm and 20mm) have been investigated for different inlet volume-flow rates ranging from 200L/h to 500L/h. A three-dimensional turbulence analysis of heat transfer and fluid flow is performed by numerical simulation. The simulation results show that the average overall heat transfer coefficients in circular plain tubes are enhanced with helical twisted tape of different widths by as much as 220∼390% at a constant tube-side temperature and the friction factor are enhanced by as much as 50% to 790%. The PEC value of the helical twisted tape inserts of different width varies between 1.60 and 3.15. Physical quantity synergy analysis is also performed. The synergy angles α, β, γ and θ are calculated, and the numerical results verify the synergy regulation among physical quantities of fluid particle in the flow field of convective heat transfer, which can guide the optimum design for better heat transfer units and high-efficiency heat exchangers.

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 by Artificial Roughness at Reynolds Numbers Related With Laminar and Transitional Regimes for High-Viscous Liquids

2010 ◽  
Author(s):  
Mikhail A. Gotovsky ◽  
Sergey A. Isaev
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Enhancement ◽  
Reynolds Numbers ◽  
High Heat ◽  
Artificial Roughness ◽  
Transfer Enhancement ◽  
Reynolds Analogy ◽  
Transition Range ◽  
Viscous Liquids ◽  
High Heat Transfer

Artificial roughness (AR) formed by annular rolling or dimpling is one of the most well-known examples of Reynolds analogy (RA) breaking in a favor of heat transfer. Surfaces which can be called ARPD - Artificial Roughness, are manufactured by wall Pressure Deformation. ARPD surfaces have some similar thermal hydraulic properties which permit to unite them in the common group. General characteristics of ARPD surfaces are considered here. But the main attention is paid to such surface performance for coolants with high Prandtl numbers. It is important that Reynolds numbers must be close sufficiently to its critical value for smooth tube. Some experimental data show that extremely high heat transfer enhancement ratio can be obtained under such conditions for substantially less pressure loss ratio increase. Similar qualitative results obtained for several types of ARPD — dimpled, annular rolled and spirally corrugated tubes — are demonstrated. These results are related partially with critical Reynolds number decrease and partially with specific character of heat transfer evolution in laminar–turbulent transition range for high-viscous liquids. Such enhancement method can be used effectively for heat exchangers with high-viscous liquids (oils, for example).

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.

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