Numerical Study on Heat Transfer and Resistance of a Tube Fitted With New Twisted Tapes for Lubricating Oil

2017 ◽  
Author(s):  
Xiaoya Liu ◽  
Ming Ding ◽  
Haozhi Bian ◽  
Changqi Yan ◽  
Chun Li
Keyword(s):  
Heat Transfer ◽  
Performance Evaluation ◽  
Numerical Study ◽  
Evaluation Criterion ◽  
Lubricating Oil ◽  
Twisted Tape ◽  
Steam Turbines ◽  
Transition Flow ◽  
Performance Evaluation Criterion ◽  
Twisted Tapes

Oil coolers are widely-used in nuclear power plants which cool oil flowed through the bearing of steam turbines to a suitable temperature in order for the safe operation of steam turbines. Owing to the high viscosity, the flow state of oil is generally laminar flow or transition flow, which easily leads to poor heat transfer capability and thus a large volume of the oil coolers. The insertion of twisted tapes in circular tube is a passive method widely-used for enhancing heat transfer of laminar or transition flow. However, little research focuses on the heat transfer of highly-viscous fluids inside tube using the twisted tapes. The article will present the numerical simulations of the swirling flow induced by a new coaxial cross twisted tape inserts in a heat transfer tube with lubricating oil. The effects of the clearance ratios and twist ratios on oil side heat transfer coefficient, friction factor and performance evaluation criterion will be numerically investigated using CFD computer software STAR-CCM+. The clearance ratios are 0.077, 0.154 and 0.231. The twist ratios are 2.0 and 4.0. The boundary condition of simulation is constant wall temperature for the Reynolds number ranging from 200 to 1300. The results indicate that the new coaxial cross twisted tapes are efficacious in enhancing the heat transfer of the lubricating oil inside tube. When the clear ratio is 0.077, the effect of heat transfer enhancement of the coaxial cross twisted tapes is better than that of traditional twisted tapes. Furthermore, the highest performance evaluation criterion is up to 2.3.

scholarly journals Investigation of Overlapped Twisted Tapes Inserted in a Double-Pipe Heat Exchanger Using Two-Phase Nanofluid

Nanomaterials ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 1656 ◽  
Author(s):  
Mehdi Ghalambaz ◽  
Hossein Arasteh ◽  
Ramin Mashayekhi ◽  
Amir Keshmiri ◽  
Pouyan Talebizadehsardari ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Performance Evaluation ◽  
Heat Exchanger ◽  
Evaluation Criterion ◽  
Twisted Tape ◽  
Performance Evaluation Criterion ◽  
Twisted Tapes ◽  
Double Pipe ◽  
Pipe Heat

This study investigated the laminar convective heat transfer and fluid flow of Al2O3 nanofluid in a counter flow double-pipe heat exchanger equipped with overlapped twisted tape inserts in both inner and outer tubes. Two models of the same (co-swirling twisted tapes) and opposite (counter-swirling twisted tapes) angular directions for the stationary twisted tapes were considered. The computational fluid dynamic simulations were conducted through varying the design parameters, including the angular direction of twisted tape inserts, nanofluid volume concentration, and Reynolds number. It was found that inserting the overlapped twisted tapes in the heat exchanger significantly increases the thermal performance as well as the friction factor compared with the plain heat exchanger. The results indicate that models of co-swirling twisted tapes and counter-swirling twisted tapes increase the average Nusselt number by almost 35.2–66.2% and 42.1–68.7% over the Reynolds number ranging 250–1000, respectively. To assess the interplay between heat transfer enhancement and pressure loss penalty, the dimensionless number of performance evaluation criterion was calculated for all the captured configurations. Ultimately, the highest value of performance evaluation criterion is equal to 1.40 and 1.26 at inner and outer tubes at the Reynolds number of 1000 and the volume fraction of 3% in the case of counter-swirling twisted tapes model.

Laminar Heat Transfer Performances in a Tube with Center-Cleared Twisted Tape of Alternate Axes

2014 ◽  
Vol 1070-1072 ◽  
pp. 1803-1807
Author(s):  
Li Xiang Chen
Keyword(s):  
Heat Transfer ◽  
Numerical Simulation ◽  
Nusselt Number ◽  
Heat Transfer Performance ◽  
Twisted Tape ◽  
Transfer Performance ◽  
Performance Evaluation Criterion ◽  
Twisted Tapes ◽  
Tubular Flow ◽  
Underlying Mechanisms

To improve the heat transfer performance of laminar tubular flow, a center-cleared twisted tape of alternate axes was developed as inserts. Numerical simulation was conducted to investigate the effect of dislocation angle of twisted tapes on the thermo-hydraulic performances. The numerical results show that, the largest Nusselt number occurs at a dislocation angle of 60°. The friction factorfis relatively larger than that when the dislocation angle is 0°, and it exhibits an obvious increment with the dislocation angle. From the value of performance evaluation criterion (PEC), the best thermo-hydraulic performance is achieved at a 60° dislocation angle. The underlying mechanisms are analyzed in terms of flow field and temperature field.

Tapered Twisted Tape Inserts for Enhanced Heat Transfer

2015 ◽  
Vol 138 (1) ◽  
Author(s):  
B. V. N. Ramakumar ◽  
J. D. Arsha ◽  
Praveen Tayal
Keyword(s):  
Heat Transfer ◽  
Numerical Study ◽  
Flow Direction ◽  
Twisted Tape ◽  
Complex Flow ◽  
Ansys Fluent ◽  
Taper Angle ◽  
Twisted Tapes ◽  
Plain Tube ◽  
Enhancing Heat Transfer

Insertion of twisted tapes in smooth channels is one of the passive methods used for enhancing heat transfer. Flow and associated heat transfer characteristics of these channels are very complex. Understanding this complex flow is helpful while designing new passive methods. Numerical methods like computational fluid dynamics (CFD) are gaining much popularity for analyzing and designing these heat transfer enhancement techniques. This paper focuses on such a numerical study. The preliminary study is focused on development of numerical methodology through validation. Successive studies are aimed at development of an innovative design for twisted tape. Twisted tapes with taper angle (tapered twisted tapes, i.e., tape width decreases along the flow direction) are developed and evaluated on the basis of the performance of these tapes with those of conventional tapes. A circular tube with tapered twisted tape with a twist ratio of 3 and taper angles of 0.3, 0.4, 0.5, 0.6, and 0.7 is considered for this study along with a plain tube. Three Reynolds numbers (Re) of 8545, 11393, and 13333 are considered to examine the sensitivity of the performance. Simulations are performed with a commercially available CFD tool, ansys fluent (v14.0). Heat transfer and pressure drop results are presented in the form of Nusselt number (Nu), friction factor (f), and overall enhancement ratio (η). An increase of 17% in overall enhancement is predicted with taper angle of 0.5.

scholarly journals Performance Evaluation Criterion at Equal Pumping Power for Enhanced Performance Heat Transfer Surfaces

2013 ◽  
Vol 2013 ◽  
pp. 1-9 ◽  
Author(s):  
Rajendra Karwa ◽  
Chandresh Sharma ◽  
Nitin Karwa
Keyword(s):  
Heat Transfer ◽  
Performance Evaluation ◽  
Thermal Performance ◽  
Heat Exchangers ◽  
Literature Survey ◽  
Evaluation Criterion ◽  
Rectangular Duct ◽  
Pumping Power ◽  
Design Constraints ◽  
Performance Evaluation Criterion

The existing equations for the thermal performance evaluation, at equal pumping power for the artificially roughened and smooth surfaced multitube and rectangular duct heat exchangers, have been critically reviewed because the literature survey indicates that a large number of researchers have not interpreted these equations correctly. Three of the most widely used equations have been restated with clearly defined constraints and conditions for their application. Two new equations have been developed for the design constraints not covered earlier.

scholarly journals Numerical Investigation of Forced Convective Heat Transfer and Performance Evaluation Criterion of Al2O3/Water Nanofluid Flow inside an Axisymmetric Microchannel

Symmetry ◽  
2020 ◽  
Vol 12 (1) ◽  
pp. 120 ◽  
Author(s):  
Misagh Irandoost Shahrestani ◽  
Akbar Maleki ◽  
Mostafa Safdari Shadloo ◽  
Iskander Tlili
Keyword(s):  
Heat Transfer ◽  
Performance Evaluation ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Convective Heat Transfer ◽  
Evaluation Criterion ◽  
Forced Convective Heat Transfer ◽  
Performance Evaluation Criterion ◽  
Macro Scale ◽  
The Heat Transfer Coefficient

Al2O3/water nanofluid conjugate heat transfer inside a microchannel is studied numerically. The fluid flow is laminar and a constant heat flux is applied to the axisymmetric microchannel’s outer wall, and the two ends of the microchannel’s wall are considered adiabatic. The problem is inherently three-dimensional, however, in order to reduce the computational cost of the solution, it is rational to consider only a half portion of the axisymmetric microchannel and the domain is revolved through its axis. Hence. the problem is reduced to a two-dimensional domain, leading to less computational grid. At the centerline (r = 0), as the flow is axisymmetric, there is no radial gradient (∂u/∂r = 0, v = 0, ∂T/∂r = 0). The effects of four Reynolds numbers of 500, 1000, 1500, and 2000; particle volume fractions of 0% (pure water), 2%, 4%, and 6%; and nanoparticles diameters in the range of 10 nm, 30 nm, 50 nm, and 70 nm on forced convective heat transfer as well as performance evaluation criterion are studied. The parameter of performance evaluation criterion provides valuable information related to heat transfer augmentation together with pressure losses and pumping power needed in a system. One goal of the study is to address the expense of increased pressure loss for the increment of the heat transfer coefficient. Furthermore, it is shown that, despite the macro-scale problem, in microchannels, the viscous dissipation effect cannot be ignored and is like an energy source in the fluid, affecting temperature distribution as well as the heat transfer coefficient. In fact, it is explained that, in the micro-scale, an increase in inlet velocity leads to more viscous dissipation rates and, as the friction between the wall and fluid is considerable, the temperature of the wall grows more intensely compared with the bulk temperature of the fluid. Consequently, in microchannels, the thermal behavior of the fluid would be totally different from that of the macro-scale.

scholarly journals Influence of Nanoparticle Shape Factor on Convective Heat Transfer of Water-Based ZnO Nanofluids. Performance Evaluation Criterion

2011 ◽  
pp. 106-112
Author(s):  
S. Ferrouillat ◽  
A. Bontemps ◽  
O. Poncelet ◽  
J. A. Gruss ◽  
O. Soriano
Keyword(s):  
Heat Transfer ◽  
Performance Evaluation ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Colloidal Suspensions ◽  
Evaluation Criterion ◽  
Transfer Coefficients ◽  
Nanoparticle Shape ◽  
Nusselt Numbers ◽  
Performance Evaluation Criterion

The convective heat transfer of ZnO/water colloidal suspensions is investigated experimentally to appreciate the influence of two shapes of nanoparticles. Pressure drop and heat transfer coefficients have been measured at two different inlet temperatures (20, 50°C) in heating and/or cooling conditions at various flow rates (200 < Re < 15,000). The Reynolds and Nusselt numbers have been determined by using thermal conductivity and viscosity measured in the same conditions as those in tests. The results obtained are compared with classical correlations. An energetic Performance Evaluation Criterion (PEC) has been defined to compare heat transfer rate to pumping power.

Thermohydraulics of Laminar Flow Through Rectangular and Square Ducts With Transverse Ribs and Twisted Tapes

2006 ◽  
Vol 128 (10) ◽  
pp. 1070-1080 ◽  
Author(s):  
Debashis Pramanik ◽  
Sujoy K. Saha
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Laminar Flow ◽  
Laminar Flows ◽  
Short Length ◽  
Full Length ◽  
Twisted Tape ◽  
Twisted Tapes ◽  
Square Ducts ◽  
Better Than

The heat transfer and the pressure drop characteristics of laminar flow of viscous oil through rectangular and square ducts with internal transverse rib turbulators on two opposite surfaces of the ducts and fitted with twisted tapes have been studied experimentally. The tapes have been full length, short length, and regularly spaced types. The transverse ribs in combination with full-length twisted tapes have been found to perform better than either ribs or twisted tapes acting alone. The heat transfer and the pressure drop measurements have been taken in separate test sections. Heat transfer tests were carried out in electrically heated stainless steel ducts incorporating uniform wall heat flux boundary conditions. Pressure drop tests were carried out in acrylic ducts. The flow was periodically fully developed in the regularly spaced twisted-tape elements case and decaying swirl flow in the short-length twisted tapes case. The flow characteristics are governed by twist ratio, space ratio, and length of twisted tape, Reynolds number, Prandtl number, rod-to-tube diameter ratio, duct aspect ratio, rib height, and rib spacing. Correlations developed for friction factor and Nusselt number have predicted the experimental data satisfactorily. The performance of the geometry under investigation has been evaluated. It has been found that on the basis of both constant pumping power and constant heat duty, the regularly spaced twisted-tape elements in specific cases perform marginally better than their full-length counterparts. However, the short-length twisted-tape performance is worse than the full-length twisted tapes. Therefore, full-length twisted tapes and regularly spaced twisted-tape elements in combination with transverse ribs are recommended for laminar flows. However, the short-length twisted tapes are not recommended.

Analytical Prediction of Heat Transfer in Tape Generated Swirl Flow

2017 ◽  
Author(s):  
R. J. Yadav ◽  
Sandeep Kore ◽  
V. N. Riabhole
Keyword(s):  
Heat Transfer ◽  
Circular Tube ◽  
Swirl Flow ◽  
Twisted Tape ◽  
Analytical Prediction ◽  
Transfer Coefficients ◽  
Numerical Predictions ◽  
Twisted Tapes ◽  
Wide Range ◽  
Prandtl Numbers

Heat transfer and pressure drop characteristics in a circular tube with twisted tapes have been investigated experimentally and numerically using different working fluids by many researchers for wide range of Reynolds number. The swirl was generated by tape inserts of various twist ratios. The various twist ratios are considered Many researchers formed generalized correlations to predict friction factors and convective heat transfer coefficients with twisted tapes in a tube for a wide range of Reynolds numbers and Prandtl numbers. Satisfactory agreement was obtained between the present correlations and the data of others validate the proposed correlations. The experimental or numerical predictions were compared with earlier correlations revealing good agreement between them. From the literature review it is observed that most studies are mainly focused on the heat transfer enhancement using twisted tape by experimental or numerical solution. An investigation with analytical approach is rarely reported. Therefore, the main aim of the present work is to form a correlation from theoretical approach for Nusselt number for circular tube with twisted tape. Application of dimensional analysis to heat transfer in tape generated swirl flow is carried out.

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