Heat transfer enhancement in a tube with twisted tape inserts placed separately from the tube wall

Bas, Halit; Özceyhan, Veysel

doi:10.1016/j.expthermflusci.2012.03.008

Cited by 185 publications

(49 citation statements)

References 37 publications

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“…The twisted tape could be attached to the tube wall using Teflon attachments manufactured according to twisted tape thickness and width to keep them separated from the tube wall as was done in a study by Bas and Ozceyhan [33] or using some other appropriate mechanism. With low twist ratios, the heat transfer performance is expected to increase, but the fluid friction will also increase.…”

Section: Physical Modelmentioning

confidence: 99%

“…The results from our numerical analysis are presented using the following parameters: The average heat transfer coefficient is given by The absorber tube's circumferential temperature difference is given as the difference between the maximum and minimum temperatures of the absorber tube according to ,max ,min rr TT   (33) The thermal enhancement factor χ for evaluating thermal performance at constant pumping is defined as [8] (…”

Section: Data Reductionmentioning

confidence: 99%

“…The Nusselt numbers increased by 171% and 182% for triple and quadruple twisted tapes while the corresponding increase in friction factors was 4.06 -7.02 times, respectively. Bas and Ozceyhan [33] presented an experimental investigation on the use of twisted tape inserts placed separately from the wall. Twist ratios of 2.0, 2.5, 3.0, 3.5 and 4.0, clearance ratios of 0.0178 and 0.0357 and Reynolds numbers in the range 5 132 and 24 989 were used.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Heat transfer and entropy generation in a parabolic trough receiver with wall-detached twisted tape inserts

Mwesigye

Bello‐Ochende

Meyer

2016

International Journal of Thermal Sciences

196

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In this paper, heat transfer enhancement in a parabolic trough receiver using wall-detached twisted tape inserts was numerically investigated. The resulting heat transfer, fluid friction and thermodynamic performance were determined and presented. The flow was considered fully developed turbulent, with Reynolds numbers in range 10 260 ≤ Re p ≤ 1 353 000 depending on the fluid temperature. The twisted tape's twist ratio and width ratio vary in the range 0.50-2.00 and 0.53-0.91, respectively. The numerical investigations are based on a finite volume method, with the realisable k-ε model for turbulence closure. The study shows considerable increase in heat transfer performance of about 169%, reduction in absorber tube's circumferential temperature difference up to 68% and increase in thermal efficiency up to 10% over a receiver with a plain absorber tube. An entropy generation analysis shows the existence of a Reynolds number for which there is minimum entropy generation for each twist ratio and width ratio. The optimal Reynolds number increases with increasing twist ratio and reducing width ratios. The maximum reduction in the entropy generation rate was about 58%. Correlations for heat transfer and fluid friction performance for the range of parameters considered were also derived and presented. Keywords

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Section: Physical Modelmentioning

confidence: 99%

Section: Data Reductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Heat transfer and entropy generation in a parabolic trough receiver with wall-detached twisted tape inserts

Mwesigye

Bello‐Ochende

Meyer

2016

International Journal of Thermal Sciences

196

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“…The pitch is chosen to be 2 for this application, as this has been shown to be effective for heat transfer for a variety of flow conditions [10]. The pressure drop of a 180 degree pipe bend (with no twisted tape insert) is calculated using [11].…”

Section: A Hydraulic Calculations -Analytical and Empericalmentioning

confidence: 99%

Modeling and Analysis of the W7-X High Heat-Flux Divertor Scraper Element

Lumsdaine

Boscary

Clark

et al. 2014

IEEE Trans. Plasma Sci.

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Abstract-The Wendelstein 7-X stellarator experiment is scheduled for the completion of device commissioning and the start of first plasma in 2015. At the completion of the first two operational phases, the inertially cooled test divertor unit will be replaced with an actively cooled high heat-flux divertor which will enable the device to increase its pulse length to steady-state plasma performance.Plasma simulations show that the evolution of bootstrap current in certain plasma scenarios produce excessive heat fluxes on the edge of the divertor targets. It is proposed to place an additional "scraper element" in the ten divertor locations to intercept some of the plasma flux and reduce the heat load on these divertor edge elements. Each scraper element may experience a 500 kW steady-state power load, with localized heat fluxes as high as 20 MW/m 2 . Computational analysis has been performed in order to examine the thermal integrity of the scraper element.The peak temperature in the CFC, the total pressure drop in the cooling water, and the increase in water temperature must all be examined to stay within specific design limits. Computational fluid dynamics (CFD) modeling is performed to examine the flow paths through the multiple monoblock fingers as well as the thermal transfer through the monoblock swirl tube channels.

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“…The enhancement of transport (mass or heat) in internal flows is a general topic and not only addressed in membrane channel flows. Thus, various methods have been proposed in literature, ranging from twisted tapes [19], internal fins, wire coil, mesh or brush inserts, up to displaced mixing devices such as spaced disks, spaced streamline shapes, flow twisting device [20] or louvered stripes, for a review of heat transfer enhancing methods see [21][22][23][24]. A second characteristic of the mass transfer in membranes is the high Schmidt number, in the order of thousand for system feed waters [25].…”

Section: Introductionmentioning

confidence: 99%

Entrance length effects on Graetz number scaling in laminar duct flows with periodic obstructions: Transport number correlations for spacer-filled membrane channel flows

Rohlfs

Lienhard

2016

International Journal of Heat and Mass Transfer

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Self-similarity and scaling laws are powerful tools in engineering and thus useful for the design of apparatus. This self-similarity is well understood for the heat and mass transfer in laminar empty channel flows, including the fully developed region as well as inlet length effects in the developing region (Graetz problem). In this study, we examine the validity of the scaling behavior arising from the Graetz solution for channel flows disturbed by periodic obstructions. Simulation results show that entrance length effects and scaling laws do not change due to the presence of obstructions if the flow field remains steady in time and the dimensionless inlet length is given by X T /D h ≈ C inl. ·Re·Pr, where C inl. ≈ 0.01 for the local and C inl. ≈ 0.03 for the average Nusselt number. The Nusselt number in the inlet region for an internal flow scales by Nu = (Re · Pr) 1/3 , similar to the empty channel flow (Shah and London, 1978). If the analogy between heat and mass transfer holds, same conclusions and relations are valid for the Sherwood number, Sh ∝ (Re · Sc) 1/3 , where Sc denotes the Schmidt number. In the fully developed region, the Nusselt number depends slightly on the Reynolds and Prandtl numbers owing to the loss in self-similarity of the velocity field (contrary to the empty channel flow). The limit of the classical self-similarity is the onset of temporal oscillations (instability) in the flow field. Beyond this limit, the length of the thermal entrance region is strongly reduced. Furthermore, a strong dependency of the Nusselt number in the fully developed region on the Prandtl number is found.

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Heat transfer enhancement in a tube with twisted tape inserts placed separately from the tube wall

Cited by 185 publications

References 37 publications

Heat transfer and entropy generation in a parabolic trough receiver with wall-detached twisted tape inserts

Heat transfer and entropy generation in a parabolic trough receiver with wall-detached twisted tape inserts

Modeling and Analysis of the W7-X High Heat-Flux Divertor Scraper Element

Entrance length effects on Graetz number scaling in laminar duct flows with periodic obstructions: Transport number correlations for spacer-filled membrane channel flows

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