Performance evaluation criteria for enhanced heat transfer surfaces

Zimparov, Ventsislav D.; Vulchanov, N.L.

doi:10.1016/0017-9310(94)90069-8

Cited by 63 publications

(20 citation statements)

References 7 publications

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“…N s,en should be less than 1 for better thermodynamic performance [34,[45][46][47][48] For convection heat transfer problems the entropy generation per unit length (S' gen ) was given by Bejan According to Kock and Herwig [40], for heat transfer and fluid flow problems involving complex geometries and complex boundary conditions, the analytical method in Eq. (15) gives large deviations compared with a method that determines the local entropy generation in the domain.…”

Section: Entropy Generationmentioning

confidence: 99%

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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

205

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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: Entropy Generationmentioning

confidence: 99%

“…Another way of assessing the performance of enhancement techniques is the consideration of the entropy generation rates as a result of applying the enhancement technique [34,46,48]. With this, the aim is to minimise the irreversibilities and the technique with the lowest entropy generation rates is desirable.…”

Section: Entropy Generationmentioning

confidence: 99%

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

205

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“…Energy or entropy criteria summarizing the effects of pressure drop and heat transfer enhancement-see, for example, Zimparov and Vulchanov [22]-are not usually as important when deciding whether static mixers or inverters are to be applied in a heat exchanger retrofit. Only in the case of a new design, and if there are no specific restrictions on geometry, fouling etc., is it useful to compare the case of a long empty pipe and a shorter pipe with inverters.…”

Section: Performance Evaluation Criterionmentioning

confidence: 99%

Heat Transfer Enhancement in a Pipe Using a Flow Inverter

Žitný

Luong

Šesták

2009

Heat Transfer Engineering

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Flow inversion, transferring a liquid from the wall region toward the center of the pipe or from the axis toward the heat transfer surface, improves heat transfer in the laminar flow regime. While a fully developed velocity profile is quickly established, a thin thermal boundary layer is preserved for a considerable distance in the pipe behind the flow inverter for highly viscous liquids. Thus the pressure drop is increased only locally (by the inverter itself), while heat transfer enhancement is also seen in a long straight section of the pipe. Two original flow inverter designs were tested in a long pipe (3 m in length) heated by condensing steam, using starch molasses as a working medium. Experiments carried out in the range of Reynolds number 4-60 and Graetz number 150-700 resulted in an increase of 20-35% in the heat transfer coefficient, accompanied by a 30-40% increase in the pressure drop. The experimental results confirm the numerical model prediction (within an extendedReynolds number range starting from 0.1). Thus an almost 40% increase in heat transfer can be expected at the optimal Graetz number in the range 50-100, using only one flow inverter located in the middle of a sufficiently long pipe.

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“…[5][6][7][8][9][10]). The field covers two main aspects of this class of flow systems: fluid flow and heat transfer performance, and ways (criteria) of evaluating performance [11][12][13][14][15]. The general trend in the field is to develop heat exchangers that offer better performance.…”

Section: Introductionmentioning

confidence: 99%

Counterflow heat exchanger with core and plenums at both ends

Bejan

Alalaimi

Lorente

et al. 2016

International Journal of Heat and Mass Transfer

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a b s t r a c tThis paper illustrates the morphing of flow architecture toward greater performance in a counterflow heat exchanger. The architecture consists of two plenums with a core of counterflow channels between them. Each stream enters one plenum and then flows in a channel that travels the core and crosses the second plenum. The volume of the heat exchanger is fixed while the volume fraction occupied by each plenum is variable. Performance is driven by two objectives, simultaneously: low flow resistance and low thermal resistance. The analytical and numerical results show that the overall flow resistance is the lowest when the core is absent, and each plenum occupies half of the available volume and is oriented in counterflow with the other plenum. In this configuration, the thermal resistance also reaches its lowest value. These conclusions hold for fully developed laminar flow and turbulent flow through the core. The curve for effectiveness vs number of heat transfer units (N tu ) is steeper (when N tu < 1) than the classical curves for counterflow and crossflow.

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Performance evaluation criteria for enhanced heat transfer surfaces

Cited by 63 publications

References 7 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

Heat Transfer Enhancement in a Pipe Using a Flow Inverter

Counterflow heat exchanger with core and plenums at both ends

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