Numerical modeling and simulation of heat transfer and fluid flow in a two-dimensional sudden expansion model using porous insert behind that

Zhao, Ziqiang

doi:10.1007/s10973-020-09505-1

Cited by 17 publications

(10 citation statements)

References 66 publications

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“…The best performance number (1.33) is obtained with porous baffles of Da = 4.38 × 10 -5 . This observation concurs with the conclusion of Zhao [20] that even low-permeable baffles could augment heat transfer at the expense of little pressure drop.…”

Section: Effects Of Porous Baffle Darcy Numbersupporting

confidence: 92%

“…Such a PN indicates that for the same pump differential pressure, the average convection to conduction heat transfer is up to 88% better when a pair of similar porous baffles are used. Zhao [20] reported that for a backward facing step flow with constant bottom wall temperature conditions at the expanded channel, a PN of > 140% is reached when a porous baffle is mounted on the bottom wall in a channel of Ld /S = 30, and at Re = 100. On the other hand, multiple baffles are prohibitive when the Reynolds number is low (e.g.…”

Section: Effects Of Channel Lengthmentioning

confidence: 99%

“…They noted that with an appropriate length and porosity, a porous insert reduces or eliminates the lower wall recirculation zone. Zhao [20] further highlighted the effectiveness of porous devices by computing the thermal-fluid phenomenon over a sudden expansion with a porous insert located right after the step. After several trials of parameters, they indicated through a performance number (the ratio of the Nusselt number improvement to pressure drop increment) metric that up to 40% improvement in heat transfer could be achieved at no cost of pressure drop increment.…”

Section: Introductionmentioning

confidence: 99%

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Numerical Analysis of Enhanced Heat Transfer Using a Pair of Similar Porous Baffles in a Backward-Facing Step Flow

Arthur¹,

Schiele²

2021

JFFHMT

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Baffles have long been known to be useful in enhancing heat transfer in channels with sudden expansions. However, their utility has been limited due to the increased differential pressure they incur in the flow. In this work, a pair of porous baffles is proposed to provide a solution to this problem. It is based on a finite-element numerical simulation of heat transfer and fluid flow through a two-dimensional channel with a backward-facing step. The baffles are modelled as matrices of two-dimensional rods arrayed downstream of the step, and on the top and bottom walls of the channel. Nondimensionalized parameters considered are the Reynolds number, Re (= 100 to 1000), normalized porous matrix location xp/S (= 0.5 to 6), normalized porous block length Lp/S (= 0.5 to 2.5), Darcy Number, Da (= 10 -2 to 10 -6 ), and normalized channel downstream length Ld/S (= 5 to 30). Results show that compared to the case of an unobstructed channel, the installation of porous baffles on both channel walls can generate up to 200% improvement in heat transfer. Optimal heat transfer effect with minimal differential power requirement is attained when the porous baffle length is half the step height S, and located 2S downstream from the step. Augmented heat transfer outcomes with minimal penalty of pressure drop are also reached at Re = 1000 and for Lu /H = 5. For such a case, for the same pressure drop requirement, convection to conduction heat transfer is 88% better when a pair of porous baffles are used, compared to an unobstructed flow.

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Section: Effects Of Porous Baffle Darcy Numbersupporting

confidence: 92%

Section: Effects Of Channel Lengthmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Numerical Analysis of Enhanced Heat Transfer Using a Pair of Similar Porous Baffles in a Backward-Facing Step Flow

Arthur¹,

Schiele²

2021

JFFHMT

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“…That work ultimately showed that compared to a flow without baffles, the inclusion of porous 147-2 baffles resulted in about 35% improvement of heat transfer at a Reynolds number of 500. Very recently, Zhao [7] studied the fluid flow and heat transfer over a backward-facing step with a porous insert mounted just after the step. That work showed that even a porous baffle with low permeability could enhance heat transfer, while incurring only a little higher pressure drop.…”

Section: Introductionmentioning

confidence: 99%

Heat Transfer Augmentation Using Dissimilar Porous Baffles in a Backward-Facing Step Flow

Arthur¹

2021

Proceedings of the 8th International Conference on Fluid Flow, Heat and Mass Transfer (FFHMT'21)

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This paper reports a numerical investigation of the use of a pair of baffles of dissimilar porosity as heat augmentation devices in a backward-facing step flow in a two-dimensional channel. The specific goal of this study is to explore the possibility of providing a pressure penalty-free heat transfer enhancement using such a pair of porous baffles in a laminar forced convection flow. The numerical simulations are done using a finite element-based COMSOL Multiphysics commercial software. The parameters studied include Reynolds number (100, 200, 300, 400, 500), porous baffle solid volume fraction ϕ (0.031, 0.125, 0.500), and the porous baffle streamwise location (0.5, 1.0, 1.5, 2.0, 2.5, 3.0 times the channel height). The results show that the porous baffles result in increments of the local peak Nusselt Numbers and global Nusselt numbers by up to 200% and 85% respectively with an increase in Reynolds number from 100 to 500. For the same pressure drop requirement, the average convection to conduction heat transfer is up to 16% better when a pair of baffles are used, compared to an unobstructed flow. For the channel tested in this work, the best location for optimal heat augmentation with least pressure penalty is reached both porous baffles are located at a streamwise distance ~2 times the channel's expanded height.

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“…A number of numerical studies have shown the prospect of using porous-like inserts to achieve this purpose at minimal differential pressure cost. However, this has been analysed mostly for laminar flows [1,2]. Studies of turbulent flow with porous inserts in backward-facing step flows are rare [3].…”

mentioning

confidence: 99%

Reduction of the Recirculation Region of a Backward-Facing Step Flow

Arthur¹

2022

International Conference on Fluid Flow, Heat and Mass Transfer

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Backward-facing step flow is a common flow phenomenon in engine inlets, combustor flame holders, and turbine blades. The flow is generally associated with an upstream flow that results in a separated shear layer as the flow transcends the step. Beneath this shear layer is a recirculation region characterized by a system of vortices whose extent is a function of the geometry of the flow system and the inlet flow conditions. As the recirculation region can be a zone of unwanted localized heating / cooling and a major contribution to head losses, it is often desirable to reduce the extent of this region through active or passive means. A number of numerical studies have shown the prospect of using porous-like inserts to achieve this purpose at minimal differential pressure cost. However, this has been analysed mostly for laminar flows [1,2]. Studies of turbulent flow with porous inserts in backward-facing step flows are rare [3]. To fill this apparent need, an experimental study of the reduction of the recirculation region for a turbulent flow using a thin porous insert is presented.The study is accomplished using an open channel backward-facing step flow system in a flume. The expansion ratio (i.e. expanded depth to upstream depth ratio) of the system is 1.3 and the aspect ratio (i.e. ratio of channel width to step height h) is 3.1. With a downstream depth of approximately 0.1m and the maximum velocity of the approach flow 0.280m/s, the Froude number and the Reynolds number (based on maximum velocity and step height) is maintained at ~ 0.28 and 6900 respectively. A porous mat is installed behind the step. The mat is of open surface area 40%, filling fraction 3%, length 8h, thickness 0.12h, and covering the entire width of the test channel. The effect of the porous mat is tested by modifying the location of the mat at 6h and 3h respectively. The results are compared with measurements without any porous insert. The measurements are based on velocity data obtained from the application of a high-resolution planar particle image velocimetry in multiple planes within the recirculation region, and along the central span of the channel flow.An examination of the reattachment lengths of the test results show that by locating the porous insert at a streamwise distance of 6h or less behind the step, the streamwise extent of the recirculation region can be reduced. While this reduction is only marginal when the porous insert is located at 6h, it is over 20% at 3h. At the reattachment region, the increment in mean wall-normal velocity due to the porous mat is significant, as are the decrements of turbulence intensities and Reynolds stresses. Consequently, there is a significant cut-back in the production of turbulence kinetic energy due to the presence of the porous insert. Regardless of these differences, the transport of turbulence kinetic energy appears to be unaffected by the presence of a porous insert. Two-point correlations of the velocity fluctuations show that the sizes of the coherent structures and their convection b...

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Numerical modeling and simulation of heat transfer and fluid flow in a two-dimensional sudden expansion model using porous insert behind that

Cited by 17 publications

References 66 publications

Numerical Analysis of Enhanced Heat Transfer Using a Pair of Similar Porous Baffles in a Backward-Facing Step Flow

Numerical Analysis of Enhanced Heat Transfer Using a Pair of Similar Porous Baffles in a Backward-Facing Step Flow

Heat Transfer Augmentation Using Dissimilar Porous Baffles in a Backward-Facing Step Flow

Reduction of the Recirculation Region of a Backward-Facing Step Flow

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