Flow and heat transfer of nanofluid in a channel partially filled with porous media considering turbulence effect in pores

The flow and heat transfer of Al2O3–water nanofluid in a channel partially filled with porous media is investigated numerically. The turbulence effect in the porous media is taken under consideration in this article. A simple case is simulated first to evaluate the accuracy of the results in comparison with the available data. The turbulent kinetic energy profile is investigated at a flow cross section. The results show that the maximum turbulent kinetic energy occurs in the clear fluid region in the vicinity of the porous media region. The turbulent kinetic energy is a decreasing function of the porosity of the porous medium. The effect of porosity on the variation of turbulent kinetic energy decreases with the increase in the porosity of the porous medium. The turbulent kinetic energy in clear fluid and porous media regions decreases with the increase in nanofluid concentration from 0.01 to 0.03, and it increases with the increase in nanofluid concentration from 0.03 to 0.05. The temperature of the nanofluid increases with the increase in the nanofluid concentration and decrease in the porosity of porous media. It is shown that for this case, with the increase in nanofluid concentration and porosity of porous media, the skin friction coefficient increases and the Nusselt number decreases.

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Discussion on improved method of turbulence model for supercritical water flow and heat transfer

Thermal Science ◽

10.2298/tsci190813007w ◽

2020 ◽

Vol 24 (5 Part A) ◽

pp. 2729-2741

Author(s):

Zhenchuan Wang ◽

Guoli Qi ◽

Meijun Li

Keyword(s):

Heat Transfer ◽

Reynolds Number ◽

Kinetic Energy ◽

Turbulent Kinetic Energy ◽

Turbulence Model ◽

Buoyancy Effect ◽

Improved Method ◽

Production Term ◽

Flow And Heat Transfer ◽

Effect Model

The turbulence model fails in supercritical fluid-flow and heat transfer simulation, owing to the drastic change of thermal properties. The inappropriate buoyancy effect model and the improper turbulent Prandtl number model are several of these factors lead to the original low-Reynolds number turbulence model unable to predict the wall temperature for vertically heated tubes under the deteriorate heat transfer conditions. This paper proposed a simplified improved method to modify the turbulence model, using the generalized gradient diffusion hypothesis approximation model for the production term of the turbulent kinetic energy due to the buoyancy effect, using a turbulence Prandtl number model for the turbulent thermal diffusivity instead of the constant number. A better agreement was accomplished by the improved turbulence model compared with the experimental data. The main reason for the over-predicted wall temperature by the original turbulence model is the misuse of the buoyancy effect model. In the improved model, the production term of the turbulent kinetic energy is much higher than the results calculated by the original turbulence model, especially in the boundary-layer. A more accurate model for the production term of the turbulent kinetic energy is the main direction of further modification for the low Reynolds number turbulence model.

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Statistics of Mathematical Two-Scale Closure of Momentum, Heat and Charge Transport Problems With Stochastic Orientation of Porous Medium Capillaries

10.1115/imece2001/htd-24157 ◽

2001 ◽

Author(s):

V. S. Travkin ◽

K. Hu ◽

I. Catton

Keyword(s):

Heat Transfer ◽

Porous Medium ◽

Porous Media ◽

Volume Averaging ◽

Governing Equations ◽

Rigorous Approach ◽

Flow And Heat Transfer ◽

Model Flow ◽

History Of ◽

Transport Problems

Abstract The history of stochastic capillary porous media transport problem treatments almost corresponds to the history of porous media transport developments. Volume Averaging Theory (VAT), shown to be an effective and rigorous approach for study of transport (laminar and turbulent) phenomena, is used to model flow and heat transfer in capillary porous media. VAT based modeling of pore level transport in stochastic capillaries results in two sets of scale governing equations. This work shows how the two scale equations could be solved and how the results could be presented using statistical analysis. We demonstrate that stochastic orientation and diameter of the pores are incorporated in the upper scale simulation procedures. We are treating this problem with conditions of Bi for each pore is in a range when Bi ≳ 0.1 which allows even greater distinction in assessing an each additional differential, integral, or integral-differential term in the VAT equations.

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Non-Linear k-ε-ζ-f Model Sensitized to Rotation for Blade Turbine Internal Cooling

Volume 5A: Heat Transfer ◽

10.1115/gt2018-76643 ◽

2018 ◽

Author(s):

Domenico Borello ◽

Alessandro Salvagni

Keyword(s):

Heat Transfer ◽

Kinetic Energy ◽

Turbulent Kinetic Energy ◽

Mutual Influence ◽

Plane Channel ◽

Suction Side ◽

Quadratic Model ◽

Internal Cooling ◽

Flow And Heat Transfer ◽

Non Linear

The need to study flow and heat transfer in turbine blade cooling design calls to develop appropriate modelling approaches able to return accurate predictions at a reduced computational costs. Here we propose and scrutinize a quadratic version of the well-known k-ε-ζ-f RANS turbulence models, aiming at sensitizing the model to the effect of rotation in configurations mimicking the flow in turbine internal cooling. Starting from the evidence that rotation modified turbulent flow through a turbulence suppression (enhancement) on the stabilized (destabilized) surface, we modified the Cμ coefficient present in the formulation of turbulent viscosity introducing a dependence on the strain and vorticity tensors, the latter explicitly including solid body rotation. The proposed model was tested on plane channel and square-sectioned duct flows, and then used for simulating a rib-duct rotating channel. Results are assessed against DNS literature data and properly developed LES computations, by examining flow variables, heat transfer and turbulence budgets. We demonstrate that, as for the channel flows, the proposed quadratic model is able to accurately reproduce velocity, temperature and turbulent variables at various angular velocity regimes. In the duct flow the flow is subjected to the mutual influence vorticity induced by rotation and turbulence anisotropy developing close the walls. In particular, the non-linear rotation-sensitized model is able to reproduce the near-wall turbulent kinetic energy distribution close to the suction side, returning a zero value in the mid-span and a small peak close to the wall on the suction side. Turbulent kinetic energy and temperature budgets analysis demonstrates the capabilities of the model in describing all the terms in the equations. Also if some tuning of the model is required, these analysis showed very encouraging results. In fact if the basic mechanisms of turbulence and heat transfer are properly predicted, then it can be expected that the model can be successfully applied to a set of different cases. For such reason, the model was applied to the analysis of flow and heat transfer in a rotating ribduct with reasonably results.

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Comparison of Numerical Models of Flow and Heat Transfer Through Porous Medium in a Vertical Channel

IOP Conference Series Earth and Environmental Science ◽

10.1088/1755-1315/850/1/012023 ◽

2021 ◽

Vol 850 (1) ◽

pp. 012023

Author(s):

G Trilok ◽

N Gnanasekaran

Keyword(s):

Heat Transfer ◽

Porous Medium ◽

Porous Media ◽

Equilibrium Model ◽

Vertical Channel ◽

Modelling Technique ◽

Local Thermal Equilibrium ◽

Pore Density ◽

Thermal Models ◽

Flow And Heat Transfer

Abstract Porous medium modelling technique has opened up ways for number of numerical studies to investigate the performance of many devices that involve heat exchanging process. Such modelling technique not only avoids huge cost and time as compared to experimental analysis but also makes computationally less time-consuming as in case of numerical simulation by exact geometry modelling of porous materials. In this regard the present paper analyses two different thermal models namely local thermal equilibrium model and local thermal non equilibrium model along with two different flow models namely Darcy flow model and Darcy extended Forchheimer model. Suitability of the mentioned models in predicting heat transfer through metal foam and wire mesh porous medium is examined subjected to variations in structural aspects of the porous medium that could be primarily represented by variation in porosity and pore density. For this purpose, a vertical channel subjected to constant heat flux capable of housing porous medium reported in literature is numerically modelled and air flow is numerically simulated through the channel. A variety of structural configuration (combination of different porosity and pore density) of the mentioned porous media are considered and among the mentioned flow and thermal models, best suited models for predicting flow and heat transfer through such medium are identified with appropriate justifications. It is revealed from the present study that, Darcy-Forchheimer and LTNE models are best suited to predict flow and heat transfer through porous media than the basic Darcy and LTE models.

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A Model for Diffusion of Turbulent Kinetic Energy for Calculation of Momentum and Heat Transfer in High FST Flows

Volume 3: Turbo Expo 2002, Parts A and B ◽

10.1115/gt2002-30204 ◽

2002 ◽

Author(s):

Savas Yavuzkurt ◽

Ganesh R. Iyer

Keyword(s):

Heat Transfer ◽

Experimental Data ◽

Boundary Layer ◽

Friction Coefficient ◽

Kinetic Energy ◽

Turbulent Kinetic Energy ◽

Free Stream ◽

Skin Friction Coefficient ◽

Data Sets ◽

Free Stream Turbulence

A modified low-Reynolds number k-ε model (named YI-diffn. model) for predicting effects of high free stream turbulence (FST) on momentum transport and heat transfer in a flat plate turbulent boundary layer is presented. An additional turbulent kinetic energy (TKE) diffusion term incorporating the effects of FST intensity (velocity scale) and length scale was included in the TKE equation. This model was developed with experience from many years of experimental and theoretical studies in the area of high FST flows. The constant cμ in the equation for the transport coefficient μt was modified using experimental data. These modifications were applied to a well-tested k-ε model (K-Y Chien called KYC in this study) under high FST conditions (initial FST intensity, Tui > 5%). Models were implemented in a 2-D boundary layer code. The high FST zero pressure gradient data sets against which the predictions (in the turbulent region) were compared had initial FST intensities of 6.53% and 25.7%. In a previous paper, it was shown that predictions of the original k-ε models became poorer (over prediction up to more than 50% for skin friction coefficient and Stanton number, and under prediction of TKE up to more than 50%) as FST increased to about 26%. In comparison, the new model developed here provided excellent results (within ±3% of experimental data) for skin friction coefficient and Stanton number for both the data sets. TKE results were excellent for Tui = 6.53%, but have scope for improvement in the case of Tui = 25.7%. The present model incorporates physics of transport of free stream turbulence in turbulence modeling and provides a new method for simulating flows with high FST. Future work will focus upon improving the model further and applying it to practical applications like flow over gas turbine blades.

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A critical review on the applications of fluid-structure interaction in porous media

International Journal of Numerical Methods for Heat &amp Fluid Flow ◽

10.1108/hff-07-2019-0592 ◽

2019 ◽

Vol 30 (1) ◽

pp. 308-327 ◽

Cited By ~ 1

Author(s):

Khalil Khanafer ◽

K. Vafai

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Porous Medium ◽

Porous Media ◽

Biomedical Applications ◽

Arterial Wall ◽

Content Type ◽

Future Studies ◽

Structure Interaction ◽

Flow And Heat Transfer

Purpose This study aims to investigate a critical review on the applications of fluid-structure interaction (FSI) in porous media. Design/methodology/approach Transport phenomena in porous media are of continuing interest by many researchers in the literature because of its significant applications in engineering and biomedical sectors. Such applications include thermal management of high heat flux electronic devices, heat exchangers, thermal insulation in buildings, oil recovery, transport in biological tissues and tissue engineering. FSI is becoming an important tool in the design process to fully understand the interaction between fluids and structures. Findings This study is structured in three sections: the first part summarizes some important studies on the applications of porous medium and FSI in various engineering and biomedical applications. The second part focuses on the applications of FSI in porous media as related to hyperthermia. The third part of this review is allocated to the applications of FSI of convection flow and heat transfer in engineering systems filled with porous medium. Research limitations/implications To the best knowledge of the present authors, FSI analysis of turbulent flow in porous medium never been studied, and therefore, more attention should be given to this area in any future studies. Moreover, more studies should also be conducted on mixed convective flow and heat transfer in systems using porous medium and FSI. Practical implications The wall of the blood vessel is considered as a flexible multilayer porous medium, and therefore, rigid wall analysis is not accurate, and therefore, FSI should be implemented for accurate predictions of flow and hemodynamic stresses. Social implications The use of porous media theory in biomedical applications received a great attention by many investigators in the literature (Khanafer and Vafai, 2006a; Al-Amiri et al., 2014; Lasiello et al., 2016a, Lasiello et al., 2016b; Lasiello et al., 2015; Chung and Vafai, 2013; Mahjoob and Vafai, 2009; Yang and Vafai, 2008; Yang and Vafai, 2006; Ai and Vafai, 2006). A comprehensive review was conducted by Khanafer and Vafai (2006b) summarizing various studies associated with magnetic field imaging and drug delivery. The authors illustrated that the tortuosity and porosity had a profound effect on the diffusion process within the brain. AlAmiri et al. (2014) conducted a numerical study to investigate the effect of turbulent pulsatile flow and heating technique on the thermal distribution within the arterial wall. The results of that investigation illustrated that local heat flux variation along the bottom layer of the tumor was greater for the low-velocity condition. Yang and Vafai (2006) presented a comprehensive four-layer model to study low-density lipoprotein transport in the arterial wall coupled with a lumen (Figure 1). All the four layers (endothelium, intima, internal elastic lamina and media) were modeled as a homogenous porous medium. Originality/value Future studies on the applications of FSI in porous media are recommended in this review.

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Simulation of turbulent flow and heat transfer over a backward facing step with ribs turbulators

Thermal Science ◽

10.2298/tsci090926044m ◽

2011 ◽

Vol 15 (1) ◽

pp. 245-255 ◽

Cited By ~ 5

Author(s):

Khudheyer Mushatet

Keyword(s):

Heat Transfer ◽

Nusselt Number ◽

Kinetic Energy ◽

Turbulent Kinetic Energy ◽

Control Volume ◽

Step Height ◽

Staggered Grid ◽

Backward Facing Step ◽

Flow And Heat Transfer ◽

Contraction Ratio

Simulation is presented for a backward facing step flow and heat transfer inside a channel with ribs turbulators. The problem was investigated for Reynolds numbers up to 32000. The effect of a step height, the number of ribs and the rib thickness on the flow and thermal field were investigated. The computed results are presented as streamlines counters, velocity vectors and graphs of Nusselt number and turbulent kinetic energy variation. A control volume method employing a staggered grid techniques was imposed to discretize the governing continuity, full Navier Stockes and energy equations. A computer program using a SIMPLE algorithm was developed to handle the considered problem. The effect of turbulence was modeled by using a k-? model with its wall function formulas. The obtained results show that the strength and size of the re-circulation zones behind the step are increased with the increase of contraction ratio(i.e. with the increase of a step height). The size of recirculation regions and the reattachment length after the ribs are decreased with increasing of the contraction ratio. Also the results show that the Reynolds number and contraction ratio have a significant effect on the variation of turbulent kinetic energy and Nusselt number.

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