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Antonio Barletta - One of the best experts on this subject based on the ideXlab platform.
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Effects of Viscous Dissipation on the convective instability of viscoelastic mixed convection flows in porous media
International Journal of Heat and Mass Transfer, 2014Co-Authors: L. S. De B. Alves, Antonio Barletta, S.c. Hirata, Mohamed Najib OuarzaziAbstract:Abstract The thermal instability induced by small-amplitude perturbations superposed to the basic horizontal through flow in a plane porous layer (Prats problem) is here revisited. The fluid saturating the porous medium is assumed to be viscoelastic, and described through the Oldroyd-B model. The effect of Viscous Dissipation is taken into account. The main features of the linear instability are first described for the special case of negligible Viscous Dissipation, namely in the limit of a vanishing Gebhart number. Transverse rolls emerge as the selected normal modes at onset of convection. This same feature also arises when Viscous Dissipation is taken into account. In the general case, neutral stability curves as well as critical values of the Darcy–Rayleigh number, wave number and frequency are obtained by the numerical solution of an eigenvalue problem. It is shown that an adequate description of the combined effects of viscoelasticity and Viscous Dissipation can be obtained with the large Peclet number approximation. Such an approximation allows a simplified numerical solution and an optimised scaling of the parameters governing the transition to convective instability.
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Mixed convection with Viscous Dissipation in an inclined porous channel with isoflux impermeable walls
Heat and Mass Transfer, 2007Co-Authors: Antonio Barletta, E. Magyari, Ioan Pop, L. StoreslettenAbstract:Combined forced and free convection flow in a fluid saturated inclined plane channel is investigated by taking into account the effect of Viscous Dissipation. Steady parallel flow is considered assuming that the temperature gradient in the parallel flow direction is constant, and the channel walls are subject to uniform symmetric heat fluxes. Two possible formulations of the Darcy–Boussinesq scheme are considered, based on two different choices of the reference temperature for modelling buoyancy. The first choice is a constant temperature, while the second is a streamwise changing temperature. It is shown that both approaches substantially agree in the formulation of the balance equations for the range of values of the Darcy–Rayleigh number such that Viscous Dissipation is important. The boundary value problem is solved analytically for any tilt angle, revealing that it admits dual solutions for assigned values of the governing parameters. The rather important effect of Viscous Dissipation in the special case of adiabatic channel walls is outlined.
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Mixed convection with Viscous Dissipation in an inclined channel with prescribed wall temperatures
International Journal of Heat and Mass Transfer, 2001Co-Authors: Antonio Barletta, Enzo ZanchiniAbstract:Abstract The fully developed laminar mixed convection with Viscous Dissipation in an inclined channel with prescribed wall temperatures is studied analytically. The mean fluid temperature is assumed as the reference temperature. Two perturbation expansions are considered. In the first, the forced convection with Viscous Dissipation is assumed as a starting condition and the effects of buoyancy for fixed values of the Brinkman number are studied. In the second, starting from the solution for mixed convection without Viscous Dissipation, the effects of the Brinkman number for fixed values of the Grashof number are analysed. The different solution methods allow a cross-check of the results. The dimensionless velocity field, the dimensionless temperature field, the dimensionless pressure field, the friction factors and the Nusselt numbers are determined and discussed. The results show that Viscous Dissipation enhances the effects of buoyancy and vice versa.
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Laminar convection in a vertical channel with Viscous Dissipation and buoyancy effects
International Communications in Heat and Mass Transfer, 1999Co-Authors: Antonio BarlettaAbstract:Abstract The fully developed and laminar convection in a parallel-plate vertical channel is investigated by taking into account both Viscous Dissipation and buoyancy. Uniform and symmetric temperatures are prescribed at the channel walls. The velocity field is considered as parallel. A perturbation method is employed to solve the momentum balance equation and the energy balance equation. A comparison with the velocity and temperature profiles in the case of laminar forced convection with Viscous Dissipation is performed in order to point out the effect of buoyancy. The case of convective boundary conditions is also discussed.
D A Nield - One of the best experts on this subject based on the ideXlab platform.
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thermosolutal convective instability and Viscous Dissipation effect in a fluid saturated porous medium
International Journal of Heat and Mass Transfer, 2011Co-Authors: A. Barletta, D A NieldAbstract:Abstract The combined effects of the double-diffusion and of the Viscous Dissipation on the convective instability in a fluid-saturated porous medium with a basic horizontal throughflow are investigated. A horizontal porous layer with an impermeable adiabatic lower wall and an impermeable isothermal upper wall is considered. The parallel boundary walls are assumed to have uniform, but unequal, concentrations of the solute. A linear stability analysis is carried out both numerically and by a first-order perturbation method. General disturbances having the form of oblique rolls are considered, reducing either to longitudinal rolls or to transverse rolls in the special cases of roll axes parallel or orthogonal to the basic flow direction, respectively. It is shown that the combined effects of Viscous Dissipation and mass diffusion may lead to the instability of the basic horizontal flow. Either the longitudinal rolls or the transverse rolls may be the preferred modes of instability depending on the value of the Viscous Dissipation parameter Ξ. The longitudinal rolls are the most unstable when Ξ
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mixed convection with Viscous Dissipation and pressure work in a lid driven square enclosure
International Journal of Heat and Mass Transfer, 2009Co-Authors: A. Barletta, D A NieldAbstract:Abstract Buoyant laminar flow in a square lid-driven enclosure is analysed. The vertical sides are kept isothermal at different temperatures, while the horizontal sides are insulated. Assisting mixed convection flow due to uniform motion of the top side is considered. The governing balance equations are solved numerically by employing a Galerkin finite element method. The effects of Viscous Dissipation and pressure work are taken into account. In order to investigate the influence of these effects, the Nusselt number is evaluated with respect to the heat fluxes at both vertical sides, for different values of the Rayleigh number and of the Peclet number based on the lid velocity. Two sample fluids are considered: a gas and a highly Viscous liquid. In the framework of the Oberbeck–Boussinesq approximation, a comparison is made between three different energy balance models: (A) enthalpy formulation (pressure work and Viscous Dissipation are included); (B) internal-energy formulation (Viscous Dissipation is included); (C) both pressure work and Viscous Dissipation are neglected. It is shown that, in the absence of a lid motion, the three models yield substantially the same predictions. On the other hand, when the forced flow induced by the lid motion becomes sufficiently large, the three models yield discrepant results, thus implying that pressure work and Viscous Dissipation are not negligible. Moreover, it is shown that, in this case, model (A) yields unphysical results, while model (B) leads to reasonable predictions.
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the modeling of Viscous Dissipation in a saturated porous medium
Journal of Heat Transfer-transactions of The Asme, 2007Co-Authors: D A NieldAbstract:A critical review is made of recent studies of the modeling of Viscous Dissipation in a saturated porous medium, with applications to either forced convection or natural convection. Alternative forms of the Viscous Dissipation function are discussed. Limitations to the concept of fully developed convection are noted. Special attention is focused on the roles of Viscous Dissipation and work done by pressure forces (flow work) in natural convection in a two-dimensional box with either lateral or bottom heating.
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resolution of a paradox involving Viscous Dissipation and nonlinear drag in a porous medium
Transport in Porous Media, 2000Co-Authors: D A NieldAbstract:The modelling of Viscous Dissipation in a porous medium saturated by an incompressible fluid is discussed, for the case of Darcy, Forchheimer and Brinkman models. An apparent paradox relating to the effect of inertial effects on Viscous Dissipation is resolved, and some wider aspects of resistance to flow (concerning quadratic drag and cubic drag) in a porous medium are discussed. Criteria are given for the importance or otherwise of Viscous Dissipation in various situations.
Zhenglun Alan Wei - One of the best experts on this subject based on the ideXlab platform.
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the advantages of Viscous Dissipation rate over simplified power loss as a fontan hemodynamic metric
Annals of Biomedical Engineering, 2018Co-Authors: Zhenglun Alan Wei, Mike Tree, Phillip M Trusty, Shelly Singhgryzbon, Ajit P YoganathanAbstract:Flow efficiency through the Fontan connection is an important factor related to patient outcomes. It can be quantified using either a simplified power loss or a Viscous Dissipation rate metric. Though practically equivalent in simplified Fontan circulation models, these metrics are not identical. Investigation is needed to evaluate the advantages and disadvantages of these metrics for their use in in vivo or more physiologically-accurate Fontan modeling. Thus, simplified power loss and Viscous Dissipation rate are compared theoretically, computationally, and statistically in this study. Theoretical analysis was employed to assess the assumptions made for each metric and its clinical calculability. Computational simulations were then performed to obtain these two metrics. The results showed that apparent simplified power loss was always greater than the Viscous Dissipation rate for each patient. This discrepancy can be attributed to the assumptions derived in theoretical analysis. Their effects were also deliberately quantified in this study. Furthermore, statistical analysis was conducted to assess the correlation between the two metrics. Viscous Dissipation rate and its indexed quantity show significant, strong, linear correlation to simplified power loss and its indexed quantity (p 0.99) under certain assumptions. In conclusion, Viscous Dissipation rate was found to be more advantageous than simplified power loss as a hemodynamic metric because of its lack of limiting assumptions and calculability in the clinic. Moreover, in addition to providing a time-averaged bulk measurement like simplified power loss, Viscous Dissipation rate has spatial distribution contours and time-resolved values that may provide additional clinical insight. Finally, Viscous Dissipation rate could maintain the relationship between Fontan connection flow efficiency and patient outcomes found in previous studies. Consequently, future Fontan hemodynamic studies should calculate both simplified power loss and Viscous Dissipation rate to maintain ties to previous studies, but also provide the most accurate measure of flow efficiency. Additional attention should be paid to the assumptions required for each metric.
A. Barletta - One of the best experts on this subject based on the ideXlab platform.
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The energy method analysis of the Darcy–Bénard problem with Viscous Dissipation
Continuum Mechanics and Thermodynamics, 2020Co-Authors: A. Barletta, G. MuloneAbstract:A nonlinear analysis of the effect of Viscous Dissipation on the Rayleigh–Bénard instability in a fluid saturated porous layer is performed. The saturated medium is modelled through Darcy’s law, with the layer bounded by two parallel impermeable walls kept at different uniform temperatures, so that heating from below is supplied. While it is well known that Viscous Dissipation does not influence the linear threshold to instability, a rigorous nonlinear analysis of the instability when Viscous Dissipation is taken into account is still lacking. This paper aims to fill this gap. The energy method is employed to prove the nonlinear conditional stability of the basic conduction state. In other words, it is shown that a finite initial perturbation exponentially decays in time provided that its initial amplitude is smaller than a given finite value.
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Effects of Viscous Dissipation on the convective instability of viscoelastic mixed convection flows in porous media
International Journal of Heat and Mass Transfer, 2014Co-Authors: L. S. De B. Alves, A. Barletta, Silvia C Hirata, Najib OuarzaziAbstract:The thermal instability induced by small-amplitude perturbations superposed to the basic horizontal through flow in a plane porous layer (Prats problem) is here revisited. The fluid saturating the porous medium is assumed to be viscoelastic, and described through the Oldroyd-B model. The effect of Viscous Dissipation is taken into account. The main features of the linear instability are first described for the special case of negligible Viscous Dissipation, namely in the limit of a vanishing Gebhart number. Transverse rolls emerge as the selected normal modes at onset of convection. This same feature also arises when Viscous Dissipation is taken into account. In the general case, neutral stability curves as well as critical values of the Darcy-Rayleigh number, wave number and frequency are obtained by the numerical solution of an eigenvalue problem. It is shown that an adequate description of the combined effects of viscoelasticity and Viscous Dissipation can be obtained with the large Péclet number approximation. Such an approximation allows a simplified numerical solution and an optimised scaling of the parameters governing the transition to convective instability.
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thermosolutal convective instability and Viscous Dissipation effect in a fluid saturated porous medium
International Journal of Heat and Mass Transfer, 2011Co-Authors: A. Barletta, D A NieldAbstract:Abstract The combined effects of the double-diffusion and of the Viscous Dissipation on the convective instability in a fluid-saturated porous medium with a basic horizontal throughflow are investigated. A horizontal porous layer with an impermeable adiabatic lower wall and an impermeable isothermal upper wall is considered. The parallel boundary walls are assumed to have uniform, but unequal, concentrations of the solute. A linear stability analysis is carried out both numerically and by a first-order perturbation method. General disturbances having the form of oblique rolls are considered, reducing either to longitudinal rolls or to transverse rolls in the special cases of roll axes parallel or orthogonal to the basic flow direction, respectively. It is shown that the combined effects of Viscous Dissipation and mass diffusion may lead to the instability of the basic horizontal flow. Either the longitudinal rolls or the transverse rolls may be the preferred modes of instability depending on the value of the Viscous Dissipation parameter Ξ. The longitudinal rolls are the most unstable when Ξ
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mixed convection with Viscous Dissipation and pressure work in a lid driven square enclosure
International Journal of Heat and Mass Transfer, 2009Co-Authors: A. Barletta, D A NieldAbstract:Abstract Buoyant laminar flow in a square lid-driven enclosure is analysed. The vertical sides are kept isothermal at different temperatures, while the horizontal sides are insulated. Assisting mixed convection flow due to uniform motion of the top side is considered. The governing balance equations are solved numerically by employing a Galerkin finite element method. The effects of Viscous Dissipation and pressure work are taken into account. In order to investigate the influence of these effects, the Nusselt number is evaluated with respect to the heat fluxes at both vertical sides, for different values of the Rayleigh number and of the Peclet number based on the lid velocity. Two sample fluids are considered: a gas and a highly Viscous liquid. In the framework of the Oberbeck–Boussinesq approximation, a comparison is made between three different energy balance models: (A) enthalpy formulation (pressure work and Viscous Dissipation are included); (B) internal-energy formulation (Viscous Dissipation is included); (C) both pressure work and Viscous Dissipation are neglected. It is shown that, in the absence of a lid motion, the three models yield substantially the same predictions. On the other hand, when the forced flow induced by the lid motion becomes sufficiently large, the three models yield discrepant results, thus implying that pressure work and Viscous Dissipation are not negligible. Moreover, it is shown that, in this case, model (A) yields unphysical results, while model (B) leads to reasonable predictions.
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Effect of Viscous Dissipation on thermally developing forced convection duct flows (Research Report 13/2005)
ETH - Chair of Physics of Buildings, 2005Co-Authors: A. Barletta, E. Magyari, B. KellerAbstract:A self-contained treatment of laminar duct-flow heat transfer is performed. The presentation includes all the necessary definitions and results which are required for the treatment of the thermal entrance problem in a duct with an arbitrary cross section. The special cases of a plane-parallel channel and of a circular duct are discussed in detail. A comparison is made between the results obtained when Viscous Dissipation is taken into account and those which are obtained when this effect is neglected. The treatment of the effect of Viscous Dissipation presented here differs from previous approaches available in the literature. The difference relies mainly in the prescription of the initial condition at the entrance cross-section. Unlike in similar treatments available in the literature, the effect of Viscous Dissipation is taken into account self-consistently, i.e. both upstream and downstream of the entrance section
Michele Dragoni - One of the best experts on this subject based on the ideXlab platform.
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Role of Viscous Dissipation in the dynamics of lava flows with power-law rheology
Journal of Volcanology and Geothermal Research, 2011Co-Authors: Antonello Piombo, Michele DragoniAbstract:Abstract We model a lava flow as a one-dimensional flow of a pseudoplastic fluid with Viscous Dissipation. The flow is horizontally unbounded and is driven downslope by the gravity force. We consider a power-law constitutive equation and we take into account the temperature dependence of the rheological parameters. Given an effusion rate and an initial temperature at the eruption vent, the flow is assumed to cool down by heat radiation. We calculate the heat produced by Viscous Dissipation as a function of lava temperature and effusion rate. The cooling rate is calculated as a function of the surface temperature and flow rate. Viscous Dissipation reduces the cooling rate by an amount which is independent of flow rate. We evaluate the effect of Viscous Dissipation on the flow thickness and velocity. The effect of Dissipation is to decrease the flow thickness and to increase the flow velocity. The effect on flow thickness is greater for smaller flow rates, while the effect on velocity is greater for larger effusion rates. In principle, the model provides a method for estimating the flow rate from in-field measurements of distances and temperatures.
