scholarly journals A Pore-Scale Investigation of the Transient Response of Forced Convection in Porous Media to Inlet Ramp Inputs

2020 ◽  
Vol 142 (11) ◽  
Author(s):  
Rabeeah Habib ◽  
Bijan Yadollahi ◽  
Nader Karimi
Keyword(s):  
Reynolds Number ◽  
Porous Media ◽  
Forced Convection ◽  
Transient Response ◽  
Temperature Fields ◽  
Navier Stokes ◽  
Pore Scale ◽  
Staggered Arrangement ◽  
Energy Equations ◽  
Convection In Porous Media

Abstract This paper investigates the transient response of forced convection of heat in a reticulated porous medium through taking a pore-scale approach. The thermal system is subject to a ramp disturbance superimposed on the entrance flow temperature/velocity. The developed model consisted of ten cylindrical obstacles aligned in a staggered arrangement with set isothermal boundary conditions. A few types of fluids, along with different values of porosity and Reynolds number, are considered. Assuming a laminar flow, the unsteady Navier Stokes and energy equations are solved numerically. The temporally developing flow and temperature fields as well as the surface-averaged Nusselt numbers are used to explore the transient response of the system. Also, a response lag ratio (RLR) is defined to further characterize the transient response of the system. The results reveal that an increase in amplitude increases the RLR. Nonetheless, an increase in ramp duration decreases the RLR, particularly for high-density fluids. Interestingly, it is found that the Reynolds number has almost negligible effects upon RLR. This study clearly reflects the importance of conducting pore-scale analyses for understanding the transient response of heat convection in porous media.

Effects of Important Parameters on the Transition from Forced to Mixed Convection Flow in a Square Cavity

2021 ◽  
Vol 406 ◽  
pp. 36-52
Author(s):  
Sofiane Boulkroune ◽  
Omar Kholai ◽  
Brahim Mahfoud
Keyword(s):  
Reynolds Number ◽  
Prandtl Number ◽  
Mixed Convection ◽  
Forced Convection ◽  
Temperature Fields ◽  
Navier Stokes ◽  
Convection Flow ◽  
Square Cavity ◽  
Left Wall ◽  
Energy Equations

Combined free and forced convection in a square cavity filled with a viscous fluid characterized by a small Prandtl number is studied numerically. The left wall is moving with a constant velocity v and is maintained at a local cold temperature Tc, while the right wall is fixed and maintained at a local hot temperature Th (Tc <Th). The top and bottom walls of the cavity is assumed to be adiabatic. The governing Navier-Stokes, and energy equations along with appropriate boundary conditions are solved using the finite-volume method. The flow and temperature fields are presented by stream function and isotherms, respectively. The effects of important parameters such as Reynolds number, Prandtl number, and Grashof number on the transition from forced convection to mixed convection are investigated. Results indicate that increasing Reynolds number results to fluid acceleration and, thus, to flow transition. Results also show that Grashof and Prandtl's numbers influenced the conditions for the transition to the mixed convection regime.

scholarly journals A pore-scale assessment of the dynamic response of forced convection in porous media to inlet flow modulations

2020 ◽  
Vol 153 ◽  
pp. 119657 ◽  
Author(s):  
Rabeeah Habib ◽  
Nader Karimi ◽  
Bijan Yadollahi ◽  
Mohammad Hossein Doranehgard ◽  
Larry K.B. Li
Keyword(s):  
Porous Media ◽  
Dynamic Response ◽  
Forced Convection ◽  
Pore Scale ◽  
Inlet Flow ◽  
Scale Assessment ◽  
Convection In Porous Media

Dendritic growth of an elliptical paraboloid with forced convection in the melt

1989 ◽  
Vol 208 ◽  
pp. 575-593 ◽  
Author(s):  
Ramagopal Ananth ◽  
William N. Gill
Keyword(s):  
Reynolds Number ◽  
Dendritic Growth ◽  
Moving Boundary ◽  
Solid Phase ◽  
Three Dimensional ◽  
Temperature Fields ◽  
Navier Stokes ◽  
Energy Equations ◽  
Theory And Experiments ◽  
Elliptical Paraboloid

All experimental observations of the growth of fully developed dendritic ice crystals indicate that the shape of the tip region is an elliptical paraboloid. Therefore, moving-boundary solutions of the three-dimensional Navier-Stokes and energy equations are obtained here for the shape-preserving growth of isothermal elliptical paraboloids by using the Oseen approximation which is valid for the low-Reynolds-number viscous flows which prevail in dendritic growth. Explicit expressions for the flow and the temperature fields are derived in a simple way using Ivantsov's method. It is shown that the growth Péclet number, PG, is a function of the aspect ratio A, the Stefan number St, the Reynolds number Re, and the Prandtl number Pr. As the Reynolds number increases PG becomes linear in St, less dependent on A and ultimately varies roughly as Re½.A comparison between the exact solutions given here and the experiments of Kallungal (1974) indicate that A decreases as Re increases. This result agrees qualitatively with the experiments of Kallungal (1974) and Chang (1985). The differences between theory and experiments for Re > 10−3 may be due to attachment kinetic resistance to growth along the c-axis and capillary effects at the tip which make ice dendrites non-isothermal and create conduction in the solid phase. However, more accurate simultaneous measurements of R1 and R2 are needed to determine definitively the mechanisms responsible for these deviations between theory and experiment.

On Combined Free and Forced Convection in Channels

1960 ◽  
Vol 82 (3) ◽  
pp. 233-238 ◽  
Author(s):  
L. N. Tao
Keyword(s):  
Forced Convection ◽  
Rectangular Channel ◽  
Complex Function ◽  
Vertical Channel ◽  
Temperature Fields ◽  
Parallel Plates ◽  
Free And Forced Convection ◽  
Energy Equations ◽  
Helmholtz Wave Equation ◽  
Transfer Problems

The heat-transfer problems of combined free and forced convection by a fully developed laminar flow in a vertical channel of constant axial wall temperature gradient with or without heat generations are approached by a new method. By introducing a complex function which is directly related to the velocity and temperature fields, the coupled momentum and energy equations are readily combinable to a Helmholtz wave equation in the complex domain. This greatly reduces the complexities of the problems. For illustrations, the cases of flows between parallel plates and in a rectangular channel are treated. It shows that this method is more direct and powerful than those of previous investigations.

scholarly journals Numerical study of forced convection heat transfer over three cylinders in staggered arrangement immersed in porous media

2018 ◽  
Vol 22 (1 Part B) ◽  
pp. 467-475 ◽  
Author(s):  
Habib-Olah Sayehvand ◽  
Sakene Yari ◽  
Parsa Basiri
Keyword(s):  
Heat Transfer ◽  
Porous Media ◽  
Forced Convection ◽  
Numerical Study ◽  
Convection Heat Transfer ◽  
Circular Cylinders ◽  
Convection Heat ◽  
State Equations ◽  
Forced Convection Heat Transfer ◽  
Staggered Arrangement

Staggered arrangement is one of the common configurations in heat exchangers that make better mixing of flow and heat transfer augmentation than other arrangements. In this paper forced convection heat transfer over three isothermal circular cylinders in staggered configuration in isotropic packed bed was investigated. In this work laminar 2-D incompressible steady-state equations of momentum and energy were solved numerically by finite volume method. Simulation was done in three Reynolds numbers of 80, 120, and 200. The results indicate that, using porous medium the Nusselt number enhanced considerably for any of cylinders and it presents thin temperature contours for them. Also is shown that by increasing Reynolds number, the heat transfer increased in both channel but the growth rate of it in porous media is larger. In addition, results of simulation in porous channel show that with increasing Peclet number, heat transfer increased logarithmically.

scholarly journals Calculation of evaporation length of a liquid bridge flowing between inclined hot tubes

2021 ◽  
Vol 2119 (1) ◽  
pp. 012056
Author(s):  
P I Geshev
Keyword(s):  
Nonlinear Integral Equation ◽  
Boundary Integral Equations ◽  
Boundary Integral ◽  
Temperature Fields ◽  
Navier Stokes ◽  
Method Of Boundary Elements ◽  
Hydrostatic Equation ◽  
Velocity And Temperature Fields ◽  
Energy Equations ◽  
Surface Tension Forces

Abstract The bridge consists of liquid held by surface tension forces between two inclined tubes in an LNG heat exchanger. The shape of the bridge is calculated by the hydrostatic equation, which is reduced to a nonlinear integral equation and resolved by the Newton method. The velocity and temperature fields in the bridge are described by the Navier-Stokes and energy equations, respectively. They are reduced to the boundary integral equations and calculated by the method of boundary elements. Heat transfer coefficient is calculated for evaporating bridge and the length of total bridge evaporation is estimated.

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