Vertical Parallel Plate Channel Research Articles

Carboxymethyl cellulose-water-based hybrid nanofluid mixed convection flow between porous vertical plates: Entropy generation analysis

This paper analyzes the thermodynamic second law analysis of mixed convection heat transfer of Carboxymethyl Cellulose (CMC)-water based viscoelastic hybrid nanofluid flow in a vertical parallel plate channel filled with porous medium. In mixed convection flow, where both buoyancy and viscous forces play significant roles in the flow behavior, the inclusion of viscous dissipation in the analysis is crucial. The governing equations of the problem are converted into a system of ordinary differential equations using appropriate similarity transformations, which are then solved by the Homotopy Analysis Method (HAM). The behavior of non-dimensional velocity, temperature, skin friction coefficient, Nusselt number, entropy generation and Bejan number profiles for a range of pertinent flow parameter values is displayed graphically and deliberated. Study reveals that a decrease in the dominance of viscous forces relative to inertial forces within the porous medium lowers entropy generation in the system.

Falling film evaporation in a partially heated parallel plate channel: Elliptic numerical analysis with an excess moisture condensation model

A fully coupled elliptic numerical method is used to conduct a detailed numerical analysis of laminar water falling film evaporation with a co-current laminar gas vapour mixture flow inside a partially heated vertical parallel plate channel. In order to obtain a fully coupled implicit solution, a complete set of elliptic two-phase two-dimensional governing equations is solved. The liquid-gas interface is obtained over a non-orthogonal structured moving mesh (grid) during the solution process. An excess moisture condensation model is proposed as a novel numerical method to address supersaturation in the system. Comparisons with the previous studies are made to verify the accuracy and capability of the present numerical model. The effects of the liquid and mixture Reynolds numbers variation on the hydrodynamic and thermal characteristics of the evaporation process inside the partially heated channel are investigated. Thermal and solutal buoyancy effects are seen in the form of recirculating flow in the gas phase.

Numerical analysis of evaporation from a falling film in a vertical parallel plate channel

A detailed numerical analysis is performed of evaporation from a laminar falling liquid film with a co-current laminar gas-vapour mixture flow in a vertical parallel plate channel. A finite volume method is used to obtain a fully coupled implicit solution of a complete set of parabolic two-phase two-dimensional governing equations. Comparisons with the previous numerical and experimental studies are made to demonstrate the accuracy and capability of the present numerical model. Water-air and ethanol-air mixtures are used to examine the effects of buoyancy forces on the flow and the thermal characteristics of the evaporation process. The effects on the heat and mass transfer of the system of the wall heat flux, the relative humidity, and the inlet pressure are investigated.

Density Modelling in Mixed Convection Flow in a Vertical Parallel Plate Channel

In this paper, a novel way of modelling the density in buoyancy term of mixed convection flow problem is presented using equation of state and Boussinesq approximation without first-order approximation of density with respect to temperature. The presented density model is used to investigate the laminar mixed convection flow in a vertical parallel plate channel under symmetric constant wall heat flux. The results obtained are compared with the results obtained using first-order approximation of density with Boussinesq approximation, and also compared with the results obtained using variable thermophysical properties with negligible viscous dissipation. Investigation is performed on the basis of flow and thermal fields for Re=150 and 300, Ri=0.1 to 25. It is found that the presented density model produces relatively better results, which is able to describe the case of developing flow under constant heat flux condition that is not evident if Boussinesq approximation with first-order approximation of density is used. An appearance of recirculatory cells when reverse flow takes place is also witnessed in vertical channel flow with constant heat flux boundary condition which was not reported earlier.

An elliptic numerical analysis of water vapour absorption into a falling film in vertical parallel plate channels

An implicitly coupled elliptic numerical model is applied to study the two-phase falling film absorption inside a parallel plate vertical channel. A complete set of two-phase two-dimensional governing equations are solved for co-current laminar flows of LiBr solution and water vapour. A precise liquid-gas interface is determined dynamically during solution over a non-orthogonal structured moving mesh. Fundamental interface boundary conditions are implemented to model the heat and mass interchange between the two phases. The capability of this new model is demonstrated through detailed comparisons with two previous parabolic and elliptic models. The impacts of the interface heat of absorption and mass fraction condition and the liquid film diffusion coefficient are investigated. New results are presented to examine the channel inlet pressure effect on the liquid film thickness development over the cold wall and the heat and mass transfer at the interface.

Pulsed Flow in a Vertical Channel with Discrete Heat Sources

This work is a numerical simulation of pulsed flow in an adiabatic vertical parallel plate channel with four discrete heat sources on one wall of the channel and subjected to a sinusoidal profile velocity at the inlet. The finite volume method was used to solve governing equations using open source OpenFoam free code. The effects of certain topical parameters such as pulsation amplitude and frequency and Richardson number are studied. The results reveal the flow behaviour and temperature distribution are strongly affected by the pulsation of the velocity at the inlet and the rate of heat transfer during a pulsation cycle increases considerably by increasing the pulsation amplitude.

Temperature and Location of Hot Spots Variation with Spacing in a Vertical Parallel Plate Channel: Conjugate View

Temperature and Location of Hot Spots Variation with Spacing in a Vertical Parallel Plate Channel: Conjugate View

Effect of Magnetic Field on the Flow of a Dusty Fluid in An Inclined Parallel Plate Vertical Channel

Effect of Magnetic Field on the Flow of a Dusty Fluid in An Inclined Parallel Plate Vertical Channel

Constructal Placement of Discrete Heat Sources With Different Lengths in Vertical Ducts Under Natural and Mixed Convection

In this study, convective heat transfer in a discretely heated parallel-plate vertical channel which simulates an IC package is investigated experimentally and numerically. Both natural and mixed convection cases are considered. The primary focus of the study is on determining optimum relative lengths of the heat sources in order to reduce the hot spot temperature and to maximize heat transfer from the sources to air. Various values of the length ratio and the modified Grashof number (for the natural convection case)/the Richardson number (for the mixed convection case) are examined. Conductive and radiative heat transfer is included in the analysis while air is used as the working fluid. Surface temperatures of the heat sources and the channel walls are measured in the experimental study. The numerical studies are performed using a commercial CFD code, ANSYS fluent. The variations of surface temperature, hot spot temperature, Nusselt number, and global conductance of the system are obtained for varying values of the working parameters. From the experimental studies, it is showed that the use of identical heat sources reduces the overall cooling performance both in natural and mixed convection. However, relatively decreasing heat sources lengths provides better cooling performance.

Fully coupled two-phase numerical model for falling film absorption in a vertical parallel plate channel

A two-phase numerical simulation is performed to investigate the absorption of water vapour into an aqueous lithium bromide solution inside a parallel plate vertical channel. The liquid film and vapour phase interactions and concurrent heat and mass interchange is modelled using a two-dimensional steady laminar flow model and a fully-coupled marching numerical scheme. The capability of this new model is examined by comparisons to the previous numerical results for a liquid film flowing over a cold wall. The numerical predictions are examined for the effect of the following operating parameters: the liquid film Reynolds number, the inlet mass fraction, and the wall temperature. New results are provided on the impact of the gas phase Reynolds number variation from 1000 to 3000 on the liquid film development along the channel.

Entropy Analysis of Mixed Convective Condensation by Evaluating Fan Velocity With a New Approach

Present paper conducts an extensive numerical study on entropy analysis of mixed convective condensation inside a vertical parallel plate channel. A new approach is proposed to separate pump velocity component/Reynolds number from inlet mixed convection velocity. Influence of inlet governing parameters on condensation heat and mass transfer at different inlet pressure, velocity, channel length, and width are widely studied. The central focus of this paper is to study entropy generation under mixed convective condensation. Variation of local as well as overall entropy generation and second law efficiency for different geometric and environmental conditions are presented. For effective condenser design, present study provides two important correlations of overall volumetric entropy generation due to thermal transport and overall volumetric entropy generation due to mass transport.

Effect of Prandtl number on the average exit temperature of coolant in a heat‐generating vertical parallel plate channel: A conjugate analysis

AbstractA coupled conduction–convection heat transfer analysis is carried out for a two‐dimensional rectangular, vertical parallel plate channel producing volumetric energy (uniform and nonuniform), subjected to laminar forced‐convection incompressible fluid flow under steady‐state conditions. The equations governing the thermal and flow field are solved by using finite difference method, and the resulting algebraic equations are solved by using the tridiagonal matrix algorithm method. Four coolants with their Prandtl numbers (Pr), namely, liquid sodium (Pr = 0.005), sodium‐potassium (Pr = 0.00753), lead (Pr = 0.02252), and helium (Pr = 0.666) are used for the present conjugate analysis. Effects of different thermal and fluid flow parameters such as Reynolds number (ReH) ranging from 500 to 1500, conduction–convection parameter (Ncc), and total heat generation (Qt) on average exit temperature (θae) of coolants are studied. From the obtained results, it is found that the θae of coolant strongly depends on Pr, ReH, Ncc, and Qt when the aspect ratio (Ar) is kept constant. It is also found that with a nonuniform rate of heat generation, the coolant θae is high compared to uniform heat generation rate, whereas with increasing Ncc, the θae decreases, and with increasing Qt, the θae increases irrespective of coolants.

Natural convection in a parallel-plate vertical channel with discrete heating by two flush-mounted heaters: effect of the clearance between the heaters

In this study, natural convection in a vertical channel is studied experimentally and numerically. One of the channel walls is heated discretely by two flush-mounted heaters while the other is insulated. The effects of the clearance between the heaters on heat transfer and hot spot temperature while total length of the heaters keeps constant are investigated. Four different settlements of two discrete heaters are comparatively examined. Air is used as the working fluid. The range of the modified Grashof number covers the values between 9.6 × 105 and 1.53 × 10.7 Surface to surface radiation is taken into account. Flow visualizations and temperature measurements are performed in the experimental study. Numerical computations are performed using the commercial CFD code ANSYS FLUENT. The results are represented as the variations of surface temperature, hot spot temperature and Nusselt number with the modified Grashof number and the clearance between the heaters as well as velocity and temperature variations of the fluid.

On the Validity of Boussinesq Approximation in Variable Property Turbulent Mixed Convection Channel Flows

ABSTRACTThe present study investigates the effects of fluid thermo-physical property variations on fully developed turbulent mixed convection flow in vertical and horizontal parallel plate channels where walls are kept at different temperatures. The main attention is paid to the validity of the Boussinesq approximation when the temperature differences are enhanced. Reynolds number based on the channel half-width and friction velocity is assumed to be 150. The governing equations are solved utilizing the large eddy simulation and the low Mach number approach on a finite-volume basis. Dealing with the sub-grid scale stress tensor and the heat flux vector, the dynamic Smagorinsky model is used. All the numerical simulations are carried out by developing a solver in OpenFOAM. The present results display that an increase in the walls' temperature difference, applying the Boussinesq approximation and neglecting the dependency of thermal conductivity and dynamic viscosity on temperature, can result in relatively large errors. Deviations of up to 33% and 45% in the prediction of friction coefficient and Nusselt number, respectively, are shown. This is true for both vertical and horizontal configurations.

On mixed convection of two immiscible layers with a layer of non-Newtonian nanofluid in a vertical channel

Mixed convection in a vertical parallel plate channel is analyzed with one region filled with Newtonian fluids and another region with non-Newtonian nanofluids. Pseudo-plastic and dilatant fluids are used as working base flow of nanofluids. Power-law modelling is adopted to predict the effect of non-Newtonian behavior on the fluid flow and thermal performance of nanofluids, and the effective kinematic viscosity and thermal conductivity are determined using linear relations as functions of nanoparticle loading parameter. The velocity and temperature fields are investigated, considering the influence of power-law index n(0.6≤n≤1.4) and nanoparticle volume fraction ϕ(0≤ϕ≤4%). Two cases have been paid special attention in the present work, that is, Case I: in the absence of viscous dissipation (Br=0, GR≠0), and Case II: in the absence of buoyancy forces (GR=0, Br≠0) when purely forced convection happens. It is observed that the power-law index has a strong effect on the shape of velocity profile, and on the scale of temperature curves. The results reveal that the power-law effect on both velocity and temperature is more observable in shear-thinning fluids than that in the dilatant flow. These findings demonstrate that, in some potential applications, the shear-thinning fluid should be chosen for its higher effectiveness on fluid driving where the non-Newtonian fluid is used to drive Newtonian flow via interface shear.

Viscous dissipation effects on entropy generation in heated vertical parallel-plate channels for mixed convection

In this study, effect of viscous dissipation on entropy generation for fully developed incompressible laminar flow mixed convection in vertical parallel-plate channels with asymmetric and symmetric uniform heat fluxes was parametrically analysed. Analytical equations were derived by using continuum approach and perturbation method. A specific MATLAB code was created to solve the governing equations. The effects of Gr/Re, the Brinkman number, and the ratio of wall heat flux on the entropy generation are presented and discussed. It is concluded that viscous dissipation has a significant effect on the entropy generation for mixed convection in heated vertical parallel-plate channels. Entropy generation resulting from fluid friction goes up, however, entropy generation due to heat transfer decreases by increasing of viscous dissipation. Consequently, it can be said that, this study will contribute to literature in optimising the systems that operates under mixed convection conditions in the vertical parallel-plate configuration.

Viscous dissipation effects on entropy generation in heated vertical parallel-plate channels for mixed convection

Viscous dissipation effects on entropy generation in heated vertical parallel-plate channels for mixed convection

Optical thickness effect on natural convection in a vertical channel containing a gray gas

The effect of radiation on natural convection heat transfer in a vertical parallel-plate channel with asymmetric heating, considering the radiation effects for both walls and participating air is presented. The channel is formed by one vertical wall heated by a uniform heat flux and by a vertical adiabatic plate. The governing equations of laminar natural convection and radiative transfer are solved by the finite volume method (FVM) and by the discrete ordinates method (DOM), respectively. The code was validated and verified with data reported in the literature. The effect of optical thickness (τ), channel width (b) and wall emissivity (εh) on the heat transfer and mass flow are investigated. The mass flow of the channel for τ=0.1 is up to 42% greater than that obtained for a transparent medium (τ=0.0). When τ=0.1, the average temperature difference between the air at the inlet and air at the outlet of the channel decreases up to 75% due to the increase of b from 0.02 to 0.10m. Varying εh from 0.1 to 0.9 increases the radiative heat flux at the heated wall up to 72% and the mass flow rate increases up to 29%. A set of correlations were obtained for the mass flow, average convective Nusselt number and average radiative Nusselt number.

A sharp‐interface elliptic numerical model of laminar two‐phase gas‐liquid downward flow in a vertical parallel plate channel

AbstractA sharp‐interface two‐phase numerical analysis is performed for co‐current downward laminar flow of a liquid film and a gas. A complete two‐phase model based on the two‐dimensional elliptic governing equations is presented. The numerical model implements a dynamically moving non‐orthogonal computational mesh that tracks the phase interface precisely. The capability of this new model is demonstrated by comparisons with two previous free surface falling film studies and one experiment. New results are presented on the effect of independent variation of the Reynolds and Froude numbers on the axial variation of the film free surface. Finally, the effects of the velocity of the gas phase on the liquid film development are examined for flow in a parallel‐plate channel. An analytical solution for the fully‐developed velocity profiles for the two‐phase flow is also presented.

Fluid flow and heat transfer characteristics of a vertical channel with detached pin-fin arrays arranged in staggered manner on two opposite endwalls

This work investigates the fluid flow and the heat transfer characteristics of a vertical parallel plate channel filled with protruding partial length, high density meshing fins on the two inside walls, considering electronic equipment cooling as one of the possible applications. The goal is to understand the flow physics and quantify the overall heat transfer enhancement achieved. Air is used as a coolant and is assumed to have constant thermo-physical properties. Full three dimensional Reynolds-averaged Navier–Stokes equations and the energy equation are solved using finite volume method for the conjugate heat transfer problem in hand. The standard k-є turbulence model with enhanced wall treatment is used to model turbulence closure, in a Reynolds number range of 2200–23,000. The performance of the system is evaluated in terms of the thermal resistance, separately defined for two plates and the pumping power. The numerical results are validated against experimental results, obtained by performing steady state forced convection heat transfer experiments in a vertical wind tunnel facility. A detailed parametric study considering the clearance distance between the plates, pin-fin diameter, transverse pin fin pitch and axial pin fin pitch as the design variables has been undertaken. From the numerical results, it is seen that the pin-fin diameter is the most dominating variable for both the pressure drop and the thermal resistance. The results of the parametric study are used to train an Artificial Neural Network using the Levenberg–Marquardt algorithm to obtain surrogate models for the objective functions. A multi-objective optimization, based on geometrical parameters, is performed using multi-objective evolutionary algorithm, NSGA-II to minimize the thermal resistance and the pumping power simultaneously. A global Pareto optimal set consisting of non-dominated solutions is then obtained using NSGA-II and is divided into five clusters by k-means clustering method to arrive at representative solutions for each cluster.