Shohel Mahmud

The second law analysis in fundamental convective heat transfer problems

Second law characteristics of heat transfer and fluid flow due to forced convection of steady-laminar flow of incompressible fluid inside channel with circular cross-section and channel made of two parallel plates is analyzed. Different problems are discussed with their entropy generation profiles and heat transfer irreversibility characteristics. In each case, analytical expression for entropy generation number (NS) and Bejan number (Be) are derived in dimensionless form using velocity and temperature profiles.

Numerical investigation of natural convection inside a wavy enclosure

Abstract In this paper, hydrodynamic and thermal behaviors of fluid inside a wavy walled enclosure are investigated. The enclosure consists of two wavy and two straight walls. The top and the bottom walls are wavy and kept isothermal. Two vertical straight walls (right and left) are considered adiabatic. The integral forms of the governing equations are solved numerically using Finite Volume method. Computational domains are divided into finite numbers of body fitted control volumes with collocated variable arrangement. Results are presented in the form of local and global Nusselt number distributions for a selected range of Grashof number (10 3 –10 7 ). Streamlines and isothermal lines are also presented for four different values (0.0, 0.05, 0.1, 0.15) of amplitude-wavelength ratios (= α / λ ) and for a fluid having Prandtl number 1.0. Throughout this study, aspect ratio (= δ / λ ) is kept equal to 0.40. Calculated results for Nusselt number are compared with the available references.

Free convection in an enclosure with vertical wavy walls

This paper describes a numerical prediction of heat transfer and fluid flow characteristics inside an enclosure bounded by two isothermal wavy walls and two adiabatic straight walls. Governing equations were discretized using the finite-volume method with collocated variable arrangement. Simulation was carried out for a range of wave ratio λ (defined by amplitude/average width) 0.00–0.4, aspect ratio A (defined by height/average width) 1.0–2.0, Grashof number Gr = 10 0 –10 7 for a fluid having Prandtl number 0.7. Streamlines and isothermal lines are used to present the corresponding flow and thermal field inside the enclosure. Local and global distributions of Nusselt number are presented for the above configuration. Lastly, velocity profiles are presented for some selected locations inside the enclosure for better understanding of the influence of flow field on the thermal field.  2002 Editions scientifiques et medicales Elsevier SAS. All rights reserved.

Laminar free convection and entropy generation inside an inclined wavy enclosure

Abstract We investigate numerically the heat transfer and fluid flow characteristics inside a wavy walled enclosure. Second law of thermodynamics is also applied to predict the nature of irreversibility in terms of entropy generation. Finite-volume method is used to discretize the governing differential equations with non-staggered variable arrangement. SIP (strongly implicit procedure) solver solves the linear equation systems with full multigrid (FMG) acceleration. Simulation was carried out for a range of wave ratio (defined by amplitude/average width) λ=0.0–0.4, aspect ratio (defined by height/average width) A=1.0–2.0, Rayleigh number Ra=100–107 for a fluid having Prandtl number equal to 0.7. The angle of inclination (θ) is varied from 0° to 360° with 15° interval. Streamlines and isothermal lines represent the corresponding flow and thermal fields. Local and global Nusselt number distributions express the rate of heat transfer. Contour of Bejan number is plotted. Volume averaged entropy generation rate is also presented.

Thermodynamic analysis of mixed convection in a channel with transverse hydromagnetic effect

An analysis has been performed to study the First and Second laws (of thermodynamics) characteristics of flow and heat transfer inside a vertical channel made of two parallel plates under the action of transverse magnetic field. Combined free and forced convection inside the channel is considered. Flow is assumed to be steady, laminar, fully developed of electrically conducting, and heat-generating/absorbing fluid. Both vertical walls are kept isothermal at the same or different temperatures. Governing equations in Cartesian coordinates are first simplified and solved analytically to develop the expressions for velocity and temperature, entropy generation number (NS), and irreversibility distribution ratio. Velocity, temperature, and entropy generation profiles are presented graphically. Full form of the governing equations are solved numerically using control-volume based finite volume method. Based on the numerical calculations, average entropy generation numbers are calculated for channels with different aspect ratios. Finally, a correlation is proposed which essentially expedite for calculating a geometric parameter (α0) that will be characterized by minimum irreversibility at a particular value of Gr/Re (ratio of Grashof number and Reynolds number) and M (Hartmann number).

Thermodynamic analysis of flow and heat transfer inside channel with two parallel plates

We investigate analytically the first and second law characteristics of fluid flow and heat transfer inside a channel having two parallel plates with finite gap between them. Fully developed forced convection is considered. Fluid is assumed non-Newtonian and followed the power law model. Analytical expressions for dimensionless entropy generation number (NS), irreversibility distribution ratio (Φ) and Bejan number (Be) are determined as a function of dimensionless distance (Y), Peclet number (Pe), Eckert number (E), Prandtl number (Pr), dimensionless temperature difference (Ω) and fluid index (m and n). Spatial distribution of entropy generation number, irreversibility ratio and Bejan number are presented graphically.

Mixed convection–radiation interaction in a vertical porous channel: Entropy generation

The present work examines analytically the effects of radiation heat transfer on magnetohydrodynamic mixed convection through a vertical channel packed with fluid saturated porous substances. First and Second Laws of thermodynamics are applied to analyze the problem. Special attention is given to entropy generation characteristics and their dependency on the various dimensionless parameters, i.e., Hartmann number (Ha), Plank number (Pl), Richardson number (Ri), group parameter (Br/II), etc. A steady-laminar flow of an incompressible-viscous fluid is assumed flowing through the channel with negligible inertia effect. The fluid is further considered as an optically thin gas and electrically conducting. Governing equations in Cartesian coordinates are solved analytically after reasonable simplifications. Expressions for velocity, temperature, local, and average entropy generation rates are analytically derived and presented graphically.

ENTROPY GENERATION IN A VERTICAL CONCENTRIC CHANNEL WITH TEMPERATURE DEPENDENT VISCOSITY

Present research efforts mainly focus on the nature of irreversibility, in terms of entropy generation, inside a vertical cylindrical annulus. Laminar mixed convective flow of Newtonian fluid is considered with variable (temperature dependent) viscosity. The temperature dependent nature of viscosity is assumed to follow an exponential model. We seek for the closed form of analytical solutions by solving the simplified governing equations in cylindrical coordinates. Isothermal boundary condition is applied. Analytical expressions for the velocity and temperature are derived which essentially expedite to obtain expressions for local and average entropy generation in the annular space

Free convection and entropy generation inside a vertical inphase wavy cavity

We examined the nature of entropy generation along with heat transfer and fluid flow characteristics inside a cavity made of two horizontal straight walls and two vertical wavy walls. Wavy walls are assumed to follow a profile of cosine curve. Horizontal straight walls are kept adiabatic, while the bent walls are isothermal but kept at different temperatures. Laminar natural convection inside the cavity is considered. Governing differential equations were discretized using the Finite Volume method with collocated variable arrangement. Simulation was carried out for a range of wave ratio, λ=0.00-0.6, aspect ratio, A=1.0-4.0, Rayleigh number, Ra=10 0 -10 7 for a fluid having Prandtl number equal to 1.0. Results are presented in the form of Nusselt number, entropy generation number, Bejan number, streamlines, and isothermal lines

Second law analysis of heat transfer and fluid flow inside a cylindrical annular space

Abstract We investigate analytically the First and Second Laws (of thermodynamics) characteristics of fluid flow and heat transfer inside a cylindrical annulus. Inside the annular gap, the relative rotational motion between the inner and outer cylinders induces fluid motion. The net surface heat flux is always equal at the inner and outer cylinders, but it is varied in magnitude. Simplified governing equations in cylindrical coordinates are solved to obtain analytical expressions for dimensionless entropy generation number ( N S ), irreversibility distribution ratio ( Φ ), and Bejan number ( Be ) as a function of flow governing and geometric parameters. Spatial distributions of local and average entropy generation rate, and heat transfer irreversibility, are presented graphically. The effects of velocity ratio ( λ ), group parameter (Br/Ω) , and Brinkman number ( Br ) on the above parameters are tested.