^{1}

^{2}

^{2}

^{1}

^{2}

This work introduces a simple method of exergy analysis in a typical circular porous fin. The entropy generation of any thermodynamic system provides a useful measure of the extent of irreversibility. The irreversibility causes the loss of useful work (exergy) in the system and hence the loss of exergy has to be minimized. Entropy generation is a parameter that quantifies the loss of exergy. Circular fins are relatively good heat transfer augmentation features with superior aerodynamic performance and as a result find application in some solar air heaters. In this paper, the entropy generation in a circular porous fin is calculated and its performance is compared with respect to entropy generation. Also shown in porous fins, with increase of porosity. The entropy generation number

The term extended surfaceis used to describe a system in which the area of a surface is increased by the attachment of fins

The entropy generated by a single porous fin in cross-flow can be evaluated based on the general model presented in Figure

The porous medium is isotropic and homogenous.

The porous medium is saturated with single-phase fluid.

Physical properties of both fluid and solid matrix are constant.

The temperature inside fin is only function of

There is no temperature variation across the fin thickness.

The solid matrix and fluid are assumed to be at local thermal equilibrium with each other.

The interactions between the porous medium and the clear fluid can be simulated by the Darcy formulation.

All conditions are the same as flow around a solid fin and only variable parameter is porosity.

Porous fin nomenclature.

Circular fin is one of the simplest geometries, since the heat transfer and drag force depend on only two dimensions, the length

Or

The first step to optimize a thermodynamic system is to determine a proper objective function. The next step is to minimize this objective function which can be done using a number of different numerical, analytical and graphical methods. Using the equation presented in, Section

The engineering significance of (

Optimum slenderness ratio of the circular porous fin for minimum entropy.

Figure

Variation of entropy generation number with Reynolds number of circular porous fin with variation of values

Figure

Comparison between fins with porosity and without porosity.

In Figures

Variation of

Variation of

Figure

Variation of

A quiet revolution is taking place in thermodynamics and it amounts to the closing of the gap between thermodynamics and heat transfer. The method and field that unite these classical disciplines is entropy generation minimization. Today EGM is an established method in both fundamental and applied heat transfer. This work introduces a simple method of analysis to study exergy in porous fin. By using the first and second laws of thermodynamics we will contribute to entropy generation. The entropy generation of any thermodynamics system provides a useful measure of the extent of irreversibility. Entropy generation is one parameter that quantifies the loss of exergy. In this paper, the entropy generation of circular porous fin in cross-flow of air and radiation is calculated

Cross-sectional area of the fins in m

Diameter of the circular cross-section

Drag force exerted by the cross-flow over the fin in N

Thermal conductivity of the working fluid in W/m

Characteristic dimension of the fins,

Length of the fins in m

Thermal conductivity ratio,

Entropy generation number

Base temperature difference,

Heat transfer through the base of the fin in w

Heat transfer to the free stream in w

Entropy generation in W/K

Free stream temperature in K

Base fin temperature in K

Free stream velocity in m/sec

Power lost due to the irreversibility in W

Kinematic viscosity

Density

Porosity

Coefficient of volumetric thermal expansion

Gravity constant

Reynolds number in Length of fin

Entropy generation number by Temperature difference

Entropy generation number by Drag force.

Solid properties

Fluid properties

Porous properties.