NUMERICAL STUDY OF HEAT TRANSFER AND ENTROPY GENERATION IN NANOFLUID FILLED ENCLOSURE

Abstract

In today's world the need and dependency of human being on mechanical system is increasing day by day. With the increasing demand, the advancement in the performance of mechanical system is one of the most important factor for energy optimization. The improvement in the performance of any mechanical system means the increase in the life of mechanical system and improvement in the working e ciency in the sense of time as well as production at optimal cost. This thesis presents a detailed numerical studies for the analysis of various aspects of

uid ow, heat transfer and entropy generation within an enclosure equipped with di erent types of thermal boundary conditions for uid and porous media with and without induced magnetic eld e ects. Comparative studies are conducted over clear uid as well as nano uid with increasing nanoparticle volume fraction to obtain the most suitable fraction of nanoparticles in the base uid in order to improve the thermal performance of mechanical systems. Method of entropy generation minimization is used for the modeling and optimization of energy systems related to heat exchangers in aircraft engines, cooling devices for cars and nuclear power plants. The total entropy generation in such systems can be minimized under some physical and geometric arrangements and some optimal con guration can provide the minimum energy loss. The numerical solution of set of non-linear coupled partial di erential equations governing the uid ow, temperature distribution and entropy generation is attained by nite volume based approach. The numerical simulation has been presented in the form of streamlines, isotherms, energy ux vectors and entropy generation in various ow conditions of industrial importance. The heat transfer rates are obtained in terms of local and average Nusselt number. Chapter-1 deals with various de nitions of ow governing parameters and solution methods used in ow governing equations. The analysis of heat i ii and mass transfer, entropy generation with their measuring and controlling parameters such as Nusselt number, entropy generation, Bejan number is made in terms of various

ow governing parameters such as Reynolds number, Rayleigh number, Richardson number and Darcy number etc. In Chapter-2, we have studied the mixed convection heat transfer e ects in a liddriven enclosure lled with copper-water nano uid due to a heated wall mounted block of constant heat ux attached along the vertical wall. A detailed analysis of ow and heat transfer properties are discussed by placing the heated mounted block on left and right vertical walls. The ow governing equations are solved numerically using streamfunctionvorticity formulation approach using nite volume method. Chapter-3 deals with the study of copper-water nano uid ow in a two-sided liddriven rectangular enclosure in which the vertical walls move in di erent directions. Three di erent con gurations have been considered on the basis of direction of movement of vertical walls to study the uid ow and heat transfer e ects to nd an optimum con guration in order to obtain maximum heat transfer. In Chapter-4 we have presented a numerical study of hydromagnetic mixed convection

ow inside a cubical enclosure lled with porous mixture. A sinusoidal time dependent discrete temperature gradient along the boundaries is considered. A time history analysis is made for ow and thermal strati cation. The uid ow and heat transfer analysis is made with the variation of Grashof number, Hartmann number, Darcy number and Prandtl number to obtain the average Nusselt number and bulk average temperature. Chapter-5 consists of the same con guration as that of chapter-3 and a detailed analysis of entropy generation in combination with heat transfer e ects is considered. The energy e ciency is discussed on the basis of performance evaluation criteria based on heat transfer and entropy generation. In Chapter-6 a similar con guration as that of chapter-4 is used to study the heat transfer and entropy generation of a magnetohydrodynamic nano uid ow. The ow is in uenced by time periodic discrete heat sources. A detailed study of uid ow, heat transfer and entropy generation is used to study the performance of the system. Based on the proposed performance evaluation criteria an optimum con guration is suggessted to obtain maximum heat transfer on the cost of minimum entropy generation. iii Bibliography is the last section of the thesis. All the computations are made by writing our own codes in MATLAB and FORTRAN, rather then using existing toolboxes. TECPLOT and MATLAB are used for plotting of simulated data.