| dc.description.abstract | In the present thesis, some problems in unsteady mixed convective boundary-layer flows with double diffusion have been numerically investigated. It consists of five chapters-the first of which is a general introduction to boundary-layer theory, while the remaining four are concerned with specific problems investigated by us.
Chapter I presents a brief introduction to boundary-layer theory with special reference to heat and mass transfer. Various methods of solutions applicable to boundary-layer flow problems are also discussed briefly.
The chapters concerned with the problems, i.e., Chapters II-V, begin with an introduction that includes the relevant literature survey. The authors’ contributions are presented next. The formulation of the problem, analysis, and method of solution follow. The results, which are presented in a graphical format at the end of each chapter, are analyzed and discussed next. A brief conclusion sums up the chapter. References cited in each chapter are listed sequentially at the end of that particular chapter. Although the various symbols used are defined as and when they occur, for easy reference the most common ones are listed in Appendix I.
For all the problems that we have investigated, the unsteadiness is assumed to be due to the free-stream velocity varying arbitrarily with time. Accelerating, oscillating, and decaying free-stream velocities are considered. The analysis covers the diffusion of various gases and vapors into air and water. Appendix II lists the Prandtl numbers and Schmidt numbers for the diffusion of some common gases into air and water. The effects of various parameters such as unsteadiness, viscous dissipation, buoyancy forces due to temperature and concentration, and mass transfer on the skin friction, heat transfer, and mass transfer coefficients as well as on the velocity, temperature, and concentration have been studied in detail.
Chapter II investigates mixed convection with mass transfer in the case of flow along a thin, long, vertical cylinder. A quasilinearization technique in conjunction with a finite-difference scheme is used to solve the non-similar partial differential equations in three independent variables. The coefficients of skin friction, heat transfer, and mass transfer increase with the net buoyancy force as well as the transverse curvature. An overshoot beyond the free-stream velocity is observed in the velocity profile when the net buoyancy force assisting the forced convective flow is relatively large.
Chapter III studies unsteady, laminar, binary, mixed convective flow along a vertical circular cone under the combined buoyancy effects of thermal and species diffusion. The analysis is confined to mass diffusion processes with low concentration levels. The governing partial differential equations are nondimensionalized, and the resulting non-similar equations involving three independent variables are solved by a quasilinearization technique in combination with a finite-difference scheme. It is observed that when the mass diffusion buoyancy force reinforces the thermal buoyancy force, the surface mass and heat transfer rates as well as the friction factor increase.
Chapter IV deals with mixed convection and double diffusion in the case of unsteady non-similar laminar boundary-layer flow over an infinite yawed circular cylinder. The efficient numerical method of quasilinearization is used along with an implicit finite-difference scheme to obtain a solution to the nonlinear partial differential equations from the starting point of the streamwise coordinate to the point of zero skin friction. The skin-friction coefficient and the heat and mass transfer rates are found to be strongly affected by the buoyancy parameters.
Chapter V investigates the unsteady, incompressible, laminar, mixed convective flow with combined heat and mass transfer about a rotating cylinder. The cases of constant wall temperature as well as constant heat flux are considered. For this problem, the rotation is also assumed to vary with time. The governing system of equations is written in the form of a first-order system. An implicit finite-difference scheme is then applied. Since the equations are still nonlinear, Newton’s method is employed to solve them. In order to do this with an efficient and stable computational scheme, a block-tridiagonal factorization technique is used. It is observed that the skin-friction, heat, and mass transfer coefficients tend to increase with rotation as well as with the net buoyancy forces. For a fixed buoyancy force effect, heating by uniform surface heat flux yields a larger coefficient of heat transfer than heating by uniform wall temperature.
Papers based on the work presented in this thesis will be communicated for publication shortly. | |
