FLOW PROBLEMS WITH HEAT AND MASS TRANSFER. In this Dissertation, investigations are carried out on Natural convection flow of fluid between two infinite vertical parallel plates for different physical situations as well as different fluid properties. The different thermal conditions considered in this dissertation include symmetric and asymmetric heating of the boundaries, periodic temperature variation on the boundaries, viscous dissipation heating as well as the role of Non- Fourier energy equation on convective heat transfer. The dissertation also investigated the influence of heat generation or absorption and mass leakage (suction/injection) through the channel boundaries. Closed form solutions are obtained for momentum, energy and concentration equations for different physical situations. It is hoped that the result presented in this dissertation will be of use in validating Computer routines for numerical solutions of more complex natural convection fluid flows in the presence of heat and mass transfer and in stimulating needed experimental work in this area.