Try these summary questions below. You may find Chapter 9 of "Fundamentals of heat and mass transfer-Frank P. Incropera" useful.
What is an extensive, quiescent fluid?
What conditions are required for a buoyancy-driven flow?
How does the velocity profile in the free convection boundary layer on a heated vertical plate differ from the velocity profile in the boundary layer associated with forced flow over a parallel plate?
What is the physical interpretation of the Grashof number? What is the Rayleigh number? How does each parameter depend on the characteristic length?
For a hot horizontal plate in quiescent air, do you expect heat transfer to be larger for the top or bottom surface? Why? For a cold horizontal plate in quiescent air, do you expect heat transfer to be larger for the top or bottom surface? Why?
For free convection within a vertical parallel plate channel, what kind of force balance governs the flow rate in the channel?
For a vertical channel with isothermal plates, what is the physical basis for existence of an optimum spacing?
What is the nature of flow in a cavity whose vertical surfaces are heated and cooled? What is the nature of flow in an annular space between concentric cylindrical surfaces that are heated and cooled?
What is meant by the term mixed convection? How can one determine if mixed convection effects should be considered in a heat transfer analysis? Under what conditions is heat transfer enhanced by mixed convection? Under what conditions is it reduced?