Please select the most appropriate answer for these multiple-choice questions.

Thank you

The Grashof number for an ideal gas is a. The non-dimensional temperature gradient at a solid surface ni a natural convection problem. b. The ratio of the buoyancy force to the viscous force. c. An indication of how important forced convection is. d. All of the above. e. None of the above. The Nusselt number is a. The resistance to conduction from the solid surface divided by the resistance to convection in the solid surface b. The dimensional temperature gradient at a solid surface c. An indication of how uniform the temperature distribution is within a solid surface d. A relation between convection coefficient, length scale and the thermal conductivity of the solid surface e. None of the above In radiation heat transfer, the grey surface is the surface where .a The emissivity is equal zero b. The transmissivity is equal zero c. The reflectivity is equal to the transmissivity d. The emissivity is equal to the reflectivity e. The emissivity is equal to the absorptivity In free convection heat transfer a. The inertia force is much important than the buoyancy force b. The buoyancy force is much important than the inertia force c. The buoyancy force is equal to the inertia force d. The viscous force is equal to the inertia force e. None of the above Consider laminar flow in a circular tube as shown in Figure 2, the flow is said to be fully developed when a. The velocity profile no longer changes with r b. The velocity profile no longer changes with xc. The mean velocity is zero d. All of the above e. None of the above