Lecture 5 - Natural Convection

Generally, natural convection occurs due to

• change in velocity of a fluid

• change in density of a fluid

• change in molecular structure of a fluid

• none of the above

The intensity of mixing of fluid in natural convection is

• more than the intensity of mixing of fluid in forced convection

• less than the intensity of mixing of fluid in forced convection

• equal to the intensity of mixing of fluid in forced convection

• unpredictable

What is the relation between convection heat transfer coefficients of natural convection and forced convection?

• convection heat transfer coefficient of natural convection is lower than the convection heat transfer coefficient of forced convection

• convection heat transfer coefficient of natural convection is more than the convection heat transfer coefficient of forced convection

• convection heat transfer coefficients in both natural and forced convection are the same for same system

• unpredictable

Below figure shows a natural convection heat transfer on a horizontal flat plate and fluid is above it. Which condition satisfies the figure below?

• Plate temperature is lower than the fluid temperature

• Plate temperature is higher than the fluid temperature

• Plate temperature is equal to the fluid temperature

• unpredictable

What is the ratio of the buoyancy force to the viscous force acting on a fluid called?

• Prandtl number (Pr)

• Reynolds number (Re)

• Nusselt number (Nu)

• Grashof number (Gr)

In natural convection, the Nusselt number (Nu) depends on

• Pr and Re

• Gr and Re

• Gr and Pr

• none of the above

The Grashof number in natural convection plays same role as

• Prandtl number (Pr) in forced convection

• Reynolds number (Re) in forced convection

• Nusselt number (Nu) in forced convection

• none of the above