5.1 Explain the physical nature of natural convection. How does it differ from f

Question

5.1 Explain the physical nature of natural convection. How does it differ from forced convection?

5.2 Explain the genesis of the Grashof number, Gr. What does it represent? Why is it important in our study of natural convection?

5.3 Describe the process you would follow to determine the correct empirical correlation for a horizontal plate natural convection problem.

5.3.4 What analysis changes do we need to make for natural convection in enclosed spaces?

5.5 What do we have to take into account when we have combined forced and natural convection? How does this change our heat transfer analysis?

Explanation / Answer

5.1

Natural convection is driven by fluid motion due to changes in its density which is a result of temperature difference.

Forced convection, as the name suggests, happens by forced motion of fluid using some fan, blower, pump etc.

5.2

The Grashof number (Gr) is a dimensionless number in fluid dynamics and heat transfer which approximates the ratio of the buoyancy to viscous force acting on a fluid. It frequently arises in the study of situations involving natural convection.

It is important for natural convection study because it takes into account buoyancy effect.

5.3

Boundary layer study need to be done to study the natural convection on flat plate.

5.4

The interaction of boundary layers from different surfaces needs to be taken into account.

5.5

Combined forced convection and natural convection, or mixed convection, occurs when natural convection and forced convection mechanisms act together to transfer heat. This is also defined as situations where both pressure forces and buoyant forces interact. How much each form of convection contributes to the heat transfer is largely determined by the flow, temperature, geometry, and orientation. The nature of the fluid is also influential, since the Grashof constant increases in a fluid as temperature increases, but is maximized at some point for a gas.

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