Question

Answer the following questions:

a) In a wall without heat generation, with temperatures T0 and T1, if the heat in T0 is adiabatic, what phenomena can occur at the end of the wall?

b) What are the conditions for Despicable Convective Resistance and negligible Conductivity?

c) In what case, can they be considered as concentrated or finned parameters?

Answer 1

a) We will consider that the wall with temperature T1 is maintained at that temperature.

Suppose that T1 >T0,

The initial state will be as follows;

As you can see, the right end of the wall is insulated meaning adiabatic ( No heat transfer).

With the passage of time, the temperature at the right end rises to T1. When this happens no heat transfer occurs as there is no temperature difference.

For the case where T1<T0;

In this case, similarly, the temperature will fall at the right end to T1 until it establishes an equilibrium, and then the heat transfer stops.

b) Convective resistance is the quantity   and physically is the resistance to heat transfer through the mode of convection.

Thermal Conductivity is the quantity defined by quantity of heat transferred by conduction per degree temperature rise. Negligible conductivity occurs in thermal insulators.

c) When the heat transfer from lateral surfaces is more than the heat transfer through the ends, it can be assumed as a fin. For most effective fin, themal conductivity (k) should be as large as possible and convective heat transfer coefficient (h)should be low. This is due to the fact that effectiveness of a fin is directly proportional to 'k' and inversely proportional to 'h'.