Question

In which mode of heat transfer is the convection heat transfer coefficient usually higher, natural convection or forced convection? Why?

Short answer

Explain the reason behind it. Answer: Forced convection has a higher convection heat transfer coefficient as compared to natural convection. The primary reason is the increased fluid velocity, mixing, and turbulence induced by the external force in forced convection, which leads to enhanced mixing of fluid layers and a higher rate of heat transfer between the surface and the fluid.

Step-by-step solution

Understand natural and forced convection

Natural convection is the process where heat is transferred through a fluid without any external force, relying solely on the buoyancy forces caused by temperature differences. On the other hand, forced convection is when heat is transferred through a fluid with the help of an external force, such as a fan or a pump, which causes the fluid to move along a surface or through a pipe.

Identify the factors affecting the convection heat transfer coefficient

The convection heat transfer coefficient (h) depends on several factors such as the fluid properties (density, viscosity, thermal conductivity, and specific heat), flow rate, and the geometry or shape of the surface through which heat is transferred.

Compare the convection heat transfer coefficient of natural and forced convection

In general, for forced convection, the velocity of the fluid motion and its mixing is much higher due to the additional external force, leading to higher rates of heat transfer. As a result, the convection heat transfer coefficient (h) is usually higher in forced convection as compared to natural convection.

Explain the reason behind the difference in convection heat transfer coefficient

The primary reason for this difference in the convection heat transfer coefficient is the increased fluid velocity and turbulence induced by the external force in forced convection. This leads to enhanced mixing of fluid layers and a higher rate of heat transfer between the surface and the fluid, which translates to a higher convection heat transfer coefficient. In conclusion, the convection heat transfer coefficient is usually higher in forced convection as compared to natural convection due to the increased fluid velocity, mixing, and turbulence induced by the external force.