Question

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

Short answer

Answer: Forced convection generally has a higher convection heat transfer coefficient compared to natural convection.

Step-by-step solution

Define natural and forced convection

Natural convection occurs when fluid motion is induced by temperature differences in a medium, while forced convection refers to fluid motion that is primarily induced by an external force, such as a pump or fan. In simple terms, natural convection relies on the natural movement of fluid due to temperature variations, whereas forced convection is driven by external forces.

Explain convection heat transfer coefficient

The convection heat transfer coefficient (h) is a measure of a fluid's ability to transfer thermal energy across a fluid-solid boundary. Higher values of h indicate more efficient heat transfer between the fluid and the solid surface. The coefficient depends on several factors, including fluid velocity, temperature difference, and the physical properties of the fluid.

Compare natural and forced convection in terms of convection heat transfer coefficient

In general, the convection heat transfer coefficient is higher in forced convection compared to natural convection. The reason for this is that forced convection relies on external forces to generate more fluid motion, thereby increasing fluid velocity. The increased fluid velocity results in the higher value of h in forced convection compared to natural convection. Moreover, forced convection allows to control the fluid motion, which can be optimized for better heat transfer depending on the application.

Conclusion

Forced convection typically has a higher convection heat transfer coefficient compared to natural convection, due to the increased and controlled fluid motion induced by external forces, which results in more efficient heat transfer between the fluid and the solid surface.