What determines the direction of flow with convection?

What determines the direction of flow with convection?

• A. The humidity determines the direction of flow.
• B. Wind speed determines the direction.
• C. The temperature; if air temperature is greater than skin temperature convection is positive and heat flows from air to skin; if skin temperature is greater than air temperature convection is negative and heat flows from body to air.
• D. The surface color determines the direction.

Answer: (C)

Convection moves heat through a moving fluid, and the direction of that heat transfer is set by the temperature difference between what’s around the surface and the surface itself. Heat naturally flows from the hotter region to the cooler region. So if the surrounding air is warmer than the skin, heat moves from the air into the skin. If the skin is warmer than the surrounding air, heat moves from the skin into the air. Wind speed, humidity, or surface color don’t determine this direction; they can affect how fast heat is transferred or what kind of heat transfer (radiation vs convection) dominates, but not the sign of the convective heat flow.

Convection moves heat through a moving fluid, and the direction of that heat transfer is set by the temperature difference between what’s around the surface and the surface itself. Heat naturally flows from the hotter region to the cooler region. So if the surrounding air is warmer than the skin, heat moves from the air into the skin. If the skin is warmer than the surrounding air, heat moves from the skin into the air. Wind speed, humidity, or surface color don’t determine this direction; they can affect how fast heat is transferred or what kind of heat transfer (radiation vs convection) dominates, but not the sign of the convective heat flow.