Which condition tends to produce a high convective heat transfer coefficient h?

Which condition tends to produce a high convective heat transfer coefficient h?

• A. Higher fluid velocity and turbulence
• B. Lower fluid velocity
• C. Higher viscosity
• D. More conductive fluids

Answer: (A)

The main idea is that the convective heat transfer coefficient h increases when the fluid flow is fast and turbulent, because turbulence enhances mixing and breaks down the thin layer of fluid directly at the surface that carries heat away. When fluid velocity is higher, the Reynolds number rises and transitions into or strengthens turbulence, and those turbulent motions disrupt and thin the thermal boundary layer. With a thinner boundary layer, heat can cross from the surface into the fluid more efficiently, so h becomes larger. If the fluid moves slowly, the boundary layer stays thicker and heat transfer is less efficient, lowering h. Higher viscosity tends to dampen flow and suppress turbulence, which also reduces h. While fluids with higher thermal conductivity k can raise h for a given boundary layer thickness, the dominant factor in boosting h is the flow regime—fast, turbulent flow yields the largest convective transfer.

The main idea is that the convective heat transfer coefficient h increases when the fluid flow is fast and turbulent, because turbulence enhances mixing and breaks down the thin layer of fluid directly at the surface that carries heat away. When fluid velocity is higher, the Reynolds number rises and transitions into or strengthens turbulence, and those turbulent motions disrupt and thin the thermal boundary layer. With a thinner boundary layer, heat can cross from the surface into the fluid more efficiently, so h becomes larger.

If the fluid moves slowly, the boundary layer stays thicker and heat transfer is less efficient, lowering h. Higher viscosity tends to dampen flow and suppress turbulence, which also reduces h. While fluids with higher thermal conductivity k can raise h for a given boundary layer thickness, the dominant factor in boosting h is the flow regime—fast, turbulent flow yields the largest convective transfer.