What happens to heat transfer coefficients when heat is transferred by forced convection and fluid velocity increases?

When heat is transferred by forced convection, the rate of heat transfer is influenced significantly by the velocity of the fluid moving over a surface. As the fluid velocity increases, the turbulent flow in the vicinity of the surface intensifies, which enhances the mixing of the fluid layers. This increased mixing reduces the thermal resistance at the fluid-surface interface, allowing for more efficient heat transfer.

The heat transfer coefficient is a measure of this efficiency and is directly proportional to the fluid velocity in forced convection scenarios. Therefore, as the fluid velocity increases, the heat transfer coefficient also increases. This phenomenon is fundamental in many engineering applications, such as in heat exchangers, where maximizing heat transfer is crucial for performance efficiency.

Thus, the correct answer reflects the direct relationship between increasing fluid velocity and the enhancement of heat transfer coefficients due to improved turbulence and mixing at the surface.