Heat transfer from one region of a fluid to another due to actual bulk motion of the fluid induced by mechanical means (fans, pumps, blowers) is called what?

Introduction / Context:
Understanding the modes of heat transfer—conduction, convection, and radiation—is essential for solving HVAC and thermal engineering problems. Convection specifically involves energy transport by fluid motion and is subdivided into free and forced convection based on the source of fluid motion.

Given Data / Assumptions:

• Fluid motion is driven by mechanical devices like fans, blowers, or pumps.
• Temperature gradients exist within the fluid and/or at boundaries.
• Single-phase convection (no boiling/condensation) is assumed for simplicity.

Concept / Approach:
Convection heat transfer combines energy carried by the moving fluid and diffusion at the boundary layer. When motion is caused by external work (mechanical equipment), the process is termed forced convection. In free convection, motion arises from buoyancy due to density differences from temperature variations; radiation is electromagnetic emission; conduction is molecular energy diffusion without bulk motion.

Step-by-Step Reasoning:

Verification / Alternative check:
Dimensionless correlations (e.g., Nusselt vs. Reynolds, Prandtl) are typical of forced convection analyses; buoyancy-based Grashof relations are for free convection.

Why Other Options Are Wrong:

• (a) Conduction involves no bulk motion.
• (b) Free convection relies on buoyancy alone, not mechanical drives.
• (d) Radiation does not require a medium and is unrelated to fluid motion.
• (e) Phase change is not necessary for convection; it can occur without boiling/condensation.

Common Pitfalls:
Confusing mixed convection (both buoyancy and forced effects) with purely forced convection; in design, the dominant mechanism is often determined by the Richardson number.

Final Answer:
Forced convection