Modes of heat transfer What do we call the process in which heat is transferred within a fluid (or along a surface to a fluid) due to the actual bulk motion of the heated particles?

Introduction / Context:
Understanding the three primary modes of heat transfer—conduction, convection, and radiation—is foundational in thermal engineering and HVAC system design.

Given Data / Assumptions:

• Fluids can move, creating bulk transport of energy.
• No special participating media effects are assumed.

Concept / Approach:
Convection is heat transfer between a surface and an adjacent moving fluid, or within a fluid, due to combined effects of conduction at the microscopic level and bulk motion (advection) of fluid parcels. The governing empirical relation is Newton’s law of cooling: q = h * A * (T_s − T_∞).

Step-by-Step Solution:
Identify the mechanism described: “actual motion of heated particles.”This points to convection (forced or natural), not purely molecular conduction or photon-based radiation.Therefore, select convection.

Verification / Alternative check:
Without motion, heat transfer through a stationary fluid is by conduction across the boundary layer. When buoyancy or external forces drive motion, convection dominates.

Why Other Options Are Wrong:

• Conduction: energy transfer via molecular interactions without bulk motion.
• Radiation: energy transfer via electromagnetic waves, no medium required.
• Phase change: a thermal process but not a “mode” by itself—evaporation/condensation accompany convection.

Common Pitfalls:
Using the term “conduction in fluids” for what is actually convection; forgetting that h depends on flow regime and properties.

Final Answer:
Convection