Question

What is external forced convection? How does it differ from internal forced convection? Can a heat transfer system involve both internal and external convection at the same time? Give an example.

Short answer

Provide an example. Answer: The difference between external and internal forced convection lies in how the fluid flows and interacts with surfaces. External forced convection involves the fluid flowing over an object and exchanging heat, while internal forced convection occurs when the fluid flows within a solid boundary, such as inside a pipe or duct, and exchanges heat with the internal surface. A heat transfer system can involve both internal and external convection simultaneously. An example of such a system is a car radiator, where coolant flows inside tubes (internal convection) to absorb heat from the engine, and air flows over the radiator fins (external convection) to dissipate the heat absorbed by the coolant, cooling the engine.

Step-by-step solution

Definition of External Forced Convection

External forced convection refers to the heat transfer process that occurs when a fluid flows over an object which is either hotter or cooler than the fluid itself. The process is caused by external forces such as the pressure difference or the action of a pump or a fan, which propel the fluid over the surface resulting in heat exchange.

Definition of Internal Forced Convection

Internal forced convection, on the other hand, occurs when a fluid flows within a solid boundary, such as inside a pipe or a duct. This heat transfer process is regulated by the fluid flowing through the cross-section of the boundary due to external or internal forces and exchanging heat with the internal surface of the solid encasement.

Differences between External and Internal Forced Convection

The main differences between external and internal forced convection are: 1. In external forced convection, the fluid flows over the object, whereas in internal forced convection, the fluid flows within a solid boundary. 2. External forced convection usually has a greater surface area exposed to the fluid, resulting in increased heat transfer, whereas in internal forced convection, the surface area for heat transfer is restricted by the solid boundary. 3. The rate of heat transfer in external convection depends on the fluid's velocity and the surface's shape and size, while internal convection depends on the fluid's velocity, pipe or duct geometry, and thermal properties of the solid encasement.

Heat Transfer System Involving Both Internal and External Convection

Yes, a heat transfer system can involve both internal and external convection simultaneously. An example of such a system is a car radiator. The radiator has coolant flowing inside the tubes (internal forced convection), which absorbs heat from the engine. Simultaneously, air is blown over the radiator fins by the fan (external forced convection), which helps dissipate the heat absorbed by the coolant, thus cooling the engine.