1. Define the convection.
Ans: Convection is a heat transfer process that will occur between a solid surface and a fluid medium when they are at different temperatures.
2. What is meant by free or natural convection?
Ans: If fluid movement occurs due to the change in density resulting from temperature gradients, the mode of heat transfer is said to be natural or free convection.
3. What is forced convection?
Ans: If the movement of the fluid is artificially created by an external force such as a blower or fan, that type of heat transfer is known as forced convection.
4. What are the dimensionless parameters used in forced convection?
Ans:
1. Reynolds number (Re)
2. Number of Nusselt (Nu)
3. Number of Prandtl (Pr)
5. Define the thickness of the boundary layer.
Ans: The thickness of the boundary layer has been defined as the distance from the surface at which the local velocity or temperature reaches 99% of the external velocity or temperature.
6. What is meant by laminar flow and turbulent flow?
Ans: Laminar flow: Sometimes called flow laminar flow line flow. In this type of flow, the fluid moves in layers and each fluid particle follows a smooth continuous path. The fluid particles in each layer remain in an ordered sequence without mixing with each other.
Turbulent flow: In addition to laminar flow, a different irregular flux is the frequency observed in nature. This type of flow is called turbulent flow. The trajectory of any individual particle is zigzagging and irregular. Fig. Shows the instantaneous velocity in laminar and turbulent flow.
7. What is the hydrodynamic boundary layer?
Ans: In the hydrodynamic boundary layer, the fluid velocity is less than 99% of the free stream velocity.
8. What is the thermal boundary layer?
Ans: In the thermal boundary layer, the temperature of the fluid is less than 99% of the free stream velocity.
9. Define the Grashof number (Gr).
Ans: It is defined as the product ratio of inertia force and flotation force to the square of viscous force.
Gr = Force of inertia / Absorption force (Viscous force) 2
10. Define the Reynolds number (Re).
Ans: It is defined as the relationship between the force of inertia and the viscous force.
Re = force of inertia / viscous force
11. Define the number of prandtl (Pr).
Ans: It is the relation of the diffusivity of moment of the thermal diffusivity.
Pr = Impulse Diffusivity / Thermal Diffusivity
12. What mode of heat transfer is the coefficient of heat transfer by generally higher convection, natural or forced convection? why ?
Ans: The convection heat transfer coefficient is usually higher in forced convection than in natural convection because it depends mainly on factors such as density, velocity and viscosity of the fluid.