# Manufacturing Engineering Questions & Answers – Heat Transfer-2

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This set of Manufacturing Science Puzzles focuses on “Heat Transfer-2”.

1. Ratio of rate of heat conduction to the rate of internal energy storage is in solid is known as?
a) Biot number
b) Drag coefficient
c) Eckert number
d) Fourier number

Explanation: Fourier number is the ratio of heat conduction to the rate of heat storage. The significance of Fourier number is 1. It signifies the degree of penetration of heating or cooling effect, 2. It is a measure of heat conducted through a body relative to heat stored.

2. Ratio of pressure drop for internal flow through ducts is known as?
a) Friction factor
b) Grashof number
c) Colburn factor
d) Nusselt number

Explanation: Friction factor (µ) is defined as the ratio between the force required to move a section of pipe and the vertical contact force applied by the pipe on the seabed, in simpler terms, it is the ratio of pressure drop for internal flow though ducts.

3. Ratio of buoyancy to viscous forces is known as?
a) Prandtl number
b) Grashof number
c) Colburn factor
d) Nusselt number

Explanation: Grashof number in natural convection is analogous to the Reynolds number is forced convection. Grashof number indicates the ratio of the buoyancy force to the viscous force. Higher Gr number means increased natural convection flow.
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4. Which of the following is known as the dimensionless heat transfer coefficient?
a) Friction factor
b) Grashof number
c) Colburn factor
d) Weber number

Explanation: Colburn factor obtained from the Reynold-Colburn analogy relates to the local skin friction coefficient (from fluid mechanics) to the local convective heat transfer coefficient.

5. Which of the following is known as the dimensionless heat transfer coefficient?
a) Friction factor
b) Grashof number
c) Nusselt number
d) Prandtl number

Explanation: Nusselt number is a dimensionless number and it is defined as the ratio of convective heat flux to the conductive heat flux (where fluid is in rest). Convection in fluid = conduction in fluid + advection in fluid (occurs due to motion of fluid). So, practically we can understand it as a comparison of heat taken by fluid due to moving fluid and heat taken by a static fluid when flowing over a heated plate (or inside a pipe).

6. Ratio of convection heat transfer to conduction is known as?
a) Friction factor
b) Grashof number
c) Colburn factor
d) Nusselt number

Explanation: The Nusselt number is the ratio of convective to conductive heat transfer across a boundary.
Nu = $$\frac{hl}{k}$$, where, h = heat transfer coefficient, l = characteristic length and k = thermal conductivity.

7. Product of Prandtl number and Reynolds number is also known as?
a) Peclet number
b) Prandtl number
c) Rayleigh number
d) Biot number

Explanation: Peclet number is the product of Prandtl number and Reynolds number, in other sense, it is the ratio of the heat transfer by convection to the heat transferred by conduction. So, you can consider a pipe with some wall thickness. The wall conducts heat to the fluid. While the heat can also be carried away by the fluid in motion which is called as advection. If the advection term is dominant, then the Peclet number is going to large and thus the hat transfer from the wall is of less importance. Conversely, the heat transfer form the wall to the fluid can be of higher importance in the case of a smaller Peclet number.

8. Ratio of molecular diffusivity to thermal diffusivity is also known as?
a) Biot number
b) Prandtl number
c) Rayleigh number
d) Biot number

Explanation: Prandtl number as explained by others here, is a dimensionless number, which is the ratio of molecular diffusivity of momentum to molecular diffusivity of heat. It shows the relative thickness of the velocity boundary layer to the thermal boundary layer.

9. Product of Grashof and Prandtl is known as?
a) Peclet number
b) Biot number
c) Rayleigh number
d) Reynolds number

Explanation: Rayleigh number is the product of Grashof and Prandtl number.

10. Ratio of inertia to viscous forces is known as?
a) Stanton number
b) Prandtl number
c) Rayleigh number
d) Reynolds number

Explanation: The Reynolds number is the ratio of inertial forces to viscous forces. The Reynolds number is a dimensionless number used to categorize the fluids systems in which the effect of viscosity is important in controlling the velocities or the flow pattern of a fluid.

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