Boiling and Condensation: Comprehensive Learning Quizzes for Mechanical Engineering

Question 1

What is the definition of critical heat flux (CHF) in boiling?

Accepted Answer

The maximum heat transfer rate achievable from a heating surface to a boiling fluid before the boiling regime shifts to film boiling.

Answer

The heat flux at which the boiling process becomes unstable.

Answer

The heat flux where the vapor bubbles detach from the heating surface.

Answer

The minimum heat flux required to initiate the boiling process.

Question 2

Which heat transfer mechanism is dominant during condensation?

Accepted Answer

Latent heat release

Answer

Conduction

Answer

Convection

Answer

Radiation

Question 3

How does the heat transfer rate in pool boiling typically compare to that in flow boiling?

Accepted Answer

Higher in pool boiling

Answer

Similar in both

Answer

Independent of the boiling regime

Answer

Lower in pool boiling

Question 4

Which parameter is NOT a primary factor affecting the condensation rate on a vertical surface?

Accepted Answer

Fluid pressure

Answer

Condensation coefficient

Answer

Surface temperature

Answer

Vapor velocity

Question 5

What is the defining characteristic of dropwise condensation?

Accepted Answer

Small, distinct condensate droplets forming on the surface, leading to higher heat transfer rates.

Answer

Formation of large, unstable vapor bubbles on the surface.

Answer

A continuous film of condensate forming on the surface.

Answer

The condensation process occurring at a constant rate.

Question 6

How does the heat transfer coefficient typically differ between flow boiling and pool boiling?

Accepted Answer

Higher in flow boiling

Answer

Lower in flow boiling

Answer

Dependent solely on the fluid viscosity

Answer

Similar in both

Question 7

In which boiling regime does the Leidenfrost effect occur?

Accepted Answer

Film boiling

Answer

Nucleate boiling

Answer

Convection boiling

Answer

Transition boiling

Question 8

Which statement is NOT a characteristic of nucleate boiling?

Accepted Answer

Boiling occurs at a uniform temperature across the entire surface.

Answer

The boiling process is highly dynamic.

Answer

Vapor bubbles form on the heated surface.

Answer

High heat transfer rates are observed.

Question 9

What factor primarily influences the heat transfer coefficient in flow boiling?

Accepted Answer

Fluid velocity

Answer

Ambient pressure

Answer

Heat flux

Answer

Surface tension of the liquid

Question 10

Which boiling regime is associated with a significant reduction in heat transfer due to the formation of a vapor film?

Accepted Answer

Film boiling

Answer

Nucleate boiling

Answer

Transition boiling

Answer

Convection boiling

Question 11

When condensation occurs on a vertical surface, which type of condensation is most likely to form?

Accepted Answer

Filmwise condensation

Answer

Transition condensation

Answer

Nucleate condensation

Answer

Dropwise condensation

Question 12

What is the primary driving force behind condensation?

Accepted Answer

The difference in vapor pressure between the vapor and the liquid.

Answer

The surface tension of the liquid.

Answer

The temperature difference between the vapor and the surface.

Question 13

Which factor has the most significant impact on the heat transfer coefficient during condensation?

Accepted Answer

The type of condensation (filmwise or dropwise)

Answer

The ambient pressure

Answer

The fluid velocity

Answer

The surface material of the condenser

Question 14

The Leidenfrost effect describes a phenomenon where:

Accepted Answer

A liquid droplet levitates above a heated surface due to a vapor film.

Answer

Nucleate boiling is initiated at a lower temperature.

Answer

Condensation occurs faster due to increased surface tension.

Question 15

What is the primary objective of a heat exchanger used for condensation?

Accepted Answer

Transfer heat from the vapor to the cooling fluid.

Answer

Reduce the pressure of the vapor.

Answer

Increase the boiling point of the fluid.

Question 16

Which of the following is NOT a typical application of boiling and condensation processes?

Accepted Answer

Generating electricity from solar power.

Answer

Power plant steam cycles.

Answer

Refrigeration systems.

Question 17

Which of the following is NOT a characteristic of nucleate boiling?

Accepted Answer

Large, stable vapor bubbles form at the heating surface.

Answer

High heat transfer coefficients.

Answer

Rapid bubble growth and departure.

Question 18

A condenser in a refrigeration system has a significant amount of condensate accumulating on its surface. What type of condensation is most likely occurring?

Accepted Answer

Film condensation

Answer

Mixed condensation

Answer

Dropwise condensation

Answer

Nucleate condensation

Question 19

Which of these factors would INCREASE the heat transfer coefficient during pool boiling?

Accepted Answer

Increasing the surface roughness of the heating surface.

Answer

Decreasing the pressure of the surrounding fluid.

Answer

Reducing the heat flux.

Question 20

In a forced convection boiling system, what primarily drives the fluid flow?

Accepted Answer

An external pump or fan.

Answer

Vapor bubble formation and movement.

Answer

Natural buoyancy forces.

Answer

Surface tension gradients.

Question 21

A kettle filled with water is heated on a stove. As the water reaches its boiling point, what happens to the heat transfer coefficient?

Accepted Answer

It increases significantly.

Answer

It fluctuates randomly.

Answer

It remains constant.

Answer

It decreases slightly.