Mechanical Aptitude Test Mechanical Aptitude Heat Transfer and Thermodynamics Questions and Answers 3

Question 1

A bimetallic strip in a thermostat bends when heated because:

Accepted Answer

The two bonded metals have different coefficients of thermal expansion

Answer

The bimetallic strip curves toward the less-expanding metal because the two bonded metals expand at different rates, creating internal stress that bends the strip.

Question 2

Fins on a radiator or engine heat sink are designed primarily to:

Accepted Answer

Increase surface area for more efficient heat dissipation

Answer

Fins dramatically increase the surface area in contact with the cooling air, allowing far more heat to be transferred by convection per unit time.

Question 3

Why is water commonly used as an engine coolant?

Accepted Answer

Its high specific heat capacity allows it to absorb large amounts of heat

Answer

Water's exceptionally high specific heat capacity (4,186 J/kg·K) means it absorbs a large amount of heat energy for each degree of temperature rise, making it a very effective coolant.

Question 4

An expansion valve in a refrigeration system causes the refrigerant to:

Accepted Answer

Cool down rapidly as its pressure drops sharply

Answer

As refrigerant passes through the expansion valve, the sudden pressure drop causes rapid cooling and partial vaporization via the Joule-Thomson effect.

Question 5

Heat pipes transfer heat so efficiently because they utilize:

Accepted Answer

The large latent heat of a fluid's vaporization and condensation cycle

Answer

Heat pipes evaporate a working fluid at the hot end and condense it at the cool end, exploiting the large latent heat of phase change for highly efficient, passive heat transport.

Mechanical Aptitude Test Practice Test

Mechanical Aptitude Test Practice Test

Mechanical Aptitude Test Mechanical Aptitude Heat Transfer and Thermodynamics Questions and Answers 3