Which of the following is most effective in transferring heat in a heat exchanger?
A High material thickness
B High surface area
C Low fluid temperature
D High fluid velocity
In a heat exchanger, a high surface area allows better heat transfer between the two fluids. This is because the larger the surface area, the more area is available for heat exchange, improving efficiency.
What does heat flux represent in heat transfer?
A Heat transfer rate per area
B Thermal conductivity
C Heat capacity
D Temperature difference
Heat flux represents the amount of heat transferred per unit area. It quantifies the heat flow through a material, typically expressed in watts per square meter (W/m²), and is directly influenced by the temperature gradient and material properties.
Which material property is crucial for heat conduction?
A Density
B Specific heat
C Emissivity
D Thermal conductivity
Thermal conductivity is the material property that determines how well heat is conducted through a material. Materials with high thermal conductivity, such as metals, conduct heat more efficiently compared to insulators like wood or plastic.
What is the effect of increasing the temperature difference on the rate of heat transfer?
A No effect
B Becomes constant
C Increases heat transfer
D Decreases heat transfer
The rate of heat transfer is directly proportional to the temperature difference between two objects. A higher temperature difference results in faster heat transfer, whether through conduction, convection, or radiation, according to Fourier’s Law.
What type of heat transfer occurs in a vacuum?
A Convection
B Conduction
C Radiation
D None of the above
In a vacuum, where there are no molecules for conduction or convection, heat transfer occurs solely through radiation. Radiation is the transfer of energy via electromagnetic waves, which can travel through the vacuum of space.
Which of the following best describes the process of boiling?
A Phase change from liquid to gas
B Heat loss to surroundings
C Heat transfer via radiation
D Heat transfer through conduction
Boiling is a phase change process where a liquid absorbs heat and converts into vapor. This occurs at the boiling point and requires latent heat, which is absorbed without a temperature change during the phase transition.
In a heat exchanger, which of the following is used to increase heat transfer efficiency?
A Insulation
B Thermal resistance
C Heat source temperature
D Fins
Fins are used in heat exchangers to increase the surface area available for heat exchange. This improvement in surface area allows for better heat dissipation or absorption, making the heat transfer process more efficient.
What is the key factor affecting the performance of thermal insulation?
A Material density
B Surface area
C Thermal conductivity
D Heat flux
The performance of thermal insulation depends on its thermal conductivity. Materials with low thermal conductivity are better insulators because they resist heat flow more effectively, preventing heat loss or gain in thermal systems.
What is the primary mechanism of heat transfer in the atmosphere?
A Radiation
B Convection
C Conduction
D Evaporation
In the atmosphere, heat is primarily transferred by convection. Warm air rises and cooler air sinks, creating a continuous flow of air that transfers heat from the Earth’s surface to the higher atmosphere.
What does the term “specific heat” refer to?
A Heat required to raise temperature
B Energy absorbed during phase change
C Heat transferred by radiation
D Heat loss to surroundings
Specific heat is the amount of heat required to raise the temperature of a unit mass of a substance by one degree Celsius (or Kelvin). It is a material property that varies depending on the substance being heated.
Which of the following increases the effectiveness of fins in heat transfer?
A Decreasing surface area
B Increasing material thickness
C Increasing air velocity
D Decreasing heat flux
Increasing air velocity enhances the convective heat transfer rate between the fins and the surrounding air. Faster-moving air removes heat more efficiently from the fins, improving the heat dissipation rate and overall system performance.
What is the role of the thermal resistance in heat transfer?
A Increase heat transfer
B Controls heat source temperature
C No effect on heat transfer
D Decrease heat transfer
Thermal resistance opposes the flow of heat. The higher the thermal resistance, the less heat is transferred through the material. Insulating materials are designed to have high thermal resistance, reducing heat flow between systems.
What is a heat pipe used for?
A Heat transfer in electronics
B Heat insulation
C Heat storage
D Heat conduction
Heat pipes are used in electronics to transfer heat from hot components, such as processors, to cooler areas. They operate by using evaporation and condensation within a sealed pipe, making them highly efficient for heat management.
Which of the following materials is typically used in cryogenic applications?
A Insulating foam
B Steel
C Copper
D Aluminum
Steel is commonly used in cryogenic applications due to its strength and ability to maintain its structural integrity at very low temperatures. It is also resistant to cracking, which is critical when handling cryogenic fluids.
What is the effect of increasing the fluid velocity in a convective heat transfer process?
A Becomes unstable
B Decreases heat transfer
C Increases heat transfer
D No effect
Increasing the fluid velocity enhances convective heat transfer because faster-moving fluid can remove more heat from a heated surface and replace it with cooler fluid. This process accelerates the heat exchange rate.
