1. What is the primary purpose of extended surfaces (fins) in heat transfer?
a) To reduce the surface area for faster heat dissipation
b) To increase the surface area for enhanced heat transfer
c) To insulate the surface from external temperature changes
d) To decrease the temperature gradient within the material
Answer: b) To increase the surface area for enhanced heat transfer.
Extended surfaces or fins are designed to increase the surface area available for heat transfer, thereby improving the efficiency of heat dissipation or absorption.
2. Which of the following parameters affects the heat transfer from a straight fin?
a) Length of the fin
b) Width of the fin
c) Material conductivity of the fin
d) All of the above
Answer: d) All of the above.
The length, width, and material conductivity of a fin all influence its heat transfer characteristics. Longer fins generally provide more surface area for heat transfer, while wider fins increase the contact area. Higher conductivity materials enhance the efficiency of heat transfer.
3. What does fin efficiency represent in the context of extended surfaces?
a) The ratio of actual heat transfer to ideal heat transfer
b) The ability of a fin to dissipate heat to the surroundings
c) The measure of surface roughness of the fin
d) The rate of temperature change along the fin
Answer: a) The ratio of actual heat transfer to ideal heat transfer.
Fin efficiency compares the actual heat transfer from a fin to the heat transfer that would occur if the entire fin were at the base temperature. It indicates how effectively the fin utilizes its surface area for heat transfer.
4. In which scenario would a thermometer well error most likely occur?
a) When the thermometer is placed in a fluid with uniform temperature
b) When the thermometer is inserted into a thermally insulated container
c) When the thermometer is not in direct contact with the fluid being measured
d) When the thermometer is calibrated correctly
Answer: c) When the thermometer is not in direct contact with the fluid being measured.
Thermometer well error typically arises when the thermometer is not in direct contact with the fluid whose temperature is being measured. This can result in inaccurate readings due to temperature gradients between the fluid and the thermometer.
5. What does fin effectiveness measure in extended surface analysis?
a) The ability of a fin to withstand thermal stress
b) The ratio of actual heat transfer to heat transfer without fins
c) The efficiency of a fin in maintaining a uniform temperature
d) The resistance of a fin to corrosion
Answer: b) The ratio of actual heat transfer to heat transfer without fins.
Fin effectiveness quantifies how much improvement in heat transfer is achieved by using fins compared to a situation without fins. It helps evaluate the practical benefit of employing fins in a heat transfer system.
6. Which type of conduction involves temporary disturbances in temperature distribution within a material?
a) Steady-state conduction
b) Transient conduction
c) Periodic conduction
d) Radiative conduction
Answer: b) Transient conduction.
Transient conduction refers to the temporary variation or disturbance in temperature distribution within a material due to changes in boundary conditions or external factors. It contrasts with steady-state conduction, where temperature distributions remain constant over time.
7. What type of systems exhibit infinite thermal conductivity in the context of unsteady heat conduction?
a) Insulators
b) Metals
c) Fluids
d) Superconductors
Answer: d) Superconductors.
Superconductors are materials that exhibit zero electrical resistance and infinite thermal conductivity when cooled below a critical temperature. In the context of unsteady heat conduction, they can rapidly distribute heat without any thermal resistance.
8. What is the response of a thermocouple in the context of unsteady heat conduction?
a) It measures the rate of heat transfer
b) It measures the change in thermal conductivity
c) It indicates the transient temperature variations
d) It provides information on the material’s specific heat
Answer: c) It indicates the transient temperature variations.
Thermocouples are temperature sensors that produce a voltage proportional to the temperature difference between their junctions. In unsteady heat conduction, thermocouples can detect and record the transient temperature changes occurring within a material or system.
9. When would periodic conduction occur in a material?
a) When the material has non-uniform thermal properties
b) When the material is subjected to alternating heat sources
c) When the material experiences cyclic temperature variations
d) When the material undergoes phase transitions
Answer: c) When the material experiences cyclic temperature variations.
Periodic conduction occurs when a material undergoes repetitive or cyclic variations in temperature over time. This can result from external factors such as alternating heat sources or environmental conditions.
10. What is the purpose of heating and cooling bodies with known temperature distributions in unsteady heat conduction analysis?
a) To induce phase transitions in the material
b) To measure the thermal conductivity of the material
c) To study the transient response of the material
d) To determine the specific heat capacity of the material
Answer: c) To study the transient response of the material.
Heating and cooling bodies with known temperature distributions allow researchers to analyze the transient behavior of materials in response to changes in thermal conditions. This helps in understanding how materials respond to variations in temperature over time.
11. How does the fin efficiency affect the performance of an extended surface in heat transfer applications?
a) Higher fin efficiency results in increased heat transfer effectiveness
b) Higher fin efficiency decreases the required surface area of the fin
c) Lower fin efficiency reduces the overall heat transfer rate
d) Fin efficiency has no significant impact on heat transfer performance
Answer: a) Higher fin efficiency results in increased heat transfer effectiveness.
Fin efficiency directly influences the effectiveness of extended surfaces in enhancing heat transfer. Higher fin efficiency means that more heat is effectively transferred from the fin to the surroundings, leading to improved heat dissipation or absorption.
12. In what situation would fin effectiveness be close to 1?
a) When the fin is made of a low-conductivity material
b) When the fin is very short
c) When the fin is exposed to high-velocity airflow
d) When the fin is highly effective in transferring heat
Answer: d) When the fin is highly effective in transferring heat.
Fin effectiveness approaches 1 when the fin efficiently transfers heat from the base to the surroundings. This can occur when the fin is appropriately designed, made of a high-conductivity material, and operates under favorable conditions for heat transfer.
13. What is the primary advantage of using annular fins compared to straight fins in heat transfer applications?
a) Annular fins have a larger surface area
b) Annular fins provide more uniform heat distribution
c) Annular fins offer better resistance to thermal stresses
d) Annular fins are easier to manufacture
Answer: a) Annular fins have a larger surface area.
Annular fins, due to their circular shape, typically have a larger surface area compared to straight fins of similar dimensions. This increased surface area enhances heat transfer efficiency, making annular fins advantageous in certain heat transfer applications.
14. Which statement best describes the significance of periodic conduction in practical applications?
a) Periodic conduction ensures uniform temperature distribution within materials
b) Periodic conduction is essential for maintaining steady-state heat transfer
c) Periodic conduction allows for the analysis of cyclic thermal stresses
d) Periodic conduction is primarily observed in highly conductive materials
Answer: c) Periodic conduction allows for the analysis of cyclic thermal stresses.
Periodic conduction is crucial for understanding how materials respond to cyclic variations in temperature, which can lead to thermal stresses. This knowledge is essential for designing materials and structures that can withstand cyclic thermal loading without failure.
15. How does a thermometer well error impact temperature measurement accuracy?
a) It leads to overestimation of temperature
b) It results in underestimation of temperature
c) It causes fluctuations in temperature readings
d) It has no significant effect on temperature measurement
Answer: b) It results in underestimation of temperature.
Thermometer well error typically results in the thermometer not being in direct contact with the fluid being measured, leading to underestimation of temperature. This occurs because the thermometer measures the temperature of the well rather than the actual fluid temperature.