Which material has the highest thermal conductivity?
A Air
B Water
C Copper
D Wood
Copper has one of the highest thermal conductivities among common materials, making it an excellent conductor of heat. Its high conductivity allows it to efficiently transfer heat in various applications, such as in heat exchangers and electrical wiring.
What does the heat transfer coefficient represent?
A Rate of heat transfer
B Temperature gradient
C Material heat resistance
D Rate of conduction
The heat transfer coefficient quantifies the rate at which heat is transferred between a solid and a fluid (or between fluids). It depends on the nature of the fluid, the surface texture, and the flow characteristics.
Which method of heat transfer does not require a medium?
A Convection
B Radiation
C Evaporation
D Conduction
Radiation transfers heat through electromagnetic waves and does not require a medium, unlike conduction and convection. Heat from the Sun reaches Earth through radiation, traveling through the vacuum of space.
Which of the following increases the thermal resistance of an insulating material?
A Higher density
B Lower surface area
C Higher thermal conductivity
D Higher thickness
Thermal resistance increases with the thickness of an insulating material. A thicker layer reduces the heat flow, as it provides more resistance to the heat transfer, making it an effective insulator.
What happens to the heat transfer rate when the temperature difference increases?
A Decreases
B Becomes zero
C Increases
D Stays constant
According to Fourier’s Law and Newton’s Law of Cooling, the heat transfer rate is directly proportional to the temperature difference between two bodies. A higher temperature difference results in a faster heat transfer rate.
In which process is latent heat involved?
A Boiling
B Radiation
C Convection
D Conduction
Latent heat is involved during phase changes, such as boiling. During boiling, heat energy is used to convert liquid into vapor without changing the temperature, which is known as latent heat of vaporization.
Which material is most commonly used for heat exchangers?
A Steel
B Copper
C Plastic
D Aluminum
Copper is widely used in heat exchangers because of its high thermal conductivity, which allows efficient heat transfer. It is also corrosion-resistant, making it durable for heat transfer applications.
What does the Stefan-Boltzmann Law relate to?
A Thermal conductivity
B Thermal expansion
C Radiant heat transfer
D Fluid flow
The Stefan-Boltzmann Law describes the power radiated by a blackbody in terms of its temperature. The total radiated energy is proportional to the fourth power of the temperature, influencing heat transfer through radiation.
What is the main factor that affects the efficiency of a heat pipe?
A Fluid type
B Temperature difference
C Pipe diameter
D Pipe length
The efficiency of a heat pipe is primarily influenced by the type of fluid used inside. The fluid’s ability to vaporize and condense effectively, along with its thermal properties, determines the heat transfer performance of the heat pipe.
Which is the main effect of cryogenics on heat transfer?
A Increases conduction
B Increases radiation
C Increases thermal resistance
D Reduces heat flow
Cryogenics deals with extremely low temperatures, which reduce molecular motion and therefore heat flow. This results in lower thermal conductivity and slower heat transfer in materials at cryogenic temperatures.
What factor primarily influences the rate of convective heat transfer?
A Temperature gradient
B Surface area
C Fluid velocity
D Emissivity
In convection, the rate of heat transfer is primarily influenced by the velocity of the fluid. Faster fluid movement enhances heat transfer by carrying more thermal energy from the heated surface to cooler regions.
What occurs during the condensation process?
A Heat is absorbed
B Gas turns into liquid
C Liquid turns into gas
D Solid turns into gas
During condensation, a gas loses heat and transitions into a liquid. This process releases latent heat, which is absorbed by the surrounding medium, such as air or water.
What is the effect of increasing the surface area on heat transfer?
A No effect
B Decreases heat transfer
C Increases heat transfer
D Decreases resistance
Increasing the surface area enhances heat transfer because it provides more space for heat to flow between the two bodies involved. More surface area leads to better heat exchange, whether by conduction, convection, or radiation.
What is the main role of insulation in thermal systems?
A Prevent heat loss
B Increase temperature gradient
C Increase heat transfer
D Speed up heat flow
Insulation is used to reduce heat loss or gain in a system. It helps maintain a constant temperature by preventing unwanted heat from escaping or entering, which improves energy efficiency in thermal systems.
Which of the following represents a phase change that involves heat transfer?
A Melting
B Boiling
C Freezing
D All of the above
All phase changes, such as freezing, boiling, and melting, involve heat transfer. Each phase change absorbs or releases latent heat, which is essential for the transition from one state of matter to another.