What does the heat transfer coefficient depend on in convection?
A Heat source
B Fluid properties
C Fluid temperature
D Surface roughness
The heat transfer coefficient in convection depends on the properties of the fluid, such as its thermal conductivity, viscosity, and specific heat. These properties influence how well the fluid can transfer heat from a surface.
What is the key factor affecting the rate of heat transfer in boiling?
A Vaporization rate
B Surface area
C Fluid flow rate
D Temperature difference
In boiling, the rate of heat transfer is greatly influenced by the vaporization rate. As the liquid turns into vapor, latent heat is absorbed, and a higher vaporization rate improves the heat transfer efficiency.
What is the main factor that governs the temperature gradient in heat conduction?
A Material thickness
B Fluid velocity
C Thermal conductivity
D Heat source temperature
The temperature gradient in heat conduction is influenced by the thermal conductivity of the material. Higher thermal conductivity results in a faster heat transfer, thus reducing the temperature difference across the material.
What occurs when the temperature of a fluid increases during convective heat transfer?
A Increased density
B Increased heat capacity
C Decreased thermal resistance
D Decreased viscosity
As the temperature of a fluid increases during convective heat transfer, its viscosity typically decreases. This makes it easier for the fluid to move and carry heat away from the heated surface.
Which of the following is the primary mode of heat transfer in a vacuum?
A Radiation
B Conduction
C Convection
D Advection
In a vacuum, heat transfer occurs mainly through radiation. Radiation does not require a medium and transfers heat via electromagnetic waves, such as sunlight traveling through space to reach Earth.
What happens when the thermal conductivity of a material increases?
A Heat transfer decreases
B Material becomes an insulator
C Heat transfer increases
D No effect
Thermal conductivity determines how well a material conducts heat. When the thermal conductivity increases, the material transfers heat more efficiently, leading to an increase in heat transfer.
What is the main purpose of fins in heat exchangers?
A Increase heat capacity
B Increase surface area
C Control temperature
D Reduce fluid velocity
Fins are used in heat exchangers to increase the surface area available for heat exchange. A larger surface area enhances the heat transfer rate, improving the efficiency of the system.
What is the effect of reducing the temperature gradient on heat transfer?
A Increases heat transfer
B No effect
C Becomes constant
D Decreases heat transfer
Heat transfer is directly proportional to the temperature gradient. A smaller temperature difference between the two regions reduces the driving force for heat transfer, thus decreasing the rate of heat flow.
What type of heat transfer occurs in a boiling liquid?
A Radiation
B Conduction
C Convection
D Evaporation
In boiling, convection is the dominant heat transfer mechanism. As the liquid near the heating surface heats up, it rises, and cooler liquid moves down to replace it, thus transferring heat through the liquid.
What is the role of temperature gradient in heat transfer?
A Drives heat transfer
B Determines fluid viscosity
C Affects fluid density
D Decreases heat capacity
The temperature gradient is the difference in temperature between two points. It drives heat transfer, as heat flows from the hotter region to the cooler region. The larger the gradient, the faster the heat transfer.
How does an increase in fluid velocity affect convective heat transfer?
A Reduces heat transfer
B No effect
C Increases heat transfer
D Reduces fluid density
In convective heat transfer, an increase in fluid velocity enhances heat transfer by moving the heated fluid away from the surface faster, allowing cooler fluid to replace it and continue the heat transfer process.
What is the effect of a high heat transfer coefficient?
A Slower heat transfer
B Higher thermal resistance
C Faster heat transfer
D No effect
A high heat transfer coefficient indicates that heat is transferred more effectively between the surface and the fluid. This results in faster heat transfer, as the heat exchange between the two is more efficient.
What happens to the rate of heat transfer if the surface area of the object increases?
A Increases heat transfer
B Decreases heat transfer
C Increases thermal resistance
D No effect
Increasing the surface area allows more space for heat to be transferred between the object and the surrounding fluid. This improves the efficiency of heat exchange, increasing the overall heat transfer rate.
What is the relationship between the rate of heat transfer and the heat flux?
A Inversely proportional
B No relationship
C Depends on fluid type
D Directly proportional
The rate of heat transfer is directly proportional to heat flux. Heat flux is the amount of heat transferred per unit area, and a higher heat flux results in a higher rate of heat transfer through the material.
How does an increase in the temperature difference between two bodies affect heat transfer?
A No effect
B Increases heat transfer
C Reduces thermal resistance
D Decreases heat transfer
Heat transfer is directly proportional to the temperature difference between two bodies. As the temperature difference increases, the rate of heat transfer also increases, as the heat flows more rapidly from the hot to the cold body.