What is the primary mode of heat transfer in solids?
A Radiation
B Convection
C Conduction
D Evaporation
Conduction is the primary mode of heat transfer in solids, where heat flows due to the vibration of molecules. This mode occurs when particles in a material collide, transferring energy from the hotter region to the cooler region.
Which of the following is used to increase the heat transfer rate in a heat exchanger?
A Fins
B Cooling fans
C Compressors
D Insulation
Fins are commonly used in heat exchangers to increase the surface area for heat transfer. The larger surface area allows more heat to dissipate or absorb, improving the efficiency of the heat exchanger.
Which law governs the conduction of heat in a material?
A Newton’s Law of Cooling
B Stefan-Boltzmann Law
C Planck’s Law
D Fourier’s Law
Fourier’s Law governs the conduction of heat, stating that the rate of heat transfer through a material is proportional to the negative gradient of the temperature and the material’s thermal conductivity.
What is the unit of thermal conductivity?
A Joule per second (J/s)
B Watt per meter Kelvin (W/m•K)
C Watt per meter squared (W/m²)
D Watt per Kelvin (W/K)
Thermal conductivity is measured in watts per meter per Kelvin (W/m•K). It indicates how well a material can conduct heat. The higher the thermal conductivity, the better it conducts heat.
In which of the following does convection occur?
A Ice melting
B Metal heating up
C Water boiling
D Sunlight warming the earth
Convection occurs in fluids (liquids and gases) when warmer regions of the fluid rise and cooler regions sink. In boiling water, hot water rises, and cold water sinks, transferring heat throughout the liquid.
What is the key factor influencing the rate of heat transfer by radiation?
A Emissivity
B Temperature difference
C Thermal conductivity
D Surface area
Emissivity is the ability of a material’s surface to emit thermal radiation. Higher emissivity allows more heat to be radiated. This property, along with the temperature difference, greatly influences the heat transfer rate.
What is the heat transfer mechanism in a heat pipe?
A Conduction
B Evaporation and condensation
C Radiation
D Convection
In a heat pipe, heat is transferred through the phases of evaporation and condensation. A liquid inside the pipe evaporates at the hot end, then condenses at the cooler end, transferring heat efficiently through the pipe.
What is thermal resistance in heat transfer?
A The ability to conduct heat
B The flow of heat in fluids
C The opposition to heat flow
D The ability to absorb heat
Thermal resistance is the opposition that a material offers to the flow of heat. Higher thermal resistance means less heat transfer. It is the inverse of thermal conductivity, and can be influenced by material properties and thickness.
Which of the following is used to reduce heat transfer in walls?
A Insulation
B Radiators
C Fins
D Coolants
Insulation is used in walls to reduce heat transfer. It creates a barrier that prevents heat from entering or escaping, keeping the temperature constant within a building and reducing energy consumption.
Which of the following is a key principle of Newton’s Law of Cooling?
A Heat flows from cold to hot
B Heat always flows from hot to cold
C Convection increases with temperature
D Heat transfer rate is proportional to the temperature difference
Newton’s Law of Cooling states that the rate of heat transfer between an object and its surroundings is directly proportional to the temperature difference between the object and the surrounding medium.
What is the main principle behind phase change heat transfer?
A Change in temperature
B Change in heat capacity
C Change in material state
D Change in density
Phase change heat transfer occurs when a substance changes from one state of matter to another (e.g., from liquid to gas during boiling). This requires significant heat energy, known as latent heat, for the phase transition to occur.
Which property of a material affects its ability to resist thermal expansion?
A Thermal conductivity
B Coefficient of thermal expansion
C Heat capacity
D Emissivity
The coefficient of thermal expansion quantifies how much a material expands or contracts with temperature changes. Materials with a low coefficient expand less with heat, making them better at resisting thermal expansion.
What is the primary method of heat transfer from the Sun to the Earth?
A Convection
B Conduction
C Radiation
D Evaporation
The primary method of heat transfer from the Sun to the Earth is radiation. Solar radiation travels through the vacuum of space, transferring energy without the need for a medium like air or water.
In which system is HVAC commonly used?
A Building climate control
B Refrigeration
C Solar panels
D Heat exchangers
HVAC (Heating, Ventilation, and Air Conditioning) systems are used to regulate the temperature, humidity, and air quality inside buildings. They maintain comfortable indoor environments, improving energy efficiency and air circulation.
What factor influences heat transfer in boiling?
A Fluid velocity
B Temperature gradient
C Thermal conductivity
D Vaporization rate
During boiling, the vaporization rate (the rate at which liquid turns into vapor) influences heat transfer. A higher vaporization rate improves heat transfer efficiency, as more energy is absorbed in the phase change from liquid to gas.