Nate Exam Flashcards
Most of the heat transfer from the heat exchanger is by which of the following:
Radiation
Convection
Evaporation
Conduction
Convection
Convection is the transfer of heat between a solid surface and a fluid (gas or liquid) that is in motion.
The fluid moves over the surface and carries away heat by conduction and diffusion.
(BLANK) is the process in which solid turns directly into a vapor without going through the liquid phase:
Saturation
Superheating
Sublimation
Subcooling
Sublimation
Some common examples of sublimation include dry ice, iodine, and camphor
In a refrigeration system, miscibility is the ability of a fluid to:
Reacts with water and forms alkaline com-pounds
Reacts with water and forms acidic compounds
Readily mix with other fluids
Reacts with air and forms corrosion comp
Miscibility refers to the ability of a refrigerant to mix with a lubricant. A refrigerant that is miscible with a lubricant will mix with the lubricant and form a single phase. This helps in improving the efficiency of the system.
Relays and contractors are (BLANK) control switches:
Pressure activated
Electrically operated
Temperature operated
Manually operated
Electrically operated
Relays are typically used for low-current ap-plications, such as controlling small motors or lights. Contactors are typically used for high-cur-rent applications, such as controlling motors, air conditioners, and other large loads.
Which of the following law states that the total pressure of a confined mixture of gases is the sum of pressures of each of the gases in the mixture:
Flemings law
Boyles law
Dalton’s law
Charles law
Dalton’s law
The (Blank) is used to measure the relative humidity of the air.
A.) Both Dry Bulb & Wet Bulb Temperature
B.)Dry Bulb temperature
C.)Wet bulb temperature
Wet bulb temperature
Which of the following gas is used for purging or pressurizing a refrigerant or air conditioning system:
Oxygen
Air
Nitrogen
All of the options are correct
Nitrogen is an inert gas, which means that it does not react with other substances. This makes it a safe and reliable choice for purging or pressurizing refrigerant or air conditioning systems.
In Fire tube boiler, which of the following pass through the tubes:
Hot water
All the options are correct
Flue gases
Steam
The flue gases are a mixture of carbon dioxide, water vapor, and other combustion products which are hot and contain a lot of energy. When the flue gases pass through the tubes, they heat the water, causing it to turn into steam. The steam is then used to heat water or other fluids, or to generate power.
At 32F. 1lb of ice can be changed to 1 lb of water by adding (Blank) Btu:
36 Btu
72 Btu
108Btu
144Btu
The latent heat of fusion is the amount of heat required to change a solid into a liquid without changing its temperature. For water, the latent heat of fusion is 144 Btu/lb.
The larger the diameter of the center hose, higher will be evacuation time of the refrigerant from the system:
True
False
False
A larger diameter hose will allow for a faster flow of refrigerant, which will result in quicker evacuation of the system.
(Blank) _are the most common way to control the speed of a refrigeration system’s compressor:
Belt connections
VFDs
Variac
Auto Transformer
A Variable Frequency Drive (VFD) system is a device that controls the speed of an electric motor by adjusting the frequency of the electrical cur-rent. This allows the motor to operate at different speeds, which can be used to control the refrigeration system’s capacity
Which of the following compressor uses pistons, cylinders and valves to compress the refrigerant
gas:
Reciprocating compressor
Screw compressor
Centrifugal compressor
Lobe compressor
Reciprocating compressors are typically used in large refrigeration systems, such as those used in commercial buildings and industrial ap-plications. reciprocating compressors are a reliable and efficient type of compressor that is used in a variety of applications. However, they can be noisy and require regular maintenance.
The tubes of the indoor evaporator coils are made of which of the following:
Steel
Copper
Aluminum
All the options are correct
The tubes of the indoor evaporator coils are typically made of copper, steel, or aluminum. Howev-er, Copper is the most common material used for evaporator coils because it is a good conductor of heat and it is relatively corrosion-resistant.
Which one of the following is known as the line that connects the metering device and the evaporator:
Inlet line
Discharge line
Suction line
Liquid line
The liquid line is an important part of the refrigeration system and it transports the refrigerant from the metering device to the evaporator.
Which of the following is used to remove the trapped air from a low pressure system from the top of the condenser:
Discharge unit
Recover unit
Purge unit
Compressor unit
A purge unit is used to remove trapped air from a low-pressure system from the top of the con-denser. The purge unit has a pump that creates a vacuum inside the condenser. This vacuum draws the trapped air out of the condenser and into the purge unit. The purge unit then vents the trapped air to the outside.
Turning the TXV valve stem in (Blank) direction increase superheat:
Counter clockwise
Clockwise
The TXV valve stem controls the flow of refrigerant into the evaporator. When the stem is turned clockwise, it closes the valve, which reduces the flow of refrigerant. This causes the refrigerant to vaporize more completely in the evaporator, which increases the superheat.
What is sensible heat?
Is heat energy when added or removed from a material, will cause a change in temperature or heat energy that you can measure with a thermometer
What is Latent heat?
Is heat energy that when added or removed from a substance, will cause a change in state not a change in temperature
