Core: Refrigerant Cycle Review

If we increase the pressure acting on a liquid, what state can the substance change to? (Assume constant temperature) A. Solid B. Liquid C. Vapor D. Water

A. If we increase the pressure acting on a liquid, the molecules will move closer and closer together.Eventually, if the pressure keeps increasing, the liquid can turn to a solid.

When refrigerant exits the metering device, what is the state of the refrigerant? A. Low pressure liquid B. High pressure liquid C. Low pressure vapor D. High pressure vapor

A. Refrigerant is a high pressure liquid when it enters the metering device. The metering device decreased the pressure, but didn't do anything to change the state of the refrigerant, so it is still a liquid.

The condenser is doing an opposite job of which component? A. Evaporator B. Compressor C. Metering Device D. Suction Line

A. The condensers job is to decrease the temperature of the refrigerant by exposing it to outdoor air.This is opposite of the evaporator, which increases the temperature of the refrigerant because this cools the indoor air.

What is the condenser's job? A. To cool the high pressure vapor B. To heat the high pressure vapor C. To increase the pressure D. To decrease the pressure

A. The job of the condenser is to decrease the temperature of the refrigerant by exposing it to outdoor air.

What is the function of the metering device? A. To decrease pressure B. To increase pressure C. To decrease temperature D. To increase temperature

A. The metering device's job is to decrease pressure so that the refrigerant can be cycled back to the evaporator to absorb more heat from indoor air.

Refrigerant absorbs heat from your indoor air in order to (Select all that apply) A. Change state from vapor to liquid B. Change state from liquid to vapor C. Make your house cooler D. Evaporate into the air

B and C. Refrigerant absorbs heat from your hot indoor air in. This is what makes your house cooler. As temperature of the refrigerant increases, it changes state from vapor to liquid.

Which components are on the high pressure side? (Select all that apply) A. Evaporator B. Compressor C. Condenser D. Metering Device

B and C. The compressor increases the refrigerant's pressure and passes the refrigerant to the condenser. These two components form the high pressure side of the refrigeration cycle.

Which components change the refrigerant's pressure? (Select all that apply) A. Evaporator B. Compressor C. Condenser D. Metering Device

B and D. The compressor increases the refrigerant's pressure and the metering device decreases the refrigerant's pressure.

After the evaporator, which component does the refrigerant go to next? A. Condenser B. Compressor C. Metering Device D. Your AC Unit

B.

When the refrigerant enters the evaporator, what state is it in? A. Solid B. Liquid C. Vapor D. Water

B. Refrigerant starts off as a liquid in the evaporator. Here, the refrigerant absorbs heat from the air to change state from liquid to vapor. This means that it starts off as a liquid.

When refrigerant enters the metering device, what is the state of the refrigerant? A. Low pressure liquid B. High pressure liquid C. Low pressure vapor D. High pressure vapor

B. The refrigerant enters the metering device as a high pressure liquid. The condenser cools the refrigerant until it changes state to a liquid. As the pressure of the refrigerant had been increased by the compressor, it becomes a high pressure liquid going from the condenser to the metering device.

As the temperature of a liquid increases, what phase does it turn into? (Assume constant pressure) A. Solid B. Liquid C. Vapor D. Water

C.

What is the compressor's job? A. To cool the superheated vapor B. To increase the temperature C. To increase the pressure D. To decrease the temperature

C.

When the refrigerant enters the compressor, what state is it in? A. Supercooled vapor B. Supercooled liquid C. Superheated Vapor D. Superheated liquid

C. After the evaporator, all of the refrigerant has heated beyond its boiling point, making it a superheated vapor. This means that from the evaporator, entering into the compressor, the refrigerant is in superheated vapor state.

When the refrigerant exits the evaporator, what state is it in? A. Low pressure liquid B. High pressure vapor C. Low pressure vapor D. High pressure liquid

C. In the evaporator, refrigerant absorbs heat from the indoor air to change state from liquid to vapor. So, when the refrigerant leaves the evaporator, it is fully in vapor state (low pressure).

When the refrigerant exits the evaporator, what state is it in? A. Solid B. Liquid C. Vapor D. Water

C. In the evaporator, refrigerant absorbs heat from the indoor air to change state from liquid to vapor. This means that when the refrigerant leaves the evaporator, it is fully in vapor state.

When refrigerant enters the condenser, what state is the refrigerant in? A. High pressure liquid B. Low pressure liquid C. High pressure vapor D. Low pressure vapor

C. Recall that the compressor increased the pressure of the refrigerant before it reaches the condenser. And the refrigerant was is still a vapor from when it boiled in the evaporator. So refrigerant enters the condenser as a high pressure vapor.

Which of the following states has the highest temperature? (Assume constant pressure) A. Solid B. Liquid C. Vapor D. Water

C. Vapor has the highest temperature of the three states.

Does the refrigerant change state in the compressor? A. Yes, it changes from a vapor to a liquid B. Yes it changes from a liquid to a vapor C. Yes, it changes from a liquid to a solid D. No, it does not change state

D. The refrigerant does not change state in the compressor.It enters the compressor as a low pressure vapor, and exits as a high pressure vapor. So, even though the pressure has increased, the state has not changed.

The boiling point of most refrigerants is 212 °F. Select one: True False

False. The boiling point of water is 212 °F. Different substances generally have different boiling points. This means they will change from liquid to vapor at different temperatures. We choose substances with much lower boiling points to use as refrigerants.We'll see why in the next module.

The vapor leaving the compressor is lower in pressure than vapor entering the compressor. Select one: True False

False. The job of the compressor is to increase the pressure of the refrigerant. So the vapor refrigerant leaving the compressor would be higher pressure than the vapor refrigerant entering it.

Your air conditioning works by adding cold air into your house. Select one: True False

False. This is false. Your air conditioning works by absorbing heat from your indoor air, not by adding cold air.

You are boiling a pot of water with the lid on. As the water heats up and starts to boil, you notice that drops of water form on the bottom of the pot lid. This is an example of condensation. Select one: True False

True.

Boiling requires the addition of heat. Select one: True False

True. Adding heat will increase the temperature of the substance until it reaches it boiling point, which changes its state from liquid to vapor.

The boiling point is the temperature of a substance where it turns from liquid to vapor. Select one: True False

True. This is the definition of the boiling point.

If we decrease the pressure of a substance, its boiling point decreases. Select one: True False

True. This is true. Decreasing pressure decreases the boiling point of a substance.

For the same substance, the average speed of the molecules in a vapor is faster than the average speed of molecules in a liquid. Select one: True False

True. This is true. Recall that temperature is a measure of the average speed at which molecules are moving. The higher the temperature, the higher the speed of the molecules. The temperature of a vapor will be greater than the temperature of a liquid of the same substance. Since the temperature is higher, so is the average speed of the molecules.

Condensation happens when a gas or vapor cools down and becomes liquid. Select one: True False

True. This is true.Condensation is the state change from vapor to liquid. This is because the temperature of the vapor decreases.

In the condenser, the refrigerant changes state. Select one: True False

True. True. In the condenser, refrigerant cools by coming into contact with outdoor air. As it cools, it changes from a high pressure vapor to a high pressure liquid.