RAC 40 Quiz 3 review

It takes ___ btu of heat energy to melt 1lb of ice at 32F

144 Btu

A ton of refrigeration is equal to

288,000 Btu/24-Hr

The temperature inside the refrigerator fresh food section should be about _______.

35 degrees F

When engineers design air conditioning units what parameters are used.

A pressure/enthalpy chart. On the chart it shows pressure and btu/lb, it also shows saturation points of liquids and vapors.

The evaporator in a refrigeration system

Absorbs heat from the product to be cooled

What is another word for flash gas?

Adiabatic expansion

When the refrigerant leaves the metering device, it is not 100% liquid. Why?

Because flash gas occurs and causes the 100% liquid to turn into 25% vapor and 75% liquid.

Why are evaporators usually feed from the bottom?

Because vapor naturally rises and ther is time for the liquid in the evaporator to boil off before it enters the compressor.

R-438a

Blue

R-422d

Bright green

The ___________ __________ is referred to as a kinetic displacement compressor.

Centrifugal Compressor

What temperature will the Hawaii health department use to gauge med temp chill boxes and low temp freezers?

Chill box 35-40 degrees F Freezer 0--10 degrees F

What type of equipment would you find R-407c refrigerant in?

Chill box, R-22 retrofit, Commercial refrigeration

Is the heart of the refrigeration system

Compressor

Rejects both sensible and latent heat from the refrigeration system.

Condenser

The _______________ are used to change the vapor to a liquid and the liquid from back into a vapor the refrigeration cycle.

Condenser and evaporator

R-114

Dark Blue

What type of equipment would you find R-410a refrigerant in?

Ductless split units

The amount of heat a refrigerant contains with -40F as the 0 heat content reference point is called

Enthalpy

Abort heat from the system

Evaporator

T/F If a cylinder of R-22 is moved from a 100F truck

False

T/F The only location where the refrigerant vapor is superheated is in the evaporator.

False

T/F Vapor is more dense than liquid and, as the liquid refrigerant boils, it has a tendency to sink.

False

R-22

Green

R-407a

Green

Ice melts in iceboxes because _________.

Heat enters when the door is opened, Heat flows through the insulated walls, Heat enters when warm food is placed in the icebox

How does refrigeration slow down food from spoiling?

It brings down the temperature of food so that bacteria growth begins to slow down.

What will high discharge temperatures affect your compressor?

It will cause the oil temperature to rise and create acid. Acid will eat at the winding in the compressor and cause a short.

R-134a

Light Blue

When a refrigerant enters the compressor, it is a ______ and when it leaves the compressor, it is a __________.

Low pressure Low temperature super heated vapor, High pressure High temperature super heated vapor

What type of equipment would you find R-404a refrigerant in?

Low temp and Medium temp refrigeration

R-407c

Medium brown

R-408a

Medium purple

What type of equipment would you find R-401a refrigerant in?

Medium temp refrigeration, Low temp, R-12 replacement

A valve or small fixed-size tubing or orifice that meters liquid refrigerant into the evaporator

Metering device

The four (4) major components of a vapor compression refrigeration system are the compressor, condenser, evaporator, and ________ ______.

Metering device

What is the purpose of the metering device?

Meters the flow of refrigerant entering the evaporator, reduces the boiling point to create a pressure/temperature drop

R-11

Orange

R-404a

Orange

R-502

Orchid

R-401a

Pink

The compressor in a refrigeration system _______.

Pumps the refrigerant throughout the system

R-113

Purple

From a performance standpoint, a substitute for R-12 is

R-134A

Which of the following refrigerants has the lowest boiling temperatures at atmospheric pressure?

R-502

Name the 4 positive displacement compressors.

Reciprocating, Rotary, Scroll, Screw

The condenser

Rejects heat from the refrigerant

What is the process of refrigeration?

Removing heat from a place where it isn't wanted to a place where it makes little or no difference.

R-410a

Rose

The _____ compressor is another positive displacement compressor and is used for larger air conditioning and refrigeration applications.

Screw Compressor

R-717

Silver

The refrigerant vapor picks up additional heat as it flows from the evaporator to the compressor. The heat is picked up from the

Suction line

Explain system subcool?

System subcool is the amount of heat the subcooled liquid has cooled off from the exit of the condensor to the inlet of the TXV. System subcool should be around 15-20F

Explain system superheat?

System superheat is the amount of heat the refrigerant vapor picked up from the exit of the evaporator to the inlet of the compressor. It's measured the same way as superheat and should be around 20F

The __________ relationship correlates the vapor pressure and the boiling point of water and is the basis for controlling the cooling system's temperatures.

Temperature/pressure

Explain what the evaporator does?

The evaporator is a bundle of tubing that absorbes heat from the system. It also boils off liquid refrigerant to bring down the coil temperature, and makes sure no liquid refrigerant returns to the compressor.

Explain what the metering device does?

The metering device controls the flow of refrigerant going into the evaporator. It changes the 100% liquid from the condenser and makes it 25% vapor 75% liquid going into the evaporator.

Refrigeration can be described as _______.

The process of removing heat from a place where it isn't wanted to place where it makes little or no difference

What is the meaning of THOR?

Total heat of rejection

T/F An expansion valve is the pressure reducing device that controls the flow of liquid refrigerant into the evaporator

True

T/F Modern refrigerators have become state of the art appliances and some models even include automatic beverage and ice dispensers, built in television screens and connections to the world wide web.

True

T/F Only liquid refrigerant should enter the metering device.

True

T/F The boiling point of a refrigerant should be low enough at atmospheric pressure to keep the system pressure above psig when operating at low temperatures.

True

T/F The discharge gas from the compressor is a high pressure, high temperature, superheated vapor.

True

T/F The evaporator can be though of as a "heat sponge"

True

T/F The evaporator in a refrigeration system must be colder than the refrigerated space in order to absorb heat.

True

T/F The halide leak detector should be used in well ventilated areas as the resulting blue or green flame indicated that phosgene gas is being produced.

True

R-12

White

R-290

White

The law requires technicians to recover refrigerant from all refrigeration systems so that they ________.

Will not be released into the atmosphere, May be used again, May be reclaimed for future use.

R-500

Yellow Orange

Reciprocating compressors have

A piston and cylinder

High temperature refrigeration is that produced by ________.

An air conditioning system

Good ventilation is important when working around refrigeration equipment because modern refrigerants ______.

Are heavier than air and may displace the oxygen around you

What type of equipment would you find R-134a refrigerant in?

Automotive, Low temp, Medium temp, High temp

Explain what the compressor does?

The compressor is also known as a vapor pump. There should only be 100% vapor going through the compressor. The main job of the compressor is to pump refrigerant through the system.

Explain what the condenser does?

The condenser is a bundle of tubing, it's main job is to reject heat from the system. The condenser also desuperheats the hot vapor refrigerant coming from the compressor and condenses it into liquid.