Chows Unit 3

Question 1

_____________ is another positive positive displacement compressor and is used for larger air conditioning and refrigeration applications

Answer 1

Screw

Question 2

The four major components of a vapor compression refrigeration system are the compressor, condenser, evaporator, and…

Answer 2

Metering device

Question 3

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

Answer 3

Enthalpy

Question 4

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

Answer 4

R134a

Question 5

The ________ is referred to as a kinetic displacement compressor

Answer 5

Centrifugal

Question 6

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

Answer 6

Suction line

Question 7

What is the purpose of the metering device?

Answer 7

The primary purpose of the metering device is to control the flow of refrigerant into the evaporator coil. This is very important for effective heat exchange and system performance.

Question 8

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

Answer 8

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

Question 9

Match the refrigerant cylinder with the correct color code

Answer 9

A. R-11 - orange
B. R-12 - white
C. R-22 - green
D. R-113 - purple
E. R-134a - light blue
F. R-114 - dark blue
G. R-500 - yellow-orange
H. R-502 - orchid
I. R-717 - silver

Question 10

Good ventilation is important when working around refrigeration equipment because modern refrigerant

Answer 10

Are toxic and can poison you and are heavier than air and may displace the oxygen around you

Question 11

The ________ relationship correlates the vapor pressure and the boiling point of water and is the basis for controlling the cooling systems temperatures

Answer 11

PT

Question 12

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

Answer 12

R-502

Question 13

The compressor in a refrigeration system ______.

Answer 13

Pumps the refrigerant throughout the system

Question 14

A ton of refrigerant is equal to ________

Answer 14

288,000 BTU/24-HR

Question 15

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

Answer 15

Will not be released into the atmosphere, may be used again, maybe reclaimed for future use

Question 16

Refrigeration can be described as

Answer 16

The process of removing heat from a place where it is not wanted to a place where it makes little or no difference

Question 17

The temperature inside the refrigerator fresh food section should be about……

Answer 17

35°F

Question 18

The evaporator in a refrigeration system…….

Answer 18

Absorbs heat from the product to be cooled

Question 19

High temperature refrigeration is that produced by…….

Answer 19

An air conditioning system

Question 20

Reciprocating compressors have…….

Answer 20

A piston and cylinder

Question 21

What happens when room temperature soda is poured into a glass of ice?

Answer 21

The ice melts because it is absorbing heat from the soda

Question 22

The condenser…….

Answer 22

Rejects the heat from the refrigerant

Question 23

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

Answer 23

Low pressure low temperature superheated vapor/high pressure high temperature superheated vapor

Question 24

The……….. are used to change the vapor to a liquid and the liquid form back into a vapor the refrigeration cycle

Answer 24

Condenser and evaporator

Question 25

Ice melts in ice boxes because………

Answer 25

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

Question 26

True or false if a cylinder of our 22 is moved from a 100°F truck body into an 80°F shop, the quantity of liquid refrigerant in the cylinder will remain the same.

Answer 26

False

Question 27

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 worldwide web

Answer 27

True

Question 28

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

Answer 28

True

Question 29

The discharge gas from the compressor is a high-pressure, high temperature, superheated vapor

Answer 29

True

Question 30

True or false An expansion valve is the pressure reducing device that controls the flow of liquid refrigerant into the evaporator

Answer 30

True

Question 31

True or false the evaporator can be thought of as a heat sponge

Answer 31

True

Question 32

True or false vapor is more dense than liquid and, as a liquid refrigerant boils, it has a tendency to sink

Answer 32

False

Question 33

True or false only liquid refrigerant should enter the metering device

Answer 33

True

Question 34

True or false the only location where the refrigerant vapor is super heated is in the evaporator

Answer 34

False

Question 35

True or false the evaporator in a refrigeration system must be colder than the refrigerator space in order to absorb heat

Answer 35

True

Question 36

True or false the halide leak detector should be used in well ventilated areas as the resulting blue or green flame indicates that phosgene gas is being produced

Answer 36

True

Question 37

Match the refrigerant cylinder with the correct color code

Answer 37

A. R408a - medium purple B. R290 - white C. R410a - rose D. R404a - orange E. R407a - green F. R407c - medium brown G. R422d - bright green H. R401a - pink I. R438a - blue

Question 38

What is another word for flash gas?

Answer 38

Adiabatic expansion

Question 39

What is the meaning of THOR?

Answer 39

Total heat of rejection. This is in reference to the total heat absorbed in the refrigeration cycle.

Question 40

How will high discharge temperatures affect your compressor?

Answer 40

High discharge temperatures will lead to high heat levels inside the compressor. This will cause compressor oil to burn off, high current draws, and copper oxidation that will be trapped against the valve plate.

Question 41

Name the four positive displacement compressors

Answer 41

Screw, scroll, Rotary, and reciprocating

Question 42

When engineers designed air conditioning units of what parameters are used?

Answer 42

Outside temperatures (air) Inside temperatures (air)

Question 43

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

Answer 43

Median temp chill boxes should be maintained at 35°F to 39°F. Low temp freezers 0°F to -10°F

Question 44

How are refrigeration compressors rated?

Answer 44

HP and amperage

Question 45

Where are evaporators fed from and why?

Answer 45

They are fed from the bottom because liquid needs to boil upward to absorb heat from the heated space

Question 46

What type of equipment will you find R410a refrigerant in?

Answer 46

High temp refrigeration systems

Question 47

What type of equipment will you find R404a refrigerant in?

Answer 47

Low temp refrigeration systems

Question 48

What type of equipment will you find R407c refrigerant in?

Answer 48

Chillers

Question 49

What type of equipment will you find? R134a refrigerant in?

Answer 49

Medium temperature refrigeration systems

Question 50

What type of equipment will you find R32 refrigerant in?

Answer 50

Window units

Question 51

What is system superheat? How would you check it?

Answer 51

System superheat is the total super heat within the system. This can be measured 6 inches away from the inlet of the compressor.

Question 52

What is system subcooling?

Answer 52

System sub cooling is the amount of heat removed from the entire system. This includes the liquid line from the condenser outlet to the metering device, inlet and can be measured a couple of inches away from the inlet of the metering device.

Question 53

………….. ensures that no liquid returns to the compressor

Answer 53

Super heat

Question 54

True or false 404a and 410a are known as near orangetropic blends

Answer 54

False

Question 55

How would you calculate standard condenser efficiency?

Answer 55

Ambient temperature +30°F

Question 56

Draw the pressure/entropy shape from the refrigeration cycle. Add as much detail as you can.

Answer 56

Question 57

__________ and __________ are responsible for naming refrigerants and identifying there characteristics.

Answer 57

ASRAE and AHRI