Ammonia Exam Questions Flashcards
Primary refrigerants change state and have a ________ heat process
latent
Secondary refrigerants do NOT change state, _______ heat gain or loss only
sensible
Secondary refrigerants usually have _____ as a base
water
Some of the substances used to make secondary refrigerants when mixed with water are;
- 2.
3.
- brines (calcium chloride or sodium chloride)
- glycol (methylene, ethylene, propylene)
- Alcohol (ethyl, methyl)
Name a few main categories of secondary refrigerants; 1. 2. 3. 4. 5. 6.
- brines
- salt and water
- glycols
- water
- refrigerants
- alcohols and water
A eutectic system is a mixture of chemical compounds or elements that has a single chemical composition that __________ at a lower temp than any other composition
solidifies
sodium ________ is added to keep brine slightly alkaline
hydroxide
Sodium chloride brine is cheaper than calcium chloride brine but cannot be used below its eutectic point of __F
-6F
The corrosiveness of a brine is determined by using a __ tester
PH
PH levels run 1-14. What numbers are considered neutral, more alkaline, more acidic?
Ph level 7 is neutral
below 7 is more acidic
above 7 is more alkaline
*The PH levels of ____ brines should be between 7 and 8.5
salt
Systems using aqueous solutions of alcohol or glycol are more susceptible to ________ than those using salts
leakage
Which type of brine would corrosion inhibitors be used
alcohol type
*What type of glycol is used in food processing?
propylene glycol
- A solution of any salt in water has a specific concentration at which the freezing point is at its minimum thus it is called a _______ mixture
Eutectic mixture
The temperature at which the brine freezes is called the ________ temperature
eutectic
Eutectic mixture ratios must be followed. Too much glycol results in gel forming and the freezing point of the remaining solution _________. Too little glycol results in ice ________ forming and damage to system components
increases, crystals
Name 2 typical brine types for food freezing/meat packing applications;
- calcium chloride
2. sodium chloride
With what tool do you determine a solution mixture?
hydrometer
What does a hydrometer measure?
specific gravity
Recommended specific gravity’s for calcium chloride and sodium chloride?
calcium chloride: 1.2 @ 60F
sodium chloride: 1.17 to 1.2 @60F
___ is extremely harmful in a brine system
air
what does air in a brine system promote?
corrosion
Air also causes ________ in the brine pumps, and can displace the brine to the extent that the brine will overflow down the drain
cavitation
Hydrometers may be used to measure;
battery acid, glycol solutions, salt brines, alcohol
A heavy liquid read by a hydrometer is in what range? name two examples
1.0 - 2.0
eutectic solutions, battery acids, glycol
A light liquid read by a hydrometer is in what range?
name two examples
0.7-1.0
water impurities, alcohol
Best way to get air out is to shut the brine pump off and let the air rise to the top of the header, and release it at the ______ _____ valve
header purge valve
What are some common methods of dehumidification?
refrigeration, desiccants, or air
How would you control the temp of water coming into a cooling tower on a low ambient day?
You can use a diverter valve
Name the two ways multi stage compression can be accomplished;
direct staging and cascade staging
- Direct staged systems use one refrigerant and one circuit with more than one ________
- This method is used on systems that have _____ compression ratios
- compressor
2. high
What is the practical temp limit in direct staging systems?
-125F
________ are required to cool discharge gas from first stage compression before entering second stage
intercoolers
Cascade systems use ___ or more refrigerant circuits each using refrigerants with progressively lower ________ points
two, boiling
Cascade systems are normally used in ultra ____ temperature applications
low
_______ are not normally used in cascade systems because they are critically charged
receivers
Why are intercoolers used?
avoid overheating the higher stage compressor from excessive discharge temperatures
name three types of intercoolers;
- open ____ type intercooler
- closed shell and ____ type intercooler
- the dry ________ type intercooler
- open flash
- closed shell and coil
- the dry expansion type
In open type intercoolers the liquid from the condenser is expanded in the intercooler and its temperature is reduced by ______ down to intermediate temperature
flashing
- In open type intercoolers the discharge gas is de superheated by causing it to ______ up through the liquid and the sub cooler
- name two advantages to open type intercoolers;
- bubble
2. simple operation, low cost, good liquid temp reduction
Cooling towers are heat rejectors. They do not condense _______ so they are not considered condensers
refrigerants
Entering wet bulb temperature is the lowest temperature that water can theoretically reach by ________
evaporation
_________ ___ ____ temperature is the most important parameter in tower selection
entering wet bulb
For most areas in North America, an entering wet bulb temp of ___F is common.
78F
Approach is the difference between water _____ the tower and the entering ____ ____ temp of the air
leaving, wet bulb
What is drift in cooling towers?
water that gets entrained in airflow and discharged to the atmosphere
*Cooling tower fill helps the water gain maximum exposure to ______
airflow
*___ is the most commonly used material for fill
PVC
*Current designs for HVAC tend not to use _____ for fill
wood
*The addition of fill surface to the traditional evaporative condenser design reduces __________ in the coil section, reducing the potential for scaling and fouling.
evaporation
