Secondary Refrigerants |
All indirect systems will have some type of secondary refrigerant for cooling or heating applications. There are 3 types of secondary refrigerants used.
1. Salt solutions (Brines)-Below - 32 F
2.Glycol solutions – Below 32 f
3. Straight water solution – Above 32 F
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Definition Of a Eutectic Mixture |
A solution of any salt in water of a certain concentration to lower the solutions freezing temp
- Freezing point = Eutectic Point
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Two types of Brines |
1. Sodium Chloride: Application = Food processing (table salt)
2. Calcium Chloride: Application = All other applications where there would be no contact with food stuff
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Solution comparisons |
Calcium Chloride
-Lower enthalpy (capacity) then sodium
-Lower obtainable eutectic point -67F
-Corrosive
-Additives include to reduce formation of scaling and corrosions
Sodium Chloride
-Higher enthalpy (Capacity)
-High eutectic point -6F
-Corrosive
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Corrosion Control For Salt Based Brines |
The corrosiveness of a brine (eutectic Mixture) is determined by using a PH tester which will indicate a number between 1 to 14
The number 7 = Being neutral
A number under 7 = Being acidic
A number over 7 = Being Alkaline
The PH level for salt based brines should be kept between 7 and 8.5 (slightly alkaline). This will prevent excessive corrosive action. Also excessive aeration should be avoided
Normally calcium chloride brines are chemically treated during the manufacturing process with caustic soda to reduce acidity and dichromate to reduce alkalinity
Freezing point or eutectic point of a solution is determined by the salt concentration with the solution
A high salt concentration could cause precipitation at some temp above the eutectic point. This could result in solidification of the mixture.
*In addition the higher the concentration the lower the enthalpy becomes
Solution mixture is determined by using a: Hydrometer
Which means specific gravity of the mix
Specific Gravity: Is the density of that substance divided by the density of water (1 lb/ Cu ft)
Density is mass divided by volume of a substance
Recommended specific gravity:
-Calcium chloride = 1.2 at 60F
-Sodium chloride = 1.17 to 1.2 at 60F
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Types Of Hydrometers |
Hydrometers can be used to measure:
-Battery acids
-Glycal Solutions
-Salt brines
2 Forms:
-Glass Tube
-Incased
Scaled Hydrometers:
Heavy liquids 1 to 2
-Eutectic solutions
-Battery acids
-Glycal solutions
Light liquids 0.7 to 1.0
-Water impurities
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Glycol Based Solutions |
Types:
-Ethylene Glycol
-Propylene Glycol (Food Safe)
This type of solution base is probably the most popular with in the industry. Its advantages over salt based solutions is that its non-corrosive and is normally purchased with inhibiters to maintain its non-corrosive ability
As with salt based solutions the freezing temp is determined by the solution. A mix of 60% glycol and 40% water is desirable. This probably maintains -60F and maintains excellent specific heat value
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