1. Definition of refrigerant:
Refrigerant (coolant) is an intermediate substance used to transfer the cold heat generated by the refrigerator to the object to be cooled or heated. Commonly used refrigerants include air, water, salt water, organic compounds and their aqueous solutions. The first principle of selection is that the refrigerant in the heat exchanger does not freeze.
2.Characteristics of refrigerant:
The refrigerant is usually a liquid and generally does not undergo phase change during heat transfer.
A good refrigerant should have the characteristics of high boiling point, high heat capacity, high thermal conductivity, low freezing point, low viscosity, low toxicity, non-flammable, non-explosive, non-corroding metal, and non-polluting the environment.
3. Refrigerant type:
Commonly used refrigerants for ice block machines include industrial brine solutions, organic compound refrigerants, such as sodium chloride aqueous solution, calcium chloride aqueous solution, ethylene glycol aqueous solution, propylene glycol aqueous solution (food grade), etc.
3.1 Commonly used industrial brine solutions include sodium chloride (Nacl) aqueous solution and calcium chloride aqueous solution (CaCL2). Salt water solutions are highly corrosive to metals and can corrode pipes and equipment. Its corrosiveness is related to the purity of the salt and the oxygen content in the solution.
Actions that can be taken:
a) Use high-purity salt to prepare brine solution;
b) Reduce the chance of contact between solution and air, use a closed circulation system or cover the brine tank;
c) Add a certain amount of corrosion inhibitor to make the solution weakly alkaline and keep its pH value between 7.5 and 8.5. Commonly used are: sodium hydroxide (NaOH) and sodium dichromate (Na2Cr2O7), the mass ratio is NaOH: Na2Cr2O7=27:100.
d) The difference between sodium chloride and calcium chloride when used as refrigerant:
If you are making frozen brine, use 30% calcium chloride solution, freezing point -50°C (lowest); use 23% sodium chloride solution, freezing point -21°C (lowest).
e) Use anti-corrosion materials for parts in contact with the brine.
3.2 Organic compound refrigerant
Commonly used are ethylene glycol aqueous solution, propylene glycol aqueous solution (food grade) and ternary solution (mass percentage 40% ethylene glycol, 20% ethanol, 40% water, freezing point is -64°C). This type of refrigerant has no effect on the equipment. Corrosive, but has low volatility, so a closed circulation system is recommended
4. Summary:
Comparison of the above commonly used refrigerants: industrial salt (sodium chloride and calcium chloride) has a lower cost and is suitable for use in large refrigerators. The initial investment is mainly for equipment refrigerators. Propylene glycol solution and ethylene glycol solution are suitable for small-scale refrigerators. The use of freezers does not require high equipment, and the operating costs are higher than those of sodium chloride and calcium chloride.
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