How to Choose a Plate Freezer for Quick Freezing
1. Ammonia Refrigeration System
The refrigeration system that uses ammonia as the refrigerant is called an ammonia refrigeration system. The low-pressure vapor of ammonia is compressed by the compressor into high-pressure superheated vapor; after passing through the oil separator, it is condensed into liquid ammonia by the condenser, transferring heat to the water. The high-pressure liquid ammonia exits the receiver and passes through an expansion valve to throttle and reduce pressure. After being separated in the ammonia liquid separator, the liquid ammonia enters the evaporator, where it evaporates, cooling the air through the air cooler and thereby lowering the temperature of the surrounding air and materials. The low-temperature, low-pressure vapor from the evaporator passes through the ammonia liquid separator and then returns to the compressor for compression.
2. Freon Refrigeration System
The refrigeration system that uses Freon as the refrigerant is called a Freon refrigeration system, abbreviated as a Freon system. The main differences between the Freon and ammonia refrigeration systems lie in the addition of a filter-drier, a liquid-to-suction heat exchanger, a thermostatic expansion valve, and a solenoid valve.
Figure 14-19 Freon Refrigeration System
Freon refrigeration system flow diagram (schematic):
Compressor → Oil Separator → Condenser → Filter-Drier → Solenoid Valve → Liquid-to-Suction Heat Exchanger → Expansion Valve → Liquid Distributor → Evaporator → Pressure Controller
Main components and numbering (according to original figure):
1—Refrigeration compressor 2—Freon oil separator 3—Condenser 4—Filter-drier 5—Solenoid valve 6—Liquid-to-suction heat exchanger 7—Expansion valve 8—Liquid distributor 9—Evaporator 10—Pressure controller
Figure 14-19 Main components and piping connections of the Freon refrigeration system (based on original diagram annotations)
The low-pressure Freon vapor is compressed by the refrigeration compressor into high-temperature, high-pressure vapor, then enters the Freon oil separator, where the entrained lubricating oil is separated out. Afterwards, it is condensed into liquid by the condenser; since the filter-drier removes any moisture and impurities, the Freon liquid, after being subcooled in the liquid-to-suction heat exchanger, expands via throttling through the thermostatic expansion valve, and then the low-pressure Freon liquid is uniformly distributed to the evaporator by the liquid distributor for evaporation.
In a Freon refrigeration system, a pressure controller is typically installed, connected to the discharge and suction pipes of the refrigeration compressor. When the discharge pressure exceeds the rated value or the suction pressure falls below the rated value, the pressure controller will forcibly stop the refrigeration compressor to prevent accidents.
The solenoid valve installed on the connecting pipeline between the condenser and the evaporator is used to automatically control the opening and closing of the liquid supply line. When the refrigeration compressor stops, the solenoid valve immediately cuts off the liquid supply line, preventing a large amount of Freon liquid from entering the evaporator, which could cause liquid slugging (wet operation) when the unit restarts. When the refrigeration compressor starts, the liquid supply line opens automatically.