Refrigerating plants make use of the fact that a refrigerant evaporates at low pressure. In absorption refrigeration systems, the absorption of ammonia in the water produces this low pressure. The absorption process is driven by thermal energy, which can come for example from industrial waste heat or solar collectors to operate these systems. This basic principle of an absorption refrigeration system is demonstrated in the experimental unit taking the example of an ammonia-water solution with the ammonia acting as refrigerant. In the evaporator the liquid ammonia evaporates and withdraws heat from the environment. To keep the evaporation pressure low, the ammonia vapour in the absorber is absorbed by the water. In the next step, ammonia is permanently removed from the high concentration ammonia solution to prevent the absorption process from being halted. For this purpose, the high concentration ammonia solution is heated in a generator until the ammonia evaporates again. In the final step, the ammonia vapour is cooled in the condenser to the base level, condenses and is returned to the evaporator. The low concentration ammonia solution flows back to the absorber. To maintain the pressure differences in the system, hydrogen is used as an auxiliary gas.
Learning Objectives/Experiments
Demonstrate the basic principle of an absorption refrigeration system
Absorption refrigeration system and its main components
Operating behaviour under load
Specification
Operation of an absorption refrigeration system
Main system components: evaporator, absorber, boiler with bubble pump, condenser
Ammonia-water solution as working medium, hydrogen as auxiliary gas
Boiler to separate ammonia
Bubble pump for transportation in the circuit
Adjustable electrical heater at the evaporator serves as cooling load
Boiler is alternatively heated by electrical heater or gas burner
Piezoelectric igniter for gas operation
Digital displays for temperature and power
Technical Data
Working medium: ammonia-water solution
Auxiliary gas: hydrogen
Electric heater: 125W
Gas burner, adjustable: propane gas
Evaporator heater, adjustable: 50W
Measuring ranges
temperature: 4x -80…180°C
power: 0…150W
230V, 50Hz, 1 phase
230V, 60Hz, 1 phase
120V, 60Hz, 1 phase
