Refrigeration systems with two-stage compression are used for the generation of particularly low temperatures. At very low temperatures large pressure differences are required between the evaporator and condenser. In a compressor the volumetric
efficiency drops significantly at high pressure ratios. Therefore, two compressors are connected in series, with each compressor only having a relatively low pressure ratio. This makes a more favourable dimensioning of the low pressure stage compressor possible. Due to the large specific volume it requires a larger capacity at lower drive power.
In addition, intercooling between the low pressure compressor (LP) and the high pressure compressor (HP) reduces the outlet temperature of the HP compressor to harmless values and improves the efficiency of the compression.
Manometers and temperature measuring locations at all relevant circuit points enable the evaluation of the two-stage process. To determine the compressor capacity, both compressors are equipped with an electrical power measurement. Valves allow for the injection intercooling or the heat exchanger for refrigerant supercooling to be switched off. This can demonstrate their effect on the system.
The online representation of the refrigeration process on the PC makes it easy for the student to understand the processes.
The well-structured instructional material sets out the fundamentals and provides a step-by-step guide through the experiments. The unit shall perform the following experiments and investigations:
Learning Objectives / Experiments
Design and function of a refrigeration system with two-stage compression and injection intercooling
Effect of the inlet temperature at the HP compressor on the efficiency of the compression
With intercooling
Without intercooling
Effect of the additional refrigerant intercooling
Distribution of the compressor pressure ratios
Represent and understand the refrigeration cycle
Process in the log p-h diagram
Specification
Refrigeration system with two-stage compression
Hermetic low and high pressure compressors
Adjustable intercooling via refrigerant injection
Heat exchange for additional supercooling of the liquid refrigerant
Closed refrigeration chamber contains evaporator with fan and adjustable electric heater as cooling load
Digital display for temperatures, drive power of the compressors and cooling load power
Software for data acquisition with USB under Windows Vista or Windows 7 with online display of the log p-h diagram