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Ateneo
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Ateneo

Refrigeration Laboratory

Description

The lab is composed of several test benches where different plants can be run and monitored and data can be acquired for a post-processing of the tests results. In particular three systems are now present in the lab: 1) air cycle; 2) cascade cycle; 3) air to air heat pump.

Cascade cycle
An air cycle uses air as refrigerant, therefore reducing the environmental load due to working fluids. The open air cycle used in the prototype unit (AIRS) has been designed and built by Earthship Co Ltd of Japan. The air at atmospheric pressure is drawn from the freezing unit through the low-pressure section of the regenerator to the primary compressor. Here it is compressed and precooled, then the air is expanded in the turbine where it is reduced to approximately atmospheric pressure and to a temperature of -70°C, needed to cool the freezing chamber.

Ciclo in cascata
In industrial applications, the cascade refrigeration cycle is useful when low temperatures (i.e. below -40°C) are required. A cascade cycle consists of two separate refrigeration cycles, one working at a higher temperature (HTS) and the other at a lower temperature (LTS). The condenser in the low-temperature stage is cooled by the evaporator in the high-temperature stage. The plant was tested with natural refrigerants or their blends. Amongst the natural refrigerants, carbon dioxide is of special interest because it is non-flammable and it has a low toxicity and a low Global Warming Potential (GWP). Blending carbon dioxide with other low boiling refrigerants, such as N2O (R744A) and HCs, it is possible to go lower than the CO2 triple point.

Air-to-air heat pump
The test rig is composed of an-to-air reversible heat pump, using R410A as refrigerant fluid, with air channels for the external and internal air circulation arranged in a closed loop. The channels are made of expanded polyurethane covered with aluminum sheets, that provides thermal insulation and avoids air leakages. The air is blown inside the channels by means of fans. The fan on the indoor side is provided with an inverter, thus it is possible to vary the air flow rate for the experimental tests purposes. The aim of the closed air channel circuits is to simulate the indoor and outdoor environment. Each channel collects the air at the outlet of the heat pump and, depending on the considered side (outdoor or indoor) and operative mode (heating or cooling), heats or cools it up to the necessary inlet conditions and then sends it back into the heat pump. In this way it is possible to test the system at different outdoor and indoor conditions. The air heating inside the channels is made by means of a 12kW electric resistance, while the air cooling by means of a water cooling circuit. Both the systems are regulated with a PID controller that keeps the air input temperature at the desired set-point values by varying the power in the former and the water flow rate in the latter system.

Research activity

1)Performance analysis of different refrigeration technologies for low termperature applications: air cycle and cascade cycle

Figure 1.  Load chamber (freezing unit): a schematic (left side) and a picture (right side).

Figure 2.  Ciclo ad Aria

Figure 3.  Ciclo in cascata

2) Performance analysis of a reversible air to air heat pump by varying the heat exchanger used as evaporator/condenser: mini-channel heat exchanger

Figure 3.  Test rig

Figure 4.  A picture of the mini-channel heat exchanger.

Figure 5.  Refrigerant velocity (m/s) cut-off contour on the inlet sections of the multiports of the heat exchanger. .

Sono inoltre in corso di svolgimento prove con accumuli termici a base di materiali a cambiamento di fase (PCM, phase change material) che, sfruttando il calore latente di particolari sostanze, permettono l’utilizzo di forni solari anche durante l’assenza/intermittenza della radiazione solare.

Facility

The lab is equipped with instrumentation to test refrigeration systems. In particular acquisition systems for temperature, pressure, flow rate and power sensors are available, where labview interfaces are used to elaborate the recorder data. Water heat sources/reservoir are available to manage thermal loads injection and rejection during refrigeration systems operation..

Research manager
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