About the project

In refrigeration systems with evaporation pressure below atmospheric pressure (i.e. coolers operating with isobutane), the air present in the external environment can infiltrate into the circuit through the micro holes present in the suction line. Alternatively, if the evacuation process is not efficient, a small amount of air may be housed inside the pipe. Since air consists predominantly of nitrogen gas having a low boiling point, it remains in the vapor phase throughout the cooling circuit, ie not condense. A non-condensable gas can then adversely affect the system operation conditions, reducing its efficiency and increasing the level of noise generated by the flow. In order to investigate the effect of non-condensable gases in domestic refrigerators, POLO developed an experimental apparatus and a method controlled injection of nitrogen in the refrigeration circuit. In addition, the laboratory has accelerometers to capture the vibration caused by the internal flow on the wall of the evaporator inlet pipe, and a high-speed camera to record the flow pattern at the entrance of the capillary tube through a filter drier developed acrylic. A study was conducted where a specific refrigerator realized in some cases, when the mass fraction of nitrogen in the system was very small, the product had not changed their performance, and sometimes showed slightly better performance. Assigned to these cases the possibility of the capillary tube not be perfectly dimensioned such operating points, and the inlet vapor bubbles in the tube caused an increase in its restraining power, leading to a small improvement in performance. In cases where the nitrogen concentration was too high, the product performance was negatively affected. Finally, it is noted that a degree of subcooling higher than normal is a strong indication of the presence of non-condensable gases.

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