The invention discloses an automatic oil return device of a
carbon dioxide cascade refrigeration system. The automatic oil return device comprises a shell-and-tube
heat exchanger, adjusting valves, electromagnetic valves, a pressure-differential adjusting valve connected with the top of the shell side of the shell-and-tube
heat exchanger, a liquid level meter connected with the shell side of the shell-and-tube
heat exchanger, and two liquid level switches, wherein one adjusting valve and one
electromagnetic valve are connected with the middle part of the shell side of the shell-and-tube heat exchanger; and the other adjusting valve and the other
electromagnetic valve are connected with the bottom of the shell side of the shell-and-tube heat exchanger. The whole oil return device comprises 5 ports connected with external devices, namely port 1 connected with a condenser or a liquid reservoir, port 2 connected with an expansion valve, port 3 connected with a
carbon dioxide pump outlet pipeline, port 4 connected with a circulatory
barrel, and port 5 connected with an air suction port of a compressor. Through the adoption of the automatic oil return device disclosed by the invention, during the operation of the
refrigeration system,
refrigerant oil dissolved in
carbon dioxide in the low-pressure circulatory
barrel can be automatically extracted and returned to the compressor, so that the heat exchange efficiency of
refrigeration equipment is improved; and the refrigerating capacity of the refrigeration
system is not lost during operation, and the operation of the compressor is not influenced, so that the practicability is high.