Operating characteristics of natural circulating CO{sub}2 secondary loop refrigeration system working with NH{sub}3 primary loop

摘要

A secondary loop refrigeration system, using a vapor compression ammonia (NH{sub}3) cycle as the primary loop and a natural circulating carbon dioxide (CO{sub}2) cycle as the secondary loop, is investigated experimentally. The conventional CO{sub}2 secondary loop is circulated by a pump, but in the system studied the loop circulates naturally by gravity based on the difference in density between liquid and vapor lines. An experimental secondary loop system is constructed, and its behavior and performance are examined. The flow of CO{sub}2 is sensitive to the unexpected occurrence of cavity or vapor in the liquid line, but it is stabilized by the vent line effectively. The experimental secondary loop with the CO{sub}2 liquid head of 0.9 m shows reasonable cooling capacity and COP. The natural circulating CO{sub}2 secondary loop system is feasible as the practical refrigeration system using natural refrigerants, though it has a restriction that the intermediate heat exchanger must be located higher than the cooler.