Experimental Investigation On Finned Tube Condenser With Falling Film

In order to work out how to reduce the refrigerant charging quantity under the maintaining performance of an air conditioner, in this paper,a finned tube falling film condenser has been proposed and employed, and the characteristics of refrigerant hold-up and heat transfer performance of condensers were experimentally studied in enthalpy different laboratory under four refrigerating conditions. The total refrigerant charging quantity of improved machine which employs falling film condenser increases from 550 g to 750 g by 100 g, while total refrigerant charging quantity of the standard machine which is on sale was 1050 g.In order to analyze the influence of refrigerating conditions and refrigerant charging quantity on heat transfer coefficient and the amount of refrigerant hold-up, the calculation models of heat transfer performance and the quantity of refrigerant hold-up has been established based on the refrigerant properties and structure of air-cooled condenser. The data analyzed by models of heat transfer performance indicated that the heat transfer coefficient of improved machine increased with increasing mass flow rate, the in-tube heat transfer coefficient separately increased by 8.8% and 10.7% in the superheat section when the refrigerant charging quantity was 650 g and 750 g,while it separately increased by 7.8% and 16% in the two-phase section. Above all, the increase of over-all heat coefficient k of condenser reached 29.6~45.3% under four refrigerating conditions.The data analyzed by models for calculating the quantity of refrigerant hold-up indicated that the maximum thickness of liquid film was 0.066 mm, which was far less than it of standard machine. Thinner liquid film can enhance heat transfer and reduce the quantity of refrigerant hold-up at the same time. There were 54%~65% of the total refrigerant hold-up in the condenser of standard machine, while there were only 17%~34% in the condenser of improved machine.The analysis based on the thermography demonstrated that the temperature difference in two-phase section of falling film condenser was less than it of standard machine. When the refrigerant charging quantity was not less than 650 g, the average temperature of fin surface was higher than it of condenser of standard machine, and it kept the heat at great lever.