EFFECTS OF EVAPORATING TEMPERATURE ON FLOW PATTERN IN A HORIZONTAL EVAPORATOR

摘要

In this paper, the effect of evaporating temperature on the void fraction and flow pattern of R290 in an evaporator of air conditioning unit has been studied. The analysis was carried out for evaporator diameter of 7.9 mm and 6.3 mm and cooling capacity of 2.64 kW and 5.28 kW. The analysis was conducted at evaporating temperature of -20°C to +5°C with an increment of 5°C. At the inlet of evaporator, the void fraction ranges from 0.932 to 0.984. Meanwhile, at the outlet the void fraction is 1. Testing the void fraction by using 3 available correlations gives the good agreement, with an average error of less than 5%. For all ranges of evaporating temperature, the analysis of flow pattern using larger pipe and smaller cooling capacity results in the domination of wavy flow and slug flow. Using smaller pipe and smaller cooling capacity provides transition from wavy and slug flow to annular flow, and results in the domination of annular flow up to 75%. Doubling the cooling capacity with smaller evaporator pipe increases the portion of annular flow up to 84%. In general, lower evaporating temperature will give the higher void fraction and higher annular flow portion.