2020 Volume 37 Issue 4 Pages 423-
In this study, a frost layer was fabricated for 60 minutes by reproducing the temperature and humidity environment of the outdoor heat exchanger during heating operation of the air conditioner, and its effective thermal conductivities and densities were measured every 15 minutes. The environmental conditions at the time of the experiment were as follows: the air temperature at 1.3 to 1.8 ℃, the absolute humidity at 0.0033 to 0.0036 kg/kg(DA), the wind velocity near the substrate at 2.0 to 2.3 m/s and the cooling surface temperature at -17.7 to -17.2 ℃. The thermal conductivities was measured by 3ω method, and the growth process of the frost layer was observed by a digital microscope. The thermal conductivities and densities of the frost layer increased with an increasing elapsed time, the thermal conductivities was in the range of 0.05 to 0.14 W/ (m·K), and the densities was in the range of 55 to 115 kg/m3. The increasing rate of frost layer formation was remarkable in the formation time of 15 to 30 min, and was gradual after the formation time of 30 min. In addition, the thermal conductivities increased with an increasing density.
