R32 is widely used in room air-conditioners

with heat-transfer characteristics affected by the intermiscibility of the oil. Therefore

it is necessary to determine the optimal intermiscibility of the oil to improve heat transfer characteristics. This study investigated the influence of stratification

caused by the intermiscibility of the R32-oil mixture

on the heat transfer characteristics. The flow boiling heat transfer coefficient and pressure drop of a completely miscible R32-oil mixture

a partially miscible R32-oil mixture

and a completely immiscible R32-oil mixture were tested experimentally. To cover the working conditions of air conditioners and reflect the different intermiscibilities of the R32-oil mixtures

the test conditions included evaporating temperatures from -5 ℃ to 15 ℃

vapor quality from 0.2 to 0.7

and averaged oil concentrations of 1% and 5%. The results showed that partially miscible oil had the highest heat transfer coefficient and the lowest pressure drop; at an evaporating temperature of 5 ℃

vapor quality of 0.7

and averaged oil concentration of 5%

the advantage of a partially miscible R32-oil mixture over that of the completely miscible and completely immiscible mixtures increased. The maximum increases in heat transfer coefficient were 36.8% and 357.8%

and the maximum decreases in pressure drop were 9.0% and 58.2%

respectively. Among the three types of oils

the partially miscible oil exhibited the best heat transfer and pressure drop characteristics and thus has the best application prospects.