This paper studies the evaporation heat transfer of R32 inside two different diameters of horizontal tubes under saturation temperatures of 0 ℃

5 ℃

and 10 ℃. The evaporation heat transfer coefficient of the refrigerant was obtained by using a heat resistance separating method. Taking mass flux and saturation temperature as the influencing factors

the experiment results include two parts：analysis of single-tube thermal resistance and evaluation of single-tube comprehensive performance. The experimental results indicate that the heat transfer coefficient and pressure drop rise as the mass flow rate increases. The diameter has a great influence on the heat transfer coefficient

and the heat transfer coefficient of No.1 is 1.1~1.3 times as that of No.2. The effect of temperature on the heat transfer coefficient and the pressure drop differs under different mass flow rate. As the mass flow rate increases

the proportion of the external water side-tube resistance to the total thermal resistance increases

while that of the inside gradually decreases. The heat transfer coefficient per pressure drop of two single tubes decreases as the mass flow rate increases. The saturation temperature shows various effects on the parameters at different mass flow rate.