Some problems were investigated with the immersion liquid method, which is a basic technique to measure droplet diameters and their distribution in mist flow, and which is also adopted to confirm adequacy of the data obtained by a Phase-Doppler particle analyzer. On the basis of experiments
conducted using water mist and silicone oil as the immersion liquid, we conclude that when the shutter opening time is selected to give the maximum local number density of droplets per unit area of the oil surface, the coalescence of the droplets hardly affects the Sauter mean diameter. Thus accurate and efficient measurement is possible. Moreover, a simple simulation of droplet coalescence was attempted. The results agree well with the characteristics found in the experiment.