Liquid ice is useful as a cold thermal storage material. In our previous work, a heat transfer experiment in a 22 mm diameter vertical straight pipe was carried out, and the empirical correlation of capacity coefficient of heat transfer K-a [-] was obtained. In this work the effects of pipe diameter on K-a for straight-and coiled-pipe systems have been investigated. Experimental results showed that the coiled-pipe system was useful for continuous formation of liquid ice and enabled a compact device. For the straight-pipe system, K-a was proportional to the ratio of water and coolant mass flow rates. For the coiled-pipe system, on the other hand, K-a was independent of pipe diameter and was expressed only by an exponential function of the ratio of water and coolant mass flow rates.