where *T*_{sat} denotes the saturation temperature. Here, in Fig. 5, the measured temperature outside the hydrogel (TC2) can be considered as the refrigerant temperature because of the low thermal conductivity of air. Hence, the saturation temperature is assumed as the measured temperature outside the hydrogel shown in Fig. 5. As shown in Fig. 5, the both temperatures of TC1 and TC2 became stable. On the other hand, before 15 s, the temperature of TC1 was fluctuated. The cause of fluctuation may be the high vapor quality flow due to insufficient subcooling by the precooler. Therefore, this assumption is valid after 15 s, as shown in Fig. 5. Solving these equations, the heat transfer coefficient, *h*, can be expressed asDisplay Formula

(8)$h=qrori[Tsurf-Tsat-qrokslnrori]-1$