for providing hot water in a specific time of the day once
the water flow restarts. In this experiment, the SWH system -fl'Yt.t^t
is kept in stagnationi, mode with no water circulation while
the collectors absorb the solar radiation continuously, which results in trapping the heat in the tubes (maximum energy storage). Temperature variation inside the evacuated tubes are shown in Fig. 10 for both normal and stagnation operation mode.
Under normal operation (Fig. lOa), the temperature
inside the tubes increases, eventually stabilizing at a maximum value. The results show that standard tubes are
heated up to ,140 °C, while the PCM integrated tubes after sunilar exp'dsureT to sunlight to reach to the temperature around 90 =L 10 °C. The rate of cooling in a typical tube with no PCM is very fast, with the temperature falling within a few minutes. In Ae case of PCM filled tubes, the cooling process is significantly slower and the heat pipe can operate for several hours. The paraffin filled tube temperature shows a higher latent heat release compared with the Erythritol filled tubes, where the heat release happens around750C The reason is that due to higher melting temperature ofErythritol compared to paraffin, Erythritol