Page 123 - A Comprehensive Guide to Solar Energy Systems

Chapter 6 • Solar Water Heaters 121

FIGURE 6.11 Schematic of the SWH system with water-PCM storage [27]. PCM, phase change material.

FIGURE 6.12 Schematic of a conventional LHP device [28]. LHP, loop heat pipe.

mass. The extremely high vapor speed, for example, as high as sonic or supersonic level,
will limit heat pipe’s further heat take-up because the heat pipe would be choked. The
results show that the capillary was usually the governing limit of the system heat transfer,
while the entrainment may be the alternative when the pipe diameter was below 5.6 mm.
He et al. [33] and Zhang et al. [34] proposed a novel heat pump assisted solar facade
lHP water heating system (Fig. 6.14). The average thermal efficiency of the lHP module
was much better than that of the non-heat-pump-assisted lHP module under the same
solar radiation and ambient temperature condition. The water temperature increased
throughout the heat pump turn-on period and could reach the maximum temperature of
around 58°C.