Page 125 - A Comprehensive Guide to Solar Energy Systems

Chapter 6 • Solar Water Heaters 123

thermal performance of the MCHP was governed by the strength of evaporation and the
circulation effectiveness of condensate from the condenser to the evaporator [36]. With
the advantages of high heat transfer performance, high reliability, low cost, and small con-
tact thermal resistance, MCHPs makes an excellent addition to a SWH system.
A novel flat-plate solar collector with a MCHP installed at the angle of local lati-
tude to receive maximum annual solar irradiance was investigated by deng et al. [37]
(Fig. 6.15). The evaporator of the MCHP was located below the condenser of the MCHP
to enhance the ability of condensate returning to the liquid pool in the evaporator. It
was found that the temperature difference between the evaporator and condenser was
less than 1°C, leading to excellent isothermal ability and quick thermal respond speed.
The surface temperature along the length of the MCHP was stable within 2 min of op-
eration.
Zhu et al. [38] investigated the thermal performance of a vacuum tube solar collector
based on a MCHP as shown in Fig. 6.16. The heat was collected in the vacuum tube and
released at the end of the MCHP, which was fitted with fins. The result showed that the
efficiency of the collector increases with a decrease of the inlet temperature due to lower
heat losses to the environment.

FIGURE 6.15 Schematic of the novel flat-plate solar collector with a MCHP [37]. MCHP, microchannel heat pipe array.

FIGURE 6.16 Schematic of the MCHP-based vacuum tube [38]. MCHP, microchannel heat pipe array.