*8.2. Limitations in Parabolic Trough Solar Collector Systems*

In PTSCs, the main challenge is that most of the studies shown in the literature were of pilot-scale tests, and thus further investigations are needed on the real-life application itself. Moreover, systematic studies are required to understand and standardize the influence of operational parameters such as high pressure, high temperature, flow rate, particles concentration, and suspension thermophysical properties on the system performance. Furthermore, there is still a need for a better understanding of the fouling build-up mechanism that is commonly associated with the use of nanofluids in systems of elevated temperatures as this newly introduced thin-film is likely to change the wettability behavior of the

surface, and with it the dynamics of the flow [493–495]. Knowing this can open the door for introducing systematic washing routines, whether online, offline, or both, that can help in extending the heat transfer efficiency of the PTSC. Other aspects such as the friction factor and pressure drop should also be considered and explored intensively due to the nature of nanofluids having higher effective viscosity than conventional fluids.
