Thermal Efficiency Evaluation of a Solar Thermal Steam Generating System Using Thermosiphon Technique with Parabolic Trough Collector

Parabolic trough solar collectors are the most widely used concentrators for solar thermal applications in the world. This is because very high temperatures of 150°C to 350°C can be attained with its use without any noticeable degradation in the performance of the collector. In this work, a parabolic trough collector (PTC) was designed using simple parabolic equations and constructed with locally sourced materials. The developed PTC was used to converge direct solar radiation to a heat receiver (a copper pipe enclosed in an evacuated glass tube) placed at the focal line of the trough to heat up the water in the pipe to steam. Natural circulation (thermosiphon) was employed to drive the water from the heat source to the heat sink (tank) with the difference in density as the driving force of the system. Temperature sensors were installed at different points of the solar thermal system to experimentally investigate temperature distribution within the system, hence thermal performance. A pressure sensor was also installed in the tank to measure the pressure within the system. The results obtained shows that the solar thermal system generated low-mid temperature steam of up to 105°C at a pressure of approximately 120 kPa on a day when the global solar radiation intensity attained a value of 1109.5 W/m². A thermosiphon mass flow rate of up to 0.042 kg/s was also recorded through a constant orifice of 12 mm diameter. The instantaneous efficiency of the receiver reached 46.48%.