Browsing by Author "Van Zyl, Jacobus Gerhardus"

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    Development of a pilot low temperature solar thermal co-generation system for water distillation and energy production.
    (Stellenbosch : Stellenbosch University, 2023-12) Van Zyl, Jacobus Gerhardus; Owen, Michael; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: This study aimed to develop a pilot system for low temperature solar thermal combined power and clean water co-generation. The system comprised a solar thermal steam generation system (6.5 kWth external compound parabolic concentrating collector array and kettle-type boiler) coupled to a condensing steam engine (reciprocating steam expander and condenser). The system uses solar thermal energy to produce steam at ~1 atm from raw feedwater. The steam is used to drive the steam expander (both through steam work and condensation) to produce mechanical work (which can be used directly for pumping or converted to electricity). The vapor exiting the engine is condensed and collected, providing distilled water for human use. The steam expander was designed by the University of Southampton and was manufactured at Stellenbosch University. The rest of the overall system (solar steam generator and condenser) was designed and constructed as part of this work with the intent to integrate the expander. Unfortunately, the expander did not operate, and this thesis thus reports on the design of the overall system and the measured performance of the solar steam generator and condenser (including measured distilled water production). The mechanical and electrical energy generation of the system was estimated using the measured steam generation and engine thermal efficiencies from literature. Results from three day-long on-sun tests are provided and prove that the steam generation system was able to meet its performance requirements (specifically providing steam at the required flow rate and condition to the condensing engine). The system produced distillate at an average specific energy consumption (SEC) of 2125 kWh/m3 and an estimated average mechanical energy output of 0.039 kWh/m2 of collector aperture area per day. The monthly and annual distillate production and energy generation were also estimated to illustrate the longer term expected performance with an estimated annual yield of 17.1 kWh/m2 mechanical energy and 1012 L distilled water. Compared to existing low temperature energy systems (e.g. organic Rankine cycles for low-grade power generation), and various technologies for solar desalination (notably solar PV powered reverse osmosis), the investigated system proves to be infeasible based on its high SEC, low overall efficiency and relative complexity (notably in terms of the condensing engine).