Mechanical design and flow simulation of a steam generator for parabolic trough solar thermal energy harnessing plant

A steam generator is designed for a parabolic trough solar thermal plant of aperture area 22.3 m(2), which uses Mobil Therm-605 as the heat transfer fluid (HTF). The potential energy input rate from the plant to the steam generator is 4.56 kW, and the flow rate and temperature of the HTF of the plant are 1 l min(-1) and 268 degrees C respectively. The steam generator was designed as a shell and tube heat exchanger and the tubes are arranged in reflection symmetric configuration (n= 6). Flow simulations was done by using SolidWorks CAD software, based on Finite Element Method were carried out for the steam generator design in order to find the optimum conditions by varying the parameters such as tube diameter, HTF flow velocity distribution and thickness of HTF thermal barrier, while minimizing the fluid pressure and maintaining even flow distribution through the tubes. The simulation scheme narrowed down to simulate for the commercially available sizes of food-grade stainless steel tube diameters of 1/8, 1/4, 3/8, 1/2 and 3/4 inch. Simulations reveal that the non-moving HTF layer (which acts as a thermal barrier) for the above tube diameters were 0.0 %, 0.0 %, 4.1 %, 10.7 % and 27.6% respectively. Adding cost factors to the simulation outputs, it was found that the minimum material cost of tube bundle can be achieved when the tubes of diameter 1/4 inch is used and the expected length of the tubes with that diameter is found to be 72 mm.