Modeling of fluid flow and heat transfer in a trough solar collector

This paper analyzed the flow and heat transfer processes in a trough solar collector of the direct steam generation (DSG) system. A flow and heat transfer model of the working fluid in the absorber was established and solved using the finite difference method. Experimental results of liquid water and dry air heating processes validated the model. The experimental results, got under the condition that the vacuum in the tube was destroyed, were used to test the developed model. The calculation results of the model agreed with the experimental data. The dynamic characteristics of the collector outlet parameters under variations of solar radiation intensity were analyzed in this paper. The impulse response of the DSG system was complex as a short-time fluctuation of the solar radiation notably affected the water region length, the two-phase region length and the steam region length, which led to large fluctuations in the outlet temperature. Therefore, the outlet temperature of the once-through DSG system was difficult to control. Extra heat was required to maintain the normal operation of the system.