화학공학소재연구정보센터
Solar Energy, Vol.196, 530-539, 2020
Ledinegg instability analysis on direct vapor generation inside solar collectors
Compared with direct steam generation (DSG), direct vapor generation (DVG) system based on organic working fluid has better application potential in low and medium temperature distributed system. However, there is a lack of understanding of the two-phase flow instability that commonly occurs in DVG systems and can cause fatal damage to the system. in this paper, Ledinegg instability is considered as a common flow instability, and its occurrence characteristics and avoidance strategies are presented. First, a theoretical model was established to study Ledinegg instability of organic working fluid. Then, the effects of heat flux q, inlet subcooling T-c length-to-diameter ratio L/D and fluid properties are analyzed. Particularly, a characteristic parameter R-L representing the possibility of Ledinegg instability is proposed for the first time in performance evaluation of Ledinegg instability, The results show that as L/D decreases from 200 to 100, R-L reduces from 0.88 to 0.25. As q increases from 10 kW/m(2) to 30 kW/m(2), R-L increases from 0.54 to 1.03. When T-c is less than 3 degrees C, R-L approaches 0 and Ledinegg instability disappears. With the increase of surface tension a and the latent heat of vaporization r, the decreases of vapor-liquid density ratio rho(sv)/rho(sl) and the decreases of vapor-liquid viscosity ratio mu(sv)/mu(sl), R-L increases. The physical equation describing R-L of Ledinegg instability is helpful to guide DVG system to reduce or avoid Ledinegg instability in design and operation.