Study On Flow Instability Inside Multiple Parallel Pipes Of Direct Steam Generation

Flow instability in parallel pipes is closely related with the application of direct steam generation (DSG) for parabolic trough solar power technology. Maldistribution of the flow rate may occur in heated parallel pipes with common inlet and outlet manifolds. Therefore, it is necessary to carry out the instability mechanism studies to provide a reference value for actual operation.In this paper, we present the pressure drop calculation of a single pipe based on the model of parallel pipes of DSG for parabolic trough solar power plant. Analysis of horizontal double pipes system is then extended by single pipe analysis, and it allows obtain all the steady-state solutions. Linear stability analysis is carried out to differentiate into the stable solutions and unstable solutions. The time-dependent equations are applied to simulate the response of the system to finite disturbances and the performance due to variations in operating conditions.According to the principle of similarity, we designed and made the experimental bench. Steady-state solutions are calculated by MATLAB, and the numerical results compared with the experimental data to verify the correctness of the theoretical analysis. What’s more, we calculate the numerical steady-state solutions of double pipes and multiple parallel group (three or four pipes) respectively, and linear stability analysis is applied to distinguish the stable and unstable ones, revealing the flow rate distribution in real operation situation. In addition, the theoretical analysis on four parallel pipes during different heating loads is carried out to indicate all the possible steady-state solutions. It is shown that the number of parallel pipes and different heating conditions are the important factors to the system instability.Transient simulation is applied by Simulink of MATLAB to simulate the response of the system to finite disturbances and the performance due to variations in operating conditions like the total inlet flow rate and heating power. This work allows verify the correctness of the linear stability analysis, and further reveais the specific behavior of flow instability.In addition, A method is proposed to improve flow distribution uniformity in parallel pipes by installing a resistant orifice at the inlet of each pipe where is not heated. The numerical solutions compared well with the experimental results.