The study on minimum throttle coefficient flow to eliminate two-phase instability of parallel pipes at solar thermal power

The problems of uneven flow distribution of vapour-liquid in the parallel pipes widely exist in power boilers, steam generators, heat exchangers and boiling water reactors. The root cause of instability is that the pressure drop versus mass flow rate curve of the system shows an “N-shape” behaviour. To solve this two-phase instability, the simplest and the most effective method is to install the throttle valve at the entrance of pipeline, so that the pressure drop characteristics of flow shows monotonic and at the same time the installation of the throttle valve consume more pump power. In order to find the best balance of the contradiction between security and economy of the device, a new method is proposed to find out the pressure drop versus the flow rate in a single pipe under the different operating condition. And the numerical result is compared with the experimental data to verify the theoretical model. Furthermore the minimum throttle coefficient is calculated and confirmed to keep single value in the parallel pipes during operation.