Numerical analysis on the flow instability of parallel channels in water wall of an ultra-supercritical CFB boiler

A general calculation model based on the time-domain method is established for analyzing flow instability in parallel channels. In this model, the governing equations of mass, momentum, and energy are discretized and solved using the first-order upwind scheme. A numerical computational program called Dynsys is developed in Fortran language to analyze the flow instability occurring in the water wall of an ultra-supercritical CFB boiler with annular furnace. Comparing the calculation results of Dynsys with the experimental results shows that the model is reasonable and accurate for practical engineering application. On the basis of the validated model, the typical parallel channels in water wall of ultra-supercritical CFB boiler are simulated. Results show that, under the condition of invariable inlet pressure, temperature, and total mass flow rate, as well as 1.2 times heat flux disturbance applied on the parallel channels of ultra-supercritical CFB boiler, the fluctuation of inlet flow rate versus time in two channels is out of phase. In addition, the amplitude of flow pulsation decreases with time first and then returns to the steady state. Therefore, the flow in the parallel channels of ultra-supercritical CFB boiler with annular furnace is stable. Compared with the flow instability in single channel, the calculating results show that the flow in parallel channels was more stable within the range of parameters in the present paper.