Influences of Boundary Conditions on Pulsation Characteristics and Stability Boundary of Density Wave Oscillation

The influence of operational parameters on density wave oscillation (DWO) has already been investigated by experiments. Special attention is paid to the influence of boundary conditions on the pulsation characteristics and stability boundaries of DWO in this experimental investigation. The investigated boundary conditions include the inlet resistance coefficient at the main pipe and the branch tubes, as well as the upstream compressible volume. The fast Fourier transform method is used to analyze the experimental data.

The pulsation curve observed in the stability experiments is a superposition of the in-phase and out-of-phase DWOs without pressure drop oscillation. With or without the upstream compressible volume, increasing the inlet resistance coefficient at the main pipe stabilizes the system by suppressing the in-phase DWO, while increasing the inlet resistance coefficient at the branch tubes stabilizes the system by suppressing the out-of-phase DWO within the parameter range of these experiments.

For a low pressure drop at the main pipe, the pulsation is predominantly characterized by the in-phase DWO. For a low pressure drop at the branch tubes, the pulsation characteristics are dominated by the out-of-phase DWO. Increasing the upstream compressible volume affects the in-phase DWO pulsation characteristics by suppressing high-frequency pulsation with a low amplitude while enhancing low-frequency pulsation with a high amplitude. The systems becomes unstable when the upstream compressible volume increases. Without an upstream compressible volume, the pulsation period of the in-phase DWO is much smaller than the fluid transit time in the tube. For the in-phase DWO with upstream compressible volume and all out-of-phase DWOs, the ratio of the pulsation period to the fluid transit time is about 0.5 to 2.