Research on characteristics and mechanism of fluid exciting force in Seawater Reverse Osmosis System

The rotary energy recovery device (RERD) is used in the seawater desalination process. The rotor of the RERD is completely covered by the outer shell. So, the RERD is similar to the "black box". In order to solve the problem that the operative state is difficult to detect directly, a detection method of operative state based on vibration signal is proposed. It is found that the main vibration frequency corresponded well to the 8 times rotational frequency by analyzing the vibration frequency of the outer shell and the rotational frequency of the rotor. A relationship between the main frequency and the rotational frequency is established. On this basis, the method of obtaining the rotational frequency information from vibration signals is studied, including eliminating baseline drift by wavelet transform, demodulation of vibration signals to better reflect the rotational frequency, and estimating the frequency range to avoid frequency interference. The main vibration frequency is obtained to calculate the rotational speed. The results show that the maximum error rate of rotational speed is 2.55% under the steady state and the maximum error rate is 4.58% under an unsteady state. It can meet the requirements of real-time, accurate, and online detection of the RERD operative state.