An analysis system of infrared non-contact recognition of raw-milk gas-liquid two-phase flows

A model illustrating the gas-liquid two-phase flows (GLTFs) of slug raw-milk in micro tubes was built, and an infrared-curtain-based sensor was designed for non-contact recognition of raw milk in GLTFs. An infrared curtain signal acquisition site was set at both upstream and downstream for analysis of time domain, frequency spectrum and cross-correlation. Photos of two-phase flows were taken by a high-speed camera and used as a synchronous control of signal analysis. The analysis of infrared curtain signals shows that the spectral energy of raw-milk GLTFs at low-speed condition is concentrated at the low-frequency section, but at high-speed condition it shifts to the high-frequency section with two peaks nearby. Therefore, the infrared-curtain-based non-contact sensor succeeded in recognition of raw milk GLTFs in micro tubes. Compared with a contact-typed pressure sensor, this non-contact sensor can extremely reduce the interference on flow patterns. This sensor severs as a theoretical basis for further research on pattern recognition and flowing mechanism of GLTFs. This study also provides some clues for exploration of infrared-curtain-based non-contact computation of raw-milk flow quantity.