Bag filters are used to prevent dust exposure in many environments. They require maintenance to retain their filtration efficiency. The typical maintenance approach is pulse jet backwashing, but this method is not entirely effective for maintaining filters in all environments as its reverse air pressure is insufficient for some applications. Hence, there has been a recognized need to amplify the backwashing air.
A new type of device was recently developed on the basis of the Coandă effect, which amplifies the backwashing air and results in greater efficiency. However, it still does not offer sufficient performance (particularly when multiple devices are connected, as happens under actual use conditions), and its actuating mechanism is unclear. In this study, we investigated fluid behavior in the device and attempted to improve its design using computation fluid dynamics (CFD). We found that the Coandă effect injector does indeed improve efficiency by inducing more outer air into the device and forming a negative pressure area via overexpansion of sonic flow. We also developed an improved device that has 1.2 times higher reverse air cleaning efficiency. Our improved device improves the nozzle angle and the wall shape of the device to smoothen the supersonic flow attachment to the wall.
The CFD analysis further established that tapering to a square pipe is effective for providing a uniform supply of compressed air to multiple connected amplifying devices. In addition, this shape shortens the time to onset of amplification, and compressed air can be more effectively used. These effects were experimentally confirmed.