Why does the waterproof fan have a reverse wind phenomenon?

The waterproof fan has been widely used in some departments due to its unlimited width in theory, as well as the advantages of large air volume and small size. Although many scholars have studied the horizontal waterproof fan, there are still some basic problems to be further explored. For example: what is the gas flow through the cascade twice, how the vortex that controls the flow field in the impeller is formed, what the gas flow direction depends on (that is, how the air inlet and outlet are determined), etc. For this purpose, experimental studies were carried out. In order to facilitate the observation of the flow field, photography and the measurement of static pressure, the test is simulated with water.

For the waterproof fan, if it is not properly designed, it may cause a reverse wind phenomenon, that is, the air inlet and the air outlet are exchanged with each other. To this end, a simulation test study was carried out in a water tank.

The casing of the waterproof fan, the cross-flow fan is generally composed of a curve GF (rear wall) with a gradually increasing gap with the impeller, a circular arc or other shape of the vortex tongue BD and the upper boundary DE. The length of the volute tongue and the angle γ between it and the upper boundary DE of the air outlet have a great influence on the performance of the fan.

(1) The asymmetric outer boundary (including the asymmetry with the impeller gap) is the basic condition for the waterproof fan to make the fluid flow stably in a certain direction.

(2) When the impeller drives the fluid to rotate, if there is only a straight line boundary in the flow field, a vortex will be formed near the boundary, downstream of the small gap along the rotation direction of the impeller, and at the inner edge of the impeller. The rotation direction of the vortex of the waterproof fan is the same as that of the impeller, and the strength of the vortex mainly depends on the speed of the impeller and the boundary conditions. The flow field inside and outside the impeller is mainly controlled by this vortex.

(3) If there are multiple boundaries, the flow field depends on the combined influence of each boundary. The vortex appears near the boundary where the flow resistance difference is very large, and there is only one vortex.

(4) For the waterproof fan, in order to make it work normally and not against the wind, compared with other boundaries, the vortex tongue should have a larger flow resistance difference.

Post time: Mar-14-2022