Abstract

Energy saving of room air-conditioner (RAC) is strongly required due to growing environmental concern. It is difficult to work a cross flow fan (CFF) at the most efficient operating point (OP) because a surging phenomenon occurs near this efficient OP. The conventional method for suppressing the surging phenomenon by increasing a rotation speed is unfavorable because a fluidic noise and a fan power consumption increase. Therefore, we investigated the new method for suppressing the surging phenomenon focusing on a structure of a fan casing.

It is known that the surging phenomenon is likely to occur from both right and left ends of the CFF. However, an area where surging occurs and a flow pattern in this area have not been revealed in detail. In this study, we experimentally investigated the area where surging occurs by measuring the outlet air velocity distribution across the CFF. In addition, the flow pattern in this area was compared with that of the center area using simulation. Simulation results showed that an area ratio of a vortex flow inside the CFF is high at both ends of the CFF, and a part of the mainstream flows back to the upstream side through a gap between the tongue and the CFF. Therefore, we thought that the function of the tongue, which divide inflow and outflow, is not sufficient.

The influence of modifying the tongue shape was experimentally evaluated. The test results showed that the surging limit shifted to the low flow rate and high static pressure side, and the noise at the condition of the surging limit decreased. The surging phenomenon was suppressed by modifying the tongue shape at both ends of the CFF compared to the center area. This technique makes it possible to work the CFF in a more efficient OP.

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