Abstract: Due to the needs of urban construction, more and more cities adopt underground cable tunnels to transmit electricity. The tunnel fire accidents threaten city safety and power transmission seriously. The smoke generated by the cable fire is an important factor hindering the rescue process of firemen. The current existing smoke control methods mainly consider how to discharge the smoke from the tunnel quickly from the perspective of tunnel ventilation, mainly including natural smoke exhaust and mechanical smoke exhaust, which has certain limitations. Acoustic agglomeration is the process in which an intense sound field is applied to promote relative motion and rapid agglomeration among aerosol particles. The existing literature show that the use of acoustic agglomeration technology can effectively eliminate polystyrene fire smoke, and the characteristics of power tunnel fire smoke are similar to polystyrene.So we attempt to use acoustic agglomeration technology to eliminate power tunnel fire smoke.The TSI 3330 optical particle size analyzer was used to measure the particle size of fire smoke particles, the results show that the particle size of VV cable smoke is mainly distributed around 1 μm, while YJV cable smoke contains more 0.3 μm particles in addition to fine particles of about 1 μm submicron particles. By measuring the transmitted light intensity, the smoke transmittance, visibility, smoke rate and other parameters can be calculated. The smoke generation characteristics of cable fire smoke under the conditions of horizontal and vertical laying was tested. Smoke generation characteristics of cable outer sheath, filling layer and insulating layer, the smoke generation characteristics of the cable under continuous heating, heating for 20 s and heating for 50 s, were tested too. The results show that the cable material has a greater impact on its combustion and smoke production. The VV cable produces a large amount of smoke. After burning for about 60 s, its light transmittance drops to around 0.2, while the YJV cable produces less smoke than the VV cable; When burning horizontally, the overall light transmittance of smoke is lower than that of vertical burning; the smoke produced by the outer sheath material of the cable is the most after burning, and the light transmittance drops to around 0 at about 60 s, and the agglomeration chamber is filled with a lot of white smoke.Lastly, the acoustic agglomeration platform was built to eliminate smoke in power tunnels. The sound wave is generated by a signal generator, amplified by a power amplifier, and then driven by a compression driver to sound, to analyze the change of light transmittance of cable fire smoke with and without sound wave. The result shows that acoustic agglomeration can quickly increase the visibility of cable fire smoke. When the sound power is 12 W and the frequency is 1.5 kHz, it only takes 0.2 min to increase the light transmittance of the reunion room to 0.6, reaching the threshold of safe escape. Frequency is the key parameter when sonic smoke is eliminated. The agglomeration effect of cable fire smoke is very sensitive to the frequency of sound waves. The best frequency of cable fire smoke is 1.5 kHz. The smoke effect has a greater impact. The greater the sound power, the better the smoke suppression effect. When the sound power reaches a certain level, the rate of increase in the reunion efficiency slows down.

Key words: acoustic agglomeration; cable fire; fire smoke; aerosol; power tunnel; transmittance