A noise source analysis
Inseparable from the pumps, pipes and valves in the heating system, but these also are the source of the noise generated facilities.
1, when the said first pipe, the liquid flowing through the pipe, since the turbulence and friction pressure disturbance will generate noise excitation, especially when the Reynolds number Re> 2400 when a turbulent state, which contains a large number of irregular small turbulent vortices, you can say that they themselves are "noisy" state. In particular, flows through the throttle or down valves, pipes or abrupt cross-section mutant elbow bend, turbulence and fluid through part of these obstacles vortex interaction noise, the sound power level (dB) with a flow rate of change in the relationship can be expressed to: △ Lw = 60lg, if poorly designed piping can also generate cavitation noise;
2, say valve, pressure limiting valve with throttling or effect, is a liquid transmission pipeline greatest impact noise source. When sufficient fluid flow rate in the pipe, if the valve is partially closed, the inlet valve is formed in a large area of the choke, the choke area of the liquid flow rate to increase in the internal static pressure reduced when the flow rate is greater than or equal to the critical velocity of the medium, the static pressure less than or equal to the vapor pressure of the medium, the formation of bubbles in the fluid. Bubbles with the liquid flow, the flow rate gradually decreases downstream of the throttle valve area, the static pressure increases, the bubbles have been squeezed to break, causing the fluid pressure fluctuations without rules, this particular phenomenon is called cavitation turbulence, thereby generating the noise is called cavitation noise. In the flow, high pressure pipe, almost all of the throttle valve can produce cavitation noise, cavitation noise which can be very far downstream along the pipeline under the spread, the random noise can stimulate the valve or pipe natural vibration of the movable member, and spread to other neighboring parts pipe surface through these parts, thus producing similar metal collision resulting tonal sounds. Seven cavitation noise is proportional to the velocity of sound power or eight parties, so as to reduce the noise can be a multi-stage cascade valve valve, the purpose is progressively reduced flow rate. We often use as cut-off valve, using a flow of low prices, so that when the fluid flows through the valve chamber, the valve will be in control of the following (ie choke area) to form the high-speed low-pressure area, resulting in bubbles. By forming a high-pressure valve after the low-speed region, bubbles have been squeezed broken cavitation noise.
Based on the above analysis shows that the noise pipe, valves and noise are concerned with the state of the liquid flow, in other words, with the pressure and flow rates.
