I have been dealing with air velocity measurement in order to obtain air distribution on air-cooled fin and tube condenser. In this respect, have been produced a traverse system which have 3 mm hot bulb anemometer but I am worried about vibration effect. Have you anyone knowledge or experience about this problem.Thank you in advance
Ergin,
Enclosed is a 1981 Physical Oceanography journal article that may provide some insight into the phenomenon you are studying.
Eric
Dear Eric,
Thank you very much for your information and sharing. This issue is very important for my research to get accurate measurement.
I guess you have in mind vibration of the sensor on the traversing system arm? Then you really have to ensure that during the measurements the bulb is pritty stable what means you have to wait until the arm with the sensor is stabilized. Otherwise, your position is changing. It also depends on the accuracy with which you want to measure. Maybe couple of tenth of mm does not matter. But in principle try to stabilize the traverse arm with the sensor. From our experience when the system with the sensor scans automatically, it always vibrates (unless the structure is very rigid) and we have to wait couple of seconds.
I agree with Miroslav that if you sensor is connected well then there should not be any problem in measurements. Now many instruments have compensations for such vibrations as well.
Mechanical vibrations will induce an additional velocity fluctuation, next to fluctuations existing in the flow. Anemometers are in general non-linear devices. For example when you consider a simple hot-wire anemometer, the signal is proportional to the square-root of the flow velocity. This is due to the dependency of the boundary layer thickness on the flow velocity (roughly square root). When the instrument is fast enough to follow the fluctuations this is not a problem (the average velocity does correspond to the averaged measured velocity). When the probe is slow the measured signal is a time average of the square-root of the velocity. The effect of oscillation of the probe will not average out. This implies that due to the non-linearity of the response there will be a systematic error in the measured averaged velocity proportional to the square of the ratio of velocity fluctuation u' to main flow velocity u. So you should check square of the ratio (u'/u) induced by the vibration, and decide wether such a systematic error is acceptable. The same occurs with mass transport in a wet bulb or with heat transfer in a thermometer.
Addition to what our colleagues said, the amplitude of the vibrations and the measurements acoustic regimes play an important role. For example, if the amplitude of vibrations are few microns and the variations of the measured flow parameters are big, I think the vibration will not affect your results.
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