Under what operating conditions is it necessary to perform frequency calculations for the thermometer sleeve?
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When the medium under test flows, the thermometer probe THERMOWELL inserted into it vibrates passively, a phenomenon known as drift. The frequency of the wake is known as the wake frequency; it depends on the flow velocity of the medium and the diameter of the thermometer probe. The thermometer bulb itself has a natural frequency, which depends on the structure of the bulb as well as the material properties of the thermometer bulb. When the tail-vibration frequency fw is close to or equal to the natural frequency fn, the thermometer sleeve undergoes intense vibration (resonance), which can cause the thermometer sleeve to break. For the safety of the thermowell THERMOWELL, it is required that the frequency ratio be less than 0.8: r = frequency of thermowell oscillation / natural frequency of the thermowell, with r < 0.8. When manufacturers of thermometer casings produce these casings, if the calculated frequency ratio r is equal to or greater than 0.8, then the structural dimensions of the thermometer casing should be modified: its length should be reduced and/or its diameter increased. For casings used in flow rates exceeding 80 m/s, support beams should be added. Frequency calculation is not necessary when the flow is stationary or at low speeds (such as when the thermometer probe is installed on large equipment); however, for flow speeds exceeding 30 m/s, it is advisable to perform frequency calculation for the thermometer probe.
Your understanding of the issue regarding frequency calculation for thermometer casings is very accurate. In simple terms, frequency calculation is necessary in the following situations: 1. When the flow velocity of the medium being measured is high, exceeding 30 m/s, the thermometer probe inserted into it may experience vibrations; such vibrations are known as drift. At this point, frequency calculations are necessary to prevent the flutter frequency from approaching or reaching the natural frequency of the casing, thereby avoiding intense resonance that could lead to the casing breaking. 2. When the structure or material of the sleeve changes, it may affect its natural frequency. At this point, frequency calculation is also required to determine whether the new natural frequency will resonate with the tail-vibration frequency. In general, frequency calculation is primarily aimed at ensuring the safe use of the thermometer sleeve, preventing resonance under high flow rates that could lead to the rupture of the sleeve. .
It’s my first time dealing with this issue; I’ve learned something!
You can download the calculation software from the Wika website.