Design Procedure***The purpose of this design procedure is to enable the user to determine if a well selected for thermometry considerations is strong enough to withstand specific application conditions of temperature, pressure, velocity, and vibration. Well failures are caused by forces imposed by static pressure, steady state flow, and vibration. Separate evaluations of each of the above effects should be made in order to determine the limiting condition. This design procedure does not allow for effects due to corrosion or erosion. The natural frequency of a well designed in accordance with Fig. 1.1 and of the dimensions given in Table 1.1 is given by the following equation: where The wake or Strouhal frequency is given by: where
ƒ_{w} = wake frequency, cycles per sec The ratio of wake to natural frequency (ƒ_{w}/ƒ_{n}) shall not exceed 0.8, and when this condition is met, the Magnification Factor, relationship of dynamic to static amplitude is given by: For r ≤ 0.8 Stress AnalysisThe maximum pressure that a thermometer well can withstand for a given material at a given temperature shall be computed from the following: where The maximum length that a thermometer well can be made for a given service is dependent upon both vibratory and steady state stress. The necessity for keeping the frequency ratio at 0.8 or less imposes one limitation on maximum length. The other limitation is one of steady state stress considerations, as given by the following equation: where Table 1.1 well dimensions, in Inches
Fig. 1.1 power test code
*** Power Test Code Thermometer Wells, J. W. Murdock, Journal of Engineering for Power, Trans. ASME, vol. 81, 1959. |