Bubbles in the sensing line of nuclear power plant pressure transmitters: the shift of spectrum resonances

Pressure Sensing Line Diagnostics in Nuclear Power Plants

“…Therefore, to simulate a pressure measuring system, both the sensing line and the pressure transmitter should be modelled. A number of representations have been developed to study pressure transmitters and sensing lines dynamics (Barbero et al, 2000;Bergh & Tijdeman, 1965;Hashemian et al, 1993;Iberall, 1950;Müllens & Thie, 1989). The models presented in this chapter aim at deriving the pressure sensing system transfer function to facilitate the investigation of the pressure signal power spectral densities (PSDs) obtained for noise analysis.…”

“…A homogeneous air-water mixture exists only when the air volume fraction is less than one percent (Sherstyuk, 2000). In the presence of air bubbles, the total volume inside the sensing line is the sum of the air volume, V a , and water liquid volume, V w , and the density of the air-water mixture can be expressed as (Barbero et al, 2000) …”

“…Note that the voids are most likely air or water vapour; and the sensing line void model developed herein is valid for both cases. A two-phase fluid has the elasticity of a gas and the density of a liquid (Barbero et al, 2000) so that the sound velocity decreases significantly, and consequently C increases. For a homogeneous mixture, the sound velocity can be calculated as (Landau & Lifshitz, 1959) (30) and (32) into Eq.…”

“…However, in a sensing line absent of flow, gas and liquid components eventually separate into a heterogeneous arrangement, which is now addressed. Similar to the homogeneous air-water mixture case, a method that replaces the original R, L, and C parameters with new values calculated using the modified fluid density and sound velocity can be applied to the heterogeneous air-water mixture case (Barbero et al, 2000) as depicted in Fig. 14(a).…”

“…16 that even though the air volumes for both pockets are equal, the system transfer functions vary significantly depending on where the void is located. These differences in transfer functions are physically attributable to the nonlinear system behaviour that results from sitedependent sound speed differences due to the air position (Barbero et al, 2000) as well as the concomitant changes in the standing wave frequencies (Schohl & Vigander, 1989).…”