Abstract
The sonic nozzle is commonly used in flow measurement. However, the nonequilibrium condensation phenomenon of moist air in the nozzle has a negative effect on the measuring accuracy. To investigate this complex phenomenon, the experiments on the oscillating condensation flow of moist air were conducted by an adjustable humidification apparatus with different relative humidities (0%-100%), temperatures (30-50°C), and carrier gas pressures (1-6 bar), where the microsize pressure measuring system was designed by Bergh-Tijdeman (B-T) model. The accurate mathematical model of nonequilibrium condensation was also built and validated by the experimental data of time-averaged pressure distribution. Then, the frequency and intensity of pressure fluctuation of oscillating flow at a wide range of operation condition were obtained combining experimental data and physical simulation model. Importantly, a new semiempirical relation of dimensionless frequency deduced from dimensionless analysis was identified accurately by experimental data. Finally, the signal nonstationarity was also observed using the continuous wavelet transform (CWT). The instantaneous frequency saltation and the energy attenuation of pressure signals were observed in the condensation flow.
Highlights
The sonic nozzle is widely used to measure mass flow rate [1]-[2]
The non-equilibrium condensation in sonic nozzle can result in the lower measurement accuracy, due to both steady and unsteady flow which is caused by the supercritical heat addition, namely thermal choking [14], depending on the inlet stagnation condition [15], especially subcooled temperature or humidity of the moist gas
The dominant frequency is calculated in frequency domain using power spectral density (PSD) [45]
Summary
The sonic nozzle is widely used to measure mass flow rate [1]-[2]. The discharge coefficient is a crucial performance parameter for ISO 9300 sonic nozzle which is affected by humidity (by Li [3], Lim [4], Chahine [5]), roughness (by Anthony [6], Alper [7], Wang [8]), geometry (by Park [9], Kim [10]) and vapor condensation (by Li [11], Ding [12]-[13]). The non-equilibrium condensation in sonic nozzle can result in the lower measurement accuracy, due to both steady and unsteady flow which is caused by the supercritical heat addition, namely thermal choking [14], depending on the inlet stagnation condition [15], especially subcooled temperature or humidity of the moist gas. Ding [13] designed a sonic nozzle, according to ISO standard 9300, to experimentally research the condensation phenomenon of the moist gas in the inlet pressure of both 4 bar and 8 bar, and relative humidity ranging from 42% to 63% with a constant temperature. The characteristics of frequency and intensity of oscillating condensation flow in sonic nozzle at different inlet humidity, temperature and carrier gas pressure should be investigated further. The experiments on the unsteady non-equilibrium condensation flow of the moist air in a sonic nozzle were conducted by using an adjustable humidification apparatus.
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