Abstract
A mobile steam expansion chamber has been developed to investigate experimentally homogeneous and heterogeneous nucleation processes in steam, both in the laboratory and at power plants using the steam withdrawn from the steam turbine. The purpose of the device is to provide new insight into the physics of nonequilibrium wet steam formation, which is one of the factors limiting the efficiency and reliability of steam turbines. The expanded steam or a mixture of steam with a non-condensable gas rapidly expands in the expansion chamber. Due to adiabatic cooling, the temperature drops below the dew point of the steam at a given pressure. When reaching a sufficiently high supersaturation, droplets are nucleated. By tuning the supersaturation in the so-called nucleation pulse, particles of various size ranges can be activated. This fact is used in the present study to measure the aerosol particles present in the air. Homogeneous nucleation was negligible in this case. The experiment demonstrates the functionality of the device, data acquisition system and data evaluation methods.
Highlights
A mobile steam expansion chamber has been developed to investigate experimentally homogeneous and heterogeneous nucleation processes in steam, both in the laboratory and at power plants using the steam withdrawn from the steam turbine
Heterogeneous nucleation can be an important mechanism of early droplet formation, because it requires a lower supersaturation to start [3, 4]
During its transport in the connecting tubing and in the expansion chamber, the diluted sample is kept at a constant temperature sufficiently high to avoid any
Summary
Heterogeneous nucleation can be an important mechanism of early droplet formation (the so-called early condensate), because it requires a lower supersaturation to start [3, 4]. The droplets dry out and low-volatile compounds (typically simple salts and oxides) dissolved in the droplets form fine particles. Such particles would be completely or partly soluble. Pioneering work [5] by the present team showed 3×108 to 6×109 particles per kilogram of steam in various power plants. Chemical analysis of condensed steam samples showed that only a small fraction of the low-volatile matter was captured by the present instrumentation, leading to the hypothesis that most of the matter is dispersed in a large number of particles smaller than 3 nm (the present detection limit).
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