The article focuses on the experimental determination of the amount of released gas due to cavitation using an optical evaluation method. Cavitation is induced by the mineral oil flow through a throttle valve which characterizes commonly used valves in oil hydraulic systems. Cavitation zones are influenced by the defined experimental conditions. The influence of flow velocity, downstream pressure, and valve displacement on the development of gas phase due to cavitation is evaluated. Depending on the defined experimental conditions and the throttle valve displacement, a specific amount of released gas phase is monitored in the assembled observation window. The results give an overview of the amount of gas phase in the form of the bubble size distributions, volume and mass fractions that are released from the mineral oil when cavitation occurs under the defined experimental conditions. With respect to empirically acquired data, it can be said that the volume and mass fraction evolution of released gas phase, depending on the cavitation number, can be suitably described by a power law with an appropriate order of scaling. At the same time, a change in the determined curves during the initial phase of cavitation is found. Based on measured data, it can also be said that depending on the experimental conditions, up to 1 vol. % of air is present in the assembled observation window. It is also determined that up to 8% of air is released from the dissolved state depending on the achieved experimental conditions.

A natural circulation helium loop appears to be a perspective passive method of a nuclear reactor cooling. When designing this device, it is important to analyze the mechanism of an internal flow. The flow of helium in the loop is set in motion due to a difference of hydrostatic pressures between cold and hot branch. Steady flow at a requested flow rate occurs when the buoyancy force is adjusted to resistances against the flow. Considering the fact that the buoyancy force is proportional to a difference of temperatures in both branches, it is important to estimate the losses correctly in the process of design. The paper deals with the calculation of losses in branches of the natural circulation helium loop by methods of CFD. The results of calculations are an important basis for the hydraulic design of both exchangers (heater and cooler). The analysis was carried out for the existing model of a helium loop of the height 10 m and nominal heat power 250 kW.

A supersonic gas ejector in conjunction with a liquid ring vacuum pump is used for creating and maintaining vacuum in a chamber for technological purposes. In this paper the authors submit an overview about the problematics of suction pressure reduction with a supersonic gas ejector used as a pre-stage of a liquid ring vacuum pump. This system has also the function of a cavitation protection due to the higher pressure present at the suction throat of the vacuum pump. A part of this paper is devoted to the governing equations used at the definition of the flow through an ejector. The experimental studies are then carried out in or own laboratory for verification purposes.

The paper presents a method for analysing the pressure signal at the compressor outlet, which allows to detect when the machine operating point approaches the area where a stall is about to occur. The signal analysis method is based on nonlinear feature extraction from the dynamic signal. The correlation dimension ($d_{\text{corr}}$) is used to quantify the complexity of the measured signal, its value decreasing if the analysed signal originates from deterministic processes. The results presented indicate that the correlation dimension of the signal decreases at flow rates approximately 10% above the flow rate at which negative effects on machine performance occur. This trend has been observed across multiple rotor speeds. These findings suggest that the perturbations associated with the onset of the stall can propagate to the compressor outlet, leading to less chaotic pressure behaviour that reflects the dynamics of these perturbations. The fact that stall can be identified from the pressure signal in the space between the rotor and the diffuser in its early stages is well known, but the possibility of identifying stall at the compressor outlet, where the perturbations are significantly attenuated, has not been documented in the literature.

This paper deals with the one-dimensional unsteady fluid flow model of a natural circulation loop. The governing equations are solved according to both the Euler and Lagrange approaches on two parallel computational grids. The linearization of equations and a semi-implicit discretization scheme are used to enhance the algorithm’s effectiveness. The results of the simulations were verified by using experimental data obtained on an experimental rig that was a scale model of an emergency system for the removal of residual heat after reactor shutdown. The parameters compared were the helium temperature at two locations and the heater outlet pressure. The simulation results generally did not differ from the experimental data by more than 10%. The best agreement was obtained for scenarios in which the helium pressure was highest in combination with slow changes in the input parameters (less than 4%). Conversely, the results differed the most for the scenario with extremely fast device cooling (20%).