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Cavitation refers to the formation of vapour bubbles in flowing fluids due to strong low pressure. As the flow velocity increases, the static pressure of the fluid falls to the vapour pressure and leads to the formation of vapour bubbles. The bubbles are carried along by the flow and implode if, with decreasing velocity, the static pressure rises above the vapour pressure of the fluid.
ST 250 is suitable for the demonstration of cavitation processes using the example of a Venturi nozzle. Pressure energy is converted into kinetic energy and vice versa in the Venturi nozzle. Vapour bubbles form in the narrowest cross-section.
To visualise the flow processes the experimental unit includes a Venturi nozzle made of transparent plastic. There are three pressure measuring points on the Venturi nozzle: at the inlet, at the narrowest point and at the outlet. The input pressure can be adjusted via a pressure reducing valve. The flow rate and the pressures can be adjusted via two ball valves which are located at the inlet and outlet of the pipe system.
The pressure distribution within the Venturi nozzle is shown on three manometers. The flow can be read off a rotameter. The temperature is measured directly upstream of the Venturi nozzle and is displayed on the thermometer.
The well-structured instructional material sets out the fundamentals and provides a step-by-step guide through the experiments.
Learning Objectives / Experiments
- function of a Venturi nozzle
- pressure as a function of the flow rate
- cavitation processes at different flow rates and pressures