The main data of the Cavitation Tunnel is as follows:
Pressure regulation from relatively high vacuum to above atmospheric pressure measured at the pressure regulation container 1 bar Approx
Cavitation number adjustable in wide range down to belows = 0.2
Total length including stiffening girder not including the length required for the impeller drive 20.4 m Approx.
Measuring section 850 mm x 850 mm
Length of measuring section 4000 mm
Contraction ratio of the nozzle 4.99:1 Approx.
Maximum velocity of the water in the measuring section 12 m/s
Total height from the floor at which the tunnel foundations are supported to the highest part of the cavitation tunnel, inclusive stiffening girders, not including additional height for the separate pressure regulation container and not including the height for setting in propeller dynamometers or other test equipment 12.9 m.
The pressure through the nozzle can be controlled by a ball valve located on the discharge side of the nozzle. The Inlet, Throat and Outlet pressures are displayed on a pressure gauge via a three-way selector switch. Cavitation demonstration apparatus is a bench top unit designed for use on Hydraulics Bench. It consists of a tube through which water can be pumped by the hydraulic bench. The apparatus comprises of a clear acrylic nozzle mounted on a support plate. The throat pressure can be varied in either of two ways. The first way is to vary the discharge. Reduction of discharge causes a corresponding reduction of the pressure drop as the flow accelerates into the throat because the velocities are reduced, so that the pressure in the throat increases and cavitation ceases. The tube has an initial diameter of 25mm. It then has a linear contraction to a throat diameter of 5mm. This is followed by a 10mm length of parallel-sided tube, after which it flows through a linear diffuser until the diameter is back to 25mm. The contraction ratio (measured in terms of cross-section area) is therefore 25:1. The second way is to throttle the flow out of the apparatus using the ball valve. From a situation where there is no cavitation, increasing the discharge increases the pressure drop as the flow accelerates into the throat because the velocities are increased.
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The cavitation tunnel installed at the Laboratory for Hydraulic Machines provides high speed visualization of various types of cavitation phenomena, including leading edge cavitation, wake cavitation, and tip vortex :
Cavitation nuclei control
Pressure transducers
High speed visualization
5 components load cell
Optical instrumentation: particle image velocimetry, Laser Doppler velocimetry.
The additional measuring sections Nos. 2, 3 and 4 are exchangeable against the standard measuring section so that the tunnel can be made suitable for a wide range of test work.
The main data of a Cavitation Tunnel with the standard measuring section are as follows:
Contraction ratio of the nozzle 5.96 : 1
Measuring section 60 cm x 60 cm
Cavitation number adjustable in a wide range down to below
Total length including stiffening girders, not including the length required for a propeller dynamometer and a wake rake 13.9m
Maximum velocity of the water in the measuring section 12m/s
Pressure regulation from relatively high vacuum to above atmospheric pressure measured at the pressure regulation container 1 bar Approx.
Total height from the floor at which the tunnel foundations are supported to the highest part of the cavitation tunnel, inclusive stiffening girders, not including some additional height for the separate pressure regulation container and not including the height required for setting in propeller * dynamometers or other test equipment 9.3m.
High Speed / Frame Rate Camera system for observing cavitation.
Window mounting hydrophone system for use in the educational cavitation tunnels.
Educational Wake Rake with integrated pressure transducers for measuring the wake profile within the tunnel.
Flat Plate and Cylinder Model Experiment for use in Tunnels.
Pitot Static tube for use in measuring section of Tunnel.
The dynamometers have been designed for low friction torque at the propeller shaft and for this reason shaft seals are not fitted. As a result, the dynamometers are not watertight. If watertight propeller dynamometers are required, alternative designs are available. All dynamometers have a similar appearance although vary in size / rating to suit the intended specification required. The Dynamometers are compact with low weight and small dimensions and as such are suitable for use with models over a wide range of sizes however also offer with suitable accessories the ability of mounting two dynamometers driven through a gear box to allow the testing of twin screw models. The self propulsion dynamometer measures thrust and torque of the propellers during propulsion tests with ship models on smooth water and in waves in towing tanks.
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The Cavitation Demonstration Unit offers a clear andeasy-to-understand display of cavitation. Students create clearly visiblecavitation in a Venturi and take measurements of flow and pressure. The causes and effects of cavitation are one of the mostimportant subjects in any course on fluid mechanics. In severe cases, cavitationwill damage machines and hydraulic systems. It alsoallows students to understand the Venturi by studying upstream and throatpressures. Studentsuse theory and practical experiments to learn how to predict the onset ofcavitation. They gain practical experience of using the continuity equation and Bernoulli's equation. They use these to calculate flow and pressure, differentmethods of creating cavitation and causes of error. The apparatus is aself-contained, mobile unit. Designers and engineers must beaware of cavitation when they create a new design or installation. Cavitation Demonstration Unit is a purpose-designed teaching unit which enables efficientand effective investigations into the causes and effects of cavitation. The frame includes a handy worktop for student paperwork. It consists of a robust frame which holds a watertank (or reservoir), an electric pump, a flow-control valve, a flow meter and aVenturi.
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Cavitation can play a major role in the vibration of pumps during operation. The pump and tank are interconnected by hoses. Valves and manometers in the delivery and intake lines allow various operating conditions to be set. The transparent plastic pump housing provides a view into the interior of the pump during operation. With the accessory set, cavitation can be experimentally induced and its influence on the vibration spectrum investigated. The principal elements of the accessory set are a single-stage centrifugal pump and a storage tank. This enables the formation of cavitation bubbles to be observed.
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Use of Venturi tube applied to cavitation phenomenon, concept used to change the pressure conditions inside a tank.
Theoretical and practical aspects of Venturi effect.
Bernoullis theorem, including the observing and the application of related aspects in practical fields as industry, agriculture and leisure.
Performable Experiments:
With Ventury Effect Bernoulli And Cavitation system, it is possible to perform the following experiments:
Reduction of the pressure inside the tank in order to obtain cavitation phenomenon and observe new conditions.
Flow determination through the use of the static volumetric system.
Diaphragm calibration and utilization to determine the flow value.
Bernoullis theorem demonstration along a Venturi tube.
Pressure loss calculation in a Venturi tube.
Study of cavitation identifying the pressure, relevant temperature and flow levels.
For the full operating of this system, it is necessary to connect the item to the hydraulic bench or a suitable hydraulic energy source. The Cavitation Phenomenon system for the demonstration of the cavitation phenomenon is a simple and practical equipment including a Venturi tube where the cavitation phenomenon occurs when we have the depression created by the flow acceleration (Venturi effect). In order to grant easy observation of the phenomenon, Venturi tube is made of methacrylate. The equipment also includes a pressure gauge and a vacuum gauge to measure the generated overpressure and low pressure; a membrane valve is included for precise flow control adjustments.
Performable Experiments:
Observation of the cavitation phenomenon in the Venturi tube.
Calculation of the minimum required water flow necessary to observe the phenomenon.
Calculation and testing of the pressure and temperature conditions in which the phenomenon occurs.
Operating Conditions:
Operating environment:Laboratory
Operating relative humidity range: 80% at temperatures < 31C decreasing linearly to 50% at 40C
Operating temperature range:+5C to +40C
Storage temperature range:25C to +55C (when packed for transport).
Open impeller to observe the blades during operation
Continuously adjustable pump speed via frequency converter
Visualisation of cavitation in centrifugal pumps
Transparent pump housing and pipe at the inlet side
Display of the pressures at inlet and outlet side of the pump via manometers
Closed water circuit with tank and temperature display
Digital display of speed, water temperature in the return and flow rate
Temperature control via heater and external cooling via water supply
Flow measurement using rotameter.
Investigation of cavitation processes in a Venturi nozzle
Flow measurement using rotameter
Venturi nozzle with 3 pressure measuring points
Pressure reducing valve, adjustable
Thermometer for measuring the temperature
Manometer for displaying the pressure curve in the Venturi nozzle
Adjustment of the flow rate via ball valves.
Cavitation Demonstration is a small scale apparatus designed to demonstrate Cavitation utilizing an Hydraulics Bench
Flow control valves upstream and downstream of the test section allow flow conditions to be optimised for the demonstration of Cavitation
The apparatus consists of a circular Venturi shaped section manufactured from clear acrylic
Three Bourdon gauges indicate the static pressure upstream of the contraction, inside the throat and downstream of the expansion
Educational software available as an option
Quick release fitting for easy connection to hydraulics bench.
