Atomising Seeding Generator

A high pressure, high volume Laskin seeder for PIV and Flow Visualisation.

Principal of Operation

The seeding generator works by injecting air into a fluid (normally oil) at near sonic velocity via a number of Laskin nozzles. Each nozzle produces micro-bubbles with micro-droplets (typically 1 micron) inside. These bubbles reach the free oil surface and burst, releasing the micro-droplets. Internal baffles are used to remove unwanted large droplets that can be produced by the splash when a bubble bursts. The density of micro-droplets is determined by the air flow rate through the nozzles and the number of nozzles. It is important to have a large free surface where the bubbles burst to avoid foaming. This sets the upper limit to the micro-droplet production rate. Control of the micro-droplet production rate is provided by turning nozzles on and off and by adjusting the air flow rate/pressure. This level of control tends to produce a fixed seed density at a variable flow rate. In order to provide control of the seed density and avoid the need for a mixing plenum in the experiment, dilution air can be admitted to the generator so that lower seed densities can be produced when required.

Recommended Working Liquids

The VisiSeeder works with a number of fluids. Most work is done with corn oil as it produces drpolets around 1 micron diameter and is readily available at low cost. Olive oil is often used where elevated temperatures are expected (e.g. combustion studies) as it has a higher flash point and decomposition temperature. For very high temperatures or low pressure studies, silicone vacuum oils may be used.

Specifications

• Operating principle Laskin atomizer nozzles Fully adjustable through control of individual seeding nozzles
• Typical particle size 1 µm (peak in PDF of size distribution)
• Seed materials include:corn oil, olive oil, silicone fluids (e.g. Dow Corning), water
• One way valves on gas feeds
• Operates up to 12 bar overpressure, 20 bar option safety valve set to maximum working pressure
• Supply pressure 20 bar max, uses regulator
• Dilution air inlet from main air supply
• Visible level indicator
• Stainless steel pressure vessel  meets appropriate  standards (CE marked)

Options and Accessories

Solenoid valves for remote operation High pressure (to 20 bar) rating Outlet pressure gauge Flow meter Air compressor