Hydrogen Bubble Flow Visualisation System

Introduction

      The hydrogen bubble technique is popular, simple and cost effective method for flow visualisation.

The technique involves the evolution of small hydrogen bubbles from a fine wire cathode which is positioned normal to the fluid flow. The bubbles are swept from the wire and following the flow accurately, due to their  small size, are made clearly visible by a mean of light guided the fluid surface.

The Hydrogen Bubble Flow Visualisation System has been designed to allow viewing of the complex flow patterns associated with water flowing past solid objects or boundaries.

    The hydrogen bubble technique is highly visual and is particularly useful for laboratory and lecture theatre work.

    A stream of small hydrogen bubbles accurately follows the water and clearly shows any changes in the direction of the water as it flows around objects in its path.

DESCRIPTION

The Hydrogen Bubble Flow Visualisation System is compact, bench mounted and self-contained requiring only filling with water and connecting to a mains electrical supply.

     It comprises a flow tank, a separate electronic control console and a comprehensive set of clear acrylic flow visualisation models.

    The top of the flow tank is manufactured from GRP for durability and incorporates a wide, shallow working section with a flat black acrylic bed for flow visualisation studies. A smooth flow of water at variable velocity is passed through the working section. This is achieved by using a unique fluid drive unit, in combination with flow straightness. The depth in the working section can be changed by a set of weir strips at the discharge end.

A number of acrylic models are provided with the equipment, such as an aerofoil section and cylinders of different diameter. These can be positioned in the working section to show the flow effects around these shapes. User defined models can also be used.

   A lighting module, placed in the water at the side of the working section, produces a wide beam of light below the surface of the water and illuminates the hydrogen bubbles to aid visualisation of the flow patterns.

   The hydrogen bubbles are produced by fine platinum/iridium cathode wire located under the surface of the water and normal to the direction of flow. The wire is kept taut by a forked holder (supplied in three widths) and is held in the required position by an adjustable support tripod. Hydrogen bubbles can be produced using plain tap water; however Glauber’s salt is also supplied with the unit for more detailed studies.

The electronic control console provides all of the necessary electrical services for the flow tank and incorporates the hydrogen bubble generator. All operating parameters are displayed on a liquid crystal display. Controls are included for the water pump, light source and hydrogen bubble generator. The size of the hydrogen bubbles can be varied by adjusting the current to the cathode wire. The generator automatically maintains the current at the required value by varying the supply voltage to compensate for changes in the loop resistance.