IMPROVEMENTS IN AND RELATING TO MEASUREMENT OF FLUID FLOW VELOCITY

摘要

The invention provides an improved method and apparatus, for measuring gas flow velocity. The invention is particular well suited for use in measuring flow velocity of noxious and/or explosive gases in a corrosive environment such as landfill sites. Gas flow velocity is measured by varying the energy content of a volume of gas at a first preselected point (18) thereby creating a thermal label in a flow path (1) and detecting the said variation in energy at subsequent preselected points (34) in the flow path. The time taken for peaks of these thermal labels to pass detectors (34) enables flow velocity to be calculated. This may be achieved by a computer at a remote position. Preferably the energy content is reduced by injecting an amount of liquefied gas (17) into the gas flow path. The invention avoids the use of heaters and there is therefore no risk of sparks occurring which may ignite explosive gas mixtures.