miercuri, 5 octombrie 2011

Application example for axial flow fans

The volume flow measuring determines the operating volume flow of an axial fan installed in an air-handling installation.The system greatly facilitates the determination of fan volume flow.As a result the cost and effort required for in duct measurements on the system side,as often carried out during commissioning,can be significantly reduced.Mereover adjustments are faster and easier to carry out.The measuring accuracy of the volume-flow measuring system is approx. ± 5%.

Description of the measuring system

The volume flow measuring measuring system is firmly mounted on the fan to determine the volume flow in its installed condition.The reading is obtained by a simple differential pressure measurement between the sockets of the pressure measuring lines connected to the measuring system.The calibration curve is prepared individually taking into account fan-specific parameters.Key influencing variables include fan type,inlet density rpm and fan design size.Being established individually with reference to the above parameters.
Key influencing variables include fan type ,inlet density ,rpm and fan designsize.Being established individually with reference to the above parameters,the calibration curve is not transferable to other fan types and sizes.At fan operating speeds deviating from the rated rpm level major in accuracies will be obtained ,especially when the fan is running at slower speeds.
The measuring system consists of an additional casing extension made of sheet steel,pre-installed measuring lines for the pressure measurement ,and a sheet aluminium hub body attached to,and rotating with ,the fan impeller. The pressure measurement ring line consists of plastic hose as employed in pneumatic applications,as well as brass screw-in adapters.The four measuring points ,spaced evenly over the circumference ,are connected into a ring line by means of T-fittings.The connection to a pressure measuring instrument is likewise made via a T-fitting.

Technical description

The calibration curves can be computed for flow medium throughput conditions as habitually employed in ventilation technology ,and apply to air only.
The measuring system is standardized for AXN series fans in the 315 to 2000 size range.
The accuracy of the system depends essentially on its installation conditions and on the inlet side approach flow situation.
The measuring range of the differential pressure instrument should be 0 ÷2000 Pa,at a resolution of 1Pa.

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