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HM 260


Technical Description

Fluids are accelerated in nozzles, while the pressure decreases. When using compressible fluids (e.g. air) very high speeds can be achieved by this process, often in the supersonic range. Nozzles are used in steam turbines, in injector devices, in supersonic aircraft and rockets. The impact forces or thrust (action or reaction force) occurring in the fluid is referred to when designing the shape of nozzles.

HM 260 offers two experiment layouts for nozzles, in which either the occurring action force or reaction force of the fluid is considered. Characteristics such as flow velocity and nozzle efficiency are measured. In addition, the "choking effect" is demonstrated, where the mass flow stops increasing upon reaching the critical pressure ratio. Air is used as a compressible fluid.

In the first experiment layout to determine the reaction force, a nozzle is inserted into the force measuring device. The force measuring device consists of a bending beam, whose deformation is measured electronically. The air pressure upstream and downstream of the nozzle can be adjusted. Compressed air flows through the nozzle and the occurring reaction force (thrust) of the fluid is measured. 

In the second experiment layout, the baffle plate is inserted into the force measuring device and the nozzle is positioned above the baffle plate. The position of the nozzle is adjustable, so that the distance between the nozzle and the baffle plate can be varied. The flow at the nozzle outlet impacts against the baffle plate and the action force (impact force) of the fluid is detected by the deformation of the bending beam.

Pressures and mass flow are also detected in addition to the force. The temperatures are also measured, in order to determine the mass flow precisely. Four convergent-divergent and one convergent nozzle as well as a baffle plate are available for experiments.

The well-structured instructional material sets out the fundamentals and provides a step-by-step guide through the experiments.

Learning Objectives / Experiments

- determining the critical pressure ratio
- demonstration of the "choking effect"
- determining flow velocity in the narrowest cross section
- measurement of the reaction or action force of the flowing fluid 
- determine nozzle efficiency by thrust


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