EN 1029 Laboratory
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2.1 Impact of a Water Jet
2.2 Flow Through a Venturi Meter
3.Experimental procedures and results
3.1 Experimental procedure – Impact of a Water Jet
3.2 Experimental procedure – Flow through a Venturi Meter
3.3 Results– Impact of a Water Jet
3.4 Results– Flow through a Venturi meter
4.1 Impact of a water jet
4.2 Venturi meter
Rate of flow was measured in two different experiments, Impact of a water jet and flow through a Venturi meter. The main objective was to calculate the change in momentum and energy loss in flow which was put under pressure. The experiment showed that results obtained can significantly defer from the theory if energy losses are not neglected.
Water is the most commonly used resource of renewable energy. In 21st century, hydropower is used in more than 150 countries around the world. It is also the most efficient method of producing energy with 90% efficiency output. Impact of a Water Jet is used to show how mechanical work can be created from water flow. When a fluid is put under pressure, the pressure gives it high velocity in a jet. Jet strikes the vanes of the turbine wheel. This wheel then rotates under the impulse created by the water jet hitting the vanes. Venturi meter is used to measure discharge along a pipe. In this experiment, when pressure is dropped, there is an increase in velocity. Pressure magnitude is dependent on rate of flow, so by measuring the pressure drop, discharge can be calculated. Main objective of both experiments is to calculate rate of flow under pressure.
2.1 Impact of a Water Jet
From impulse-momentum change equation it can be assumed that force is generated due to the change in momentum of the water. In other words, force equals the difference between the initial and final momentum flow. Arrangement of jet impact apparatus used is given in Figure 1
Jet impinging on a vane is shown in Figure 2. Control volume V is used, bounded by a control surface S. The entering velocity is u1 (m/s) and it’s in the x –direction. The vane deflects water jet and the leaving velocity is u2 inclined at an angle β2 to the x – direction. Pressure over the surface of the jet, apart from the part where it flows over the surface of the vane is atmospheric. The change in direction is due to force generated by pressure and shear stress at the vane’s surface. The mass flow rate is . Mass flow rate is the mass of substance which passes through a given surface per unit time [kg/s]. Experiment was done for flat and hemispherical vane.
Force on the het in the direction x is FJ (N), then momentum equation in the s- direction is
FJ =(u2 cos β2 - u1) (1)
From Newton's Action- Reaction law, force F on the vane is equal and opposite to Fj
F =(u1 - u2 cos β2 )
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