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Civil engineering level 1 Fluid Mechanics Lab report (oriphis and free jet flow)

Used to restrict flow through the line. Used to control the velocity of fluid within the piping. Extensively used to measure flow rate within the piping. Orifice in the form of orifice plates is widely used for injecting constant flows to the apparatus. They are vital part of electronic fuel ignition systems where metered amount of fuel is injected within the combustion chamber through orifice, as they provide very stable flow. Orifices used for such critical applications are designed with great effort. They must be smooth enough to reduce frictional effects which greatly affect the efficiency of orifice(Kinseler.com). Also while designing an orifice for a specific flow application, ratio of length vs orifice diameter are strictly monitored. Not only this, orifice is an integral part of jet flows as well which is in fact closely lying to orifice(Sarco, 2000). Measuring the jet flows is really important in calculating the steam acting upon the turbine in the power plant. It is also integral part of many other chemical plant operations. Orifices are extensively being used in the fields of bioinformatics and botany. Gaseous flow for the processes of respiration and photosynthesis is measured by using orifice. In this case differential pressure at upstream and downstream is calculated and is directly proportional to the flow of fluid out of the orifice(Parkinson and .Day, 1979). This differential pressure is then maintained at certain level to get required results. THEORY Vena contracta is

the reduction of fluid jet area after the fluid emerges out of the orifice. It is the minimum diameter observed in the profile of the jet flow and lies close to the orifice opening along the axis of jet flow. According to the Bernoulli’s equation, the velocity of fluid at vena contracta is given by: Velocity of fluid is also affected by the frictional affects introduced by the reservoir walls and orifice, Reynolds number etc. These are compensated by introducing a constant, , the resulting expression is: In or der to determine the relation between horizontal distance,, and coefficient of velocity, , first the expression horizontal distance is determined as the flow of jet is in horizontal direction if no other force is being applied on it. Due to the action of gravity, jet flow is in projectile motion and produces a parabolic profile. The effect of gravity is calculated in terms of the vertical displacement, given by: Value of t can be determined as: Substituting value of t in the horizontal displacement equation gives: This Implies, Putting value of v in the velocity equation gives: After simplification, we get the Cv-x relationship: This expression clearly indicates that is the slope of the , curve. This Implies, METHODOLOGY In this experiment we made use of F1-17, orifice and free jet flow instrument by armfield. The apparatus is provided with a head tank, provided with a baffle plate. Constant head of fluid is maintained within the tank, for which adjustable over flow pipe is provided. Fluid to the tank is supplied by the piping connecting the tank with the hydraulic bench. At the bottom of the tank, required orifice is fitted along the vertical back frame. Needles are provided to track the flow trajectory from the orifice; simply adjusting the needles by unscrewing them. The position of the needles can then be marked on the graph paper

Author : christian03

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