Head Loss Individual Lab

Head Loss Individual Lab - Head Loss across a Valve Jacob...

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Head Loss across a Valve Jacob Taylor July 28, 2011 Fluid Mechanics I-ENGR 01342 1 Jesse F. Van Kirk Introduction Valves play a vital role, not only in engineering practices, but in everyday life. Whenever a sink is turned on, a garden is watered, or a gas grill is ignited, valves are being used. Valves inside the human heart even control blood flow throughout the body and ensure that the heart maintains the correct pumping action. In engineering terms, valves act like variable resistors on an electrical circuit, and the amount of resistance, or head loss, across a valve depends on the amount that the valve is open. In completing this lab, the objective was to determine the head loss characteristics of a valve controlling the flow of air through a horizontal pipe. This was accomplished by measuring the pressure drop, ∆p, across the valve as a function of flowrate, Q. Using Bernoulli’s equation as a
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means of calculation, the head losses and loss coefficients of each data set were calculated using a dimensional analysis approach. While this was a simplistic set-up, it provides a blueprint for solving such problems in the real world. Relevant Theory In completing this lab, air flowed through a horizontal pipe equipped with a valve and manometer. As air flowed through the pipe at a given flowrate, Q, the valve was closed completely and then opened N turns from its closed position. When the valve was opened N turns, the manometer fluid provided a height difference, h, that was used to calculate the pressure drop, Δp, across the valve. By determining Δp, the head loss, h L , and loss coefficient, K L , across the valve could be calculated. In order to determine the head loss, Bernoulli’s equation first needed to be considered. (1) p = Pressure at given points in the system (lb/ft 2 ) γ = Specific weight of fluid (lb/ft 3 ) V = Velocity at given points in the system (ft/s) g = Acceleration due to gravity (32.174 ft/s 2 ) z = Height at given points in the system (ft) h s = Shaft work head (ft) h L = Head loss (ft) Because there is no change in the diameter of the pipe indicated in the experiment, it can be assumed that the velocity of the air remains constant from the beginning of the pipe to the end of the pipe. Therefore, V 1 and V 2 are equal. The height of the air also remains constant because the pipe is on a horizontal plane, thus z 1 is equal to z 2 . Since there is also no shaft work in the system (i.e. a pump or turbine), h s carries a value of zero. Based on these assumptions, Bernoulli’s equation can then be reduced to: (2)
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Because Δp is equivalent to the specific weight of the manometer fluid times the height difference of the fluid in the manometer, Δp can be easily calculated based on data collected in the lab. In order to then find the K L values across the valve, the formula for head loss was used: (3) K L = Loss Coefficient (Unitless) V = Velocity of given particle flowing through pipe (ft/s) This formula can then be rearranged to calculate for K
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This note was uploaded on 11/17/2011 for the course ENGINEERIN 1 taught by Professor Cag during the Spring '08 term at Rowan.

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Head Loss Individual Lab - Head Loss across a Valve Jacob...

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