DETERMINATION OF STATIC, VELOCITY AND TOTAL PRESSURE USING MANOMETERS AND PITOT TUBE PDF

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UNIVERSITY OF RIZAL SYSTEM Morong, Rizal College of Engineering

Mechanical Engineering Laboratory I (ME Lab 1)

Activity No. 4 DETERMINATION OF STATIC, VELOCITY AND TOTAL PRESSURE USING MANOMETERS AND PITOT TUBE

Aquino,Carl Lowie Celajes, Jan Karl Cercado,Ezekiel R. ___________Penalosa, Jessie_______ Name

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October 04,2020____________ Date Submitted

RATING

______________________ Engr. Merie Ann C. Dudang Instructor

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ACTIVITY NO. 4 DETERMINATION OF STATIC, VELOCITY AND TOTAL PRESSURE USING MANOMETERS AND PITOT TUBE I.

INTRODUCTION:

The instrument called a manometer and pitot tube are devices that measure the pressure and velocity of the fluid. The pitot tube is a flow measurement device which measures the velocity of a fluid and the manometer measures the pressure acting on a fluid.The basic pitot tube comprises a tube indicated specifically into the fluid stream. As this tube contains fluid, a weight can be measured; the moving fluid is brought to rest (stagnates) as there's no outlet to permit the stream to proceed. This weight is the stagnation pressure of the fluid, too known as the total pressure or (especially in flying) the pitot pressure.The stagnation pressure is not enough to determine the fluid flow velocity.By using the bernoulli's equation which states that “Stagnation pressure = static pressure + dynamic pressure” the fluid velocity can be calculated.The dynamic pressure, at that point, is the distinction between the stagnation pressure and the static pressure. The dynamic pressure is at that point decided employing a diaphragm inside an encased holder. If the air on one side of the diaphragm is at the static pressure, and the other at the stagnation pressure, at that point the avoidance of the diaphragm is relative to the dynamic pressure. According to BrightHubEngineering. (2009, December 03) in their article entitled “Fluid Velocity Measurement Using a Pitot Tube (Pitot Static Tube)”.Stagnation pressure is also a measure of the amount that fluid pressure exceeds local atmospheric pressure, but it includes the effect of the fluid velocity converted to pressure. It is measured through a flat opening that is perpendicular to the direction of fluid flow and facing into the fluid flow. Stagnation pressure (also called total pressure) measurement is illustrated with the second U-tube manometer in the diagram at the left.Dynamic pressure (also called velocity pressure) is a measure of the amount that the stagnation pressure exceeds static pressure at a point in a fluid. It can also be interpreted as the pressure created by reducing the kinetic energy to zero.Static Pressure, Stagnation Pressure and Dynamic Pressure, Relationship,The symbol, P, is often used for static pressure. Dynamic pressure is given by the expression,1⁄2 ρV2. The stagnation pressure is then given by the following equation: Pstag = P + 1⁄2ρV2 + γh ,Where: ρ is the fluid density (slugs/ft3), γ is the specific weight of the fluid (lb/ft3),h is the height above a specified reference plane (ft), V is the average velocity of the fluid (ft/sec). With the specified units for the other parameters, pressure will be in lb/ft2. Velocity Measurement with a Pitot Tube, For pitot tube measurements and calculations, the reference plane is taken to be at the height of the pitot tube measurements, so the equation for stagnation pressure becomes: Pstag = P + 1⁄2 ρV2 , which can be rearranged to: V = (2ΔP/ρ)1/2 Where ΔP = Pstag – P. The pressure difference, Δp, (or Pstag – P), can be measured directly with a pitot tube like the third U-tube in the figure above, or with a pitot tube like that shown in the figure at the right. This is a concentric pitot tube. The inner tube has a stagnation pressure opening (perpendicular to the fluid flow) and the outer tube has a static pressure opening (parallel with the fluid flow).

According to Benson, T. (n.d.) in his article entitled “Pitot Tube”. Pitot tubes are used on aircraft as speedometers. The actual tube on the aircraft is around 10 inches (25 centimeters) long with a 1/2 inch (1 centimeter) diameter. Several small holes are drilled around the outside of the tube and a center hole is drilled down the axis of the tube. The outside holes are connected to one side of a device called

the axis of the tube. The outside holes are connected to one side of a device called a pressure transducer. The center hole in the tube is kept separate from the outside holes and is connected to the other side of the transducer. The transducer measures the difference in pressure in the two groups of tubes by measuring the

3 strain in a thin element using an electronic strain gauge. The pitot tube is mounted on the aircraft so that the center tube is always pointed in the direction of travel and the outside holes are perpendicular to the center tube. (On some airplanes the pitot tube is put on a longer boom sticking out of the nose of the plane or the wing.)

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OBJECTIVES: 1. To learn how to get total pressure measurement, static pressure measurement, and velocity pressure measurement using manometer and pitot tube. 2. To understand why industries and machines use this kind of instruments. 3. To learn how manometer and pitot tube works.

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MATERIALS/EQUIPMENT:

Manometer Manometer is used to measure the pressure exerted by a fluid on a surface.

Pitot tube Pitot tube is used to measure the flow velocity of a fluid.

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ILLUSTRATION / DIAGRAM:

PITOT TUBE: A. Pitot tube is used in wind tunnel experiments and on airplanes to measure flow speed. It's a slender tube that has two holes on it. • The front hole is placed in the airstream to measure what's called the stagnation pressure. • The side hole measures the static pressure. Type of Manometer U Tube-The U Tube contains water or mercury in a U-shaped tube, and is usually used to measure gas pressure. One end of the U tube is exposed to the unknown pressure field and the other end is connected to a reference pressure source (usually atmospheric pressure)

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PROCEDURE: 1. Show step by step Static Velocity measurement using manometer include sample calculations.

Figure 3 shows two devices that measure fluid velocity based on Bernoulli’s principle. The manometer in Figure 3(a) is connected to two tubes that are small enough not to appreciably disturb the flow. The tube facing the oncoming fluid creates a dead spot having zero velocity (v1=0) in front of it, while fluid passing the other tube has velocity v2. This means that Bernoulli’s principle as stated in P1+12ρv12=P2+12ρv22P1+12ρv12=P2+12ρv22 becomes P1=P2+12ρv22P1=P2+12ρv 22 Figure 3. (a) The Bernoulli principle helps explain lift generated by a wing. (b) Sails use the same technique to generate part of their thrust.Thus, pressure P2 over the second opening is reduced by 1/2ρv2^2, and so the fluid in the manometer rises by h on the side connected to the second opening, whereh∝12ρv2^2(Recall that the symbol ∝ means “proportional to.”) Solving for v2, we see thatv2∝√h Figure (b) shows a version of this device that is in common use for measuring various fluid velocities; such devices are frequently used as air speed indicators in aircraft.

5 Sample Calculations

2. Show step by step Static velocity measurement using pitot tube include sample calculations

A Pitot tube consists of two tubes in one probe that sense both total and static pressure. The flow impacts on one tube, pointing directly into the fluid flow, that senses the total pressure in the duct or pipe. Radial holes perpendicular to the flow sense the static pressure in the duct. The space between the inner and outer tubes permits transfer of sensed pressures to the pressure connections on the opposite of the Pitot tube.

6 The pressure connections of the Pitot tube are then connected to a differential pressure instrument, such as a manometer or Magnehelic® Differential Pressure Gage. The pressure reading shown by the instrument is the velocity or dynamic pressure, which is the difference of the total pressure (on the high pressure port) and the static pressure (on the low pressure port). The fluid velocity is directly proportional to the velocity pressure and can be calculated using the formula V = 1096.7 √hv/d for air, with V the velocity, d the density of air in the application, and hv the velocity pressure from the measuring device.

Sample Calculations Consider a pitot tube being used to measure air velocity in a heating duct. The air is at 85 oF and 16 psia. The pitot tube registers a pressure difference of 0.021 inches of water (Pstag – P). Calculate the velocity of the air at that point in the duct? Solution: Convert the pressure difference of 0.021 inches of water to lb/ft2 (psf) using the conversion factor, 5.204 psf/in water. 0.021 inches of water = (0.021)(5.204) psf = 0.1093 psf The density of air at 85oF and 16 psia can be calculated using the ideal gas law, to be 0.002468 slugs/ft3. Now V can be calculated: V = (2ΔP/ρ)1/2 = [(2)(0.1093)/0.002468] 1/2 = 9.41 ft/sec 3. Show step by step Pressure measurement using manometers include sample calculations

Pressure is defined as a force per unit area - and the most accurate way measure low air pressure is to balance a column of liquid of known weight against it and measure the height of the liquid column so balanced. The units of measure commonly used are inches of mercury (in. Hg), using mercury as the fluid and inches of water (in. w.c.), using water or oil as the fluid.

Fig. 2-1. In its simplest form the manometer is a U-tube about half filled with liquid. With both ends of the tube open, the liquid is at the same height in each leg. Fig. 2-2. When positive pressure is applied to one leg, the liquid is forced down in that leg and up in the other. The difference in height, "h," which is the sum of the readings above and below zero, indicates the pressure....