Experiment No. 1
Fluid Flow Measurements
Group No.6
Cabreros, Ken Nicles
Rivera, Kenneth
I. Objectives To measure volume flow rate of fluid like air at various loads, by use of pitot-static tube, venture meter, and orifice flow meter.
II. Theory Fluid flow measurements are performed across the breadth of engineering, eg. flows of oil, gas, petrol, water, process chemicals, effluent are all necessarily and routinely measured. In the research laboratory, advanced flow measurements are providing new insights into a wide range of engineering flow problems in hydrodynamics (eg. wave impact loading on coastal defenses, beach erosion) combustion (eg. low NOx burners, IC engines), aerodynamics (eg. wind turbine optimization and performance prediction) to list but a few. Measurements of flow rates of fluids through a system can be measured in various ways. The amount of fluid in a certain volume during a given period of time will determine the flow rate. It is expressed in terms of volume or mass per unit time. The most common industrial flow measurement requirement is a measure of the volume or mass of fluid flowing per second through a given cross-section of a pipe. A wide range of devices exist for these purposes reflecting the wide range of conditions which may prevail – liquid flow, gas flow, fluid temperature, pressure, viscosity, conductivity, the cleanliness of the fluid, the presence of flow disturbance. Manometers are used for measuring pressure. They are read directly by the operator which makes it easy to use. These are connected into various instruments for measuring fluid flow. Pitot tube is a small open tube with its open end pointed upstream intercepting the kinetic energy of the flowing fluid, and measures the total pressure. A pitot-static tube is an instrument combining a pitot tube and a static tube. Static pressure is the pressure imparted by the flowing fluid measured at right angles to the flow. Stagnation pressure is the point in the center stream of the fluid flow where the velocity becomes zero. The fluid flows into the opening,thus, pressure builds up and remains stationary at the stagnation point. The difference of the static pressure and stagnation pressure represents the pressure rise. It measures the difference between the pressures in the two tubes to obtain the relative velocity of a fluid in motion. The Venturi meter (after Giovanni Venturi, 1746−1822) is designed to cause minimal head loss as the flow passes the restriction. It is a short tube with a tapering-in construction to have a throat at mid-length of tube that causes increase in the velocity of e flow of fluid and a corresponding decrease in fluid pressure and followed by the tapering-out to original diameter of the tube. The quantity of fluid flow in the venturi meter is determined by the equation: Q =C2gP1-P2W1-A22A12 (1) Where C = coefficient of discharge of venturi meter
A1= Cross sectional area of pipe at station 1 A2= Cross sectional area of throat of venturi meter W= Specific weight of air in the manometer g = acceleration due to gravity Orifice in a pipe or duct is an opening in a thin plate obstruction inside apipe of duct line used as flow rate measuring device. It consists of concentric sharp edged circular hole in a thin plate that is clamped between the flanges of the pipe or duct. The flow characteristics is the minimum cross section of the stream occurring further downstream from the obstruction plate. The quantity Q of the fluid flow is similarly obtained from the equation for the venturi meter. However, several factors contribute to the contracting of flow cross section that a coefficient K replaces the coefficient of discharge of the venturi meter, thus Q =K2gP1-P2W1-A22A12 (2)
Where K = coefficient of flow of orifice flow meter Q=CAVave (3)
III. Materials and Equipment
Fig. 1 Pitot-Static tube
Fig. 2 Venturi Meter
Fig. 3 Manometer
Fig. 4 Set of Circles and Bamboo Corks
Damper
Orifice
Fig. 5 Damper and Orifice Flow Meter
IV. Methodology The manometer (Fig. 3) was placed on solid mounting, leveled accurately and the built-in level was adjusted to zero. Initial reading of the manometer was recorded to read the small pressure differential. Cross section of the duct (Fig. 1) was subdivided into sixteen regions of equal areas and pitot tube was allowed to transverse each station. While the damper was set (Fig.5), the air temperature and barometer reading were recorded. The damper was set at point 1 during the use of pitot tube (Fig. 1), venturi meter (Fig. 2) and orifice flow meter (Fig. 5). The pitot-static tube was connected in such a way that the static pressure was read from the tube manometer. Rubber tubing was connected with the static pressure connection of the pitot-static tube and then connected to the manometer liquid reservoir of the tube manometer.
V. Data and Results:
Table 1. Differential Pressure Measurement in Pitot-Static Tube Duct Transverse | Damper Setting (No. of Turns) | | 2 | 4 | 6 | 8 | 16 | | Ps | Pt | ∆P | Ps | Pt | ∆P | Ps | Pt | ∆P | Ps | Pt | ∆P | Ps | Pt | ∆P | 1 | 2216 | 2416 | 216 | 11216 | 2216 | 616 | 11216 | 2216 | 616 | 11216 | 2 | 416 | 11016 | 2216 | 816 | 2 | 2216 | 2416 | 216 | 11216 | 2216 | 616 | 11216 | 2216 | 616 | 11216 | 2 | 416 | 11016 | 2216 | 816 | 3 | 2216 | 2416 | 216 | 11216 | 2216 | 616 | 11216 | 2216 | 616 | 11216 | 2 | 416 | 11016 | 2216 | 816 | 4 | 2216 | 2416 | 216 | 11216 | 2216 | 616 | 11216 | 2216 | 616 | 11216 | 2 | 416 | 11016 | 2216 | 816 | 5 | 2216 | 2416 | 216 | 11216 | 2216 | 616 | 11216 | 2216 | 616 | 11216 | 2 | 416 | 11016 | 2216 | 816 | 6 | 2216 | 2416 | 216 | 11216 | 2216 | 616 | 11216 | 2216 | 616 | 11216 | 2 | 416 | 11016 | 2216 | 816 | 7 | 2216 | 2416 | 216 | 11216 | 2216 | 616 | 11216 | 2216 | 616 | 11216 | 2 | 416 | 11016 | 2216 | 816 | 8 | 2216 | 2416 | 216 | 11216 | 2216 | 616 | 11216 | 2216 | 616 | 11216 | 2 | 416 | 11016 | 2216 | 816 | 9 | 2216 | 2416 | 216 | 11216 | 2216 | 616 | 11216 | 2216 | 616 | 11216 | 2 | 416 | 11016 | 2216 | 816 | 10 | 2216 | 2416 | 216 | 11216 | 2216 | 616 | 11216 | 2216 | 616 | 11216 | 2 | 416 | 11016 | 2216 | 816 | 11 | 2216 | 2416 | 216 | 11216 | 2216 | 616 | 11216 | 2216 | 616 | 11216 | 2 | 416 | 11016 | 2216 | 816 | 12 | 2216 | 2416 | 216 | 11216 | 2216 | 616 | 11216 | 2216 | 616 | 11216 | 2 | 416 | 11016 | 2216 | 816 | 13 | 2216 | 2416 | 216 | 11216 | 2216 | 616 | 11216 | 2216 | 616 | 11216 | 2 | 416 | 11016 | 2216 | 816 | 14 | 2216 | 2416 | 216 | 11216 | 2216 | 616 | 11216 | 2216 | 616 | 11216 | 2 | 416 | 11016 | 2216 | 816 | 15 | 2216 | 2416 | 216 | 11216 | 2216 | 616 | 11216 | 2216 | 616 | 11216 | 2 | 416 | 11016 | 2216 | 816 | 16 | 2216 | 2416 | 216 | 11216 | 2216 | 616 | 11216 | 2216 | 616 | 11216 | 2 | 416 | 11016 | 2216 | 816 | Average | 2216 | 2416 | 216 | 11216 | 2216 | 616 | 11216 | 2216 | 616 | 11216 | 2 | 416 | 11016 | 2216 | 816 |
Using the equation in determining the velocity of fluid in the duct: V =2g(Delta P)W
Where W = 11.45N/m3 Table 2. Velocity of fluid in duct Damper Setting | Velocity (m/s2) | 2 | 0.4628 | 4 | 0.8016 | 6 | 0.8016 | 8 | 0.6545 | 16 | 0.9256 |
VI. Data Analysis Basing from the data from Table 1, the pressure difference is directly proportional to the number of damper settings. The higher the number of turns, the higher the pressure difference. On Table 2, the velocity is directly proportional to the damper setting. Based from the data on Table 4, the velocity of the fluid in the Venturi Meter is directly proportional to the damper setting. On the orifice flow meter, the velocity of the fluid is inversely proportional to the damper setting.
VII. Conclusion The velocity of the fluid in the duct is directly proportional to the number of turns in the damper. The greater number of turns, the faster the fluid can flow throughout the system. The transversing of pitot-static tube in each station does not really affect in the pressure readings and pressure differences in the duct. Velocities in the Venturi meter are directly proportional to the number of turns in the damper setting. The greater number of turns, the lesser flow is backfired to the Venturi meter. Velocities in the Orifice flow meter are inversely proportional to the number of turns in the damper setting. The greater number of turns, the more pressure is read in the manometer, in which the orifice is close to the damper setting.
VIII. Questions 1. What is stagnation pressure? How is the concept of stagnation pressure used to determine the total velocity of a flowing fluid? * It is the point in the center stream of the fluid flow where the velocity becomes zero. At a stagnation point the fluid velocity is zero and all kinetic energy has been converted into pressure, in which it is read by the manometer 2. What are the relative advantages of the venture and orifice in measuring airflow? * They are simple and robust, not affected by upstream flow performance, may be used on gases, liquids and mixtures, not affected by erosion.
XI. References * Flow Measurement Methods by Tom Bruce * Laboratory Manual * Experimental Methods for Engineers 4th Edition by J.P. Holman * Fluid Flow Measurement and Selection by A.L. Ling
