Experiment No.5 Flow Over Weirs in a Flume-ROSAROS.pdf
- 1. UNIVERSITY OF THE EAST COLLEGE OF ENGINEERING CIVIL ENGINEERING DEPARTMENT NAME: ROSAROS, KENT ARNEL T. GRADE: SUBJECT & SECTION: NCE 3206-CE2 EXPERIMENT NO. 5 FLOW OVER WEIRS IN A FLUME I. OBJECTIVES: 1. To become familiar with a teaching flume, its use and its components. 2. To determine the characteristics of flow over a sharp-crested weir and a trapezoidal weir. 3. To determine the relationship between upstream head and flowrate for water flowing a sharp crested weir and a trapezoidal weir. 4. To calculate the discharge coefficient and to observe the flow patterns obtained. II. MATERIALS/INSTRUMENTS: Hydraulic Bench Teaching Flume Sharp-crested Weir Trapezoidal Weir Vernier Level Gauge III. THEORY A notch is an opening in the side of a measuring tank or reservoir extending above the free surface. These notches are used to measure discharge of open channel flows, by passing or placing or constructing them across the stream. Notches are generally used for measuring discharge in small open channels or laboratory flumes. Notches can be of different shapes such as triangular, rectangular, trapezoidal, stepped notch, etc. the bottom of the notch over which the water flows is known as crest or sill and the thin sheet of water flowing through the notch is known as nappe or vein. The edges of the notch are bevelled on the downstream side so as to have a sharp-edged sides and crest resulting in minimum contact with the flowing fluid. Figure 1. Types of Weirs According to Shape
- 2. UNIVERSITY OF THE EAST COLLEGE OF ENGINEERING CIVIL ENGINEERING DEPARTMENT The discharge over notch is measured by measuring the head acting over the notch. As water approaches the notch, its surface becomes curved. Therefore, the head over the notch is to be measured at the upstream of the notch where the effect of curvature is minimum. Also, it should be close to the notch so that the loss of energy between head measuring section and notch is negligible. In practical, the head over notch is measured at a distance of 3 to 4 times the maximum head from the notch. Figure 2. Cross-Section of a Rectangular Weir Figure 3. Longitudinal Section of a Rectangular Weir Figure 4. Trapezoidal Weir
- 3. UNIVERSITY OF THE EAST COLLEGE OF ENGINEERING CIVIL ENGINEERING DEPARTMENT IV. PROCEDURE A. Flow over a Sharp-crested Weir 1. Ensure the flume is level, with no stop logs installed at the discharge end of the channel. 2. Measure and record the actual width “b” of the sharp crested rectangular weir. 3. Install the weir in the flume with the sharp edge upstream. Ensure that the weir is secured with its bottom at the bed of the flume. 4. The datum for all the measurements will be the top edge of the weir plate. Carefully adjust the level gauge to coincide with the top of the weir, taking care not to damage the edge of the weir then record the datum reading as ho. 5. Alternatively, to avoid damages to the weir, open the flow control valve and admit water into the channel until it discharges over the weir then close the flow control valve to stop the flow of water. When the water stops flowing over the weir adjust the level gauge to coincide with the surface of the water and record the datum reading as ho. 6. Open the flow control valve and set to 50 L/min. 7. Allow a steady flow to develop before taking a reading. Record this as hf. 8. Adjust the flow control valve to three more different flow rates. Note that the flow rates must be set so as not to fully submerged the weir, that is, the downstream must remain unsubmerged. 9. Tabulate the result in Table A1. B. Flow over a Trapezoidal Weir 1. Measure the properties of the trapezoidal weir. 2. Repeat the steps using the trapezoidal weir and tabulate the data in Table A2. 3. Note that the flow rates must be set so as not to submerge the upstream and downstream of the trapezoidal weir. V. DATA AND RESULTS Table A1. Sharp Crested Weir, b = _0.085_ m No. Qa (L/min) Qa (m3/s) hf (m) ho (m) H = hf- ho (m) Qth (m3/s) Cd=Qa/Qth 1 50 0.000833 0.16 0.13 0.03 1.304X10-3 0.64 2 100 0.00167 0.179 0.13 0.049 2.723X10-3 0.6134 3 150 0.0025 0.191 0.13 0.061 3.782X10-3 0.6611 4 170 0.00283 0.20 0.13 0.07 4.649X10-3 0.6088 Average Cd 0.6299 Table A2. Trapezoidal Weir, bbot =0.045 m, btop= 0.07 m, = 14.04 deg from the vertical No. Qa (L/min) Qa (m3/s) hf (m) ho (m) H = hf- ho (m) Qth (m3/s) Cd=Qa/Qth 1 50 0.000833 0.127 0.085 0.042 1.144X10-3 0.7281 2 55 0.000917 0.129 0.085 0.044 1.226X10-3 0.748 3 60 0.001 0.131 0.085 0.046 1.311X10-3 0.7628 4 65 0.0011 0.134 0.085 0.049 1.441X10-3 0.7633 Average Cd 0.7506
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- 7. UNIVERSITY OF THE EAST COLLEGE OF ENGINEERING CIVIL ENGINEERING DEPARTMENT VII. ILLUSTRATION / SET UP OF THE EXPERIMENT VIII. OBSERVATION AND CONCLUSION
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