- Discharge Over Weirs V Notch And Rectangular Weir Weirs Are Typically Installed In Open Channels Such As Streams To De 1 (32.37 KiB) Viewed 27 times
- Discharge Over Weirs V Notch And Rectangular Weir Weirs Are Typically Installed In Open Channels Such As Streams To De 2 (48.87 KiB) Viewed 27 times
- Discharge Over Weirs V Notch And Rectangular Weir Weirs Are Typically Installed In Open Channels Such As Streams To De 3 (49.92 KiB) Viewed 27 times
- Discharge Over Weirs V Notch And Rectangular Weir Weirs Are Typically Installed In Open Channels Such As Streams To De 4 (64.8 KiB) Viewed 27 times
- Discharge Over Weirs V Notch And Rectangular Weir Weirs Are Typically Installed In Open Channels Such As Streams To De 5 (52.67 KiB) Viewed 27 times
- Discharge Over Weirs V Notch And Rectangular Weir Weirs Are Typically Installed In Open Channels Such As Streams To De 6 (76.07 KiB) Viewed 27 times
- Discharge Over Weirs V Notch And Rectangular Weir Weirs Are Typically Installed In Open Channels Such As Streams To De 7 (46.13 KiB) Viewed 27 times
- Discharge Over Weirs V Notch And Rectangular Weir Weirs Are Typically Installed In Open Channels Such As Streams To De 8 (30.03 KiB) Viewed 27 times
Objectives To determine the head - discharge relationship, coefficient of discharge and the experiment for head factor, for sharp crested rectangular weir and V-notch weir. Materials and Equipment • Hydraulics Bench • Rectangular V-notch weir plate. • Hook and point gauge (Figure 1). Fine adjustment nut Scale Vernier Instrument carrier Weir plate - Thumb nuts Stilling baffle Delivery Nozzle Sliding mast - Weir carrier Point gauge Fine adjustment Scale nut Delivery Nozzle Instrument carrier Stilling baffle Sliding mast Point gauge Weir plate Weir carrier Thumb nuts Figure 1. Test Apparatus
Theory The theoretical discharge for: • The rectangular notch is given by: Q = /2gb (1) Ignoring head losses and considering head loss coefficient Ca due mainly to the contraction of the flow area downstream of the notch, the actual discharge Q is considerably less and may be expressed as: Q=Cay2gbH (2) (3) • The V-notch weir of angle 20: Q = V2g tan(0/2) Ignoring head losses and considering head loss coefficient Ca: Q = (a/2g tan(0/2) (4) Where, b: Breadth of the rectangular notch H= Height of flow over notch 8 = Angle of vee notch Generally, all constants are collected in m: Q = mH" Can take log of both sides: log(0) = log(m) + n log(H) (5) (6) H Water Flow b) Figure 2 - (a) Triangular weir, (b) Rectangular weir
Procedure 1. Set up the equipment as shown in Figure 1. 2. Admit water to channel until water discharges over the weir plate. 3. Close flow control valve and allow water level to stabilize. 4. Set Vernier Height Gauge to a datum reading using the top of the hook. 5. Position the gauge about half way between the weir plate and the stilling baffle. 6. Admit water to the channel, adjust flow control valve to obtain heads, H, increasing in steps of about 1 cm. 7. For each flow rate, stabilize conditions, measure and record H. 8. Take readings of volume and time using the volumetric tank to determine the flow rate. 9. Find Cd and n for each case directly from the reading, and using log-log plot. Raw Data, Results and Sample Calculations • Rectangular weir: b = 30 mm Reading No. Log Q (m/s) Log (Q) (H) Cd Cd Experimental Theoretical %Error 1 2 3 4 5 Volume of Time, Water, T (sec) (L) 5 4.9 5 5.5 5 6.1 5 8.9 5 10.6 ת ת ת ה ט Head of Water, H (m) 0.0643 0.0596 0.054 0.0435 0.038
Q (m/s) H5/2 Cd Experimental Cd Theoretical %Error V-notch weir: 0 = 90° Volume No. of Time T Water, (sec) (L) 1 5 13.75 2 5 16.25 3 5 19.75 4 5 32.3 5 5 35.2 unul Head of Water H (m) 0.038 0.036 0.033 0.030 0.026 Nmi Plot and Calculations: • Plot of Log (Q) vs. Log (H) for Rectangular Weir and determine the slope and Intercept of the plot. • Plot Q vs HS/2 and use it find Cd. • Plot a graph of Qly-axis) against 43/4x-axis) for the rectangular weir • Use a linear function to plot the best fit and express the relationship between Q and H" and in the form of: Q = mH",in which the exponent value nis 1.5 for the rectangular weir and 2.5 for the triangular weir. • Calculate the coefficients of discharge Cd (theoretical method) using equations: C4 iV292 Ca= is 29 tano/2 Record Cd values calculated from the theoretical method in the Result Tables. Compare the experimental results to the theory by calculating the percentage of error.
9 8 7 6 5 3 2 10 9 8 7 6 5 4 3 2 10 9 B 7 6 5 4 3 2 10 ONO 7 5 3 2 2 2 3 5 6 7 8 9 10 2 3 . 4 5 6 7 8 910 3 4 5 6 7 8 9 10
40 30 20 10 -10 02 30 10 10 10 20 30 10
Discussion and Conclusion: • Discuss the results and the plots. • What is the purpose of V-notch and Rectangular weir? • What are the advantages of V-notch over rectangular notch? • Why does the V-notch give more accurate flow measurement? • Compare the experimental results to the theory by calculating the percentage of error. • Why would you expect wider variation of Cd values at lower flow rates? Compare the results for Cs of the weirs utilized in this experiment with those you may find in a reliable source (e.g., textbooks). Include in your report a copy of the tables or graphs you have used for textbook values of Cd. • Discuss your observations and any source of errors in calculation of Cd.