Losses In Pipe Bends

Objectives:
To determine the variation of friction factor with Reynolds Number.
To determine the relationship between total head loss and flow rate for pipe bends and other common pipe fittings.
To determine the loss coefficient for each fitting.

Apparatus:
The apparatus shown in figure (2), consists of two separate hydraulic circuits, each one containing a number of pipe system components. Both circuits are supplied with water from the same hydraulic bench. The components in each of the circuits are as follows:

• Dark Blue Circuit: 
  

1. Gate Valve (D)
   
2. Standard Elbow Bend (C) with radius 12.7 mm 
   
3. 90o Miter Bend (B)
   
4. Straight Pipe, length 914.4 mm, small diameter = 13.6mm, large diameter = 26.2mm, pipe material is copper (e=0.0015mm)
   

• Light Blue Circuit:
  

1. Globe valve (K)
   
2. Sudden Expansion (E).
   
3. Sudden contraction (F).
   
4. 150 mm 90 radius bend (J).
   
5. 100 mm 90 radius bend (H).
   
6. 50 mm 90 radius bend (G).
   

In all cases (except the gate and globe valves) the pressure change across each of the components is measured by a pair of pressurized piezometer tubes. In the case of the valves pressure measurement is made by U-tube containing mercury


Procedure:

1. Close the globe valve K and open the gate valve D, see figure2. Switch on the bench pump and open the bench supply valve to admit water to dark blue circuit. Allow water to flow for 2 to 3 minutes.
   
2. Close the gate valve D and bleed all of the trapped air into the top of the manometers tubes. Check that all the manometers show zero pressure difference.
   
3. Open the gate valve and then, by carefully opening the bled screws at the top of the mercury U tube, fill each limb with water. Make sure that all air bubbles have been expelled, then close the bleed screws.
   
4. Close the gate valve, open the globe valve, and repeat the procedure for the light blue circuit.
   
5. Open fully the bench supply valve. Then close the globe valve and open fully the gate valve to obtain the maximum flow rate through the dark blue circuit.
   
6. If necessary, adjust the water levels in manometers by pumping air into, or releasing air from the bleed valves at the tops of the manometers.
   
7. Record the readings of each of the manometers in the dark blue circuit. Note the reference of each manometer and also record the type of filling next to each pair of results. Also read the levels in the mercury U tube connected between the inlet and outlet of the gate valve D.
   
8. Measure the flow rate by timing the collection of water in the bench weighing tank.
   
9. Measure the water temperature by holding a mercury thermometer in the flow at exit-from the outlet hose.
   
10. Close the gate valve to reduce the differential manometer reading by about 10%. Again read the manometers and the U tube, then measure the flow rate.
    
11. Repeat the procedure until you have about 10sets of readings over the whole range of flow.
    

Results and Discussions:

• The loss coefficient does not vary with the flow rate, it depends only on the fitting or shape
  
• My calculations for K are close to those of the standard data.
  
• The calculation of head loss for flow through a pipe with known conditions is generally carried out as follows. If the fluid velocity and the pipe diameter are known, the Reynolds number can be calculated. The Reynolds number and the pipe roughness are used to determine the friction factor, f, from the Moody plot using the appropriate curve. Once, the friction factor is known, the major head loss can be calculated. The head loss can then be used to determine the pressure drop between two sections.