1. Chapter 4: Pipe Networks December, 2011

2. Have you been doing the homework? Student who did not keep up with homework after seeing final class grade!

4. EGL, HGL Energy drives water through pipes. Visual tools to assist with overview of pipeline systems are the Energy Grade Line: V 2 /2g+z+p/ ρ g since we have a figure, the pipe is located at z so the energy grade line is the sum of the velocity and pressure heads above (sometimes below) the pipe The energy grade line (EGL) gives a visual picture of energy loss/gain in the system. Where is most of the head loss occurring? Something important to an engineer Hydraulic Grade Line: z+p/ρg which is one pressure head away from the pipe; as such it gives a visual measure of the pressure in the system; pressures too high rupture pipes and exacerbate leaks Negative pressure can lead to cavitation

5. Figure 4.1

7. Figure 4.3 Energy grade line and hydraulic grade line of a pumping station

9. Tips for EGL/HGL Some hints for drawing hydraulic grade lines and energy grade lines are as follows: 1.By definition, the EGL is positioned above the HGL an amount equal to the velocity head. Thus if the velocity is zero, as in a lake or reservoir, the HGL and EGL will coincide with the liquid surface. 2.Head loss for flow in a pipe or channel always means the EGL will slope downward in the direction of flow. The only exception to this rule occurs when a pump supplies energy (and pressure) to the flow. Then an abrupt rise in the EGL occurs from the upstream side to the downstream side of the pump. 3.In point 2, we noted that a pump can cause an abrupt rise in the EGL because energy is introduced into the flow by the pump. Similarly, if energy is abruptly taken out of the flow by, for example, a turbine, the EGL and HGL will drop abruptly as in Fig. 5-8. Figure 5-8 also shows that much of the velocity head can be converted to pressure head if there is a gradual expansion such as at the outlet. Thus the head loss at the outlet is reduced, making the turbine installation more efficient. If the outlet to a reservoir is an abrupt expansion, all the kinetic energy is lost; thus the EGL will drop an amount of aV 2/2g at the outlet. 4.In a pipe or channel where the pressure is zero, the HGL is coincident with the water in the system because p/  g= 0 at these points. This fact can be used to locate the HGL at certain points in the physical system, such as at the outlet end of a pipe, where the liquid discharges into the atmosphere, or at the upstream end, where the pressure is zero in the reservoir. Note: switch back and forth to figure on next slide

10. Example used in tips Efficiency: round reservoir exit, larger/smoother pipe, round exit

11. Tips, continued 5.For steady flow in a pipe that has uniform physical characteristics (diameter, roughness, shape, and so on) along its length, the head loss per unit of length will be constant; thus the slope of the EGL and HGL will be constant along the length of pipe. 6.If a flow passage changes diameter, such as in a nozzle or a change in pipe size, the velocity therein will also change; hence the distance between the EGL and HGL will change. Moreover, the slope on the EGL will change because the head loss per unit length will be larger in the conduit with the larger velocity. 7.If the HGL falls below the pipe, p/  g is negative, thereby indicating sub- atmospheric pressure. If the pressure head of water is less than the vapor pressure head of the water (approximately -33 ft at standard atmospheric pressure and (T =60°F), cavitation will occur. Generally, cavitation in conduits is undesirable. It increases the head loss and can cause structural damage to the conduit from excessive vibration and pitting of the conduit walls. If the pressure at a section in the pipe decreases to the vapor pressure and stays that low, a large vapor cavity can form leaving a gap of water vapor with columns of water on either side of the cavity. As the cavity grows in size, the columns of water move away from each other. Often these columns of water will rejoin later, and when they do, a very high dynamic pressure (water hammer) can be generated, possibly rupturing the pipe. Furthermore, if the pipe is relatively thin walled, such as thin-walled steel pipe, sub-atmospheric pressure can cause the pipe wall to collapse. Therefore, design engineer should be extremely cautious about negative pressure heads in the pipe.

12. Practice Locations Develop a pump and pipeline design that addresses a particular set of physical conditions of your own devising. http://www.ce.utexas.edu/prof/maidment/gishydro /ferdi/webedu/utflow/utflow.html http://www.ce.utexas.edu/prof/maidment/gishydro /ferdi/webedu/utflow/utflow.html http://www.ce.utexas.edu/prof/maidment/ce319f/ webtools/visiflow/visiflow.htm http://www.ce.utexas.edu/prof/maidment/ce319f/ webtools/visiflow/visiflow.htm

13. quiz

14. Figure 4.7 Multiple reservoirs connected at a junction We will not solve network problems by hand

15. Figure P4.6.7 A network problem

16. Networking Example

17. EPANET Free Software http://www.epa.gov/nrmrl/wswrd/dw/epanet.html Image: Water tower. EPANET tracks the flow of water in each pipe, the pressure at each node, the height of the water in each tank, and the concentration of a chemical species throughout the network during a simulation period. EPANET Software That Models the Hydraulic and Water Quality Behavior of Water Distribution Piping Systems * Description * Capabilities * Applications * Programmer’s Toolkit * Multi-Species Extension * Support * Downloads – updated 5/27/08 Description Developed by EPA's Water Supply and Water Resources Division, EPANET is software that models water distribution piping systems. It is a Windows 95/98/NT/XP program that performs extended-period simulation of the hydraulic and water quality behavior within pressurized pipe networks. Pipe networks consist of pipes, nodes (pipe junctions), pumps, valves, and storage tanks or reservoirs. EPANET tracks the flow of water in each pipe, the pressure at each node, the height of the water in each tank, and the concentration of a chemical species throughout the network during a simulation period. Chemical species, water age, source, and tracing can be simulated.

20. Water Hammer

21. Water Hammer Examples http://www.youtube.com/watch?v=Kb6feUfHgAU http://www.youtube.com/watch?v=PUyuaOKXYY8 http://www.youtube.com/watch?v=oZbguheiVs4&f eature=related http://www.youtube.com/watch?v=oZbguheiVs4&f eature=related

22. Home Fix Water Hammer Description Engineered Water Hammer Arrester © 2007 Sioux Chief Manufacturing Company, Inc. Water Hammer (hydraulic shock) is by far the loudest and most common plumbing noise problem in the home. You hear it in a home having high water flow rates (around 10 feet per second) when a faucet or water valve is shut off quickly. Older homes have (or should have) what is called an "air chamber" located on each hot and cold water line at or near each faucet or water inlet valve. The purpose of the air chamber is to act like a shock absorber for water when it is flowing at high speed under pressure. Since air compresses (it's a vapor) and water doesn't, the air chamber allows the water a place to temporarily expand into and softens the blow of the water shock wave when the faucet is turned off quickly. Air chambers are often fabricated on-site by the plumber and installed at the faucet's water supply. They typically consist of a vertical length of capped pipe about 12" long or longer and are the same diameter as the water supply pipe. The problem with these things is that they are sometimes made too short and undersized and eventually fill up with water and you have no more shock absorber. The result? Water hammer!. If you have a water filled air chamber it can be easily fixed by draining and recharging the plumbing system. A better solution to alleviate the problem is to have a mechanical or engineered water hammer arrestor installed. These mechanical plumbing devices are charged with air or gas and will not fail like typical air chambers.engineered water hammer arrestor http://homerepair.about.com/od/plumbingrepair/ss/pipe_noises_3.htm

23. Irrigation Fix The easiest method to fix water hammer is to lower the water pressure for your entire irrigation system. It will not get rid of all of the water hammer, but it will sometimes reduce it to a level you can live with. If you have an automatic system, you may be able to rid water hammer by simply changing the order in which the valves operate. Simply find out which valve uses the least water. This will probably be the one with the least amount of sprinklers, but not always. Once you figure it out, rewire the controller so that the valve that uses the least water is the last valve to run. Try a water hammer arrestor. This mostly only works with just water hammer caused from washingmachines and dishwashers. But it is worth a try with sprinkler related water hammer. Install it per the instructions on the package and try putting it on a hose bib to the point where the irrigation system connects to the house water. If you have a hose bib on the irrigation system mainline, that is an even better place. Or you can tap into the irrigation mainline to install it. If it does not work, remove it and return it to the store where you purchased it. An air chamber will not drain properly if it is clogged. Remove its cap and ream out the accumulated scale inside the chamber.