1 / 29

Understanding Energy Equations and Hydraulic Grade Lines in Fluid Mechanics

This educational resource covers the fundamentals of energy equations in fluid mechanics, focusing on Bernoulli’s Equation, kinetic energy, pressure energy, and potential energy. It explains how energy is supplied by pumps, lost to turbines, and affected by friction losses through various components. The guide details how to plot Energy Grade Line (EGL) and Hydraulic Grade Line (HGL) graphs, calculate head losses using the Darcy-Weisbach equation, and apply these concepts to practical scenarios like pipe flow and energy storage systems. Gain insights into hydraulic behavior and energy management in fluid systems.

candie
Download Presentation

Understanding Energy Equations and Hydraulic Grade Lines in Fluid Mechanics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. CTC 261 • Energy Equation

  2. Review • Bernoulli’s Equation • Kinetic Energy-velocity head • Pressure energy-pressure head • Potential Energy • EGL/HGL graphs • Energy grade line • Hydraulic grade line

  3. Objectives • Know how to apply the energy equation • Know how to incorporate head (friction) losses into EGL/HGL graphs • Know how to calculate friction loss using the Darcy-Weisbach equation • Know how to calculate other head losses

  4. Energy Equation • Incorporates energy supplied by a pump, energy lost to a turbine, and energy lost due to friction and other head losses (bends, valves, contractions, entrances, exits, etc)

  5. Pumps, turbines, friction loss • Pump adds energy • Turbine takes energy out of the system • Friction loss-loss out of the system as heat

  6. Energy Equation PE+Pressure+KE+Pump Energy= PE+Pressure+KE+Turbine Losses+Head Losses

  7. Energy/Work/Power • Work = force*distance (in same direction) • Power = work/time • Power=pressure head*specific weight*Q • Watt=Joule/second=1 N-m/sec • 1 HP=550 ft-lb/sec • 1 HP=746 Watts

  8. Hints for drawing EGL/HGL graphs • EGL=HGL+Velocity Head • Friction in pipe: EGL/HGL lines slope downwards in direction of flow • A pump supplies energy; abrupt rise in EGL/HGL • A turbine decreases energy; abrupt drop in EGL/HGL • When pressure=0, the HGL=EGL=water surface elevation • Steady, uniform flow: EGL/HGL are parallel to each other • Velocity changes when the pipe dia. Changes • If HGL<pipe elev., then pressure head is negative (vacuum-cavitation)

  9. Transition Example • On board

  10. Reservoir Example • On board

  11. Pumped Storage • Energy use is not steady • Coal/gas/nuclear plants operate best at a steady rate • Hydropower can be turned on/off more easily, and can accommodate peaks • Pumping water to an upper reservoir at night when there is excess energy available “stores” that water for hydropower production during peak periods

  12. Break

  13. Head (Friction) Losses • Flow through pipe • Other head losses

  14. Studies have found that resistance to flow in a pipe is • Independent of pressure • Linearly proportional to pipe length • Inversely proportional to some power of the pipe’s diameter • Proportional to some power of the mean velocity • If turbulent flow, related to pipe roughness • If laminar flow, related to the Reynold’s number

  15. Head Loss Equations Darcy-Weisbach Theoretically based Hazen Williams Frequently used-pressure pipe systems Experimentally based Chezy’s (Kutter’s) Equation Frequently used-sanitary sewer design Manning’s Equation 15

  16. Darcy-Weisbach hf=f*(L/D)*(V2/2g) Where: f is friction factor (dimensionless) and determined by Moody’s diagram (handout) L/D is pipe length divided by pipe diameter V is velocity g is gravitational constant

  17. For Class Use Only: Origin Not Verified!!! 17

  18. For Class Use Only: Origin Not Verified!!! 18

  19. Problem Types • Determine friction loss • Determine flow • Determine pipe size • Some problems require iteration (guess f, solve for v, check for correct f)

  20. Example Problems PDF’s are available on Angel: Determine head loss given Q (ex 10.4) Find Q given head loss (ex 10.5) Find Q (iteration required) (ex 10.6) 20

  21. Find Head Loss Per Length of Pipe • Water at a temperature of 20-deg C flows at a rate of 0.05 cms in a 20-cm diameter asphalted cast-iron pipe. What is the head loss per km of pipe? • Calculate Velocity (1.59 m/sec) • Compute Reynolds’ # and ks/D (3.2E5; 6E-4) • Find f using the Moody’s diagram (.019) • Use Darcy-Weisbach (head loss=12.2 per km of pipe) 21

  22. For Class Use Only: Origin Not Verified!!! 22

  23. Find Q given Head Loss • The head loss per km of 20-cm asphalted cast-iron pipe is 12.2 m. What is Q? • Can’t compute Reynold’s # so calculate Re*f1/2 (4.4E4) • Compute ks/D (6E-4) • Find f using the Moody’s diagram (.019) • Use Darcy-Weisbach & solve for V (v=1.59 m/sec) • Solve Q=V*A (Q=-.05 cms) 23

  24. For Class Use Only: Origin Not Verified!!! 24

  25. Find Q: Iteration Required Similar to another problem we did previously; however, in this case we are accounting for friction in the outlet pipe 25

  26. Iteration • Compute ks/D (9.2E-5) • Apply Energy Equation to get the Relationship between velocity and f • Iterate (guess f, calculate Re and find f on Moody’s diagram. Stop if solution matches assumption. If not, assume your new f and repeat steps). 26

  27. Iterate 27

  28. Other head losses • Inlets, outlets, fittings, entrances, exits • General equation is hL=kV2/2g Not covered in your book. Will cover in CTC 450

  29. Next class • Orifices, Weirs and Sluice Gates

More Related