Energy Gradient lines

HGL

  1. It is obtained by doing joining several locations along the pipe and drawing a curve through the liquid levels in the piezometers.

  2. The vertical distance above the pipe center is a measure of pressure within the pipe.

  3. It can increase or decrease and it always lies below the EGL but TEL only decreases in the direction of flow.

  4. The line that represents the sum of the static pressure and the elevation heads, is called (HGL).

  5. The height of the HGL decreases as the velocity increases, and vice versa.

  6. At a pipe exit, the pressure head is zero (atmospheric pressure) and thus the HGL coincides with the pipe outlet.

  7. The mechanical energy loss due to frictional effects causes the EGL and HGL to slope downward in the direction of flow.

  8. The gauge pressure of a fluid is zero at locations where the HGL intersects the fluid.

  9. The pressure in a flow section that lies above the HGL is negative, and the pressure in a section that lies below the HGL is positive.

  10. HGL can rise or fall in the flow direction but can never exceed EGL.

  11. Gauge pressure is 0 at location HGL will intersects fluid

  12. For a pipe of uniform section, slope of hydraulic gradient line is equal to the slope
    of energy gradient line.

  13. Hydraulic grade line as compared to the centre line of conduct should always be above the conduct.

  14. In fluid flow, the line of constant piezometric head passes through two points which have the same Velocity

EGL

  1. It is obtained by joining several locations along the pipe and drawing a curve through the liquid levels in the Pitot tubes.

  2. The line that represents the total head of the fluid, is called EGL

  3. The difference between the heights of EGL and HGL is equal to the dynamic head.

  4. For stationary bodies such as reservoirs or lakes, the EGL and HGL coincide with the free surface of the liquid.

  5. EGL is always above HGL and These two curves approach each other as the velocity decreases, and they diverge as the velocity increases, TEL always lies above HGL and they cannot intersect unless velocity head becomes zero (no flow).

  6. In an idealized Bernoulli-type flow, EGL is horizontal, and its height remains constant. This would also be the case for HGL when the flow. velocity is constant.

  7. For open-channel flow, the HGL coincides with the free surface of the liquid, and the EGL is a distance V2/2g above the free surface.

  8. The slope is a measure of the head loss in the pipe.

  9. A component that generates significant frictional effects such as a valve causes a sudden drop in both EGL and HGL at that location.

  10. A steep jump occurs in EGL and HGL whenever mechanical energy is added to the fluid (such as by a pump).

  11. A steep drop occurs in EGL and HGL whenever mechanical energy is removed from the fluid (such as by a turbine).

  12. Both the above lines enables us to avoid situations in which the pressure drops below the vapor pressure of the liquid (which may cause cavitation).

  13. EGL cannot increase in the flow direction unless energy is supplied to the fluid.

  14. HGL rises in the diffuser section as the velocity decreases, and the static pressure recovers somewhat; the total pressure does not recover, however, and EGL decreases through the diffuser.

  15. In converging and diverging passages EGL and HGL are not parallel to each other in ideal flow.

  16. TEL and HGL are coincident and lie in the free surface for the body of liquid at rest. (e.g. Large reservoir).

  17. TEL can never be horizontal or slope upward in the direction of flow, if the fluid is real and no energy is being added.

  18. The locus of elevations that water will rise in a series of pitot tube is called EGL