 Civil Engineering Questions
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Join this group to post and comment. Ali Hamza
Mechanical
28 Jan 2019

# Energy of a Liquid in Motion :

ENERGY OF A LIQUID IN MOTION

KINETIC ENERGY

A body of mass m when moving at a velocity v possesses a kinetic energy, K.E = ½ mv2

Kinetic head = 𝐾.𝐸𝑤𝑒𝑖𝑔ℎ𝑡=12𝑚𝑣2𝛾 (𝑉𝑜𝑙)=𝑣22𝑔

units (metres or ft)in a flow of real fluid the velocities of different particles will usually not be the same, soit is necessary to integrate all portions of the stream to obtain true value of kineticenergy. It is convenient to express the true value in terms of mean velocity v and afactor α. Hence,𝑡𝑟𝑢𝑒 𝐾. 𝐸𝑤𝑒𝑖𝑔ℎ𝑡= 𝛼𝑣22𝑔

First law of thermodynamics: Energy can neither be created nor destroyed.

POTENTIAL ENERGY

The potential energy of a fluid particle depends on its elevation above any arbitrary datum plane. We are usually interested only in differences of elevation, and therefore the location of the datum plane is determined solely by considerations of convenience.

A fluid particle of weight W situated a distance z above datum possesses a potential energy of Wz. Thus its potential energy per unit weight is z.

Potential head = 𝑃.𝐸 𝑊𝑒𝑖𝑔ℎ𝑡 =  𝑚𝑔𝑧 𝑚𝑔 = z

PRESSURE ENERGY

It is energy possessed by a liquid particle due to

its pressure. If a liquid particle is under pressure

P, then pressure energy head is P/γ

Pressure head = 𝑃

𝛾

z + P/γ is static head or piezometric head

v