Energy Equation

The energy equation of a continuing system can be presented by means of the first law of thermodynamics and the energy balance of a flow system as

V_m 2 V y

Dh + g dz + d

= o “

T ds + ^ + g dz + d^ = 0 . (4.32)

Dh = T ds + v dp = T ds + ^ ^

P

As the potential energy term has an essential meaning in hydrome­chanics, the static head is selected as a comparison quantity. When the energy equation (4.32) is divided by g and integrated, it gives the Ber­noulli flow tube equation

+ ?! + ^ = & + 2, + Јe2 + f2 Ids = , (4.33)

Pg 2g pg ~ 2g J-Lg 1

Where

H1 = hydraulic head

2

It2 = velocity head 2 g 7

Z = elevation head = pressure head

Pg

R2 Y

Ht— —ds = resistance head

F Jig

All flow losses are included in the term hf, w’hich in a flow system consists of two parts:

1. Friction resistance

2. Local resistance

Posted in INDUSTRIAL VENTILATION DESIGN GUIDEBOOK