# Cooling tower material balances (Chemical Engineering)

Here are the governing relationships for the makeup flow rate, the evaporation and windage losses, the draw-off rate, and the concentration cycles in an evaporative cooling tower system:

M = Make-up water in m³/hr
C = Circulating water in m³/hr
D = Draw-off water in m³/hr
E = Evaporated water in m³/hr
W = Windage loss of water in m³/hr
X = Concentration in ppmw (of any completely soluble salts … usually chlorides)
Xm = Concentration of chlorides in make-up water (M), in ppmw
Xc = Concentration of chlorides in circulating water (C), in ppmw
Cycles = Cycles of concentration = Xc / Xm
ppmw = parts per million by weight

A water balance around the entire system is:

M = E + D + W

Since the evaporated water (E) has no salts, a chloride balance around the system is:

M (Xm) = D (Xc) + W (Xc) = Xc (D + W)

and, therefore:

Xc / Xm = Cycles = M / (D + W) = M / (M – E) = 1 + {E / (D + W)}

From a simplified heat balance around the cooling tower:

(E) = (C) (∆T) (cp)/ Hv

where:
Hv = latent heat of vaporization of water = ca. 2260 kJ / kg
∆T = water temperature difference from tower top to tower bottom, in °C
cp = specific heat of water = ca. 4.184 kJ / kg / °C

Windage losses (W), in the absence of manufacturer's data, may be assumed to be:

W = 0.3 to 1.0 percent of C for a natural draft cooling tower
W = 0.1 to 0.3 percent of C for an induced draft cooling tower
W = about 0.01 percent of C if the cooling tower has windage drift eliminators
Concentration cycles in petroleum refinery cooling towers usually range from 3 to 7. In some large power plants, the cooling tower concentration cycles may be much higher.

(Note: Draw-off and blowdown are synonymous. Windage and drift are also synonymous.)

## Replies

You are reading an archived discussion.

## Choked flow of gases (Chemical engineering)

The velocity of a gas flowing through an orifice or an equipment leak attains a maximum or sonic velocity and becomes "choked" when the ratio of the absolute upstream pressure...

## Conversion of air pollutant concentrations (Chemical engineering)

Various governmental agencies involved with environmental protection and with occupational safety and health have issued regulations limiting the allowable concentrations of gaseous pollutants in the ambient air or in emissions...

## Natural gas processing (Chemical Engineering)

The diagram below depicts the typical processing of raw natural gas required to produced sales pipeline gas and to remove and recover the natural gas liquids (NGL) such as: ethane...

## hello

hi i m gunjan new to crazy group help me plz send me any new seminar topic of computer science:smile:

## The Joule-Thomson coefficient (Chemical engineering)

When a real gas, as differentiated from an ideal gas, expands at constant enthalpy (i.e., no heat is transfered to or from the gas, and no external work is extracted),...