
61
Magtrol WB/PB Dynamometers
Chapter 3 – Cooling
3.4
COOLING WATER ISSUES
Despite the fact that water is necessary for cooling, it represents a risk. Rust, corrosion, erosion and
scale deposits have a negative effect on the functioning of the dynamometer.
3.4.1
i
mPuritieS
As a matter of fact, running water may contain dust; mud; calcium or magnesium carbonates; calcium
or magnesium sulfates; silicates; iron; carbons; sulfides or algae; and other fungi.
If the cooling water is not analyzed and treated, scale may become deposited on the inside surface of
the tubing, reducing the heat transfer and the water flow rate. A 0.5 mm thick scale deposit reduces
the cooling system tubing diameter by 30%. A 1 mm thick scale deposit reduces the heat transfer
by about 10% which, in turn, increases the dynamometer temperature.
The higher water temperature increases the speed of scale depositing. Also, the warmer the water,
the faster the corrosion and erosion. A water temperature increase of 10 °C (50 °F) multiplies the
corrosion effect by a factor of two or even four.
3.4.2
h
ArdneSS
The following table indicates the water hardness in German degrees [°dH]. The total hardness is
defined as the sum of the temporary and the permanent hardness. The temporary hardness can
be removed by boiling the water, which only takes the calcium and magnesium carbonates and
bicarbonates into account. The permanent hardness is caused by the presence of calcium and
magnesium sulfates in the water and cannot be removed by boiling. Soft water has a hardness
between 3 and 6 °dH, whereas hard water may have a hardness of more than 16 °dH.
Open-circuit
Cooling
Closed-circuit
Cooling
pH value
6 – 8
6 – 8
Total hardness
< 20 °dH
< 15 °dH
Temporary hardness
< 10 °dH
< 6 °dH
Permanent hardness
< 10 °dH
< 9 °dH
Free carbon dioxide (CO
2
)
< 10 mg/l
< 3 mg/l
Organic substances
< 10 mg/l
< 10 mg/l
Algae and fungal attacks
not acceptable
Sand and mud
0 mg/l
0 mg/l
Sulfates (SO
4
2
-)
< 50 mg/l
< 50 mg/l
Chlorides (Cl-)
< 30 mg/l
< 30 mg/l
Solute iron (Fe
2
+ and Fe
3
+)
< 1 mg/l
< 1 mg/l
Phosphates (PO
4
3
-)
0 mg/l
0 mg/l
Total salt content (NaCl)
< 3000 mg/l
< 3000 mg/l
Manganese (Mn)
< 0,1 mg/l
< 0,1 mg/l