Magtrol WB Series User Manual

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Magtrol WB Series User Manual Manual pdf 71 page image

61Magtrol WB/PB DynamometersChapter 3 – Cooling3.4 COOLING WATER ISSUESDespite the fact that water is necessary for cooling, it represents a risk. Rust, corrosion, erosion andscale deposits have a negative effect on the functioning of the dynamometer.3.4.1 imPuritieSAs a matter of fact, running water may contain dust; mud; calcium or magnesium carbonates; calciumor 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 ofthe tubing, reducing the heat transfer and the water flow rate. A 0.5 mm thick scale deposit reducesthe cooling system tubing diameter by 30%. A 1 mm thick scale deposit reduces the heat transferby 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 thecorrosion effect by a factor of two or even four.3.4.2 hArdneSSThe following table indicates the water hardness in German degrees [°dH]. The total hardness isdefined as the sum of the temporary and the permanent hardness. The temporary hardness canbe removed by boiling the water, which only takes the calcium and magnesium carbonates andbicarbonates into account. The permanent hardness is caused by the presence of calcium andmagnesium sulfates in the water and cannot be removed by boiling. Soft water has a hardnessbetween 3 and 6 °dH, whereas hard water may have a hardness of more than 16 °dH.Open-circuitCoolingClosed-circuitCoolingpH value 6 – 8 6 – 8Total hardness < 20 °dH < 15 °dHTemporary hardness < 10 °dH < 6 °dHPermanent hardness < 10 °dH < 9 °dHFree carbon dioxide (CO 2 ) < 10 mg/l < 3 mg/lOrganic substances < 10 mg/l < 10 mg/lAlgae and fungal attacks not acceptableSand and mud 0 mg/l 0 mg/lSulfates (SO 42 -) < 50 mg/l < 50 mg/lChlorides (Cl-) < 30 mg/l < 30 mg/lSolute iron (Fe 2 + and Fe 3 +) < 1 mg/l < 1 mg/lPhosphates (PO 43 -) 0 mg/l 0 mg/lTotal salt content (NaCl) < 3000 mg/l < 3000 mg/lManganese (Mn) < 0,1 mg/l < 0,1 mg/l