Langelier Index Calculation

As an example, suppose the drinking water supplied to animals has the following analysis. The LSI index is calculated at two temperatures: 25^oC (room temperature) and 82^oC (cage wash cycle). The colder incoming water will warm to room temperature in the manifolds. Residual water in the rack manifold can be heated to 82^oC when the rack is in the cage washer.

• Water Analysis:

  • pH = 7.5

  • TDS = 320 mg/L

  • Calcium = 150 mg/L (or ppm) as CaCO₃

  • Alkalinity = 34 mg/L (or ppm) as CaCO₃

• LSI Formula:

  • LSI = pH - pH_s

  • pH_s = (9.3 + A + B) - (C + D) where:

    • A = (Log10[TDS] - 1)/10 = 0.15

    • B = -13.12 x Log10(^oC + 273) + 34.55 = 2.09 at 25°C and 1.09 at 82°C

    • C = Log10[Ca²⁺ as CaCO₃] - 0.4 = 1.78

    • D = Log10[alkalinity as CaCO₃] = 1.53

• Calculation at 25^oC:

  • pH_s = (9.3 + 0.15 + 2.09) - (1.78 + 1.53) = 8.2

  • LSI = 7.5 - 8.2 = - 0.7

  • Hence No Tendency to Scale

• Calculation at 82^oC:

  • pH_s = (9.3 + 0.15 + 1.09) - (1.78 + 1.53) = 7.2

  • LSI = 7.5 - 7.2 = + 0.3

  • Hence Slight Tendency to Scale

Consult the Water Glossary, Water Cooling Towers

See also: Calcium carbonate, Carbon dioxide, Chlorination, Dissolved oxygen, Langelier calculation, Langelier index, Larson-Skold index, Oddo-Tomson index, pH, Puckorius index, Ryznar index, Scaling Indices, Stiff-Davis index, Total dissolved solids, Water corrosivity