cooling-tower-chem

The water-stability and corrosion math for cooling towers, as a small, dependency-free Python library.

Water-treatment engineers screen cooling-tower and process water with a handful of classical indices — Langelier, Ryznar, Puckorius, Larson-Skold — plus the evaporation / blowdown / makeup balance that sets cycles of concentration. Those formulas are scattered across textbooks and spreadsheets. cooling-tower-chem puts them in one tested, documented, importable place.

Try it in your browser: the interactive water-stability calculator computes LSI, RSI, PSI, and CCPP live — no install required, and cross-checked against this library.

# From PyPI:
pip install cooling-tower-chem

# Or install the latest development version from source:
pip install git+https://github.com/Madhvansh/cooling-tower-chem

No third-party dependencies. Pure standard-library Python, fully type-hinted, tested on CPython 3.9–3.13.

Quick start

from cooling_tower_chem import WaterSample

# One analysis in, every index out.
sample = WaterSample(
    ph=8.2,
    temperature_c=32,
    calcium_hardness=450,     # mg/L as CaCO3
    total_alkalinity=250,     # mg/L as CaCO3
    conductivity_us_cm=2400,  # TDS is derived from this if not given
    chloride=180,             # mg/L (for the Larson-Skold index)
    sulfate=120,              # mg/L
)

print(sample.lsi())   # 1.38  -> scale-forming
print(sample.rsi())   # 5.44  -> heavy scale
report = sample.report()
print(report["lsi"]["description"])
# "LSI +1.38: scale-forming; calcium carbonate will tend to precipitate."

Prefer plain functions? Every index is available directly:

from cooling_tower_chem import (
    langelier_saturation_index,
    ryznar_stability_index,
    puckorius_scaling_index,
    larson_skold_index,
)

lsi = langelier_saturation_index(
    ph=7.5, temperature_c=25, tds=400,
    calcium_hardness=240, total_alkalinity=180,
)   # -> +0.19

From the command line

Installing the package also gives you a ctchem command:

$ ctchem report --ph 8.2 --temp 32 --calcium 450 --alkalinity 250 \
      --conductivity 2400 --chloride 180 --sulfate 120
pH of saturation (pHs): 6.821
LSI: 1.379  [scale_forming]
    LSI +1.38: scale-forming; calcium carbonate will tend to precipitate.
RSI: 5.443  [severely_scale_forming]
    RSI 5.44: heavy scale formation expected.
...

$ ctchem lsi --ph 7.5 --temp 25 --tds 400 --calcium 240 --alkalinity 180
LSI = +0.189

Add --json to any command for machine-readable output.

What's included

Stability & corrosion indices

Precipitation potential (CCPP)

Beyond the direction the indices give, calcium_carbonate_precipitation_potential reports the quantity: the signed mass of CaCO₃ (mg/L as CaCO₃) that must precipitate (+) or dissolve (−) to reach calcite saturation, solved for a closed system with the Plummer & Busenberg (1982) equilibrium constants and a Davies activity model. It reproduces Wojtowicz's (2001) worked examples, and is also available on WaterSample.ccpp() and the ctchem ccpp CLI.

Cooling-tower water balance

cycles_of_concentration, evaporation_loss (energy balance), drift_loss, blowdown_loss, makeup_water, cycles_from_flows, water_saved_by_increasing_cycles, and TDS ↔ conductivity conversion.

The CoolingTower object ties the balance together and can project how makeup water concentrates in the basin:

from cooling_tower_chem import CoolingTower, WaterSample

tower = CoolingTower(circulation_rate=1000, delta_t_c=6, cycles=5)  # m3/h
print(tower.water_balance())
# {'evaporation': 10.2514, 'drift': 0.2, 'blowdown': 2.3629, 'makeup': 12.8143, 'cycles': 5}

makeup = WaterSample(ph=7.8, temperature_c=32, calcium_hardness=90,
                     total_alkalinity=60, conductivity_us_cm=400)
basin = tower.concentrated(makeup)   # conservative species x cycles
print(round(makeup.lsi(), 2), "->", round(basin.lsi(), 2))  # -0.26 -> 1.07

Interpretation

interpret_lsi, interpret_rsi, interpret_psi, interpret_larson_skold, interpret_aggressiveness each return a coarse Tendency and a one-line explanation, so you can turn a number into an actionable message.

Unit conversions

Water data arrives in mixed units. as_caco3 / caco3_to_ion (plus named calcium_as_caco3, magnesium_as_caco3, bicarbonate_as_caco3) convert between mg/L-of-ion and mg/L-as-CaCO3; grains_per_gallon_to_mg_l and celsius_to_fahrenheit (and inverses) cover the common US/metric gaps.

If your analysis is already in customary US units — temperature in °F and hardness/alkalinity in grains per gallon (as CaCO₃) — skip the manual conversions and use WaterSample.from_us_units:

from cooling_tower_chem import WaterSample

# 90 °F, 26.3 gpg calcium hardness, 14.6 gpg alkalinity (both as CaCO3).
sample = WaterSample.from_us_units(
    ph=8.2,
    temperature_f=90,
    calcium_hardness_gpg=26.3,
    total_alkalinity_gpg=14.6,
    conductivity_us_cm=2400,   # TDS/conductivity keep their usual units
)
print(round(sample.lsi(), 2))  # same result as the SI constructor

It converts °F and grains/gallon internally (via fahrenheit_to_celsius and grains_per_gallon_to_mg_l) and returns an ordinary WaterSample, so every index method behaves exactly as if you had built it in SI units.

Runnable examples

See the Examples section below, or browse examples/ directly.

Examples

Runnable, dependency-free cookbook scripts in examples/ — each prints a plain-text table (real output in the examples README):

For the theory behind the cycles sweep, see the Cycles of concentration doc — the COC mass balance and the water-savings vs. scaling-risk trade-off, worked through with the library.

Units & conventions

• Calcium hardness and total alkalinity: mg/L as CaCO₃
• TDS and ions (chloride, sulfate): mg/L
• Temperature: °C
• Flows: any consistent volumetric unit (m³/h, gpm, …) — results carry the same unit

Inputs that would break a logarithm (non-positive hardness, alkalinity, or TDS) raise a clear ValueError rather than returning a silent fallback.

Why this exists

These indices are the daily bread of industrial water treatment, but the Python ecosystem had no small, focused, well-tested home for them. cooling-tower-chem was extracted from the physics engine of TGF, a cooling-tower dosing-control project, and hardened into a standalone library so any process-engineering or water-treatment codebase can depend on it.

References

• Langelier, W. F. (1936). The Analytical Control of Anti-Corrosion Water Treatment. J. AWWA 28(10).
• Ryznar, J. W. (1944). A New Index for Determining Amount of Calcium Carbonate Scale Formed by a Water. J. AWWA 36(4).
• Puckorius, P. R. & Brooke, J. M. (1991). A New Practical Index for Calcium Carbonate Scale Prediction in Cooling Tower Systems. Corrosion 47(4).
• Larson, T. E. & Skold, R. V. (1958). Laboratory Studies Relating Mineral Quality of Water to Corrosion of Steel and Cast Iron. Corrosion 14(6).

The interpretation thresholds are the conventional screening bands from these sources; they are guides, not a substitute for site-specific engineering judgment.

Contributing

Issues and pull requests are welcome — see CONTRIBUTING.md. Good first contributions: additional well-referenced indices, further unit-conversion helpers, and more worked examples from the literature to expand the test suite.

License

MIT — see LICENSE.