Calculators › Renewables and on-site generation Cooling-tower evaporation rule calculator
Cooling-tower evaporation rule
Approximation: for each 10 Δ°F cooling range, about 1% of circulation evaporates in the reference rule. Approximation: for each 5.56 Δ°C cooling range, about 1% of circulation evaporates in the reference rule.
Units IP (US) SI (metric)
V ˙ evap = V ˙ circulating × 0.01 × Δ T 10 \dot{V}_{\text{evap}} = \frac{\dot{V}_{\text{circulating}} \times 0.01 \times \Delta T}{10} V ˙ evap = 10 V ˙ circulating × 0.01 × Δ T V ˙ evap = V ˙ circulating × 0.01 × Δ T × 9 50 \dot{V}_{\text{evap}} = \frac{\dot{V}_{\text{circulating}} \times 0.01 \times \Delta T \times 9}{50} V ˙ evap = 50 V ˙ circulating × 0.01 × Δ T × 9
Calculator
Enter the values you know and leave one box empty. Calculate finds the empty one, the result or any input.
Worked example
Given
V ˙ circulating \dot{V}_{\text{circulating}} V ˙ circulating 2,400 gpm Δ T \Delta T Δ T 12 °F V ˙ evap = 2400 × 0.01 × 12 10 = 28.8 \dot{V}_{\text{evap}} = \frac{2400 \times 0.01 \times 12}{10} = 28.8 V ˙ evap = 10 2400 × 0.01 × 12 = 28.8
Given
V ˙ circulating \dot{V}_{\text{circulating}} V ˙ circulating 150 L/s Δ T \Delta T Δ T 6 K V ˙ evap = 150 × 0.01 × 6 × 9 50 = 1.62 \dot{V}_{\text{evap}} = \frac{150 \times 0.01 \times 6 \times 9}{50} = 1.62 V ˙ evap = 50 150 × 0.01 × 6 × 9 = 1.62
Symbols and units
Symbol Meaning Unit
V ˙ evap \dot{V}_{\text{evap}} V ˙ evap evaporation flow gpm V ˙ circulating \dot{V}_{\text{circulating}} V ˙ circulating circulating-water flow gpm Δ T \Delta T Δ T tower water temperature drop °F
Symbol Meaning Unit
V ˙ evap \dot{V}_{\text{evap}} V ˙ evap evaporation flow L/s V ˙ circulating \dot{V}_{\text{circulating}} V ˙ circulating circulating-water flow L/s Δ T \Delta T Δ T tower water temperature drop K
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