Compressed Air Aftercooler Condensation Load & Outlet Humidity Calculator
Calculate condensate mass flow and outlet relative humidity using inlet humidity, discharge pressure, aftercooler temperature, and air mass flow.
Enter the known values and review the calculated result
Input parameters
Use consistent values and select the intended engineering units.
Inlet conditions
Compression & aftercooler
Flow
Results
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Method, application and limitations
Review the calculation method, intended application and engineering assumptions before using the result in a design decision.
Formula and calculation method
Condensate mass flow formula:
psat(T) = 610.78 · exp((17.27 · (T − 273.15)) / ((T − 273.15) + 237.3))
win = 0.622 · (RHin · psat(Tin)) / (pin − RHin · psat(Tin))
wsat,out = 0.622 · psat(Tcool) / (pout − psat(Tcool))
Δw = win − wsat,out
ṁcond = ṁair · max(0, Δw)
Relative humidity after cooling formula:
RHout = 1, when Δw > 0
RHout = win / wsat,out, when Δw ≤ 0
where:
- ṁcond — condensate mass flow (kg/s)
- RHout — relative humidity after cooling (-)
- psat(T) — saturation vapour pressure at temperature T (Pa)
- win — inlet humidity ratio (kg/kg)
- wsat,out — saturated humidity ratio at aftercooler outlet (kg/kg)
- Δw — humidity ratio difference across the aftercooler (kg/kg)
- RHin — inlet relative humidity (-)
- pin — inlet pressure (Pa)
- pout — discharge pressure (Pa)
- Tin — inlet temperature (K)
- Tcool — aftercooler outlet temperature (K)
- ṁair — air mass flow (kg/s)
When to use this calculator
When to use this calculator:
- Estimate condensate mass flow after cooling compressed air from a defined inlet temperature to a defined aftercooler outlet temperature.
- Check whether the aftercooler outlet air reaches saturation after compression and cooling.
- Evaluate condensate load for a compressed-air line using air mass flow and humidity ratio reduction.
- Compare inlet humidity and outlet saturated humidity ratio to determine whether liquid water is formed.
- Calculate outlet relative humidity after aftercooling when no condensate is removed.
How to interpret the result
Condensate mass flow is defined as the amount of liquid water removed per unit time when the inlet humidity ratio exceeds the saturated humidity ratio at the aftercooler outlet.
Outlet relative humidity is defined as saturated air after cooling when condensation occurs, and as the ratio between inlet humidity ratio and outlet saturated humidity ratio when condensation does not occur.
Condensate mass flow depends on air mass flow and humidity ratio reduction. Increasing air mass flow increases condensate mass flow when the humidity ratio reduction is positive. Lowering aftercooler outlet temperature decreases the saturated outlet humidity ratio and can increase condensate mass flow.
- Safe — returned when the aftercooler outlet temperature is not below the calculated pressure dew point and condensate mass flow is zero.
- Warning — returned when condensate mass flow is greater than 0.
- Invalid — returned when the input state violates the validation rules, including zero or negative air mass flow, zero or negative pressure, relative humidity outside 0 to 1, discharge pressure lower than inlet pressure, ineffective cooling, inlet oversaturation, saturation exceeded during compression, or invalid outlet saturation.
The result is used to evaluate whether the aftercooler creates liquid condensate and whether the outlet air leaves the cooler saturated.
Calculation example
Example:
A user checks condensate formation after cooling compressed air from a hot inlet state to a lower aftercooler outlet temperature.
- pin — Inlet pressure: 101325 Pa
- Tin — Inlet temperature: 353.15 K
- RHin — Relative humidity: 0.50
- pout — Discharge pressure: 800000 Pa
- Tcool — Aftercooler outlet temperature: 303.15 K
- ṁair — Air mass flow: 0.10 kg/s
Result: ṁcond = 0.0187 kg/s and RHout = 1.00.
Assumptions and limitations
- Saturation vapour pressure is calculated from temperature using the exponential equation implemented in the calculator.
- Humidity ratio is calculated from vapour pressure, total pressure, and the constant 0.622.
- Condensate is formed only when inlet humidity ratio is greater than the saturated humidity ratio at the aftercooler outlet.
- Outlet relative humidity is set to 1 when condensation occurs.
- Aftercooler outlet temperature must be lower than inlet temperature.
- Discharge pressure must be greater than or equal to inlet pressure.