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Pipe Condensation Calculator

Calculate moisture condensation when warm humid air flows through cold pipes. For WWTP aeration blowers, compressed air distribution, and outdoor ductwork.

Air Conditions

Ambient intake sets the moisture content. The blower heats the air but doesn't change its moisture.

%
m

P_atm = 101.3 kPa

Typically ambient + 25-35°C (from manufacturer data)

Pipe inlet RH22.6 %
Dew point at line pressure22.8 °C
Pipe & Environment

OD 168.3 mm, ID 161.5 mm

Results
Air outlet temperature5.0 °C
Dew point (at line pressure)22.8 °C
Pipe inlet RH22.6 %
Condensation occurs — air cools below dew point
Condensate rate2.1 L/hr
Condensate rate50 L/day
Total heat loss3.25 kW
Air velocity2.0 m/s
Reynolds number30634
Flow regimeTurbulent
Inner h12.6 W/m²·K
Overall U7.54 W/m²·K
Inlet humidity11.7 g/kg
Outlet humidity3.6 g/kg

How This Calculator Works

When warm, humid air from a blower or compressor enters a pipe exposed to cold ambient conditions, the air loses heat through the pipe wall. If the air cools below its dew point, water vapor condenses on the inner pipe surface. This calculator couples two analyses to predict the condensation rate:

  • Heat transfer — uses the NTU (Number of Transfer Units) method to calculate the air outlet temperature. Internal forced convection uses the Dittus-Boelter correlation for turbulent flow (Re > 4000) or Nu = 3.66 for laminar flow. External convection accounts for wind speed. Insulation resistance is included when selected.
  • Psychrometrics — the Buck equation calculates the saturation vapor pressure of water at each temperature. The humidity ratio (g of water per kg of dry air) at inlet and outlet determines how much moisture condenses.

WWTP Aeration Blowers

Wastewater treatment plants use aeration blowers to supply air to diffusers in biological treatment basins. The blowers are typically housed indoors, but the air delivery pipes often run outdoors to reach the basins. In cold climates, the warm humid blower discharge air can cool dramatically in the outdoor pipe run, causing significant condensation. This water can accumulate in low points, block diffusers, and accelerate pipe corrosion. Common mitigation strategies include insulating outdoor pipe runs, installing condensate drains at low points, and sloping pipes to drain toward collection points.

When to Insulate

Even a modest thickness of insulation (25-50 mm) dramatically reduces heat loss and can keep the air above its dew point, preventing condensation entirely. Use this calculator to compare bare vs insulated scenarios and determine the minimum insulation thickness needed to avoid condensation. For detailed insulation heat loss analysis, see our Insulation Thickness Calculator. For steam system condensate loads, see the Condensate Load Calculator. For industrial compressed air moisture removal (aftercoolers and dryers), use the Compressed Air Moisture Calculator.

Air flow rates are specified in Normal cubic metres per hour (Nm³/h) at 0°C and 101.325 kPa. Steam and water properties in other SimuPipe tools use the IAPWS-IF97 formulation — see our Steam Tables Calculator. For full pipe network simulation, try SimuPipe.

Frequently Asked Questions

Why does condensation form inside compressed air pipes?
When warm, humid air from a compressor or blower flows through pipes that are cooler than the air's dew point, the pipe wall cools the air below its saturation temperature. The excess moisture condenses on the inner pipe surface. This is particularly common in aeration systems at wastewater treatment plants, where blowers discharge warm saturated air into long outdoor pipe runs.
How does pipe insulation prevent condensation?
Insulation reduces heat loss from the air to the surroundings, keeping the air temperature above its dew point for longer. With sufficient insulation, the air may reach the end of the pipe run without cooling below the dew point, eliminating condensation entirely. The calculator's insulation option lets you compare bare vs insulated pipe performance and find the minimum insulation thickness needed.
What is the NTU method used in this calculator?
NTU (Number of Transfer Units) is a heat exchanger analysis method that predicts the outlet temperature of a fluid flowing through a pipe losing heat to the environment. It accounts for the pipe's internal convection (Dittus-Boelter or laminar correlation), pipe wall conduction, insulation thermal resistance, and external wind convection. The effectiveness-NTU approach gives the air temperature at the pipe outlet without iterating.
How does altitude affect condensation calculations?
Higher altitude means lower atmospheric pressure, which slightly changes the saturation properties of moist air. At 1000 m elevation, atmospheric pressure is about 89.9 kPa instead of 101.3 kPa at sea level. This calculator adjusts atmospheric pressure using the standard atmosphere model, which affects humidity ratio calculations and dew point temperatures.
What is the difference between pressure dew point and atmospheric dew point?
Pressure dew point is the temperature at which air becomes saturated at the system operating pressure. Atmospheric dew point is the dew point if the air were at ambient pressure. Compressed air has a much higher pressure dew point because the same mass of water vapor is in a smaller volume. For aeration blowers operating at low gauge pressures (0.3-1 bar), the difference is moderate but still significant for condensation prediction.

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