How this calculator works
Actual volume flows are converted to dry-air mass flows using each inlet state. Water and enthalpy are then mixed on a dry-air basis, using ASHRAE ideal-mixture equations. If the unconstrained mixture would exceed saturation, the calculation solves a saturated outlet with retained liquid water and includes its sensible enthalpy. Inlet temperatures are limited to 0 to 100 C, avoiding ice formation. Pressure drop, external heat exchange and droplet volume are neglected.
Formula
w = 0.621945 pv/(p - pv); h = 1006t + w(2501000 + 1860t), t in C; mdry = Vdot/v; wmix = sum(mdry w)/sum(mdry); hmix = sum(mdry h)/sum(mdry).
Worked example
Mix equal actual volume flows of completely dry air at 280 K and 320 K under the same pressure. Their dry-air mass flows are inversely proportional to temperature, giving a mixed temperature of 298.666667 K, rather than the arithmetic average 300 K.
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Frequently asked questions
Why are volume flows not simply averaged?
Actual volume per kilogram changes with temperature and humidity, so dry-air mass is the conserved weighting basis.
What if water condenses?
The outlet is solved at saturation and the excess water is reported as a liquid condensation rate. The model retains its energy at the outlet temperature.
What does a dry-air dew point mean?
With exactly zero water vapour there is no finite dew point; the table reports that explicitly.