Humid-Air Mixing: Blend Streams on a Dry-Air Mass Basis

Define the Phase or Process Boundary

ASHRAE's adiabatic air-mixing discussion bases the mixing relation on dry-air masses. For a steady boundary without condensation, heat transfer or other streams, dry-air mass, water-vapor mass and moist-air enthalpy balances describe the mixed state.

Review a Hypothetical Comparison

Suppose fictional Stream A carries 2 kg/s dry air with W_A=0.006 and h_A=40 kJ/kg dry air. Stream B carries 1 kg/s dry air with W_B=0.018 and h_B=80. Mixed dry-air flow is 3 kg/s. The water balance gives W_m=(2×0.006+1×0.018)/3=0.010. The energy balance gives h_m=(2×40+1×80)/3≈53.33 kJ/kg dry air. Averaging the two humidity ratios equally would give 0.012 and ignore the unequal dry-air flows.

Keep the Evidence with the Decision

Convert any volume-flow measurements to the applicable dry-air mass basis before assigning weights. Keep property reference states consistent. Check whether the proposed mixed state remains single-phase; if liquid forms, include its water and enthalpy inventory rather than forcing a gas-only formula to represent fog.

The inlet properties are assigned for bookkeeping. No final temperature or real mixing-box performance is predicted, and this is not a liquid-solvent volume-additivity rule.

What mixture humidity and enthalpy follow from two supplied dry-air flow inventories?

This blank worksheet is for your own project. It contains no H M machine trial result.

Customer Questions

Primary References

These references support the technical principles discussed in this guide. The worked examples and review questions are educational.

• ASHRAE's adiabatic air-mixing discussion
• Reference from hmpharmamachines.com