Method
Dry-air mass, water-vapour and enthalpy conservation for steady adiabatic mixing.
Equations
ṁ3 = ṁ1 + ṁ2
W3 = ṁ1 · W1 + ṁ2 · W2ṁ3
h3 = ṁ1 · h1 + ṁ2 · h2ṁ3
Symbols and units
| Symbol | Quantity | Unit |
|---|---|---|
| Inputs | ||
| ṁ1 | Stream 1 dry-air mass flow | kg/s |
| W1 | Stream 1 humidity ratio | kg/kg dry air |
| h1 | Stream 1 enthalpy | kJ/kg dry air |
| ṁ2 | Stream 2 dry-air mass flow | kg/s |
| W2 | Stream 2 humidity ratio | kg/kg dry air |
| h2 | Stream 2 enthalpy | kJ/kg dry air |
| Results | ||
| ṁ3 | Mixed dry-air mass flow | kg/s |
| W3 | Mixed humidity ratio | kg/kg dry air |
| h3 | Mixed enthalpy | kJ/kg dry air |
Assumptions and limits
- Steady state.
- Adiabatic mixing.
- No condensation.
- Common enthalpy reference basis.
- Dry-air mass basis.
In practice
- Take W and h of each stream from the psychrometrics note; the flows are dry-air mass flows, not volume flows.
Worked example
The input values are the calculator's own verification test, run through the calculator. They show the working; they are not design values.
Inputs
| ṁ1 | Stream 1 dry-air mass flow | 1 kg/s |
| W1 | Stream 1 humidity ratio | 0.008 kg/kg dry air |
| h1 | Stream 1 enthalpy | 40 kJ/kg dry air |
| ṁ2 | Stream 2 dry-air mass flow | 3 kg/s |
| W2 | Stream 2 humidity ratio | 0.012 kg/kg dry air |
| h2 | Stream 2 enthalpy | 60 kJ/kg dry air |
Results
| ṁ3 | Mixed dry-air mass flow | 4 kg/s |
| W3 | Mixed humidity ratio | 0.011 kg/kg dry air |
| h3 | Mixed enthalpy | 55 kJ/kg dry air |
A preliminary check for engineer review, not an engineering approval. The project calculation to the applicable codes, authority requirements and specification governs.