The mixed state slides along the line from A to B as the flow ratio changes — try the slider above.
05Conservation balance
06Report
DENOVAPractical Engineering Software
AIR MIXING SUMMARY
Rev P00
Prepared By
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Checked By
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Approved By
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Status
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Project Notes
NOT FOR CONSTRUCTION
⚠ FOG CASE · NOT PHYSICALLY RESOLVED
The theoretical mixed state is supersaturated (RH>100%). A physical mixed state would lie on the saturation curve with condensate present. Reported mixed properties are pre-condensation theoretical values and must not be used as final coil/process conditions.
Design Conditions
Inlet Streams
Calculation Summary
Figure 1 · Mixing Schematic
Figure 2 · Psychrometric Process
Conservation Balance
Calculation Notes
Adiabatic, steady-flow mixing of two moist-air streams: hmix = (ṁA·hA + ṁB·hB) / (ṁA + ṁB). Psychrometrics per ASHRAE 2017 (Hyland–Wexler saturation). Results are preliminary and based on entered inputs; not a substitute for professional verification, manufacturer-certified data, or authority approval.
DENOVAPractical Engineering Software
Air Mixing · v0.2 · Beta · — · NOT FOR CONSTRUCTION
Apply a preset to load both streams and a sensible flow split. All values reload in your active unit system.
How to use
Pick a mixing topology
Three scenarios — duct junction, mixing plenum, or AHU mixing box. The math is identical (adiabatic mixing); the diagram makes the equipment context legible.
Define both inlet streams
Each stream can be defined by any two of: dry-bulb, wet-bulb, dew point, relative humidity, or humidity ratio. Pressure and altitude are shared.
Set the flow split
Enter volume (L/s or CFM) or mass flow for each stream — or just drag the mass-flow fraction slider. The slider keeps total mass flow constant and redistributes between A and B.
Read the mixed state on the chart
The mint pin sits exactly on the line between the cyan A pin and the amber B pin, at the position dictated by the mass-flow ratio. Drag the slider — watch it glide.
Three topologies, one physics
Adiabatic mixing of two streams is the same set of conservation equations no matter what hardware
delivers it. The three schematics differ in equipment context — choose whichever matches what you're
actually modelling. They don't change the numbers.
Duct junctiontee / Y-merge
A branch duct joining a main duct — outdoor air bleeding into a return, an exhaust spur joining a riser,
a takeoff fitting in supply work. The streams are at full duct velocity; mixing happens in the
turbulent wake just downstream of the fitting. No active control — proportions are set by upstream pressures
and damper authority elsewhere in the system.
Mixing chamberplenum
A generic enclosed volume where two streams meet, slow down (velocity pressure → static pressure), and exit
blended. Could be a fan-coil return cabinet, a small expansion plenum, a ducted induction unit, or any
equipment item with two inlet connections. No dampers, no modulation — proportions are whatever the
upstream system happens to deliver. Use this when the mixing topology matters but the controls don't.
AHU mixing boxcontrolled
A specific air-handler component with motorized dampers on each inlet (outdoor-air damper and
return-air damper, usually interlocked so opening one closes the other). The dampers are the control
mechanism — a BMS or economizer logic modulates them to hit minimum-OA, free-cooling, freeze-protection,
or smoke-mode setpoints. The schematic shows the damper blade angles tracking the current flow share.
Use this when modelling AHU operating sequences, economizer changeover, or minimum-OA verification.
When the difference matters: If you're sizing a fitting or analysing pressure drop, use duct junction.
If you're modelling a sealed cabinet or a generic plenum, use mixing chamber. If you're checking the
operating logic of an AHU with damper-controlled OA, use AHU mixing box — the dampers (visually tracking
flow share) make the control sequence legible.
The lever rule, in one image
On a psychrometric chart, adiabatic mixing is a straight line. The mixed state lies on the
segment between A and B; its distance from A is proportional to the mass fraction of B (and vice versa).
Conservation of moisture (W) and enthalpy (h) — both linear in mass —
guarantees this. Section 05 (Conservation balance) shows the arithmetic spelled out.
Fog / supersaturation
When the mixing line crosses the saturation curve, the theoretical mixed state has RH > 100% —
physically, moisture condenses out as fog. The status chip flips to FOG · CONDENSATION,
the chart's mixing line dashes through the fog region, and the schematic flags it. The mixed-state values
shown are the theoretical (pre-condensation) state; the fog-resolved physical state is future scope (not yet implemented).
Notes
Switching input pairs preserves the current state — the new fields pre-fill with that property's
current value. Switching between SI and IP auto-converts every input, so the underlying physical
state never changes — only its units.
About
What this is
DENOVA Air Mixing computes the mixed state of two moist-air streams under steady, adiabatic
conditions — the classic HVAC mixing-box problem. Sibling tool to DENOVA Air Properties; same
Hyland–Wexler saturation curve, same ASHRAE-grade math, same brand language.
The conservation laws
Adiabatic mixing conserves three quantities. Given dry-air mass flows
ṁA, ṁB:
Dry-air massṁA + ṁB = ṁmix
The dry-air component is inert through the mixing process.
MoistureṁA·WA + ṁB·WB = ṁmix·Wmix
Mass-flow-weighted average of humidity ratios.
EnthalpyṁA·hA + ṁB·hB = ṁmix·hmix
No heat in, no heat out — so enthalpy flows add.
Together these say: Wmix and hmix are
mass-fraction-weighted averages. Dry-bulb temperature is then recovered from
T = (h − 2501·W) / (1.006 + 1.86·W), and the rest of the psychrometric properties
from (T, W). The mixed state lies on the straight line between A and B on the
(T, W) chart — the lever rule.
Hyland & Wexler (1983), Formulations for the Thermodynamic Properties of the Saturated Phases of H2O from 173.15 K to 473.15 K — saturation vapor pressure correlation, water branch and ice branch.
This release is single-page, single-pressure, two-stream, adiabatic. What's intentionally out of scope for this version:
Fog-resolved state — when supersaturation occurs, only the theoretical state is shown. The physical state (latent heat released, condensed water removed) is future scope.
N-stream mixing — the lever rule generalises to a mass-weighted centroid on (W, h). Future.
Save & share — state URLs, named scenarios. Future.
Cross-tool linking — pull a state from Air Properties, push the mixed state out. v0.3.
DENOVA · Air Mixing v0.2 · AXIOM v4.6 · sibling to Air Properties.