Why is air-stream mixing a straight line on the chart?

For adiabatic mixing at the same pressure, dry-air mass balances make both humidity ratio and enthalpy mass-weighted averages. On a W versus dry-bulb chart the mixed point therefore lies between the two streams.

Is wet-bulb temperature exact here?

No. The simulator uses a common approximation suitable for ordinary HVAC ranges. Precise psychrometrics require iterative equations and pressure corrections.

Psychrometric Chart

A psychrometric chart organizes moist-air properties used in HVAC and meteorology. This simulator uses sea-level pressure and common engineering formulas to compute saturation pressure, humidity ratio W, dew point, wet-bulb temperature, and moist-air enthalpy from dry-bulb temperature and relative humidity. A second air stream can be mixed with the first; because adiabatic mixing is approximately linear in humidity ratio and enthalpy, the mixed state lies on the straight line connecting the two stream points. The chart is a teaching approximation: pressure altitude, ice-region corrections, coil bypass behavior, fog/supersaturation, and detailed heat-and-mass-transfer equipment are omitted.

Who it's for: HVAC, thermodynamics, building science, meteorology, and heat-and-mass-transfer introductions.

Key terms

Psychrometric chart
Relative humidity
Humidity ratio
Dew point
Wet-bulb temperature
Moist-air enthalpy

This is a sea-level HVAC psychrometric model using common engineering approximations. It omits pressure altitude, ice-region corrections, coil bypass factors, and detailed evaporative-cooling hardware.

Live graphs

How it works

Interactive psychrometric chart for moist air: dry-bulb temperature, relative humidity, dew point, wet-bulb approximation, humidity ratio, enthalpy, and mixing of two air streams.

Key equations

W = 0.62198 pv / (p − pv), pv = RH · pws(Tdb)

h ≈ 1.006 Tdb + W(2501 + 1.86 Tdb); mixing is linear in h and W

Frequently asked questions

Why is air-stream mixing a straight line on the chart?: For adiabatic mixing at the same pressure, dry-air mass balances make both humidity ratio and enthalpy mass-weighted averages. On a W versus dry-bulb chart the mixed point therefore lies between the two streams.
Is wet-bulb temperature exact here?: No. The simulator uses a common approximation suitable for ordinary HVAC ranges. Precise psychrometrics require iterative equations and pressure corrections.

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