Free · Physics models
Two-Stream Sensible Temperature Mixing
Find a weighted air temperature using entered fractions or a separate equal-property volumetric-flow approximation.
- Formula & worked example
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Calculator inputs
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How to use this calculator
- Enter the known values in the units shown. Results update as you type.
- Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
- Use the worked example to check the method. Reset restores the starting fields.
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Formula and method
A 25% stream at 10°C mixed with 75% at 30°C gives 25°C; 100 and 300 L/min give the same result under the equal-property assumption.
Tmix = f T1 + (1−f)T2; flow form Tmix = (Q1T1+Q2T2)/(Q1+Q2).
Worked example
Enter these known values and leave the other values blank.
- Temp. T==1==
- 10 °C
- Temp. T==2==
- 30 °C
- Comp. P==1==
- 25 %
- Temperature of outside air (T==oa==)
- 10 °C
- Temperature of return air (T==ra==)
- 30 °C
- Flow rate of outside air cfm==oa==
- 100 L/min
- Flow rate of return air cfm==ra==
- 300 L/min
- Comp. P==2==
- 75 %
- Mixed air temperature (T)
- 25 °C
- Mixed air temperature (T==s==)
- 25 °C
Assumptions and limitations
- The fraction relation assumes equal specific heat and fractions proportional to thermal capacity flow, such as matching dry-air mass flow.
- The volumetric-flow relation additionally approximates the streams as equal density and heat capacity. Large temperature, pressure or humidity differences require mass/enthalpy mixing instead.
- Mixing is adiabatic with no condensation, phase change or external heat transfer. This page does not compute mixed humidity.
- Fractions lie between zero and 100%; temperatures must exceed absolute zero and both entered flow rates are positive.
- Enter known quantities and leave the unknown blank. Editable quantities support inverse solutions and locks; inconsistent locked quantities are reported. Unit selectors convert the quantity independently of its display.
Common questions
When is volumetric-flow weighting a good approximation?
When the two streams have sufficiently similar density and heat capacity, and mixing has no heat loss or phase change.
Does this find mixed humidity?
No. It treats sensible temperature. Moist-air mixing with condensation needs mass and enthalpy relations.
How do I use the inverse calculation?
Clear the quantity you want to find and enter the remaining known values in their selected units. The model can only solve branches with enough independent information.
References
The calculation equations, inverse formulas, units, and input rules were imported from this source. Bookify provides the interface and equation solver.