MoistAirTab™ Example 2 - Mixing Streams
Example 2
A stream of 2 m3/s of outdoor air at 4°C dry-bulb temperature and 2°C wet-bulb temperature is mixed with 6.25 m3/s of recirculated air at 25°C dry-bulb and 50% relative humidity. What is the dry-bulb, wet-bulb temperatures and relative humidity of the mixed stream?
Solution
The solution is presented below as a table generated from Excel. The gray shaded areas represent the input data.
| Soution: | Units | Steam-1 | Stream-2 | Mixture |
| Total pressure | bar | 1.01325 | 1.01325 | 1.01325 |
| Moist air volumetric flow rate | m3/s | 2.00 | 6.25 | 8.25 |
| Dry bulb temperature | °C | 4.00 | 25.00 | 19.67 |
| Wet bulb temperature | °C | 2.00 | 17.88 | 14.58 |
| Relative humidity | % | 71% | 50% | 58% |
| | | | |
| Obtain the mixed stream's humidity ratio: | | | | |
| Specific volume (dry air) | m3/kgdry air | 0.7848 | 0.8444 | 0.8293 |
| Mass flow rate (dry air) | kgdry air/s | 2.55 | 7.40 | 9.95 |
| Humidity ratio | kgw/kgdry air | 0.0036 | 0.0099 | 0.0083 |
| Moisture flowrate | kgw/s | 0.01 | 0.07 | 0.08 |
| | | | |
| Obtain the mixed stream's specific humidity: | | | | |
| Specific enthalpy of moist air | kJ/kgdry air | 12.97 | 50.42 | 40.83 |
| Enthalpy flow | kJ/s | 33.06 | 373.20 | 406.26 |