Other Humidity Process

Super-heated steam

Dry-bulb temperature Figure 8.7 Schematic illustration of humidification processes.

For humidification: /’ =———

A W

Adiabatic humidification:	Iw = if at Twb, process i = const.
Hot water:	Iw < ig at Tdb, process TDb i
Saturated steam:	Iw = ig at Tdb, process TDB = const.
Super-heated steam:	IK > ig at TDB, process TDB О

2.3.5 Adiabatic Mixing of Air

Eliminate m., We obtain

(‘, -i3) = m2(i3 ~h)

/??, (W, -W3) = m2(W3 — W2)

So

Rii i3 i2 W3 W2

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Example

Return air at 25°C, 50% relative humidity and flowing at a rate of 5 m3/s is mixed with outside air at 35°C and 60% relative humidity and flowing at a rate of 1.25 m3/s. Determine the mixed air condition and flow rate.

Given: T1J2,01,02, Qi(Vi), Q2(V2)

Find: T3,03, W-i, m3

Solution:

From the psychrometric chart (ASHRAE PSYCHROMETRIC CHART N0.1 [sea level], chart 1 />), we can determine the point 1 and 2

Return Air Outdoor Air

/’] (kJ kg) 50.8 90.5

Wi (kg water kg dry air) 0.010 0.0215

Vi (m3 kg dry air) 0.858 0.902

Then we find the mass flow rates:

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And the enthalpy, etc..

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Posted in Fundamentals of Heating. Ventilating, and Air-Conditioning