mech3020-s11-hw11 - MECH 3020 Thermodynamics II Homework...

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Unformatted text preview: MECH 3020 Thermodynamics II: Homework set #11, Due 03/11 Background notes: The first law for an air conditioning application (heating or cooling), with a single air flow in and out, is ˙ Q = ˙ m a ( h 2- h 1- ( ω 2- ω 1 ) h l ) (1) where ˙ m a is the mass flow rate of dry air, h 1 , h 2 are the enthalpies of the air/vapor inlet and exit streams, per unit mass dry air, and h l is the enthalpy of the liquid condensate. The last term appears appears only when the steam is cooled below the dew point temperature. The air/vapor enthalpies can be read from the psychro- metric chart. Alternatively, one can use data from the water tables, h 2- h 1 = c P,a ( T 2- T 1 ) + ω 2 h g ( T 2 )- ω 2 h g ( T 1 ) in which h g ( T ) is the enthalpy of the saturated water vapor at temperature T . The enthalpy h l can be obtained from the water saturation tables via h l ≈ h f ( T 2 ). I would recommend that you use the values from the chart – it is much easier....
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