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Mixing Humid Air

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Mixing Humid Air

Introduction

Two parcels of humid air at known conditions are mixed. This application will calculate the temperature of the resulting mixture, and plot the thermodynamic process on a psychrometric chart.


> 

restart; with(ThermophysicalData); with(plots); with(Units[Standard])

Parameters

Mass of first parcel of humid air

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m__1 := 1000*Unit('kg')

Temperature of of first parcel of humid air

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T__1 := 303.15*Unit('K')

Relative humidity of first parcel of humid air

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R__1 := .6

Mass of second parcel of humid air

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m__2 := 1500*Unit('kg')

Temperature of of first second of humid air

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T__2 := 283.15*Unit('K')

Relative Humidity of second parcel of humid air

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R__2 := 1

Pressure of both air parcels

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pressure := 10^5*Unit('Pa')

Calculations

Specific enthalpy of first and second air parcels

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h__1 := Property(H, HumidAir, T = T__1, P = pressure, R = R__1)

71926.78769*Units:-Unit(('J')/('kg'))

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h__2 := Property(H, HumidAir, T = T__2, P = pressure, R = R__2)

29616.01063*Units:-Unit(('J')/('kg'))

Humidity Ratio of first and second air parcels

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hr__1 := Property(humidityratio, HumidAir, T = T__1, P = pressure, R = R__1)

0.1633493511e-1

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hr__2 := Property(humidityratio, HumidAir, T = T__2, P = pressure, R = R__2)

0.7765108778e-2

Mixture enthalpy from an adiabatic heat balance

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h__mix := (h__1*m__1+h__2*m__2)/(m__1+m__2)

46.54032144*Units:-Unit(kJ/kg)

Mixture relative humidity from a mass balance

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R__mix := (R__1*m__1+R__2*m__2)/(m__1+m__2)

.8400000000

Mixture humidity ratio

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hr__mix := Property(humidityratio, HumidAir, H = h__mix, P = pressure, R = R__mix)

0.1115076321e-1

Mixture temperature

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T__mix := Property(T, HumidAir, H = h__mix, P = pressure, R = R__mix)

291.3305675*Units:-Unit('K')

 

Plotting the Thermodynamic Process

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pts := `~`[`~`[convert]]([[T__1, hr__1], [T__mix, hr__mix], [T__2, hr__2]], unit_free)

[[303.15, 0.1633493511e-1], [291.3305675, 0.1115076321e-1], [283.15, 0.7765108778e-2]]

> 

mixPoints := pointplot(pts, connect = false, symbol = solidcircle, symbolsize = 15, color = RGB(150*(1/225), 40*(1/255), 27*(1/255))); mixLines := pointplot(pts, connect = true, thickness = 5)
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display(PsychrometricChart(), mixLines, mixPoints)

NULL