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Swamp Cooler

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Swamp Cooler

Introduction
 

A swamp cooler reduces the temperature of air through evaporative cooling.

 

Hot dry air at 40°C and 10% relative humidity passes through a swamp cooler. Water is added as the air passes through a series of wicks and the mixture exits at 27 °C.  This application calculates

 

• 

the relative humidity of the air exiting the cooler,
• 

the mass of water added,
• 

and the lowest achievable temperature at the outlet,

 

and plots the process on a psychrometric chart.

Calculations
 
> 

restart; with(ThermophysicalData); with(plots)
> 

T1 := 40+273.15:
> 

W1 := Property(W, HumidAir, Tdb = T1, pressure = 101325, R = .1)

0.458815922768428600e-2

The lowest possible temperature and humidty ratio is the wet-bulb temperature at the inlet conditions.

 

> 

T_lowest := ThermophysicalData:-Property(Twb, HumidAir, Tdb = T1, pressure = 101325, R = .1);

291.697570144506244

> 

W_lowest := ThermophysicalData:-Property(W, HumidAir, Tdb = T_lowest, pressure = 101325, R = 1);

0.134556886875402664e-1

The outlet relative humidity and humidity ratio are

> 

R2 := ThermophysicalData:-Property(R, HumidAir, Tdb = T2, pressure = 101325, Twb = T_lowest);

.444247577124856352

> 

W2 := ThermophysicalData:-Property(W, HumidAir, Tdb = T2, pressure = 101325, Twb = T_lowest);

0.992726950779089859e-2

 

Hence the mass of water added per mass of dry air is

> 

W2-W1

0.5339110280e-2

> 

mixingPlotPoints := plots:-pointplot([[T1, W1], [T2, W2], [T_lowest, W_lowest]], connect = false, symbol = solidcircle, symbolsize = 15, color = RGB(150*(1/225), 40*(1/255), 27*(1/255))):
> 

display(PsychrometricChart(), mixingPlotPoints, mixingPlotLines)

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