Abstract
Psychrometry is concerned with the behaviour of humid air and the prediction of its properties. More strictly it covers the behaviour of any vapour (not just water vapour) when mixed with a gas (not just air). However, because the air/water system is of huge importance, not least to food processing, and is the most commonly encountered gas/vapour mixture, the terminology employed often appears to be specific to air and water. Prediction of the properties of moist air, for example, humidity, maximum possible humidity, temperature, density and so on, is especially important in drying operations. The psychrometric chart is a simple graphical method of presenting this information, and the principles behind the chart are explained in this chapter. The outcome of a drying process can often be followed more easily by monitoring the condition of the air with the aid of a psychrometric chart than by directly measuring the moisture content of the substance being dried. Of equal interest is the establishment of the correct atmospheric conditions for food storage.
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Abbreviations
- a :
-
Length
- b :
-
Length
- c p :
-
Heat capacity at constant pressure
- h :
-
Film heat transfer coefficient
- h fg :
-
Latent heat of vaporisation of water
- H :
-
Humidity
- H o :
-
Saturated humidity
- H s :
-
Saturated humidity at adiabatic saturation temperature
- H w :
-
Saturated humidity at wet bulb temperature
- k g :
-
Film mass transfer coefficient
- m :
-
Mass flow rate of dry air
- M A :
-
Mean molecular weight of air
- M w :
-
Molecular weight of water
- N :
-
Mass flux of water vapour
- p g :
-
Mean partial pressure of the humid gas
- p w :
-
Partial pressure of water vapour
- p wo :
-
Partial pressure of water vapour at saturation
- P :
-
Total pressure
- q :
-
Heat flux
- R :
-
Universal gas constant
- T :
-
Dry bulb temperature
- T s :
-
Temperature; adiabatic saturation temperature
- T w :
-
Wet bulb temperature
- ρ g :
-
Mean density of humid gas
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Smith, P. (2011). Psychrometry. In: Introduction to Food Process Engineering. Food Science Text Series. Springer, Boston, MA. https://doi.org/10.1007/978-1-4419-7662-8_9
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DOI: https://doi.org/10.1007/978-1-4419-7662-8_9
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Publisher Name: Springer, Boston, MA
Print ISBN: 978-1-4419-7661-1
Online ISBN: 978-1-4419-7662-8
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