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Psychrometry

  • P.G. Smith
Chapter
Part of the Food Science Text Series book series (FSTS)

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.

Keywords

Water Vapour Absolute Humidity Percentage Saturation Saturated Humidity Percentage Relative Humidity 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Nomenclature

Nomenclature

a

Length

b

Length

cp

Heat capacity at constant pressure

h

Film heat transfer coefficient

hfg

Latent heat of vaporisation of water

H

Humidity

Ho

Saturated humidity

Hs

Saturated humidity at adiabatic saturation temperature

Hw

Saturated humidity at wet bulb temperature

kg

Film mass transfer coefficient

m

Mass flow rate of dry air

MA

Mean molecular weight of air

Mw

Molecular weight of water

N

Mass flux of water vapour

pg

Mean partial pressure of the humid gas

pw

Partial pressure of water vapour

pwo

Partial pressure of water vapour at saturation

P

Total pressure

q

Heat flux

R

Universal gas constant

T

Dry bulb temperature

Ts

Temperature; adiabatic saturation temperature

Tw

Wet bulb temperature

Greek Symbols

ρg

Mean density of humid gas

Copyright information

© Springer Science+Business Media, LLC 2011

Authors and Affiliations

  • P.G. Smith
    • 1
  1. 1.School of Natural and Applied SciencesUniversity of LincolnLincolnUK

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