CHAPTER
7
DRYING
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Introduction
Basic
Drying Theory
Three
States of Water
phase
diagram for water
vapour
pressure/temperature curve for water
Heat
Requirements for Vaporization latent
heat of vaporization latent
heat of sublimation
Heat
Transfer in Drying
Dryer
Efficiencies
Mass
Transfer in Dryingmass
transfer coefficient
Psychrometryabsolute
humidityrelative
humidity
dew
pointhumid
heat
Wet-bulb
Temperaturesdry
bulb temperatureLewis
number
Psychrometric
Charts
Measurement
of Humidityhygrometers
Equilibrium
Moisture Content
Air
Dryingdrying
rate curves
Calculation
of Constant Drying Rates
Falling
rate Drying
Calculation
of Drying Times
Conduction
Drying
Drying
Equipment
Tray
Dryers
Tunnel
Dryers
Roller
or Drum Dryers
Fluidized
Bed Dryers
Spray
Dryers
Pneumatic
Dryers
Rotary
Dryers
Trough
Dryers
Bin
Dryers
Belt
Dryers
Vacuum
Dryers
Freeze
Dryers
Moisture
Loss in Freezers and Chillers
Summary
Problems
Examples in this Chapter:
7.1.
Heat energy in air drying
7.2.
Heat energy in vacuum drying
7.3.
Heat energy in freeze drying
7.4.
Efficiency of a potato dryer
7.5.
Partial pressure of water vapour
7.6.
Relative humidity
7.7.
Relative humidity, enthalpy and specific volume of air
7.8.
Relative humidity of heated air
7.9.
Water removed in air drying
7.10.
Humidity of air leaving a dryer
7.11.
Reheating of air in a dryer
7.12.
Air conditioning
7.13.
Rate of evaporation on drying
7.14.
Heat transfer in air drying
7.15.
Temperature and RH in air drying of carrots
7.16.
Lewis relationship in air drying
7.17.
Time for air drying at constant rate
7.18.
Time for drying during falling rate
7.19.
Moisture content of breakfast food after drum drying
Figures in this Chapter:
7.1
Phase diagram for water
7.2.
Vapour pressure/temperature curve for water
7.3
Psychrometric chart
7.4
Equilibrium moisture contents
7.5
Drying rate curves
7.6
Drying curve for fish
7.7
Generalized drying curve
7.8
Dryers
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