1. Equilibrium Moisture Content (EMC) in Drying
Muanmai Apintanapong

2. At equilibrium : determine
sample
Constant T, RH
Heated air
Moisted air
At equilibrium : determine
Moisture content
Temperature RH
EMC :
Loss of water = desorption
Gain of water = adsorption

3. Ideally Desorption and Adsorption
EMC
Time
Adsorption
Desorption

4. Practically Desorption and Adsorption
EMC
Time
Adsorption
Desorption

6. Relationship between EMC and RH
EMC Isotherms
EMC RH
Adsorption
Desorption

8. Relationship between EMC, T and RH
Low Temp  High Temp

10. Types of Equations (Models) used to represent EMC Data or Isotherm
3 variables : RH, MC and T
MC = f (RH, T)
EMC = f (ERH, T) at equilibrium
RH = f (MC, T)

11. Henderson’s equation 1 – RH = exp(-c.T.Mn)
Use in grain and food materials
1 – RH = exp(-c.T.Mn)
Where c, n = constant
RH = relative humidity in decimal
M = moisture content in %db
T = temperature in Rankin

12. Modified Henderson’s equation
For desorption isotherms (drying)
1 – RH = exp[-K.(T+C)(100.M)N]
Where c, n = constant
RH = relative humidity in decimal
M = moisture content in %db
T = temperature in Rankin

13. Modified Henderson’s equation
Type K N c
Peanuts
(kernel)
X 10-5
1.4984
50.561
Soybean
X 10-5
1.2164
Rough rice
(paddy)
X 10-5
2.4451
51.161

14. RH = exp[-A/(T+c) exp(-B.M)]
Chung’s equation
For desorption isotherms (drying)
RH = exp[-A/(T+c) exp(-B.M)]

15. Chung’s equation Type K N c Peanuts (kernel) 254.9 29.24 33.892
Soybean
328.3
13.917
Rough rice
(paddy)
594.61
21.732
35.703

16. Example of EMC Model