Equilibrium Moisture Content (EMC) in Drying Muanmai Apintanapong

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

Ideally Desorption and Adsorption EMC Time Adsorption Desorption

Practically Desorption and Adsorption EMC Time Adsorption Desorption

Relationship between EMC and RH EMC Isotherms EMC RH Adsorption Desorption

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

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)

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

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

Modified Henderson’s equation Type K N c Peanuts (kernel) 65.0413 X 10-5 1.4984 50.561 Soybean 30.5327 X 10-5 1.2164 134.316 Rough rice (paddy) 1.9187 X 10-5 2.4451 51.161

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

Chung’s equation Type K N c Peanuts (kernel) 254.9 29.24 33.892 Soybean 328.3 13.917 100.288 Rough rice (paddy) 594.61 21.732 35.703

Example of EMC Model