GIFSQ Tools · Module 17 — Food Processing, Thermal Engineering & Utilities · Tool 329 of 500
Split a drying run into its constant-rate and falling-rate periods and work out the time each takes, from dry solids, moisture contents and the constant drying rate.
Try sample values — fills the form with the worked example below.
–
Constant-rate time (h)
–
Falling-rate time (h)
–
Total drying time (h)
Equation: Constant-rate time = Ms × (Mi − Mc) / 100 ÷ (Rc × A); falling-rate time = (Ms / (Rc × A)) × ln((Mc − Me) / (Mf − Me)); total = the two added. Moistures are dry-basis percent.
Method: Two-period drying model of standard mass-transfer practice (Heldman and Singh; Geankoplis): constant rate to the critical moisture, then a falling rate proportional to free moisture.
Assumptions: the falling rate is proportional to free moisture (moisture above equilibrium); the constant rate and area stay fixed; dry solids mass does not change.
Limitations: real falling-rate behaviour is often not a simple exponential; the model is an estimate for sizing and planning, not a substitute for a measured drying curve.
Rounding: all times to 2 decimal places; intermediates unrounded.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Method: Two-period drying model of standard mass-transfer practice (Heldman and Singh; Geankoplis): constant rate to the critical moisture, then a falling rate proportional to free moisture.
Assumptions: the falling rate is proportional to free moisture (moisture above equilibrium); the constant rate and area stay fixed; dry solids mass does not change.
Limitations: real falling-rate behaviour is often not a simple exponential; the model is an estimate for sizing and planning, not a substitute for a measured drying curve.
Rounding: all times to 2 decimal places; intermediates unrounded.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Worked example: 50 kg dry solids, 150% to 60% critical to 12% final (dry basis), equilibrium 5%, constant rate 1 kg/m²·h over 10 m²: constant-rate time 4.50 h, falling-rate time 10.31 h, total 14.81 h.
Enter values above to see results.
Moisture here is dry-basis: kg water per 100 kg dry solids. Convert wet-basis moisture first if your data is wet-basis. Tool 329 of 500 — GIFSQ
