drying
Drying
We are primarily concerned with drying wet, porous solids
(granules).
Important to ensure proper moisture content in the granules:
low enough to prevent product degradation and ensure good powder flow, but high enough to provide good tablet properties B. Amsden
CHEE 440
Definitions psychrometry determination of the vapor concentration and carrying capacity of drying gas
wet bulb T dry bulb T relative humidity (RH)
Pwater in air
%RH =
×100
Pw,sat(T )
moisture content
B. Amsden
CHEE 440
Psychrometric
Chart
Determine the relative humidity and moisture content in the air if the wet bulb T is 35 ºC and the dry bulb T is 50 ºC.
B. Amsden
CHEE 440
Types of Dryers
B. Amsden
CHEE 440
Static Dryers
Tray/truck driers
B. Amsden
CHEE 440
Drying behavior for static bed
B. Amsden
CHEE 440
Fluidized Bed
B. Amsden
CHEE 440
Spray Dryer
B. Amsden
CHEE 440
Drying Equations
Tray/Truck Dryers
constant rate drying stage only dm hcAΔT
=
dt λ • parallel flow over a static bed
8.8G0.8
hc = 0.2
D
• perpendicular flow through a bed
0.585
Nu =1.17Re
B. Amsden
0.333
Pr
CHEE 440
Drying Equations
Fluidized beds and spray driers
use correlation for flow past an individual spherical particle 0.5
Nu=2.0+0.61Re Pr
B. Amsden
0.333
CHEE 440
Example
Wet granules (density = 1.5 g/cm3) are spread onto a screen at an amount of 10 kg/m2 of screen. The bed porosity is 45% and the wet granules have an average diameter of 300 m. Air at 60ºC(dry bulb) and a wet bulb temp of 25ºC is passed through the bed at a velocity of 0.15 m/s. How long will it take to dry the granules from 20 to 10 % moisture? The critical moisture content of the granules is 9 %.
B. Amsden
CHEE 440
We are primarily concerned with drying wet, porous solids
(granules).
Important to ensure proper moisture content in the granules:
low enough to prevent product degradation and ensure good powder flow, but high enough to provide good tablet properties B. Amsden
CHEE 440
Definitions psychrometry determination of the vapor concentration and carrying capacity of drying gas
wet bulb T dry bulb T relative humidity (RH)
Pwater in air
%RH =
×100
Pw,sat(T )
moisture content
B. Amsden
CHEE 440
Psychrometric
Chart
Determine the relative humidity and moisture content in the air if the wet bulb T is 35 ºC and the dry bulb T is 50 ºC.
B. Amsden
CHEE 440
Types of Dryers
B. Amsden
CHEE 440
Static Dryers
Tray/truck driers
B. Amsden
CHEE 440
Drying behavior for static bed
B. Amsden
CHEE 440
Fluidized Bed
B. Amsden
CHEE 440
Spray Dryer
B. Amsden
CHEE 440
Drying Equations
Tray/Truck Dryers
constant rate drying stage only dm hcAΔT
=
dt λ • parallel flow over a static bed
8.8G0.8
hc = 0.2
D
• perpendicular flow through a bed
0.585
Nu =1.17Re
B. Amsden
0.333
Pr
CHEE 440
Drying Equations
Fluidized beds and spray driers
use correlation for flow past an individual spherical particle 0.5
Nu=2.0+0.61Re Pr
B. Amsden
0.333
CHEE 440
Example
Wet granules (density = 1.5 g/cm3) are spread onto a screen at an amount of 10 kg/m2 of screen. The bed porosity is 45% and the wet granules have an average diameter of 300 m. Air at 60ºC(dry bulb) and a wet bulb temp of 25ºC is passed through the bed at a velocity of 0.15 m/s. How long will it take to dry the granules from 20 to 10 % moisture? The critical moisture content of the granules is 9 %.
B. Amsden
CHEE 440