Jump to content



Featured Articles

Check out the latest featured articles.

File Library

Check out the latest downloads available in the File Library.

New Article

Product Viscosity vs. Shear

Featured File

Vertical Tank Selection

New Blog Entry

Low Flow in Pipes- posted in Ankur's blog

2

Constant Rate Drying Equation During Flash/pneumatic Drying

constant rate drying flash drying pneumatic drying

1 reply to this topic
Share this topic:
| More

#1 cheminst

cheminst

    Veteran Member

  • Members
  • 33 posts

Posted 20 June 2019 - 12:33 AM

I had this problem while calculating the constant drying rate during flash/ pneumatic drying.

 

Drying rate can be calculated by two ways. These are the equations I found in literature for calculating the constant drying rate for flash/pneumatic drying. (Free moisture is only evaporated. particle temperature normally doesn't exceed 50 Celsius)

 

w = drying rate (kg/ m2 s)

k = mass transfer coefficient

Ts = Solid temperature = 303 K = 30 C

Tg = Gas temperature = 413 K = 140 C

Mw = molecular weight of H2O (18 e-3 kg/mol)

Mg = molecular weight of dry gas (30 e-3 kg/mol)

R = Gas constant (8.314 J/mol K)

 

P = atmospheric pressure (101325 Pa)

Psat = Saturation water vapor pressure at solid temperature, 303 K = 4247 Pa

Source: https://www.engineer...sure-d_599.html

 

Drying gas has 12% moisture by volume.

PH2O = partial pressure of gas =101325*0.12 = 12159 Pa

 

H = humidity in gas (H2O kg/ dry gas kg) = (0.12*18) / (0.88*30) = 0.0818

 

1) First Method (for single particle)

 

w = k (Psat *Mw / R*Ts  -   PH2O*Mw / R*Tg)

 

However, the drying rate is negative. since (4247/303 - 12159/413) < 0

 

2) Second method (for bulk of the particles)

 

w = k { [Mw*Psat /  Mg*(P - Psat) ] -   H }

 

However drying rate is negative. since  [ 18*4247/30*(101325 - 4247) ] - 0.0818  < 0 is negative.

 

 

Can anyone please explain why the drying rate is negative. Is there anything wrong with the equations or my calculations?

 



#2 PhilippM

PhilippM

    Gold Member

  • Members
  • 81 posts

Posted 31 July 2019 - 03:27 PM

You wrote that you found these equations in literature. Can you provide a source citation? That might make it easier to understand the problem.






Similar Topics