[daf44]

Hi all,

I am currently trying to make some calculations regarding the indirect drying of some feed material.
Basically, the feed enters the dryer in which water evaporates from the feed due to indirect heating.

The energy balance should contain:
 - the amount of energy needed to heat up the material from T1 to T2 --> m_feed (kg/s) * Cp (J/kg*K) * del T (K)
 - the amount of energy needed to change the liquid H2O to gaseous H2O --> Lh_H20 (J/kg) * m_evaporation (kg/s)

So Q = m_feed*Cp*del T + Lh_H2O*m_evaporation

My question is regarding the m_feed. The outlet mass flow will be lower due to fact that some water inside the material has been evaporated.
Should m_feed be equal to the inlet mass flow or an average between the inlet and outlet massflow?

Any help is much appreciated

[mjc123]

You're presumably going to have to heat up the water contained in the feed to T2 to get it to evaporate. Some might be coming off at lower temperatures, but as a first approximation assume that you heat up the wet feed to T2 and then the water evaporates.
Now, what are you going to use for Cp?

[daf44]

For Cp, I take an average between the inlet Cp and the outlet Cp: Cp = (Cp_in + Cp_out) / 2