CondensersCondensers are used in chemical industry to change the phase from Vapor to Liquid. This means that the vapor has to be cooled to below its dew point.

To design condensers we need to divide the condenser to zones. Condenser can have:

1. Desuperheat2. Condensation3. Subcooling

The condenser needs to be divided into zones since the heat transfer coefficient in each of the zones is different. Lets look at the condensation zone, since the desuperheat and subcooling are single phase operations, and have been dealt with in many courses in chemical engineering. For the condensing stream the condensation can be integral or differential condensation.

Integral condensationIntegral condensation happens when the vapor and liquid are close enough to maintain equilibrium. The condensate formed during the condensation process is carried along with the vapor to the outlet. In a vertical in-tube condensation the liquid formed by condensation flows along with the vapor.

Differential condensationIn differential condensation the liquid condensate in not in contact with the vapor. This has a effect of lowering the dew point of the remaining vapor as the components which are low boiler condense first. This phenomenon happens in a knockback reflux condenser where the liquid condensate drains due to gravity while the vapor rises to the outlet.

Condensation in the shell is between a true integral or differential condensation.

Design of condensers need to address the following:

1. Sufficient area is available to do the heat transfer2. Pressure drops (shell side as well as tube side) are within allowable limits

The selection involves selecting a TEMA shell and tube type. TEMA classification of shell types:

Inputs requiredFluid flow rates, Temperatures (In/Out), Pressures, allowable pressure drops, Fouling resistance.

OutputThe output of the design produces

1. Shell sidea. Type Shell diameterb. Baffle spacingc. Number of bafflesd. Pass layout

2. Tube sidea. Tube diameterb. Tube lengthc. Number of tubesd. Tube pitch and pattern

Design

De-superheating

CondensingSub-cooling

Coolant

Temperatur

e

dz

dQ

Heat Curve

For any small segment, dZ the heat transferred dQ is

dQ = U.dA.(Tcondensing – Tcoolant)

If we divide the condenser into n Segments, dA = A/N. The numerical algorithm starts from one end and solve the heat balance in a marching fashion to the other end.