Shellside condensation

Condensers in which condensate is formed on the outside of horizontal shell-and-tube equipment may be partially flooded with condensate. Shellside baffles must be provided and the flow path through the baffle cut is essentially a V-notch weir, as shown in Figure 22-5. The height of liquid in the shell can be estimated using the equation below ... 

The shape of the coohng and warming curves in coiled-tube heat exchangers is affected by the pressure drop in both the tube and shell-sides of the heat exchanger. This is particularly important for two-phase flows of multicomponent systems. For example, an increase in pressure drop on the shellside causes boiling to occur at a higher temperature, while an increase in pressure drop on the tubeside will cause condensation to occur at a lower temperature. The net result is both a decrease in the effective temperature difference between the two streams and a requirement for additional heat transfer area to compensate for these losses. 

ESDU 84023 (1985) Shell-and-tube exchangers pressure drop and heat transfer in shellside downflow condensation. 

Shellside is for viscous and condensing fluids. Pressure drops are 1.5 psi for boiling liquids, and 3-9 psi for other services. 

The frictional pressure drop for shellside condensation can be calculated ... 

Venting of shellside condensers is more difficult. Several methods are available. The best method depends upon the size of the condenser and the method of condensate removal. 

The method described above is not adequate for situations in which condensate levels are expected on the shellside. Operation in this manner is not recommended as discussed in Chapter 31. If a level must be maintained in the shell, venting can be accomplished as described below. 

Better heat transfer is obtained at high condensate loading. Vertical condensers are generally more economical than horizontal shellside condensers employing lowfinned tubes. 

Pressure drop is generally lower for vertical vapor-in-tube condensers. However, for very low operating pressures (below 50 torr) shellside condensing will provide lower pressure drop if equipment is appropriate designed. 

Shellside distribution may also be effected by installing perforated plates downstream of the inlet nozzle. This approach is often used for condensers when the shellside fluid makes only one pass across the tube bundle. The perforated plate must be adequately positioned above the tube bundle to prevent excessive jetting and impingement. 

The manner is which an exchanger is piped up influences its performance. Horizontal units should have inlet and outlet nozzles on the top and bottom of the shell or channel. Nozzles should not be on the horizontal centerline of the unit. In general, fluids should enter the bottom of the exchanger and exit at the top, except when condensation occurs. Units are almost always designed to be counterflow and the piping must reflect this. When concurrent flow has been specified, it is equally important that equipment be piped to suit. For multipass units, the shellside fluid can be admitted at either end of the shell without affecting the thermal performance. However, for some cases better distribution or mechanical reliability can be achieved with the inlet nozzle at a specific location. 

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