Most flooded condensers are of the horizontal type with vapor on the shell side and coolant in the tubes as shown in Figure 15.1 (see also Figure 3.1). As the liquid level in the shell varies, so do heat-transfer area and rate of condensation. We would like to find out how condensing pressure and rate of condensation are affected by rate of vapor flow into the condenser, back pressure downstream of the vent valve, and rate of removal of liquid from the condenser shell. We will make several simplifying assumptions:
1. The sensible heat load is small enough in comparison with the latent heat load that it may be neglected.
2. Submerged heat-transfer area, As, is proportional to liquid level above the bottom of the lowest tube. The change in condensing area, Ac, is then the negative of the change in A,. This assumption is not bad if there are many tubes and if they are not "layered." To make this assumption valid may require that in some cases the tube bundle be slighdy rotated about its axis.
3. For the time being, we will assume that the vent valve position is fixed.
4. Heat storage in the heat exchanger metal may be neglected.
We may now write the following equations, some in the time domain and some in the s domain:
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