31 - Condensation

For a vertical tier of \(N\) horizontal tubes, the relation between heat transfer coefficient for the one tube (\(h_D\)) and the average heat transfer coefficient over the \(N\) tubes (\(h_{D,N}\)) is given as \[h_{D,N} = \frac{h_D}{N^{1/4}}\] Such an arrangement is often used in condenser design.

A reduction in the heat transfer coefficient with increasing \(N\) may be attributed to an increase in the average film thickness for each successive tube due to accumulation of drip from the upper tubes. Obviously it is advantageous to stagger the tubes as the accumulation of drip from the upper rows is at least partially offset by the splashing effects, i.e., by the agitation caused by the drip as it falls from one tube to another. That is, instead of square pitch arrangement of tubes, triangular or rotated square pitch arrangement would be better.