Q1-5 New RPM for Shellside Condensation of Mixtures in the Presence of Non-condensable Gases

Z. H. Yang and J. W. Palen

For more than two decades, HTRI has conducted analytic and experimental research on shellside condensation of mixtures and pure components with and without non-condensable gases. Based on the more than 1800 data points accumulated, two condensation methods were developed, the Resistance Proration Method (RPM) and the Composition Profile Method (CPM). The RPM, although much simpler to use, does not handle mixtures with large amounts of non-condensables well. The CPM method handles these mixtures more accurately but is difficult to use with multicomponent industrial mixtures because it requires very accurate composition profiles for each component.

Currently, HTRI is working on a project to improve the RPM so that it more accurately predicts mixtures with large amounts of non-condensables. Our new method offers several advantages. Although no harder to use than the original RPM, it permits prediction of heat transfer performances within ± 25% for mixtures with up to 94 mole percent non-condensables. This new method also handles both plain tubes and finned tubes and improves prediction for wide condensing range mixtures without non-condensables. Details of this improved RPM are documented in HTRI Report CS-9. In addition to the normal RPM input, the new RPM requires only the inlet mole fraction non-condensable.