BG1-9 Single Tube Boiling Data for Hydrocarbon Mixtures at High Pressure - Analysis of Paderborn Data

J. W. Palen
1992; rev 09/2015

This report presents an analysis of nucleate pool boiling data at high pressures for a mixture of ethane, propane, and n-pentane taken under HTRI contract at Paderborn University, Germany, by Professor D. Gorenflo and coworkers. The data were taken at higher pressures than previous HTRI data and were needed for better understanding of the severe decrease in the nucleate boiling mixture correction as the critical pressure was approached.

Through these data it was possible to show that the heat transfer to boiling mixtures becomes diffusion-limited as the boiling pressure approaches the critical pressure. This means that the boiling heat transfer coefficient does not increase exponentially when boiling pressure nears the critical pressure (as is the case for pure components), but instead increases very gradually as the boiling mechanism shifts from heat-transfer-limited to diffusion-limited.

A new theoretical equation for the maximum heat transfer coefficient for a diffusion-limited boiling system was derived. The boiling data at reduced pressure above 0.9 were shown to closely approach this theoretical limit. The Theoretical Boiling Range Method (TBR), described in HTRI Report BG1-8, was found to predict these new data well after modification of the mass transfer coefficient correlation to include a pressure effect. The new correlation was shown to predict the previous HTRI pool boiling data and most of the early data by Cichelli and Bonilla for a mixture of propane and n-pentane at high pressures as well.

The previous HTRI Empirical Boiling Range Method (EBR), however, did not predict the data well for reduced pressures above about 0.6. It was not attempted to modify this method further since now it has no advantages in ease of application over the TBR Method. When used in the future, the EBR Method must be limited not to exceed the theoretical maximum heat transfer coefficient at high pressures. Recommendations are given for updates of HTRI calculation procedures and for future research.