BT-6 Vertical Thermosiphon Boiling in Spiral Plate Heat Exchangers

S. B. Yilmaz and C. C. Yang

This report documents the results of vertical thermosiphon boiling experiments with two spiral plate heat exchangers (SPHE) of different geometries which were tested in the HTRI boiling and condensation research plant. As thermosiphon reboilers, these two SPHEs can perform exceptionally well at low LMTDs for both atmospheric pressure and vacuum operation. At low LMTDs where a shell-and-tube thermosiphon reboiler performance can drop significantly, the SPHEs continued to boil and gave high heat transfer rates. For the LMTD range studied, it was found that the SPHE II with a smaller (0.375-in. or 9.5-mm) boiling channel spacing performed significantly better than the SPHE I with a 0.625-in. (15.9 mm) boiling channel spacing. The degree of subcooling of the liquid feed to the SPHE II showed a strong effect on heat flux and circulation rates. More study will be required before all questions are resolved about SPHEs as thermosiphon reboilers. However, the data obtained permitted a modification of the HTRI Computer Program RTF-2 to give reasonable good prediction of the performance of these units.