Heat transfer across a scraped surface

Investigations using three experimental scraped surface falling film vertical heat exchanger tubes (6 in., 12 in. and 24 in. by 1 in. D.) have been made. Water and water‐glycerol mixtures have been heated in the tubes by passing them down the heated inside surface which was continuously scraped by rotating blades. Flowrates between 306 lb/hr.ft. and 1070 lb/hr.ft. were used, the rate of rotation was varied from 370 to 1600 rpm whilst the number of blades on the shaft was varied between 1 and 4. As a result of these experiments the following equation accurate within ± 20% is proposed for correlating the heat transfer coefficient in the range of the variables studied: Visual observations of the flow of the liquid down the tube indicate that the liquid is held as a continuous fillet in front of each blade. This fact is used in the Appendix* for the alternative suggestion for the characteristic dimension in the correlation.