Flow phenomena in a scraped-surface heat exchanger (“Votator”-type)

✍ Scribed by A.M. Trommelen; W.J. Beek

• Publisher: Elsevier Science
• Year: 1971
• Tongue: English
• Weight: 784 KB
• Volume: 26
• Category: Article
• ISSN: 0009-2509
• DOI: 10.1016/0009-2509(71)86035-9

✦ Synopsis

In order to understand the mechanisms governing heat transfer and power consumption in a scraped-surface heat exchanger @SHE), it is necessary to study the flow in this type of apparatus.

By suspending polyethene beads in glycerol/water solutions, and operating a glass-walled SSHE with this suspension, it was established that the flow was either in the Couette flow regime or in the Taylor vortices regime. The flow in the Couette regime was further studied in a perspex model of the SSHE in which a dye could be injected at different positions. In this way streamline patterns and velocity profiles were determined. The streamlines are concentric circles outside the blade area (for cutaway blades). The streamlines contract and expand near the blades. The resulting velocity profile is similar to that between two parallel plates, one of which is moving, and with a pressure gradient in the direction of the flow.

Residence time distributions were measured both in the Couette and Taylor regime by injecting a pulse of dye near the inlet of a SSHE and sampling continuously at the outlet. The axial dispersion is so great that for some of the heat transfer measurements the effective driving force for heat transfer is smaller than calculated for the plug flow model.