Spiral plate heat exchangers have a niche in some industrial heat transfer applications due to their
• compact geometry (up to 70 m2/m3)
• good temperature control facilitated by nearly ideal countercurrent flow
• improved laminar heat transfer from low L/D values
• increased turbulent heat transfer from centrifugal force enhanced convection
• good performance for slurries as well as viscous and fouling fluids
HTRI has conducted extensive testing on a spiral-spiral single-phase flow unit for a wide range of Reynolds (6.5 to 74,000) and Prandtl (3.8 to 2260) numbers. These data were used to evaluate open literature and HTRI methods. The experimental data provides confidence in the use of existing models in new commercial software for the thermal and hydraulic evaluation of spiral plate heat exchangers. The new software, Xspe, will become available in early 2006 as a new component of HTRI Xchanger Suite, and uses an exchanger-based three-dimensional incrementation approach based on localized methods and process conditions.
The HTRI heat transfer method takes into account near wall convection effects, which could be significant for highly viscous fluids commonly used in spiral plate heat exchangers. A factor not currently accounted for in any model is the effect of spacer studs in pressure drop and heat transfer predictions. Spacer studs are usually present in spiral plate heat exchangers to maintain channel spacing during fabrication and pressure flexation during operation. These studs are believed to prevent true laminar flow by promoting turbulence. Future models should be further enhanced by explicitly accounting for the effect of various spacer stud patterns.
Fernando J. Aguirre/Christopher A. Bennett
Heat Transfer Research, Inc. (HTRI)
College Station, Texas, USA
