Three-dimensional modeling of a Helixchanger® heat exchanger using CFD

Detailed three-dimensional computational fluid dynamics (CFD) simulations have been performed to explore the performance of a helically baffled heat exchanger, commercially referred to as the Helixchanger (R) heat exchanger. The CFD simulations employ the HEATX computer simulation program, which is designed for the simulation of shell-and-tube heat exchangers. The simulation accounts for the complex helical geometry of baffles, leakages, and nozzle entrance and exit. Three cases are presented that correspond to helix angles of 10 degrees, 25 degrees, and 40 degrees, defined with respect to the radial axis. Inspection of the computed flows reveals distinct inner and outer regions, with the outer region showing a very desirable plug flow characteristic. The inner region, however, displays recirculation zones due to back mixing at the small helix angle, which suggests potential vibration problems but also creates a desirable temperature uniformity. A comparison with plug flow showed that the helically baffled heat exchanger had a fluid turn ratio of 0.64, 0.78, and 0.77 for the 10 degrees, 25 degrees, and 40 degrees helix angles, indicating more overall plug-likeflowfor the higher helix angles. Computed pressure drops compare reasonably well with ABB Lummus Heat Transfer correlation results, although nozzle entrance and exit losses require further study.