Flow dead zone analysis and structure optimization for the trefoil-baffle heat exchanger

Abstract

The distribution and volume fraction of the dead zones in the shell side of the trefoil-baffle heat exchanger were studied, and a structure optimization was presented to improve flow condition. By applying the residence time distribution method, the dead zones were analyzed quantitatively, and it is found that the volume fraction of dead zone is about 28% in the shell side of the trefoil-baffle heat exchanger, which is larger by about 13% than that in the shell side of the segmental baffle heat exchanger. According to the velocity contours in the shell side, the magnitude of the fluid velocity in the main flow region is much larger than that near wall, and the fluid near the shell wall flows in much slower velocity. The dead zones mainly distribute near the walls of shell and baffles. Another study was carried out adopting the unit duct model without concerning the influence of the shell wall, and it is shown that the volume fraction of the dead zone is less than 0.5%. It is concluded that the main dead zone in the shell side is near the wall of the shell. To reduce the main dead zone, an optimized structure of tube layout was presented, and it is found that the volume fraction of dead zone reduced by about 13% at the different flow rates. The methods and conclusions provide a reference for analysis of dead zone and structure improvement of heat exchangers.