CFD analysis on hydro-thermal behavior of shell and tube waste heat boilers

Shell-and-tube waste heat boilers (STWHBs) are essential in the recovery of waste heat from high-temperature industrial processes. Kettle-type STWHBs are known to experi-ence failures due to hold-up of steam, a significant concern in the industry. Multiphase CFD simulations are used to study the effect of tube cross-section and tube layout on the steam hold-up of an industrial-scale STWHB. Different design specifications are simulated includ-ing tube cross-section, tube layout, heat flux, and pitch to predict steam hold-up performance and analyze thermo-hydrodynamic phenomena within the tube bundle. Ellipse, an alterna-tive tube cross-section with the same cross-sectional area as in circular one, is introduced in the application of STWHBs due to its ease of manufacturing to determine its impact on steam hold-up performance. Simulation results show that, for similar tube bundle shape and size, 45° rotated square tube bundle layouts perform better, with respect to steam hold-up, than the square and triangle layouts for a range of heat flux duties. Elliptical cross-section tube proves better performance in steam hold-up with 45° rotated square tube bundle layouts.But, the steam hold-up performance of elliptical cross-section tube deteriorate with square tube bundle layouts and that with triangle layout remains unchanged. It is found that steam hold-up increases linearly with increasing heat flux and decreasing tube pitch, for the conditions simulated. The turbulent kinetic energy of the bubbly flow is greatly influenced by increasing phase fraction. Visualizations of the flow of water and steam within and around the tube bundle show that there is a vertical flow deviation for both staggered tube patterns (rotated square and triangle) which has profound influence on the steam hold-up within tube bundle for each tube cross-section. These results motivate further multiphase CFD-basedstudy of the thermo-hydrodynamics of STWHBs for improved understanding, retrofit and new designs.