Chemical: Baffle Cut Effect on Shell and Tube Heat Exchanger

Baffle Cut Effect on Shell and Tube Heat Exchanger CFD Simulation

Description

Shell and tube heat exchangers are a workhorse of the chemical process industry, and this project investigates how baffle design affects their thermal performance. Baffles, typically made of a highly conductive metal, redirect the shell-side fluid flow to improve heat distribution across the shell, boosting overall heat transfer. The tradeoff is pressure drop: adding more baffles improves thermal performance but also increases the resistance the fluid has to work against, so the baffle cut geometry and spacing need to be chosen carefully rather than maximized blindly.

This project simulates the baffle cut effect using ANSYS Fluent, treating the problem as a conjugated heat transfer case where the metal baffles themselves are modeled as solid domains participating directly in the heat exchange. Cool water enters the shell at 300 K with a flow rate of 0.5 kg/m³, equivalent to a velocity of 0.7 m/s, while the inner tubes are held at a constant wall temperature of 450 K to represent the hot side. Water's physical properties are defined as piecewise-linear functions of temperature rather than fixed constants, which improves the accuracy of the heat transfer prediction. The goal is to see how effectively the baffles' high thermal conductivity spreads heat away from the hot tubes into the surrounding fluid.

Geometry & Mesh

The geometry was built in Design Modeler with a shell measuring 600 mm in length and 90 mm in diameter. Six baffles, each 4 mm thick, are spaced 86 mm apart center-to-center, with a baffle cut of 36%. Seven tubes, each 20 mm in outer diameter, are arranged in a triangular pattern inside the shell with a 30 mm center-to-center spacing. The mesh was generated in ANSYS Meshing as an unstructured grid with 1,953,754 elements and a 30 mm element size, with a boundary layer mesh added near the walls to satisfy the Y-Plus requirements of the standard wall function.

Methodology

The case was solved as a steady-state problem using the pressure-based solver in ANSYS Fluent, with gravitational effects included. Turbulence was captured using the realizable k-ε model with standard wall functions. The SIMPLE algorithm handled pressure-velocity coupling, with standard spatial discretization for pressure and first-order upwind schemes for momentum, turbulent kinetic energy, turbulent dissipation rate, and energy. The shell wall was treated as adiabatic, while the tube wall was fixed at 450 K, and the outlet was set as a pressure outlet at 0 Pa gauge.

Conclusion

The results show the shell-side water heating up from its 300 K inlet temperature to roughly 360 K at the outlet as it flows past the hot tubes. Heat transfer coefficient and total heat transfer rate both converge steadily as the solution progresses. By modeling the baffles and fluid together in a conjugated heat transfer setup, the results show that the baffles noticeably speed up temperature diffusion throughout the shell, raising the average fluid temperature and improving the heat transfer coefficient accordingly. The pressure contour at the exchanger's mid-plane shows a pressure drop of around 1 kPa, giving a clear picture of the tradeoff between the improved thermal performance and the flow resistance the baffles introduce.