Shell side baffle number governs thermal hydraulic trade offs in a marine shell and tube heat exchanger

Shell-and-tube heat exchangers are widely used in marine cooling systems, where shell-side flow maldistribution can limit heat rejection and increase pumping-power demand. This study investigates whether increasing the number of shell-side baffles can improve cooling performance without causing an excessive hydraulic penalty. A three-dimensional steady-state CFD model was developed in ANSYS Fluent based on the incompressible single-phase RANS equations, the energy equation, and the SST k-ω turbulence model. Three configurations were compared, including no baffles, two baffles, and four baffles. The tube-side seawater inlet temperature and velocity were fixed at 288.15 K and 1.5 m/s, respectively, while the shell-side hot-water inlet temperature was 336 K and the shell-side mass flow rate varied from 1 to 5 kg/s. The results show that increasing the baffle number enhances shell-side flow redistribution, reduces low-velocity regions, and increases heat-transfer conductance, but also increases pressure drop. At 1 kg/s, the hot-water outlet temperature decreases from 325.17 K without baffles to 323.00 K with two baffles and 320.30 K with four baffles. At 5 kg/s, the shell-side pressure drop increases from 5.4 kPa to 5.6 kPa and 5.8 kPa for the two- and four-baffle cases, respectively. Relative to the no-baffle baseline, the overall conductance increases by approximately 10–23% for the two-baffle case and 32–52% for the four-baffle case. The performance evaluation criterion remains above unity for all baffled cases, indicating that the heat-transfer gain outweighs the hydraulic penalty within the studied operating range. By linking baffle-number-induced flow redistribution with system-level indicators including heat duty, energy closure, overall conductance, hydraulic power, and performance evaluation criterion, this study provides an integrated assessment of baffle-number effects under marine-relevant seawater–freshwater boundary conditions.