Mass and heat transfer performance of a horizontal serpentine tube heat exchanger/reactor at the bottom of a stirred tank

The present study investigates the mass and heat transfer (by analogy) behavior of a horizontal serpentine tube located at the bottom of a square stirred tank reactor. The serpentine tube serves as a cooler, heater, or catalyst support for diffusion-controlled reactions. Mass transfer rates were measured electrochemically using the limiting current technique in a tank of 15 × 15 cm base and 25 cm height, with variables including impeller speed, tube diameter, and pitch. Results show that the mass transfer coefficient increases with impeller speed (k∝n0.45 for axial flow, k∝n0.47 for radial flow) but decreases with tube diameter and pitch. The data were correlated using dimensionless analysis with regression performed in Microsoft Excel, yielding equations for axial flow (Sh=0.118Sc0.33Re0.45(d/T)0.18(p/T)−0.22) and radial flow (Sh=0.138Sc0.33Re0.47(d/T)0.27(p/T)−0.18) turbines. The developed correlations can be used to predict both mass and analogous heat transfer coefficients, facilitating reactor scale-up and design. The axial flow turbine exhibited lower mass transfer but higher energy efficiency. The horizontal serpentine tube enhances transfer rates by breaking the hydrodynamic boundary layer and improves energy utilization, especially with axial flow impellers. This configuration offers significant advantages over traditional slurry reactors and conventional cooling methods, making it suitable for immobilized cell/enzyme biochemical reactors.