Semi‐conjugate and fully‐conjugate computational fluid dynamic investigations of the flow and heat transfer in a 25 L pilot‐scale unbaffled stirred tank reactor with a plain jacket are reported. A hot heat transfer fluid (DW‐Therm) flows through the plain jacket and heats water in the vessel, which is agitated by a pitched three‐blade impeller. The shape of the free‐surface of the vortex formed in the unbaffled vessel is captured by the use of a homogeneous multiphase and free‐surface flow model. The simulations of flow and heat transfer are carried out using the ANSYS CFX (V.15) code. The semi‐conjugate simulation considers the vessel wall and the vessel contents, and the fully‐conjugate simulation also includes the flow in the jacket. The upward flow in the jacket is uneven and this dominates the distributions of heat transfer coefficients and shear stresses on the inner and outer surfaces of the vessel wall. The downward motion created by the impeller generates very high heat transfer on the base surface of the vessel, but this is nullified by a stagnation zone in the base region of the jacket. Overall heat transfer coefficients evaluated from average film heat transfer coefficients values from the simulations are around 15 % higher than those evaluated from correlations in the literature. In this pilot plant facility, the combined thermal resistances for the convection in the jacket and across the glass wall dominate the overall heat transfer coefficient.

Recent literature on thermal runaway reaction research in vessels, such as that conducted by Rudniak et al. [2011], still assumes a constant jacket temperature. In this investigation, three-dimensional steady state CFD simulations are performed for the plain jacket of a pilot scale vessel, which predict that the jacket temperature can vary by tens of degrees Celsius across different parts of the jacket even in reactors under a third of a metre in diameter, and that the distribution of heat transfer coefficients is strongly dependent on the flow path. The CFD output values are compared with experimental data of temperature measurements and with the use of correlations to predict heat transfer coefficients from the experimental data. The commercial code Ansys CFX Version 15 has been used to simulate the flow of the commercial heat transfer oil "DW-Therm" through a plain jacket of a pilot scale stirred tank reactor that is boiling water inside the vessel, to approximate a constant process temperature.

Accurate modeling of process temperatures within jacketed batch reactors has the potential to mitigate the risk of thermal runaways and enhance process control. A non-adiabatic heat-transfer model is derived for the investigation of heat transfer in laboratory to pilot-scale reactors of 0.5–40 L. By accounting for heat removed from the process by a total condenser and losses through the process lid, the model is able to predict process temperature profiles within the uncertainty limits of the experimental measurements. Heat losses from the outer jacket wall had a negligible impact on the evolution of process temperature but may contribute significantly to utility costs. Jacket duty measurements implied greater heat accumulation within the reactor vessel than anticipated, equivalent to ∼60% of that in the process fluid at 40 L scale. This raises the potential for heat-transfer coefficients to be systematically under-estimated by adiabatic models, particularly at the laboratory to pilot scale.