Continuous-flow microwave heating of liquid whole egg in helical tubing: Numerical modeling and experimental validation

In this study, continuous-flow heating of liquid whole egg (LWE) was conducted in a specially designed 915 MHz microwave heating unit equipped with one-coil helical tubing. LWE was heated at 3 and 4 kW microwave powers at fixed flow rate (2 Lpm). The measured temperatures at seven cross-sectional locations at the outlet using a thermocouple assembly was used to obtain average exit temperature. The computational model, which was performed using COMSOL Multiphysics, was validated against the experimental temperature measurements performed with the one-coil system. Heating efficiency in case of longer tubing (two-coil) inside the cavity was then explored computationally using the validated model. The results showed that the average temperatures measured at the outlet of the one-coil tubing were 30.1 ± 4.2 °C and 36.7 ± 3.1 °C at 3 kW and 4 kW, respectively. The simulated counterparts were 30.0 ± 0.2 °C and 36.4 ± 0.4 °C. The heating efficiency did not improve upon changing the design from one-coil to two-coil configuration. However, electric field distribution and absorbed microwave energy along the tube were strongly affected. Sensitivity analysis showed that heat transfer coefficient and dielectric properties implemented in the base model exhibited the greatest proximity to the experimental results. This study showed one-coil helical tube was appropriate tube design to achieve efficient and uniform heating of LWE. The findings of this study demonstrate the efficacy of employing this system for pre-heating in the pasteurization unit, therefore enhancing production capacity and reducing total energy consumption.