Evaluating Applicator Designs for Heating Nanoparticle Flow Chemistries Using Single-Mode Microwave Energy

A single-mode microwave system can provide an electro-magnetic field with very sharp peaks and high power densities which can heat chemical process fluids rapidly on a much shorter time scale than by convective means. This type of microwave heating provides the opportunity to reduce thermal gradients within process fluids which are important, for example, in the control of reactive precipitation processes used to produce colloidal nanomaterials. Here, the effects of flow applicator design on the thermal gradients and energy efficiency of the microwave-assisted heating is considered as a function of flow rate. A heat efficiency model is developed to simulate the single-mode microwave heating of a continuous flow process fluid over a variety of flow rates and powers. To validate the model, an experimental setup is developed involving a three kW 2450 MHz microwave processing system. The system was used to heat salt water over a range of concentrations while temperature change across a microwave heating zone was measured using in-situ fiber optic probes. Experimental results were found to be in good agreement with the model yielding an average error for all cases of 4.8% and an average error for cases with salinity of 17.3%. The model is used to evaluate the effects of applicator design on thermal gradients and energy efficiency with changes in flow rate.