The microwave (MW) heating of liquids is used in the food industry (cooking, pasteurization, extraction) and the chemical industry (microwave-assisted organic synthesis).
In all cases, MWs are used to accelerate the heating processes, because they penetrate materials causing volumetric heating. Other common benefits of MW heating include safety (no flame or high temperatures) and efficiency (faster processes, reduced energy loss).
Modelling the microwave heating of liquids involves solving Maxwell’s equations for electromagnetics (EM), Navier-Stokes equations for hydrodynamics (HD), combined with the heat transfer equation. This is a three-way coupled conjugate problem.
Microwave heating of water in rectangular waveguide
This problem involves a vertically oriented rectangular waveguide with an open (topside) water reservoir inside. MWs (2.45 GHz, TE10 mode) are introduced at the inlet port at the top of the waveguide. The incident wave reaches the free surface of water, where much of its energy is reflected, and exits the computational domain through the inlet port. The transmitted wave penetrates and heats water, inducing buoyancy-driven flow. The Marangoni effect (surface tension dependence on temperature) is taken into account.
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Continuous flow microwave heaters are used to process liquids in large quantities. In simulation below we demonstrate continuous flow of water in a circular duct inserted
into the MW cavity. Dielectric constants and viscosity are temperature dependent. With our models all kind of fluids including non-Newtonian can be modeled in laminar and turbulent regimes.