A Triple-Layer Electromagnetic Heat Exchanger With Plane Poiseuille Flow: Control and Local Onset of Thermal Runaway

An electromagnetic (EM) heat exchanger (HX) is a device which converts EM energy into a usable form of heat. In this article, we present a 2-D multiphysics model mimicking the operation of a layered EM HX and simulating the nonlinear interaction between EM wave propagation, energy transport, and fluid flow. A triple-layer geometry of the EM HX represents a lossy ceramic slab surrounded by two channels with a plane Poiseuille flow of a lossless coolant. Validation of the model developed in COMSOL Multiphysics is done by comparing the results with the output of another numerical model, which uses a second-order implicit-explicit scheme where advective and diffusive terms are treated implicitly and the nonlinear heat source is treated explicitly. Layer thicknesses are chosen such that an electric field resonance is achieved in the central layer. Because of the resonance, a power response curve is found to be a double S-curve. We show that EM HXs operating on the middle branch of the double S-curve are favorable and efficient compared to the those operating on the lower or upper branch. Careful examination of transient evolution of temperature confirms that thermal runaway occurs when the local maximum temperature reaches a critical value. The model predicts a hotspot in ceramic region when thermal runaway initiated locally. We generate power response curves for increasing Péclet numbers, which is defined as the ratio of heat convection to conduction within the fluid region, and show that temperatures of upper and middle branches keep dropping with Péclet numbers.