Electromagnetic-Thermal Model Of A Millimeter-Wave Heat Exchanger Based On An Aln:Mo Susceptor

Purpose - The paper introduces and illustrates the use of numerical models for the simulation of electromagnetic and thermal processes in an absorbing ceramic layer (susceptor) of a new millimeter-wave (MMW) heat exchanger. The purpose of this study is to better understand interaction between theMMWfield and the susceptor, choose the composition of the ceramic material and help design the physical prototype of the device.Design/methodology/approach - A simplified version of the heat exchanger comprises a rectangular block of an aluminum nitride (AlN) doped with molybdenum (Mo) that is backed by a thin metal plate and irradiated by a plane MMW. The coupled electromagnetic-thermal problem is solved by the finite-difference time-domain (FDTD) technique implemented in QuickWave. The FDTD model is verified by solving the related electromagnetic problem by the finite element simulator COMSOL Multiphysics. The computation of dissipated power and temperature is based on experimental data on temperature-dependent dielectric constant, loss factor, specific heat and thermal conductivity of the AlN:Mo composite. The non-uniformity of patterns of dissipated power and temperature is quantified via standard-deviation-based metrics.Findings - It is shown that with the power density of the plane wave on the block's front face of 1.0W/mm(2), at 95 GHz, 10 x 10 x 10-mm blocks with Mo = 0.25 - 4% can be heated up to 1,000 degrees C for 60-100 s depending on Mo content. The uniformity of the temperature field is exceptionally high - in the course of the heating, temperature is evenly distributed through the entire volume and, in particular, on the back surface of the block. The composite producing the highest level of total dissipated power is found to haveMo concentration of approximately 3%.Research limitations/implications - In the electromagnetic model, the heating of the AlN:Mo samples is characterized by the volumetric patterns of density of dissipated power for the dielectric constant and the loss factor corresponding to different temperatures of the process. The coupledmodel is run as an iterative procedure in which electromagnetic and thermal material parameters are upgraded in every cell after each heating time step; the process is then represented by a series of thermal patterns showing time evolution of the temperature field.Practical implications - Determination of practical dimensions of the MMW heat exchanger and identification of material composition of the susceptor that make operations of the device energy efficient in the required temperature regime require and expensive experimentation. Measurement of heat distribution on the ceramic-metal interface is a practically challenging task. The reportedmodel is meant to be a tool assisting in development of the concept and supporting system design of the newMMWheat exchanger.Originality/value - While exploitation of a finite element model (e.g. in COMSOL Multiphysics environment) of the scenario in question would require excessive computational resources, the reported FDTDmodel shows operational capabilities of solving the coupled problemin the temperature range from 20 degrees C to 1,000 degrees C within a fewhours on aWindows 10 workstation. Themodel is open for further development to serve in the ongoing support of the systemdesign aiming to ease the related experimental studies.