Computational Characterization of a Millimeter-Wave Heat Exchanger with AlN:Mo Cylindrical Susceptors

Hogan, Catherine M.

Student Work

Computational Characterization of a Millimeter-Wave Heat Exchanger with AlN:Mo Cylindrical Susceptors

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Electromagnetic (EM) heating has traditionally been applied in fields such as food engineering, chemistry, and materials science. More recently, a new field of EM heating has emerged for applications in power beaming technology. The EM heat exchangers (HX) are used in beamed energy propulsion, solar thermal collectors, and wireless energy transfer. A new type of EM HX for ground-to-ground millimeter-wave (MMW) power beaming applications has been recently introduced by the US Air Force Research Laboratory (AFRL). This device is comprised of an array of ceramic susceptors attached to a metal baseplate along the back surface. An incident wave is projected onto he ceramic elements, which absorb the EM power and are heated up, subsequently heating up the attached baseplate. Fluid channels housed in the baseplate are then used to carry the heat away. Computer modeling of the MMW HX with a susceptor made as a single rectangular block of a ceramic composite (aluminum nitride doped with molybdenum, AlN:Mo) has recently shown elevated energy efficiency and high level of uniformity of the temperature field in the ceramic block. Currently, the further development of a MMW HX device which utilizes cylindrical susceptors is of particular interest, due to the practicality and cost of production. In this MQP, we present results of numerical computations that demonstrated feasibility of the design of the experimental system made of five AlN:Mo cylinders on a square metal plate. Simulation of the EM and thermal processes is performed via the 3D finite-difference time-domain technique implemented in the simulator QuickWave. It is shown that while the energy efficiency of this system depends on the concentration of molybdenum doping in the composite, all concentrations provide sufficiently high temperature distribution. Computations are also made for the systems whose layouts are suggested by the highest density packing of equal circles in a square and feature four, nine and sixteen cylinders. We show that, in each of the various multi-cylinder models, a maximum energy efficiency can be achieved with different concentrations of Mo, whereas all concentrations provide excellent uniformity of temperature distribution within each ceramic cylinder. The results of this project are being adopted by the AFRL, Kirtland, AFB, NM as supporting data in the experiments with the new MMW HX for ground-to-ground wireless power transfer.

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