We report the design, construction, and performances of a microwave (MW) heating device for laboratory experiments with non-contact, homogeneous internal heating. The device generates MW radiation at 2.47 GHz from a commercial magnetron supplied by a pulsed current inverter using proprietary, feedback based command and control hardware and software. Specially designed MW launchers direct the MW radiation into the sample through a MW homogenizer, devised to even the MW power distribution into the sample's volume. An adjustable MW circuit adapts the MW generator to the load (i.e., the sample) placed in the experiment chamber. Dedicated heatsinks maintain the MW circuits at constant temperature throughout the experiment. Openings for laser scanning for image acquisition with a CCD camera and for the cooling circuits are protected by special MW filters. The performances of the device are analyzed in terms of heating uniformity, long term output power stability, and load matching. The device is used for small scale experiments simulating Earth's mantle convection. The 30 × 30 × 5 cm3 convection tank is filled with a water‑based viscous fluid. A uniform and constant temperature is maintained at the upper boundary by an aluminum heat exchanger and adiabatic conditions apply at the tank base. We characterize the geometry of the convective regime as well as its bulk thermal evolution by measuring the velocity field by Particle Image Velocimetry and the temperature field by using Thermochromic Liquid Crystals.
The present work was funded by the Executive Agency for Higher Education, Research, Development and Innovation Funding (UEFSCDI), Project Nos. 1 RO-FR-22-2011 and 44N/2009 PN09-44 (partially) for the Romanian team and by the Agence Nationale de la Recherche (ANR), Project No. ANR-11-IS04-0004, for the French team.
I. INTRODUCTION II. THE MICROWAVE HEATING DEVICE A. The microwave circuits B. Power and control blocks C. The experiment chamber III. MICROWAVE HEATING DEVICE PERFORMANCES A. Heating uniformity B. MW power stability C. Adapting versatility IV. INTERNAL HEATING CONVECTION EXPERIMENT A. Experimental fluids B. Convection experiment design C. Internal heating convection results V. CONCLUSIONS