A hybrid electro heat drying system

This thesis presents a hybrid dryer based on heat pump and radio frequency drying technologies for the batch drying of brick materials. In the first part of the thesis the experimental aspects are detailed. The test apparatus has been commissioned by retro-fitting a radio frequency (rf) generator to the drying chamber of an existing heat pump dryer. A dynamic weighing system has been built and forms the central part of an extensive drying process data acquisition system. A number of practical difficulties due to thermal effects associated with drying and high frequency electromagnetic interference have been addressed. Drying results of the combination system are presented, including those obtained by a novel application of pulsed rf energy in association with heat pump technology for the drying of wet particulates and green house bricks. Limitations of the original experimental apparatus are highlighted and solutions given. A test cell, specially designed and built for carrying out dielectric property measurements of the processed materials, has produced good repeatable results. In the second part of the thesis a theoretical scheme is presented based upon the balance equations of the 'volume averaged' drying load for a modelling of the combined drying process. Particular attention has been paid to the electric field, generated within the material during drying, which depends on the rf electrode voltage and the changing dielectric properties of the drying load. A validation test of the model shows good agreement with the experimental results and demonstrates the ability of such, albeit simplistic, model to investigate different combination drying cases. (author)