| Waste electric and electronic equipment(WEEE) is now the fastest-growing solid castoff in China with the advances of information technology and products renews. More than3000million tons of electronic waste turn up in our country every year, thus most of them were transported by other countries. In some areas, serious pollution are found by heavy metals and chemicals because of poor manual dismantling and recovery technology in family workshops. As results, e-waste has caused serious harm to the enviroment and human health. The huge economic value contained in the waste has been a widespread concern taken by more and more country in the world at the same time. At present many universities and rearch institutions are investing in this field to find an enviroment-friendly and highly efficient way to dispoal and recoery waste. Microwave pyrolysis is now widely concerned as a promising recovery and utilization technology for large-scale application. The selective and volumetric features of microwave heating are coupled well with the complex electronic offal for the disposal of electronic waste(e-waste).The existence of metals in the wastes can lead to apparent microwave discharge during microwave-induced pyrolysis. Besides the sparking, our group also notice some special phenomena in our experiments. For instance, the existence of metals can lead to pyrolysis enhancement, formation of local hot points as well as local melting, the insertion of a thermocouple could lead to field enhancement. In this theis, the author well-designed and carried out some experiments by modelling in a decoupling-coupling way. The metal discharge under microwave irradiation was first isolated by mixing metals and microwave-penetrating media, and its effects were determined through direct measuring together with indirect denoting based on the nonnegligible effects. Based on the test results, the electric field E and temperature field of the microwave heating object were studied when the metal strips were inserted in the microwave oven. This will promote the development of the coupling mechnism of microwave absorption and metal discharge for e-waste.Firstly, the energy utilization of an microwave oven during microwave heating were studied. From the laws of conservation of energy and balance of heat, the effects of microwave irradiation time, volume, microwave output power and placement of the objects were introduced respectively. In the end, we concluded that changes of load would not influence the thermal efficiency from electrical power.Secondly, this paper studied the various factors on the heating effects of microwave discharge. The discharge under microwave irradiation were isolated by mixing metals and microwave-penetrating media, and its heating effects were determined through direct infrared measuring together with indirect denoting. The effects of microwave power, irradiation time, numbers of iron strips, and atmosphere types were all investigated in our experiments. On the basis, some regular rules were found for the heating effects of microwave discharge caused by the appearance of metals. It can be inferred that at some local points1000℃has been exceeded, and the energy conversion ratio can be as much as53%.Finally, numerical simulation study of metal discharge was designed and carried out. The temperature field of microwave heating in our experiment was presented by the latter method. Heat transfer model of the discrete liner heat source was built based on the metal appearance and placement. With the assistance of Ansys, boundary conditions of the model were set and meshed. Then, with the assistance of HFSS, the electric field distribution and change were analyzed in the circumstance of metal. And the author summarized the rules of the heating effects triggered by metals through experiments and modelling in a decoupling-coupling way. |
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