Study And Application On Heat Transfer Characteristics Of Heat Insulating And Retaining Ceramic Porous Material By Using Fractal Theory

In recent years, heat insulating and retaining ceramic material is a new energy-saving material which is applied comparatively extensively to the industrial furnace. It has advantages of cheap, resisting high temperature, fighting thermal impact. In order to master how the thermal characteristics vary, a new research method is offered in this paper: fractal theory is used to research the heat transfer characteristics of refractory fiber material and ceramic regenerator the two types of heat insulating and retaining ceramic porous material based on their physical characteristics of complex microstructure.Fractal theory is used in this paper based on the microstructure characteristics of refractory fiber. The microstructure is described with fractal dimension and fiber volume fraction as the major parameters. The model of heat transfer has been established with the equivalent thermal resistance under high temperature. The formula for efficient thermal conductivity is given out in this paper. The efficient thermal conductivity has been compared between theoretical calculation and experimental results. It shows that theoretical calculation is almost in agreement with the experimental results. Its maximal relative error is smaller than 15 %. It has been shown that the theoretical calculative formula, which is based on fractal description, has higher precision. The calculative results show that the efficient thermal conductivity rises as temperature rises under a constant fiber volume fraction, and it is proportional to the third power of absolute temperature; it increases as fiber volume fraction and fractal dimension increase under a constant temperature and the increase rate is faster as the two parameters increase.The ceramic regenerator is the key unit of regenerative heat exchanger. The ceramic ball-packed regenerator is researched in the paper. It has characteristics of porous media, and its internal structure for heat transfer is similar to refractory fiber. The formula for comprehensive heat transfer coefficient of ceramic regenerator is given out based on the fractal heat transfer model of refractory fiber material in this paper. The formula is used to calculate and compare the heat transfer coefficient of ceramic ball-packed regenerator with different material and different parameters of geometric structure. The results are given out: the heat transfer coefficient of ceramic ball-packed regenerator is far greater when ceramic balls are in the foursquare arrangement than the ones in the triangular arrangement; it decreases as the diameter of ceramic ball increases. And combined with material characteristics of ceramic regenerator, the conclusion can be drawn through calculating and analyzing: the heat transfer coefficient is the maximum value when ceramic ball regenerator is in foursquare arrangement, the diameter of 10mm, and material of Si₃N₄. The formula for comprehensive heat transfer coefficient of ceramic regenerator is introduced to the design of regenerative heat exchanger based on the conclusion. A more convenient and complete design plan is made.A new method is introduced in the paper about that fractal theory is used to research the heat transfer characteristics of heat insulating and retaining ceramic porous material. The formula for efficient thermal conductivity of refractory fiber and the formula for comprehensive heat transfer coefficient of ceramic regenerator are given out. Theory foundation and design method are provided for design, using and extension of regenerative heat exchanger. Practical application of energy recycling of industrial furnace is guided by conclusions and methods drawn in the paper about the heat transfer characteristics of heat insulating and retaining ceramic porous material. And it is favorable to further explore other characteristics of heat insulating and retaining ceramic porous material, to develop new types ceramic porous material and to give research on heat and mass transfer in porous media and fractal theory application a push forward.