【作者】 刘美慧；

【导师】 胡仰栋；

【作者基本信息】 中国海洋大学 ， 化学工程， 2008， 硕士

【摘要】 工业电炉是普遍使用的加热设备,对其进行优化设计的研究具有重要意义。本文对电阻炉核心加热元件的传热特性进行了较细致的模拟计算和分析,具体研究工作有以下几个方面:1、对电加热体材料的研究。本文从电热体结构、尺寸、表面温度三个方面对电加热体进行研究,得出圆管状的电热体的内外温度分布比较均匀。当电热体的直径D>5cm时,棒状及方棒电加热体的内外温差比较高,而管状电加热体则相对比较低。电加热体外表面温度对电加热体的影响也比较明显,半径一定时,温差与电热体外表面温度近似成平方关系,当外表面温度一定时,电加热体温差随着半径的增大而升高。2、高温电加热条件下,对于含有大分子碳化硅杂质颗粒的石墨电加热材料进行三维稳态模拟,得知电流对碳化硅颗粒与石墨电加热体之间的温差影响最大,当电流密度达到20A/mm2时,温差达到35℃。而且,碳化硅颗粒的存在,也使石墨体的温度升高,碳化硅颗粒粒度越大,石墨体内部升温越高。3、研究了非稳态情况下各种电加热元件的传热特性。对于管状电热元件,内部绝热材料的压紧对应着密度的变化,它对电热体升温及内部温度分布都有很大的影响,压紧的绝热材料比未压紧的升温快而且内部温差较低。对于J GQ型电加热元件,在压紧的状态下加热元件外表面达到70℃所用的时间明显少于未压紧状态下所用的时间。另外,在未压紧时加热元件内部的温度明显高于压紧情况下的温度对于石墨电热体。研究了石墨体非稳态电加热升温过程中,电加热体的升温速率与石墨体的密度有直接关系,根据模拟得知在电加热过程中石墨体温度分布均匀,因此反推出升温速率与电热体密度的关系,关系式为:,当密度较小时计算结果与模拟结果相吻合。对于有裂纹存在的棒状及管状石墨电热体,裂纹的存在对石墨电加热体升温过程中的影响非常严重,由于裂纹的存在,棒状石墨电热体升温速率下降,对于10mm的棒状电加热体,对于直径为10mm的棒状电加热体,无裂纹时,1s钟后的温度为524.95℃,而有裂纹时的最高温度才为434.587℃,并且温度的最高点和最低点都集中在裂缝附近,这就会在裂缝处产生很大的热应力。对于厚度为10mm管状电热体由于裂纹的存在,使电热体温度分布极不均匀,电热体温度为1000℃左右时,裂纹处的温度就已经达到2400℃,这样继续加热下去,石墨体未达到工作温度,就会超过石墨体熔点,造成石墨体的烧结。在辐射和热传导耦合情况下模拟了直径随轴向逐渐减小石墨体的温度场和应力场分布状况,结果表明,直径越小升温速率越高,但是轴向上温度梯度却是逐渐减小的。更多还原

【Abstract】 Industrial furnace is commonly used heating equipment, it is very important to design and optimize the furnace. In this paper, it simulates and optimize the heat transfer characteristics of the core of the resistance furnace detailed. Specific studies in the following areas:1 the research of the electric heaterThis article studies the electric heating from the electric structure, size, and the surface temperature of the three aspects. The inside and outside temperature is distributing more uniform, when the cross-section of the electric heating is the circular ring. When D>5cm, the internal and external difference in temperature of circle rods and square rods is higher, but tube electricity heat body stand opposite each other lower. The surface temperature affects the electric heating rods obviously. When radius is a certain value, it is the approximate to last square relation between with difference in temperature and external surface temperature. When the outer surface temperature is a certain temperature, the heating temperature difference with a radius of the increasing rise2 Under the conditions of high temperature electric heating three-dimensional steady-state simulate the macromolecular particles containing impurities in the graphite heating materials. It’s finding that the current is greatest impact the heat of the graphite containing impurities. For silicon carbide particles, the greater the current, the greater the temperature difference between the particles, and temperature difference is directly proportional to the square with the current relations. When the current is 20 A/mm2,the temperature difference has reached 35℃. In addition to Current, the impurities in the size of particles also directly affect the temperature of the electric distribution. In addition to Current, the size of particles also directly affects the temperature of the electric distribution. 3 This paper studies the heat transfer characteristics of variety of electric heating elements, under the unsteady-state status. For the Tubular electric heating elements, internal insulation materials affect the velocity of calefactive and the inner distribution of temperature on the electric heating. For J GQ style tubular electric heating elements, pinched heating elements under the surface reached to 70℃, the time spent significantly less than the state did not pinched , another is the temperature of loosen heating elements is higher obviously than that pinched circumstances. For the graphite electric element, at the condition of radiating outside of heat, the temperature of the graphite electric element is absent quickly. The heating rate is relative to the density. According to simulation, the temperature distributed equality, so receive the relative is: When the density is small, the result of calculation and simulation result are identical. For the graphite electric element which has crack on the surface, the exist of the crack are effect the heat rate very much, the exist of the crack causes the decline of the heat rate. a 10mm- diameter graphite electric element, a second latter, the temperature reach 524.95℃if there is no a crack .But it highest temperature is 434.587℃when there is a crack. At the round of the crack the temperature is smaller than the main body of the graphite electric element. There is a big difference in temperature, which result the heat stress. The existence of the crack in tubular graphite electric element result the un-equality of the element temperature For a 10mm-deepth tubular graphite electric element, when the temperature of the crack achieve to the work temperature, the temperature of the body is at only a small point(about500℃).So if continues to heat the temperature of the body has not reach the work temperature, the crack temperature has exceed the melting point.更多还原