炭黑水泥砂浆板的电热试验与传热分析
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摘要
导电混凝土在智能结构、融雪化冰、地面辐射采暖、电磁屏蔽、钢筋保护等领域具有广阔的应用前景。本文从试验、理论计算、数值模拟等不同方面对纳米炭黑水泥砂浆板的导电性能、电热性能和采暖效果做了研究探讨。主要工作如下:
1)试验表明,炭黑的类型对炭黑水泥砂浆板的电阻率有一定的影响;炭黑比表面积大时,样品的导电性能比较好;远红外辐射涂料在电热试验中对空气升温的影响不大;发泡炭黑水泥砂浆板比普通炭黑水泥砂浆板的电热性能要好。
2)通过累计时间长达300小时的电热试验,明确了不同采暖条件下房间内板和空气的升温规律和系统耗电量,并且可以肯定炭黑水泥砂浆板的电功率稳定,电热功能重复性好,系统控温性能良好,取得了比较好的试验效果。在房间放置一些室内填充物,对比空房间,可以有效的减少耗电量,节能10%以上。
3)炭黑水泥砂浆板的对流系数和辐射系数受到发热板的形状、所处环境等多种因素影响。计算了各种工况下的对流、辐射系数,房间内辐射换热量占到总换热量的58%以上。根据导热微分方程和能量守恒定律,得到了发热板的温度变化方程和房间的热平衡方程,求出了方程的解。并且得出:在维持室内温度一定的情况下,随着外界温度的降低,所需功率和板面温度逐渐增加。
4)采用有限元方法模拟发热板发热及室内的温度分布,模拟结果和试验结果比较接近,发热板存在比较小的热应力。
以上的研究对炭黑水泥砂浆板在室内采暖或者其他的工程应用方面具有一定的借鉴价值。
Conductive concrete can be used in many fields,such as health monitoring of civil engineering structures,melting snow and deicing,shielding of electromagnetic waves etc.In this paper,experimental,analytical and numerical investigations were conducted on electrical properties and electrical heating effect of carbon black cement mortar(CBCM)board.Main conclusions are drawn up as follows.
1)CBCM containing carbon black with larger specific surface area has lower resistivity.The infrared paint makes little influence on the electrothermal effect as it is coated on CBCM plate.While,using lightweight cement as the matrix can improve the electrothermal effect.
2)The heating test lasting over 300 hours has shown that the heating power and resistivity have good stability.The temperature of CBCM and indoor air,energy consumption under different indoor control temperature and different outdoor temperature are measured.Energy consumption decreases more than 10 percent as the furniture is laid in the room.
3)Coefficients of convection and radiation are affected by several factors such as the shape of board and surrounding.Coefficients of convection and radiation under different situations are calculated.The result indicates that the heat radiation occupies up to 58%of the total heat quantity generated from the floor.According to the heat conduction differential equation and the energy conservative law,the temperature rising function of CBCM and the heat balance equation of the room are drived.
4)By means of the finite element method,the heating process and temperature distribution are simulated.The calculating results are in agreement with the experimental ones.Thermal stress in the CBCM board is small.
The studies of CBCM for indoors heating and other engineering applications are of great importance.
1)试验表明,炭黑的类型对炭黑水泥砂浆板的电阻率有一定的影响;炭黑比表面积大时,样品的导电性能比较好;远红外辐射涂料在电热试验中对空气升温的影响不大;发泡炭黑水泥砂浆板比普通炭黑水泥砂浆板的电热性能要好。
2)通过累计时间长达300小时的电热试验,明确了不同采暖条件下房间内板和空气的升温规律和系统耗电量,并且可以肯定炭黑水泥砂浆板的电功率稳定,电热功能重复性好,系统控温性能良好,取得了比较好的试验效果。在房间放置一些室内填充物,对比空房间,可以有效的减少耗电量,节能10%以上。
3)炭黑水泥砂浆板的对流系数和辐射系数受到发热板的形状、所处环境等多种因素影响。计算了各种工况下的对流、辐射系数,房间内辐射换热量占到总换热量的58%以上。根据导热微分方程和能量守恒定律,得到了发热板的温度变化方程和房间的热平衡方程,求出了方程的解。并且得出:在维持室内温度一定的情况下,随着外界温度的降低,所需功率和板面温度逐渐增加。
4)采用有限元方法模拟发热板发热及室内的温度分布,模拟结果和试验结果比较接近,发热板存在比较小的热应力。
以上的研究对炭黑水泥砂浆板在室内采暖或者其他的工程应用方面具有一定的借鉴价值。
Conductive concrete can be used in many fields,such as health monitoring of civil engineering structures,melting snow and deicing,shielding of electromagnetic waves etc.In this paper,experimental,analytical and numerical investigations were conducted on electrical properties and electrical heating effect of carbon black cement mortar(CBCM)board.Main conclusions are drawn up as follows.
1)CBCM containing carbon black with larger specific surface area has lower resistivity.The infrared paint makes little influence on the electrothermal effect as it is coated on CBCM plate.While,using lightweight cement as the matrix can improve the electrothermal effect.
2)The heating test lasting over 300 hours has shown that the heating power and resistivity have good stability.The temperature of CBCM and indoor air,energy consumption under different indoor control temperature and different outdoor temperature are measured.Energy consumption decreases more than 10 percent as the furniture is laid in the room.
3)Coefficients of convection and radiation are affected by several factors such as the shape of board and surrounding.Coefficients of convection and radiation under different situations are calculated.The result indicates that the heat radiation occupies up to 58%of the total heat quantity generated from the floor.According to the heat conduction differential equation and the energy conservative law,the temperature rising function of CBCM and the heat balance equation of the room are drived.
4)By means of the finite element method,the heating process and temperature distribution are simulated.The calculating results are in agreement with the experimental ones.Thermal stress in the CBCM board is small.
The studies of CBCM for indoors heating and other engineering applications are of great importance.
引文
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[25]Reza F,Batson G B,Yamamuro JA,et a.l Volume electrical resistivity of carbon fiber cement composites[J].ACIMaterials Journa,l 2001,98(1):25-35
[26]Sihai Wen,D.D.L.Chung.Electric polarization in carbon fiber-reinforced cement.Cment and Concrete Research,2001,(31):141-147
[27]陈兵,姚武,吴科如.用交流阻抗法研究碳纤维混凝土导电性.材料科学与工程,2001,19(1):76-79
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[29]毛起炤,杨元霞,李卓球,沈大荣.外加剂对CFRC导电性能的影响.无机材料学报.1997,12(3):415-419
[30]孙明清,李卓球,毛起炤.碳纤维混凝土电热特性的研究.武汉工业大学学报,1997,19(2):72-74
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