含水率与孔隙率对粉煤灰传热性能影响

Influence of moisture content and porosity on heat transfer performance of fly ash

以粉煤灰传热为研究对象,选取不同含水率和孔隙率粉煤灰试样,建立自主研制的两侧恒温差立方体实验台,对阜新市热电厂的漂珠型粉煤灰进行温度实验测试;根据半无限大物体导热原理,采用非稳态法对试样有效导热系数进行计算,研究含水率与孔隙率对粉煤灰传热性能的影响。引入Brinkman-Forchheimer扩展Darcy模型进行修正,考虑流体密度随温度变化,局部热平衡,建立二维粉煤灰传热数值模型,完成试验与模型互相验证。结果表明:孔隙率为0.26时,随着含水率增加,粉煤灰的有效导热系数由0.24增大至0.27,保温隔热性能变弱;孔隙率增大有利于粉煤灰保温隔热性能的提高,其有效导热系数由0.25降低至0.19;含水率变化对压实型粉煤灰内部热传输方式影响不大,热传输方式为热传导;疏松型粉煤灰热传输方式以导热为主,有轻微对流换热迹象,粉煤灰内传热应考虑孔隙率变化对其影响。

Heat transfer of fly ash is studied. Fly ash samples of different moisture content and porosity is selected. Independently developed experiment table of constant temperature difference at two sides is established. Experimental temperature measurement of floating bead fly ash from Fuxin thermal power plant is carried out. According to heat conduction principle of a half infinite object, samples＇ effective thermal conductivity is calculated using unsteady state method. Influence of moisture content and porosity on heat transfer performance of fly ash is studied. The Brinkman-Forchheimer-extended Darey model is introduced for correction. The variation of fluid density with temperature is considered. Local heat balance is considered. Two-dimension fly ash heat transfer numerical model is established. Experiment and modal are verified by each other. The results shows that： when porosity is 0.26, with the increase of moisture content, effective thermal conductivity increases from 0.24 to 0.27, heat insulation performance is weakened; increase of porosity is good for performance of fly ash, effective thermal conductivity decreases from 0.25 to 0.19; influence of porosity variation on heat transfer pattern of compacted fly ash is small, heat transfer pattern is heat conduction; heat transfer patterns of loosened fly ash are mainly heat conduction and slightly heat convection. Porosity variation should be considered when heat transfer in fly ash is studied.