倾斜内螺纹管中超临界水的传热和流动阻力特性研究

Heat Transfer and Resistance Characteristics of Water in an Inclined Internally Ribbed Tube Under Supercritical Pressure Conditions

为探究超(超)临界锅炉机组内螺纹管螺旋管圈型水冷壁的传热和流动阻力特性,在外径35 mm、壁厚7.75 mm的六头内螺纹管中进行了实验研究,实验参数为压力22.5~28 MPa,热流密度300~500 kW/m 2,质量流速600~1000 kg/(m 2·s),内螺纹管倾斜角度5°~45°。研究了倾斜角度和质量流速对超临界压力下水的传热和流动阻力特性的影响,用5个传热关联式对传热实验数据进行了评估,拟合了超临界水的对流传热和摩擦阻力系数实验关联式。结果表明:内螺纹管内壁面温度和水的传热系数几乎不随倾斜角度的变化而改变;随着质量流速的增加,内壁面温度减小,传热系数增大;随着倾斜角度的增大,水的摩擦阻力系数和摩擦阻力压力降均显著增大;随着质量流速的增加,摩擦阻力系数减小,不同压力下摩擦阻力压力降呈现不同的变化规律;拟合的传热关联式与实验数据吻合良好,95.8%的拟合值与实验值偏差在±20%之内;拟合的摩擦阻力系数关联式与实验数据吻合良好,拟临界点前后分别有84.2%和88.2%的拟合值与实验值偏差在±20%之内。

The heat transfer and resistance characteristics of spiral wall with internal rib in supercritical(ultra-supercritical)boiler at different inclination angles are explored,and experiment is carried out in aΦ35 mm×7.75 mm six-head internally ribbed tube.Experimental parameters are as follows:pressure from 22.5 to 28 MPa,heat flux from 300 to 500 kW/m 2,mass flux from 600 to 1000 kg/(m 2·s),inclination angles of the internally ribbed tube from 5°to 45°.The effects of inclination angles and mass flux on the heat transfer and resistance characteristics of the supercritical water are discussed according to the experimental results,five heat transfer correlations are used to evaluate the test data,and a convective heat transfer correlation and a friction resistance coefficient correlation are developed.Results show that the inner wall temperature and the heat transfer coefficient are almost unchanged with the change of the inclination angles.With the increase of the mass flux,the inner wall temperature decreases and the heat transfer coefficient increases.With the increase of the inclination angles,the water friction resistance coefficient and the friction resistance pressure drop increase significantly.And with the increase of the mass flux,the friction resistance coefficient decreases and the friction resistance pressure drop varies under different pressures.The developed heat transfer correlation is in good agreement with the experimental data,and about 95.8%of the calculated values are within the error of±20%from the experimental values.The developed friction resistance coefficient correlation is in good agreement with the experimental data,about 84.2%of the calculated points before the pseudo-critical point and 88.2%of the calculated points after the pseudo-critical point of have deviations within±20%from the experimental data.