高效宽负荷率超超临界锅炉垂直管圈水冷壁在低质量流速下的传热特性

Heat-transfer Performance of Vertical Water Wall in an Ultra-supercritical Pressure Boiler with High Efficiency and Wide Regulation Load at Low Mass Flux

在压力p=21~29.8 MPa、质量流速G=600~1 100kg/(m^2·s)、热负荷q=330~793kW/m^2工况范围内,对低质量流速优化内螺纹管的传热特性进行了实验研究,并根据实验数据得到了近临界压力区和超临界压力区的传热实验关联式.结果表明:在近临界压力区,亚临界部分的传热特性好于超临界部分的传热特性,质量流速增大能推迟传热恶化,热负荷增大则使传热恶化提前发生,内螺纹管抑制膜态沸腾(DNB)的能力有所减弱;在超临界压力区,压力越低,大比热容区内强化传热作用越显著,在其他条件一定时,超临界水的热物性变化对管内传热的作用由质量流速和热负荷共同决定;质量流速不变,继续增大热负荷,大比热容区内的传热将由强化转变为恶化.

Heat-transfer performance of an internally ribbed tube was experimentally studied at low mass flux under the condition of p=21-29.8 MPa, G=600-1 100 kg/（m2 ~ s） and q=330-793 kW/m2, follow- ing which relative heat-transfer correlations were derived by sorting out the experimental data in the near and super critical pressure region. Results show that in the near critical pressure region, where the capaci- ty to restrain the DNB of rifled tube is weakened, heat-transfer performance in the subcritical part behaves better than that in the supercritical part~ heat-transfer deterioration can be delayed by increasing the mass flux and lowering the heat flux. In the supercritical pressure region, the lower the pressure is, the stronger the heat-transfer enhancement would be in the large specific heat region~ keeping all other parameters constant, the influence of thermal physical properties of supereritical water on the heat-transfer process would be significantly affected by both the mass flux and heat flux; continuously increasing the heat flux while keeping the mass flux unchanged, heat-transfer reduction would take the place of heat-transfer improvement in the large specific heat region.