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- 2018
超临界压力CO2竖直管内传热恶化抑制实验
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Abstract:
为抑制浮升力导致的超临界压力流体传热恶化，该文采用光管内插螺旋结构，增强管内湍流发展，提高流体管内换热性能。对超临界压力CO2在竖直光管、内插螺旋管内对流换热进行了实验研究，比较了热流密度、进口Re、流动方向等因素对换热的影响，讨论了内插螺旋结构对传热恶化现象的抑制作用。研究结果表明：由于浮升力传热恶化作用，流体在光管内向上流动壁温分布呈非线性变化趋势，壁温峰值区域随热流密度升高逐渐向入口区域移动；光管内插入螺旋结构可以有效抑制由浮升力产生的传热恶化作用，显著提高超临界压力CO2管内对流换热强度，内插螺旋结构管相对于光管可以提高对流换热系数约200%以上；超临界压力CO2在内插螺旋结构管内流动与换热时，在热流密度较高情况下，浮升力依然会对换热起到一定的恶化作用，流体向下流动时沿程对流换热系数略高于向上流动。
Abstract：The heat transfer can deteriorate with supercritical pressure fluids flowing in vertical tubes due to buoyancy. This study used a helical insert in the tube to change the flow structure and improve fluid heat transfer. Convection heat transfer of supercritical pressure CO2 in a vertical bare tube and with a helical insert was investigated experimentally to identify the effects of the heat flux, inlet Re, and flow direction on the heat transfer for both cases. The wall temperature distribution is nonlinear due to the buoyancy effect with the peak wall temperature gradually moving towards the entrance as the heat flux increases. The helical structure inserted into the bare tube effectively suppresses the heat transfer deterioration caused by the buoyancy effect and significantly increases the convective heat transfer the supercritical pressure CO2 in vertical tubes. The buoyancy effect can still reduce the heat transfer with supercritical pressure CO2 upward flow even with the helical insert structure for high heat fluxes.
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