扭曲扁管在蒸发器中的运行特性实验研究

Experimental investigation on running characteristics of twisted tube in evaporator

对扭曲扁管与普通直管在蒸发器工况下的传热、流动阻力和污垢特性进行了对比实验研究。实验采用45 mm×3 mm的普通直管和由同种直管制成的扭曲扁管,扭曲扁管导程St分别为450,550,650 mm。通过实验,研究了Re和St对各特性的影响。结果表明,在实验Re数条件下,管壁污垢热阻增长呈渐近线型特性,扭曲扁管渐近污垢热阻为直管的0.15—0.29倍,流动阻力系数为直管的1.48—1.63倍。实验还得出,实验扭曲扁管的强化传热作用随着St减小而增大,扭曲扁管的传热系数在洁净状态下为直管的1.29—1.51倍,在运行8 h后,由于扭曲扁管具有较强的抑垢作用,传热系数趋近为直管的1.96—2.79倍。

The comparable experimental investigation on the heat-exchange,resistance and fouling characteristics of normal straight tubes and twisted tubes in evaporator was carried out.The normal tube size is 45 mm×3 mm,the twisted tubes were consisted of the normal tubes,and the screw pitch St was 450,550 and 650 mm.The effect of Re and St on characteristics was studied in the experiment.The results show that the fouling resistance is asymptotic within the experimental region;compared with the normal tubes,the fouling resistance of the twisted tubes is about 0.15-0.29 times and the flow resistance coefficient is about 1.48-1.63 times;the effect of enhanced heat exchange increases with the decrease of the screw pitch St,the heat transfer coefficient of the twisted tube is 1.29-1.51 times that of the normal tubes when tube is clean,and tends to 1.96-2.79 times as it runs 8 h because of the effect of anti-fouling of twisted tube.