低温多效蒸发海水淡化装置中流动阻力对传热温差的影响
Analysis of Flow Resistance on the Heat Transfer Temperature Difference in Low？？Temperature Multiple Effect Distillation Desalination Plant

为了确定低温多效蒸发(LT？？MED)海水淡化装置中流动阻力对传热温差的影响,基于考虑阻力损失的LT？？MED热力过程数学模型,计算了各项流动阻力引起的温差损失在装置各效蒸发/冷凝器中的分布,分析了蒸发/冷凝器数量、平均表观传热温差对阻力引起的传热温差损失的影响。结果表明:平均表观传热温差一定时,每效蒸发/冷凝器内各项阻力随蒸发/冷凝器序列数的增加先减小后增大,相应温差损失逐渐增大;随蒸发/冷凝器数量增加,管内凝结和除沫器流动阻力引起的温差损失所占比例均上升,而管束流动阻力呈下降趋势;装置中阻力引起的传热温差损失比例随蒸发/冷凝器数量增加、平均表观传热温差增大而增大,且相当可观,对装置性能的影响不可忽视。
A thermodynamic mathematical model of the low？？temperature multiple effect distillation (LT？？MED) desalination plant was developed to investigate the influence of the flow resistances on the heat transfer process. The distribution of various flow resistances was obtained. The effects of the number of evaporators/condensers and the average apparent heat transfer temperature difference (ΔTa) on the thermodynamic losses were analyzed. The results indicate that when ΔTa keeps constant, the flow resistances firstly descend and then rise as the sequence of evaporators/condensers increases. The corresponding temperature difference losses will keep growing. The proportions of the flow resistances across the demister and during the condensation process both get raised with the number of evaporators/condensers, and the flow resistance across the tube bundle goes down. The total temperature difference loss due to flow resistance increases with the number of evaporators/condensers and ΔTa. In addition, there is a considerable proportion of temperature difference loss due to the flow resistances, whose influence on the system performance should not be ignored