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Steam ejector performance considering phase transition for multi-effect distillation with thermal vapour compression (MED-TVC) desalination system
Applied Energy ( IF 11.2 ) Pub Date : 2020-09-17 , DOI: 10.1016/j.apenergy.2020.115831
Chuang Wen , Liang Gong , Hongbing Ding , Yan Yang

The multi-effect distillation with thermal vapour compression (MED-TVC) desalination system is efficient to produce freshwater. The steam ejector performance is not fully understood as the phase transition has been ignored in many studies. The present work develops a two-phase condensing flow model to assess the steam ejector performance considering nonequilibrium condensation phenomena. The transition of the flow structure from an under-expanded flow to an over-expanded flow in the steam ejector is investigated in detail. We present that the maximum Mach number can reach 4.02 in the under-expanded flow, which is weakened to 2.88 in the over-expanded flow. The steam undergoes several expansion-compression processes in the steam ejector in the under-expanded flow, which induces the formation and evaporation of massive droplets. In the over-expanded flow, the steam is compressed and then expanded after leaving the primary nozzle and the condensation process is not observed in mixing and constant sections. The increasing suction chamber pressure significantly improves the entrainment ratio while leading to an increasing entropy loss coefficient. The entrainment ratio is improved from 0.25 for the under-expanded flow to 1.69 for the over-expanded flow, while the entropy loss increases from 0.081 for the under-expanded flow to 0.29 for the over-expanded flow. This indicates that the transition of the flow structure from an under-expanded flow to an over-expanded flow can entrain more steam from the last effect while causes more entropy losses in a steam ejector for the MED-TVC desalination system.



中文翻译:

考虑相变的蒸汽喷射器性能,用于采用热蒸汽压缩(MED-TVC)脱盐系统的多效蒸馏

带有热蒸气压缩(MED-TVC)脱盐系统的多效蒸馏可有效生产淡水。由于在许多研究中都忽略了相变,因此蒸汽喷射器的性能尚未完全被理解。本工作开发了一种两相冷凝流模型,以考虑非平衡冷凝现象来评估蒸汽喷射器的性能。详细研究了蒸汽喷射器中流动结构从膨胀不足流到膨胀过度的过渡。我们提出最大马赫数可以在膨胀不足的流量中达到4.02,而在过度膨胀的流量中则可以降低到2.88。蒸汽在欠喷射流中在蒸汽喷射器中经历了几个膨胀-压缩过程,这导致了大液滴的形成和蒸发。在过度膨胀的气流中,蒸汽离开主喷嘴后被压缩,然后膨胀,在混合段和恒定段中未观察到冷凝过程。吸入腔压力的增加显着改善了夹带率,同时导致熵损失系数增加。夹带率从膨胀不足流量的0.25提高到膨胀流量的1.69,而熵损失从膨胀不足流量的0.081增大到膨胀流量的0.29。这表明流动结构从膨胀不足的流动过渡到膨胀过度的流动可以从最后的作用带走更多的蒸汽,同时在MED-TVC脱盐系统的蒸汽喷射器中引起更多的熵损失。蒸汽在离开主喷嘴后被压缩然后膨胀,在混合段和恒定段中未观察到冷凝过程。吸入腔压力的增加显着改善了夹带率,同时导致熵损失系数增加。夹带率从膨胀不足流量的0.25提高到膨胀流量的1.69,而熵损失从膨胀不足流量的0.081增大到膨胀流量的0.29。这表明流动结构从膨胀不足的流动过渡到膨胀过度的流动可以从最后的作用带走更多的蒸汽,同时在MED-TVC脱盐系统的蒸汽喷射器中引起更多的熵损失。蒸汽在离开主喷嘴后被压缩然后膨胀,在混合段和恒定段中未观察到冷凝过程。吸入腔压力的增加显着改善了夹带率,同时导致熵损失系数增加。夹带率从膨胀不足流量的0.25提高到膨胀流量的1.69,而熵损失从膨胀不足流量的0.081增大到膨胀流量的0.29。这表明流动结构从膨胀不足的流动过渡到膨胀过度的流动可以从最后的作用带走更多的蒸汽,同时在MED-TVC脱盐系统的蒸汽喷射器中引起更多的熵损失。吸入腔压力的增加显着改善了夹带率,同时导致熵损失系数增加。夹带率从膨胀不足流量的0.25提高到膨胀流量的1.69,而熵损失从膨胀不足流量的0.081增大到膨胀流量的0.29。这表明流动结构从膨胀不足的流动过渡到膨胀过度的流动可以从最后的作用带走更多的蒸汽,同时在MED-TVC脱盐系统的蒸汽喷射器中引起更多的熵损失。吸入腔压力的增加显着改善了夹带率,同时导致熵损失系数增加。夹带率从膨胀不足流量的0.25提高到膨胀流量的1.69,而熵损失从膨胀不足流量的0.081增大到膨胀流量的0.29。这表明流动结构从膨胀不足的流动过渡到膨胀过度的流动可以从最后的作用带走更多的蒸汽,同时在MED-TVC脱盐系统的蒸汽喷射器中引起更多的熵损失。熵损失从膨胀不足的流量的0.081增加到膨胀过度的流量的0.29。这表明流动结构从膨胀不足的流动过渡到膨胀过度的流动可以从最后的作用带走更多的蒸汽,同时在MED-TVC脱盐系统的蒸汽喷射器中引起更多的熵损失。熵损失从膨胀不足的流量的0.081增加到膨胀过度的流量的0.29。这表明流动结构从膨胀不足的流动过渡到膨胀过度的流动可以从最后的作用带走更多的蒸汽,同时在MED-TVC脱盐系统的蒸汽喷射器中引起更多的熵损失。

更新日期:2020-09-18
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