Abstract:

An experimental investigation of vertical out-tube falling film heat transfer with different inlet spray densities of ammonia water mixture and inlet hot water temperatures was conducted. The falling film evaporator had a total height of 6000mm and the cycling working fluids were high concentration 60% and 50% ammonia water. We mainly studied the influence of spray density and inlet temperature of hot water on heat transfer coefficient，ammonia vapor amount and evaporation pressure. The experiment showed that heat transfer coefficient and ammonia vapor amount increased first and then decreased with increasing inlet spray density. The higher the hot water temperature，the higher the evaporation pressure. Heat transfer coefficient increased lineany with increasing hot water temperature. The experimental heat transfer coefficient of ammonia water solution was significantly higher than that of water reported in literature. For 50% water，optimum spray density was between 0.2200 and 0.2500 kg/(m·s)；for 60% ammonia water，optimum spray density was between 0.2600 and 0.2900 kg/(m·s). In this experiment，heat transfer performance of 60% ammonia water was better than 50% ammonia water.

摘要：

发生器和吸收器的传热性能是影响制冷机组和双工质发电机组做功效率的关键因素，为了提高中低温地热（余热）在热泵机组和地热双工质发电系统中的利用效率，本文选用50%和60%的氨水溶液作为循环工质，对约6 m长的竖管降膜蒸发器的传热特性进行实验研究，分别讨论喷淋密度和热水温度对垂直降膜蒸发器的传热系数、氨蒸气量和蒸发压力的影响。结果表明，降膜蒸发器的传热系数和氨蒸气量随喷淋密度的增加先增大后减小，传热系数和蒸发压力随着热源温度的增大而增加；50%和60%的氨水溶液喷淋密度最佳值分别在0.2200～0.2500 kg/(m·s)和0.2600～0.2900 kg/(m·s)；传热系数和热源温度呈线性关系。氨水溶液的实验传热系数明显高于现有文献中水的实验传热系数，通过两种不同浓度的溶液对比发现，60%的氨水溶液传热性能明显优于50%的氨水溶液。