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在降膜蒸发器设计过程中,现有的多组分降膜蒸发传热计算方法未考虑传质的作用,其计算结果与实际工程设计相比存在较大的偏差。文中探讨了多组分降膜蒸发传热机制,充分考虑降膜蒸发的传热传质耦合作用,提出了适用于多组分降膜蒸发传热计算的关联式。针对多组分物料物性随蒸发浓缩发生变化的特点,建立了降膜蒸发器蒸发传热的分段设计方法。完成了丙二醇水溶液降膜蒸发不同单元数的分段传热计算,计算结果表明:分段计算与不分段计算的管内传热系数与总传热系数的偏差率分别为23%—30%及12%—16%。随着计算单元数的增加,降膜传热系数偏差率的变化会逐渐减小,设计计算过程中可以根据精度要求确定最佳计算单元数。此研究工作为降膜蒸发器的工艺设计提供了参考。 相似文献
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《化学与生物工程》2018,(11)
采用降膜蒸发器处理含盐污水,考察了进料量、蒸发温度和传热温差等对水平管降膜蒸发器和垂直管降膜蒸发器传热系数的影响。结果表明,随着进料量的增加,水平管降膜蒸发器的传热系数呈先增大后减小的趋势,在进料量为2t·h~(-1)左右时,传热系数最大,约为2.48kW·m~(-2)·℃~(-1);随着蒸发温度的升高,两种降膜蒸发器的传热系数呈增大的趋势,但是在相同条件下,处理的含盐污水浓度越高,传热系数越小;另外,在同样的蒸发温度下,垂直管降膜蒸发器的传热系数小于水平管降膜蒸发器的,且随着蒸发温度的升高,两种降膜蒸发器的传热系数差别越明显;随着传热温差的增大,两种降膜蒸发器的传热系数逐渐减小。 相似文献
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利用传统的多管排列式蒸发器对高黏度、易结垢的混合物进行蒸发,容易造成布液器堵塞,且结垢后的传热管难以清理。因此根据物料特性,本文设计了一种新型的降膜蒸发器,采用大降液孔加倾斜环板进行布膜,利用内径较大的锥筒作为传热壁面,并以粗甲酯作为试验工质对蒸发器的降膜蒸发传热系数随蒸发器筒体半锥度角、液膜流动雷诺数以及输入热通量之间的关系进行了试验研究。结果表明:该型蒸发器对于上述工质具有较好的适用性,蒸发系统能够在保持较高的传热系数的条件下,连续运行而不发生堵塞;蒸发器筒体锥度角有效地强化了降膜蒸发传热过程,而较大的热通量及进料流量在一定程度上却不利于蒸发传热。最后建立了降膜蒸发传热系数随蒸发器筒体半锥角和流动准数之间的经验关联式。 相似文献
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用于浓碱液蒸发的旋转薄膜蒸发器 总被引:4,自引:2,他引:2
介绍了一种用于将烧碱溶液从NaOH含量30%(Wt)进一步浓缩蒸发的新型高效蒸发器。这种蒸发器具有很高的传热系数和蒸发强度,只需使用低压加热蒸汽(130℃左右)供热,大大减缓了碱液对设备的腐蚀,从而可用普通奥氏体不锈钢代替价值昂贵的镍材来制造浓效蒸发器。通过工厂使用实例的介绍和分析,说明这种蒸发器不但总传热系数很高,而且其热阻主要不是液膜或盐垢,而是来自导热系数较低的不锈钢材料。 相似文献
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污水源热泵供热是城市污水热能利用的重要途径。为提高原生污水源热泵机组回收城市污水余热的能效,本文提出反冲洗降膜式污水源热泵机组供热系统,建立了污水源热泵机组供热性能实验系统,可与满液式污水热泵机组的供热性能进行比较研究,为解决直接换热式污水源热泵系统遇到的原生污水堵塞问题,本文还设计了污水反冲洗系统,并测试了反冲洗频率和时长对机组换热性能的影响。实验结果表明:降膜式污水蒸发器的平均传热系数要显著高于满液式污水蒸发器,降膜式污水蒸发器的平均传热系数比满液式污水蒸发器高了60.17%;在文中工况下,利用降膜式污水蒸发器的污水源热泵机组的供热性能系数要显著高于满液式污水蒸发器的污水源热泵机组,降膜式污水源热泵机组的供热性能系数比满液式污水蒸发器高了9.52%;污水反冲洗方式可以有效解决直接换热式原生污水源热泵系统的堵塞问题,在使用反冲洗模式时,反冲洗的时间间隔应尽可能短,以确保平均传热系数不会减小。因此,利用反冲洗降膜式蒸发器的污水源热泵机组可以更加高效地利用污水热能。 相似文献
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为了得到水平管降膜蒸发器传热系数,建立了水平管降膜蒸发传热实验台。通过对实验结果的归纳,分析了水平管降膜蒸发器总传热系数随顶排管喷淋密度、蒸发温度的变化规律,并给出了总传热系数在水平管降膜蒸发器内部空间的分布。结果表明,总传热系数随喷淋密度、蒸发温度的增大而增大。在空间分布上,传热系数沿管长方向受凝结过程的影响前5 m先增大,后3 m逐渐减小;在垂直方向由上向下逐渐减小。另外传热系数随管排数的增加而降低,并且当喷淋密度较小时,总传热系数下降的趋势更明显。 相似文献
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水平管降膜蒸发器和垂直管降膜蒸发器用于油田废水处理的比较 总被引:1,自引:0,他引:1
针对油田废水的蒸发浓缩,计算和对比了水平管和垂直管降膜蒸发器的特性,考查进料流量和温度都对两种降膜蒸发器传热系数的影响程度。结果表明,垂直管降膜蒸发器要差于水平管降膜蒸发器具有的传热性能。而且水平管降膜蒸发器具有处理大流量、高温度废水的性能,当然也需要在汽液分离方面进行改善以获得理想的蒸发效果。 相似文献
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本文以水和5%~40%的碳酸钾溶液为工作介质,对伞板式降膜蒸发器的传热性能进行了实验研究,分析了影响伞板式降膜蒸发器传热的主要因素,并且得到了伞板降膜蒸发侧无因次传热系数的实验关联式。通过对液膜破裂的实验研究,证明了此结构的蒸发器在小流量情况下液膜不易破裂的特性。 相似文献
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Mathematical modeling of the multiple effect evaporation (MEE) desalination process has been carried out to determine the effects of the important design and operating variables on the parameters controlling the cost of producing fresh water. The model assumes the practical case of constant heat transfer areas for both the evaporators and feed preheaters in all effects. In addition, the model considered the impact of the vapor leak in the venting system, the variation in thermodynamic losses from one effect to another, the dependence of the physical properties of water on salinity and temperature, and the influence of noncondensable gases on the heat transfer coefficients in the evaporators and the feed preheaters. The modified fixed-point iterative procedure is used to solve the large number of highly nonlinear equations describing the MEE desalting system. The algorithm consists of 10 calculation blocks and 6 logical blocks. The algorithm is implemented using L-A-S computer aided language. Results show that the heat transfer coefficients increase with the boiling temperature. Also, the heat transfer coefficient in the evaporator is always higher than that in the feed preheater at the same boiling temperature. The plant thermal performance ratio is nearly independent of the top brine temperature and strongly related to the number of effects. The specific heat transfer area increases by raising the number of effects and reducing the top brine temperature. The effect of the top brine temperature on the specific heat transfer area is more pronounced with a larger number of effects. The required specific heat transfer areas at a top brine temperature of 100°C are 30.3% and 26% of that required at 60°C when the number of effects are 6 and 12, respectively. The specific flow rate of cooling water is nearly constant at different values of top brine temperature and tapers off at a high rate as the number of effects is increased. Two correlations are developed to relate the heat transfer coefficients in the preheater and the evaporator to the boiling temperature. Design correlations are also developed to describe variations in the plant thermal performance, the specific heat transfer area, and the specific flow rate of cooling water in terms of the top brine temperature and the number of effects. 相似文献
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Infrared thermography of brazed plate heat exchangers for evaporators and condensers recently was used to quantify maldistribution. With the knowledge of the secondary fluids heat transfer coefficient and a given secondary fluids distribution, the local heat transfer coefficient of the primary fluid (refrigerant) and its distribution to the channels can be calculated. A sensitivity analysis shows ± 10 % difference of the surface temperature to the wall center temperature at the expected ratios of heat transfer coefficients. The method is presented in this paper using an exemplary infrared picture. 相似文献
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The objective of this work was to investigate nucleate pool boiling heat transfer performance and mechanism of R134a and R142b on a twisted tube with machine processed porous surface (T-MPPS tube) as well as to determine its potential application to flooded refrigerant evaporators. In the experimental range, the boiling heat transfer coefficients of R134a on a T-MPPS tube were 1.8-2.0 times larger than those of R134a on a plain tube. In addition, the developed experimental correlations verified that the predictions of the heat transfer coefficients of boiling R134a and R142bon a T-MPPS tube at the experimental conditions were considerably accurate. 相似文献
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Georges Belfort 《Desalination》1979,28(3):295-310
Laboratory and pilot scale tests were carried out to obtain an efficient liquid distributor that could be easily manufactured and installed on thin film vertical tube evaporators.Experimental results compare screw-type with cone-type distributors and show that the former ones guarantee an adequate loss in head and a proper distribution of the feed on the tube periphery and among tubes in a bundle.Heat transfer coefficients for smooth tubes are appreciably higher with this type of distributor than with a cone-type one. Liquid pressure drops and overall heat transfer coefficients are in fair agreement with predictions from mathematical models. 相似文献
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热泵在蒸发器中,尤其是在多效降膜式蒸发器中作为节能装置频频出现,使用热泵后是否能达到预期效果,与热泵的设计、蒸发器热量衡算、换热面积的确定、制造安装及蒸发参数的控制有关.文中仅以RNJM01-1000型单效降膜式蒸发器在液态奶生产中的应用为例进行阐述. 相似文献
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In recent years, vertical tube falling film evaporators have been widely used in desalination industries. In this paper mathematical modeling of a multiple effect evaporators (MEE) system has been carried out for brackish water desalination. The system includes a set of forward feed vertical tube evaporators with thermal vapor compression (TVC) and a condenser. Modeling has led to calculation of several parameters such as overall heat transfer coefficients, entrainment ratio and recovery of the process which is restricted by scale formation. A scaling prediction chemical model has been employed to calculate the allowable rate of recovery for prevention of scale formation. Physical properties of streams have been assumed as functions of temperature and salinity. A code has been developed for simulation of the process based on mass and energy balance equations. Results showed maximum allowable recovery of 74% for the treated brackish water sample with total dissolved solid (TDS) of 14,761 ppm is achievable. Dealing with mentioned sample under specified set of conditions, it was concluded that changing the number of effects from 3 to 8, enhances gained output ratio (GOR) value from 3.8 to 7.5. However, specific heat transfer surface is increased from 215 to 1052. 相似文献