Heat transfer studies in a climbing film evaporator: Part I. Heat transfer from condensing steam to boiling water

Hard water was concentrated using steam heating in a single tube climbing film evaporator, of length 9 ft. and external diameter 1 inch. The heat flux Q/A in BTU/hr. sq. ft. was found to be related to the feed rate of the water M lb./hr. and its temperature T_i °F by the equation Q/A = ψ M^0.6 + 90.3 (T_b – T_i) C_p where ψ is a graphically read function of the temperature difference driving force between the condensing steam and the boiling water. The data fit the above equation with a standard deviation of 2.6%. The empirically derived equation for heat flux was also found to represent the data for other aqueous solutions with reasonable accuracy.     

Heat transfer in condensation and boiling in a tubular film evaporator

The results of a study of heat transfer in condensation and boiling in a tubular evaporator with smooth and rough surfaces under the gravity flow of a water film are presented. Relationships are derived for calculating a heat-transfer coefficient, and the effect of helical roughness on heat transfer is revealed.     

Heat and mass transfer in the evaporating film of a molecular evaporator

The hydrodynamic conditions in the wiped-film on the evaporating cylinder of a molecular evaporator have a considerable effect on the distillation output and composition of outlet streams from the evaporator. In this study, selected parameters are investigated in the laminar and turbulent regimes in the film, depending on the evaporator’s liquid load and temperature. Results show that in the case of a turbulent film without concentration and temperature gradients at the same temperature of the evaporating cylinder surface, a higher portion of the feed is evaporated at a lower content of the more volatile component in the distillate. The model studied shows that there are only small differences in the relative volatility as a measure of separation efficiency in the turbulent or laminar film on the evaporating cylinder. The qualitative agreement between experimental results and the results from the model proposed shows that the model describes well the phenomena that occur within the distillation space of the molecular evaporator.     

3万t/a镍升膜蒸发装置的改造

我厂有两套升膜蒸发装置,其中一套升膜蒸发器的加热室和蒸发室材质为不锈钢,设计产能为3万t/a ;另一套升膜蒸发器的加热室材质为镍,蒸发室上部材质为不锈钢,底部为不锈钢衬镍,设计产能为2万t/a 。两套装置的进料和成品冷却共用一套系统。生产出来的成品主要通过两个换热器降温冷     

Heat transfer in a rotating disk evaporator

Experiments were carried out in a rotating disk evaporator with and without a wiper on the evaporation side. The tests were carried out with copper and with monel disks. Overall heat transfer coefficients were obtained directly from the measurements. In addition, evaporation heat transfer coefficients were calculated and the results were correlated. The effectiveness of the wiped film evaporator was clearly manifested in the larger heat transfer coefficients that were obtained.     

Heat transfer in turbulent flow on a horizontal tube falling film evaporator. a theoretical approach

A simplified theoretical approach for the prediction of evaporation (no-nucleate boiling) heat transfer coefficient in a horizontal tube falling film is proposed. The correlation is derived from an analysis of the thermal boundary layer under the assumption of turbulent flow regime and taking into account the thermal developing region. A diagram to evaluate $\text{h}$(μ²/ρ²gk³)^{$\text{1}\text{3}$} as a function of Re and Pr is proposed.A regression analysis of the numerical computations allows us to provide a dimensionless formula $\text{h}$(μ²/ρ²/gk³)^{$\text{1}\text{3}$} = 0.046 Re^0.18Pr^0.47 valid in the ranges Re = 1500–5000 and Pr = 1–5.     

升膜蒸发器在天然碱制烧碱行业中的应用

首次将升膜蒸发器应用于天然碱制烧碱行业。介绍了该设备的工艺设计参数及结构设计方案。工厂实际应用表明 ,节能效果良好     

板式升膜蒸发器在离子膜烧碱中的应用

介绍了升膜蒸发的原理及影响传热量的因素。重点介绍了板式升膜蒸发器在离子膜烧碱蒸发系统中的应用情况及蒸发装置的特点。     

螺旋扁管干式蒸发器的传热性能

对螺旋扁管干式蒸发器（TDE）和常规折流板干式蒸发器（BDE）的传热性能进行实验研究。研究了蒸发温度（T_e）、冷凝温度（T_c）、管外壳程流体Reynolds数（Re_o）和热通量（q_i）对传热性能的影响。研究表明,随着T_e、Re_o和q_i的增大,TDE和BDE的传热性能均提高。随着T_c的增大,TDE和BDE的传热性能降低。对装配TDE和BDE的风冷热泵分别进行了测试,测试表明,在相同制冷工况下,TDE的总传热系数比BDE提高了36.3%,风冷热泵的制冷性能系数（COP）相应地提高了6.0%;在相同制热工况下,TDE的总传热系数比BDE提高了41.7%,风冷热泵的制热COP值相应地提高了15.8%;说明TDE可应用于风冷热泵,且其性能优于BDE。     

高分子中空纤维蒸发器传热过程分析

蒸发器广泛应用于化工、食品等行业,传统的金属管蒸发器由于其耐酸碱腐蚀性差、表面易结垢等弱点,一定程度上限制了其应用范围,而具有优良性能的高分子中空纤维管可有效解决这些问题,具有很好的应用前景。采用自制的高分子改性中空纤维管,制备出非金属换热器,并进行了蒸发传热实验。结果表明,高分子中空纤维蒸发器的性能与料液温度有密切关系,沸腾进料时蒸发器的传热系数、产水量和热量利用率均高于低温进料;传热热阻主要集中在管外蒸汽加热侧和管壁的导热性能,当沸腾进料时管壁热阻占总传热热阻的66%以上,而管内蒸发侧传热热阻所占比重较低,均低于15.3%,且随着料液流速的增大而降低到5%以下;随着料液温度的降低,蒸发过程的传热系数、能量利用效率以及产水量均显著下降。     

水平管降膜蒸发器传热系数空间分布

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。     

关于提高降膜蒸发器镍管使用寿命的探讨

通过计算镍管的强度极限及失稳破坏条件，分析了片碱引进工程进口设备降膜蒸发器出现中心镍管过早损坏的原因，提出以国产镍管替换进口材料以及提高降膜蒸发器中心镍管使用寿命的措施。     

RTD studies in a falling film graphite evaporator with internal spiral fins: Influence of the geometry

A hydrodynamic study of a new graphite evaporator has been performed. In this exchanger the fluid flows as a thin film on a spirally wound fin which forms a spiral staircase inside a tube. The slope θ_m of the spirally wound fin is modifiable. The residence time distribution (RTD) of the film was measured for different fin slopes θ_m and several film flowrates m_f. The flow pattern was then modelled thanks to the DTS software as a cascade of perfect mixed cells and the mean residence time τ_m was calculated. The evolution of τ_m as a function of θ_m and m_f is accurately represented by a power law relation.     

Modelling of flow in a wiped film evaporator

In a wiped film apparatus, the hydrodynamic conditions of the flow have a direct effect on the film thickness and on the residence time of the molecules and thus on the effectiveness of mass and heat transfer. Measurements of the residence time distribution (RTD), for different stirring velocities, allowed to propose a model for the flow as a series of perfectly mixed cells in parallel with a series of perfectly mixed cells exchanging mass with a dead zone.     

Heat and mass transfer in non-isothermal absorption of gases in falling liquid films Part II: Theoretical description and numerical calculation of turbulent falling film heat and mass transfer

A mixing length turbulence model is presented, which was used for the numerical calculation of turbulent falling film heat and mass transfer coefficients. Numerous proposals of different authors for the prediction of eddy transport coefficients are discussed. Good agreement between calculated heat and mass transport coefficients and experimental data was achieved by the combination of Hubbard, Mills and Chung's proposal for the calculation of eddy transport near the film surface with a modified form of van Driest's, the latter being for the eddy transport near the solid wall. Furthermore, the dependence of the turbulent falling film heat transfer coefficients on the Prandtl number is discussed. It is shown that, besides the Prandtl number, a further dimensionless group must be considered in order to describe the effect of liquid properties on heat transfer.     

带平板蒸发器的紧凑型三维脉动热管传热特性

设计制作了带平板蒸发器的紧凑型三维脉动热管,蒸发器的铜板尺寸为40 mm×40 mm×3.5 mm,内部含有平行圆通道,通道内径为2 mm;热管的冷凝段则由内、外径分别为2 mm和3 mm的铜毛细管构成。以乙醇和去离子水为工质,对该脉动热管在不同放置方式（竖直、水平和侧放）和体积充液率（20%～70%）下的启动和传热性能进行了比较研究。实验结果表明,充液率介于30%～70%之间时脉动热管大都能正常启动且稳定运行,表现出优异的传热性能。热管的启动温度随着充液率的提高而升高,启动温度由低到高排列顺序为竖直、侧躺和水平放置。竖直放置时该热管的传热性能优于水平放置,且两种放置情况下的传热性能总体上均随着充液率的减小而提高。相比于乙醇,使用去离子水时该脉动热管拥有更低的蒸发段平均温度,显示出更好的传热性能和均温性。     

电场强化微槽道结构毛细芯蒸发器的传热特性

该实验以R141b作为工质,采用圆柱形电极,在不同运行压力条件下,实验研究了电场强度对微槽道结构换热表面蒸发/沸腾传热特性的影响。实验结果表明：随着电场强度的增加,传热强化效果越明显;运行压力对强化换热的效果具有重要的影响,在施加相同电场强度的条件下,不同运行压力的强化传热效果明显不同,传热系数最大可强化为未施加电场条件下传热系数的1.28倍。     

Heat transfer mechanisms in gas fluidized beds. Part 3: Heat transfer in circulating fluidized beds

Part 1 of this contribution reported on the effects of system properties on heat transfer between heating or cooling surfaces and bubbling fluidized beds. This investigation produced four correlations which define the respective maximum heat transfer. Part 2 of this study suggests that the heat transfer between exchanger surfaces and bubbling fluidized beds depends on superficial gas velocity, expressed as dimensionless excess gas velocity. The present paper shows that heat transfer coefficients in circulating fluidized beds can be predicted by evaluation of a state diagram, which combines three dimensionless groups: Nusselt number, Archimedes number and a dimensionless pressure gradient. A comparison of coal combustion experiments with own cold model measurements indicates that the radiative component of heat transfer coefficients is only evident at very low dimensionless pressure gradients.     

伞板式降膜蒸发器传热性能的实验研究

针对专利设备伞板式蒸发器,建立了一套实验装置。以水和5%~40%的碳酸钾水溶液为工作介质,对实验装置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,证明了该结构的蒸发器在小流量情况下液膜不易破裂的特性。     

伞板式降膜蒸发器传热性能研究

对伞板式降膜蒸发器进行了合理的结构设计,并对此蒸发器的传热性能进行了实验研究。结果表明,伞板式降膜蒸发器在低温差下仍能保持较高的传热系数,得出了伞板降膜蒸发侧无因次传热系数的实验关联式并与竖直光滑管的传热性能进行了比较。同时对伞板式蒸发器进行了液膜破裂的实验研究,得出了液膜破裂条件的实验关联式并与竖直管的破断条件进行了比较,从而得出了此蒸发器在小流量下,液膜分布均匀不易破裂等特性。