Experimental analysis of bubble mode in a plate-type absorber

An experimental analysis of ammonia-water absorption was performed in a plate-type absorber. The flow of water and ammonia gas was performed in the bubble mode. The experiments were made to examine the effects of solution flow rate and gas flow rate on the performance of the absorber. It was found that the increase of solution flow rate rarely affected the mass transfer, but improved the heat transfer. As the gas flow rate increased, slugging occurred in the bubble mode and influenced the thermal boundary layer. Finally, the results were converted into dimensionless numbers to elucidate physical phenomena and plotted as Sherwood number versus Reynolds number for mass transfer performance and Nusselt number versus Reynolds number for heat transfer performance.     

EXPERIMENTAL STUDY FOR HEAT AND MASS TRANSFER IN WAVY FILM ABSORPTION WITH THE PRESENCE OF NON-ABSORBABLE GASES

Experimental measurements for the heat and mass transfer in laminar wavy film absorption with the presence of non-absorbables are presented. Water vapor was absorbed into a falling film of aqueous lithium chloride solution on a vertical tube with the air present in the gas phase acting as the non-absorbable whose concentration was accurately detected by a mass spectrometer gas analyzer. Although the depressing effect of the air on the absorption rate was much more significant in the low air concentration range, the absorption reduction rate with increasing air concentration was found to be lower than that reported previously. The reduction was found to be continuous even up to 30% of air content. Besides the non-absorbables, the effects of other operational parameters such as solution flow rate, inlet solution temperature, inlet solution concentration, absorber wall temperature, absorber water vapor pressure, and effective contact length on the absorption rate were also tested. These effects were shown to follow trends similar to those predicted by a numerical solution for smooth film absorption. The heat and mass transfer coefficients were correlated by using Reynolds number, Prandtl number, Schmidt number, capillary-buoyancy coefficient and air concentration.     

Experimental investigation on gas–liquid flow,heat and mass transfer characteristics in a dual-contact-flow absorption tower

As a kind of chemical reactor, the dual-contact-flow absorption tower has been widely used for SO₂ absorption in recent years. However, studies on heat transfer characteristics of the absorber have been rarely carried out. There is also lack of an integrated partition map of flow pattern in the dual-contact-flow absorption tower. In this paper, the gas–liquid flow, heat and mass transfer characteristics in the dual-contact-flow absorption tower have been experimentally investigated. Direct observation, probability density function (PDF) and power spectral density function (PSD) methods are comparatively adopted in the flow pattern analysis. The partition map of flow pattern in the dual-contact-flow absorption tower is obtained through integrating a large quantity of experimental data. In addition, empirical formulas of both heat and mass transfer performances have been developed. Application of empirical formulas has also been stated. The research results obtained in the present study can provide guidance for estimating the practical application performance.     

发生器、吸收器传质效率对高温吸收式热泵性能的影响

研究分析了水／二甘醇高温吸收式热泵的发生器、吸收器传质过程及效率对系统性能的影响。当发生器、吸收器传质效率提高,系统性能系数COP、Yong效率η及Yong指标I均增大,而溶液循环比FR减小,通过回归分析,获得了评价热泵性能的关联式。     

Four stages of the simultaneous mass and heat transfer during bubble formation and rise in a bubbly absorber

We studied nonisothermal absorption of a solvable gas from growing at an orifice and rising bubble when the concentration level of the absorbate in the absorbent is finite (finite dilution of absorbate approximation). It is shown that simultaneous heat and mass transfer at all stages of bubble growth and rise in a bubbly absorber can be described by a system of generalized equations of nonstationary convective diffusion and energy balance. Solutions of diffusion and energy balance equations are obtained in the exact analytical form. Coupled thermal effects during absorption and absorbate concentration level effect on the rate of mass transfer are investigated. It is found that the rate of mass transfer between a bubble and a fluid increases with the increase of the absorbate concentration level. The suggested approach is valid for high Peclet, Prandtl and Schmidt numbers. It is shown that for the positive dimensionless heat of absorption K thermal effects cause the increase of the mass transfer rate in comparison with the isothermal case. On the contrary, for negative K thermal effects cause the decrease of the mass transfer rate in comparison with the isothermal case. The latter effect becomes more pronounced with the increase of the concentration level of the absorbate in the absorbent. Theoretical results are consistent with the experiments of Kang et al. (Int. J. Refrigeration 25 (2002) 127) for absorption from ammonia gas bubbles rising in water and aqueous ammonia solutions.     

水平管降膜吸收局部传热传质特性的数值模拟

为分析滴状和柱状流型下纯水蒸气水平管外降膜吸收过程的局部传热传质特性,建立非稳态数值模型考虑吸收过程中降膜区和管间区内液相的实际流动特征及气液两相的传质,同时对多管排区域采用实际边界条件,且考虑气液两相的传热过程。溶液的液膜Reynolds数范围为11~38。结果表明,与文献实验对比,相同流量下溶液出口浓度和温度的平均相对误差在2%以内;滴状和柱状流型下,降膜区溶液的平均浓度和温度均迅速下降,管间区先上升后下降,降膜区溶液的局部吸收速率分别约为管间区的10倍和7倍;柱状流型下降膜区的吸收速率明显小于滴状流型,管间区相差很小;吸收达到稳定后,滴状流型下溶液的平均浓度和温度变化均大于柱状流型,四排管降膜区溶液的浓度变化量依次增大,温度变化量依次减小。     

R134a/R23-DMF溶液气泡泵输送性能实验

搭建了气泡泵输送性能实验装置,对提升管管径为6、8、12 mm的气泡泵输送不同R134a/R23-DMF浓度溶液的性能进行实验研究。结果表明,在相同制冷剂浓度情况下,三种管径气泡泵的气相流量随着输入功率的增加均呈线性增加趋势,液气比随着气相流量的增加均呈现反向趋势,发生温度随着输入功率增加而线性升高,而输入功率对于系统压力的影响较小。在不同制冷剂浓度情况下,R134a/R23浓度对液气比的影响不明显,但对系统压力影响很大,R134a/R23浓度的增加使得发生温度有微小的升高。8 mm管径气泡泵液气比和稀溶液流量变化幅度居中,而气相流量变化范围最宽,发生温度最低,比较适合用于扩散吸收制冷系统。这些实验结果对扩散吸收制冷系统的气泡泵设计具有重要参考价值。     

膜反转板式降膜吸收过程

结合板式降膜技术与膜反转技术的优势,提出了一种新型膜反转板式降膜吸收器。设计并建立了膜反转板式降膜吸收试验台,在试验台上完成了不同吸收压力、溶液流量、进口温度、冷却条件等对膜反转板式降膜吸收器传热传质性能影响的系列实验研究,得到该吸收器的传热传质性能。为膜反转板式降膜热质传递设备的科学研究、工程设计和实际应用提供了一定依据,也为进一步开发高效紧凑的热质传递元件及设备提供了一些方法和思路。     

SIMULTANEOUS ABSORPTION OF H2S AND CO2 INTO A SOLUTION OF SODIUM CARBONATE

The simultaneous absorption of H₂S and CO₂ has been studied both experimentally and theoretically. A model has been developed which predicts the absorption rates of H₂S and CO₂ into a sodium carbonate solution. The absorption rates are calculated according to the two-film theory. In the liquid film, the finite rate of the CO₂ reaction was considered. Otherwise, in the liquid film as well as in the liquid bulk, equilibrium conditions for all reactions were assumed. Absorption experiments were performed on a packed column using a counter-flow strategy. In the experiments the influence of the initial carbonate concentration, the gas flow rate and the temperature on the removal efficiencies of H₂S and CO₂ and the selectivity of H₂S were investigated. It is desirable to absorb the H₂S but not the CO₂. The agreement between the absorption model and the experimental results from the absorber tower was satisfactory. The mass transfer coefficients were determined by fitting the experimental data to the model with respect to the H₂S and CO₂ content in the outgoing gas. The H₂S content was used to determine the gas side mass transfer coefficient and the CO₂ content was used to determine the liquid side mass transfer coefficient, The effective contact area of mass transfer was taken from published data. With a constant packing height, both the experiments and the model indicated that high carbonate concentration benefits the removal efficiency of H₂S. Higher gas flow rate also benefits the selectivity for H₂S. However, the removal efficiency will decrease. At higher temperatures the selectivity and the removal efficiency of H₂S decreased. Under the conditions investigated, the absorption of H₂S was essentially controlled by gas-side mass transfer and the absorption of CO₂ was controlled by liquid-side mass transfer     

SIMULTANEOUS ABSORPTION OF CARBON DIOXIDE AND HYDROGEN SULFIDE IN HOT CARBONATE SOLUTIONS IN A PACKED ABSORBER-STRIPPER UNIT

An experimental investigation for the simultaneous absorption of CO₂ and H₂S in 20 wt% hot K₂CO₃ solution have been conducted in a pilot scale packed absorber-stripper. The effects of liquid circulation rate, gas flow rate, inlet gas composition, steam pressure at bottom of stripper, and DEA promoter concentration, on the individual gas removal % and stripping efficiency were studied. The results showed that the performance of the absorber and stripper influenced one another and so must be considered together.     

Modeling of heat transfer in granular flow in rotating vessels

Heat transfer in particulate materials affects a wide variety of applications ranging from multi-phase reactors to kilns and calciners. In catalyst manufacturing, heat transfer through granular media (catalyst) occurs in the impregnation and calcinations stages. We use the discrete element model to simulate flow, mixing, and heat transport in granular flow systems in rotary calciners and impregnators. Granular flow and heat transport properties are taken into account in order to develop a fundamental understanding of their effect on dryer and calcination performance. Simulations have shown that as rotation speed decreases, both heat transfer and temperature uniformity of the granular bed for both calciner and impregnator increase. Depending on baffle size, baffles can either increase or decrease heat transfer in double cone impregnators. Granular cohesion does not affect heat transfer in the range of values examined.     

管内降膜式第二类吸收热泵性能实验研究

分别考察了在垂直螺旋管内降膜式第2类吸收热泵系统中,溶液流量、循环热水流量、操作温度对吸收器传热传质系数、系统性能系数COP及热效率Eth的影响。实验结果表明:随着溶液流量的增加,吸收器的传热传质系数也逐渐增大,而COP与Eth则有下降趋势;增加循环热水流量,吸收器传热传质系数也增大,但对COP与Eth的影响却较小;对于操作温度,吸收器传热传质系数会随着废热温度的升高而增大,随着冷却水温度的降低而增大。同时,通过软件ABSIM的模拟计算,得到的数据与实验数据吻合较好。     

Carbon dioxide absorption in a cross-flow rotating packed bed

This work investigates the feasibility of applying the cross-flow rotating packed bed (RPB) to the removal of carbon dioxide (CO₂) by absorption from gaseous streams. Monoethanolamine (MEA) aqueous solution was used as the model absorbent. Also, other absorbents such as the NaOH and 2-amino-2-methyl-1-propanol (AMP) aqueous solutions were compared with the MEA aqueous solution. The CO₂ removal efficiency was observed as functions of rotor speed, gas flow rate, liquid flow rate, MEA concentration, and CO₂ concentration. Experimental results indicated that the rotor speed positively affects the CO₂ removal efficiency. Our results further demonstrated that the CO₂ removal efficiency increased with the liquid flow rate and the MEA concentration; however, decreased with the gas flow rate and the CO₂ concentration. Additionally, the CO₂ removal efficiency for the MEA aqueous solution was superior to that for the NaOH and AMP aqueous solutions. Based on the performance comparison with the conventional packed bed and the countercurrent-flow RPB, the cross-flow RPB is an effective absorber for CO₂ absorption process.     

Experimental study of falling film evaporation heat transfer outside horizontal tubes

The heat transfer process of falling film horizontal evaporation includes evaporation outside tubes and condensation inside tubes, the heat transfer coefficient of the former is about 50% of that of the latter. So the overall heat transfer coefficient is influenced mainly by the falling film evaporation outside tubes. An experimental study of falling film heat transfer outside horizontal tubes was carried out in order to show how the heat transfer coefficient is affected by different parameters such as flow density evaporation temperatures, temperature difference between wall and saturation water, and mass concentration of the seawater. Experiments were conducted using 14 mm outer diameter Al-brass tubes heated by internal electric heaters so that a uniform heat flux was generated on the outside surface of tubes. The results show that when flow density Γ varies between 0.013 kg/ms < Γ< 0.062 kg/ms, the heat stransfer coefficient of falling film evaporation outside horizontal tubes h increases with the increase in liquid feeding, evaporation boiling temperature and heat flux. h also increases with an increase in distributor height, however there is a maximum height in which any height above this. Besides, the amount of non-condensing gas has significant effect on h. The difference of heat transfer coefficient between freshwater and seawater is small. These results contribute to further improving the performance of heat transfer process and developing new evaporator.     

热管式降膜吸收器的传热传质

对热管式降膜吸收顺溶液吸收传热传质并通过热管移出吸收热的过程进行了数值研究，根据所建立的数学模型，通过求解热管加热段外壁面溶液波动降膜的动态二维偏微分方程和热管传热方程，研究了膜雷诺数，低位余热温度，输出温度等因素对传热管质过程的影响，对进一步工作提出了新的见解。     

CO2化学吸收法中再生气的陶瓷膜余热回收特性

在CO₂化学吸收法工艺中,采用富液分流工艺,利用在贫富液换热器前分流的冷富CO₂吸收剂溶液回收再生塔顶排出的热再生气（一般为CO₂和水蒸气混合气）的余热,有助于降低CO₂再生热耗。本文在乙醇胺（MEA）基富液分流化学吸收工艺中,以纳米级多孔亲水陶瓷膜作为分流冷富液和热再生气之间的换热介质,利用水的热质耦合传递强化余热的回收性能。以余热回收通量为指标,探讨了分流的MEA富液流量、温度、质量分数、CO₂负荷和热再生气流量及再生气中水蒸气摩尔分数对陶瓷膜热回收性能的影响,并对比了不同分离层孔径陶瓷膜的余热回收性能。结果显示,陶瓷膜的余热回收性能随MEA富液流量的增加而增加,但却随富液温度的升高而大幅下降。同时,随着气体流量和再生气中水蒸气摩尔分数的增大,热回收通量均会增大。由水传质所引发的对流换热对热回收通量具有促进作用,可占总热回收量的10%左右。由于CMHE-10陶瓷膜的分离层孔径与孔隙率均大于CMHE-4陶瓷膜,因而其水传质通量大于CMHE-4陶瓷膜。但CMHE-10陶瓷膜的有效热导率却低于CMHE-4陶瓷膜,因而热回收过程中其水蒸气的冷凝总量要小,导致其热回收性能低于CMHE-4陶瓷膜。     

无填料热源塔吸热效率实验

建立无填料热源塔热泵系统实验平台,研究不同进风位置、喷嘴位置、室外空气干球温度、相对湿度、风量、溶液入口温度下无填料热源塔吸热效率的变化规律。结果表明：进风位置和喷嘴位置对热源塔的吸热效率会产生影响,下喷式无填料热源塔吸热效率高于上喷式无填料热源塔;干球温度与吸热效率无明显相关性,但干球温度升高,热源塔从空气中吸收的总热量增加;相对湿度和风量升高,吸热效率提高;溶液入口温度升高,热源塔的吸热效率明显提高。与其他参数相比,溶液入口温度对热源塔的吸热效率影响最大。     

分离式热管管内凝结换热的研究

在1:1模型上对分离式热管管内换热特性及不凝结气体扩散规律和对凝结换热的影响进行了试验,得出分离式热管换热器有一最佳充液率,其值为40%左右,凝结换热系数随着蒸汽压力的增加略有降低,在本实验的压力范围内,降低了9.3%。不凝结气体对分离式热管的凝结换热仅影响冷凝段下部一小部分,通过排气阀排出不凝性气体可有效地改善冷凝段下部的凝结换热,随着压力的增加不凝结气体对分离式热管冷凝段的影响减小。     

Dynamic modeling and validation of absorber and desorber columns for post-combustion CO2 capture

The paper evaluates, by modeling and simulation, carbon dioxide capture in aqueous solution of mono-ethanolamine (MEA) in packed absorption columns to be used in power sector for reducing greenhouse gas emissions. The mathematical model of carbon dioxide absorption and rich amine regeneration process includes transfer processes: mass and heat to study the coupled effect of temperature and concentration on the rate of absorption. The reaction kinetics and the vapor-liquid equilibrium (VLE) are other important parts of the model. The present dynamic mathematical model can be used to analyze the absorption rate, to understand the micro level interaction of various processes taking place inside the absorption and desorption column, and to improve the overall design of the system.The aim of the project was to validate the absorber and desorber models, as well as to understand the dynamic behavior of the whole capture-regeneration steps.     

基于BP神经网络的不凝性气体对脉动热管传热影响的分析

不凝性气体的存在会影响脉动热管的传热性能。本文以去离子水和聚丙烯酰胺（PAM）溶液为工质,搭建了脉动热管半可视化传热性能实验系统,研究了不凝性气体的存在对脉动热管传热特性和运行特性的影响;通过建立BP神经网络模型,在不同不凝性气体压力条件下,对脉动热管传热热阻做出了回归预测,并进行了验证。结果表明：不凝性气体的存在会恶化脉动热管的传热性能。随着加热功率的增加,在不同不凝性气体分压力条件下的热阻呈现下降趋势。而随着不凝性气体分压力的增大,工质的蒸发段平均温度明显增大。通过BP神经网络可以对不同不凝气体分压力下脉动热管热阻作出可靠的回归预测,可为脉动热管运行状态的优劣提供判定思路。