基于化学势的吸收过程热力学分析

溴化锂浓溶液对水蒸气的吸收与凝结的热力学过程,一般都用浓度梯度这个驱动势(Fick定律)来分析,但这并不完善。而化学势是引起质传递的真正驱动势,本文基于化学势这一理论对水蒸气的被吸收过程进行了热力学分析,得出蒸发器的水蒸气虽温度低于喷淋溶液的温度,但它的化学势高于溶液中水的化学势,所以被溶液吸收,且溶液温度(浓度)越高化学势差值越大,水蒸气越易被吸收,针对这一特点,本文提出了对吸收器设计的改进意见。     

填料型绝热吸收器影响因素实验研究

为了研究绝热吸收器内溴化锂溶液降膜吸收水蒸汽传质强化过程,本文首先建立了溴化锂溶液降膜绝热吸收循环实验台,然后分析了喷淋溶液温度、喷淋溶液流量、喷淋溶液浓度和吸收压力等参数变化对吸收过程传质系数的影响,并得出有指导意义结论.     

气相界面活性剂对溴化锂水溶液吸收水蒸气的影响

目前在溴化锂吸收式制冷机/热泵中被广泛采用的界面活性剂是2-ethyl-1-hexanol(2EH)和1-octanol。传统的界面活性剂的添加方式是,将界面活性剂以液相形式投入到溴化锂溶液中。如果在三效循环中仍采用这样的方式将2EH加入到溴化锂溶液中,由于发生器的温度较高,势必有界面活性剂被蒸发而进入冷媒系统。为探讨三效循环界面活性剂的可能添加方式,同时试图研究界面活性剂以气相形式投入对溴化锂溶液吸收水蒸气的影响,本文针对几种可能有效的界面活性剂,做了界面活性剂的气相添加对吸收速度影响的测试实验。经过对2-ethyl-1-hexanol、1-heptanol和1-hexanol等添加剂的静态池实验,结果表明,气相添加的效果与液相投入没有明显的差别,同样可以大大提高溴化锂溶液吸收水蒸气的速度。     

界面活性剂的混合添加对溴化锂溶液表面张力及吸收水蒸气的影响

本文从将两种有效添加剂混合添加的角度,来研究其对溴化锂水溶液吸收水蒸气的影响.采用静态池吸收实验测试溶液吸收水蒸气的效果.通过对正辛醇、仲辛醇、异辛醇、正己醇四种物质采用单种添加和两种混合添加的测试实验表明,混合添加后的效果与其中较好的添加剂单独添加的效果接近.采用吊板法测量溶液的表面张力.通过对添加以上混合添加剂后的溴化锂水溶液的表面张力的测试表明,混合添加后溶液的表面张力与其中较大程度降低溶液表面张力的添加剂单独添加后的表面张力接近.     

3363/3364离子膜在NH_3-H_2O-LiBr吸收式制冷系统中的应用研究

由于NH3-H20-LiBr三元溶液中溴化锂的存在会使溶液性质发生改变,易于发生过程的进行,但阻碍了吸收氨的传质过程,对吸收性能不利.对此提出了一种膜分离技术,可将溴化锂从进入吸收器的溶液中分离出来,进而改善吸收性能.为检验对溴化锂的分离效果,采用装有3363/3364异相离子交换膜堆的膜分离装置进行实验。实验结果表明NH3-H20-LiBr三元溶液在膜分离器中一次循环后分离溴化锂的效率达90%,两次循环后分离效率达95%以上。基于上述实验中的分离效率,利用Aspen Plus模拟器,进一步模拟分析了带有这种膜分离装置的NH3-H20-LiBr三元吸收式制冷系统,并计算其性能系数.结果表明,与普通三元吸收式制冷系统相比,采用膜分离技术后,NH3-H20-LiBr吸收式制冷系统的性能系数可提高近10%.     

光滑表面与切槽表面喷雾冷却的实验研究

本文通过改变喷雾的流量(压力)、喷射高度和喷射倾斜角对平板和切槽表面喷雾冷却进行了实验研究。实验用的强化表面是将表面切割出0.2mm高、0.2 mm宽的方形翅块。实验结果表明:流量、喷射高度均存在最优值,大的喷射倾角会削弱冷却性能;对比同样条件下的平板表面,切槽表面显著强化了喷雾冷却的性能,对流换热系数提高约30%。     

添加剂对LiBr溶液吸收蒸汽过程中的强化机理

利用吊板法测量了加有正辛醇和异辛醇这两种添加剂的溴化锂溶液的表面张力 ,利用激光照相的可视化方法研究了在静池吸收过程中添加剂对溴化锂溶液吸收水蒸汽的强化影响 .实验结果显示液体添加剂和蒸汽添加剂都能显著地降低溴化锂溶液的表面张力 ;蒸汽添加剂不仅和液体添加剂一样可以在吸收表面引起马拉戈尼对流 ,而且对吸收具有更好的强化效果 .根据对实验现象的分析 ,得出了添加剂对吸收的强化机理 :由于溶液表面层对液体添加剂或蒸汽添加剂的表面吸附作用 ,造成吸收界面处表面张力分布不均匀 ,从而在吸收界面引起马拉戈尼对流现象 ,强化了吸收过程中的传热、传质性能     

添加正辛醇的溴化锂水溶液汽液界面微观形态

采用分子动力学方法研究303 K时,添加正辛醇(1-octanol)的溴化锂水溶液汽液界面的微观形态、密度分布和结构性质.模拟结果表明: Li+、Br在汽液界面处解吸;正辛醇分子吸附在汽液界面并在界面处优势取向;醇分子的亲水基会尽可能多地趋向水分子,二者在界面处以氢键相互作用.同时,在非平衡条件下,采用分子动力学方法模拟了添加或未添加正辛醇的溴化锂水溶液吸收水蒸气的动态过程,发现在短时间内,部分水蒸气分子吸附在汽液界面处或到达溶液内部.     

辛醇对LiBr水溶液汽液界面的影响

采用分子动力学方法分析303.15 K时,添加不同量异辛醇的水或溴化锂水溶液汽液界面的微观结构,发现;未吸收水蒸气时,当异辛醇较少时,醇分子在界面处分布不均匀;当异辛醇较多时,异辛醇在界面处均匀分布,但排列比较松散;随着异辛醇数目的继续增加,异辛醇在界面处形成双层结构。异辛醇亲水羟基中的氢与阴离子存在氢键作用,而阳离子与异辛醇的氧之间存在着较强的静电相互作用。在非平衡条件下,采用分子动力学方法对添加或未添加正辛醇的溴化锂水溶液吸收水蒸气的动态过程模拟0到100ps,发现;加有正辛醇的溴化锂水溶液与未添加正辛醇的溴化锂水溶液相比,吸收的水分子数目明显增多。     

喷淋吸收过程模型及实验研究

开式循环吸收式热泵是用于HAT循环烟气水回收的新型技术手段.本文以喷淋吸收器为对象,对应用氰化钙溶液的吸收过程进行了研究.首先通过理论建模预测了吸收过程的温度及浓度分布,并且就温度及浓度等参数的影响进行了分析;其次对喷淋吸收过程进行了实验研究并与冷却水喷淋减湿进行对照,结果表明要达到相同的吸收效果,冷却水流量要多于溶液流量5倍以上.     

WATER VAPOR ABSORPTION ENHANCEMENT IN LiBr/H2O FILMS FALLING ON HORIZONTAL TUBES

An experimental investigation was conducted into the enhancement of water vapor absorption in aqueous lithium bromide solution films falling on horizontal tubes. The variable parameters included the solution flow rate, the inlet temperature of the cooling media, the solution inlet temperature, and the effective extended surface. The experimental results, which were correlated with the film Reynolds number, showed that the cooling effect of the tube wall was the governing factor in the absorption process for small solution flow rates, but the inlet solution subcooling dominated the absorption performance for large flow rates. Also, the R tube, which has a unique ridged fin shape, exhibited the best absorption performance among the tested tubes.     

太阳能溴化锂吸收制冷系统的优化模拟分析

基于溴化锂吸收制冷循环的效率受太阳能热源温度较低的影响,文中对太阳能溴化锂吸收制冷系统的循环进行了改进,提出了改进型太阳能溴化锂增压抽气吸收制冷循环,以充分利用太阳能低温热源。新循环不仅克服了传统循环的缺点,降低了驱动热源温度,而且制冷循环相对稳定即使热源温度有波动时,新循环与传统循环的制冷系数也基本相当。     

太阳能与生物质能耦合供能系统的应用研究

介绍了太阳能与生物质能溴化锂吸收式制冷机的工作原理,分析了太阳能集热器及溴化锂制冷机组的热效率,利用生物质汽化炉余热弥补太阳能不稳定的缺陷,证明了利用清洁能源作为溴化锂吸收式中央空调热源问题的可行性。     

立式升温型溴化锂吸收式热泵的设计与变工况研究

本文对立式升温型溴化锂吸收式热泵循环和各部件建立了数学模型,并设计了85℃热水驱动产110℃热水的立式降膜升温型溴化锂吸收式热泵,吸收器输出功率为50 kW。然后对其在热源热水温度和流量变化、冷却水入口温度和流量改变等非设计工况下的工作特性进行了计算与分析研究,得到变工况对于机组性能系数,效率和机组负荷的影响关系图。发现在我们的研究范围内,热源水参数的变化对机组性能的影响要大于冷却水。并且在热源水参数变化过程中,机组性能存在性能急剧变化的拐点,实际运行中应当避免。     

Isentropic compressibility, effective pressure, classical sound absorption and shear relaxation time of aqueous lithium bromide, sodium bromide and potassium bromide solutions

Densities, speeds of sound and viscosities of aqueous lithium bromide, sodium bromide and potassium bromide solutions were measured as functions of concentration (0.0085≤m (mol kg⁻¹)≤14.06) and temperature (273.15≤T(K)≤323.15). Allied properties like isentropic compressibilities, effective pressure, classical sound absorption and shear relaxation time were calculated by using the measured data. The interaction in these three bromide solutions vary in the order of NaBr>KBr>LiBr. The primary hydration shells are saturated at 10.8, 5.1 and 5.8 mol kg⁻¹ with 5.1, 10.9 and 9.6 number of water molecules in the primary hydration shell of lithium bromide, sodium bromide and potassium bromide solutions respectively. The cationic environment is found to influence the hydration phenomena of the anion.

The non-Arrhenius temperature dependence of shear relaxation time were analysed by using the Vogel-Tammann-Fulcher (VTF) equation. The concentration dependence of shear relaxation time is different in these three bromide solutions. Such an effect is attributed to the competitive effects of hydrogen bonding, structure forming/breaking effect of ions and the formation of ion pairs.     

NH3-H2O-LiBr吸收式制冷系统的可行性研究

针对目前氨水吸收式制冷系统的缺点由于高压侧(发生器和冷凝器)的工作压力过高带来的不安全隐患以及发生出来的气体中还有较多的水蒸汽而带来的系统过于庞大等问题,提出了相应的改进方案,在氨水系统中加入溴化锂,期望能够降低其工作压力以及气相中水蒸汽的含量。为了对该三元混合工质的可行性进行研究,在自行搭建的实验平台上,对其压力及温度进行了测试,测试温度范围从20℃到90℃,压力最高到2MPa,测试用溴化锂质量浓度范围从5%到60%。实验结果表明,与相同浓度下的氨水溶液相比,三元溶液的气液平衡压力降低了近30%～50%,气相中水蒸汽的含量最低可降到2.5%。实验结果为工业上的推广使用提供了理论依据。     

不同类型的添加剂对制冷效能的影响分析

为了提高溴化锂吸收式制冷系统的制冷效率,通常在制冷剂中添加表面活性剂,以提高制冷系统中溶液蒸发、吸收和冷凝过程中热量传递效率.通过研究溴化锂吸收式制冷系统的工作原理和工作过程,得到了活性剂对制冷性能影响关系式.在此基础上,对戊基甲醇、正六醇和1-羟基己烷这三种添加剂的制冷性能进行对比测试,实验表明添加浓度为150ppm...     

COMPARISON OF HEAT AND MASS TRANSFER IN FALLING FILM AND BUBBLE ABSORBERS OF AMMONIA-WATER

An experimental analysis of ammonia-water absorption process was performed for the falling film and bubble modes in a plate-type absorber. 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 bubble mode is superior to the falling film mode for mass transfer performance, and more heat was generated in the bubble mode. Increase of solution flow rate rarely affected the mass transfer, but improved the heat transfer. As the gas flow rate increased, fluidization occurred in the bubble mode and influenced the thermal boundary layer. However, channeling appeared in the falling film mode and decreased the heat transfer area. Increase of the gas flow rate greatly enhanced the performance of heat transfer in the bubble mode but made it worse in the falling film mode. Finally, the results were converted into dimensionless numbers to elucidate physical phenomena and we plotted Sherwood number versus Reynolds number for mass transfer performance and Nusselt number versus Reynolds number for heat transfer performance.     

Thermodynamic study of advanced absorption heat transformers—II. Double absorption configurations

A thermodynamic analysis has been carried out to study the performance of double absorption heat transformers (DAHT) assuming water/lithium bromide as the working fluid. The performance of single (SSHT) and two stage heat transformers (TSHT) analyzed in Part I, was compared with the performance of double absorption heat transformers (DAHT) under the same operating conditions. The results showed that single stage heat transformers (SSHT) were the simplest and most efficient. Greater absorber temperatures were reached with two stage heat transformers (TSHT). However, these systems were in general less efficient than the others and technically the most complex. Double absorption heat transformers (DAHT) were technically simpler than two stage heat transformers (TSHT) and may reach absorber temperature as high as these systems.