Measurement of solubility and density of water + lithium bromide + lithium chloride and water + lithium bromide + sodium formate systems

Solubility of aqueous solutions containing lithium bromide + lithium chloride and lithium bromide + sodium formate were measured (LiBr/NaHCO₂ = 2 and LiBr/LiCl = 2 by mass ratio) at different temperatures. Visual polythermal method was used in the temperature range of (283.15–340.15) K and mass fraction range of (0.4–0.8). Also density of mentioned systems was reported in the temperature range of (288.15–333.15) K. Each set of experimental measurements were correlated using least-square regression as a function of temperature. Our results indicate that solubility of LiBr + LiCl is higher than LiBr and its density is lower than density of aqueous solution of LiBr.     

Model for absorption of water vapor into aqueous LiBr flowing over a horizontal smooth tube

A model for absorption of water vapor into aqueous LiBr flowing over a horizontal smooth tube is developed. The flow is divided into three regimes: (1) falling film in contact with the tube, (2) drop formation at the bottom of the tube, and (3) drop fall between the tubes. Governing equations are formulated for each flow regime, and the variations of solution temperature, LiBr mass fraction, mass absorption rate and heat transfer rate are discussed including the effect of inlet subcooling. It is shown that the temperature variation across the film exhibits a nonlinear profile near the top of the tube and this effect leads to the necessity of a two-dimensional formulation in the falling film regime for accurate prediction. As has been observed previously, the mass fraction boundary layer at the vapor/liquid interface is found to be very thin and this explains the low absorption flux. The model predicts that significant absorption takes place in the drop formation regime with a considerable variation of temperature and mass fraction.     

Thermodynamic properties for the quaternary system H2O + CH3OH + LiBr + ZnCl2

The thermodynamic properties (solubility, vapour pressure, density, viscosity, heat capacity and heat of mixing) of the H₂O + CH₃OH + LiBr + ZnCl₂ (9:1 H₂O:CH₃OH and 1:1 LiBr:ZnCl₂ by mass) system using H₂O + CH₃OH as the working media and LiBr + ZnCl₂ as the absorbents were measured. The solubility data were obtained in the temperature range from 270.35 to 389.55 K. The measurements of vapour pressure, density, viscosity and heat capacity were carried out at various temperatures and absorbent concentrations. The differential heat of dilution and differential heat of solution at 298.15 K were measured for solutionw with absorbent concentrations from 0 to 75.2 wt%. The integral heat of mixing data at 298.15 K were obtained from both sets of experimental data. The integral heats of mixing for this quaternary system showed exothermic behaviour. The vapour pressure data were correlated with an Antoine-type equation. An empirical formula for the heat capacity was obtained from experimental data. The experimental data for the basic thermodynamic properties of this quaternary system were compared with those of the basic H₂O + LiBr system.     

Physical properties of the lithium bromide + 1,3-propanediol + water system

The experimental measurements of the basic four physical properties (solubility, vapor pressure, density and viscosity) of the lithium bromide + 1,3-propanediol + water system (LiBr/HO(CH₂)₃OH mass ratio = 3.5), a possible new working fluid for absorption heat pump, were carried out. Solubility was measured by the visual polythermal method in the temperature range from 264.65 to 358-95 K, and vapor pressure by the boiling point method from 330.75 to 408.45 K. Densities and viscosities were also measured by using a set of hydrometers and Ubbelohde-type capillary viscometers in the temperature range from 283.15 to 343.15 K. Each measured data set was correlated with a proper equation, and all the correlation results showed good agreement between measured and calculated values. Using the correlation results the Dühring chart was constructed and thus the system was found to be able to have a high absorber temperature, which is essential for the design of air-cooled absorption chiller.     

Effect of pressure and concentration on performance of a vertical falling-film type of absorber and generator using lithium bromide aqueous solutions

Experiments on an absorber and generator in an absorption refrigerating machine were made using a vertical falling-film type of stainless steel column. Three lithium bromid e aqueous solutions (40, 55 and 60wt% LiBr) were used as working fluid. The experimental apparatus was operated at 1.3 kPa (the pressure for a practical absorber) and 5.3 kPa (the intermediate pressure between absorber and generator). The measured absorption (evaporation) rate decreased with reducing pressure an d increasing concentration of LiBr in the falling liquid. The rate agreed with the values obtained from the analysis of heat and mass transfer in a falling film. Therefore, a falling-film type of absorber and generator can be designed and operated by a consistent method.     

An absorption based miniature heat pump system for electronics cooling

The development of an absorption based miniature heat pump system is motivated by the need for removal of increasing rates of heat from high performance electronic chips such as microprocessors. The goal of the present study is to keep the chip temperature near ambient temperature, while removing 100 W of heat load. Water/LiBr pair is used as the working fluid. A novel dual micro-channel array evaporator is adopted, which reduces both the mass flux through each micro-channel, as well as the channel length, thus reducing the pressure drop. Micro-channel arrays for the desorber and condenser are placed in intimate communication with each other using a hydrophobic membrane. This acts as a common interface between the desorber and the condenser to separate the water vapor from LiBr solution. The escaped water vapor is immediately cooled and condensed at the condenser side. For direct air cooling of condenser and absorber, offset strip fin arrays are used. The performance of the components and the entire system is numerically evaluated and discussed.     

纳米溴化锂溶液稳定性及其沸腾温度研究

对既有溴化锂溶液、纳米微粒及其相应分散剂配制的纳米溶液,对比测试其与纯溴化锂溶液的表面张力和沸腾温度,探讨了该纳米溶液的热物性及稳定性。实验发现,添加纳米微粒溶液的表面张力明显降低,经过温度工艺处理后,发现溶液中纳米微粒的颗粒度降低,纳米微粒在溴化锂溶液中几乎完全溶解,纳米溶液显现出很好的稳定性,其表面张力和沸腾温度均比纯溴化锂溶液有所降低。研究表明,最佳组份配制的纳米溶液与纳米微粒和相关分散剂有关,经过严格温度处理工艺流程,可获得稳定性、热物性良好的纳米溴化锂溶液,有利于在工程中应用。     

界面活性剂的混合添加对溴化锂溶液吸收水蒸气的影响

在静态池吸收实验中将两种有效添加剂混合添加,测试其对溴化锂水溶液吸收水蒸气的影响,从而探寻不同界面活性剂之间的促进或者抑制作用。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,例如,正辛醇在四种添加剂中效果最好,其它添加剂与正辛醇混合添加的效果都与正辛醇单独添加时的效果相近。     

Impact of plate design on the performance of welded type plate heat exchangers for sorption cycles

Numerical and experimental analysis was carried out to examine the heat transfer and pressure drop characteristics of welded type plate heat exchangers for absorption application using Computational Fluid Dynamics (CFD) technique. The simulation results based on CFD are compared with experimental results. A commercial CFD software package (FLUENT) has been used to predict the characteristics of heat transfer, pressure drop and flow distribution within the plate heat exchangers. In this paper, a welded plate heat exchanger with a plate of chevron embossing type was tested by controlling mass flow rate, solution concentration, and inlet/outlet temperatures. The working fluid is H₂O/LiBr solution with the LiBr concentration of 54–62% in mass. The numerical simulation examines the internal flow patterns, temperature distribution and the pressure distribution within the channel of the plate heat exchanger. Three plates of embossing types; chevron embossing, elliptic and round, are proposed and simulated in this paper. The simulation results show reasonably good agreement with the experimental results. Also, the numerical results show that the plate with the elliptical shape gives better performance than the plate of the chevron shape from the viewpoints of heat transfer and pressure drop.     

Heat and mass transfer enhancement of binary nanofluids for H2O/LiBr falling film absorption process

The objectives of this study are to measure the vapor absorption rate and heat transfer rate for falling film flow of binary nanofluids, and to compare the enhancement of heat transfer and mass transfer under the same conditions of nanofluids. The key parameters are the base fluid concentration of LiBr, the concentration of nanoparticles in weight %, and nanoparticle constituents. The binary nanofluids are H₂O/LiBr solution with nanoparticles of Fe and Carbon nanotubes (CNT) with the concentrations of 0.0, 0.01 and 0.1 wt %. The vapor absorption rate increases with increasing the solution mass flow rate and the concentration of Fe and CNT nanoparticles. It is found that the mass transfer enhancement is much more significant than the heat transfer enhancement in the binary nanofluids with Fe and CNT. It is also found that the mass transfer enhancement from the CNT nanoparticles becomes higher than that from the Fe nanoparticles. Therefore, the CNT is a better candidate than Fe nanoparticles for absorption performance enhancement in H₂O/LiBr absorption system.     

Experimental study on LiCl solution falling-film generation process outside a vertical tube

For the purpose of the development of a generator with higher performance utilizing LiCl/H₂O as the working pair in a two-stage absorption refrigeration system, an experimental investigation of LiCl solution falling film generation outside a vertical tube as the high-pressure stage solution cycle was conducted. An experimental setup was established to study heat and mass transfer process in a falling-film generator for LiCl/H₂O using low-temperature heat source. The experiments showed effect of the flow rates of hot water and falling film solution, temperature of heat source, concentration of the solution and generation pressure on the LiCl/H₂O generation process. To compare with conventional LiBr/H₂O solution, some comparative experiments of falling film generation were tested in order to discuss the mass transfer performance of two different working pairs in a high-pressure generator. The results showed that the two working pairs had similar mass transfer rate. The LiCl/H₂O solution had a similar mass transfer rate to that of the LiBr/H₂O solution, while the concentration of LiCl/H₂O solution was much lower with smaller circulation ratio of the solution, and it could make for possible improvement in the thermal performance of the absorption refrigeration system.     

Vacuum freezing type ice slurry production using ethanol solution 1st report: Measurement of vapor–liquid equilibrium data of ethanol solution at 20 °C and at the freezing temperature

In this study, an original method for the production of ice slurry from ethanol solution without using a refrigerator is proposed. This system has advantages compared with similar existing systems using materials other than ethanol solution. In this paper, the vapor–liquid equilibrium data of ethanol solution at 20 °C and at the freezing temperature are measured, which is necessary to calculate the COP of this ice slurry producing system. In the experiments, two experimental methods are proposed to measure the saturated pressure and the vapor composition of ethanol solution. Each method has an advantage in their operating temperature range. As a result, the vapor–liquid equilibrium diagrams of ethanol solution at 20 °C and at the freezing temperature, and approximations of saturated pressure of various concentrations of ethanol solution for varying liquid temperature, are obtained.     

Determination of thermal properties of dilute LiBr-water solutions

We are developing an absorption air cooling system which can supply 2°C chilled water for air cooling by the usage of dilute solutions of LiBr in water with an evaporating temperature of −6°C as a nonfreezing refrigerant. However, there are few published data for the thermal properties of dilute LiBr water solutions (0 to 30%) below 10°C. In this paper, the freezing temperature and the saturated vapor pressure are reported. The results clearly show the possibility of developing a new type of LiBr absorption refrigerating machine to generate evaporating temperatures below 0°C. To obtain accurate data for the design of this new type of absorption refrigerating machine, an apparatus has been developed to measure the thermal properties of dilute LiBr water solutions below 10°C. The experimental arrangement consists of a cooling bath (340×240×190 mm) filled with fluorocarbon, a glass measuring bottle (ϕ120×100 mm), and an absolute pressure gauge (0–1.3 kPa). The accuracy of the temperature, pressure, and density are within ±0.1°C, 0.01 kPa, and ±0.005%, respectively. Paper presented at the Fourth Asian Thermophysical Properties Conference, September 5–8, 1995, Tokyo, Japan.     

Decomposition of atmospheric water content into cluster contributions based on theoretical association equilibrium constants

Water vapor is treated as an equilibrium mixture of water clusters (H₂O)_i using quantum-chemical evaluation of the equilibrium constants of water associations. The model is adapted to the conditions of atmospheric humidity, and a decomposition algorithm is suggested using the temperature and mass concentration of water as input information and used for a demonstration of evaluation of the water oligomer populations in the Earth's atmosphere. An upper limit of the populations is set up based on the water content in saturated aqueous vapor. It is proved that the cluster population in the saturated water vapor, as well as in the Earth's atmosphere for a typical temperature/humidity profile, increases with increasing temperatures.     

The effect of micro-scale surface treatment on heat and mass transfer performance for a falling film H2O/LiBr absorber

The objectives of this paper are to develop a new method of wettability measurement, to study the effect of micro-scale surface treatment on the wettability across horizontal tubes and to apply it for numerical analysis of heat and mass transfer in a H₂O/LiBr falling film absorber. Three types of tubes with roughness are tested in a test rig. Inlet solution temperature (30–50 °C), concentration (55–62 wt.% of LiBr) and mass flow rate (0.74–2.71 kg/min) are considered as key parameters. Reynolds number ranged from 30 to 120 by controlling the inlet mass flow rate. The wettability on the roughened tubes was higher than that for the smooth tubes. The wettability decreased linearly along the vertical location but was proportional to the solution temperature and mass flow rate. The experimental correlations of the wettability for the smooth and the roughened tubes were developed with error bands of ±20 and ±10%, respectively. These are used for the heat and mass transfer analysis of absorbers with micro-scale hatched tubes.     

一种低饱和蒸气压润滑脂的真空蒸发特性测试

针对一种国外进口的空间活动部件用低饱和蒸气压润滑脂,应用真空物理的基础理论,以及现有的试验设备和仪器条件,设计了蒸发速率测试方案,评价了该润滑脂的真空蒸发损失特性,回归出饱和蒸气压随温度变化的方程。为预测其在真空下长期使用中的蒸发损失量,以及验证在常温下的饱和蒸气压指标提供了一种方法。     

全氟甲烷(CF4)饱和蒸气压在139.53 K～217.53 K温度范围内的实验

在温度范围139．53K-217．53K内,采用自行设计的循环法实验装置精确测量了30组CF4（R14）的饱和蒸气压实验数据,并且运用Wagner方程和另一种Wagner型方程对实验数据进行了拟合。对计算值与实验数据进行了偏差分析,结果显示两种方程的计算值非常接近,与实验数据拟合地较好,从而得到以上温度范围内的CF4饱和蒸气压方程。     

Vapor absorption by LiBr aqueous solution in vertical smooth tubes

Heat and mass transfer in a falling film vertical in-tube absorber was studied experimentally with LiBr aqueous solution. The presented results include the effect of solution flow rate, solution subcooling and cooling water temperature on the absorption in a smooth copper tube 16.05 mm I.D. and 400 mm long. The experimental data in the previous report for a 1200-mm-long tube was also re-examined and compared. It was demonstrated by the observation of the flow in the tube that the break down of the liquid film into rivulets leads to deterioration of heat and mass transfer at lower film Reynolds number or in longer tubes. An attempt to evaluate physically acceptable heat and mass transfer coefficients that are defined with estimated temperature and concentration at the vapor–liquid interface was also presented.