Absorption of water vapour into lithium bromide-based solutions with additives using a simple stagnant pool absorberAdsorption de la vapeur d'eau par des solutions à base de bromure de lithium à l'aide d'un absorbeur simple de type à surface liquide stagnante

Absorption of water vapour into the 50 mass % lithium bromide solution with four eight-carbon alcohol additives such as n-octanol, 2-octanol, 3-octanol, and 2-ehtyl-1-hexanol were investigated by using a simple stagnant pool absorber. Four solutions of the 60 mass % lithium bromide + water, 68 mass % lithium bromide + ethylene glycol + water (LiBr/HO(CH₂)₂OH = 4.5 by mass), 60 mass % lithium bromide + lithium iodide + water (LiBr/Lil = 4 by mole), and 70 mass % lithium bromide + zinc chloride + water (LiBr/ZnCl₂ = 1 by mass) containing the 2-ethyl-1-hexanol additive were also considered to examine the additive effect on mass transfer of water vapour into the different types of absorbents. The experimental apparatus could be used with good confidence and accuracy particularly for studying mass transfer enhancement over the effective range of additive concentration which, in this work, is mostly between 10 and 500 ppm. A vigorous interfacial turbulence was observed during absorption process using additives. The water vapour absorption rate remarkably increased with increasing the additive concentrations up to about 200 ppm and then stopped increasing above 200 ppm for all the systems considered. The onset additive concentrations for enhancing mass transfer were located between 5 and 8 ppm for all systems except two systems of the 50 mass % lithium bromide solution with 3-octanol and 70 mass % lithium bromide + zinc chloride solution with 2-ethtyl-1-hexanol for which the corresponding concentrations were 2.5 and 35 ppm, respectively.     

Part-load characteristics of a new ammonia/lithium nitrate absorption chiller

A pre-industrial prototype of a new water-cooled ammonia/lithium nitrate absorption chiller was characterised at part-load operation mode. The chiller was built using brazed plate heat exchangers in all its components, including the absorber and the generator.A test campaign was carried out varying the thermal load in the chilled water circuit and keeping the hot and cooling water temperatures constant.Part-load curves of the thermal and electrical coefficients of performance were obtained, plotted and compared with data from the literature on small capacity absorption chillers with conventional working pairs, namely ammonia/water and water/lithium bromide. The experimental results showed that to achieve a higher electrical coefficient of performance at part-load operation, it was much more convenient to use an ON-OFF control than to modify the hot water temperature. Furthermore, using a simple ON-OFF control strategy, the behaviour of the new absorption chiller was more agile and responded more quickly.The part-load curve of the electrical coefficient of performance was obtained by adjusting the experimental data to the shape of the curve proposed in the standard prEN-14825:2011 for air-to-water chillers. The Cc coefficient was 0.7985 matching the value obtained dividing the remaining electrical consumption measured during the OFF half cycles by the total energy consumption generated.     

Electrical conductivity of the ferroelectric sodium vanadate,potassium vanadate,lithium vanadate and their solid solutions

The d.c. electrical conductivity of sodium vanadate, potassium vanadate, lithium vanadate and their solid solutions sodium-potassium vanadate, sodium-lithium vanadate were measured by a two-probe method in the temperature range covering their transition points. These materials show sharp change in conductivity at their phase transition temperatures. In sodium, potassium and lithium vanadates an exponential increase in d.c. conductivity is observed in ferroelectric region while discontinuities are observed above the transition temperatures. The activation energy in paraelectric state of the solid solutions is found to be higher than in ferroelectric state. In solid solutions the activation energy depends upon sodium vanadate concentration.     

Absorption of water vapour into falling films of aqueous lithium bromide

In this study, experiments have been performed for water vapour absorption into 50 and 60 mass% aqueous lithium bromide solution films flowing down a vertical surface to investigate the effects of liquid diffusivity values, molecular properties of the concentrated solutions and non-absorbable gases. The experimental results for wavy films over a film Reynolds number range of 15–90 indicate larger dimensionless mass transfer rates than for strictly laminar flow when the diffusivity of water in a concentrated lithium bromide solution is less than that in a dilute solution. The complete set of results shows that the physical property data for lithium bromide solutions including the diffusivities measured by Kashiwagi are sufficient to explain mass transfer behavior.     

添加剂和纳米粒子强化溴化锂水溶液／氨水吸收特性研究进展

吸收式制冷以其节能、环保等诸多优点得到了越来越广泛的应用。本文总结与分析添加剂和纳米粒子强化溴化锂水溶液及氨水吸收特性的机制和相关实验研究的发展现状。针对吸收式制冷系统中吸收器传质系数和换热系数小而导致的制冷效率低的问题,很多学者进行了添加剂和纳米粒子对吸收过程影响的实验研究,并据此采取措施增大传质传热效率。实验主要包括以下几个方面：表面张力实验、静态池吸收实验、降膜吸收实验和氨水鼓泡吸收实验。实验结果均表明添加剂和纳米粒子可以提高吸收器中溴化锂水溶液及氨水的传热传质性能。该研究对于提高吸收式制冷系统的制冷效率有很大帮助,同时为该技术在实际系统中的应用奠定基础。     

Combined momentum, heat and mass transfer in vertical slug flow absorbers

Numerical solutions have been obtained for the system of equations of momentum, heat and mass transfer describing the absorption of a refrigerant vapour from a Taylor bubble into the refrigerant-absorbent solution film around the bubble. The numerical results are compared with Nusselt's solution of the energy equation and with the penetration theory solution of the mass diffusion variation. Experimental data have been collected in vertical tubular absorbers in the slug flow region with the systems ammonia-lithium nitrate and ammonia-sodium thiocyanate. Four different absorber tubes have been tested with internal diameters of 10, 15, 20, and 25 mm. These data are compared with the numerical and theoretical results. The effect of the bubble nose on mass transfer is studied. Typical temperature profiles during the absorption process in absorption cooling/heating systems are shown.     

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.     

Thermal Property Measurements and Enthalpy Calculation of the Lithium Bromide+Lithium Iodide+1,3-Propanediol+Water System

The lithium bromide+lithium iodide+1,3-propanediol+water [LiBr/LiI mole ratio=4 and (LiBr+LiI)/HO(CH₂)₃ OH mass ratio=4] solution is being considered as a potential working fluid for an absorption chiller. Heat capacities at four temperatures, 283.15, 298.15, 313.15, and 333.15 K, were measured in the range from 50 to 70 mass%. In addition, the differential heats of dilution at 298.15 K were measured in the range from 45.3 to 71.8 mass%. Each individual data set was correlated with a proper regression equation with a high accuracy. A new enthalpy calculation method for the working fluids containing organics was proposed. The calculation method correlated the heat capacity (at various temperatures and concentrations) and the differential heat of dilution (at ambient temperature and various concentrations). The present method was applied for the construction of enthalpy–concentration (H–T–X) diagrams with high confidence.     

Absorption heat pump performance for different types of solutions

Increasing interest in absorption heat pumps has led to research on new working fluids. In this work, the thermodynamics of binary solutions is applied to a simple heat pump model to determine which type of solution optimizes thermal performance for a given refrigerant (ammonia).It is found that although solutions with negative deviations from Racult's law enhance the performance, there is a limit as to how strongly the solution should negatively deviate. The dependence of the refrigerant activity coefficient on temperature and concentration is also studied, and the ranges that optimize heat pump performance are indicated.     

Numerical simulation of an advanced energy storage system using H2O–LiBr as working fluid, Part 1: System design and modeling

The advanced energy storage technology proposed and patented by authors can be applied for cooling, heating, dehumidifying, combined cooling and heating, and so on. It is also called the variable mass energy transformation and storage (VMETS) technology in which the masses in one or two storage tanks change continuously during the energy charging and discharging processes. This paper presents an advanced energy storage system using aqueous lithium bromide (H₂O–LiBr) as working fluid. As one of VMETS systems, this system is a closed system using two storage tanks. It is used to shift electrical load and store energy for cooling, heating or combined cooling and heating. It is environmental friendly because the water is used as refrigerant in the system. Its working principle and process of energy transformation and storage are totally different from those of the traditional thermal energy storage (TES) systems. The electric energy in off-peak time is mostly transformed into the chemical potential of the working fluid and stored in the system firstly. And then the potential is transformed into cold or heat energy by absorption refrigeration or heat pump mode when the consumers need the cold or heat energy. The key to the system is to regulate the chemical potential by controlling the absorbent (LiBr) mass fraction or concentration in the working fluid with respect to time. As a result, by using a solution storage tank and a water storage tank, the energy transformation and storage can be carried out at the desirable time to shift electric load efficiently. Since the concentration of the working solution in the VMETS cycle varies continuously, the working process of the VMETS system is dynamic. As the first part of our study, the working principle and flow of the VMETS system were introduced first, and then the system dynamic models were developed. To investigate the system characteristics and performances under full-storage and partial-storage strategies, the numerical simulation will be performed in the subsequent paper. The simulation results will be very helpful for guiding the actual system and device design.     

ABSIM — modular simulation of advanced absorption systems

The computer code ABSIM has been developed for simulation of absorption systems in a flexible and modular form, making it possible to investigate various cycle configurations with different working fluids. Based on a user-supplied cycle diagram, working fluid specification and given operating conditions, the program calculates the temperature, flowrate, concentration, pressure and vapor fraction at each state point in the system and the heat duty at each component. The modular structure of the code is based on unit subroutines containing the governing equations for the system's components. A main program calling these subroutines links the components together according to the cycle diagram. The system of equations for the entire cycle is thus established, and a mathematical solver routine is employed to solve them simultaneously. Property subroutines contained in a separate database serve to provide thermodynamic properties of the working fluids.ABSIM has been employed over the past decade by many users worldwide to simulate a variety of absorption systems in different multi-effect configurations and working fluids. The paper will describe the current capabilities of the program and recent improvements made in it. Improvements to the method of cycle specification and solution have enhanced considerably the convergence capability with large and complex cycles. Additional units and working fluids have been added, resulting in much-enhanced simulation capability and applicability. A Windows version has recently been developed with an improved user-interface, which enhances user-friendliness considerably. It makes it possible to create the cycle diagram on the computer screen, supply the data interactively, observe the results superimposed on the cycle diagram and plot them. The paper describes examples of simulation results for several rather complex cycles, including lithium bromide–water double-, triple- and quadruple-effect cycles and ammonia–water GAX, branched GAX and vapor exchange (VX) cycles.     

Flow patterns and heat and mass transfer coefficients of low Reynolds number falling film flows on vertical plates: Effects of a wire screen and an additive

The effects of the surface geometry and of a surfactant on the characteristics of LiBr–water solution falling films are experimentally investigated. Two different surfaces (flat copper plate and the same copper plate covered with a copper wire screen) are tested with four fluids (pure water and 50% lithium bromide–water solution with or without 100 ppm of 2-ethyl-1-hexanol) for Reynolds numbers from 40 to 110. Flow patterns and heat and mass transfer coefficients are discussed. Marangoni convection was observed in water-cooled LiBr–water flows resulting in significant heat and mass transfer enhancement. 2-ethyl-1-hexanol enhances heat and mass transfer in LiBr–water flows by more than a factor of two. 2-ethyl-1-hexanol in water makes copper surface strongly hydrophobic. The wire screen promotes absorption process in adiabatic conditions but hinders the process in non-adiabatic conditions by reducing the Marangoni convection induced by 2-ethyl-1-hexanol. The experimental heat and mass transfer coefficients are presented in dimensionless forms.     

溴化锂填料吸收器中绝热吸收过程的实验研究

针对传热、传质分离的填料吸收器，设计、加工了一个溴化锂绝热降膜吸收的循环实验装置；实验研究了溴化锂水溶液在填料层上的绝热吸收特性；分析了溶液温度、浓度、降膜雷诺数对吸收效率和传质系数的影响。     

Solid-liquid equilibria in the systems NH3-H2O-LiBr and H2O-LiBr at p=1 atm in the range from −35 to 80°C

Solid-liquid equilibria at ambient pressure and solid-liquid-vapor equilibria at T=303.15 K have been measured in the system ammonia-water-lithium bromide for various initial concentrations of lithium bromide. Liquid phases have been analyzed using ion selective electrodes. A ternary phase diagram of the system at T=303.15 K is provided showing a triple line and several regions in which solid phases of different kind occur. This will restrict considerably the use of these systems as working fluids in absorption machinery.Paper dedicated to Professor Jospeh Kestin.     

Estimation of differential heat of dilution for aqueous lithium (bromide,iodide, nitrate,chloride) solution and aqueous (lithium,potassium, sodium) nitrate solution used in absorption cooling systems

The differential heat of dilution data are estimated theoretically using Duhring's diagrams for water/LiBr, water/(LiBr + LiI + LiNO₃ + LiCl) with mass compositions in salts of 60.16%, 9.55%, 18.54% and 11.75%, respectively, and water/(LiNO₃ + KNO₃ + NaNO₃) with mass compositions in salts of 53%, 28% and 19%, respectively, as these can be potentially utilized as working fluids in absorption cooling systems. The differential heat of dilution data obtained were correlated with simple polynomial equations for the three working fluids as a function of the solution concentration and temperature. The results showed that the differential heat of dilution of the non-conventional working fluid mixtures is lower than that of water/LiBr at typical operating temperature and concentration of interest in absorption cooling cycles employing these working fluid mixtures. The correlations developed could be useful in predicting the differential heat of dilution value while performing heat and mass transfer analyses of these potential non-conventional working fluid mixtures in absorption cooling systems.     

Conceptual design and performance analysis of absorption heat pumps for waste heat utilization

The potential of the absorption cycle for recovering low temperature waste heat (60°C) as a first step towards the construction of a working system to provide process heat is assessed. The system is considered with lithium chloride-, lithium bromide-water solutions as working fluids.     

Vapor-deposited metal-gas alloys of sodium and ammonia

Films of sodium and ammonia were formed directly from vapor onto substrates held at or below 5 K. The electrical resistivity of the films was measured as a function of sodium concentration. A metal-nonmetal transition as a function of composition was observed at concentrations in the 45–50 mole % range. The transition was found to be anomalous in that the resistivity was not a monotonic function of the sodium concentration. The data indicate that there is enhanced conductivity over a narrow concentration range on the nonmetal side of the transition. The conductivity is not magnetic field dependent up to the maximum available field of 4 kOe. No evidence was found for the anomalous electrical conductivity previously reported for bulk, dilute sodium-ammonia solids that were quick-frozen from liquid solutions.Supported in part by the Department of Energy under contract EY-76-02-1569 and by the Graduate School of the University of Minnesota.     

State-of-the-art review on crystallization control technologies for water/LiBr absorption heat pumps

The key technical barrier to using water/lithium bromide (LiBr) as the working fluid in air-cooled absorption chillers and absorption heat-pump systems is the risk of crystallization when the absorber temperature rises at fixed evaporating pressure. This article reviews various crystallization control technologies available to resolve this problem: chemical inhibitors, heat and mass transfer enhancement methods, thermodynamic cycle modifications, and absorption system-control strategies. Other approaches, such as boosting absorber pressure and J-tube technology, are reviewed as well. This review can help guide future efforts to develop water/LiBr air-cooled absorption chillers and absorption heat-pump systems.     

The interfacial turbulence in falling film absorption: effects of additives

The results of vertical falling film experiments on the absorption of water vapor to aqueous lithium bromide solutions with an additive, 2-ethyl-1-hexanol, are reported. During the absorption, the film becomes highly turbulent. Consequently, the heat and mass transfer is significantly enhanced by turbulent mixing. In addition, the instability mechanisms are detailed. In the vicinity of water absorption, surface-tension gradients due to the lower LiBr concentration, the lower additive concentration, and the higher temperature at the interface, can favor instability of the falling film.