Aqueous Lithium Bromide Solution Research Articles

Determination of operating temperature in main generator of a two-stage absorption refrigeration machine working on an aqueous solution of lithium bromide

This paper examines the thermal characteristics of a two-stage absorption refrigeration machine. When carrying out a numerical analysis, it turned out that the secondary generator’s temperature was not constant, and it was also found that the coefficient of thermal performance of this cycle increased significantly at the beginning, then stabilized at a certain value for the temperature degree of the primary generator. But this result is not the right value for calculating the absorption refrigeration cycle; it might cause crystallization inside the cycle and This was verified based on the thermodynamic relationship chart (h-X-T) for LiBr-water solution. In addition, the decisive point for determining the appropriate temperature is to study the change in refrigeration capacity in the process when the temperature of the generator changes. In this case, the design temperature for the primary generator should be in the range between the temperature corresponding to the highest refrigeration capacity and the temperature far from the crystallization phenomenon.

Use of Ionic Liquid as Crystallization Inhibitor in Water-Lithium Bromide Absorption Chiller

Chillers are used in commercial buildings and industrial plants to provide air conditioning, refrigeration, and process fluid cooling. There are two basic types of chiller cycles: vapor compression and sorption. Sorption chillers are available as either absorption or adsorption designs, depending on the state of the sorbent. Absorption chillers use fluid refrigerants and absorbents (liquid or dissolved), while adsorption chillers employ a solid sorbent (typically silica gel) in combination with a fluid refrigerant. Among the former category, the use of highly hygroscopic LiBr salt as absorbent in combination with H2O as refrigerant comprises LiBr-H2O absorption chillers. Such chillers possess cooling capacities ranging from a few kilowatts (kW) to megawatts (MW) which match with small residential to large scale commercial or even industrial cooling needs. One of the major debilitating factors associated with LiBr-H2O absorption chillers is crystallization. A crystallization event causes a loss of cooling and requires de-crystallization by applying external heat, which results in extensive down-time and requires redundancy designed into a chiller plant. We investigated the use of the imidazolium-based ionic liquid, 1-butyl-3-methylimidazolium bromide ([BMIm]-Br), as crystallization inhibitor additive to LiBr-H2O in the ratio 1:19 [BMIm]-Br:LiBr. It was found that under the operating boundary conditions of 27°C/9°C (cooling water inlet temperature/chilled water outlet temperature), the LiBr-H2O absorption chiller can be operated without modifications and with around 10 K higher heating water inlet temperatures when adding [BMIM]-Br before crystallization occurs compared to pure LiBr-H2O solution. When using the [BMIM]-Br ionic liquid, the refrigeration capacity of the absorption chiller under the above operating conditions and at 85°C heating water inlet temperature exhibited 10% increase after optimizing the solution flow, that lead to higher outputs, such as lower cooling water temperatures. By adding the [BMIM]-Br to the aqueous lithium bromide solution the operating range of the absorption refrigeration system could also be extended to resorption mode, which allows refrigeration below 0 °C. Thus, there is an excellent potential for a significant extension of the application range of LiBr-H2O chillers, e.g. in the field of food cooling and refrigeration processes. Figure 1

Effect of Lactate-Based Protic Ionic Liquids on the Thermodynamic and Transport Properties of Aqueous Lithium Bromide Solutions at Different Temperatures

Effect of Lactate-Based Protic Ionic Liquids on the Thermodynamic and Transport Properties of Aqueous Lithium Bromide Solutions at Different Temperatures

The effect of external and operating conditions on a solar Lithium Bromide absorption chiller

The excessive consumption of fossil energies (electrical energy) during summer caused by the technological development involves more and more climate warming, in order to relieve insistency between electric supply and demand, heat driven absorption chillier is pretty promising, it consists on using heat (solar) as motive energy to provide cold energy. The single effect absorption cycle is the simplest absorption cycle, it’s composed of four main components which are all heat exchangers using a diversity couple of refrigerant. Lithium bromide aqueous solution is one of many others solutions widely used in the absorption chiller for cooling purposes; it possesses several advantages over the other type of absorption systems, such as It highest coefficient of performance compared to other absorption units at the same conditions. A simple flat plat collector can assume the energy required for heating the solution in the generator. Even though, LiBr solution may cause the problem of the crystallization and the limitation of this machine on cooling did not affect the economical aspect of LiBr absorption chiller. The main aim of this article is to study the effect of thermal and environmental parameters each compound of an absorption chiller which produce a cool power equal to 1 kW.

Waste Heat Recycling Absorption Refrigeration Circulation System

To maximize energy use, this paper designs a lithium bromide absorption refrigeration system that is used to recycle and use low-temperature energy and industrial residual heat. Firstly, the mathematical model of the system is established using the lithium bromide aqueous solution status equation and the equation of the state of water and steam to obtain the state parameters in the thermodynamic calculation process of the system. Secondly, according to the principle of mass economy, energy saving, and heat transfer, the thermodynamic parameters of each process of the system are obtained to assist the design of the system. Finally, the influence of some key parameters on the system is simulated and analyzed to obtain the optimal parameters which can make the system recovery efficiency the highest. The simulation results show that the system conceived in this article can efficiently recycle waste gas and achieve the purpose of refrigeration. Therefore, it has a certain value of popularization.

Viscosity Correlation for Aqueous Lithium Bromide Solution

A correlation for dynamic viscosity of aqueous lithium bromide solution is proposed. The correlation is based on an empirical approach accounting for physical limitations. The data are compiled from 11 sources over a temperature range from − 20 ^{circ }C to 110 ^{circ }C and from pure water to salt mass fractions of 65 %. The correlation succeeds in predicting the solution’s viscosity over the chosen range of measured data. In most parts of its validity range the accuracy is significantly improved compared to previous equations.

Experimental study on heat and mass transfer characteristics between a novel ionic liquid and air under low-humidity conditions

Functional ionic liquids (ILs) are a promising alternative to traditional liquid desiccants. This work is mainly concerned with an experimental investigation on the dehumidification and regeneration performance of an adiabatic falling-film device working with a novel ionic liquid (IL). A specialty of this report is the operation under rather low air temperature as well as low absolute humidity. The effect of air and solution volume flow on the coupled heat and mass transfer coefficient was evaluated based on the state parameters of air and solution by means of the NTU-Lef model. Additionally, aqueous lithium bromide solution (LiBr-H2O) was used for comparison. The results indicated that both IL and LiBr-H2O can dehumidify moist air to nearly 2.2 g/kgda, and the regeneration rate of IL is significantly larger than that of LiBr-H2O. The heat and mass transfer coefficient of IL in dehumidification process is less than that of LiBr-H2O, while the regeneration process is the opposite. It is found that the low wettability of IL on the surface of falling-film plate limits its excellent dehumidification potential, whereas its high mass transfer coefficient in the regeneration process makes up for the disadvantage of poor regeneration potential. Besides, a new correlation for the coupled heat and mass transfer coefficient of IL is proposed. From the perspective of operation optimization, increasing the wettability of IL on falling-film plate will significantly improve the dehumidification rate, and the optimal flow range of IL needs to be considered in the regeneration process. This study establishes a basis for the optimization of heat and mass transfer process between ILs and moist air, and provides guidance for the application of liquid desiccant dehumidification under low-humidity conditions.

Marangoni convection within thermosolute and absorptive aqueous LiBr solution

The Marangoni convection during steam absorption into an aqueous lithium bromide (LiBr) solution is investigated numerically. In order to obtain a better understanding of the physical mechanism of thermal convection in the solution, the influence of surface tension on the absorbing solution is explored. For this purpose, this paper proposes the radial basis function (RBF) meshless method for numerical simulation of thermosolutal convection and vapor absorption in aqueous LiBr solution problems. The spatial terms of the governing equation are discretized using the RBF meshless method. The fractional step method is used for solving the continuity equations and momentum equations. The coupled energy and species equations are solved iteratively. The semi-algebraic system is solved using an implicit backward Euler scheme to maintain stability. The no-slip boundary conditions are imposed on solid wall surface. The surface tension gradient and the energy balance due the phase change are imposed on the interface of vapor and solution interface. The thermosolutal convection problem is presented to examine the accuracy of proposed method. An analytical solution is also presented for validating the vapor absorption problem results for zero Marangoni number (Ma). The Marangoni number used has a range of 0 ≤ Ma ≤ 1000. The increase in Marangoni number for low Prandtl number values does not significantly affect heat and mass transfer. However, increasing Ma for LiBr solution has a significant effect. It is also found that the velocity of convection flow can be improved by adding a solid object to the interface.

Experimental data on the physicochemical and thermodynamic properties of the aqueous lithium bromide modified by the addition of lithium salt

Due to the good performance in absorption systems, lithium bromide plus water solution is the most widely used working pair. The disadvantages of this system, including, in particular, the tendency to crystallize, makes it necessary to search for new solutions. Properly choosing additives to conventional lithium bromide aqueous solution to improve the performance of the cycle is an important part of the lithium bromide absorption refrigeration studies, including ours. This paper is a continuation of our comprehensive research in this area. Mixtures consisting of lithium bromide + lithium acetate + water, and lithium bromide + lithium lactate + water, and lithium bromide + lithium trifluoroacetate + water are thought to be promising alternatives to the conventional system. In this research, the influence of three lithium salts on solubility are presented. Based on solubility measurement, two additives are selected and vapour pressure, and physicochemical properties for {lithium bromide + lithium acetate, or lithium lactate + water} systems is presented. Measurements of vapor pressure, dynamic viscosity, and the liquid density are carried out over a wide range of temperatures and compositions. Empirical equations are used to correlate dynamic viscosity, and density data. Based on the comparison between experimental results presented here and literature data for.a conventional binary system, the effect of the additive on physicochemical and thermodynamic properties is characterized and the possibility of the potential application of such new ternary systems in absorption refrigeration technology is determined.

Vapor Pressure and Physicochemical Properties of {LiBr\u2009+\u2009IL-Based Additive\u2009+\u2009Water} Mixtures: Experimental Data and COSMO-RS Predictions

In recent years, many compounds have been proposed as additives to conventional working fluids to improve the performance of the absorption refrigeration system. The main aim of this research is to show the influence of ionic liquid based additives on thermodynamic and physicochemical properties of {LiBr + water} solutions. The following additives: 3-(1-methyl-morpholinium)propane-1-sulfonate, N,N-di(2-hydroxyethyl)-N,N-dimethylammonium bromide, and N,N,N-tri(2-hydroxy-ethyl)-N-methylammonium bromide have been added to aqueous lithium bromide solutions (IL to LiBr mass fraction, w2 = 0.3). The physicochemical and thermodynamic properties of {LiBr (1) + additive (2) + water (3)} and {LiBr + water} systems including (vapor + liquid) phase equilibria (VLE), density (ρ) and dynamic viscosity (η) were determined over wide temperature and composition ranges. The conductor-like screening model for real solvents (COSMO-RS) was used for the VLE data prediction. For the density and dynamic viscosity correlations, empirical equations were applied. A comparison of experimental data for {LiBr + additive + water} with those for {LiBr + water} systems shows the influence of using the additives proposed in this work. The data presented are complementary to the current state of knowledge in this area and provide directions for future research.

Study on characteristics of the cavitation bubble dynamics of lithium bromide aqueous solution with ultrasonic interaction

Solar absorption refrigeration (SAR) system occupies large building energy consumption, due to its low generation efficiency. Depending on the mechanism of enhanced disturbance and convection, this paper proposes the application of ultrasound heat-transfer enhancement technology in the boiling heat-transfer of LiBr/H2O solution in the generator to enhance system performance. At present, there are few theoretical and experimental studies about the ultrasound on heat-transfer enhancement in the salt solution, especially in the field of multi-frequency ultrasound (MFU) bubble dynamics. The motion of a cavitation bubble has significant impact on the disturbance and convection in the solution. Thus, the mathematical models of cavitation bubble dynamics (CBD) are constructed to evaluate the solution cavitation characteristics, the CBD on boiling heat-transfer in the generator is investigated, and the effect of the number of ultrasonic vibrators (UVs) on the cavitation bubble radius (CBR) is investigated to explore the cavitation characteristics of MFU. The results indicate that: the low-frequency ultrasound on the heat-transfer in vacuum generator is more obviously effect, due to enhance solution mixing around the heating surface; the maximum CBR could be increased by increasing the number of UVs, while the maximum CBR is increased by no more than 1% at the number of UVs of 24–25 and the total sound intensity of 1 W/cm2, respectively; the solution in vacuum generator could produce transient-cavitation with MFU. This study, not only reaffirms the benefit of using the MFU for generator of SAR system, but also provides some rules of the cavitation characteristics of MFU.

Relationship between the Photoluminescence Spectra and IR Spectroscopy of Mesoporous Silicon Samples during Long-Term Storage: The Effect of Immersion in an Aqueous LiBr Solutions

Studies are devoted to determining the effect of long-term storage (up to 200 days) of untreated and immersion-treated layers of mesoporous silicon in an aqueous lithium bromide solution obtained by anodizing with a current density of 10 mA/cm2 in electrolyte HF: CH3OH = 2: 1. It was found that an increase in the PL intensity and its saturation with a storage time of more than 100 days in all samples is observed. A detailed analysis of absorbance on bonds in m/por-Si showed that during storage, hydrogen bonds are destroyed, and the PL peak intensity is proportional to the increasing concentration of non-stoichiometric oxide, in which oxygen atoms forms radiative states. It was shown that in the treated samples, the PL intensity decreases with increasing immersion time, but the mechanism of photoluminescence through the quantum size confinement (QSC) effect in mesoporous silicon without and with immersion in an aqueous LiBr solution is not significant.

Evaluation of a new air water generator based on absorption and reverse osmosis

The evaluation of a new air water generator (AWG) based on absorption and reverse osmosis is described. For the evaluation, an aqueous lithium bromide solution has been selected from a wide range of liquids as the absorbent. At high salt mass fractions, the aqueous lithium bromide solution has a low vapour pressure and a high osmotic pressure. The low vapour pressure ensures that the water vapour can be absorbed from the air, but the high osmotic pressure leads to high pressures over the membrane. Due to the high osmotic pressures, several reverse osmosis membrane modules are necessary and salt solution has to be present on both sides of the membrane, which leads to an additional inlet on the permeate side. Models for the absorber, the reverse osmosis membrane module and the complete multi-stage reverse osmosis system have been developed in Python. The model of the complete system has then been used to simulate the performance of the AWG at different boundary conditions. The simulations have shown that based on the defined assumptions, extracting water from the air with absorption and reverse osmosis is possible and that the energy demand per litre of pure water is similar to AWG systems which use condensation.

Green Synthesis of Free Standing Cellulose/Graphene Oxide/Polyaniline Aerogel Electrode for High-Performance Flexible All-Solid-State Supercapacitors.

The cellulose/graphene oxide (GO) networks as the scaffold of free-standing aerogel electrodes are developed by using lithium bromide aqueous solution, as the solvent, to ensure the complete dissolution of cotton linter pulp and well dispersion/reduction of GO nanosheets. Polyaniline (PANI) nanoclusters are then coated onto cellulose/GO networks via in-situ polymerization of aniline monomers. By optimized weight ratio of GO and PANI, the ternary cellulose/GO3.5/PANI aerogel film exhibits well-defined three-dimensional porous structures and high conductivity of 1.15 S/cm, which contributes to its high areal specific capacitance of 1218 mF/cm2 at the current density of 1.0 mA/cm2. Utilizing this cellulose/GO3.5/PANI aerogel film as electrodes in a symmetric configuration supercapacitor can result in an outstanding energy density as high as 258.2 µWh/cm2 at a power density of 1201.4 µW/cm2. Moreover, the device can maintain nearly constant capacitance under different bending deformations, suggesting its promising applications in flexible electronics.

The study on the influence of glycols on the vapor pressure, density and dynamic viscosity of lithium bromide aqueous solution

This paper is a continuation of our comprehensive research on finding the most effective additive to the conventional {lithium bromide + water} system, which is commonly used in absorption refrigeration technology. Serious disadvantages of commercially used working pairs in absorption refrigeration make it necessary to modify them. Such modification can be carried out by finding and characterizing new additives to conventional systems that will improve the operation of the refrigerator, which this work relates to. The addition of a chemical compound to such a system is one of the possibilities to improve the properties of the working pair, increase the efficiency of the absorption refrigerator and eliminate their main disadvantages. The main disadvantage of {lithium bromide + water} system is the crystallization of this salt. In recent years, many compounds have been proposed as additives to this conventional system to improve the functioning of the absorption aggregate. Based on the results obtained in our previous research, we selected substances that most effectively affected the solubility of lithium bromide in water. In this work, tests on ethylene glycol, diethylene glycol, triethylene glycol, and glycerol (additive to LiBr mass fraction w2 = 0.3) which were added to the binary {LiBr (Boryta, 1970) [1] + water (Iyoki et al., 1990) [2]} system were performed. Measurements of vapor pressure, dynamic viscosity and liquid density were carried out over a wide range of temperatures and composition. Experimental VLE data were predicted using the conductor-like screening for real solvents model, COSMO-RS. Empirical equations were used to correlate dynamic viscosity and density data. Based on the comparison of results obtained in the case of ternary systems to the properties of a conventional binary system, the effect of the additive on physicochemical properties was characterized and the possibility of potential application of such new ternary systems in absorption refrigeration technology was determined.

Experimental investigation of saturated pressure and mass transfer characteristics of nano-lithium bromide solution

The purposes of this study are to measure the saturated vapor pressure and the mass transfer rate of lithium bromide (LiBr) aqueous solution in the presence of 40 nm CuO nano-particles with the concentrations of 0.0, 0.01, 0.05, 0.1 and 0.12 wt%, and to research the effects of nano-particles, solution concentration and temperature on the saturated vapor pressure and the water vapor absorption rate. Experimental results demonstrate that nano-particle is the main factor affecting the saturated vapor pressure and the mass transfer rate. The saturated vapor pressure decreases with nano-particle mass fraction up to an optimum concentration (0.1 wt% in CuO nanofluids) while increases by increasing the concentration of nano-particle further, and the effective change ratio of saturated vapor pressure increases first and then decreases as mass fraction of nano-particle increases. The mass transfer rate is also initially increased with increasing nano-particle concentration and then emerges a slowly rising tendency. The effective absorption ratio is enhanced when the nano-particle concentration increases, and the value of maximum effective absorption ratio is obtained when the nano-particle concentration is 0.1%. The effective absorption ratio has the maximum values of 2.20 and 2.85 in 58% LiBr solution with nano-particle concentration of 0.05% and 0.1%, respectively.

Motion of a single vapor Taylor bubble in the vertical tube of small diameter

An experimental study of the dynamics of the Taylor vapor bubble in water and in an aqueous solution of lithium bromide at vapor saturation pressure was carried out. The Taylor bubble was formed after boiling-up of the overheated degassed liquid in 16 mm diameter tube. The study has shown that the dynamics of the vapor cavity during boiling up leads to a qualitative difference from the dynamics of the vapor bubble in a large volume. There are also qualitative differences in the nature of motion of the vapor bubble and that of the gas bubble. This is due to the fact that the mass of the gas bubble and the temperature of the liquid do not change during the rise near the bubble, whereas the mass of the vapor bubble and the temperature of the vapor in the bubble and the liquid near the bubble can vary significantly due to evaporation of the liquid and steam condensation. This is due to the change of bubble height and level of fluid in the tube. The liquid level in the tube depends on the height of the bubbles, but the height of the liquid level in the tube depends on the volume of the bubbles.

Desorption of Aqueous Solution of Lithium Bromide on Enhanced Surfaces in a Single-Stage Lithium-Bromide Absorption Chiller

This article presents values of heat transfer coefficients at pool boiling of aqueous solution of lithium bromide on smooth and fin tubes. The experimental studies were performed under conditions typical of absorption chiller with single-stage desorption. More exactly, the condensation pressure was about 7.8–8.5 kPa, and the concentration of lithium bromide solution was 60–61 wt%. The outer diameter of the smooth and fin tubes was 16.0 mm; the inner diameter was 12.0 mm. The surface roughness factor of the fin tubes ranged from 2.7 to 6.0. The studies have shown that for fin tubes the heat transfer coefficient reduced to a surface unit is up to 30 percent higher as compared with a smooth tube.

Model evaluation of lithium bromide aqueous solution and characteristics of water transport behaviors in liquid–vapor systems by molecular dynamics

Understanding heat and mass transfer between LiBr aqueous solution and vapor is a crucial issue in absorption refrigeration and air dehumidification for the purpose of intensifying transfer and conversion. This is difficult to be realized by macro experiments due to failing to catch detailed information of water molecules. Molecular dynamics has been resorted to for exploring mechanisms of chemical processes but the used force field dominates the simulation accuracy. In order to discover suitable force fields to describe interactions in LiBr solution, three recent models developed based on infinite dilution were evaluated in terms of static and transport properties. Results show that all models could predict the density with high accuracy. The model of Koneshan et al. achieves most properties with satisfactory accuracy and is the best one to simulate the surface tension, which indicates good interfacial performance. Further, by selecting the model of Koneshan et al., the energy and mass transport phenomenon through liquid–vapor interface was simulated and analyzed. Four behaviors of water molecules including absorption, release, replacement and reflection were observed near the interface of LiBr solution. It is found that the replacement behavior only occurs under high liquid temperature conditions and the reflection behavior is characterized by a steep energy ravine. This research provides data reference for the force field selection, setting a solid foundation for studying heat and mass transfer between LiBr solution and vapor by molecular dynamics. This research could also disclose the molecular behaviors between aqueous solution and air.

Ab Initio Molecular Dynamics Simulations of the Influence of Lithium Bromide Salt on the Deprotonation of Formic Acid in Aqueous Solution.

The deprotonation of formic acid is investigated using metadynamics in tandem with Born–Oppenheimer molecular dynamics simulations. We compare our findings for formic acid in pure water with previous studies before examining formic acid in aqueous solutions of lithium bromide. We carefully consider different definitions for the collective variable(s) used to drive the metadynamics, emphasizing that the variables used must include all of the possible reactive atoms in the system, in this case carboxylate oxygens and water hydrogens. This ensures that all the various possible proton exchange events can be accommodated and the collective variable(s) can distinguish the protonated and deprotonated states, even over rather long ab initio simulation runs (ca. 200–300 ps). Our findings show that the formic acid deprotonation barrier and the free energy of the deprotonated state are higher in concentrated lithium bromide, in agreement with the available experimental data for acids in salt solution. We show that the presence of Br– in proximity to the formic acid hydroxyl group effectively inhibits deprotonation. Our study extends previous work on acid deprotonation in pure water and at air–water interfaces to more complex multicomponent systems of importance in atmospheric and marine chemistry.