LiBr Aqueous Solution Research Articles

Experimental investigation of aqueous LiBr solution absorber bundle with horizontal elliptical tubes

This article reports on the results of experimental studies on combined heat and mass transfer in the absorption of water vapor by aqueous LiBr solution under laminar falling film flow on the horizontal elliptical tube (HET) bundle. The performance of the absorber with HET has been calculated based on the measured parameters. The outputs are shown with respect to absorbent inlet mass concentration and Reynolds Number (Re), coolant inlet temperature and flow rate, and absorber vapor pressure. The results are compared with the published experimental results on absorber bundle with horizontal circular tubes (HCT). The results show that the heat and mass transfer coefficients enhanced on HET at aspect ratio (Ar ) > 1 with respect to HCT and improve with the increase of absorbent mass flow rate, absorber vapor pressure, coolant flow rate, and also with the decrease of absorbent concentration and coolant inlet temperature. Because of film thickness increasing and droplet flying off from the tube bundle, the maximum heat transfer coefficient is attained in an optimum absorbent mass flow rate around Re = 45. Finally, the empirical correlations for outside Sherwood number (Sh) and Nusselt number (Nu) are found to depend on the Re, Schmidt number (Sc), mass concentration and absorber vapor pressure.

Experimental Methane Hydrate Dissociation Conditions in Aqueous Solutions of Lithium Salts

Gas hydrate dissociation pressures have been determined for methane in aqueous solutions of LiBr w = (0.05, 0.10, 0.15, and 0.2655) and LiCl w = (0.05, 0.10, 0.15, and 0.20) along the hydrate–liquid–gas equilibrium line in the temperature range (260 to 290) K and for pressures up to 22.5 MPa by applying an isochoric method. LiBr showed a more pronounced inhibition effect than LiCl as expected from the different degree of hydration caused by the different anion sizes.

Heat Transfer and Thermodynamic Performance of LiBr/H2O Absorption Heat Transformer with Vapor Absorption Inside Vertical Spiral Tubes

In this paper, an absorption heat transformer (AHT) with falling film of aqueous LiBr solution inside vertical spiral tubes is installed and tested. The variations of coefficient of performance (COP), thermal efficiency (Eth ), and the heat transfer coefficient of the absorber at different falling film flow rates, hot water flow rates, and operating temperatures are investigated experimentally. The results demonstrated that the coefficient of performance and thermal efficiency of the system decrease with the increase in the flow rate of LiBr solution, and the influence of flow rate of hot water on COP and Eth is insignificant. The available COP in the experiments is higher than 0.4. The heat and mass transfer coefficients of the absorber increase with the increase of the flow rate of LiBr solution, up to 400W/m2/K and 0.013 kg/m2/s (temperature of waste heat is 90°C). The heat transfer coefficient of the absorber increases with the increase of the temperature of waste heat, and decreases with the increase of the cooling water temperature. Meanwhile, the computer code ABSIM (Absorption Simulation) is used to simulate the AHT systems, and the simulated results are compared with the experimental data.

E124 排熱回収型吸収式ヒートポンプによる高温生成および吸収液膜熱伝達

Heat transfer in a heating-up mode of LiBr-water absorption heat pump was experimentally studied. The experiment was performed for a single heat transfer tube working as absorber. Overall heat transfer coefficient and convective heat transfer coefficients between the tube wall and a film of LiBr aqueous solution flowing down on the inside wall of a spiral tube were determined. Overall heat transfer coefficient was 31.9 W/(m^2・K), whose magnitude was a little lower than that obtained in the bench scale examination due to difference of the convection heat transfer condition around the outside of the tube. The average film heat transfer coefficient was 252 W/(m^2K) and lower than the prediction estimated from an empirical correlation reported conventionally for single phase fluid flow. The difference might be caused because absorption liquid absorbed water vapor from evaporator on the surface of the liquid film, which was accompanied with heat generation and change of the liquid properties along the stream in the present heat transfer system.

Exergy calculation and analysis of a dehumidification system using liquid desiccant

Liquid desiccant dehumidification is an effective method for extracting moisture from humid air and consumes less energy than conventional methods. Exergy is an essential tool to analyze liquid desiccant dehumidification systems. The problem with current exergy analysis of liquid desiccant dehumidification systems is that the exergy calculation for humid air is inconsistent with the exergy calculation for liquid desiccant. The choice of the dead state is the key issue in exergy analysis. In this paper, the saturated air state of ambient temperature is selected as the ultimate dead state. The ultimate dead state of liquid desiccant is defined by limitation of the infinitely diluted solution that will guarantee the uniqueness of the ultimate dead state in the system and address the previously mentioned inconsistency. The exergy flow in the liquid desiccant dehumidification cycle is also calculated (LiBr aqueous solution is used as an example), and exergy expressed per kilogram of dry air and per kilogram of solute can simplify the calculations. Exergy destruction, a measurement of irreversibility in the heat and mass transfer process, indicates the direction of system improvement.

Performance analysis on a new multi-effect distillation combined with an open absorption heat transformer driven by waste heat

In this paper, a new water distillation system, which consists of either a single- or multi-effect distiller combined with an open absorption heat transformer (OAHT), has been proposed.The new integrated system can be used for distilling waste water with high amounts of SiO2 from heavy oil production, and the resultant distilled water can be supplied to steam boilers to produce high quality steam which in turn is injected into oil reservoirs to assist with heavy oil recovery. The thermodynamic cycle performances for these new integrated distillation systems were simulated based on the thermodynamic properties of the aqueous solution of LiBr as well as the mass and energy balance of the system. The results indicate that combined with OAHT, the waste heat at 70 °C can be elevated to 125 °C and thereby produce steam at 120 °C in the absorber, which is able to drive a four-effect distiller to produce distilled water. For a single-effect and four-effect distiller, the coefficients of performance (COP) are approximately 1.02 while the performance ratios are 2.19 and 5.72, respectively. Therefore, the four-effect distillation system combined with an OAHT is more thermally effective and is an ideal option to process the waste water in oilfields.

Experimental Analysis of Effects of Non-Structural Factors on Performance of Liquid-Gas Ejector Driven by Aqueous LiBr Solution

Miniaturization and high-efficiency plays an important role in the further development of absorption refrigeration. In order to improve the mass transfer efficiency, liquid-gas ejector is intended to be used in refrigeration system. Experimental analysis of effects of non-structural factors on Liquid-Gas Ejector driven by aqueous LiBr solution is presented. Solution concentration, solution temperature, evaporator temperature and back pressure are varied to analyze the ejector performance. The results show that the large difference between refrigerant vapor pressure and partial pressure of solution enhances absorption of water into aqueous lithium bromide solution. The optimal solution concentration range is 56.61wt%~57.61wt% when the throat diameter of convergent-divergent nozzle is 1.5mm. Cooling capacity increases with the decreasing of back pressure.

Numerical Study on Vapor Absorption into Aqueous LiBr Solution in a Liquid-gas Ejector Using Convergent Nozzle

In this study, we have a numerical study on vapor absorption into aqueous LiBr solution in a liquid-gas ejector using convergent nozzle. A model of heat and mass transfer process in absorption of water vapor into a lithium bromide solution in liquid-gas ejector was developed. The model can predict vapor entrainment rate and mass fluxes. The effect of operating condition has been investigated. It has been observed that the absorption mass flux and the vapor entrainment rate increase as the mass flow rate of the inlet solution increases, the inlet solution concentration increases, the inlet solution temperature decreases and the absorber pressure increases. In our results, we get that the mass flux and vapor entrainment rate increases with the mass flow rate, inlet solution concentration, absorber pressure; the mass flux and vapor entrainment rate increases as the inlet solution temperature decreases; the mass flux rapidly decreases at first and slowly to zero value along flow direction.

The Pumping Up Phenomenon of Double-Stage Bubble Pump with Water and Aqueous LiBr Solution

The double-stage bubble pump, using thermal energy as driving force to transport the solution, can replace the mechanical solution pump in the double-effect lithium bromide absorption chiller. By building a bench, a lot of experimental research and analysis were conducted with water and different concentrations of lithium bromide solution as the working fluid of the bubble pump. The first-stage bubble pump in the experiment pumps up by the external heat source. The heat for driving the second-stage bubble pump is provided by refrigerant steam produced from the first-stage bubble pump. The experiment data shows that the heating of refrigerant vapor is only one of the elements of pump-up phenomenon. Another is that the intermediate solution flashes to vapor to become bubbles. The pump-up phenomenon of double-stage bubble pump has much to do with the pressure difference of intermediate solution and first-stage refrigerant vapor. With water as the working fluid, when the pressure difference between refrigerant vapor and the intermediate liquefied refrigerant is 3.5-3.9 kPa, the bubble pump can pump up and run for some time and the start-up time decreases with the driving head. When the working fluid is lithium bromide solution, the pressure difference of the double-stage bubble pump increases with the solution concentration and is bigger than that of water. The start-up time increases with the concentrations of lithium bromide solution within the range of 45.5 to 54% and decreases within the range of 54-59.5%. The start-up time is largest at 54% under this experimental condition. The experimental result is also compared with the single-stage bubble pump. The start-up time of double-stage bubble pump decreases with the driving height, which is contrary to the single-stage bubble pump.

Effect of Surfactant Concentration on Aqueous LiBr Solution Absorption Rate

It is well known that small amounts of surfactants, such as 1-Octanol, in the aqueous solution can increase the absorption rate significantly. In this paper, experimental data were obtained for absorption of water vapour into an aqueous LiBr solution with different concentrations of 1-Octanol. An experimental rig was specifically designed and developed in this work in order to investigate the effect of surfactant (1-Octanol) on the enhancement of the heat and mass transfer in the absorption process, in addition to, the investigation of the impact of the use of magnetic stirrer inside the absorber. The experimental rig for this study was based on the refrigeration mode of the intermittent vapour absorption system. In order to study the heat and mass transfer in water-lithium bromide vapour absorption air conditioning systems, it was necessary to monitor the concentration of the solution continuously. As a consequence, two procedures for obtaining the LiBr solution concentration were used. The first method was based on the measurement of the density and temperature of the solution, while the second was based on its electrolyte conductivity and the temperature. The experimental results showed that the surfactant concentration has a significant effect on the absorption rate; this is called the Marangoni instability. It has been concluded that, in order to clarify the absorption enhancement phenomenon, it is necessary to understand the physicochemical aspects of the absorption process and the effect of surfactants on the enhancement of such process. Additionally, it has been concluded that new approaches are needed to explain the observed behaviour.

The study on the critical heat flux and pool boiling heat transfer coefficient of binary nanofluids (H2O/LiBr + Al2O3)

In this study, we measured the critical heat flux (CHF) and boiling heat transfer coefficient of H2O/LiBr-based binary nanofluids. By using the PVA (polyvinyl alcohol) as a stabilizer, Al2O3 nanoparticles could be stably dispersed in H2O/LiBr. The plate copper heater (10 × 10 mm2) is used as the boiling surface. The concentration of nanoparticle varies 0–0.1 vol%, dispersed in H2O/LiBr solutions (3, 7 and 10 wt% of LiBr). The results show that the boiling heat transfer coefficient of the binary nanofluids becomes lower than that of the base fluid as the concentration of nanoparticles increases while CHF of it becomes higher. We obtained an enhanced CHF of ∼48.5% (compared to the base fluid) with the 0.1 vol% Al2O3 in 10 wt% LiBr aqueous solution.

Effect of LiBr pore-filling on morphological, optical and electrical properties of porous silicon membrane

This study describes the developmental properties of PS membrane derived from the pore-filling with aqueous LiBr solutions. A complete process is described and the effect of pore-filling with Lithium bromide (LiBr) on PS membrane structural, optical and electrical properties is investigated. The microstructural and surface morphology of the elaborated samples were characterized mainly by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The AFM shows an increase of the nanoparticles dimension compared to the initial dimension of the PS membranes nanostructure. This result shows that LiBr covers the nanoparticles of PS membranes, which was confirmed by photoluminescence study. A modification of PS membranes morphology accompanied with significant decrease of reflectivity. The rise of the conductivity is significant after pore-filling with LiBr solution. The conductivities of porous silicon membrane are 0.021S/cm before pore-filling and 0.019S/cm after pore-filling with LiBr solution. This suggests the choice of LiBr as filler to improve the electrical conductivity of porous silicon membrane.

Molecular weight distribution and solution properties of silk fibroins with different dissolution conditions

Four regenerated silk fibroin (SF) samples were prepared under different dissolution conditions and their molecular weight (MW) distributions and solution properties in water and formic acid were examined. SFL, produced by dissolving in LiBr aqueous solution for 6h, showed the highest MW level. In the three SFC samples, produced by dissolving SF in CaCl2/H2O/EtOH solution for dissolution times ranging from 3 to 180min, the MW of the SFs decreased with increasing dissolution time and a new band appeared at low MW. Interestingly, SFL presented as a relatively transparent aqueous solution with 10–30nm particle size, whereas the three SFC samples exhibited a turbid solution with 100–300nm particle size. SF formic acid solutions showed a higher viscosity than SF aqueous solutions and exhibited almost Newtonian fluid behavior, whereas SF aqueous solutions displayed abrupt shear thinning in the low shear rate region (0.1–3s−1).

Experimental Research on Effects of Diffuser and Mixing Chamber on Liquid-Gas Ejector Driven by Aqueous LiBr Solution

From the standpoint of offering reference for its optimal design, liquid-gas ejector is applied to absorption refrigerator in order to improve mass transfer efficiency. The experimental performance of ejector driven by aqueous LiBr solution was investigated. The experimental results indicate that the diffuser with larger diameter of throat could improve the system cooling capacity while reducing the volume of absorber; the larger diameter of the mixing chamber could improve the cooling capacity, but the extent of improvement is little and the required absorber volume per kW of cooling capacity greatly is increased.

A novel approach for modelling LiBr–H2O falling film absorption on cooled horizontal bundle of tubes

A two-dimensional numerical model is developed to describe the coupled heat and mass transfer phenomena for treating the two-dimensional water vapour absorption into an aqueous solution of LiBr, flowing over a bundle of smooth horizontal tubes. Unlike other studies, the partial differential equations describing the transport phenomena of the absorption process are solved using an efficient computational method. Emphasis is given in describing the electrolytic nature of the aqueous solution, introducing the effect of variable heat of absorption on the temperature field. The increase of solution mass flow rate results in the reduction of the solution temperature and concentration at the outlet of the tube bank. For solution mass flow rates higher than a certain value, the solution temperature and concentration remain unchanged. Thus, for given cooling water and solution inlet conditions, the maximum efficiency of the absorption process is directly related to a certain number of horizontal tubes.

Experimental study on vertical vapor absorption into LiBr solution with and without additive

Absorption cycles have been attracting more and more attention in the energy saving industry. Environmentally friendly working fluids were employed, such as LiBr and water. Heat and mass transfer enhancement are both critical to improve the efficiency of absorption cycles. It is well known that significant enhancements of heat and mass in the absorber could be obtained by adding small amounts of additives. Experimental studies of vapor absorption into LiBr solution were presented outside vertical tubes. Various effects of operation parameters on mass transfer were investigated. Strong mass transfer enhancement occurred with 2EH (2-ethyl-1-hexanol) of 90 ppm in LiBr aqueous solution.

The preparation of high performance silk fiber/fibroin composite

An all-silk composite, in which uniaxially-aligned and continuous-typed Bombyx mori silk fibers were embedded in a matrix of silk protein (fibroin), was successfully prepared via a solution casting process. The structure, morphology, mechanical and thermal properties of such silk fiber/fibroin composites were investigated with X-ray diffraction, scanning electron microscopy, tensile and compression tests, dynamic mechanical analysis and thermogravimetric analysis. The results demonstrated that the interface adhesion between silk fiber and the fibroin matrix was enhanced by controlling the fiber dissolution through 6 mol L−1 LiBr aqueous solution. Compare to those of the pure fibroin counterparts, the overall mechanical properties as well as the thermal stability of such silk fiber/fibroin composites were significantly improved. For example, the composite with 25 wt% fibers showed a breaking stress of 151 MPa and a breaking elongation of 27.1% in the direction parallel to the fiber array, and a compression modulus of 1.1 GPa in the perpendicular direction. The pure fibroin matrix (film), on the other hand, typically had a breaking stress of 60 MPa, a breaking elongation of 2.1% and a compression modulus of 0.5 GPa, respectively. This work suggests that such a controllable technique may help in the preparation of animal silk based materials with promising properties for various applications.

A mathematical model with experiments of single effect absorption heat pump using LiBr–H2O

A mathematical model of a single effect, LiBr–H2O absorption heat pump operated at steady conditions is presented. This model took into consideration of crosscurrent flow of fluids for heat and mass exchangers, two-dimensional distribution of temperature and concentration fields, local values of heat and mass transfer coefficients, thermal parameter dependent physical properties of working fluids and operation limits due to the danger of the LiBr aqueous solution hydrates and crystallization. Improvements of the calculation method make this simulation much more convenient and efficient. An improved absorber experiment set-up and a complete absorption heat pump were built and tested for further study. It was found that the mass flux of vapor increased with the increase of absorber pressure, coolant flow rate, spray density of LiBr solution and decrease of coolant and input temperature of solution. And the vapor mass flux increased almost linearly with the increase of absorber pressure. Results derived from this model show agreement within 7% with experimental values.

Mass transfer performance comparison of two commonly used liquid desiccants: LiBr and LiCl aqueous solutions

Mass transfer performance of two commonly used liquid desiccants, LiBr aqueous solution and LiCl aqueous solution, is compared in this paper on the basis of the same solution temperature and surface vapor pressure. According to the analysis of the analytical solutions of heat and mass transfer processes, the key performance influencing factors are heat capacity ratio of air to desiccant m * and mass transfer unit NTU m . The heat capacities of the two liquid desiccants are about the same at same volumetric flow rate, and LiBr solution has higher density and smaller specific heat capacity. The variance of mass transfer unit with different operating conditions and liquid desiccants are derived based on the experimental results. In the condition of the same desiccant mass flow rate, the dehumidification performance of LiCl solution is better, and the regeneration performance of LiBr solution is a little better or almost the same as that of LiCl solution. In the condition of the same desiccant volumetric flow rate, the dehumidification performance of LiCl solution is a little better or about the same compared with LiBr solution, and the regeneration performance of LiBr solution is better. The COPs of the liquid desiccant systems using these two desiccants are similar; while LiCl solution costs 18% lower than LiBr solution at current Chinese price.

The influence of Reynolds number on the galvanic corrosion of the copper/AISI 304 pair in aqueous LiBr solutions

The influence of Reynolds number on the galvanic corrosion of the copper/AISI 304 stainless steel pair in a concentrated lithium bromide solution was investigated according to the mixed potential theory. A hydraulic circuit was designed to study dynamic corrosion processes in situ. A potential relation between corrosion current density ( i corr) and Reynolds number (Re) was found for copper, showing a mixed control of a chemical step and mass transport through the corrosion products film with the predominance of the former. No dependence of i corr on Re could be established for AISI 304, showing a chemical step control. Moreover, under stagnant conditions, partial passivation may occur in AISI 304; however, under flowing conditions passivation is not possible. Copper is the anodic element of the pair under all flowing conditions analysed. The galvanic phenomenon is more important as Re increases, but the results show compatibility of both materials at all Re values analysed. Similarly, a potential relation between galvanic current density ( i G) and Re was found, showing a mixed control of a chemical step and mass transport with the predominance of the latter. Copper corrosion resistance decreases more rapidly as Re increases due to the AISI 304 galvanic effect: there is a synergy between the galvanic effect and the hydrodynamic conditions. Under stagnant conditions, the galvanic behaviour of the materials is close to the compatibility limit and an inversion of the anodic element of the galvanic pair takes place.