LiBr Solution Research Articles

Thermal performance investigation of LiBr solution–based nanofluids in plate heat exchangers

ABSTRACT The poor heat transfer performance of LiBr solution is one of the main obstacles to improving the performance of absorption cooling systems. In this study, the combined effects of the heat transfer enhancement and pressure loss increment of LiBr solution-based nanofluids in plate heat exchangers are investigated theoretically. First, a correlation for predicting the Nusselt number of the LiBr solution in a chevron plate heat exchanger with different chevron angles is developed based on the experimental data, and the prediction error is in the range of−3.8% to 6.0%. Second, the heat transfer coefficients and friction factors of Al2O3 nanofluid and MWCNT nanofluid are numerically calculated. The nanofluids have higher heat transfer rates than the LiBr solution. The heat transfer enhancement of the nanofluid in the 30°Chevron type plate heat exchanger is similar to that in the 60°Chevron type plate heat exchanger. The Nusselt number and heat transfer coefficient of the Al2O3 nanofluid with a 2.5% volume fraction are about 2.2% and 9% higher than those of the LiBr solution. The Nusselt number and heat transfer coefficient of the MWCNT nanofluid with 0.05% volume fraction are about 7.8% and 8.1% higher than those of the LiBr solution. The friction factor increases with the rising nanofluid volume fraction because the viscosity increases. When the nanofluid volume fractions are one-third and two-thirds of the equivalent value, the performance coefficient improvement of MWCNT nanofluid is about two to four times higher than that of the Al2O3 nanofluid. When the volume fraction is one-third of the equivalent value, the performance coefficient improvement of Al2O3 is about 30% to 40% higher than that of the MWCNT nanofluid. When the volume fraction of MWCNT nanofluid is between 0.01% vol. and 0.02% vol. and that of Al2O3 nanofluid is between 1% vol. and 1.5% vol. the heat transfer performance and economic performance of the two nanofluids can be regarded as equivalent. Finally, the appropriate selections of LiBr-solution based nanofluids for different application requirements are presented.

Experimental investigation on heat transfer and pressure drop of brazed plate heat exchanger using LiBr solution

To improve the performance and miniaturization of the absorption system, it is required to use a plate heat exchanger as a solution heat exchanger and to predict its performance accurately. In this study, the thermal performance of solution heat exchangers was investigated under operating conditions of the solution heat exchanger in the double-effect absorption system and new correlations of Nu and Fanning friction factor were developed and compared. As a result, the hot-side Nu of the high-temperature solution heat exchanger was 6.3–23.1, which was higher than that of the low-temperature solution heat exchanger (4.8–20.1). The thermal properties of the LiBr solution depending on the temperature were significantly sensitive. The developed Nu correlation (Nu = 0.273Re0.693Pr1/3) had a high accuracy with experimental results. In addition, the Fanning friction factor correlation was proposed as f = 1.601/Re0.123. The developed Fanning friction factor was lower than in other literature because the Fanning friction factor was affected by geometry parameters (chevron angle, pitch, height, and size).

Dehumidification performance improvement by using liquid desiccant blends – An experimental study

To minimize global warming and consumption of electricity, a desiccant-based air conditioning system has been proposed as a better alternative to control air humidity, compared to the conventional air conditioning system. In the present study, the performance of the hybrid desiccant was compared with the pure LiBr and KCOOH solution. Blends of LiBr and KCOOH at different weight ratios were used as desiccants. The performance of the system was compared based on its moisture removal rate and dehumidification effectiveness. The performance of the system increased with increasing desiccant flow rate, the concentration of the solute and the airflow rate. From the tested concentrations, the blend of 40% LiBr and 10% KCOOH concentration showed the highest MRR and dehumidification effectiveness among all blends of LiBr and KCOOH. From the study, it can be concluded that by using an optimized blend of LiBr and KCOOH as a desiccant in place of neat LiBr, the limitations of pure LiBr can be partly resolved without sacrificing much on the dehumidification performance.

Liquid desiccant-based deep dehumidifier working with a novel ionic liquid: Prediction model and performance comparison

Deep dehumidification system with energy conservation and stable operation is expected to be used in industrial occasions with low-humidity environment. Compared with solid desiccant dehumidification, liquid desiccant-based dehumidification is a promising alternative because of its advantages of continuous operation and low regeneration temperature. However, corrosion and crystallization problems exist with liquid desiccant-based deep dehumidifier (LDDD) using salt solutions. In this work, LDDD using a novel ionic liquid (IL) was introduced, and the heat and moisture transfer model was established based on the finite difference method. Meanwhile, the moisture transfer characteristics were numerically simulated under different operating parameters (i.e., inlet humidity ratio wa,in, air velocity va, solution mass concentration X, solution temperature ts and solution volume flow Vs). Besides, the significance of various factors and their interactions were analyzed based on response surface methodology. The numerical model is validated against the experiment of the LDDD test bench with a relative deviation of 3%-8%. Numerical results show that the LDDD using IL can achieve deep air dehumidification, and outlet humidity ratio of less than 4 g/kgda is possible. In particular, the order of significance for influencing factors of outlet humidity ratio is: wa,in > X > ts > va > Vs. Moreover, it is found that dehumidification rate of 60% LiBr solution (saturated state) is less than that of 90% IL. This study establishes a prediction model of moisture transfer between IL and air under the coupling of multiple physical fields, and provides guidance for the application of LDDD using ILs.

Thermodynamic and Economic Performance Assessment of Double-Effect Absorption Chiller Systems with Series and Parallel Connections

Absorption cooling technologies converting excess heat and renewable heat resources to cooling energy have shown progress in recent years. In this study, two 400 kW LiBr solution absorption chiller types with series and parallel connected are analyzed over a range of parameter values to better understand their applicability for different uses. Thermodynamic models for the components were constructed and validated. The performance of the chillers related to heat transfer, energy, exergy, and economy performance was comprehensively analyzed. The operating performance was investigated by considering the external variables, including inlet cooling water, chilled water, and inlet steam temperatures and the solution allocation ratio. The results indicate that the parallel connected chiller reaches higher energy and exergy performance than the series-connected chiller, but the heat transfer and economic performance was lower. The coefficient of performance and the exergy efficiency of the parallel chiller were for the reference system 1.30 and 24.42%, respectively. Except for the exergy efficiency, the inlet steam and inlet chilled water temperature had positive impact on the heat transfer, energy, and economic performance, while the inlet cooling water temperature trends the opposite. The sensitivity analysis on solution allocation ratio showed that a higher ratio decreases the heat transfer and economic performance, but considering the energy and exergy performance, a suitable allocation ratio would be 0.54.

Experimental and theoretical investigation of nanofiltration membranes for liquid desiccant regeneration in air conditioning applications

Multi-stage nanofiltration (NF) has been proposed to decrease the energy consumption of conventional reverse osmosis (RO) desalination for potable water production. But multi-stage NF can also be used for liquid desiccant (LD) regeneration. Existing theoretical studies of multi-stage NF desalination do not account for the influence of high LD concentration and applied pressure on the NF membrane behaviour. In this study, we experimentally investigate four commercial NF membranes using LD solutions of LiCl, LiBr and MgCl2 to show how the salt rejection changes with LD concentration (investigated range of 10–43 wt%) and applied pressure (of 30–39 bar). We present equations and an iterative solution to calculate the reflection coefficients of the membranes. These methods are integrated into existing models to simulate more accurately the multi-stage NF regenerator. The experiments showed that LiCl gives slightly lower rejection than LiBr and MgCl2, but permeate flux is 1.3 to 5 times higher. Although it increases with applied pressure, rejection is mostly too low. The first membrane of the multi-stage LD regenerator would require rejections of 10–30%, compared to values of only 6% achieved in this study when using concentrated LDs typical of LDAC applications. To achieve higher rejections, fabrication of membranes able to withstand higher operating pressures is needed. Using current commercial membranes (applied pressure <41 bar), the multi-stage NF regenerator coupled with a LD cooling system achieves a coefficient of performance (COP) of 3.37. But using future membranes with an operating pressure of 80 bar, a COP of 15 could be achieved.

Nitride Layer on TC4 Alloy Prepared by Ultrasonic Surface Rolling and Plasma Nitriding and Its Effect on Corrosion Resistance in LiBr Solution

Nitride Layer on TC4 Alloy Prepared by Ultrasonic Surface Rolling and Plasma Nitriding and Its Effect on Corrosion Resistance in LiBr Solution

Effect of structure and operation parameters on heat and mass transfer coefficients of single‐bubble absorption for lithium bromide solution

Bubble absorption has an efficient performance in absorption units, and lithium bromide (LiBr)-H2O is the most popular working medium in absorption system due to its safety and environmental protection. Limited to the vacuum operation, the researches of bubble absorption for LiBr solution are less reported and the bubble absorption characteristic for LiBr solution is still not clear. In this study, a single-bubble heat and mass transfer model is established to investigate the heat and mass transfer coefficients of bubble absorption for LiBr solution under vacuum condition. A visible experimental platform is established to validate the feasibility of vacuum operation and the model accuracy. The experimental results showed the relative deviation is less than 11.9%. Base on the current model, the effects of structure and operation parameters are comprehensively analyzed to explore the appropriate configuration. The results indicate that the heat and mass transfer coefficients increase significantly with the increase of the orifice diameter and the bubble velocity, while they reduce with the increase of solution concentration. It can be explained that large orifice diameter expands the contact area, and high velocity strengthens the convection, which promote the absorption. Dilute solution concentration reduces the viscous force and surface tension, thereby enhancing the heat transfer. It is expected to provide guidance for the heat and mass transfer mechanisms and contribute to advance the structure and configuration of absorption system.

Performance optimization of a solar air-conditioning with a three-phase accumulator based on the energy-economic analysis

The intermittent and instability problem of solar energy is solved by using "three-phase accumulator" with the medium of LiBr–H2O instead of the auxiliary heater in a solar air conditioning (SAC) system based on independent-developed solar parabolic trough collectors (PTC), in which, "three-phase" refers to LiBr solution, LiBr crystal and vapor. The multi-objective optimization is conducted based on the energy and economy analysis. Pareto frontier for the multi-objective optimization has been obtained with NSGA II. The optimal points have been selected by LINMAP and TOPSIS decision-making methods. The multi-objective optimization results show that the solar fraction, the energy storage density and the system efficiency of the SAC system with TOPSIS are 89.67%, 624.67 kWh/m³, 0.833, respectively, compared with LINMAP, which are 88.31%, 604.22 kWh/m³, 0.848. Based on the TOPSIS decision-making results, the annual average investment of the SAC system is 161,100RMBY, the economic indexes of the system, i.e., AFC (annual cash flow), PBP (payback period), NPV(net present value) and IRR (internal rate of return) are 38,100RMBY, 5.53 years, 140,500RMBY and 7.82%, respectively. In addition, the economic sensitivity analysis results show that the prices of PTCs and refrigeration equipment have a greater impact on the economic index.

Analysis and Experimental Study on Water Vapor Partial Pressure in the Membrane Distillation Process.

In membrane distillation, the vapor pressure difference is the driving force of mass transfer. The vapor pressure is generally assumed by the saturation pressure and calculated by the Antoine equation. However, in the actual operation process, the feed solutions usually flow in a non-equilibrium state, which does not meet the theoretical and measurement conditions of the vapor-liquid equilibrium (VLE) state. This study tested the actual water vapor pressure of the pure water, lithium bromide (LiBr) solution, lithium chloride (LiCl) solution, and calcium chloride (CaCl2) solution under different flow conditions. The results showed that the actual water vapor pressure was lower than the saturation pressure overall, and the difference increased with temperature but decreased with the mass concentration. Therefore, in vacuum membrane distillation (VMD), air gap membrane distillation (AGMD), and sweeping gas membrane distillation (SGMD), the membrane flux calculated by water vapor saturation pressure was higher than the actual membrane flux, and the relative difference decreased and was less than 10% after 60 °C. In direct contact membrane distillation (DCMD), the water vapor pressure difference on both membrane sides was almost the same by using the saturation vapor pressure or the tested data since the pressure errors were partially offset in parallel flow or counter-flow modes.

Intraarticularly injectable silk hydrogel microspheres with enhanced mechanical and structural stability to attenuate osteoarthritis

A silk fibroin (silk) hydrogel was prepared by using diglycidyl ether (BDDE), a chemical crosslinker commonly used to generate Food and Drug Administration (FDA)-approved hyaluronic acid (HA) medical products. The silk/BDDE hydrogels exhibited high elasticity (compressive modulus of 166 ± 15.0 kPa), anti-fatigue properties, and stable structure and mechanical strength in aqueous solution. Chemical crosslinking was conducted in a high concentration (9.3 M) of lithium bromide (LiBr) solution, a salt that is commonly used to dissolve degummed silk fibers during silk solubilization. The unfolded and extended structure of silk molecules with these reaction conditions, as well as the unique ionic environment provided by LiBr facilitated a high degree of crosslinking in the hydrogel. Similar hydrogels were not obtained when the silk was dissolved in other silk fiber-dissolving reagents (e.g., Ajisawa's, formic acid (FA)/LiBr, FA/CaCl2 solutions), likely because partially folded silk structures and the ionic conditions with these reagents were less favorable for the crosslinking reaction. Based on these findings, silk/BDDE hydrogel spheres were prepared using an oil/water (o/w) emulsification method and biocompatibility and biodegradation were evaluated in vivo, along with other silk gel control systems (e.g., enzyme-catalyzed di-tyrosine and pulverized silk/BDDE gel particles with irregular shapes). Histological and immunohistochemical analyses demonstrated that the silk/BDDE hydrogel spheres were biocompatible and served as a bio-lubricant to treat osteoarthritis (OA). The intra-articular injection of the gel spheres reduced pain as measured with OA rats, reduced cartilage damage and resisted the digestive environment in the articular cavity for extended time frames (>4 weeks), suggesting utility for pain relief and sustained drug release for future OA treatments.

Study of the influence of surfactants and surface treatments on the minimum wetting rate of falling films of aqueous LiBr and Carrol solutions

The wettability is one of the critical properties of the falling film type absorber, limiting the wetting area in the absorber, hence the total mass transfer performance. To achieve low values of wetting rate in the absorber is an interesting feature to decrease the pumping power and, therefore, the size of the solution pumps. However, studies about the relationship between surface tension, contact angle, and minimum wetting rate are limited. In this work, working pairs LiBr - H2O and Carrol - H2O (Carrol contains LiBr and EG - Ethylene glycol - with a mass ratio at 4.5:1) with additives 2 - EH (2 - Ethyl - 1 - hexanol) and PCM (1 - Phenylethanol) are studied focusing on the surface tension and minimum wetting rate. The surface tension of the two solutions is measured at various temperatures and concentrations employing the Du Rouy method. The experimental results demonstrate the surface tension of both solutions and the effect of liquid/gaseous surfactants on the surface tension is similar. Also, the minimum wetting rate (MWR) is measured in an annular falling film experimental set-up employing the dewetting method using different materials tubes and fluids. The experimental results of MWR test agree with theoretical predictions and empirical correlations with a discrepancy of less than 10%. When the tube is coated with a hydrophilic surface, a contact angle at 30∘ is achieved, and the minimum mass flow of water to achieve complete wettability on the coated SS tube is reduced from 0.096 to 0.025 kg·m−1·s−1.

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.

Corrosion behavior of 316 stainless steel, copper, and brazed joint in lithium bromide solution at different temperatures

Abstract Lithium bromide (LiBr) corrosion on austenitic 316 stainless steel (AISI 316) and copper will largely determine the overall performance of refrigeration compression systems. In this work, the corrosion behavior of AISI 316, copper, and brazed joint was studied in LiBr solution at different temperatures by using the polarization curve and electrical impedance spectroscopy. The morphology and chemical composition of the samples before and after corrosion were characterized to elucidate the corrosion mechanism. The passivation film of AISI 316 stainless steel is more prone to breakdown as the temperature increases, and the corrosion resistance of copper and brazed joint also decreases with the increasing temperature. Zero-resistance ammeter technology was employed to analyze the effect of temperature on galvanic corrosion. The degree of galvanic corrosion increases with temperature for all galvanic pairs (AISI 316-Cu, AISI 316-brazed joint, and Cu-brazed joint). For AISI 316-Cu and AISI 316-brazed joint galvanic pairs, AISI 316 functions as the cathode, while copper or brazed joint serves as the anode. For the Cu-brazed joint pair, the brazed joint is preferred to be corroded at room temperature, whereas at 50 and 75 °C, copper corrosion occurs in priority.

Bioinspired Photo-Cross-Linking of Stretched Solid Silks for Enhanced Strength.

In this study, solid fibroin fibers (FFs) were directly cross-linked by employing a ruthenium-mediated redox pair under visible light at room temperature for the first time. The chemical cross-link through dityrosine connection was confirmed by Fourier-transform infrared (FTIR) spectroscopy, fluorescence spectra, and a solubility test. The resultant cross-link density of fibers was calculated based on their swelling ratio evaluation in LiBr solution. Further applying stretch to the fibers during irradiation increased the fiber strength to higher values. The break stress and Young's modulus of photo-cross-linked 15% stretch FFs reached a 60-90% increase in comparison to the original FFs in dry and wet conditions. This approach constitutes an easy and straightforward strategy for strengthening FFs, which is scalable industrially to enhance FFs in a wide range of applications.

Experimental study on a novel air conditioning system for deep cascade utilization of waste heat

• A novel air conditioning system cascade driven by 80 °C hot water is established. • Both the conventional LiBr solution and cheaper KCOOH solution can be used in this novel system. • The increase of dilute solution flow rate will decrease the COP of system for both solutions. The existing combined absorption refrigeration and liquid desiccant dehumidification systems have the disadvantages of small temperature difference in waste heat utilization and high cost of working pair. For effective and deep utilization of low-grade heat below 80 °C, a novel air conditioning system cascade driven by waste heat is established. In this system, the low-grade heat is used to drive an absorption chiller to produce chilled water for air cooling and then drive a liquid desiccant system for air dehumidification. The cheaper and non-corrosive KCOOH solution is selected as the comparative working pair of LiBr solution to conduct the experimental study in the system. Operation parameters such as inlet temperature, flow rates of both hot water and cooling water that directly affect the application of the system are studied. The results show that the system can be driven by 80 °C hot water, which is much lower than that of the conventional single absorption refrigeration system. Besides, both working pairs can be used for the system. As the inlet parameters of supply air are fixed, the cooling capacity of KCOOH solution is 10% lower than that of LiBr solution. The KCOOH solution has comparable COP compared to LiBr solution only when the dilute solution flow rate is low. The conclusion is summarized that considering the much lower cost, the KCOOH solution is a promising working pair for this novel air conditioning system, nevertheless, the structure of this system needs to be redesigned to match this working pair.

Development of an Absorption Chiller with 1 to 3 °C Output Using Dilute LiBr Solution

Development of an Absorption Chiller with 1 to 3 °C Output Using Dilute LiBr Solution

Development of thermally-driven hybrid LiBr-water absorption system for simultaneously supplying steam and refrigeration effect

• A hybrid LiBr-water absorption system for producing steam and refrigeration effect. • System characteristics with respect to part-load conditions. • The overall COP of the proposed hybrid absorption system of 0.463. • Experimental thermodynamic states concerning several operating modes. • Pay-back analysis of the proposed system compared to the existing business cases. Waste heat is a form of renewable energy discarded into the atmosphere. Waste heat-driven absorption systems (i.e., heat pumps and refrigeration systems) have attracted attention as district heating and cooling systems. This study proposes a waste heat-driven hybrid lithium bromide-water absorption system for the simultaneous generation of available steam and refrigeration effects. The proposed system is a form of the combined closed thermal cycle between the sub-heat pump and the sub-refrigeration system. It shares a generator and condenser, which allows the system to be more compact and flexible. We first present a description of the proposed system, designed for a cooling capacity of 350 kW with a steam generation rate of 200 kg/h. Our preliminary study proposed a pilot-scale system to clarify the flexible and simultaneous control means of the heating and cooling capacities by partially distributing the flow rate of the LiBr solution entering each sub-cycle. In addition to the results from the preliminary study, the present work examined the effect of part-load conditions on the operating parameters of the hybrid absorption system. The results showed that the coefficient of performances of sub-refrigeration and sub-heat pump cycle were approximately 0.787 and 0.658, respectively, and as a result, the total coefficient of performance of 0.463 was achieved. The theoretical model was validated by the experimental data, and the payback analysis was suggested to assure the economic validity of the proposed system. It was noted that the proposed hybrid absorption system demanded high initial facility cost than the comparison groups, but a payback of 2.79 and 2.36 years was evaluated because of the use of low-grade energy.

Cellulose I nanocrystals (CNCs I) prepared in mildly acidic lithium bromide trihydrate (MALBTH) and their application for stabilizing Pickering emulsions

This study proposed a sustainable method to prepare cellulose I nanocrystals (CNCs I) from microcrystalline cellulose (MCC) in a mildly acidic lithium bromide trihydrate (MALBTH) system, a concentrated (50 wt%) solution of LiBr in water with recyclable formic acid (FA). First, the MCC was treated in the MALBTH system to generate CNCs with a uniform size, yield higher than 68.49% and crystallinity of 84.02%. Then, the CNCs could application for stabilizing Pickering emulsions for at least 15 days. Furthermore, FA was easily recycled from the MALBTH system, and the yield of the CNCs produced from the hydrolysis of MCC by using the recycled FA was still higher than 60%. Finally, this study provided a sustainable and green production of CNCs. A low-cost and environmentally friendly pathway to recover FA from the MALLBTH system at a high yield was still realized.

Energy and exergy analysis of heat to salinity gradient power conversion in reverse electrodialysis heat engine

Environmental issues have attracted greater concerns, leading to more efforts being devoted to industrial waste heat and renewable energy utilization fields. The reverse electrodialysis heat engine is an emerging method to improve the efficiency of industrial processes by recovering waste heat to generate electricity. Besides, it can also be used to harvest low-grade heat in the renewable energy field, such as solar power, geothermal and ocean thermal energy. Its predominating advantage is to harvest low-grade heat with temperatures below 100 °C, which other power generation techniques can hardly utilize. However, the low efficiency of heat to salinity gradient power conversion and poor property of conventional solution has constrained its application. A cycle using unconventional working fluid LiBr solution is developed and experimentally validated to study the heat to salinity gradient power conversion. Influences of the condensation temperature, generation temperature, temperature of reverse electrodialysis cells, and charge concentration were investigated through energy and exergy analysis. The generation process is divided into two sub-stages during the analysis, namely the solution preheat stage and the solution separation stage. It is concluded that an increase in the energy consumption in the solution separation stage and a decrease in the energy consumption in the solution preheat stage can enhance both the energy and exergy efficiencies of the system. The maximum energy efficiency of 6.05% and exergy efficiency of 56.55% are obtained at respective conditions. Moreover, recovering 49.22% condensate heat for solution preheating would increase the energy efficiency by 173.74% at the basic working condition.