Lithium Bromide Water Solution Research Articles

Thermal Analysis of Absorption Air Conditioning Cycle Using Glycerin in Hot and Cold Storage Tanks

Increasing demand for cooling operations in the oil and other sectors, this has led to an increase in electrical energy consumption. The most sustainable solution is to use absorption cooling technology by utilizing solar heat as driving energy instead of electricity. The primary advantage of absorptive cooling is lower electricity costs. In this study, the effect of changing the thermal storage capacities of hot and cold storage tanks and the solar collector area on the performance of the absorption air conditioning cycle was investigated. The optimum operating conditions, the maximum number of processing hours, and the optimum performance coefficient of the absorption conditioning cycle system were selected. The water-lithium bromide solution was used as a fluid in the sorption cycle, and glycerin was used in the hot and cold tank cycle and in the solar collector because it can with stands both high and low temperatures. The simulation process was carried out using (Fortran 90) program with the help of (Port log) program, (Carrier HAP420) program and (Curve Expert) program. The absorption conditioning cycle was simulated during the day to choose the best capacity for hot and cold storage tanks, as well as to choose the solar collector with the best performance factor. Changing the area of the solar collector (from 9.6 m2 to 16.7 m2), and the volume of the hot tank (from 0.55 m3 to 1.4 m3) have been done to provide the maximum temperature that the hot tank can reach with varying expected cooling load per hour, as well as the size of the tank cold (from 0.9 m3 to 1.6 m3) which gets additional cooling capacity, since the effect of these variables was tested separately. According to the research results, the best and most suitable volume for the hot tank is (0.55 m3), and for the cold tank is (1.5 m3), and the best and appropriate area for a solar concentric collector is (11.7 m2), which can provide longer running hours. Finally, the higher the generator's temperature, the higher the system's coefficient of performance (COP). The lowest COP value (0.68) is used to guarantee that the system runs for longer periods of time.

PARAMETRIC ANALYSES OF AN ABSORPTION REFRIGERATION SYSTEM WITH WATER AND LITHIUM BROMIDE IN STEADY STATE POWERED BY SOLAR ENERGY

The demand of energy utilization is increasing expressively as fast as the development of countries. Besides being available everywhere and virtual inexhaustible, renewable energy is undoubtedly necessary to avoid depleting the planet’s natural resources and global warming. Even considering the primordially environmental importance, the result of no emissions by renewable energy grant attractive also for political and economics statement. It should be noted the sun is the most abundant primary energy source in the planet and essential for eco-friendly process like photosynthesis, wind action, water cycle as well direct uses as electric and thermal generations. Consequently, nowadays several methodologies have been applied in order to transfer energy between the cycle and its surroundings optimizing for instance the coefficient of performance and heat exchangers. An absorption system is widely applied in these cases due to supply a unique solution for a range of technological problems from solar cooling to steam-driven refrigeration. Alternatively, this article main objective is modulating an absorption refrigeration system (ARS) which uses water-lithium bromide as a working fluid. Therefore, using the software Engineering Equation Solver (EES) is possible to obtain a thermodynamic single effect code that allows elaborating parametric analyses. In other words, performed and verified the influence of some input parameters over other output parameters. First, it was necessary to consider the cycle operating as reversible and steady state. Furthermore, it is assumed that no chemical reactions occur between water and lithium bromide. Thus, in the meantime apply the heat exchangers and a Solar Collector to receive the thermal energy and provide to the refrigeration cycle. Similarly, water from external sources was used to change heat with the fluid water-lithium bromide. Satisfactory results were founded and it enable to calculate and evaluate all system heat transfers rates and coefficient of performance. Almost all of input parameters introduced brought adequate values over output parameters, but the most convenient were: mass balance of water-lithium bromide solution and temperature of cold water from outside source. Clearly, results always can be found but in conclusion this article can be used to verify parameters sensitivity, optimized absorption refrigeration solutions and supply knowledge for future applications.

Energy, exergy, exergoeconomic and exergoenvironmental analysis on a novel parallel double-effect absorption power cycle driven by the geothermal resource

This paper proposes a novel parallel double-effect absorption power cycle using lithium bromide-water solution to make better use of the geothermal source. The comprehensive energy, exergy, exergoeconomic and exergoenvironmental models of this system are developed, and the comparative studies on the thermodynamic, exergoeconomic and exergoenvironmental performance of this system and the traditional absorption power cycle are conducted to reveal the superiority of this system. Besides, the parametric analysis of this system from the exergetic, exergoeconomic and exergoenvironmental viewpoints are performed to determine the effect of the decision parameters on the system performance. The results show that the proposed system driven by geothermal resource can enhance the net power output by 41.3% as well as the exergy efficiency by 12.31% and meanwhile reduce the total product unit cost by 10.12% with slight increase of 1.99% in the total product unit environment impact, compared with the traditional absorption power cycle. In addition, the absorber and the low-temperature generator provide the highest exergy destruction and loss rate with the lowest device exergy efficiency. Moreover, both the highest overall cost rate and the maximum overall environmental impact rate belong to the absorber, followed by the high-temperature turbine. Besides, the operation conditions of this system can be rectified by searching optimal high-temperature turbine inlet pressure or enhancing the high-temperature turbine inlet temperature and the pressure ratio as well as the low-temperature turbine inlet temperature or reducing the absorber outlet temperature and the lithium bromide mass fraction to improve the energy, exergy, exergoeconomic and exergoenvironmental performance of the proposed system.

Exergy approach in decision-based design of absorption refrigeration system using artificial intelligence and simulink

Exergy approach is essential for the design and possible operation of the absorption system with energy loss minimization. Operational limitations of absorption refrigeration system are due to Gibbs phase rules-base. Optimized operational decision rules are extracted from machine learning algorithm C4.5 which is suitable for different exergy evaluation methods and reference conditions. This study investigates proposed and investigated classification models for the same which are based on different thermodynamic features and operational design data. ANN model is used to predict the thermodynamic properties of the working fluids using improved thermodynamics properties of data patterns. Mathematical expressions are formulated from validated artificial neural network for predicting specific enthalpy and entropy of water–lithium bromide solution. Exergy design data are estimated on 356 thermodynamic design data pattern of absorption refrigeration system by MATLAB Simulators. Pearson’s correlation heatmap is used for extracting 14 thermodynamic features. 94.38% is the highest performance observed with 12 feature class six classification model.

Performance of a Solar Absorption Cooling System Using Nanofluids and a Membrane-Based Microchannel Desorber

In this work, the performance of a single effect absorption cooling system fed by solar thermal energy is evaluated. The absorption chiller includes a membrane-based microchannel desorber using three types of nanoparticles: Al2O3, CuO, or carbon nanotubes (CNT). Correlations available in the open literature to calculate the thermal conductivity of nanofluids are reviewed. Using experimental data for the water-lithium bromide solution (H2O-LiBr) with Al2O3 and CNT nanoparticles, the most appropriate correlation for thermal conductivity is selected. Nanofluid properties are evaluated using a concentration of nanoparticles of up to 5% in volume. The largest increase in the desorption rate (7.9%), with respect to using pure H2O-LiBr solution, is obtained using CNT nanoparticles and the maximum concentration of nanoparticles simulated. The performance of the chiller is evaluated and the daily solar coefficient of performance (SCOP) for the solar cooling facility is obtained. The best improvement with respect to the conventional system (without nanoparticles) represents an increase in the cooling effect of up to 6%. The maximum number of desorber modules recommended, always lower than 50, has been identified.

Effect of Ejector Location in Absorption Refrigeration Cycles Using Different Binary Working Fluids

In this study, three novel modifications of ejector-absorption refrigeration cycles (E-ARC) are investigated to evaluate the effect of ejector location on cycle performances. In the first modification (triple pressure level absorption refrigeration cycle TPL-ARC), the ejector is located at the evaporator inlet. In the second modification (double ejector absorption refrigeration cycle DE-ARC), two ejectors are used; one is located at the evaporator inlet and the other at the absorber inlet, which are coupled to each other. In the third modification (low pressure condenser absorption refrigeration cycle LPC-ARC), the steam ejector is installed at the downstream of the vapor generator discharging line. An additional flow splitter is integrated to the steam ejector outlet and part of the vapor is extracted and returned to the absorber at a pressure equal to the diffuser pressure. Effect of ejector location on thermodynamic performances are evaluated considering three different working fluids, namely ammonia–water solution (NH3–H2O), lithium bromide-water solution (H2O–LiBr), and lithium chloride–water solution (H2O–LiCl). Even though all three configurations enhance the conventional absorption refrigeration cycle (C-ARC) performances, the LPC-ARCs work at high temperature and improve the cycle performance. The TPL-ARC proves to improve the COP and exergy efficiency up to 9.14% and 7.61%, respectively, presenting the highest thermodynamic performance enhancement and lowest operating temperature.

Energy and exergy costings of organic Rankine cycle integrated with absorption system

This paper presents enhancement efficiency of an organic Rankine cycle (ORC) by using an absorption system, which the 3 ORC-absorption models are considerably investigated. R-245fa is used to generate power of the ORC system. The 2 absorption types of an ammonia-water (NH3-H2O) solution and a water-lithium bromide (H2O-LiBr) solution are chosen as the absorption working fluids. The optimal systematical model is evaluated by using the energy efficiency, exergy efficiency, levelized electricity cost (LEC) and exergy cost (EC) indicators. From the simulation results, the conventional ORC unit showed the average energy and exergy efficiencies as approximately 6.98% and 11.51%, respectively. The suitable absorption type was the H2O-LiBr absorption unit at the higher energy and exergy coefficient of performances compared with that of the NH3-H2O absorption unit at approximately 37.23% and 22.69%, respectively. The model 1 (absorption unit replaced the ORC condenser) could simultaneously generate power and cooling energies at the average energy and exergy efficiencies of 20.61% and 21.54%, respectively, which was similarly with the model 2 (absorption unit combined with the ORC condenser to extract heat) at approximately 15.89% and 17.15%. The model 3 (absorption unit was used to produce cooled water for reducing heat at the ORC condenser) showed the highest energy and exergy efficiencies for only generating power as 7.21% and 12.16%. The suitable integrated model was the ORC-absorption model 1 because of the highest exergy efficiency, which was particularly supported by the lowest economics results of the LEC and EC values of 0.074 USD/kWh and 0.080 USD/kWh, respectively.

Partial load efficiency analysis of a CCHP plant with RICE and H2O-LiBr absorption chiller

This paper presents a model for calculating and analyzing the global efficiency of a trigeneration system (CCHP) using 3 reciprocating internal combustion engines (RICE) as prime mover for heat and electric loads. RICE operate simultaneously and at the same load. The CCHP plant delivering energy for the office buildings of an economic operator includes also 2 absorption chillers with water-lithium bromide solution for air conditioning. The system has been analyzed for RICE partial load operation mode, linking the thermal energy output to the cooling power generation. The amount of thermal energy production is influenced by the required energy for cooling. The total cooling load in the summer is determined by both the indoor office-rooms cooling load and the data center cooling load (the energy dissipated by the data center’s components and electrical circuits). An vapor-compression chiller is operated for cooling peak load. During yearly thermal load variation, RICE are switched on or off, operate at nominal capacity or in partial load mode. The thermal efficiency of each engine changes according to the demanded heating load, determining the global efficiency variation of the trigeneration system.. The electrical efficiency of the system is also dependent on the RICE operating load that leads the electric generators. The EER factor for the absorption chillers results accordingly at partial or nominal load operating mode. The functioning graphics for each system equipment were developed based on the thermal load curve of the RICEs and the global efficiency variation graph of the trigeneration system was plotted. Finally, conclusions resulted regarding the optimal functioning of the studied trigeneration system.

Advanced Exergy Analysis of a Compression–Absorption Cascade Refrigeration System

This work presents a theoretical thermodynamic study of a compression–absorption cascade refrigeration system using R134a and a lithium bromide–water solution as working fluids. First and second law of thermodynamics analyses were carried out in order to develop an advanced exergetic analysis, by splitting the total irreversibility and that of every component. The potential for improvement of the system is quantified, in the illustrated base-case 55.4% of the irreversibility is of avoidable nature and it could be reduced. The evaporator is the component that shows a significant potential for improvement, followed by the cascade heat exchanger, the compressor, and finally, the generator. The results of the advanced exergetic analysis can be very useful for future design and experimentation of these kinds of systems.

Multi-objective optimization of double effect series and parallel flow water–lithium chloride and water–lithium bromide absorption refrigeration systems

In this study, multi-objective optimization of the series and parallel flow type double effect absorption refrigeration systems is presented. Genetic algorithm is used to find the optimal solutions and the Pareto-optimal fronts. First, a thermodynamic model is developed to simulate the double effect series and parallel flow configurations with water–lithium chloride and water–lithium bromide solution pairs. Energy and exergy balances are applied to evaluate coefficient of performance, exergy efficiency and irreversible losses in the system components separately for the two working fluid pairs. Next, optimization is done considering coefficient of performance, exergy efficiency and the total system irreversibility rate as objective functions. The low and high pressure generator temperatures are taken as decision variables in the series configuration while for the parallel system; additionally the distribution ratio is also taken as a decision parameter. The optimization is done for four different cases of fixed evaporator, absorber and condenser temperatures. For each case, the optimal decision parameter values are determined for both the water–lithium chloride and water–lithium bromide operated double effect series and parallel configurations. The optimized coefficients of performance were found slightly lower for water–lithium chloride. Contrary to this, the optimal exergy efficiencies were more and the total system irreversibility were less for water–lithium chloride. Further, the optimal performances of the double effect water–lithium chloride systems were obtained comparatively at lower generator temperatures than those of the water–lithium bromide systems.

Experimental characterisation of a novel adiabatic membrane-based micro-absorber using H2O-LiBr

In the interest of reducing the size of absorption chillers, a novel adiabatic membrane-based micro-absorber prototype is experimentally studied. Water–lithium bromide solution is used as the working fluid flowing through 50 rectangular microchannels of 0.15 mm height, 3 mm width and 58 mm length. In the present study, a laminated microporous PTFE membrane of 0.45 µm pore diameter, separating the solution from the vapour, is tested. It incorporates a supporting layer of polypropylene. Different operating parameters were tested, including the inlet solution mass flow rate, temperature and concentration and the pressure potential for absorption. The measured concentration and temperature of the solution at the absorber outlet are used to evaluate the mass transfer characteristics of the micro-absorber. It is demonstrated that the process is controlled by the solution mass transfer resistance. Calculated results of the absorption rate and the absorption ratio show the advantages of the proposed design considering its compactness. The cooling power of a hypothetical chiller equipped with the tested micro-absorber of 73.7 cm3 effective volume, for the range of variables considered in this study, is 41 W. The modular configuration of the absorber allows to easily scale-up the cooling capacity.

Energy and exergy analysis of advanced absorption power cycles using salt-water mixtures as working fluids

In advanced absorption power cycles (AAPCs), a jet ejector is installed at the absorber inlet and serves for two main functions; it assists pressure recovery, and improves the mixing between the weak solution and the vapour coming from the turbine. These effects enhance the absorption of the vapour into the solution resulting in a better performing power cycle. The influence of the jet ejector on the energy and exergy efficiencies of an AAPC is evaluated, and the thermodynamic efficiencies of the AAPC are compared to those of conventional absorption power cycle (APCS) using three different working fluids, namely ammonia-water solution (NH3-H2O), lithium bromide-water solution (LiBr-H2O), and lithium chloride-water solution (LiCl-H2O). Five cases are studied that represents the improvement in the AAPCS efficiencies as results of jet ejector integration in the cycle. Results of parametric studies depict that LiCl-H2O exhibits the highest energy and exergy efficiencies used in AAPC.

Numerical simulation of non-isothermal absorption in a liquid film moving over a cooled horizontal surface under the action of a gas flow

Mathematical model of absorption on a horizontal film of lithium bromide water solution flowing on a cooled wall under the action of shear stress is numerically investigated in this paper. The shear stress on the film surface is set by the motion of co-current or counter-current surrounding saturated water vapor flow. It is known that the external shear stress is caused by the motion of surrounding saturated water vapor intensificate the process of non-isothermal absorption in comparison with the fixed-vapor regime. Our calculations have shown that at low values of heat flux the film temperature and vapor concentration in the solution downstream increases due to absorption.

Modeling of conjugated heat and mass transfer in the entrance region of falling liquid film at various values of the Froude number

Mathematical model of conjugated heat and mass transfer in absorption on the entrance region of the semi-infinite liquid film of lithium bromide water solution is investigated for different values of Froude number. The calculations shown that larger values of Froude number corresponds to a smaller thickness of the falling film. It was demonstrated that for large values of the Froude number the heat transfer from the surface is greater than for smaller values.

Heat transfer coefficients for helical components inside an Absorption Heat Transformer

The evaporator and absorber are relevant components inside an Absorption Heat Transformer, because the refrigerant reaches a high latent heat, which is absorbed by the strong binary mixture at high pressure for obtaining the useful heat. Their heat transfer coefficients influence on the design and performance of an AHT. This paper shows the local and overall heat transfer coefficients for evaporator and absorber, by using experimental tests in a compact AHT of 2 kW, which was designed, built and characterized using only two shells (low and high pressure). Every component was made with nested helical coils and water-lithium bromide solution was used as working solution. The variables considered for this analysis were the heating temperature, the mass flux rate, pressure and concentrations. For the evaporator, an overall heat transfer coefficient of 1227.6 W/m2 K was reached with a heating temperature of 358.2 K. In the absorber, the strong binary mixture influences notoriously for the heat transfer coefficients, where the best result was of 157.2 W/m2 K with a concentrations delta of 6%.

Improving liquefaction process of microgrid scale Liquid Air Energy Storage (LAES) through waste heat recovery (WHR) and absorption chiller

Liquid air energy storage systems (LAES) store liquid air produced by a liquefaction cycle and convert it into electric/cooling power when needed. A small-scale Liquid air energy storage system represents a sustainable solution in microgrid and distributed generation, where small energy storage capacities are required. The main drawback of these systems though, is the low round trip efficiency due to a high specific consumption of the liquefaction cycle. In this work, a single-effect absorption chiller using a Water-Lithium Bromide solution is integrated with a small air liquefier with a liquid air production capacity of 0.834 t/h. In the proposed solution, the waste heat of the compression phase of the liquefaction cycle is recovered and used to drive the absorption cycle, where the resulting cooling power is used to decrease the specific consumption and improving the exergy efficiency of the system. The operative parameters of the absorption chiller reflect the specifications of the most common commercial models available in the market and the size has been selected to maximize the heat power recovered. The results of simulation of the absorption chiller integration show a reduction of the specific consumption of around 10% (537 kWh/t to 478 kWh/t) and an increase of exergy efficiency of around 11.5%.

A power dispatch model for a ferrochrome plant heat recovery cogeneration system

A Organic Rankine Cycle waste heat recovery cogeneration system for heat recovery and power generation to relieve grid pressure and save energy cost for a ferrochrome smelting plant is investigated. Through the recovery and utilization of previously wasted heat from the facility’s internal smelting process off-gases, the cogeneration system is introduced to generate electrical power to supply the on-site electricity demand and feed electricity back to the utility grid when it is necessary and beneficial to do so. In addition, the cogeneration system generates cooling power through a lithium bromide-water solution absorption refrigeration cycle to meet the cooling requirements of the plant. The heat recovery process for power generation is modeled and the optimal power dispatching between the on-site loads and the utility grid is formulated as an economic power dispatching (EPD) problem, which aims to maximize the plant’s economic benefits by means of minimizing the cost of purchasing electricity from the utility and maximizing revenue from selling the generated electricity to the grid. Application of the developed model to a ferrochrome smelting plant in South Africa is presented as a case study. It is found that, for the studied case, more than $1,290,000 annual savings can be obtained as a result of the proposed heat recovery power generation system and the associated EPD model. In addition to this, more than $920,000 annual savings is obtained as a result of the generated cooling power via the proposed absorption refrigeration system. The combined cogeneration system is able to generate up to 4.4MW electrical power and 11.3MW cooling power from the recovered thermal energy that was previously wasted.

Economic Dispatch of a Grid-connected Cogeneration Ferrochrome Plant

Abstract A bottoming and organic rankine cycle cogeneration system for heat recovery and power generation for a South African smelter is studied. The goal is to investigate the potential benefits of generating electrical power from the process waste heat to supply its on-site loads and feed the generated electricity to utility grid when it is beneficial to do so. To achieve this, an economic power dispatch (EPD) model is developed to optimally manage the power flows to the on-site loads and that to the utility grid. The heat recovery process for power generation is modeled first to facilitate the development of the EPD model that maximizes the plant's economic benefits in terms of minimizing electricity cost and maximizing revenue from selling the generated electricity. The potential of generating cooling power through a lithium bromide-water solution absorption refrigeration cycle is also investigated and the economic benefits of the proposed system, when operated by the EPD model designed, are also studied.

A new method for online measurement of the concentration of working fluids in absorption refrigeration systems

This paper proposes a new method for online measurement of the concentration of working fluids in absorption refrigeration systems: electrical conductivity is measured to determine the concentration of the solution. Compared with the common density-concentration method, electrical conductivity-concentration method has the same accuracy but helps to save cost when applied in absorption systems with ammonia–salt solutions. This novel method is also suitable for systems with traditional working fluids like water–lithium bromide solution. Electrical conductivities of ammonia–lithium nitrate, ammonia–sodium thiocyanate and water–lithium bromide solutions were measured between (293.15 and 333.15) K, using an Industrial Conductivity Meter. The ammonia mass fraction varied from 0.35 to 0.48 for ammonia–lithium nitrate solution and from 0.35 to 0.50 for ammonia–sodium thiocyanate solution. For water–lithium bromide solution, the mass fraction of lithium bromide was within the range of 40%–60%. The experimental data were correlated as a function of temperature and composition using the extended Casteel–Amis equation. In addition, correlations of refrigerant mass concentration as a function of electrical conductivity and temperature of the solution are proposed.

Advanced exergy analysis applied to a single-stage heat transformer

This study presents an advanced exergy analysis of a single-state absorption heat transformer operating with a lithium bromide water solution. A traditional exergy analysis was also conducted to identify the components with the highest contribution to the exergy destruction, and an advanced exergy approach was developed to estimate a realistic design and improve the operating conditions of the system. According to the base case of this study, when calculating the total reversibility of the cycle, only 14.78% could be reduced by improving its design and configuration. In addition, a parametric study was presented to discuss the sensitivity of splitting exergy destruction concepts taking into account temperature variations in the heat source, sink, and seawater outlet. Considering improvements to the generator a top priority, followed by improving the absorber, the condenser and finally the evaporator. The numerical results of this work have been developed to help design engineers experiment and assemble future equipment.