Single-stage Absorption Research Articles

Enhanced characteristic equation method for single stage absorption heat pumps

The method of characteristic equations aims to describe the part-load behavior of sorption heat pumps and chillers as well as heat transformers as simply as possible but yet still accurately. Based on an approach by T. Furukawa for heat transformers, the method was further developed by F. Ziegler and others for absorption heat pumps and generalized for application in multistage processes. Clever simplifications were made, to represent the cooling capacity Q˙E of absorption chillers with a characteristic temperature difference ΔΔt as a simple linear equation Q˙E=sE·(ΔΔt−ΔΔtmin,E). In ΔΔt, the average hot, cooling, and chilled water temperatures are combined, and the slope and loss parameters, sE and ΔΔtmin,E are constant. However, in practical applications of this established method, inconsistencies arise. For example, the calculated slope parameter sE does not match the slope when plotting simulated or measured cooling capacities against ΔΔt. Furthermore, the loss parameter ΔΔtmin,E is actually not constant.In this work a more precise formulation of the characteristic equation is derived which takes into account that the solution entering the absorber and desorber is generally superheated or subcooled. By means of a domain-wise heat transfer calculation, these effects can be implemented into the method and explain the above mentioned inconsistencies. The new formulation allows for explicit consideration of different heat exchanger designs and cooling water configurations. No iterations or regression analyses are required. Thus, the calculation method can be easily implemented in industrial controllers e.g. for the model predictive control of absorption chillers and heat pumps.

Performance analysis of residential hybrid cooling and heating system operating under low solar radiation

Renewable energy sources are becoming increasingly important due to rising energy consumption and environmental pollution caused by greenhouse gases. In the study, a system was designed to provide year-round air conditioning in a residential located in regions with low solar radiation. This design consists of a single-stage absorption cooling system to meet the cooling need in summer and a solar energy-supported natural gas combi boiler heating system to meet the heating need in winter. The designed system was subjected to a comprehensive analysis, taking into account the integration of four different collector types: flat plate collector, evacuated tube collector, compound parabolic collector and parabolic trough collector. A thermal energy storage unit is integrated into the system to increase its efficiency. In the study, the feasibility and efficiency of the solar energy system recommended for residences in low-radiation regions were investigated. Appropriate system conditions were determined by evaluating economic and environmental aspects. In the study, a maximum net present value (NPV) of 3.941.49 US$ and 4 % exercise efficiency were calculated for the system designed using ETC collectors at 80°C generator and 6°C evaporator temperature. At the same time, the hybrid system can prevent annual carbon dioxide emissions of 800.28 kg compared to coal-fired systems and 62.42 kg annually compared to natural gas systems. These results show that the designed system is economically feasible and contributes positively to environmental sustainability.

Comparative analysis of thermodynamic performance of high-temperature absorption heat transformers using various ionic liquids as working pairs

The study investigated six sets of ionic liquid (IL) working pairs based on high-temperature vapor-liquid equilibrium data. These sets were modeled using the NRTL activity coefficient model and integrated into a single-stage absorption heat transformer (AHT) for system cycle simulation analysis. A comparison was made with traditional H2O + LiBr working pairs commonly used in AHTs. The study aimed to assess the feasibility of using IL working pairs in high-temperature AHTs to achieve higher output temperatures when dealing with heat sources exceeding 120 °C. Compared to the traditional H2O + LiBr working pair, which has strong COP and ECOP but a limited temperature range, IL pairs offer advantages under various conditions. For instance, H2O + [HMIM][Cl] and H2O + [BMIM][Br] can operate at higher condensation temperatures, providing broader temperature ranges. H2O + [HMIM][Cl] has a wider operational temperature range, suitable for unstable waste heat sources. It also has the highest optimal ECOP value of 0.64 at 197 °C absorption temperature, and shows good cyclic performance, achieving temperature rises of about 78 °C. ILs can maintain stable COPs and circulation ratios over a wide range of absorption temperatures, thus achieving higher temperature rises or meeting the need for higher absorption temperatures. Notably, although the H2O + IL combination exhibits slightly higher exergy loss than the traditional H2O + LiBr pair when comparing exergy losses in the AHT system among different working pairs, its low corrosiveness, lack of crystallization, and wide operating temperature range make these drawbacks insignificant.

Absorption Chiller Efficiency Increasing at Waste Heat Recovery of Cogen-eration Plants using a Vapor Compression Chiller as a Backup Cold Source

Cooling efficiency in a trigeneration cycles is one of the most frequently problems. A single-stage hot water absorption chiller is a universal solution for the gas engine waste heat utilization. How-ever, trigeneration centers exploitation experience shows the need for a more detailed technical and economic analysis to achieve maximum efficiency of the three-generation cycle. The purpose of this article is to substantiate the use of two-stage absorption cycles increasing the utilization rate of waste gas heat. The study presents the results of assessing the efficiency of using energy resources on the example of a three-generation center with more than 14 years of exploitation experience, including two single-stage absorption chillers (Q0= 0.65 MW each) and a chiller with a screw compressor (Q0= 0.8 MW). A comparison of actual energy consumption with designed indicators was carried out. The influ-ence of external and internal factors on the efficiency of heat recovery from a gas engine in single-stage absorption refrigeration machines with a water-heated generator is considered. The dependence of the change in the average annual cooling coefficient during the calendar year was obtained. Based on the study, proposals were formulated to improve the energy efficiency of refrigeration supply, giving an increase in refrigeration capacity of 6.1% with a commensurate reduction in the load on the screw chiller. The option of using a combined two-stage cycle chiller (type 2) under similar operating conditions showed a COP=1.43, which provides savings of 67.45 MWh of electricity or 5.4%, on an annualized basis (assuming only waste heat is used). Additional advantages of such a cycle include increased accu-racy and stability of maintaining the water temperature at the absorption chiller evaporator due to more flexible adjustment of the temperature of the lithium bromide solution in the high-temperature generator.

Sensitivity analysis and thermodynamic evaluation of a combined cooling, heating and power system utilizing exhaust gases of smelting furnace

Exhaust gases from the smelting furnace have high temperature and mass flow rate, and there is huge potential to use them for energy-related purposes such as electricity generation, cooling and heating. Utilization of the gases for energy-related purposes would lead to fuel savings and emissions reduction. To use this potential, it is necessary to design proper systems and cycles and apply a heat recovery unit. Several technologies are useable for heat recovery depending on the characteristics of exhaust gases, such as their mass flow rate, temperature and compositions. Due to the higher potential of combined heating, cooling and power (CCHP) generation systems compared with the systems with a single output, a CCHP is designed and investigated in the present study by consideration of the specifications of the exhaust gases. The applied system in this study comprises a Supercritical CO2 (SCO2) cycle, heat exchanger and single-stage absorption chiller for simultaneous heating, cooling and power production. Engineering Equation Solver (EES) is employed to model the proposed system by considering the properties of the flows and characteristics of the components. To get deep insight into the effective parameters on the outputs of the designed system, the impact of three factors, namely the mass flow rate of the gases, the effectiveness of heat exchanger and temperature of exhaust gases, are analyzed and investigated by the implementation of sensitivity analysis. As one of the main conclusions, it is found that an increment in the mass flow rate of exhaust gases from 30 kg/s to 70 kg/s causes augmentation in the power generation from 2037 kW to 4754 kW. Furthermore, exergy analysis is carried out, and it is found that an increase in the temperature or mass flow rate of exhaust gases or a decrease in the effectiveness of heat exchangers would lead to decrement in the exergy efficiency of the system. According to the performed sensitivity analysis, the mass flow rate of exhaust gases has the most remarkable influence on the heating and cycle-generated power among the considered factors.

Thermodynamic Modeling of a Solar-Driven Organic Rankine Cycle-Absorption Cooling System for Simultaneous Power and Cooling Production

Humanity is facing the challenge of reducing its environmental impact. For this reason, many specialists worldwide have been studying the processes of production and efficient use of energy. In this way, developing cleaner and more efficient energy systems is fundamental for sustainable development. The present work analyzed the technical feasibility of a solar-driven power-cooling system operating in a particular location in Mexico. The theoretical system integrates organic Rankine and single-stage absorption cooling cycles. A parabolic trough collector and a storage system integrated the solar system. Its performance was modeled for a typical meteorological year using the SAM software by NREL. The analyzed working fluids for the organic cycle include benzene, cyclohexane, toluene, and R123, while the working fluid of the absorption system is the ammonia-water mixture. The cycle’s first and second-law performances are determined in a wide range of operating conditions. Parameters such as the energy utilization factor, turbine power, COP, and exergy efficiency are reported for diverse operating conditions. It was found that the highest energy utilization factor was 0.68 when the ORC utilized benzene as working fluid at ORC and ACS condensing temperatures of 80 °C and 20 °C, respectively, and at a cooling temperature of 0 °C. The best exergy efficiency was 0.524 at the same operating conditions but at a cooling temperature of −10 °C.

Performances of an absorption heat transformer cycle with water/deep eutectic solvents working fluids: Modelling and screening using a multiscale approach

In this work, a tool was developed to evaluate the performances of working fluids composed of deep eutectic solvents as absorbents and water as refrigerant in a single-stage absorption heat transformer. The thermophysical properties required for the simulation were obtained using a multiscale approach involving the COSMO–SAC(+OH–ClBr) model for the vapour-liquid equilibria and group contribution models for the densities and heat capacities of the DESs. The predictive power of the model was assessed by comparing the results with the ones obtained with a conventional approach based on the non-random two-liquid model and empirical correlations derived from experimental data. The performances of the absorption heat transformer were evaluated using several criteria including the coefficient of performance, the circulation ratio and the heat input. The results are in agreement with the ones obtained with the classical approach. The performances of 32 deep eutectic solvents as well as the influence of the different temperatures of the process on the results are investigated. Results show that the best performances are obtained with deep eutectic solvents composed of ethylene glycol, glycerol, tetramethylammonium chloride, choline chloride and betaine, with coefficient of performance values comprised between 0.438 and 0.441, circulation ratio between 14.75 and 9.66 and heat input between 1982.11 and 2006.77 kJ.kg−1. In particular, the best performances were achieved with the pair water/{ethylene glycol:[tetramethylammonium][chloride]}, ratio [2:1]. Overall, the deep eutectic solvents with a higher ratio of hydrogen bond acceptor and lower molar masses showed better performances as absorbents in absorption heat transformers.

Performance potential and optimal configuration study for low-GWP R161-DMETEG single-stage absorption refrigeration system via pinch technology

New low-GWP R161-DMETEG mixture showed its high feasibility as an alternative working pair to overcome shortcomings of traditional ones. Its internal heat recovery capacity significantly influences operating performances. To systematically explore its ideal performance potentials and heat integration principles of the traditional single-stage absorption refrigeration system (SSARS), this paper conducted the internal heat recovery optimization and derived optimal systems by establishing an approach via pinch technology as a comprehensive planning. The ideal optimal system for maximum heat recovery under different conditions was derived initially using problem tables and Q-T graphical methods. Among all DMETEG-based fluids, R161-DMETEG exhibits the highest average performance potential of approximately 0.677 and an ideal performance improvement of 108%. Subsequently, a new configuration, called MFD-SSARS, was derived using the gird method. Its actual performances and economic feasibility under different parametrical conditions and control strategies were further explored. MFD-SSARS achieves COPs between SSARS and the ideal potential, and it can flexibly adjust internal heat recovery according to varying conditions to stimulate the performance potential. MFD-SSARS maximumly improvs COPs by approximately 65.953% relative to SSARS, reaching 96.167% of its potential under basic conditions. Despite its higher total capital costs than SSARS, it showed the lowest payback period of 2.23 years, thus proving the economic feasibility. Overall, the adopted environment-friendly working pair with designed high-performance configuration of this work serves as a technical solution to overcome current limitations of traditional absorption refrigeration technologies.

A biomass-based polygeneration system for a historical building: A techno-economic and environmental analysis

Combined cooling, heating, and power systems (CCHP) are considered one of the most efficient energy systems since they have a less detrimental environmental impact, and therefore sustainable energy savings, and eventually less CO2 emissions. An even higher advantage is possible when a renewable energy fuel source (e.g., Biomass) is used. The proposed study presents the energy modeling of a 169 kWe capacity, biomass-based CCHP system retrofitted to a historical building, located in Perugia, Italy. Two well-known simulation software’s, ASPEN Plus and TRNSYS, are purposely integrated. In the first phase of the study, a wood biomass combustion-based externally fired gas turbine (EFGT) along with an Organic Rankine Cycle (ORC) system is modeled in Aspen Plus. In the later phase, a historical building “Sant’ Apollinare” model, and the remaining CCHP system are developed in TRNSYS. The transient system is modeled such that it fulfills the peak thermal energy demands of the retrofitted building. The main components of the system are a heat exchanger (HE), storage tanks (TK), a single-stage LiBr-H2O absorption chiller (ACH), and balance of plant (BOP) components. A heat exchanger recovers heat from the gas cycle, which is then utilized for running an ORC, heating and cooling of the end-user building, biomass drying, and domestic hot water (DHW) supply. A storage tank supplies direct heat to the end-user in winter and drives the ACH in summer. The results of the model provide data on the performance parameters of different components of the CCHP system such as temperature, power consumption, and energy profiles that allow evaluating the overall energy performance of the CCHP system. Finally, a feasibility analysis of the system is carried out on the basis of economic indexes such as simple pay back (SPB) period, net present value (NPV) and profitability index (PI), for two different case scenarios assumed for fuel (e.g., biomass) supply cost. The SPB is 2.93 years, when biomass is obtained for free. Whereas, if biomass is purchased from the market the SPB becomes 7.15 years. From an environmental perspective, the plant ensures a decrease of 632 tons of CO2 emissions annually.

Benefits of an innovative polygeneration system integrated with salinity gradient solar pond and desalination unit

Solar energy accumulation, low-temperature thermal heat stockpiling, and more sustained performance are the attractive specifications of a salinity-gradient solar pond (SGSP). Extracted low-grade heat from these components can be employed for various residential applications such as electric power, cooling load, and freshwater production. An innovative energy generation system consisting of a flat plate collector (FPC), single-stage absorption chiller (SSAC), thermoelectric generator (TEG), desalination unit, NaClO plant, SGSP, and a wind turbine farm is proposed. The theoretical investigations demonstrate the multidimensional benefits of the system throughout the year. A comprehensive thermodynamic, economic, and exergoenvironmental assessments of the annual operation of the system is conducted. For a comparative evaluation of the system performance, the individual scenarios are outlined. Results from energy and exergy studies show that the associated efficiencies are 27.3 % and 19 %, respectively. Also, the system has the capability to supply a cooling load capacity of 2391 kW, net electricity power of 583.9 kW, hydrogen of 1.48 m3/s, freshwater of 0.01445 m3/s, and sodium hypochlorite of 0.001416 kg/s. Moreover, the payback period and the factor of environmental damage effectiveness for the system are 3.2 years and 2.223, respectively.

Investigations on a bubble-pump-aided diffusion absorption heat transformer using deep eutectic solvent for harvesting and upgrading thermal energy

Absorption heat transformer shows promising potential in thermal energy harvesting and upgrading, while the corrosion and crystallization risks of existing working substance restrict its promotion. A bubble-pump-aided diffusion absorption heat transformer using deep eutectic solvent is proposed in this study. The influence of operating parameters of bubble pump is analyzed, indicating that motive head should be as large as possible while diffusion gas flow rate has the optimum. Because of worse pumping ability, deep eutectic solvent has narrower normal operating range compared with LiBr, but the optimal energy performance shows little difference. Ethaline exhibits the best performance among deep eutectic solvents. With heat source of 90 ℃, COP and ηEX of 0.401 and 48.9% can be reached to output thermal energy of 120 ℃, leading to a CO2 emission reduction of 20.1 Mt per year. Parametric analysis demonstrates that single-stage diffusion absorption heat transformer using ethaline can realize temperature lift up to 50 ℃, which delivers comparative performance against existing AHT systems, except for operating range. Approaches are discussed to enlarge its operating range and further improve its performance as well. The results in this paper contribute to: 1) providing a promising absorption heat transformer configuration for large-scale and long-term use; 2) quantitatively demonstrating the prospect of deep eutectic solvent; 3) enlightening insights in the recovery of industrial waste heat, the upgrading of thermal energy and the reduction of CO2 emission.

Evaluation of a rough-surface evaporator applied to an absorption heat transformer for water desalination

Abstract The purpose of this work is to evaluate the performance of a rough-textured evaporator applied to a single-stage absorption heat transformer for water desalination (SAHT-WD). The stainless-steel evaporator was subjected to an abrasive material release treatment (sandblast texture) to provide a texture that fosters phase change heat transfer compared to a smooth surface. To determine the performance of the evaporator, the evaluation has been divided into an experimental and a theoretical analysis. The experimental analysis focused on determining the operating conditions that favor the performance of the evaporator and the SAHT-WD. For the theoretical analysis, a mathematical model was developed to predict the wetting efficiency and the heat-transfer coefficients of the evaporator. To quantify the improvement in the performance of the rough-surface evaporator, the experimental results were compared with those reported in a reference work. The results indicate that the sandblasted texture improved the performance of the evaporator as well as that of the SAHT-WD. The results of the mathematical model suggest that the rough tube improved the wetting efficiency of the evaporator.

Economic and Energetic Assessment and Comparison of Solar Heating and Cooling Systems

Solar heating and cooling (SHC) systems are currently attracting attention, especially in times of increasing energy prices and supply crises. In times of lower energy prices, absorption SHC systems were not competitive to compression cooling supported by photovoltaic (PV) modules due to the high investment costs and total energy efficiency. This paper aims to discuss the current changes in energy supply and energy prices in terms of the feasibility of the application of a small absorption SHC system in a mild Mediterranean climate. The existing hospital complex restaurant SHC system with evacuated tube solar collectors and a small single-stage absorption chiller was used as a reference system for extended analysis. Dynamic simulation models based on solar thermal collectors, PV modules, absorption chillers and air-to-water heat pumps were developed for reliable research and system comparison. The results showed that primary energy consumption in SHC systems designed to cover base energy load strongly depends on the additional energy source, e.g., boiler or heat pump. Absorption SHC systems can be price competitive to air-to-water heat pump (AWHP) systems with PV collectors only in the case of reduced investment costs and increased electricity price. To reach acceptable economic viability of the absorption SHC system, investment price should be at least equal to or lower than a comparable AWHP system.

Experimental studies on absorption-compression hybrid refrigeration system using 1,1,1,2-tetrafluoroethane/tetraethylene glycol dimethyl ether as working pair

The feasibility of combining novel halogenated hydrocarbon-based working pairs with low-pressure compression-assisted absorption refrigeration system (LCARS) was proved for the first time from the experimental perspective. An experimental prototype of the absorption-compression hybrid refrigeration system with a 1 kW cooling capacity was designed and tested to explore actual performances of selected R134a-DMETEG and performance improvements from compression in LCARS. At an evaporation temperature of approximately 5 °C, as the hot water inlet temperature and the solution flow rate change from 75 to 95 °C and 1.2–2.7 L/min, respectively, the coefficient of performance (COP) in the single-stage absorption refrigeration system (SSARS) varies from 0.211 to 0.412. At an increased evaporation temperature of approximately 10 °C, as the hot water inlet temperature and flow rate increase from 70 to 80 °C and 1.18–2.89 L/min, respectively, the COP in the SSARS varies from 0.238 to 0.552, while the COP in LCARS is improved and varies from 0.470 to 0.617. The LCARS increases the COP by a maximum of 91.04 % and can utilize a lower-grade heat source more efficiently due to its higher optimal COP at reduced hot water inlet temperatures. This study provided one feasible technical approach of combined use of R134a-DMETEG and LCARS to make up for the application limitations of traditional working pairs, contributing to application promotions of absorption systems, especially for the occasions with high requirement on safety and lightweight.

Modeling of a LiBr-H2O absorption air conditioner system driven by a solar flat plate collector

In regions with hot and mixed climates, the principal energy users in buildings are the systems that provide cooling and air-conditioning. Buildings consume more energy as a result of their reliance on traditional electrically powered systems. Solar energy has emerged as an important alternative for many uses, including cooling and air-conditioning. In this paper, to simulate a solar-assisted single-stage LiBr-H2O absorption air conditioner system, a mathematical model is presented. The model may simulate either the static or the quasi-static state of the system. The model is constructed using mass and energy balances that are applied to the various components found on the inside of the machine. The experimental data that were acquired for one of the other works in the body of literature are used to validate the model that was developed. In this study, the quantity of energy given by a flat plate solar collector to cool the air in a room in Meknès city on a typical summer day is compared to the cooling load imposed by a cooling fan in the same room. The simulation shows that a flat plate solar collector to power our system can only be used effectively under specific solar irradiance conditions.

Перспективы применения российских абсорбционных термотрансформаторов на ПГУ-ТЭЦ

The electrical power of power plants based on gas turbines (GT) decreases with an increase in air temperature and, as a result, a decrease in its mass flow at the compressor inlet. This makes it relevant to develop methods for increasing air density by lowering its temperature when wor¬king in hot arid regions and regions with a tropical humid climate. To cool the air, it is proposed to use absorption chillers (LBAC). It is shown that for air cooling in a dry hot climate, it is sufficient to use LBAC with single-stage absorption. For a humid tropical climate, where deeper air cooling is required with a simultaneous decrease in its moisture content, it is proposed to use ABCM with two-stage absorption, which are capable of producing cold at negative temperatures. To do this, it is proposed to introduce an additional evaporation and absorption unit with peri¬pheral equipment into the standard industrial design of the LBAC with single-stage absorption. Comparative energy efficiency of LBAC of standard design and LBAC with two-stage absorption during air cooling at the GT compressor inlet has been evaluated. For such critical facilities for the Russian economy as gas pumping stations using gas turbines, an LBAC unit with two-stage absorption and removal of absorption heat by water-circulating cooling systems based on cooling towers, or using air coolers (drycoolers) with the ability to turn off an additional evaporation unit if necessary, is proposed. and absorption.

Optimization model of solar cooling system with latent heat storage

Today, the fastest growing end-use in the buildings sector is cooling demand, notes the International Energy Agency (IEA). In the last few years, the interest in solar cooling systems has been growing globally. Solar cooling systems are the next solution to meet the growing demand for air conditioning. The literature analysis shows that solar cooling systems mainly use single-stage absorption chillers, with water as the working fluid, and only a small fraction of them use phase change materials to improve heat storage. Based on previous studies on solar-assisted cooling systems, the use of phase change materials for thermal storage should be investigated.The paper will present a study of a solar cooling system with the optimized PCM thermal storage, with the aim of stabilizing the operation of heat storage, taking into account the volatility of solar energy, the impact of short-term operations and peak hours on the amount of heat produced. This means that the amount of electricity consumed to heat up the accumulation tank will be significantly reduced. The optimization model in simulation software will be performed to test solar cooling system with latent heat storage, with aim to investigate the efficiency of the developed latent energy storage and provide technical guidance for the implementation of such system in the practice. All indicators, including environmental impact and economic calculations, will be identified in order to determinate the specific systems for foresight market uptake.

Integration of cycles by absorption for the production of desalinated water and cooling

This work aims to evaluate a system integrating an absorption heat transformer (AHT) and an absorption cooling system (ACS) for the simultaneous production of desalinated water and cooling from a low-thermal level heat source. The integration is carried out through the interaction of the LiBr-H2O solution streams between both cycles and by implementing a water desalination system allowing heat recycling between them. Mathematical models were developed in the Matlab programming language to perform a parametric analysis of four different configurations. The configuration in which the hottest streams transfer the energy to the coolest streams in the heat exchangers in both cycles was the most efficient. The results showed that this configuration produced up to 152.4kg/h of desalinated water and 82.64 kW of cooling load achieving a EUF of 0.90 at a heat source temperature of 74 °C and an evaporator temperature of the ACS of 7 °C. The interaction of the solution streams and the heat recycling analyzed in this work serve as a record of the possibilities of integration between single-stage absorption cycles to produce desalinated water and cooling.

Optimizing single-stage double-effect LiBr-H2O absorption chiller in micro-trigeneration system using an atom search optimization algorithm

Wastes produced from several processes are focused on by many scientific researchers in order to reuse them, achieve energy savings, and reduce cost and environmental pollution. Recently, many organizations have utilized a micro-trigeneration system as a primary energy source, as it produces cooling, heat, and power in a combined effect. Various scholars designed numerous trigeneration systems in recent years. However, it is challenging to attain energy-efficient operation. Therefore, this current research focuses on developing an optimal micro combined cooling, heating, and power generation (MCCHP) to improve energy efficiency and reduce cost. The major components of the trigeneration system are the diesel engine, heat exchanger, boiler, absorption chiller, and chilled water storage system. In order to improve the cooling output of the proposed system, a single-stage, double-effect absorption chiller (LiBr-H2O absorption chiller) is utilized with the atom search optimization (ASO) algorithm. The variables of the condenser in the absorption chiller are given as input for optimization. The results show that the proposed system has a cooling capacity of 16 kW. Compared with the existing algorithms, it is efficient with 98% temperature minimization and cost-effectiveness. This micro-trigeneration device can be used in hospitals and the food production industry and is cost-effective.

Simulation of an ammonia-water absorption cycle using exchanger effectiveness

• NH 3 /H 2 O absorption chiller modeling based on exchanger effectiveness. • Tuning of the numerical model on experimental results. • Comparison of simplified and effectiveness-based modeling. • Characterization of performance for changing operating conditions. • Parametric study changing the size of components. This paper presents the numerical simulation of an efficient ammonia-water single-stage absorption chiller integrating a new combined desorber, able to produce and purify the refrigerant vapor. An experimental campaign was conducted on the pilot plant by varying the main operating parameters, namely the temperatures of external sources and the mass flow rate of the working fluid. Direct experimental measures were analyzed and indirect calculation of other physical quantities was used for tuning of the numerical models. First, a simplified model of the cycle was developed, based on fixed effectiveness and pinch temperatures. Absolute values and tendencies outside nominal working conditions were not sufficiently accurate to predict the performance of the cycle even at the small scale, so more accurate modeling was undertaken. Accordingly, components were characterized by effectiveness, modeled using three operating parameters: the Jakob number ( Ja ), the number of transfer units ( NTU ) and the energetic ratio ( R en ). The small average errors for calculated effectiveness confirm that these parameters are well suited for the application studied. Global cycle model results showed errors compared to experimental results below 6% for the COP and 15% for the cooling power output. The tuned model was used to perform a parametric analysis on the dimension of the components, highlighting the performance improvements/reductions obtainable by increasing/decreasing their size. The use of dimensionless parameters makes this approach well suited for analysis at larger scales of industrial interest, the development of more complex or combined cycles as well as to perform techno-economic or exergo-economic analysis.