Absorption Refrigeration Machine Research Articles

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

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

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.

Prospects for the use of a membrane refrigeration unit for the production of cold as an alternative to absorption

Objective. The purpose of the study is to determine the prospects for using a membrane refrigeration unit for the production of cold as an alternative to absorption. Method. The study was carried out using a numerical experiment and verification of the results obtained on an experimental bench. Result. An analysis was made of the use of a traditional absorption refrigeration machine and a membrane refrigeration machine from the point of view of energy efficiency and the number of working elements. Presented for comparison are methods for calculating the separation process of the “absorbent-refrigerant” mixture based on reverse osmosis processes and a water-ammonia absorption refrigeration unit. Conclusion. The use of separation processes in membrane apparatuses for the production of cold in mixed refrigeration machines, as an alternative to absorption refrigeration machines, will ensure a more stable process for obtaining refrigerant from the mixture, reduce material costs for the production of a refrigeration unit and increase the energy efficiency of a refrigeration unit operating on mixed components.

Modeling and simulation of a solar absorption refrigeration machine operating with lithium chloride water coupled (H2O-LiCl)

Modeling and simulation of a solar absorption refrigeration machine operating with lithium chloride water coupled (H2O-LiCl)

Electrochemical cell power generation systems for socially important facilities

There is an estimation of application of power installations in a mode of trigeneration: with gas at the input, and with electric power, heat and cold at the output, functioning in an automatic mode, positive and negative sides of their use are considered. Cogeneration systems based on gas turbine with compression or absorption chillers, satisfying consumers in electric, heat and cooling energy in a building or a group of buildings, are considered. The use of trigeneration systems allows efficient utilization of heat for heating in winter and for air conditioning and process needs in summer, for example, use of cold for freezers in hospitals. At the same time, there is no reduction in efficiency throughout the year. The trigeneration technology is an excellent alternative to conventional power plants with a large amount of electrical energy and allows the use of absorption chillers in case of high cost or shortage of electricity. Such units consume less electricity compared to compressor units and require lower costs. At the same time, the use of absorption refrigeration machines (ARM) is totally justified when operating in the mode of a mini-CHP, which produces heat in winter (as cold is not needed or is needed only in small amounts), and in summer there is no need for it, but there is a need for cold. The payback period of such a system is relatively low, the net present value is high, and the profitability index is usually greater than one. Cold storage contributes to the economic viability of a trigeneration system. Since the payback period does not take into account the time factor of investment, the net present value or, better yet, the profitability index should be used. A trigeneration system consists of several units with different service lives and different investment results.

Diffusion Absorption Refrigeration Systems: An Overview of Thermal Mechanisms and Models

The energy transition, originating in the limitation of fossil resources and greenhouse gas (GHG) emission reduction, is the basis of many studies on renewable energies in different industrial applications. The diffusion absorption refrigeration machines are very promising insofar as they allow the use of renewable resources (solar, geothermal, waste gas, etc.). This technology is often considered an alternative to vapor compression systems in cooling and refrigeration applications. This paper aims to overview the thermal mechanisms related to modeling system energy sources and highlight the primary methodologies and techniques used. We study and analyze the technology’s current challenges and future directions and, finally, identify the gaps in the existing models to pave the way for future research. The paper also gives a classification of absorption refrigeration systems (ARS) to position and limit the scope of the study. The paper will help researchers who approach the various aspects to have a global synthetic analysis of the mechanisms characterizing the modeling of energy sources of absorption refrigeration machines.

Analysis of the Energy Efficiency of the Air Conditioning System Based on Absorption Refrigeration Machine with Connection of Heat Pump and Solar Collectors

This article proposes and analyzes a circuit solution for providing heat supply to the generator of an absorption refrigeration machine (AHM) in centralized air conditioning systems using a heat pump unit (HPU) and solar collectors (SOL). Previously, such schemes have already been considered in the scientific works of Russian and foreign authors. The aim of the work is to propose new circuit solutions aimed at improving such systems, as well as confirming higher energy efficiency. This goal is achieved by solving the following problems: additional supply of the circuit with a common storage tank, operation of the absorption refrigeration machine generator and the condenser of the heat pump unit based on a common heat exchanger. Such a solution for the air conditioning complex based on an absorption refrigeration unit has been proposed for the first time. The most important results are the possibility of obtaining high values of the coefficient of performance, the possibility of achieving a number of technological advantages, increasing reliability and efficiency, as well as reducing the metal consumption of an absorption-type plant operating from solar collectors and a heat pump plant compared to similar systems. The significance of the obtained results lies in the fact that the use of a common storage tank and a combined heat exchanger (AHM generator / HPU heater) provides a significant increase in the coefficient of performance, a decrease in the metal consumption (reduction in costs) of the main equipment.

Experimental investigation and exergetic modelling of R718/LiBr bubble pump operated absorption refrigeration machine

Experimental investigation and exergetic modelling of R718/LiBr bubble pump operated absorption refrigeration machine

Experimental investigation and exergetic modelling of R718/LiBr bubble pump operated absorption refrigeration machine

Experimental investigation and exergetic modelling of R718/LiBr bubble pump operated absorption refrigeration machine

Enhancing Benefits by Rectification in the Absorption Refrigeration Systems

The main objective of this article aims to enhance a single stage absorption refrigeration machine, using the ammonia-water pair as working fluid, and this from the improvement of its exergetic performances by means of a vapor rectification system. The rectifier makes it possible to emit a vapor enriched in pure fluid (ammonia) with a high flow rate; this one is thus transformed into condensate after condensation; as it also allows evacuating a liquid (water) in the form of reflux. Moreover, in order to show the role of the rectifier and to highlight its impact on the operation of the proposed installation, the methodology adopted in this work aims to develop a thermodynamic model of numerical simulation using the FORTRAN language according to two approaches. An energetic analysis approach which aims to assess, in a first time, the performance of the studied refrigeration installation. However, the exergetic approach tries to calculate the exergy efficiency, and thus to evaluate the losses of exergies of the refrigeration installation in a second time. Therefore, the obtained results showed a clear improvement in the exergetic efficiency, accompanied against by an optimization of the losses of exergies which are due to the irreversibility of the studied thermodynamic system. The novelty brought by the present study encourages the engineers and manufacturers to realize the future absorption refrigeration machines integrating rectifier systems.

Improving energy efficiency at compressor stations using waste heat boilers at gas turbine plants

Improving the energy efficiency of compressor stations is currently an urgent problem in the gas industry. Increasing the pressure of the transported gas by compression with the use of gas turbine units as a compressor drive is the most energy-intensive heat-and-power process. The article discusses modern methods of increasing the energy efficiency of compressor s tations with gas pumping units operating based on gas turbine plants by utilizing the heat of exhaust gases from gas turbine plants. A complex system is considered, which includes a gas pumping unit, a gas turbine unit, a waste heat boiler and an absorption refrigeration machine, which allows preheating the gas in front of the combustion chamber, cooling the air before compression and heating water for the compressor station’s own needs by utilizing the heat of flue gases after the waste heat boiler and utilizing low-potential heat of compressed gas air coolers.

Techno-economic analysis of production of bio-oil from catalytic pyrolysis of olive mill wastewater sludge with two different cooling mechanisms

• A kinetic Aspen Plus model for pyrolysis of olive mill wastewater sludge. • Successful validation model with experimental results. • Calculates pyrolysis yields as a function of temperature. • A techno-economical study for a plant capacity of 100 tonnes/day for two schemes. • Monte-Carlo sensitivity analysis. A techno-economic analysis of production of bio-oil from catalytic pyrolysis of olive mill wastewater sludge has been performed with two different cooling schemes. The two configurations differ in the manner how the bio-oil vapors are quenched. In scheme-1, a vapor compression refrigeration machine is utilized for condensation of bio-oil vapors while in scheme-2, the vapor compression refrigeration machine is replaced by absorption refrigeration machine. The two schemes are modelled in Aspen Plus which provides mass and energy balances. For techno-economic analysis, Aspen process economic analyzer is employed. The model is first validated against experimental data from lab scale and then upscaled to an industrial scale of 100 tonnes/day wet biomass (93 tonnes/day dry biomass). Results show that the model with absorption refrigeration machine (scheme-2) has a slightly better process efficiency and a lower MFSP compared to the model with compression refrigeration machine (scheme-1). Total anticipated capital investment expenses for scheme-1 and scheme-2, comprising plant fixed capital investment (FCI), start-up, working capital, and interest, are expected to be €22.1 M and €17.5 M, respectively. The equipment costs are based on first quarter of 2021 and the economic life of the project is 20 years. Monte Carlo sensitivity analyses showed that the bio-oil MFSP is most vulnerable to discounted cash flow, income tax and bio-oil yield. The production cost of bio-oil varies between €2.16/GGE and €6.19/GGE for scheme-1 and €1.78/GGE and €5.01/GGE for scheme-2 when cost parameters are varied within an industrially relevant range. The findings support the viability of producing bio-oil by catalytic fast pyrolysis on a commercial scale.

Automobile Absorption Conditioner

The purpose of this study is to develop a circuit for an automobile air conditioner, which will reduce the consumption of power developed by the engine. This paper proposes the design of an automobile absorption air conditioner. A description of the principle of operation of an automobile absorption air conditioner operating on a cycle of a one-stage absorption refrigeration machine has been given in the paper. It consists of a stripper (generator), a condenser, an absorber, an evaporator. Lithium bromide (LiBr) solution has been used as an absorbent, which has a low boiling point, is non-toxic and safe. 3D-models of the absorber and generator of an automobile absorption air conditioner has been developed in the course of the research. The absorber is designed to form a weak absorbent solution. This solution is supplied to the generator heat exchanger using a liquid pump. There it is heated by the exhaust gases to the boiling point. The solution evaporates and water vapor enters the condenser (evaporator). In the generator, the solution is concentrated from 52 to 60 %. After that, water vapor is supplied to the absorber from the condenser, and a concentrated absorbent solution is supplied from the generator. It should be noted that the generator is a key element of an automobile absorption air conditioning system. Inside it is a strong LiBr solution that feeds the absorber. The design of the air conditioning system does not provide for the use of a compressor and allows to reduce the power loss of the power plant to the drive of the liquid pump. According to calculations, the pump drive power was 0.17 kW. For comparison, the compressor of a modern car air conditioner consumes 7–11 kW. An absorption car air conditioner provides the following advantages: additional engine cooling, environmental friendliness, fuel economy, efficient use of the heat of vehicle exhaust gases. A distinctive feature of this design is that it is proposed to use the heat of the exhaust gases for the process of heating the absorbent. This design can fully compete with the existing modern car air conditioners.

Моделювання та програмний комплекс для дослідження функціонування ежектора в змінних режимах

One of the current directions of development of modern energy-saving and energy-efficient technologies for ship and stationery (including municipal) energy is the use of ejector refrigeration machines, which can be used for air conditioning systems together with an absorption refrigeration machine (cascade cycle) or vapor compressor refrigeration machine as part of cogeneration or trigeneration units. Such circuit solutions can be used together with ensuring the rational organization of work processes in the main elements of the refrigeration machine, in particular in the jet device - ejector, the appropriate design of which, in turn, will further increase the thermal coefficient. Improving the design of the ejector is a rather complex and long process and does not always give positive results. It is primarily because many tests are required on full-scale models. Therefore, computer simulation of the ejector operation at different variable input parameters, considering the geometric characteristics of the flow part and variable mode characteristics during operation is more attractive in terms of finding options for rational (optimal) design. The paper presents the results of software development for modeling hydrodynamic processes in the flowing part of the ejector, considering the variable operating modes of the ejector refrigeration machine. The existing method for calculating the pressure and circulation characteristics of jet devices is used. The developed software complex "RefJet" in the design mode defines the maximum achievable coefficients of ejection of a jet ejector. In the simulation mode - provides determination of the ejection coefficients of the already designed (certain sizes) ejector at variable values of pressure at the inlet and outlet in specific operating conditions, considering its operation at the limit and partial modes. The work of the software package was tested in the development and analysis of circuit solutions of ejector refrigeration machines as part of the heat recovery circuits of three-generation units based on internal combustion engines and gas turbine engines.

INCREASING THE EFFICIENCY OF THE SYSTEMS OF COMPRESSOR-PUMPING AND REFRIGERATION UNITS SUPPLYING LIQUID CO2 AND NH3 TO THE UNIT FOR CARBAMIDE SYNTHESIS

Carbon dioxide is used in large volumes to produce urea, a highly efficient nitrogen fertilizer. It is compressed in a multistage compressor to a pressure of 15 MPa and fed to the urea synthesis unit. The specific energy consumption for the compression of carbon dioxide by a compressor reaches 0.16 kWh/kg. It may be more profitable to use in the system of compressor-pumping and refrigeration units. They can be used to liquefy carbon dioxide and compress it to pressure 15 MPa before feeding it to the synthesis of urea. In the simplest scheme, an ammonia compression refrigeration machine (ACRM) is included in the system to improve efficiency. The specific energy consumption in such a system for the liquefaction and compression of CO2 is 0.118 kWh/kg. In case of replacement of the ACRM with an absorption refrigeration machine, unit costs can be reduced to 0.09 kWh/kg. These two systems can be used to increase urea production or to ensure stable operation of the units during the summer period of their operation. The analysis showed that further improvement of the technological scheme of the entire system will completely abandon the use of the compressor method of compression of CO2 to pressure 15 MPa before its supply to the urea synthesis unit. To do this, you need to include an additional absorption lithium bromide refrigeration machine in the system. In this scheme, the compressor-pumping unit will provide the simultaneous supply of liquid carbon dioxide and ammonia for the synthesis of urea with a pressure of 15 MPa. To increase the daily production of urea from 1400 to 2000 tons, it is necessary to increase the feed liquid CO2 in the amount of 62 t/hour and liquid NH3 — 47.5 t/hour. Bibl. 14, Fig. 3.

Аналіз ефективності ежекторних холодильних машин на різних холодоагентах

Modern heat-using ejector refrigeration machines used in heat recovery systems for power plants based on gas turbine engines and internal combustion engines have many advantages over absorption refrigeration machines: smaller dimensions and weight; the ability to obtain lower temperatures. However, they are inferior in energy efficiency, and the thermal coefficient is much lower and can be 0.2…0.4. The efficiency of such refrigeration machines largely depends on the choice of the working fluid (refrigerant). Hence the need to choose a refrigerant that would provide the maximum heat factor, and hence the maximum efficiency of heat recovery. Given the relatively low efficiency of the ejector refrigeration machine, the search for a working fluid that will provide, on the one hand, higher thermal coefficients, and on the other hand high environmental friendliness, is one of the promising areas of development of heat recovery technologies in power plants. The study used the software complex developed by the authors to calculate the refrigeration cycles of heat-using refrigeration machines, taking into account the properties of many modern refrigerants, ejector characteristics, as well as basic heat exchangers (condenser, evaporator, generator). The efficiency of ejector refrigeration machines when working on the following working bodies was analyzed: R142b, R134a, R600, R600a, R1234ze(E), R1233zd(E), R1234yf, R227ea, R236fa, R245fa. R142b, R600, R600a, R245fa have the largest values of thermal coefficients. It is established that the most profitable in terms of environmental friendliness (ODP, GWP) and energy efficiency is the use of refrigerant R245fa, which has a condensation temperature range is 25…35 oC and boiling in the evaporator is 0…15 oC thermal coefficient is 0.40…1.03.

AFFECTING PARAMETERS TO THE HEAT AND MASS TRANSFER OF NH3-H2O SOLUTION FALLING ON THE HORIZONTAL ROUND TUBE

The absorption process has been confirmed as the most important process in absorption refrigeration machines in terms of improving their total efficiency. One of the key research directions is the selection of absorber structure which is expected to be fabricated in Vietnam without demand of new infrastructure investment. In this study, a local model of the coupled heat and mass transfer during absorption process of NH3 vapor by a NH3-H2O diluted solution flowing over horizontal round tubes of an absorber was made. The heat transfer coefficient obtained from the coupled heat and mass transfer mathematic model. This heat transfer coefficient is used to calculate the variation of the simulated value of heat load. The correlations which give the heat transfer coefficient and mass transfer coefficient in the absorption process in range of solution concentration ω = 28% ÷ 31%, solution mass flow rate per unit tube length Γ = 0.001 ÷ 0.03 kgm-1s-1, coolant temperature twater = 28 oC ÷ 38 oC are set as two functions. The practical decrease of wetted ratio analyses were taken into account when the solution flow from the top to the bottom of the parallel tube bundle. The deviation of theoretical heat load and experimental heat load is about 12.3%. Based on these simulations, the theoretical studies were done for absorption refrigeration system in order to narrow the working area where the experiments later focused on. The results of this study will be the basis for subsequent application research of falling film absorbers.

Refrigerants design for an absorption refrigeration machine using group contribution methods

The use of the group contribution concept in the design of refrigerants for a single effect absorption refrigeration machine is presented. Chosen functional groups were combined according to the known chemistry rules to generate refrigerant candidates. The prediction of vapor-liquid phase equilibria data using the UNIFAC (Universal Functional Activity Coefficient) model and the Peng-Robinson equation of state and the resolution of heat and mass balances over different compartments led to the coefficient of performance (COP). An exergy analysis was carried out in order to assess the performance of the machine by calculating the exergy efficiency, the second law efficiency and the exergy destruction ratio. The design strategy was tested with chosen groups such as Fluor (F) and Methyl (CH3), Carbon (C), Methine (CH) and Methylene (CH2) and with N, N Dimethylformamide (DMF) as the absorbent. The results showed Interesting refrigerant-absorbent pairs with reasonably high COP values.

Numerical study of the effectiveness of a vertical falling plate film absorber for an absorption chiller

This study investigates the impact of design and operating conditions on the performance of a falling film grooved plate absorbers integrated in a Lithium Bromide water absorption refrigeration machine. The performance of the component is described using two parameters: the mass efficiency and the absorbed vapour mass flow rate per unit plate width. The study implements a heat and mass transfer model validated with specific experimental data. The absorber effectiveness proposed by previous studies was generalized so that all absorbers’ operating conditions could be considered. A parametric study considering variation of solution Reynolds number is conducted. Based on these simulations, global and local transfers are discussed.

LPT (Local Public Transport) electric buses: innovative solutions to reduce the energy absorption of auxiliaries

The focus of the study is the analysis and sizing of the air conditioning system on board the vehicle which operates in thermal transient for the duration of the typical mission, using “fan coil” type air conditioning devices powered by a hot or cold heat vector fluid loaded into “electro-thermal” charging station and the related ground cogeneration plant (at the BUS terminus). For winter air conditioning, it was assumed that a heat transfer fluid at a temperature of 90 ° C could be stored on board. This value allows the use of water as a heat transfer fluid without pressurizing the systems, minimizing costs and supply problems, and is compatible with the characteristics of ICE cogeneration systems. For summer air conditioning, it was assumed that ice or fluid at a temperature of -20 ° C could be loaded. Also in this case it was decided to operate with a common fluid, such as a solution of water and salt (e.g. calcium chloride CaCl2). A comparative analysis of two solutions was carried out: the first involves the standard solution with BUS air conditioning system with heat pump powered by traction batteries charged by the grid and the second one analyzes the use of a high temperature Fuel Cell in a trigenerative configuration with refrigeration unit absorption fueled by the fumes of the FC. The trigeneration plant produces 100 kW of electricity via SOFC (Solid Oxide Fuel Cell) and, through an exchanger, water at 95 ° C which is stored on board the BUS for winter heating and feeds an absorption refrigeration machine that produces fluid at a temperature of -20 ° C for summer conditioning. For the two solutions, the savings of non-renewable primary energy and the reduction of GHG emissions compared to the standard solution (recharging the electric BUS from the network with on-board air conditioning powered by the traction batteries) are calculated through a WTW analysis. Consumption and emissions of electric powertrains, potentially for consumption and zero emissions, are closely linked to the methods of production and distribution of electricity.