Absorption Refrigeration Machine Research Articles

ЕКСЕРГЕТИЧНА ЕФЕКТИВНІСТЬ ТЕХНОГЕННОГО ОХОЛОДЖЕННЯ ЦИКЛОВОГО ПОВІТРЯ ГАЗОТУРБІННОЇ УСТАНОВКИ

The deterioration of the fuel efficiency of the gas turbine unit is especially severe when the temperature of the intake air 30°C and above. A significant increase in the thermodynamic efficiency of the gas turbine unit can be provided by the anthropogenic impact on the temperature and humidity of the intake air, which leads to a proportional reduction of the energy consumption for the compressor drive. Maintenance of lower temperatures of the intake air is especially important for the climatic conditions of gas producing countries in North Africa and the Middle East. Gas turbine plant has a large discharge energy potential, which can be utilized for the production of cold with a clear choice of the cooling method by using absorption refrigeration machines. To compare different combinations of gas turbine unit and waste heat recovery refrigeration machines is advisable to use exergy method of thermodynamic analysis. During the exergy analysis of gas turbine units by using of absorption refrigerating machines it is necessary to take into consideration that the reset of thermo transformed heat flows requires a supply of electricity to drive pumps and fans in the recycling water supply system and to drive the pumps, the hot coolant and pumps in the intermediate circulation loops of heating the coolant and cooling water to the air cooler in the evaporator. Exergetic evaluation of the degree of excellence of gas turbine unit with absorption refrigeration machine was made based on the methodology set out in the work of the scientific school J. Tsatsaronis. This work presents an exergy analysis of cooling efficiency of cyclic air suction in the gas turbine unit by using of lithium bromide absorption refrigerating machine with taking into account of the flow resistance of the air cooler. The results of exergetic efficiency of technical complex of gas-turbine unit with an absorption refrigeration machine were compared with the gas turbine unit without cooling air to the compressor suction. It is also shown that when you increase the flow resistance of the air cooler the growth of efficient cooling power and exergy efficiency of the gas turbine unit stops.

Investigation of Flow and Heat Transfer Characteristics in Two-Phase Flow Through Evaporator of Diffusion Absorption Refrigerator (DAR)

The application of the cooling system becomes very important for a comfortable and almost all public buildings in Indonesia using the cooling system. The cooling system is commonly requires considerable electrical power to drive the compressor used for the vapor compression cooling system in operation. Different with the diffusion absorption refrigeration system, all cycles in the system are occurred by natural circulation where the refrigerant is pressurized (partial) lower in the evaporator is obtained with the aid of an inert gas that can be either hydrogen or helium, which is mixed with the refrigerant gas, but not also react. The study was conducted by flowing the refrigerant at the evaporator copper tube passes that are part of a diffusion absorption refrigeration machine. Long dimension of passes evaporator is 2.38875 m. The method used in this study is the experimental and numerical approach, which is using Multiphase Flow Fluent CFD 6.3. simulation to validate the experimental observations of flow.Through this study, the fenonena happened to be validated by experimental observations numerically. Also can be seen flow characteristics of refrigerant flowing along the evaporator and heat transfer phenomena that occur.

ТЕПЛОВИКОРИСТАЛЬНІ ХОЛОДИЛЬНІ МАШИНИ – ШЛЯХИ РОЗВИТКУ І ВДОСКОНАЛЕННЯ

Heat-using refrigeration machines are a particular case of energy conversion systems working on the inverse thermodynamic cycles. The primary energy for such machines is thermal energy. The heat-using refrigeration machines can be divided into the three groups according to the so-called compensation process: (a) sorption (ab-sorption and ad-sorption) with thermochemical compression, (b) ejection with jet-compression, and (c) compression with mechanical compression/expansion. Development in the field of absorption refrigeration machines associates with using the water-ammonia mixture as a working fluid as well as with utilization of special schematics related to (a) rectification/dephlegmation processes and absorption process, and (b) absorption-compression machines that are most effective as low-temperature refrigeration machines and high-temperature heat pumps. Development in ejection machines goes to the direction of machines with (a) small refrigeration capacities, (b) using the natural working fluids, and (c) implementation of the renewable energy sources with different temperature levels. Development in compression heat-using refrigeration machines associates with (a) using carbon dioxide as a working fluid, (b) implementation of renewable energy sources, and (c) extended possibilities to use these machines within the tri-generation systems. Development and improvement in the field of the heat-using refrigeration machines and heat pumps are the result of long-term and successful theoretical and experimental research has been conducted in the chair “Refrigeration machines and installations” at Odessa National Academy of Food Technologies.

Parametric study of an absorption refrigeration machine using advanced exergy analysis

An advanced exergy analysis of a water–lithium bromide absorption refrigeration machine was conducted. For each component of the machine, the proposed analysis quantified the irreversibility that can be avoided and the irreversibility that is unavoidable. It also identified the irreversibility originating from inefficiencies within the component and the irreversibility that does not originate from the operation of the considered component. It was observed that the desorber and absorber concentrated most of the exergy destruction. Furthermore, the exergy destruction at these components was found to be dominantly endogenous and unavoidable. A parametrical study has been presented discussing the sensitivity of the different performance indicators to the temperature at which the heat source is available, the temperature of the refrigerated environment, and the temperature of the cooling medium used at the condenser and absorber. It was observed that the endogenous avoidable exergy destruction at the desorber, i.e. the portion of the desorber irreversibility that could be avoided by improving the design and operation of the desorber, decreased when the heat source or the temperature at which the cooling effect was generated increased, and it decreased when the heat sink temperature increased. The endogenous avoidable exergy destruction at the absorber displayed the same variations, though it was observed to be less affected by the heat source temperature. Contrary to the aforementioned two components, the exergy destruction at the evaporator and condenser were dominantly endogenous and avoidable, with little sensitivity to the cycle operating parameters.

Solution procedure and performance evaluation for a water–LiBr absorption refrigeration machine

The water–lithium bromide absorption cooling machine was investigated theoretically in this paper. A detailed solution procedure was proposed and validated. A parametric study was conducted over the entire admissible ranges of the desorber, condenser, absorber and evaporator temperatures. The performance of the machine was evaluated based on the circulation ratio which is a measure of the system size and cost, the first law coefficient of performance and the second law exergy efficiency. The circulation ratio and the coefficient of performance were seen to improve as the temperature of the heat source increased, while the second law performance deteriorated. The same qualitative responses were obtained when the temperature of the refrigerated environment was increased. On the other hand, simultaneously raising the condenser and absorber temperatures was seen to result in a severe deterioration of both the circulation ratio and first law coefficient of performance, while the second law performance indicator improved significantly. The influence of the difference between the condenser and absorber exit temperatures, as well as that of the internal recovery heat exchanger on the different performance indicators was also calculated and discussed.

Group Contribution Concept for Computer‐Aided Design of Working Fluids for Refrigeration Machines

AbstractThe operation and performance of any refrigeration system depends mainly on the choice of the working fluids. Since classical compounds like the chlorofluorocarbons and hydrochlorofluorocarbons are now completely phased out, substitutes are required. In previous works, a method for computer‐aided design and test of alternative compounds were presented. Relevance and importance of the group contribution concept for such methods are investigated, considering two model systems, namely, the ejecto‐compression and absorption refrigeration machines with specific configurations like insertion of a distillation column and elimination of the condenser, respectively. The obtained results allow extending this approach to model other complex refrigeration systems.

Modeling Liquid–Vapor Equilibrium (VLE) of Refrigerant Mixtures Contain Algeria's natural gas Used Now in The Field of Solar Refrigeration

The possibility of producing cold through the direct or indirect use of solar energy is done using an absorption machine. In this work this machine used the thermal energy of different Algerian climate zones. These regions have different radiation (6924-7516 Wh m−2) and ambient temperatures in the range (30.6 to 45 ° C). The activity coefficient and the P-T-x behaviors of the mixtures has been calculated. The mixtures studied contain Algerian natural gas are (C3H8-C6H14), (C3H8-C5H10), (C3H6-C5H10) and (C3H6-C4H10). These calculations carried out at the levels of the generator and the absorber of a single stage absorption refrigeration machine. The model is developed from the group contribution method. The results obtained constitute a database and allows for an experimental project in studied site.

Theoretical Study on Solar-Driven Air-Cooled LiBr/Water Absorption Refrigeration System

In the study, LiBr absorption refrigeration machine runs in the air-cooled condition, combined with temperature and humidity independent control and the air condition end with radiant cooling, improving the system operation mode. Calculation and simulation were carried out to study the performance of the system, and effects of the cooling air inlet temperature and flow rate, refrigerant water outlet temperature on system performance, which will have the important theoretical significance for the development and application of the minitype solar lithium bromide unit.

Modelling the absorption refrigeration cycle using partially miscible working fluids by group contribution methods

The present study concerns the cycle performance modelling of a particular configuration of an absorption refrigeration machine based on phase separation as well as development of a strategy for computer aided design of absorbents. The model uses predictive methods based on the group contribution concept for the computation of the thermodynamic phase equilibria involved such as liquid–liquid and vapour–liquid as well as enthalpy–concentration diagrams. The proposed absorbents computer-aided design strategy is based on the exploration of a number of structural group combinations obtained from a selected set of functional groups, according to the chemistry laws. The model was tested on four different absorbent–refrigerant pairs reported in the literature, namely (benzyl ethyl amine–glycerol), (water–hexanoic acid), (water–2-hexanone) and (water–ethyl propionate) as well as on pairs where the absorbent compound is generated by the proposed absorbent design strategy and the refrigerant is water. The results show that quite good values of the coefficient of performance (COP) can be obtained, indicating that this cycle configuration is promising and energetically efficient, mainly due to hardware savings, i.e. absence of condenser. However, other working fluid combinations have to be tested using the proposed model.

Hourly performance prediction of ammonia–water solar absorption refrigeration

Abstract This paper deals with the hourly performance investigation of solar absorption refrigeration (SAR) system with evacuated tube collector and ammonia–water (NH 3 –H 2 O) solution. The SAR system is presented to simulate the system characteristic variations using hourly atmospheric air temperature and solar radiation data for Adana province in Turkey. The evaluation is performed for the maximum temperature occurrence day on July 29. First, the variations of various parameters, such as absorption refrigeration machine efficiency, condenser capacity and heat transfer rate in the generator and absorber during the day, are calculated for different cooling capacities and generator temperatures. Later, the minimum evacuated tube collector surface area is determined. According to the obtained results, the SAR system is considerably suitable for home/office-cooling purposes between the hours 09:00 and 16:00 in the southern region of Turkey such as Adana province. The most suitable performance of the absorption cooling system is calculated for the generator temperature values equal to or higher than 110 °C. The performance coefficient of the cooling (COP cooling ) varies in the range of 0.243–0.454 while that of the heating (COP heating ) changes from 1.243 to 1.454 during the day. Evacuated tube collector area for a 3.5 kW cooling load capacity is found to be 35.95 m 2 for the region at 16:00 whereas it is 19.85 m 2 at 12:00.

Study of New Absorption Refrigeration Cycle Operating with Partially Miscible Fluids Pairs

In the present work a new configuration of absorption refrigeration machine based on phase separation has been studied. The main objective is to investigate the performance of this machine, using a number of binary systems (refrigerant absorbent) showing a partial miscibility and having a low critical solution temperature. A computer code has been developed for the calculation of the coefficient of performance (COP) of the machine as well as to study the influence of the operating conditions on this parameter, testing a binary mixture made of methyl diethyl amine (MDEA) as refrigerant and water as absorbent. The obtained results confirm the feasibility of this new cycle which can be regarded as a good alternative to classical cycle with no phase separation. The use of the computer code can be extended to test different working fluids for this machine, for an optimisation of the COP.

A study of a bubble absorber using a plate heat exchanger with NH3–H2O, NH3–LiNO3 and NH3–NaSCN

There is a continuous research effort being carried out worldwide on the development of absorption cooling systems with the objective of increasing their performance, one important area is the search for more efficient heat exchangers and alternative working fluids that can improve the performance of NH 3 –H 2 O and H 2 O–LiBr that are commonly used in commercial absorption refrigeration machines. In this work the study of a plate heat exchangers used as bubble absorbers with NH 3 –LiNO 3 and NH 3 –NaSCN as alternative working fluids is carried out. A mathematical model was developed in order to analyze the absorption process in a bubble absorber with NH 3 –H 2 O, NH 3 –LiNO 3 and NH 3 –NaSCN as working fluids using a plate heat exchanger at refrigeration conditions and low generator temperatures. The results show that NH 3 –H 2 O and NH 3 –NaSCN working fluids obtained higher absorber thermal loads and absorbed vapor mass values than NH 3 –LiNO 3 , the lower values for the latter were caused mainly by the high solution viscosity that decreases the efficiency of the absorption process. On the other hand, NH 3 –LiNO 3 obtained the highest COP value from a single effect absorption refrigeration system simulation, however, NH 3 –NaSCN obtained a higher COP than NH 3 –H 2 O; therefore NH 3 –NaSCN seems to be a good working fluid to be tested in an absorption machine. ► A bubble absorber is simulated with NH 3 –H 2 O, NH 3 –LiNO 3 and NH 3 –NaSCN working fluids. ► The analysis is realized with a plate heat exchanger at different working conditions. ► The NH3–LiNO 3 obtains lower absorption performance than NH 3 –H 2 O and NH 3 –NaSCN. ► The NH 3 –LiNO 3 has problems in the absorption process, due to the high viscosity. ► The NH 3 –NaSCN obtains better performance in an absorption cycle than NH 3 –H 2 O.

Evaluation of a seasonal storage system of solar energy for house heating using different absorption couples

In this paper, an innovative concept is presented for a long-term energy storage system for house heating, using the absorption process. The solar energy is stored during summer through desorption and the heat is released during winter through absorption. The originality of this concept is to allow the solution to reach the crystallization point, which is usually avoided in the absorption refrigeration machines. The storage capacity and efficiency of seven absorption couples, CaCl 2/H 2O, Glycerin/H 2O, KOH/H 2O, LiBr/H 2O, LiCl/H 2O, NaOH/H 2O and H 2O/NH 3, as a function of the temperature of absorption, temperature of evaporation, temperature of the solution before absorption and the presence of crystals in the storage tank have been studied in this paper. The appearance of crystals increases the storage capacity. The storage capacity increases with the temperature of evaporation and the temperature of the solution before absorption but decreases with the temperature of absorption.

Comparison between two different solution-pumping methods in absorption refrigeration machines

This paper presents a pumping method in absorp-tion refrigeration where a vapour-driven pump is to replace the electricity-driven pump. The vapour pump is driven by a fraction of the generator’s hot, high-pressure, vapour mixture. The refrigerator is thus exclusively heat-powered and rendered inde-pendent of the availability of electricity as the main energy source. The design and operation of the vapour pump is presented. The results obtained by a computer simulation program show a decrease in performance (COP), which is confirmed by the data obtained from a 1 kW cooling capacity refrigerator. Peak performances occur at higher generator tem-peratures when compared to a cycle using an elec-tricity-driven pump

Cooling of Ethanol Fermentation Process Using Absorption Chillers

Ethanol fermentation is an exothermic process, where the kinetics depends on temperature. This study proposes an alternative cooling system for use in ethanol fermentation using a single-eect water/lithium bromide absorption chiller, powered by waste heat from sugar and ethanol production processes, with a temperature range of 80 to 100 oC. The aim of this study is to model, simulate and analyze the behavior of an absorption refrigeration machine, according to the required cooling capacity of the fermentation system. A comparative analysis with and without the chiller is performed. The introduction of a chiller allowed a reduction in the temperature of the medium of around 1 oC and an increase of around 0.8 % in the fermentation efficiency. Under these conditions less cellular stress occurs and cellular viability is kept at higher levels. The results show that this reduction in temperature can increase the ethanol content of the wine. In the recovery of ethanol, a lower thermal load will be needed at the distillation, with a smaller amount of vinasse produced and consequently the energy efficiency of the plant will increase.

Flow boiling heat transfer of ammonia/water mixture in a plate heat exchanger

The objective of this work is to contribute to the development of plate heat exchangers as desorbers for ammonia/water absorption refrigeration machines driven by waste heat or solar energy. In this study, saturated flow boiling heat transfer and the associated frictional pressure drop of ammonia/water mixture flowing in a vertical plate heat exchanger is experimentally investigated. Experimental data is presented to show the effects of heat flux between 20 and 50 kW m −2, mass flux between 70 and 140 kg m −2 s −1, mean vapour quality from 0.0 to 0.22 and pressure between 7 and 15 bar, for ammonia concentration between 0.42 and 0.62. The results show that for the selected operating conditions, the boiling heat transfer coefficient is highly dependent on the mass flux, whereas the influence of heat flux and pressure are negligible mainly at higher vapour qualities. The pressure drop increases with increasing mass flux and quality. However, the pressure drop is independent of the imposed heat flux.

SARM: Simulation of Absorption Refrigeration Machine

The purpose of this work is: - the design of a simulation program for a refrigeration system absorption (single and double stage), working with the binary couple NH3-H2O, called SARM 'Simulation of Absorption Refrigeration Machine', - the creation of a database containing the physical and thermodynamic properties for ammonia, water and their mixtures with different concentrations - computer-aided design of the two diagrams of Oldham thermodynamic (LogP, -1/T) and Merkel , whose range has been extended (for P: from 0.1 to 50 Bars - T: from 213.15 to 513.15 K) - to size various organs (mono and exchangers diphasic) of the installation. To validate the simulation program, the results were confronted in one hand, those of R. Kuzman, J.S Gallagher on the thermodynamic properties of the binary pair NH3-H2O, and secondly, to those obtained by the software ABSIM 'Modular Simulation of Absorption Systems', about the performance cycles absorption. In both cases the results are satisfactory.

Experimental study of an ammonia–water bubble absorber using a plate heat exchanger for absorption refrigeration machines

The development of absorption chillers activated by renewable heat sources has increased due mainly to the increase in primary energy consumption that causes problems such as greenhouse gases and air pollution among others. These machines, which could be a good substitute for compression systems, could be used in the residential and food sectors which require a great variety of refrigeration conditions. Nevertheless, the low efficiency of these machines makes it necessary to enhance heat and mass transfer processes in the critical components, mainly the absorber, in order to reduce their large size. This study used ammonia–water as the working fluid to look at how absorption takes place in a plate heat exchanger operating under typical conditions of absorption chillers, driven by low temperature heat sources. Experiments were carried out using a corrugated plate heat exchanger model NB51, with three channels, where ammonia vapor was injected in bubble mode into the solution in the central channel. The results achieved for the absorption flux were in the range of 0.0025–0.0063 kg m −2 s −1, the solution heat transfer coefficient varied between 2.7 and 5.4 kW m −2 K −1, the absorber thermal load from 0.5 to 1.3 kW. In addition, the effect of the absorber operating conditions on the most significant efficiency parameters was analyzed. The increase in pressure, solution and cooling flow rates positively affect the absorber performance, on the other hand an increase in the concentration, cooling, and solution temperature negatively affects the absorber performance.

Thermo physical properties of acetone–zinc bromide for using in a low temperature driven absorption refrigeration machine

Thermal physical properties (vapor pressure, density, viscosity, specific heat capacity, specific electrical resistance and specific enthalpy of mixing) of the solution acetone–zinc bromide, which will be used as a working solution in an absorption refrigeration machine, are measured and analyzed. The experimental data were correlated with high accuracy. The required state diagrams (log p, T and h, T) for this solution as well as the log P, h-diagram for the pure acetone are calculated, represented, correlated and discussed. The results indicate that the solution acetone-zinc bromide might be suitable as a working solution to operate an absorption refrigeration machine at low temperature.

Thermodynamic analysis of an absorption refrigeration machine with new working fluid for solar applications

A theoretical analysis was undertaken to examine the efficiency characteristics of acetone-zinc bromide solutions for an absorption refrigeration machine, using low generator temperatures (47–60°C), which allows the use of flat plate solar collectors. The results of the simulation were confirmed with an experimental investigation. The main results showed that the solution is well suited to operate the machine at low temperatures (higher than 50°C).