Ammonia-water System Research Articles

Fabrication and analysis of solar operated vapour absorption refrigeration system using methanol water

This study investigates the performance assessment of methanol and water as working fluid in a solar-powered vapour absorption refrigeration system. This research clarifies the system’s performance across a spectrum of operating conditions. Furthermore, the HAP software was utilized to determine and scrutinize the cooling load, facilitating a comparative analysis between software-based results and theoretical calculations. To empirically substantiate the findings, this research investigates methanol-water as a superior refrigerant compared to traditional ammonia- water and LiBr-water systems. Through experimental analysis and its comparison with previous research, the methanol-water refrigeration system demonstrated higher cooling efficiency and better environmental compatibility. The system’s performance was evaluated under varying conditions, showing that methanol-water has a 1% higher coefficient of performance (COP) compared to ammonia-water systems, proving its superior effectiveness in solar-powered applications. This empirical model acts as a pivotal tool for understanding the dynamic relationship between methanol concentration (40%, 50%, 60%) and system performance. The results show that temperature of the evaporator (5–15 ℃), condenser (30 ℃–50 ℃), and absorber (25 ℃–50 ℃) are constant, the coefficient of performance (COP) increases with increase in generator temperature. Furthermore, increasing the evaporator temperature while keeping constant temperatures for the generator (70 ℃–100 ℃), condenser, and absorber improves the COP. The resulting data provides profound insights into optimizing refrigerant concentrations for improved efficiency.

Utilization of Geothermal Fluid as a Heat Source for Absorption Refrigeration System for Food Preservation – A Case of Bwanda and Gwisho Hotsprings

Zambia has significant geothermal resources with over 86 hotsprings identified. Installation of a 250kW off-grid pilot binary-cycle power plant is currently underway at the Bwanda and Gwisho goethermal site. It is estimated that there is 90,000 herd of cattle in the villages around the pilot power plant. Little milk from these herds of cattle reaches the market due to scarce collection points with cooling facilities. This study assesses the applicability of utilizing exhaust geothermal fluid from a binary-cycle geothermal power plant for powering an absorption refrigeration system (ARS) for storing food, specifically milk. Two absorption systems; Lithium Bromide-water and the ammonia-water ARS are compared. The COPs, energy input and mass flowrates required to produce various cooling loads (40kW – 160kW) are compared. The results show that the exhaust geothermal fluid energy (504kW) is sufficient for powering both ARSs for storing milk to its suitable storage temperature of 4oC. The results also show that the Lithium Bromide-water system is more suitable for this application, because it produces a higher maximum COP (0.76) compared to the ammonia-water system’s maximum COP (0.64), it produces a higher maximum cooling capacity (380kW) compared to the ammonia-water systems maximum capacity (216kW). It requires lower input mass flowrate and pump work at all cooling capacities (40kW – 160kW). Therefore, a Lithium Bromide-water absorption chiller for storing the amounts of milk currently collected in the study area is designed. Optimized design specifications are provided.

Bulk and interfacial thermodynamics of ammonia, water and their mixtures

Bulk and interfacial thermodynamics of ammonia, water and their mixtures

Thermodynamic modelling for absorption refrigeration cycles powered by solar energy and a case study for Porto Alegre, Brazil

The objective of this study is to develop explicit thermodynamic models for absorption refrigeration systems. The models include recent advances in calculating thermodynamic properties of ammonia-water system, the parabolic trough solar collector (PTC) model and the storage tank model. The configurations studied are the single-stage cycle (SAR-C) and the generator-absorber heat exchange absorption refrigeration cycle (GAX-C). However, the procedure can be extended to other cycles or to other refrigerant-absorber pairs. The thermodynamic model was validated with published experimental results. In terms of coefficient of performance (COP), the models of both cycles showed excellent accuracy. The average relative errors were 6.91% and 1.34%, respectively. A parametric study was performed to determine the feasible evaporation temperatures. A critical mass flow ratio was also determined. It was found that higher evaporator temperatures and lower condenser temperatures increased COP. A case study was also conducted for the city of Porto Alegre in the south of Brazil. During the summer and spring, a maximum cooling load of 18.89 kW was reached in December, while the minimum cooling load of 11.31 kW was reached in March. The system is suitable for a commercial office with a peak cooling load between 12 and 16 h.

Performance Improvement of a Solar-Powered Recompression Supercritical Carbon Dioxide Cycle by Introducing an Ammonia-Water Cooling-Power System

The wide utilization of solar energy is beneficial for the emission reduction of carbon dioxide. This paper proposes a novel power cycle system driven by solar energy, which consists of a recompression supercritical carbon dioxide cycle (RSCO2) and an ammonia-water cooling-power cycle (ACPC). The power system operates in a “self-production and self-sale” mode, which means that the refrigeration capacity produced by the ACPC is utilized to cool the main compressor inlet fluid of the RSCO2. The comprehensive energy and exergy analyses of the proposed novel system are presented. The effects of the six parameters on the system thermodynamic performance are evaluated, which are direct normal irradiation, the ammonia concentration of a basic solution, the pinch point temperature difference of an evaporator, the effectiveness of a recuperator, the pressure ratio of the RSCO2 and the molten salt outlet temperature. The results show that compared with the stand-alone RSCO2, the net power and energy efficiency of the proposed system are improved by 15.94 and 10.61%, respectively. In addition, the increasing ammonia concentration of the basic solution leads to the rise of the ACPC refrigeration output, and the inlet temperature of the main compressor can be declined to 32.97°C with the ammonia concentration of the basic solution of 0.88. Moreover, when the effectiveness of the recuperator in RSCO2 rises up to 0.98, the system energy and exergy efficiencies can reach their maximum value of 30.68 and 33.10%, respectively.

4-E analysis of an ammonia-water mixture-based automobile's air conditioning system assisted by exhaust gas and solar energy

4-E analysis of an ammonia-water mixture-based automobile's air conditioning system assisted by exhaust gas and solar energy

Comparative analysis of the performance of mixing rules for density prediction of simple chemical mixtures

Four different mixing rules (MRs) in three equations of state (EOSs) have been used to account for the intermolecular forces of attraction between dissimilar molecules of different substances that form simple mixtures. The combined effects of the co-volumes of all constituent species of the mixtures were also considered, and the densities of these simple mixtures were predicted. Thereafter, the density results obtained were compared with accurately simulated experimental density values, and the effectiveness of these MRs was determined and compared. The four MRs compared are geometric mean average (GMA), whole square root average (SRA), Expanded geometric average (EGA), and simple average (SA) of attractive force parameter. They were all used in Van der Waals, Redlich Kwong, and Peng Robinson EOSs for two simple mixtures: a binary system (Ammonia – Water system) and a ternary mixture (methyl acetate – water – toluene system). It was found that GMA and EGA gave reasonably accurate estimates of the mixture attractive force parameter (am) and hence good density prediction for both Ammonia – Water and Methyl acetate – Water – Toluene systems. SRA gave unrealistic values of mixture densities for both systems and was discarded. SA gave a somewhat good result with Peng Robinson EOS for the ammonia-water system, but not that good in Redlich Kwong EOS and very poor in Van der Waals EOS. SA does not give reasonable estimates of the mixture densities with the three EOSs considered for the methyl acetate – water – toluene system.

In Silico Modeling of a Novel Refrigeration Process of the Ammonia–Water Falling-Film Absorption

Nowadays, the ammonia–water absorption refrigeration system (AARS) has attracted much attention due to its merits such as energy conservation and environment-friendliness. Meanwhile, growing studies have focused on the key equipment of ammonia–water absorber of AARS. Based on the thermodynamic and transfer property models that are specially determined in this study for the ammonia–water system, a calculational model of the ammonia–water falling-film absorber outside vertical tubes (AW-FFA-OVT) is established. The simulation of the ammonia absorption process is then carried out by the Fortran program in silico. The reliability of the physical models and the absorber model is verified by comparing with the experimental data from the literature. The mechanism of the proposed ammonia absorber is investigated by observing various key factors. The proposed model has already been successfully applied in the design and simulation of the key equipment in an actual AARS process.

Heat and mass transfer characteristic of vertical falling film generator with annular structure for ammonia-water system

Ammonia–water solution is widely used in absorption cycle systems, but the generation of ammonia from solution requires a great amount of heat consumption. In this work, a vertical-tube heat exchanger was adopted as the generator of an ammonia–water absorption cycle. The generation of ammonia from an ammonia–water solution in the generator was experimentally analyzed. The generator has an annular structure: a falling film of ammonia–water solution flows inside the inner tube, and an upflowing water stream flows in the annular space between the outside surface of the inner tube and the inside surface of the outer tube. First, the heat transfer enhancement effect of the annular structure was confirmed using water as the working fluid; then, the effect was tested for an ammonia–water solution. It was found that the heat transfer coefficient of Annulus I (0.5 mm annulus gap) was 316.2% higher than that of Annulus III (2.5 mm annulus gap) at the water flow rate of 50 g⋅s−1 through the annulus space. When the flow rate of the upflowing fluid exceeds a certain value, the effect of heat transfer for these annuli deviates obviously. The solution in the falling film with an initial ammonia concentration of 18.7 wt. % was used in the generation experiment. The outlet ammonia concentration of Annulus I was 12.7% lower than that of Annulus III at the water flow rate of 33.3 g⋅s−1. Based on the Sieder–Tate formula, the Nusselt number correlation equations were developed with ±10% error.

Non-Equilibrium Evaporation/Condensation Model

A new mathematical model for non-equilibrium evaporation/condensation including boiling effect is proposed. A simplified differential-algebraic system of equations is obtained. A code to solve numerically this differential-algebraic system has been developed. It is designed to solve both systems of equations with and without the boiling effect. Numerical calculations of ammonia–water systems with various initial conditions, which correspond to evaporation and/or condensation of both components, have been performed. It is shown that, although the system evolves quickly towards a quasi-equilibrium state, it is necessary to use a non-equilibrium evaporation model to calculate accurately the evaporation/condensation rates, and consequently all the other dependent variables.

Diagrams of entropy for ammonia–water mixtures: Applications to absorption refrigeration systems

Abstract The objective of this work is to calculate the entropy of ammonia–water mixture as a function of temperature, pressure, concentration, and other thermodynamic properties associated to absorption process, to support energy and exergy analysis of absorption refrigeration systems. This calculation is possible because a novel mathematical modelling was developed for this attempt. This determination will allow simulation and optimisation of absorption refrigeration systems, giving major importance in determining the values of thermodynamic properties of ammonia–water mixtures, such as enthalpy and entropy. A mathematical modelling for thermodynamics properties calculation at liquid and vapour phases of ammonia–water system is developed. The studies were based on the enthalpy vs. concentration diagram obtaining the enthalpy in the liquid phase corresponding at a temperature range from 80 °C to −40 °C. The mixtures enthalpy values were calculated for ammonia (h1c) and water (h2c) by using a non-linear regression program. The evaluation of thermodynamic properties in this work was discretised by formulating appropriate equations for each type of substance. However, thermodynamic properties of mixtures can be determined based on data from simple substances and mixing laws, or from an equation of state that considers the mixture concentration. The consistency of experimental data indicates the most suitable method to be used in entropy calculation.

Study of an absorption machine for an ammonia-water system decentralized trigeneration

This paper deals with Study of an absorption machine for an ammonia-water system decentralized trigeneration. The effects of evaporator, absorber and boiler temperature on the coefficient of performance of this cycle investigate. Simulation results show that with increasing the evaporator and absorber temperature the coefficient of performance increased and decreased, respectively. By increasing boiler temperature the coefficient of performance is constant. Keywords: absorption system; trigeneration; coefficient of performance

A single stage absorption refrigeration system dynamic mathematical modeling, adjustment and experimental validation

Abstract In this paper, a dimensionless dynamic mathematical model is proposed, in order to analyze the response of single stage absorption refrigeration systems according to operating and geometric parameters. Suitable control volumes are defined in order to obtain the system dynamic response. Mass accumulation in the components is neglected, and the system is divided in two regions: i) the absorbent/refrigerant solution in the thermal compressor, and ii) pure refrigerant in the condenser, expansion valve and evaporator. The temperatures at each control volume are calculated in time with a system of ordinary differential equations (ODEs) for the refrigerant side, and with a system of non-linear algebraic equations for the absorbent/refrigerant solution side of the refrigerator. The model equations are based on conservation of mass and energy principles, and simple functions to evaluate the thermodynamic properties of the ammonia–water system. Two sets of experimental data from an absorption refrigeration prototype were used to carry out model adjustment (set 1), followed by experimental validation (set 2), which showed good qualitative and quantitative agreement, within the experimental uncertainties. Dynamic simulations were conducted to assess the adequacy of model assumptions. Since accuracy and low computational time were obtained, it is reasonable to expect that the mathematical model could be used as a reliable design, control and optimization tool for absorption refrigeration systems.

English

Absorption cooling offers the possibility of using heat to provide cooling. For this purpose heat from a conventional boiler can used or waste heat and solar energy. When the latter systems are used absorption systems minimize also the adverse effects of burning fossil fuels and thus protect the environment. Absorption systems fall into two major categories, depending on the working fluids. These are the ammonia-water systems, in which ammonia is the refrigerant and lithium bromide-water systems in which water vapor is the refrigerant. An attempt has been made in this paper to reveal the thermodynamic analysis of steam fired Water/Li-Br Vapor Absorption Refrigeration System for 30 days. The analysis includes Energy and Second Law Analysis of the system. The second law analysis is based on the concept of exergy, which can be defined as a measure of work potential or quality of different forms of energy relative to the environmental conditions. Exergy analysis applied to a system describes all losses both in the various components of the system and in the whole system. The analysis is drawn for a Vapor Absorption Plant whose cooling load on the evaporator is 1740.96 kW or 496 Ton of refrigeration. The rich solution concentration solution circulation ratio is 58%.

A kinetic study of the formation of organic solids from formaldehyde: Implications for the origin of extraterrestrial organic solids in primitive Solar System objects

Abstract Aqueous organic solid formation from formaldehyde via the formose reaction and subsequent reactions is a possible candidate for the origin of complex primitive chondritic insoluble organic matter (IOM) and refractory carbon in comets. The rate of formation of organic solids from formaldehyde was studied as a function of temperature and time, with and without ammonia, in order to derive kinetic expressions for polymer yield. The evolution in molecular structure as a function of time and temperature was studied using infrared spectroscopy. Using these kinetic expressions, the yield of organic solids is estimated for extended time and temperature ranges. For example, the half-life for organic solid formation is ∼5 days at 373 K, ∼200 days at 323 K, and ∼70 years at 273 K with ammonia, and ∼25 days at 373 K, ∼13 years at 323 K, and ∼2 × 10 4 years at 273 K without ammonia. These results indicate that organic solids could form during the aqueous alteration in meteorite parent bodies. If liquid water existed early in the interiors of Kuiper belt objects (KBOs), formaldehyde could convert into organic solids at temperatures close to 273 K, and possibly even below 273 K in the ammonia–water system.

Gas hydrates at high pressure

The behaviour of gas hydrates at high pressure is of wide interest and importance. Gas hydrates are stablised by water-gas repulsive interactions. Information on the effect of changing density on these water-gas interactions provides fundamental insight into the nature of the water potential. Gas hydrates are also widely found in nature and systems like the ammonia-water and methane-water systems form the basis of 'mineralogy' of planetary bodies like Saturn's moon Titan. Finally, gas hydrates offer the possibility of cheap environmentally inert transportation and storage for gases like carbon dioxide and hydrogen. We have been carrying out investigations of a range of gas hydrates at high pressure using neutron and x-ray diffraction as well as other techniques. Results from these studies including; the phase diagram of the ammonia water system, the occupancies of hexgonal clathrate structures, and new structures in the carbon dioxide water system, will be presented.

Analysis of ammonia separation from purge gases in microporous hollow fiber membrane contactors

In this study, a mathematical model was developed to analyze the separation of ammonia from the purge gas of ammonia plants using microporous hollow fiber membrane contactors. A numerical procedure was proposed to solve the simultaneous linear and non linear partial differential equations in the liquid, membrane and gas phases for non-wetted or partially wetted conditions. An equation of state was applied in the model instead of Henry's law because of high solubility of ammonia in water. The experimental data of CO₂-water system in the literature was used to validate the model due to the lack of data for ammonia-water system. The model showed that the membrane contactor can separate ammonia very effectively and with recoveries higher than 99%. SEM images demonstrated that ammonia caused some micro-cracks on the surfaces of polypropylene fibers, which could be an indication of partial wetting of membrane in long term applications. However, the model results revealed that the membrane wetting did not have significant effect on the absorption of ammonia because of very high solubility of ammonia in water. It was also found that the effect of gas velocity on the absorption flux was much more than the effect of liquid velocity.

Molecular dynamics investigation of the interaction between IR radiation and an ammonia-water medium

cm -1 , and the refractive index of the ammonia-water system of clusters is lowered. It is shown that the maxima of the absorption spectra and the refractive index shift to higher frequencies. Starting from a certain concentration of ammonia in the clusters, however, the integral intensity of the spectra increases.

Experimental and Analytical Investigation of Ammonia Absorption into Ammonia-Water Solution: Free Absorption

Absorption phenomenon of ammonia vapor into ammonia water solution has been investigated experimentally, by allowing superheated ammonia vapor to flow into a test cell containing a stagnant pool of ammonia water solution. Before commencing the experiment, the pressure in the test cell P1i, corresponds to the equilibrium vapor of the ammonia-water system at room temperature and initial mass fraction Ci. When the valve is opened, mechanical equilibrium is established quickly and the pressure in the test cell becomes equal to that of the ammonia vapor cylinder. The difference between the initial pressure in the vapor cylinder and the initial pressure in the test cell ΔPi is found to have a major influence on the absorption rate [1]. The interface temperature can be estimated for a transient case, by help of an inverse solution proposed by Monde [2]. The interface concentration Cint obtained by measured ammonia vapour pressure and the estimated interface temperature. The main objective of this study is to investigate the effect of the initial pressure difference and the initial concentration on the interface concentration. A correlation which gives the interface concentration as a function of the initial concentration, the initial pressure difference and time is derived. In addition, the absorbed mass at no pressure difference could be estimated from the absorbed mass at initial pressure difference.

Thermal Design of Ammonia Desuperheater-Condenser and Comparative Study with HTRI

Abstract Condensers are widely used in chemical industry, refrigeration, air-conditioning and power generation systems. In this paper, the thermal design of a desuperheater-condenser has been carried out manually as well as using HTRI software. The paper provides information about the types and classification of condensers. The primary objective of this study is to design a desuperheater-condenser for Ammonia-Water system. Ammonia-Water system is widely used in the refrigeration industry. The manual calculations are based on standard co-relations available in various literatures. The results have been compared with HTRI. After comparative analysis the reasons for variation have been identified, critically reviewed and discussed. It has been observed that manual calculations often become lengthy and iterative. HTRI has a rigorous and integral approach which gives more accurate results as well. HTRI is the most widely used software in the industry. But it is also important to verify the results with manual calculations. Likewise, manual design should also be verified with industrial software like HTRI. It may happen sometimes that due to human error, manual design results may come out to be somewhat inaccurate. So in order to have a good and optimized design, manual and software based calculations should be carried out simultaneously and verified with each other.