Ammonia-water Absorption System Research Articles

Battery–integrated combined cooling, heating and power plant (CCHP) through NH3 – H2O absorption system in a hospital facility

Combined heat and power (CHP) systems have been employed in various applications for years. They are gaining increasing attention in the residential and small industrial sectors for their primary energy saving potential and CO 2 emissions reduction. Additionally, in specific applications such as the hospital sector, CHP plants can play a critical role in replacing fossil-fueled electric generators to supply electricity during local grid outages, thus enhancing hospital facilities’ energy efficiency, while also securing reliability and efficiency of operation. Hospitals have unique energy demand profiles, with high and constant demand (particularly heating and cooling demands), making them an ideal use-case for trigeneration systems. Combined, cooling, heating and power plants (CCHP) are capable to provide not only heating and electricity, but also cooling through the efficient exploitation of a single energy source, reducing Hospitals’ reliance on the local grid. In this context, this work aims at evaluating the potential of a battery-integrated CCHP plant through an innovative ammonia-water absorption system, whose energy analysis is based on data acquired from an Italian Hospital facility. The potential of integrating an experimental combined cooling and power production ammonia-water absorption system has been investigated starting from an optimized battery energy storage system (BESS) CHP plant configuration, studied for the same facility. A proper control strategy has been developed to maximize the cooling production when required from the end-user through CHP plant’s exhaust gases waste heat recovery. The energy analysis demonstrated the advantages of the CCHP-BESS plant over the optimal CHP-BESS configuration, with an 11.22% increase in primary energy saving, a 9.85% reduction in CO 2 emissions, and a 5.03% decrease in electric peak power demand.

Analytical modelling of food storage cooling with solar ammonia-water absorption system, powered by parabolic trough collectors. Method

The study presents a new analytical model capable to reveal the thermal behaviour of all the components of the solar ammonia-water absorption system, powered by parabolic trough collectors, serving different types of food storages: refrigeration chamber, refrigerated food storage, freezing chamber and frozen food storage. The heat inputs, that determine the total cooling load, for each food storage spaces consist of: heat gains through walls, heat gains through ventilation (fresh air), heat that must be dissipated from the stored products (technological cooling load required to cool down the products) and heat gains through operation. The influence of the number of solar parabolic trough collectors and of the storage tank size on different parameters of the refrigeration plant are investigated under low and high storage temperatures.•Food cooling with solar absorption refrigeration system.•Hourly based variation of NH3-H2O solar absorption system performances.•Long term simulation of solar absorption cooling for refrigeration and cooling.

Surfactant-enhanced ammonia-water bubble absorption

An investigation into the effect of surfactants on ammonia-water bubble absorption is presented. Heat and mass transfer in a 50–200 W bubble absorber are experimentally investigated at operating conditions spanning a wide range of working and coupling fluid conditions. The effect of surfactant is assessed by adding 50–2000 PPM of 1-octanol to the ammonia-water mixture. Absorber performance is enhanced by surfactants, with the highest enhancement of 35% observed at vapor Reynolds number > 1000. The effect of surfactant concentration on bubble absorption is also discussed. A segmental model for heat and mass transfer is developed and comparison with experimental data yields good agreement with an AAD of 8.3%. Temperature and mass flow rate profiles along the height of the absorber provide insights into the absorption enhancement mechanism in the presence of surfactants. The results from this study show the potential for these passive enhancement techniques to be implemented in ammonia–water absorption systems.

Experimental study of heat and mass transfer for ammonia-water falling film absorption on novel S-shaped capillary tubes bundle

Compact absorber is beneficial for bulk reduction and cost-saving of absorption systems. This paper presents an experimental study on the heat and mass transfer performance of a novel absorber which consists of an S-shaped capillary coils bundle. Experiments were carried out for a practical ammonia-water absorption system under practical working conditions. The effects of operating parameters such as degree of subcooling, concentration and mass flow rate of inlet solution, as well as absorption pressure, on absorption were investigated. Specifically, with the selected pressures of 300kPa, 400kPa and 500kPa and concentrations of inlet solution of 6.6%, 15.5% and 22.4%, we obtained the heat and mass transfer coefficients ranging from 622~1945 Wm-2K-1 and 5.1~34.3×10-6 ms-1, respectively. The heat and mass transfer experimental data were processed in terms of the empirical correlations for the Nusselt and Sherwood numbers, respectively, and the correlations can fit all the experimental data with error bands of ±15%.

Desorber and rectifier geometries for ammonia-water absorption systems; Part II: Mass transfer, flooding, and component performance

• Integrated desorber-analyzer-rectifier developed for compact absorption systems. • Ammonia-water mass transfer coefficients determined. • Flooding limits of proposed geometries characterized. • Viability demonstrated through component-level performance. • Developed models show good agreement with present data. An experimental investigation of two compact counter-flow vapor generation units, for use in ammonia-water absorption systems, was conducted. The vapor generation units feature integrated desorber, analyzer, and rectifier sections. The branched tray design uses pool-boiling mechanisms in the desorption process, while the vertical column uses falling-film evaporation mechanisms. Experimental mass transfer coefficients for the desorbers of both concepts were quantified and compared with correlations from the literature, generally with poor agreement. The flooding limits of these counter-flow vapor generation units were investigated and agree well with available correlations. The experimental results from Part I of this study are used in this paper, Part II, to develop revised heat and mass transfer models that accurately predict component level performance.

Desorber and rectifier geometries for ammonia-water absorption systems; Part I: Experimental approach and heat transfer

Abstract An experimental study of ammonia-water desorption in compact counter-flow geometries was conducted. Two novel vapor generation units, comprising integrated desorber, analyzer, and rectifier segments that use microchannel geometries, were conceptualized. The branched-tray concept features a desorber that uses pool-boiling mechanisms, while the vertical column desorber relies on falling-film evaporation mechanisms. Both concepts rely on falling-film mechanisms in the analyzer and rectifier sections. The vapor generation unit test sections were evaluated across a range of concentrated solution mass fractions (0.400 – 0.550), desorber coupling-fluid inlet temperatures (170 – 190°C), and concentrated solution flow rates (0.70 – 1.3 g s−1). This paper, Part I, reports the experimental methodology and results while in Part II, flooding limits of these geometries and heat and mass transfer models that accurately predict component-level performance are presented.

Air-cooled absorbers for extreme-ambient absorption heat pumps

• Ammonia-water air-cooled absorber modeled and tested. • Single-pressure loop and air-handling unit used for experiments. • Baseline conditions with 51.7 °C ambient air. • Good agreement between experiments and models. An investigation of air-coupled absorbers for an ammonia-water absorption system operating in extreme ambient conditions was conducted. Heat and mass transfer modeling was used to predict the performance of round-tube corrugated-fin absorbers for a 2.64-kW absorption chiller operated at high ambient temperatures. A single-pressure ammonia-water test facility was used in conjunction with a temperature- and humidity-controlled air-handling unit to evaluate the absorbers at design and off-design conditions. Absorber performance was studied over a range of air temperatures and flow rates, inlet solution temperatures, and concentrated solution flow rates and concentrations. At design conditions, round-tube corrugated-fin absorbers of 394 and 551 fins per meter (FPM) demonstrated comparable performance, and measured heat transfer rates were predicted well. Results from this investigation can be used to guide the development of air-coupled heat and mass exchangers for compact absorption heat pumps.

Design and thermoeconomic analysis of a multi-effect desalination unit equipped with a cryogenic refrigeration system

In this paper, a hybrid tri-generation system is designed to produce LNG and freshwater simultaneously based on a multi-effect desalination system and analyzed using energy and exergy analyses. For natural gas liquefaction, the initially required cooling of the cycle is supplied by ammonia-water absorption system, and the required intermediate cooling load and liquefaction process are provided by a refrigeration system with mixed fluid. Two alternatives for providing power generation to the system and the required heat for driving the absorption cycle have been considered and compared. The first alternative relies on a natural-gas-fired power plant, while the second is based on steam-solar power plant with dish collectors. The former results in the total energy efficiency of 85.8% (LHV). The highest thermodynamic irreversibilities occur in the heat exchangers (61%), even if they have the highest exergy efficiency compared to the other plant equipment. On the other hand, using solar dish collectors enables to decrease carbon dioxide emissions by 40%, and increases freshwater and LNG production by 95% and 4.7% respectively. The power obtained per kg of LNG produced is about 0.19 kWh, which is less than or equal to the other similar patents. The results of the economic analysis with the annualized cost method of the system show that the products prime cost of both structures 1 and 2 are equal to 0.2580 and 0.1784 US$ per kg of LNG, respectively. A suitable strategy for modelling enhancement of system’s parameters is suggested by expanding of sensitivity analysis on the important parameters of the developed system.

Exergy cost analysis of ammonia–water absorption systems based on thermoeconomics

This study presents exergy cost analysis of vapour absorption refrigeration system operating with an ammonia–water mixture under steady-state conditions. Exergy cost analysis is the application of thermoeconomics and provides the cost formation process of products and residues for energy conversion systems. The authors have built the productive structure, a basic concept of the thermoeconomic modelling for the proposed absorption system. This methodology allows one to find the cost flow rates in monetary units for each flow and exergy cost of each subsystem of the proposed absorption system. It is observed that flows 12 and 13 have highest cost flow rates 82.11 and 31.3476 Rs/GJ, respectively due to their high mass flow rates. The exergy cost of the product of the generator is 2340.5 kW which is distributed among the refrigerant heat exchanger (56.2 kW), Mixture heat exchanger (425.5), evaporator (543.3 kW), absorber (1082.4 kW) and condenser (233.1 kW).

Multivariable feedback control of small-capacity ammonia-water absorption systems

Abstract This paper presents the development and experimental evaluation of a multivariable feedback controller for small-capacity ammonia-water absorption systems. Experiments were designed to identify the pairings between various controlled variables and the degrees of freedom available in the system. A small-scale experimental system was fabricated with access to all degrees of freedom in the system as tunable parameters. Transient analysis of variations in the degrees of freedom assisted in tuning the parameters of the control system to achieve fast, stable and repeatable performance. A methodology for controlling the cooling capacity of the system in response to changes in the load or operating conditions by adjusting the concentrated solution flow rate and the heat source temperature and mass flow rate is developed. In addition, the performances of the evaporator and the desorber are optimized by using flow control valves. Case studies using the developed controller demonstrated fast and stable performance of the system in achieving part-load performance as low as 50% of the baseline cooling capacity, and at off-design ambient temperature. Moreover, the system maintained high, near-design COP (0.55–0.65) values during these test cases.

Visual documentation of transfer processes in horizontal-tube falling-film ammonia–water absorbers

Flow patterns in a horizontal-tube falling-film absorber operated as part of a complete ammonia–water absorption system are presented. A tube bank consisting of four columns of six 9.5 mm nominal outer diameter, 0.292 m long tubes was installed in an absorber shell that allowed heat and mass transfer measurements and optical access for flow visualization. High-speed, high-resolution videos were recorded over a wide range of operating conditions (desorber solution outlet concentrations of 15–40% at absorber pressures of 150, 345 and 500 kPa, over solution flow rates of 0.019–0.034 kg s−1). Image analyses indicated that the droplet mode was the dominant inter-tube flow mode for the range of the experiments. Droplet characteristics and flow regime transitions are strongly influenced by the solution flow rate. Variation in the solution concentration and the operating pressure also affect the flow characteristics such as film thickness, residence time and droplet spacing.

A unified single stage ammonia-water absorption system configuration with producing best thermal efficiencies for freezing, air-conditioning and space heating applications

Abstract Various single stage ammonia-water absorption system configurations result in a confusion of determining a better one with better performance. In this paper, a unified single stage ammonia water absorption system configuration for freezing, air-conditioning, and space heating applications is proposed, and it can produce best thermal efficiencies in terms of internal heat recovery under different application conditions. The model of the unified system is established to investigate the operating parameters and the performance of the system under the representative freezing, air-conditioning, and space heating application conditions. The results verify the feasibility of the unified system, and show that the thermal efficiency is improved by 25%, 34%, and 20% respectively, compared to a conventional single stage absorption system. The calculated results also verify the key points of the system operation, which are making the feed saturated, and adjusting a proper split ratio of the strong solution to the rectifier, respectively. The 3D figures of the system thermal efficiency versus the boundary temperatures show the performance and its improvement of the unified system configuration intuitively. The cycle switching diagram is presented and provides a reference for regulating the cycle operation of the unified system.

Heat and mass transfer in microscale diabatic distillation columns for ammonia–water desorption and rectification

An experimental investigation of heat and mass transfer in novel desorber and rectifier components based on the diabatic distillation principle is conducted. Heat and mass transfer coefficients measured here are compared with predictions of correlations from the literature. Temperature profiles are compared with component-specific heat and mass transfer models. Good agreement between model predictions and experimental results is shown. While heat and mass transfer correlations from the literature provide reasonable prediction of the data, further improvement is achieved with proposed correlations for liquid mass transfer and binary mixture correction coefficients. The results from this study show the potential for these novel designs to be implemented in small-capacity ammonia–water absorption systems.

Direct-coupled desorption for small capacity ammonia-water absorption systems

An investigation of direct gas-coupled desorption for small capacity ammonia-water absorption is presented. Some applications favor or require the use of direct-coupling of the heat source for desorption; therefore, a systematic treatment of this topic is needed for the optimal design of small-capacity absorption systems. Gas-coupled desorption is accomplished through diabatic distillation, and an optimal gas side geometry is established. Gas side optimization considers pressure drop minimization as well as geometric constraints such as column diameter and number of gas tubes. A heat and mass transfer model is developed and validated with experiments. Excellent internal vapor purification is achieved and the results agree well with the heat transfer and pressure drop predictions. These results demonstrate the applicability of direct-coupled desorption to small-capacity ammonia-water absorption systems. A comparative assessment with indirect-coupled desorption components is also made.

Experimental investigation of a compact thermal compressor for an ammonia-water absorption heat pump

An experimental evaluation of the thermal compressor of an ammonia-water absorption system is presented. A compact desorber and a rectifier based on diabatic distillation principles that lead to optimized system operation are designed and fabricated. Performance of these compact components as a thermal compressor for small-capacity absorption heat pumps is measured and compared with model predictions. Optimal desorption temperatures for energetic and exergetic performance established in previous modeling work are validated. The results of this study demonstrate the utility of modeling several components of an absorption system as a thermal compressor, which facilitates system design and control.

Hydrodynamic considerations and design concepts for optimal thermal compressors

Novel and highly compact design concepts for the desorber and rectifier components are presented to facilitate development of small capacity ammonia-water absorption systems for a wide range of applications. These designs enable thermodynamically optimal diabatic distillation and can be applied for direct-coupled waste heat recovery applications or for indirect heat source coupling. A hydrodynamic design methodology is developed and applied to address liquid–vapor countercurrent flow limitations. Feasibility of these designs is validated through air-liquid flow visualization experiments that simulate target flow patterns. The effects of geometric parameters and fluid properties are investigated to specify internal component features and dimensions. Parameters for coupled heat and mass transfer modeling of these designs are identified and quantified through high-speed video analysis. The results of this study guide the design and further development of highly compact and efficient desorption components for optimal thermal compressors.

Technical engineering design, thermal experimental and economic simulation analysis of absorption cooling/heating systems in China

In low temperature heat sources driven cooling/heating absorption systems, there are many equipment combinations. Usually, there are contradictions between the equipment efficiency and their economy; for example, the high efficiency- solar collector usually has a high price. So, in this paper, ten absorption cooling/heating systems with different heat sources and different absorption technologies are investigated for technical-economic-thermal analysis. The heat sources are flat plate solar collector, evacuated U-pipe solar collector and middle-temperature high efficiency solar collector and waste heat. The absorption chillers are 1-effect LiBr absorption chiller, 2-effect LiBr absorption chiller, novel 1–2 effect LiBr absorption chiller and novel high efficiency-heat-recovery ammonia water absorption system. The results show that 2-effect absorption chiller with heat source of waste heat is the most optimized choice, which lowest payback period is about 1.9 years. The second choices are the 2-effect LiBr absorption system with novel middle-temperature solar collectors/natural gases and the novel ammonia water absorption system with waste heat sources.

Design and modeling of a microscale diabatic distillation column for small capacity ammonia–water absorption systems

The concept of diabatic distillation is applied to desorption and rectification in an ammonia–water absorption system. Results of a hydrodynamic investigation of novel components for these processes are used to develop a non-equilibrium model to predict heat and mass transfer performance. A modular modeling approach is proposed whereby physical consistency of various heat and mass transfer processes is achieved while reducing model complexity. A target vapor generation rate of 3 g s−1 with an ammonia mass fraction of 0.9985 is specified. It is shown that highly compact, lightweight desorption and rectification components can be realized. Heat source temperature and mass flow rate control are used to optimize system performance, and performance predictions are made over wide range of operating conditions. These results are also used to obtain reduced-order heat and mass transfer performance measures that facilitate incorporation of system performance into system level models and dynamic models.

Thermodynamic considerations for optimal thermal compressor design

A unified framework for the modeling of the thermal compressor of a single-effect ammonia–water absorption system is developed. An optimal thermal compressor configuration is found through a comparative assessment of various desorption and rectification configurations, and pertinent figures of merit are defined. The diabatic distillation column configuration is shown to achieve the highest thermal compressor performance. Parameters relevant to quantitative thermal compressor characterization are identified. Two optimal operating temperatures are identified, for the optimization of energetic and exergetic objectives, respectively. Statistical regression and artificial neural network analyses from thermodynamic simulations over a wide range of ambient and evaporator temperatures provide accurate prediction of thermal compressor performance and are compared. These results facilitate the assessment of absorption technology through simple predictive tools at the cycle design stage. This framework could also yield a design tool and could guide system design, optimal control, and flexible operation.

Heat integration of ammonia-water absorption refrigeration system through heat-exchanger network analysis

Abstract The heat integration of existing single-effect ammonia-water absorption system is studied. A set of possible heat modifications involving with absorption heat or rectification heat recovery are identified on energy transfer diagram, the performance of each heat modification is studied and compared, and the interaction of heat transfer in generator, absorber, rectifier and solution heat exchanger is investigated through different combinations of heat modifications. There are two approaches of increasing thermal performance, one is aimed to increase the feed temperature of the distillation column by isolating heat exchanger components. The purpose of the other approach is to reduce heat consumption through heat integration by using bridge analysis. The two approaches can both boost the thermal performance effectively. The results demonstrate 22% increases in Coefficient of Performance (COP) compared with traditional single-effect cycle under certain working conditions. In general, obtaining the maximum heat saving capacity in advance under different working conditions is necessary either for retrofit or in preliminary design stage. In this paper, the selection guidance of suitable cycle under different working conditions is provided.