Absorption Cycle Research Articles

Laboratory Determination of Absorption Refrigeration Cycles

A methodology for experimentally particularizations and analyses of thermodynamically cycles of the binary mixture at laboratory diffusion absorption refrigerators is developed. It allows estimation of the performances of the unit at cooling and heat pump mode for scientifically and education purposes. Тhe developed approach will be used to educate students in the courses of thermodynamics and renewable energy systems about the applications of the absorption cycles for utilisation of solar or waste energy for cold and heat production.

Effect of N,N′-Methylenebisacrylamide on properties of porous semi-IPN hydrogels from Acrylamide, Maleic Acid, and its use for Urea absorption

Hydrogel is a three-dimensional polymer that can absorb large amounts of reagents while maintaining structural integrity. This material has been applied in many fields especially in smart agriculture. To improve the economic viability, the reusability of hydrogels in agricultural engineering over multiple cycles of adsorption and desorption is an urgent requirement. This can be solved if the crosslinker is used properly. Therefore, in this work, a series of porous semi-IPN hydrogels based on linear polyacrylamide, acrylamide, maleic acid, and N,N′-methylenebisacrylamide (MBA) were synthesized. The hydrogels were evaluated for the impact of MBA content on the characteristics and applicability as a urea fertilizer carrier. The chemical composition, morphology, mechanical, and rheological properties, swelling behavior, urea absorption and desorption of hydrogels with crosslinker content in the range of 0.5-2.0 % were investigated. The porous structure was confirmed by scanning electron microscopy images. Changing the MBA content significantly affected all characteristics of the hydrogels. In particular, increasing the MBA content decreased the equilibrium swelling ratios in all investigated environments. The maximum amount of urea loaded into the hydrogel was also reduced from 435.88 to 188.50 mg/g. This increase also changed the swelling mechanism from non-Fickian to Fickian, whereas the urea release mechanism changed from Fickian to non-Fickian. Finally, the hydrogels demonstrated stability in soil over multiple cycles of water absorption and release. This study provides valuable insights into designing a semi-IPN hydrogel with desired properties that meet the application requirements of modern farming techniques.

Exergy-economic based multi-objective optimization and carbon footprint analysis of solar thermal refrigeration systems

The increasing carbon footprint associated with conventional cooling methods underscores the urgent need for sustainable alternatives. This study investigates the economic and environmental advantages of various solar-thermal cooling systems, with a focus on optimizing their performance across different climate conditions. Employing a multi-objective approach, the research emphasizes exergy-economic indices to optimize selected cycles. The analysis covers multiple refrigeration technologies, including liquid absorption, solid adsorption, and solid desiccant cycles. Results indicate that the liquid absorption cycle performs optimally in hot, arid climates, reducing the payback period to approximately 8 years when optimized. In hot and humid regions, the solid desiccant cycle proves most effective due to its superior humidity control, yielding a payback period of 5.3 years. For cold and mountainous areas, the solid adsorption cycle is preferred, with a payback period of 13.5 years, while moderate and humid climates benefit from the solid desiccant cycle for both cooling and humidity regulation. The exergy-economic factors for the solar refrigeration systems across semi-arid, hot and arid, hot and humid, cold and mountainous, and moderate and humid climates are 0.758, 0.602, 0.698, 0.74, and 0.575, respectively.

ABSORPTION REFRIGERATION SYSTEMS FOR WASTE HEAT RECOVERY AT THE SILICATE INDUSTRY

The glass, ceramic and cement plants are energy intensive industrial systems, releasing high amounts of greenhouse gases. The dissipation of the waste heat reduces their profitability, energy and ecological efficiency. The absorption refrigeration systems are successful solutions for the recovery of thermal energy at different temperature levels to obtain useful cooling and heating powers for technological needs, and for air conditioning of administrative and industrial buildings. Although the absorption units in a heat pump and refrigeration cycle are currently used in building and industrial systems, they have not yet penetrated widely into the silicate factories. This paper discusses possibilities for the applications of basic types of absorption cycles at heat pump and refrigeration modes to utilize waste energy at different temperature levels in glass, ceramic and cement plants. The examined variants are demonstrated via examples, diagrams and analyses of the possible energy saving.

Dopamine‐modified Highly Dispersed ZIF‐8 to Promote CO2 Absorption

AbstractCO2 capture technology has been widely used to reduce CO2 emissions, resulting in a variety of capture methods and materials. Among them, the more widely used is the chemical absorption method. However, the chemical absorption method has problems such as high energy consumption and slow absorption rate. In order to solve the above problems, we prepared an effective catalyst to improve the CO2 absorption rate. ZIF‐8 and hydrophilic ZIF‐8‐DA were prepared by in situ synthesis under ambient conditions. The catalytic effect of the hydration reaction of ZIF‐8 and ZIF‐8‐DA was tested using CO2 absorption regeneration experiments under aqueous and alkaline conditions, respectively. The results showed that the synthesized catalysts could significantly enhance the CO2 absorption in water and alkaline solution. The addition of 0.1 wt % of ZIF‐8 in alkaline solution increased the average CO2 absorption by 1.80–15.84 %, respectively, while the addition of 0.1 wt % of ZIF‐8‐DA increased the CO2 absorption by 7.01–25.36 %. In addition, both catalysts had excellent reusability and maintained high performance even after five absorption and regeneration cycles. Polymer dispersibility index (PDI) results showed that ZIF‐8‐DA dispersed more uniformly in aqueous solution.

Ti/Cr regulated and strategic Ce doped V-Ti-Cr-Mn-Fe high-entropy alloys with extraordinary reversible hydrogen storage properties at ambient temperature

High-entropy alloys (HEAs) are garnering widespread interest due to their exceptional hydrogen storage capabilities at ambient temperatures. Herein, a series of HEAs composed of V-Ti-Cr-Mn-Fe with varying Ti/Cr ratios has been synthesized via arc melting to serve as carrier materials for room-temperature hydrogen storage. Thanks to the composition of a large amount of body centered cubic (BCC) phase V32TixCr58-xMn5Fe5 exhibits excellent hydrogen storage performance, and the hydrogen absorption capacity of these HEAs escalates while the desorption capacity initially rises followed by a decline with an increase in the Ti/Cr ratio. Notably, the HEA with a Ti/Cr ratio of 1.0, namely V32Ti29Cr29Mn5Fe5, demonstrates exceptional performance by absorbing 3.55 wt% H2 within 60 min and rapidly releasing 2.16 wt% H2 within 5 min at 303 K. Further enhancement is achieved with the strategic doping of Ce in the V32Ti29Cr29Mn5Fe5, which leads to the removal of the Ti-rich phase and the incorporation of CeO2, significantly improves the activation performance, allowing the Ce-doped HEA to reach saturation in the 3rd hydrogen absorption cycle. Consequently, the hydrogen ab-/desorption capacities at ambient temperature are further augmented to 3.73 wt% and 2.26 wt%, respectively, and the enthalpies of hydrogen ab-/desorption are significantly reduced to −25.0 and 23.4 kJ/mol H2, marking a new benchmark for V-based HEAs. Dramatically, DFT calculations suggestes that the incorporation of Ce diminishes the structure energy of BCC phase structure for V32Ti29Cr29Mn5Fe4Ce1 as well as elongates the average distance of M−H from 1.955 Å to 1.969 Å, which corroborate the experimental results, offering profound insights into the underlying mechanisms of hydrogen storage within BCC-phase HEAs at ambient temperature.

CO2 absorption with polyethyleneimine solution intensified by a rotating packed bed with liquid detention

This study explored the absorption of CO2 by the polyethyleneimine (PEI) solution in a rotating packed bed (RPB). In order to boost the CO2 absorption effect, the liquid detention phenomenon in the RPB was utilized to overcome the short residence time of liquid. The effects of different operating parameters on CO2 absorption efficiency (η) and gas-phase volumetric mass transfer coefficient (KGav) in the RPB were investigated. The experimental results indicated that the RPB can greatly intensify the absorption of CO2. η and KGav increased from 3.3 % and 0.041 kmol·m−3·h−1·kPa−1 to 76.0 % and 1.634 kmol·m−3·h−1·kPa−1, respectively, as the rotational speed of the RPB rose from zero to 700 rpm with 250 mL detained liquid. It was also found that the liquid detention phenomenon can significantly elevate η and KGav as a result of extended liquid residence time and increased liquid holdup in the RPB. When the detained liquid volume increased from zero to 250 mL, η and KGav increased by 55.6 % and 113.1 %, respetively. In addition, it was observed that CO2 load in the rich PEI solution increased from 9.650 to 11.189 molCO2/kg PEI while η remained around 85 % after five cycles of absorption–desorption, suggesting an excellent cyclic stability of PEI. This work contributes to the development of viable CO2 capture technologies by intensifying the CO2 absorption process in the RPB with an efficient absorbent.

Cooling positronium to ultralow velocities with a chirped laser pulse train

When laser radiation is skilfully applied, atoms and molecules can be cooled1–3, allowing the precise measurements and control of quantum systems. This is essential for the fundamental studies of physics as well as practical applications such as precision spectroscopy4–7, ultracold gases with quantum statistical properties8–10 and quantum computing. In laser cooling, atoms are slowed to otherwise unattainable velocities through repeated cycles of laser photon absorption and spontaneous emission in random directions. Simple systems can serve as rigorous testing grounds for fundamental physics—one such case is the purely leptonic positronium11,12, an exotic atom comprising an electron and its antiparticle, the positron. Laser cooling of positronium, however, has hitherto remained unrealized. Here we demonstrate the one-dimensional laser cooling of positronium. An innovative laser system emitting a train of broadband pulses with successively increasing central frequencies was used to overcome major challenges posed by the short positronium lifetime and the effects of Doppler broadening and recoil. One-dimensional chirp cooling was used to cool a portion of the dilute positronium gas to a velocity distribution of approximately 1 K in 100 ns. A major advancement in the field of low-temperature fundamental physics of antimatter, this study on a purely leptonic system complements work on antihydrogen13, a hadron-containing exotic atom. The successful application of laser cooling to positronium affords unique opportunities to rigorously test bound-state quantum electrodynamics and to potentially realize Bose–Einstein condensation14–18 in this matter–antimatter system.

Efficient, selective and reversible capture of hydrogen sulfide by [Emim]Cl-Acetamide deep eutectic solvents

There is a particular demand to explore low-volatility and structurally tunable absorbents for efficiency, selectivity and reversibility in capturing H2S. For the first time, the performance of deep eutectic solvents (DESs) composed of 1-ethyl-3-methylimidazolium chloride ([Emim]Cl) and acetamide (AA) were examined as physical absorbents for H2S capture. The physical properties of [Emim]Cl-AA DESs, and solubilities of both H2S and CO2 in them were measured. Relevant experimental results demonstrated that the solubilities of H2S in [Emim]Cl-AA DESs (1.1 mol/kg at 298.2 K and 1.023 bar) significantly exceed those of CO2 (0.040 mol/kg at 298.2 K and 1.027 bar). [Emim]Cl-AA DESs exhibit higher H2S solubilities and superior ideal H2S to CO2 selectivities (e.g., the ideal H2S/CO2 selectivity of [Emim]Cl-AA (1:0.5) is 28.5 at 298.2 K) than those physical absorbents ever reported. The recyclability of [Emim]Cl-AA DESs for H2S selective capture was also evaluated, which was found to be very stable in ten continuous absorption and regeneration cycle experiments. The mechanism of H2S capture by [Emim]Cl-AA DESs was finally illustrated at the molecular level with the support of theoretical calculations.

Polypropylene as an absorbent layer for acoustic ceilings: Sound absorption and life cycle assessment

The substantial volume of polypropylene fabric waste generated because of its use in protective elements in hospital environments calls for the exploration of environmentally friendly solutions. This study characterises the acoustic absorption coefficient of surgical mask waste (polypropylene) to be used as absorbent layers in acoustic ceilings. Additionally, a life cycle assessment (LCA) has been carried out. Although values of absorption coefficients for polypropylene have been published, none include life cycle studies. This research is in keeping with the principles of circular economy, contributing to waste reduction while also exploring innovative applications for recycled materials. The starting point of this study is the replacement of the most common material layer on the market, mineral wool, with a polypropylene layer that has the same or better acoustic performance based on single number absorption indexes and ratings following international standards for the calculation of sound absorption coefficients and life cycles. Various waste processing methods and different densities and thicknesses have been evaluated. The results show that recycled polypropylene material exhibits suitable behaviour as an acoustic absorbent layer, particularly in acoustic ceilings. The LCA considered transport, shredding, washing, disinfection, and drying and confirms the eco-efficiency of this absorbent layer.

Deep eutectic solvents and traditional refrigerants in absorption refrigeration cycles using molecular approaches

Absorption Refrigeration Cycles (ARC) represent a sustainable technology capable of effectively producing cold with modest energy consumption from waste heat or renewable sources. However, the right choice of working fluid pair absorbent–refrigerant is essential for the system to work properly. This contribution is devoted to analysing the performance of an ARC using a wide variety of refrigerants in combination with selected deep eutectic solvents (DES) as absorbents. Three choline chloride-based and one ionic liquid (IL)-based DESs as absorbers are combined with sixteen refrigerants. The PC-SAFT equation of state is employed to assess the thermophysical properties. Accurate modelling of the absorption cycle has revealed that the phase behaviour of the working mixture significantly constrains the temperature and pressure range within which the cycle can operate. Idealised ARCs are insufficient for accurately representing the capabilities and limitations of these systems. Of the sixty-four working pair mixtures, only eighteen are suitable for ARCs based on technical and thermodynamics criteria. The Coefficient of Performance (COP) has been updated with additional key performance indicators that consider environmental and safety factors. The maximum values of the COP for this mixture are around 0.92, while many options lie in ranges around 0.60. This comprehensive analysis helps establish a ranking of the best options. The results have shown that the IL-based DES using R227ea or R236ea is the most efficient system among all the systems studied, with performances of 0.92 and 0.74.

Performance Evaluation of Novel Advanced Recompression Absorption Refrigeration Systems Equipped with Ejector and Vapor Injection Technology

The absorption refrigeration cycle (ARC) faces challenges considering its decreased working pressure and COP. By integrating Recompression technology (RAC) into ARC, these issues are partly addressed. To address these inefficiencies, in this study, ejector and vapor injection techniques are incorporated into refrigerant side of the RAC cycle, resulting in the development of advanced systems: Refrigerant ejector enhanced recompression absorption cycle (RE-RAC) and Vapor injection enhanced recompression absorption cycle (VI-RAC). Key metrics assessed are 1st and 2nd law efficiency, system exergy destruction rate, compressor load, and generator heat requirements. Conclusively, under analogous operating conditions, RE-RAC and VI-RAC demonstrate a substantial improvement in COP, achieving 76 % and 63 % enhancements, respectively, over the standard RAC system. Compared to the conventional solution ejector-based SE-RAC, these systems show performance increases of 28 % and 19 %, respectively. The findings also highlight the sensitivity of these systems to parameters such as generator temperature and pressure, evaporator temperature, absorber temperature, evaporator recovery and normal pressure ratio. At higher evaporator temperature and lower generator temperature, the performance of these systems as well as enhancement of RE-RAC over VI-RAC is higher observed. The optimal value of generator pressure and recovery pressure ratio for maximum efficiency and minimum total exergy destruction rate is also dependent upon these. At a generator temperature of 67 °C and an evaporator temperature of 8 °C, RE-RAC exhibits a 35 % higher COP compared to VI-RAC. However, at −10 °C evaporator temperature, changes in external generator heat input and compressor work reduce the COP enhancement to 5 %.

Theoretical perfection and application of entransy analysis method on absorption systems

In thermal energy utilization scenarios, absorption systems have been widely and effectively utilized as heat exchange devices. However, existing thermal research methods on absorption systems for these scenarios have limitations. Therefore, the entransy parameter, which is applicable for analyzing the heat exchange process is chosen to study. The entransy balance relationship of the absorption system is theoretically analyzed, and the entransy analysis method is further perfected to break through the limitations. First, the entransy imbalance of the reversible absorption cycle is proved, and the reason for this imbalance is clarified that two heat-work conversion processes at different temperatures occur inside the cycle. Then, the working fluid's entransy change during the conversion process is theoretically derived and defined, and a new parameter: conversion entransy is defined based on it. Moreover, the comprehensive entransy balance equation and comprehensive entransy analysis method of absorption systems are further proposed. Finally, a specific case study is carried out, and this method is compared with the existing exergy analysis method and entransy analysis method without considering the conversion entransy respectively. By using this method, the optimal process form of the absorption heat exchanger can be directly obtained without numerical simulation calculations, demonstrating significant advantages.

A Novel Phase Change Absorbent for CO2 Capture with Low Viscosity and Effective Absorption–Desorption Properties

Excessive carbon dioxide (CO2) emissions can lead to environmental problems, and the use of phase change absorbents for CO2 capture has received much attention due to their excellent absorption and desorption properties. Herein, a novel liquid–liquid phase change absorbent consisting of N‐aminoethylpiperazine (AEP), diethylene glycol dimethyl ether (DEGDME), and H2O is utilized. Under the optimal absorption conditions, the absorption capacity is 1.23 mol CO2·mol−1 amine. The rich‐phase viscosity of the AEP/DEGDME/H2O solution is only 6.2 mPa s−1, and the rich phase‐to‐volume ratio is 52.7%, which is suitable for industrial applications. After five cycles of absorption–desorption experiments, the cyclic capacity reaches 0.62 mol CO2·mol−1 amine. However, it should be noted that this leads to an increase in the viscosity of the solution with time. The 13C Nuclear Magnetic Resonance characterization is used to analyze the material distribution and phase separation mechanism, and it is found that during the absorption process, the carbamate and carbonate products generated by the reaction of the amino group in the AEP with CO2 are mainly located in the rich phase, while the DEGDME and H2O mainly remain in the lean phase. In the desorption process, most of the absorbed products are decomposed, and the regeneration efficiency is 66.8%. Through the regeneration energy consumption experiment, when the regeneration efficiency is 56%–67%, the total regeneration energy consumption is 2.71–2.89 GJ t−1 CO2, which is 0.91–1.09 GJ t−1 CO2 lower than that of the regeneration efficiency of 30 wt% MEA solution at 63%, which indicates that this absorbent has certain energy‐saving advantages.

Water–Ionic Liquid Working Fluids in Absorption Cycles: Fluid Screening, Vapor–Liquid Equilibrium Measurements and Modeling, and Performance Evaluation

Water–Ionic Liquid Working Fluids in Absorption Cycles: Fluid Screening, Vapor–Liquid Equilibrium Measurements and Modeling, and Performance Evaluation

Experimental investigation of two-stage NH3–H2O resorption heat storage system with solution concentration difference

Widespread application of solar energy is severely restricted to its instability in time and space. Heat storage system is considered to be one of the most effective pathways to achieve long-term heat supply. Among all the heat storage technologies, solution concentration difference storage technologies stand out for low heat loss and high energy density. By substituting condenser and evaporator in conventional absorption cycle with a high-pressure absorber and low-pressure generator, a resorption cycle could be established. Compared with absorption heat storage cycle, working pressure of resorption heat cycle is lower, making it possible to utilize low-pressure heat source. Two-stage heat source cycle is further proposed to lower working pressure and upgrading supply water temperature. Resorption energy storage cycle with solution concentration difference is established and studied. A prototype based on two-stage ammonia-water resorption heat storage cycle was set up and tested. The result shows that the constraint relation between ambient temperature and heat source temperature of the proposed system. In single-stage mode, the lowest working ambient temperature is 5 °C when heat source temperature is 90 °C. The lowest working ambient temperature could be declined to 0 °C when heat source temperature rises to 120 °C. In two-stage mode, the lowest working ambient temperature is 0 °C when heat source temperature is only 110 °C, which proves the adaptability of two-stage cycle. The highest ESCOP appears in the 15 °C–120 °C single-stage mode, which is 0.742. The highest COP is 1.324 under the same condition. The highest energy density occurs in two-stage mode, which is 467.07 kJ/kg when ambient and heat source is set as 15 °C, 120 °C. The advantage that two-stage mode could enlarge solution concentration difference is verified.

In-situ synthesis of superhydrophobic PLA-UiO-66-NH2@MS melamine sponge composite for high efficiency oil/water separation

In recent years, oil and organic solvent pollution of water bodies have deteriorated water quality, harmed ecosystems, and presented serious concerns to human health and biodiversity. Traditional oil/water separation technologies are inefficient, consume a lot of energy, and are difficult to operate. As a result, finding efficient, environmentally beneficial, and long-term separation solutions to manage water pollution is challenging. This paper proposes UNP@MS, a MOF-based sponge material to achieve superhydrophobicity and super lipophilicity, the material is developed on a melamine sponge loaded with UiO-66-NH2 and grafted with a polylactic acid (PLA) component. It achieves a remarkable oil/water separation efficiency of 99% even under difficult conditions (such as acidic or alkaline solutions) and displays exceptional separation efficiency for various oils. Furthermore, the oil absorption capacity maintains at 85% after ten cycles of oil absorption, exhibiting outstanding stability.

Flash spinning polyethylene/Fe3O4 magnetic drive fibers for oil absorption underwater

Oil pollution in water has destructive effect on the ecological environment of water bodies. However, the treatments for oil pollution underwater in irregularly shaped and non-open environments face a challenge owing to the difficulty in driving oil absorption materials underwater. Herein, this work reports a facile strategy to prepare flash spinning magnetic polyethylene fibers (FSMPFs) for oil absorption application in irregularly shaped and non-open underwater environments. The as-prepared FSMPFs exhibit good oil absorption performance, of which the oil absorption in air and underwater is 76.70 g/g and 65.32 g/g, respectively, and the FSMPFs can maintain their oil absorption performance in environments with different salinities (1–5 %) and pH values (2–12). Also, the FSMPFs show good magnetic responsiveness and controllability when applied to oil–water separation underwater in irregularly shaped pipes, and the oil–water separation efficiency of FSMPFs for oil–water emulsion reaches 99.6 %. Besides, the FSMPFs have good mechanical properties and reusability, of which the tensile strength and elongation at break is 185.9 cN and 41.2 %, respectively, and oil absorption is 76.28 g/g (99.5 % of the initial value) after 10 cycles of absorption–desorption. The FSMPFs have great potential in practical applications for oil absorption under irregularly shaped and non-open environments.

Impact of Modifications from Potassium Hydroxide on Porous Semi-IPN Hydrogel Properties and Its Application in Cultivation.

This study synthesized and modified a semi-interpenetrating polymer network hydrogel from polyacrylamide, N,N'-dimethylacrylamide, and maleic acid in a potassium hydroxide solution. The chemical composition, interior morphology, thermal properties, mechanical characteristics, and swelling behaviors of the initial hydrogel (SH) and modified hydrogel (SB) in water, salt solutions, and buffer solutions were investigated. Hydrogels were used as phosphate fertilizer (PF) carriers and applied in farming techniques by evaluating their impact on soil properties and the growth of mustard greens. Fourier-transform infrared spectra confirmed the chemical composition of SH, SB, and PF-adsorbed hydrogels. Scanning electron microscopy images revealed that modification increased the largest pore size from 817 to 1513 µm for SH and SB hydrogels, respectively. After modification, the hydrogels had positive changes in the swelling ratio, swelling kinetics, thermal properties, mechanical and rheological properties, PF absorption, and PF release. The modification also increased the maximum amount of PF loaded into the hydrogel from 710.8 mg/g to 770.9 mg/g, while the maximum % release of PF slightly increased from 84.42% to 85.80%. In addition, to evaluate the PF release mechanism and the factors that influence this process, four kinetic models were applied to confirm the best-fit model, which included zero-order, first-order, Higuchi, and Korsmeyer-Peppas. In addition, after six cycles of absorption and release in the soil, the hydrogels retained their original shapes, causing no alkalinization or acidification. At the same time, the moisture content was higher as SB was used. Finally, modifying the hydrogel increased the mustard greens' lifespan from 20 to 32 days. These results showed the potential applications of modified semi-IPN hydrogel materials in cultivation.

SELECTION OF A SOLAR COOLING SYSTEM FOR STRAWBERRY STORAGE IN THE SOUTH OF BRAZIL

Solar energy is an alternative to reducing dependence on non-renewable energy sources in various productive sectors. The present work has its main objective to simulate, evaluate and select a solar cooling system using a double absorption cycle (H2O – LiBr). The heat source of the generator-absorber is the water heated through different technologies of solar thermal collectors: Evacuated Tube Collector (ETC) and Parabolic Trough Collector (PTC). Five different arrangement areas were tested for each collector type. The systems were simulated in the TRNSYS® software. A 334.4 m³ cold chamber must be maintained at a constant temperature of 0 ºC. The thermal and energy analysis results indicate that the ETC configuration has the best system efficiency and the highest solar fraction throughout the year. The best option evaluated is the ETC configuration with a collector area of 100 m². In addition to supplying the thermal demand, it presents the most significant collector efficiencies, a better solar ratio, the highest savings at the end of the analysis period, and the lowest required investment value, showing as a sustainable option.