The interest in employing absorption refrigeration systems is usually related to electricity’s precariousness since these systems generally use thermal rejects for their activation. The application of these systems is closely linked to the concept of energy polygeneration, in which the energy demand to operate them is reduced, which represents their main advantage over the conventional vapor compression system. Currently, the solution pairs used in commercial absorption chillers are lithium bromide/water and ammonia/water. The latter pair has been used in air conditioning and industrial processes due to the ammonia operation’s low temperature. Few review papers on absorption chillers have been published, discussing the use of solar energy as the input source of the systems, the evolution of the absorption refrigeration cycles over the last decades, and promising alternatives to increase the performance of absorption refrigeration systems. There is a lack of consistent studies about designing requirements for absorption chillers, so an updated review covering recent advances and suggested solutions to improve the use and operation of those absorption refrigeration systems using different working fluids is relevant. Hence, this presents a review of the state-of-the-art of ammonia/absorbent based absorption refrigeration systems, considering the most relevant studies, describing the development of this equipment over the years. The most relevant studies in the open literature were collected to describe this equipment’s development over the years, including thermodynamic properties, commercial manufacturers, experimental and numerical studies, and the prototypes designed and tested in this area. The manuscript focuses on reviewing studies in absorption refrigeration systems that use ammonia and absorbents, such as water, lithium nitrate, and lithium nitrate plus water. As a horizon to the future, the uses of absorption systems should be rising due to the increasing values of the electricity, and the environmental impact of the synthetic refrigerant fluids used in mechanical refrigeration equipment. In this context, the idea for a new configuration absorption chiller is to be more efficient, pollutant free to the environment, activated by a heat substantiable source, such as solar, with low cost and compactness structure to attend the thermal needs (comfort thermal) for residences, private and public buildings, and even the industrial and health building sector (thermal processes). To conclude, future recommendations are presented to deal with the improvement of the refrigeration absorption chiller by using solar energy, alternative fluids, multiple-effects, and advanced and hybrid configurations to reach the best absorption chiller to attend to the thermal needs of the residential and industrial sector around the world.

The prognosis of wind turbine failures in real operating conditions is a significant gap in the academic literature and is essential for achieving viable performance parameters for the operation and maintenance of these machines, especially those located offshore. This paper presents a framework for estimating the remaining useful life (RUL) of the main bearing using regression models fed operational data (temperature, wind speed, and the active power of the network) collected by a supervisory control and data acquisition (SCADA) system. The framework begins with a careful data filtering process, followed by creating a degradation profile based on identifying the behavior of temperature time series. It also uses a cross-validation strategy to mitigate data scarcity and increase model robustness by combining subsets of data from different available turbines. Support vector, gradient boosting, random forest, and extra trees models were created, which, in the tests, showed an average of 20 days in estimating the remaining useful life and presented mean absolute error (MAE) values of 0.047 and mean squared errors (MSE) of 0.012. As its main contributions, this work proposes (i) a robust and effective regression modeling method for estimating RUL based on temperature and (ii) an approach for dealing with a lack of data, a common problem in wind turbine operation. The results demonstrate the potential of using these forecasts to support the decision making of the teams responsible for operating and maintaining wind farms.

This study investigates and compares the experimental heat transfer performance and simulation via computational fluid dynamics (CFD) of graphene nanoplatelets (GNP) and water nanofluids GNP/water in the double-tube-type heat exchanger (DTHE). Tests were conducted with water/water and GNP/water fluids, with the nanofluid for the hot-fluid circuit and water for the cold-fluid circuit, with counterflow direction, varying the nanofluid concentrations by weight (wt%) at 0.0125%, 0.025%, and 0.050%, the operating temperature at 50 and 60 °C, and Reynolds numbers between 2000–6000. The results showed that 0.025 wt% GNP presented better thermal performance, with a 28% increase in the temperature gain. The 0.025 wt% GNP had slightly better performance for the Nusselt number (Nu), and the 0.05 wt% GNP had a slightly better thermal effectiveness. The comparison between the experimental values showed good agreement with those calculated by empirical correlations and the CFD model, with maximum and minimum relative error values of 9% and 1%, respectively, when the Petukhov equation was used.

This study aimed to analyze and optimize the thermal induction hardening process applied to toothed transmission gears, focusing on thermal aspects, structural deformation, and topology optimization, while exploring the feasibility of various materials and operating conditions. The research simulated thermal and deformation behavior using a computer model, comparing results with experimental data through the Ansys^® platform 2022 R1. The methodology encompassed thermal and deformation analyses, topology optimization to identify removable regions without compromising part integrity, and a sensitivity study to evaluate the different materials and operating conditions. This study validates the precision of computational models in predicting thermal and deformation behavior in toothed gears under thermal induction hardening, introducing topology optimizations and alternative materials, and providing novel perspectives for the more efficient and cost-effective manufacturing of these components. Comparative thermal analysis revealed a maximum relative error of less than 6% between temperatures from the computer model and experimental results, while deformation comparisons exhibited a maximum relative error of less than 7%, affirming the simulation model’s accuracy in predicting and managing deformations within acceptable thresholds. Topology optimization successfully pinpointed removable regions without compromising structural integrity, enabling the production of lighter and more economical devices. Future endeavors should concentrate on additional tests to verify the feasibility of reducing power and cooling temperature without compromising product specifications. Furthermore, it is advisable to explore alternative materials and apply the developed methodology in diverse industrial settings to generalize the findings and amplify the impact of the proposed optimizations.

This article critically reviews advances and numerical modeling in absorbers and desorbers used in absorption refrigeration systems, emphasizing the applications, limitations, and future perspectives of computational fluid dynamics (CFD). This study’s main contribution lies in the detailed and critical analysis of the use of CFD in physical models of absorbers and generators of absorption chillers. In addition, several heat exchanger technologies, such as falling film, membranes, and bubbling, are addressed, highlighting CFD-based studies’ main findings and challenges. The article also explores the integration of artificial intelligence (AI) in CFD analyses, aiming to optimize modeling and system performance. It was found that the application of CFD analyses in absorbers and desorbers of absorption systems has proven to be an essential tool for developing and optimizing these systems. Finally, research gaps were identified, especially regarding the miniaturization and optimization of these exchangers, and directions for future studies are proposed.