Álvaro Augusto Soares Lima

Sugarcane‐derived ethanol is a key renewable fuel, contributing to energy security and climate change mitigation by replacing fossil‐based fuels in tropical regions. This article introduces an integrated exergy–economic–environmental–life cycle assessment (LCA) framework for a sugarcane cogeneration system, providing novel benchmarks and optimization insights for sustainable ethanol and bioelectricity production in Northeast Brazil. An LCA was developed to provide environmental data for the exergoenvironmental analysis. The system has a processing capacity of 200 t/h of sugarcane and produces 33 MW of electricity using two steam turbines, with 22 MW of electricity being exported and 480 m ³ of hydrated ethanol produced daily. The furnace presents the highest exergy destruction rate (32.53%). The global exergy efficiency is 29.95%. The specific costs of ethanol and electricity are 0.3882 US$/L and 0.05929 US$/kWh (59.29 US$/MWh). The cost of sugarcane is primarily due to diesel consumption in the agricultural stage and transportation to the site. The specific environmental impacts of ethanol and electricity are 829 mPt/L and 112.1 mPt/kWh. The combustion and bioelectricity phase, as well as the juice concentration phase, should have their efficiencies improved, with financial investments to reduce the cost rate of exergy destruction and increase exergoeconomic performance. The combustion and bioelectricity phase presents the highest environmental impact due to furnace emissions, while efficiency improvements in juice concentration and distillation can reduce exergy destruction and related environmental impacts.

This study aimed to evaluate the effect of whole-body vibrations (WBV) on ergonomics related to static posture during the operation of container handling machines (Portainer). A 3D numerical model of a seated man was developed using modal and harmonic analysis based on the finite element method (FEM), and implemented on the ANSYS platform to achieve this. Quantitative analyses of whole-body vibrations were carried out in actual workplaces at a port terminal in northeastern Brazil, considering the interaction between the human and the machine. A comparison was made between the real data collected at the operating sites and the values obtained from the developed model. Concerning vibration exposure, the results revealed a critical situation: in 86.2% of cases, the Acceleration of Resulting Normalized Exposure—A(8)—exceeded the alert level, and in 96.6% of cases, the Resulting Vibration Dose Value (VDV) also surpassed this threshold. Similarly, an alert level was exceeded in 97.0% of cases. According to the maximum limits established by Brazilian legislation, the acceleration from normalized exposure did not exceed the limit, while the resulting vibration dose value was surpassed in 20% of cases. The modal analysis results helped identify the critical directions of vibration response, thus supporting the assessment of human exposure effects and the structural performance of the system analyzed. The harmonic analysis showed good agreement between the model and the real acceleration data in the frequency range of 3 to 4 Hz.

This paper, as Part 2 of an educational project, details the construction and operational procedures of a didactic refrigeration system for an artificial ice rink. Building on Part 1, the work defines the configuration of a vapor compression cycle with direct expansion, using a ¼ HP condensing unit with R22 and accessory components for expansion, control, and safety. Construction aspects include mechanical arrangements, thermal insulation, and integration of a copper coil evaporator into a concrete block. Operational protocols are proposed for start-up, commissioning, and adjustment, focusing on superheating, subcooling, and pressure regulation. Leak detection, dehydration, and charging procedures are also included to ensure reliability. The system delivers a cooling capacity of 430 kcal/h, achieving –6 °C at the rink surface, with a coefficient of performance of about 3.16. Beyond its practical function, the system serves as a didactic platform for experimental validation and training. The project continues with Parts 3 and 4, under development with shell-and-tube and plate heat exchangers.

Among the most widely covered refrigeration cycles in academic literature and studied in Thermal Systems-related disciplines in mechanical engineering are simple vapor compression refrigeration cycles. In most Brazilian academic institutions, there are no didactic systems that enable an engineering-oriented approach to practical activities that consolidate knowledge and skills related to the operation of such systems in specific applications. These systems have numerous applications in residential, commercial, and industrial settings. Beyond the most common applications, their use in ice rinks draws attention due to the diverse possibilities for knowledge application and the implementation of techniques related to cooling production. Ice rinks are primarily designed for sports activities such as figure skating, hockey, speed skating, and other indoor activities, including recreational skating. This study is divided into two parts: the first aims to develop heat exchanger sizing calculations -the system’s evaporator- for the construction of a reduced-scale ice rink for didactic purposes in the field of mechanical engineering at UFRN. It presents brief fundamental concepts related to each system component. The starting point is the simple vapor compression refrigeration cycle with direct expansion and its controls, whose initial capacity was defined based on the commercially available ¼ HP condensing unit in the laboratory. As a final result, this study presents the definition of the constructive parameters for the heat exchanger -the ice rink's generating coil. In the second part, the selected component models for the complete system will be defined, concluding with all the basic design parameters required for equipment construction.

This study seeks to investigate the heat dissipation process in a minichannel heat exchanger, commonly employed for cooling electronic components. The analysis centers on two key factors: global thermal resistance (G_TR) and the heat transfer coefficient. The innovation of this study resides in the development and analysis of a mini heat exchanger optimized using chemometric methods to achieve efficient thermal dissipation. Various conditions, including the power source, volumetric flow rate, and ambient temperature, were varied at both low and high levels to assess their impact on these variables and establish the optimal conditions for heat dissipation. The cooling of electronic components, such as processors, remains a topic of ongoing research, as the miniaturization of components through nanotechnology requires enhanced heat dissipation within increasingly smaller spaces. This experimental study identifies the optimal conditions for both G_TR and the heat transfer coefficient within the examined parameters. G_TR is minimized with a power of 30 W, an ambient temperature of 29 °C, and a flow rate of 2.50 L·min⁻¹. The results indicate that electrical power was the most significant variable affecting G_TR, while ambient temperature also played a determining role in the heat transfer coefficient.

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.

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.

This paper presents a thermodynamic model developed for a prototype absorption chiller using NH₃/LiNO₃ with 10 kW of nominal capacity. The study was undertaken using thermodynamic modeling based on the mass and energy balance, takes the overall heat transfer coefficients into consideration and uses the characteristic equation method. First, the results obtained from the thermodynamic modeling developed were compared with those obtained from the characteristic equations of thermal power activation and the cooling capacity. These showed good agreement with the experimental data, there being maximum relative errors of around 5% for most of the operational conditions of the system. Secondly, a parametric analysis was made by altering the variables, such as temperature, mass flow rate, and configuring the heat dissipation that influences the overall performance of the prototype chiller.