Search

With the development of the electronic packaging industry, there is an increased demand for enhanced strength in DBA substrates. Ultrasonic soldering technology allows low-temperature joining of ceramic-metal materials under ambient air conditions. In this paper, we successfully achieved the joining between AlN ceramics and 2024Al using Sn9Zn solder and ultrasonic soldering technique, while also analyzing the joining mechanism through Comsol software simulations. It was observed that under the appropriate ultrasonic amplitude and frequency, the Sn9Zn solder exhibited complete wetting with both base materials, resulting in reliable joints. Building upon this finding, the conventional Sn9Zn solder was further optimized by adding Sb element. The addition of Sb element led to the formation of Zn 4 Sb 3 phase and β-Sn(Sb) phase with Sb acting as solute. Among them, the generation of β-Sn(Sb) solid solution phase effectively improved the joint strength. The maximum joint strength was achieved at an average value of 75.066 MPa when the Sb content reached 1 wt. %. At this point, the failure occurred within the AlN ceramic base material. [ABSTRACT FROM AUTHOR]

• Three parallel compressors more efficient than two variable speed compressors. • R452B versus R410A led to better efficiencies and compatibility at high ambient. • Reliable oil return of three parallel compressors having multiple capacity levels. • Three parallel centrifugal blowers led to improved air flow distribution. This study delineates a meticulous exploration of technologies to enhance the energy efficiency of rooftop air conditioning units, employing the DOE/ORNL heat pump design model for comprehensive engineering design and optimization. A baseline rooftop air conditioning unit, featuring a 13 ton (45.7 kW) cooling capacity and a 17.9 integrated energy efficiency ratio, served as the point of departure for substantive efficiency enhancements. Key modifications included the consolidation of two refrigerant circuits into one, integrating three parallel 2-stage (dual-speed) compressors, fan replacements with high-efficiency substitutes. Notably, a lower global warming potential refrigerant, R452B, was evaluated as a substitute for R-410A, demonstrating better performance in the lab prototype. The achieved measured integrated energy efficiency ratio of 21.4 in the lab prototype surpassed the baseline integrated energy efficiency ratio. Comparative evaluations between R410A and R452B indicated heightened efficiency with the latter, showcasing a lab-demonstrated integrated energy efficiency ratio of 22.4 at the rated capacity of 13.8 ton (48.5 kW) and 23.9 integrated energy efficiency ratio at the rated capacity of 10 ton (35.2 kW). This research underscores the successful development of a rigorous, energy efficient rooftop air conditioning unit prototype with noteworthy environmental and economic implications. [ABSTRACT FROM AUTHOR]

Defining the required trackability level of the target condition for the testing facility reconditioning unit represents an unresolved challenge in improving the reproducibility of load-based tests and corresponding performance rating standards development. To enhance the reproducibility of such testing methodology, this paper presents and discusses a new feed-forward compensation technique based on the development of a transfer function model for the delay and offset characteristics of the psychrometric room's air temperature and humidity modulations with reference to the target signal from the room emulator. It is demonstrated that the proposed methodology enables offset and delay reduction in the trackability of the return air condition within 60 s at different testing conditions, enhances the reproducibility of the test results to limit performance deviations to within 2 %, and achieves closely matched controlled parameter modulations during load-based tests. [ABSTRACT FROM AUTHOR]

• The evaluation of refrigeration systems due to the presence of malfunctions in their components was conducted through thermoeconomic methodology. • This methodology used splits physical exergy into its thermal and mechanical terms, in addition to using the fictitious term of negentropy. • A prognosis of system behaviour was derived, enabling utilization in maintenance scheduling and facilitating comprehensive energetic and exergetic analyses of both the refrigeration system and its individual components. In recent years, it has been possible to observe a significant expansion of the refrigeration and air conditioning industry. Considering that food refrigeration systems (blast chilling or freezing, cold storage, retail display, etc.) and air conditioners are large energy consumers, this work presents a methodology for evaluating the performance and behaviour of these systems using the thermoeconomic diagnosis concept. The thermoeconomic model used allowed the definition of the condenser and expansion device products, which is not trivial for these components. With that, the thermoeconomic diagnosis was used to evaluate the degradation of refrigeration system components, together with the influence of individual component degradations on efficiency, cooling capacity, operating parameters, and power consumption of the whole system. Through this analysis, a prognosis of system behaviour was obtained, which can be used for maintenance scheduling, as well as for the comprehensive energetic and exergetic analysis of a refrigeration system and each of its components. [ABSTRACT FROM AUTHOR]

The exhaust gas burner, a critical component of a solid oxide fuel cell (SOFC) thermal management system, is essential for the stable and reliable operation of the entire system. This study establishes a test bench that simulates the gas composition and temperature of the fuel cell stack anode and cathode gases and conducts comprehensive experimental research on an exhaust gas burner used in a 15-kW SOFC power generation system. The experimental results show that the burner has the operational characteristic of reliable combustion over a wide range of excess air ratios. The burner can achieve stable and reliable combustion under low-flow ignition, steam injection, reforming, and power-generation conditions with excess air ratios of 29–45, 21–28, 23–37, and 11–27, respectively. Rapid changes in the excess air ratio did not lead to combustion instability; for example, during power generation, an increase of 47.6% in the excess air ratio resulted in a 3.5% decrease in the burner outlet temperature. However, under the steam injection condition, with an excess air ratio of 28 and a steam-to-carbon ratio of 3, the temperature decreased significantly. The burner also exhibited low-pressure loss, with a maximum anode exhaust pressure drop of only 233 Pa. Furthermore, the burner exhibited excellent performance during condition transitions, although a certain time delay occurred in the temperature response to the flow rate changes. • Established a test platform to explore burner characteristics comprehensively. • Proven reliable combustion across various conditions. • Maintained stable combustion despite rapid air ratio changes. • Significant temperature drop during steam injection. • Low pressure loss and excellent performance in condition transitions. [ABSTRACT FROM AUTHOR]

• Visualization experiment using a high-speed camera of a vertical sliding vane rotary engine. • Investigate the effect of compressor rotational speed on vane contact. • Effect of oil supply amount and temperature on vane chattering. • Influences of ratio of compressor discharge pressure and supply pressure on vane and cylinder contact. In this study, the impacts of various factors on the chattering phenomenon in sliding vane compressors, which is a crucial aspect that influences their performance and efficiency were explored. The analysis focused on the compressor rotational speed, pressure ratio, and operating temperature, considering both ambient and heated conditions. The aim was to provide a comprehensive understanding of the relationship between these factors and the occurrence of chattering at different operational intervals, as well as the vane sealing performance and adherence to the chamber wall. The methodology involved examining vane behavior and the chattering occurrence across three intervals under various conditions, specifically looking at oil films formation and sealing performance degradation. The experimental results provided notable insights into the chattering phenomenon. It was shown that as the pressure ratio increased and the compressor rotational speed decreased, the sealing performance deteriorated. Moreover, when operating under heated conditions, a decrease in oil viscosity leads to reduced friction between the vane and bearing, improving vane adherence compared to ambient conditions. The methodology and findings of this study provide insights into the chattering phenomenon in vane compressors by considering the interplay between various factors. The results emphasize the importance of optimizing the compressor oil refueling flow, rotational speed, pressure ratio, and operating temperature, to ensure proper lubrication and efficient interaction between the vanes and compression chamber walls for improved compressor performance and reduced operational challenges. [ABSTRACT FROM AUTHOR]

An energy and exergy analysis of an experimental air-conditioning absorption system operating with the ammonia-lithium nitrate mixture has been performed. The system was operated under controlled and steady-state conditions. The main operating parameters, such as flow ratio, coefficient of performance, exergy coefficient of performance, and exergy destruction in each one of the main components, were determined at different heat sources and condensing temperatures. The coefficients of performance varied between 0.5 and 0.65, while the exergy coefficients of performance varied between 0.1 and 0.2. Clear trends were found for the coefficient of performance and flow ratio as a function of the generator and condenser temperatures; however, no trends were found in the exergy coefficients of performance due to the high variability of the ambient temperature. The highest values of the exergy destruction occurred in the generator, followed by the condenser and the evaporator, while the lowest values were obtained in the absorber and the economizer. [ABSTRACT FROM AUTHOR]

In this study, the replacement of hydrogen with ammonia in a laboratory Moderate or Intense Low-Oxygen Dilution (MILD) burner is being investigated by incorporating air swirling to study NO x formation in the flow field. A CH 4 /H 2 /NH 3 fuel jet is modeled using the RANS (Reynolds-Averaged Navier-Stokes equations) approach for various fuel mixtures with ammonia content ranging from 0% to 18%, while maintaining a constant methane concentration. The study is conducted under two conditions: axial coflow with hot diluted air and swirled with the swirl numbers of 0.6–1.0. The hot oxidizer consists of 9% O 2 and 6% O 2 at 1300 K. The combustion model is based on the eddy dissipation concept, and a detailed chemical mechanism is used to represent the chemical reactions. Numerical simulations suggest that swirl enhances the reactivity of nitrogen-containing reactions, with the sensitivity to swirl varying based on the inlet ammonia content. The addition of ammonia and air swirling improve the MILD index but reduce the MILD area. Swirling increases the temperature of the reacting field, while ammonia suppresses it. The results indicate the potential of swilr concept for enhanced dilution, improved flexibility in controlling NO x formation, and overcomed the ammonia reativity drwabacks. • Swirl enhances the combustion characteristics of ammonia fuel. • Hydrogen replacing with ammonia has suppressed the MILD combustion region. • The addition of ammonia and air swirling improves the MILD combustion index. • The swirl concept shows potential for controlling ammonia flame NOx formation. [ABSTRACT FROM AUTHOR]

Automotive air conditioning (ACC) system designers faced unique challenges in satisfying customer demands for efficient and comfortable operation across a broad temperature range. The AAC system's effective or fixed temperature setting makes this possible. Many climate control models, like the state flow switching controller in MATLAB control, must handle heating and cooling due to a single Simulink/environment software and frequently contain steady-state error (SSE). The present research proposes to design an automatic temperature control scheme and fuzzy logic control (FLC) for an automotive air-conditioned (AAC) system. In addition, it employs MATLAB Simulink/environment software to model the fuzzy control technique to analyze the AAC system's response. A simulation has been set up to evaluate the suggested system performance to match a selection of user-specified reference temperatures and compressor speeds. Compared with a PID-controlled AAC system, the proposed FLC-based system reduced the undershoot to only 2.30% from 33.30% respectively, and was robust, quicker, and better at controlling temperature. • Challenges in automotive air conditioning systems for designers were addressed. • An automatic temperature control scheme was proposed via fuzzy logic control. • Improved efficiency and comfort in the AAC system was achieved. • The proposed FLC-based system reduced the undershoot to 2.30% from 33.30%. • The FLC-based was more robust, quicker, and better at controlling temperature. [ABSTRACT FROM AUTHOR]

This article conducts a 20-year review of studies investigating the utilization of artificial intelligence in HVAC (Heating, Ventilation, and Air Conditioning) system control, with a particular focus on automotive HVAC systems, renowned for their unique challenges due to the highly dynamic nature of automotive cabins. Artificial neural networks (ANNs) provide adaptive modeling and control capabilities to enhance energy efficiency, thermal comfort, and air quality in HVAC systems. Nevertheless, ANNs exhibit limitations, primarily their performance being constrained by training data, impeding adaptability to unforeseen scenarios. To overcome these constraints, researchers have explored hybrid approaches that integrate ANNs with PID (Proportional, Integral, and Derivative) or PI (Proportional and Integral) algorithms, resulting in systems referred to as Neuro-PID or Neuro-PI. These systems can effectively handle unanticipated situations by absorbing errors introduced by ANNs. Nonetheless, the applicability of Neuro-PID varies depending on the specific system. It becomes infeasible in scenarios with substantial delays, prompting the choice of the appropriate approach based on the controllability factor, a ratio between system delay and time constant. A controllability factor less than 2 indicates the suitability of employing ANNs for PID controller tuning. Furthermore, the intricate interaction between temperature and humidity in HVAC control systems diminishes the effectiveness of traditional PID. To proficiently regulate both variables, a viable alternative is the amalgamation of ANNs with specific control logic or the deployment of distinct ANN algorithms for varying scenarios. The heightened variability and unpredictability within automotive HVAC systems, driven by continuous vehicle movement and door/window operations, present additional challenges. In such contexts, reinforcement learning techniques have found application, allowing systems to dynamically adapt to unforeseen events. In summary, the choice of HVAC control approach hinges on the primary goal—thermal comfort or specific variable control—as well as the system's noise level, controllability factor, and system nature. While ANNs hold significant potential, combining them with other techniques, such as PID, reinforcement learning, or specific control logic, may prove essential in addressing the intricacies of HVAC systems [ABSTRACT FROM AUTHOR]

• A CO 2 ejector-expansion system for electric vehicles is experimentally tested. • System and ejector characteristics are investigated at 45 °C ambient temperature. • Performance improvement is evaluated compared to corresponding basic system. • Effects of EXV's opening, compressor speed, and fresh air ratio are analyzed. The ejector-expansion system design is an effective approach to improve the cooling performance of transcritical CO 2 systems. In this study, a transcritical CO 2 air-conditioning system with an ejector for electric vehicles is built up to experimentally investigate the cooling performance at an extreme temperature of 45 °C. The performance improvement is evaluated compared to the corresponding basic system. The effects of electronic expansion valve's (EXV) opening, compressor speed, and fresh air ratio are analyzed. The results show that the ejector can effectively improve system COP by 4.61–16.52 % under test conditions. At 45 °C/27 °C (out-cabin/in-cabin) condition, the optimal COP of 1.52 can be obtained at EXV's opening of 65 %. The entrainment ratio significantly goes up from 0.22 to 0.60 as EXV's opening increases. [ABSTRACT FROM AUTHOR]

• Oil retention models in various types of pipelines are established. • Hierarchical iterative algorithm based on graph theory is developed. • Oil retention in various pipelines is measured for model validation. • Mass flow rate or evaporation temperature increase may reduce oil retention. A multi-split air conditioning system may suffer damage caused by oil starvation in its compressor when the lubricating oil largely retains in long pipelines, and thus a reasonable oil charge based on accurate prediction of the oil retention in pipelines is important. The purpose of this study is to present an oil retention model for pipelines and to experimentally validate this model. The structure of pipelines connecting the outdoor unit and the indoor units with arbitrary numbers installed on separated floors is described as a combination of straight pipe types, joint types, and bend types. In modeling the oil retention, all the components of straight pipes, joints, and bends are numbered to conveniently distinguish each component which is further divided into several control volumes with equal lengths along the flow direction, and the equations of oil retention, pressure drop and enthalpy difference for the control volumes are established to describe the refrigerant-oil flow behavior. A hierarchical iterative algorithm based on the graph theory is developed in order to solve the models quickly. An experimental rig is built to measure the oil retention in four types of straight pipes, and the validation results show that the predicted oil retention in straight pipes agrees with at least 74.0 % of the experimental data within a deviation of ±20 %, and the mean deviation is lower than 15.4 %. Based on the model, the effects of oil retention reduction by increasing the total mass flow rate or the evaporation temperature of refrigerant are quantitatively analyzed. [ABSTRACT FROM AUTHOR]

This paper is aimed at clear ice making. To this end, a purpose-built apparatus that controls the solidification rate was specially designed and constructed to assess the trade-offs between ice clearness (quality) and production rate (quantity). An image-based ice clearness evaluation technique was devised and adopted to compute a figure-of-merit for the ice quality. 30 ml ice cube samples were produced in a closed ice tray for either prescribed heat flux (650, 1300 and 1700 W m−2) or surface temperature (−4, −8 and −12 °C) at the bottom wall, while a 25 mm EPS insulation was adopted for top and lateral walls. The experiments were carried out using both tap and boiled water, whose initial amount of dissolved gas was monitored. The results pointed out the heat transfer and initial air concentration conditions that rule the quality and quantity trade-offs in clear ice making. [ABSTRACT FROM AUTHOR]

• risk analysis of climate-induced fatigue on wooden surfaces inside six rural Swedish churches. • Past monitoring campaigns used for gathering info about number/entity of thermal fluctuations. • Investigated constant- and variable-amplitude climate-induced fatigue behaviors. ○ Assessed possible damage accumulation caused by repeated thermal fluctuations over time. ○ Compared results with surface decay level from in-situ conservation surveys. Environmental variations of Temperature (T) and Relative Humidity (RH) in air cause a superficial and/or sub-surface deformation (shrinkage/swelling) of organic hygroscopic objects, as for example wood. These environmental variations may be due to the natural variability of climate, to the use of Heating, Ventilation and Air Conditioning (HVAC) systems and to the presence of people. This contribution focuses on a group of wooden rural churches located in harsh climates in Sweden. The churches, which are still in use for the local communities, are heated during wintertime to reach acceptable indoor comfort levels causing potentially risky T and RH fluctuations for hygroscopic objects. In this framework, the main goal is assessing the risk of fracture on wooden structural elements caused by hygrothermal fluctuations. The method is based on a preliminary approach for reconstructing the climate history experienced by a typical wooden structural element of these churches and that, over time, results in a cyclic fatigue loading, naturally induced by the outdoor climate. Then, the effect of the artificial heating on the indoor microclimate and, therefore, on the reconstructed fatigue curve is assessed. Main outcomes were obtained by using a methodology that is preliminary based on simplifying assumptions, due to a severe lack of knowledge, in literature, about the fatigue behavior of wood. Finally, main considerations on the fatigue behavior of exposed wooden elements are drawn up, namely the estimation of their residual life (or "life-to-damage"), which may support conservators or church managers in better managing the microclimate to reduce the risk of fracture on valuable objects. [ABSTRACT FROM AUTHOR]

The LNG cold energy utilization system primarily integrates additional power cycles during the gasification process to harness the cold energy released in this process efficiently. This study introduces a combined cooling and power (CCP) system, which comprises a cascade organic Rankine cycle (ORC), an air conditioning refrigeration (ACR), and a direct expansion cycle (DEC). Furthermore, the thermodynamic and economic analyses of the CCP system were evaluated, and the optimization of each influence parameters was performed by the genetic algorithms, such as the composition of the quaternary mixed working fluid (Methane: Ethane: Propane: i-Butane), condensation pressure, evaporation pressure, and the first-stage expansion pressure within the system. According to the simulation results, the suggested overall exergy destruction of the CCP system proposed by this work is reduced by 13.18% under optimized conditions, with a maximum net power generation of 230.38 kW and an exergy efficiency of 45.58%. Economic analysis reveals that the system's investment cost, annual economic benefits, and levelized energy cost are 2.02 × 106 $, 2.75 × 105 $, and 0.10 $/kWh, respectively. With the system's official operation, the investment cost will be recovered within 8.61 years. • A novel process for power generation combined with refrigeration has been proposed. • Optimized the composition of the quaternary mixed working fluid and key operation parameters. • The net out power and exergy efficiency are enhanced up to 13.40% and 7.21%, respectively. • The payback period of the system is as low as 8.61 years. [ABSTRACT FROM AUTHOR]

International regulations, such as the European Regulation EU No 517/2014, are pushing the refrigeration, heat pumps and air conditioning sectors to find suitable low-GWP working fluids as alternatives to the currently widespread high-GWP refrigerants, such as R134a and R410A. Halogenated olefins (HFOs and HCFOs) have been considered promising and, among these, trans-1,3,3,3-tetrafluoropropene (R1234ze(E)) has been identified as a potential alternative to R134a in medium temperature applications, including air-cooled and water-cooled chillers, heat pumps, refrigerators and combined with CO 2 in cascade systems. The thermodynamic properties of R1234ze(E) have been widely studied in the last decade. Instead, a comprehensive experimental knowledge on the transport properties of R1234ze(E) is still missing. In order to increase the available experimental transport property data, the present study reports thermal conductivity measurements carried out with a new transient hot-wire (THW) apparatus on R1234ze(E) in the liquid phase at temperatures from 243 K to 343 K and pressure up to 8 MPa. The reported uncertainty is estimated to be lower than 2% and the measurements resulted in agreement with the available literature data. [ABSTRACT FROM AUTHOR]

The condenser's rejected heat in a vapour compression refrigeration system when thrown into the surrounding air results in its thermal pollution and gets wasted, while it has the potential to be recovered. Another major targeted concern is freshwater scarcity which is faced by the population in many areas. Addressing these difficulties, a double-stage integrated humidification-dehumidification and air conditioning system that recovers the condenser's waste heat and is assembled in a novel duct architecture is proposed. The obtained results of the developed model are established using the experimental data. The analysis explores the outcomes of the integrated system and investigates the influences of saline water temperature, humidifier efficiency, ambient temperature, and relative humidity on the output and performance metrics. The system provides air conditioning of 31.410 kJ and desalination of 65.020 mL from a unit volume of air using 0.661 kW of power and mitigates the environmental impact of existing technology. The coefficient of energy performance, cooling performance, gained output ratio, and exergy efficiency at the specified working situations are 0.958, 1.320, 6.809, and 2.701 %, respectively. A litre of freshwater costs $ 0.0068486. [ABSTRACT FROM AUTHOR]

• To improve data center performance, it must be efficiently cooled. • This paper undertakes a detailed examination of the most recent cooling optimization techniques. • Several methods are discussed like regular air conditioning, free cooling, and liquid cooling. • An assessment of overhead and underfloor air delivery technologies is presented. • The effects of baffles, variable airflow control, and server placement are investigated. In order to increase data centers' efficiency and performance, a proper cooling system should be applied. This article provides a comprehensive assessment which explores current cooling optimization technologies for data centers. Standard traditional technologies like air conditioning, free cooling, and liquid cooling are investigated. Their limitations as well as proposed improvements are thoroughly discussed. The article also delves into underfloor and overhead air supply technologies, presenting their advantages and drawbacks. The review introduces novel approaches at the rack level cooling, including baffles, variable airflow management, and optimal server placement. Key findings stress the efficacy of optimized airflow systems and innovative rack-level cooling, underlining their role in reducing energy consumption and enhancing overall performance. Notably, potential energy savings of up to 67.2 % compared to traditional methods are demonstrated. The adoption of advanced cooling technologies, such as direct and indirect natural cooling, liquid-cooling cold plates, submersion, heat pipe, and thermosiphon-based cooling, exhibits promising energy efficiency gains and reduced Power Usage Effectiveness (PUE) values. Research into content-specific efficiency enhancements, adaptable energy-saving tactics, and all-encompassing server power consumption models is necessary. To work toward future sustainable, energy-efficient data centers, researchers should investigate how CRACs and server fans interact, find ways to integrate thermal and power management, and how artificial intelligence can be used to cool servers in an eco-friendly way. [ABSTRACT FROM AUTHOR]

This study presents an experimental analysis of the thermodynamic performance of a large-scale magnetic air-conditioning system prototype that uses a combination of La(Fe,Mn,Si) 13 H z and Gd in a sixteen-bed active magnetic regenerator (AMR) assembly. The performance of the system is compared with a previous version which operated in part load with eight regenerator beds and lower flow rates. The experiments were carried out in a relevant environment, characterizing a Technology Readiness Level (TRL) of 6, emulated by a calibrated calorimeter focusing on key performance metrics such as cooling capacity, coefficient of performance, and second-law efficiency. The experimental results demonstrate a maximum cooling capacity of 680 W, along with a temperature span of 8.7 K. Particularly noteworthy is the significant enhancement observed in the performance of the system when accounting for previously disregarded irreversibilities external to the active magnetic regenerators. From an AMR standpoint, the maximum values of the coefficient of performance and second law efficiency are 4.2 and 10.8%, respectively, but from the system perspective, these values are reduced to 0.41 and 0.84%, respectively. [ABSTRACT FROM AUTHOR]

• A MISSA algorithm is proposed to solve the central air conditioning energy-saving problem. • Cooling load prediction provides a foundation for energy-saving optimization. • The three improved strategies are introduced to obtain better operating results. • The experimental results indicate that the MISSA can find a better optimal solution. Aiming at the problem of high energy consumption caused by the nonlinear, strong coupling, and large hysteresis characteristics of central air conditioning (CAC) system, an energy-saving optimization method based on WTD–CNN–LSTM and multi-strategy improved sparrow search algorithm (MISSA) is proposed, which works to minimize the total energy consumption during the operation of the CAC system. Firstly, minimize the sum of energy consumption of chillers, freezing pumps, cooling pumps, and cooling towers as the objective function, and use the range of operating parameters of each equipment as the basic constraint conditions to establish an energy-saving optimization model for the CAC system. Then, WTD–CNN–-LSTM is used to predict the future cooling load, and the predicted results are used as key constraint condition to achieve on-demand cooling. Finally, MISSA is proposed to improve the initialization, update and convergence stages of the CAC system operation parameter optimization process, accurately obtaining the optimal operating parameters. Compared with manual experience, MISSA reduces energy consumption by 15.32 % and improves energy efficiency ratio by 20.76 %. Meanwhile, compared with other optimization algorithms, MISSA reduces energy consumption by 4.85–13.26 % and improves energy efficiency ratio by 6.53–16.33 % after optimizing the CAC system. The experiment verifies that MISSA is more energy efficient when applied to the CAC system and has the advantages of accuracy, fast convergence, strong global search capability, and the ability to jump out of local optimization. [ABSTRACT FROM AUTHOR]

Research efforts focused on Smart Building (SB) development have concentrated on the automation of resources within intelligent environments towards an enhanced experience for occupants. The process converts everyday manual activities into automatic actions, such as turning on lights upon entering a room, activating air conditioning on hot days, and switching off a television when there are no viewers. This article addresses a case study on context-aware monitoring conducted at the Laboratory of Distributed Systems and Concurrent Programming (LaSDPC) of the University of São Paulo. The focus is on a Fog layer of the IoT operating closer to sensors and reducing communication delays. Concepts of context-aware systems, multi-agent systems, ontology, and MQTT protocol were considered for the implementation of the intelligent system on-site. The programming languages used were Java and Python, leveraging libraries and frameworks dedicated to such technologies. A scalable system that does not compromise computational resource use and maintains responsiveness with low data exchange latency is proposed and tests checked the intelligent behavior of the laboratory under specific conditions using temperature, luminosity, and presence of a person as parameters. [ABSTRACT FROM AUTHOR]

• This study analyzes the effects of temperature anomalies on health using CGSS. • For every 1 °C rise in temperature anomalies, the fitness level decreased by 0.255 units. • The use of air conditioning can avoid negative effect of temperature. We explore the causal relationship between temperature and health at fitness levels in this paper by constructing temperature anomalies using the Chinese General Social Survey (CGSS). The results indicate that for every 1 °C rise in temperature anomalies, the fitness level decreased by 0.255 units, a decrease of 7.081 % of the average. We use the order probit model and the traditional temperature bins to test the results, which are consistent with the benchmark results. The effect of temperature anomalies on health is considerably stronger for males, people over 85 years old, low education, and low-income groups. Further analysis shows that the use of air conditioning can avoid such effects. In addition to the direct impact of temperature, we found that rising temperatures will lead individuals to reduce outdoor activities, thereby affecting their health level. [ABSTRACT FROM AUTHOR]

In a construction environment, project scheduling is an essential tool to measure the success of all projects. This research paper will use project crashing of Activity to decrease the project completion schedule through the CPM method of time-cost trade-off and to minimize project cost. It includes linear programming with the aid of Microsoft Excel Solver to determine the result. And at the end of the research paper, it will show the impact of crashing the activities for the HVAC mechanical installation in a project for both normal and crash time, which displays that the selected Activity that had been crashed generated an increase of 9.8 % total cost from the total project cost. [ABSTRACT FROM AUTHOR]

Experiments were conducted over a 3-yr period to evaluate the effects of bacterial inoculants on the fermentation profile and aerobic stability of whole-plant corn silage (WPC), snaplage (SNA), and high-moisture corn (HMC). Whole-plant corn was inoculated with Lentilactobacillus buchneri PJB1 in combination with Lactiplantibacillus plantarum MTD1 or with Lpb. plantarum alone (experiments 1 and 2). Snaplage (experiment 3) and HMC (experiments 4 and 5) were inoculated with Len. buchneri in combination with Lpb. plantarum or with Len. buchneri alone. After inoculation, the feedstuffs were ensiled in 7.57-L silos and stored at 21 ± 2°C for 30 or 90 d. In experiment 5, silage was subjected to air stress for 2 h every 2 wk through 42 d and then for 2 h/wk until 90 d and had samples analyzed for their bacterial community composition by metagenomics. Overall, in all experiments, silages inoculated with Len. buchneri alone or in combination with Lpb. plantarum had more acetic acid and 1,2-propanediol and fewer yeasts than uninoculated silages. After 30 d of ensiling, inoculation with Len. buchneri alone or in combination with Lpb. plantarum did not affect the aerobic stability of SNA, but it slightly increased the stability of WPC and markedly improved the stability of HMC. After 90 d of ensiling, inoculation with Len. buchneri alone or in combination with Lpb. plantarum markedly improved the aerobic stability of WPC, SNA, and HMC. In experiment 5, inoculation increased the relative abundance (RA) of Lactobacillaceae and reduced the RA of Enterobacteriaceae and Leuconostocaceae in HMC at 30 and 90 d and the RA of Clostridiaceae in non-air-stressed HMC at 90 d. Air-stressed HMC inoculated with Len. buchneri had less lactic acid, more acetic acid and 1,2-propanediol, and markedly greater aerobic stability than uninoculated air-stressed HMC at 90 d. In conclusion, inoculation with Len. buchneri PJB1 alone or in combination with Lpb. plantarum MTD1 increased the production of acetic acid and 1,2-propanediol, inhibited yeasts development, and improved the aerobic stability of WPC, SNA, and HMC. In HMC, inoculation markedly improved aerobic stability as soon as after 30 d of ensiling, and after 90 d, inoculation improved stability even under air stress conditions. [ABSTRACT FROM AUTHOR]

In a vapor compression refrigeration system, the oil enhances the efficiency of the compressor but impairs the performance of the heat exchanger. This paper focuses on the experimental study of the influence of oil quantity on the operational stability of CO 2 air conditioning system. The operational stability of the system under different oil charge quantity and operating conditions is studied. The experimental results indicate that when the oil circulation rate increases to a certain value, the adjustment of electronic expansion valve (EXV) opening or the compressor speed will cause system fluctuation and the outlet of evaporator gets close to no superheat. The critical oil circulation rate of the experimental system is about 9.2 %. The analysis of the fluctuation shows that it becomes more severe with the increasing of the refrigerant mass flow rate. When the mass flow rate increases from 210 kg∙ h −1 to 250 kg∙ h −1 at 7000 r min−1 of compressor speed, the fluctuation frequency increases from 0.072 Hz to 0.095 Hz. The occurrence of unstable phenomena has remarkable impact on system performance, the maximum difference of this system in instantaneous cooling capacity and COP during the fluctuation period is respectively 0.5 kW and 0.13. [ABSTRACT FROM AUTHOR]

An efficient fault diagnosis strategy is crucial for the operation of air conditioning systems. In this paper, a novel fault diagnosis strategy based on the signal demodulation method and deep learning model is proposed for a small sample set's fault diagnosis. The potential application of the novel method in air conditioning systems has been discussed through three fault experiments and model evaluation indicators. The signal demodulation method based on principal component analysis (DPCA) is applied in the field of image enhancement innovatively. Compared with the time-domain sample set, the DPCA sample set has stronger features and higher discrimination. The correct rate of the model using the DPCA sample set has been improved by 10.44 %, the loss rate has been reduced by 34.68 %, and the running time has been reduced by 57.13 %. The Back Propagation Neural Network- Principal Component Analysis (BPNN-PCA) model is applied to air conditioning fault diagnosis. Compared with the traditional BPNN and the CART model, the BPNN-PCA model has better fault diagnosis performance and computational efficiency. Through the test and the model performance evaluation indicators, the model optimization strategy has been proposed, and its effectiveness has been verified. This lays the foundation for the optimization and improvement of the model. [ABSTRACT FROM AUTHOR]

In this study, fuel cell vehicles (FCVs) and electric vehicles (EVs) are considered for energy, i.e., hydrogen and electricity, consumption in varying working conditions, taking into account the heating, ventilation, and air conditioning (HVAC) unit. Since climate considerably influences vehicle performance, and cooling requires more energy than heating, a sweltering condition is studied. Added to this, New York City, a populous megacity, has been selected to dynamically evaluate the behavior of FCVs in real-world driving cycles. The findings suggest that the HVAC system can alter both the electricity consumption of EVs and the hydrogen consumption of FCVs in real-world driving cycles. In light of this, activating the air conditioning (AC) unit during a 10-min ride will cause a 33% energy consumption increase in EVs. This number reaches a significant 55% for the case of FCVs. The results also show that not only would a 20% reduction in battery state-of-health (SOH) consequently cause a 34.5% decrease in the driving range, but also the effect of battery health is more than that of the fuel cell. Moreover, passengers can lower the driving range by roughly 20% and 21.3% in EVs and FCVs, respectively. • Dynamic modeling of fuel cell hybrid vehicle. • Dynamic modeling of electric vehicle and battery cooling circuit. • Investigating fuel cell energy management at different operating times. • Investigation of electric vehicle energy management in new and used battery mode. • Comparing the performance of a fuel cell and electric vehicle in the case of different number of passengers. [ABSTRACT FROM AUTHOR]

In order to obtain high power and efficiency while operating PEM fuel cells in airborne applications, pressurizing the inlet air is necessary. The control strategy for dynamic operation of an air supply module was developed in order to provide cathode inlet air at optimal conditions (mass flow, pressure, humidity and temperature) for different ambient conditions and varying power demand. A surge avoidance strategy without additional surge control valves was successfully implemented. The system was successfully tested statically and dynamically and afterwards connected to a fuel cell system. The air supply module was able to provide cathode pressure, mass flow and humidity dynamically as requested and the developed control strategy was able to avoid unstable operation. •Air supply system for pressurized hydrogen fuel cells in aviation was developed. •Control strategy for varying mass flow, pressure and power demand was developed. •Statically and dynamically stable operation over complete compressor map is achieved. •Measurement data from a combined system with a fuel cell stack is presented. [ABSTRACT FROM AUTHOR]

• The VLE data for R32/R1216 were measured at four temperatures range from 285 to 315 K. • The experimental results were correlated with PR-HV-NRTL model. • The performance of the azeotrope R32/R1216 (0.9/0.1) is between pure R32 and R410A. • Azeotrope R32/R1216 (0.9/0.1) can serve as a drop-in replacement of R32 and R410A in RAC systems. In order to accurately evaluate the performance of R32 and unsaturated fluorinated olefins (HFOs) binary mixtures in residential air condition (RAC) system, the vapor-liquid phase equilibrium (VLE) data of R32 and R1216 binary mixture has been measured with a liquid phase circulation system in the temperature range from 285 to 315 K. The experimental data were correlated by Peng-Robinson (PR) equation of state with Huron-Vidal (HV) mixing rule and non-random two-liquid (NRTL) activity coefficient model. Maximum deviation of the pressure and the mole fraction was 1.38% and 0.013, respectively. The azeotropic behavior was observed for the R32 and R1216 binary mixture when the mole fraction of R32 was around 0.9. The RAC system with standard refrigeration, heating and variable evaporation temperature operating condition was simulated. The cycle performance of binary mixtures of R32 + R1216, R1234yf and R1234ze(E) at different concentrations was compared. The azeotrope R32/R1216 (molar ratio 0.9/0.1) has an extremely low GWP, the COP, refrigeration/heating capacity per unit volume and condensation pressure close to pure R32, and lower discharge temperature. At the same time, it also has well variable operating conditions performance and can be considered as a drop-in replacement for R32 and R410A in RAC systems. [ABSTRACT FROM AUTHOR]

In this paper, we propose an event-triggered collaborative neurodynamic approach to distributed global optimization in the presence of nonconvexity. We design a projection neural network group consisting of multiple projection neural networks coupled via a communication network. We prove the convergence of the projection neural network group to Karush–Kuhn–Tucker points of a given global optimization problem. To reduce communication bandwidth consumption, we adopt an event-triggered mechanism to liaise with other neural networks in the group with the Zeno behavior being precluded. We employ multiple projection neural network groups for scattered searches and re-initialize their states using a meta-heuristic rule in the collaborative neurodynamic optimization framework. In addition, we apply the collaborative neurodynamic approach for distributed optimal chiller loading in a heating, ventilation, and air conditioning system. [ABSTRACT FROM AUTHOR]

• The exergy analysis of HPAC systems adopting R152a, R1234yf and R744 are performed. • The exergy efficiency of HPAC systems with R152a and R1234yf is at the same level. • The exergy efficiency of R744 HPAC is the lowest in cooling but highest in heating. • The measures to improve exergy efficiency are discussed. The exergy analysis of low-global warming potential (GWP) alternative refrigerants, R1234yf, R152a and R744 for heat pump air conditioning (HPAC) systems used in pure electric vehicles (EVs) is conducted via simulation. The results reveal that the system exergy efficiencies (SEEs) of R1234yf-HPAC and R152a-HPAC under identical cooling or heating capacity are similar due to their close thermodynamic properties. The largest exergy destruction component in R1234yf- and R152a-HPACs is the compressor. While for R744-HPAC, the compressor and expansion valve cause major exergy destruction. Moreover, the results also indicate that the SEE of R744-HPAC is at least 20 % lower than that of R1234yf-HPAC when producing identical cooling capacity, while it is on average twice that of R1234-HPAC when producing identical heating capacity. Furthermore, the measures to improve SEE of HPAC systems with different refrigerants are discussed by examining the effects of varying operating conditions. It is suggested to lower compressor speed under both cooling and heating conditions, increase condenser airflow or reduce evaporator airflow of R1234yf-, R152a- and R744-HPACs under cooling condition; for cabin heating, it is advisable to increase the evaporator airflow or decrease condenser airflow for R1234yf- and R152a- HPACs and enlarge condenser airflow for R744-HPAC to elevate SEE. [ABSTRACT FROM AUTHOR]

• Realization of an experimental heat pump based on elastocaloric effect. • The device is made of elastocaloric wires crossed by air as heat transfer fluid. • The energy and environmental impacts of the device with many elastocaloric materials were tested. • Evaluation of the environmental impact through a TEWI analysis compared with a HFC32 heat pump. • Ni 55.92 Ti 44.08 and (Ni 50 Mn 31.5 Ti 18.5) 99.8 B 0.2 provide a significant reduction of the environmental impact (−50/−60 %) with respect to HFC32 heat pump. Solid-state refrigeration can constitute a breakthrough point since based on solid-state refrigerants that do not have any direct greenhouse effect (GWP = 0). The refrigeration systems based on caloric effect can be categorized as: magnetocaloric, electrocaloric, elastocaloric or barocaloric. The theme of interest for the investigation introduced in this paper is elastoCaloric Effect (eCE). In this paper the environmental impact in terms of Total Equivalent Warming Impact (TEWI) of an elastocaloric rotary device ensuring continuous fluxes of cold/hot air for the air conditioning applications is evaluated. The final aim is the construction of an experimental device based on eCE working as a heat pump that operates at peak performance and that would be eco-friendly. Indeed, a rotary two-dimensional model based on finite element method was developed to couple with the device during its realization. The device has been virtually tested while mounting various elastocaloric effect materials to examine and select the ones resulting most suitable both from energetical and environmental points of view. The evaluation of the environmental impact has been perpetuated through a TEWI analysis comparing the indexes of the elastocaloric prototype operating with different elastocaloric materials (Ni 50.8 Ti 49.2 , Ni 55.9 Ti 44.1 , Ni 45 Ti 47.2 Cu 5 V 2.75 , (Ni 50 Mn 31.5 Ti 18.5) 99.8 B 0.2 and PbTiO 3) and a vapor compression heat pump (A ++/ A +) working with HFC32. The analysis was perpetuated for both the functioning modes: cooling and heating modes. The most remarkable data on the analysis is that only Ni 55.92 Ti 44.08 and (Ni 50 Mn 31.5 Ti 18.5) 99.8 B 0.2 provide a significant reduction of the environmental impact (−50/−60 %) appropriately selecting the operative conditions (air velocity ranging from 9 to 12 ms−1 and cycle frequency 0.4 ÷ 0.5 Hz). [ABSTRACT FROM AUTHOR]

The refrigerant distributor helps resolve non-uniform flow distribution issues in multi-path evaporators. Using the CFD method, this paper investigates the distribution mechanism of R410A in a centrifugal distributor under air-conditioning conditions and explores the impact of structural factors on its distribution performance. The Taguchi method is employed to identify the optimal combination of structural parameters and optimization direction for achieving distribution uniformity. Furthermore, the flow distribution characteristics of the optimized distributor are investigated under different conditions. The results show that, under the working conditions of an inlet mass flow rate of 50 kg· h −1 and an inlet quality of 0.1, the non-uniformity of the mass flow rate in the outlet branches of the optimized distributor is only 1.07 %, which represents a decrease of 7.64 % compared to the original distributor. Additionally, the non-uniformity of the outlet branch quality also decreased by 9.41 %. These findings indicate that the optimized distributor exhibits superior distribution performance. Nonetheless, the degradation of the optimized centrifugal distributor's uniform distribution performance with increasing refrigerant inlet mass flow rate and quality suggests that it is more suitable for low mass flow rate and quality conditions. [ABSTRACT FROM AUTHOR]

• Desiccant wheel's performance. • The desiccant wheel's performance has been evaluated using a new set of independent efficacy metrics. • the effects of operational factors on the performance parameters. • Correlations have been developed based on experimental data for forecasting desiccant wheel performance. • There is a high degree of agreement between experimental and anticipated results when using the correlations suggested. In order to utilize green energy and reduce the environmental effect of traditional systems, the majority of HVAC experts are now focusing on the development of sustainable and green energy-supported air conditioning technologies. The air conditioning technologies integrated with a desiccant wheel can save energy and reduce the environmental influence. The desiccant wheel is essential for every rotary desiccant integrated air conditioning system. A practical cooling system with a desiccant wheel requires much effort to analyze. But the performance of a desiccant wheel can be predicted effectively using suitable performance parameters, which is the focus of this study. The desiccant wheel's performance has been evaluated using a new set of independent efficacy metrics. Several types of research have been conducted to determine the effects of operational factors on the performance parameters. Correlations have been developed based on experimental data for forecasting desiccant wheel performance. There is a high degree of agreement between experimental and anticipated results when using the correlations suggested. [ABSTRACT FROM AUTHOR]

Potato late blight (PLB) caused by Phytophthora infestans (Mont.) de Bary, its incidence and development are highly dependent on meteorological conditions. To solve the problem of PLB in mountainous terrain under the condition of limited meteorological monitoring capability, the air temperature and humidity was estimated based on the basic meteorological datasets, the forecast effect of the onset period and infection cycle of PLB based on CARAH rules was evaluated. The average MAE, RMSE and CI of the estimated air temperature and observations were 1.17 °C, 1.52 °C and 0.95, respectively. The average MAE, RMSE and CI of the estimated relative humidity and observations were 8.0 %, 10.7 % and 0.53, respectively. The curve of the infection cycle of PLB at different locations were estimated from the basic meteorological datasets based on the CARAH rules, and the false alarm and missing ratios were 8.8 % and 4.6 % respectively. It may be delayed by 1 or 2 fungal generations compared to the observations, and then the protective fungicide should be adjusted to a systemic fungicide. The false alarm of the infection cycle of PLB may increase in dry air conditions, and the missing report may occur in humid condition. [ABSTRACT FROM AUTHOR]

• Viscosities were measured for saturated solutions of R-290 with POE 75, PAG 68, and PVE 68 from 303.15 to 348.15 K. • The effect character of absorbed R-290 on oil viscosity was given. As a natural refrigerant, propane (R-290) with a similar cooling capacity of R-22 is being increasingly widely attention in refrigeration and air conditioning (RAC). In the refrigeration cycle, the working fluid is actually a mixture of refrigerant/oil. To gain insight into the performance of vapor-compression refrigeration using R-290 as a refrigerant, the thermophysical properties of R-290/oil mixtures should be well known, especially the viscosity behavior. A self-designed double-capillary apparatus was applied to measure the viscosities of saturated solution for R-290 with three synthetic oils (PAG 68, POE 75 and PVE 68) from 303.15 to 348.15 K. The results show that the viscosities of three blends have the similar trend as rising solubility. The absorbed R-290 has a great impact on the oil viscosity in the low temperature region. Viscosities of R-290/oil mixtures could be well represented by the Eyring-MTSM model. [ABSTRACT FROM AUTHOR]

• Performance of an AAC system was investigated for different types of compressors and refrigerants. • The COP of the R1234yf system with VCC and FCC is about 13.6% and 20.1% lower than the R134a one, respectively. • The exergy destroyed in the system with VCC is 1.7%... 52.7% lower than that with FCC. • The exergy destroyed in the evaporator and condenser for R1234yf is less than that for R134a. In this study, the performance of R1234yf as an alternative to R134a has been experimentally investigated in an experimental automobile air conditioning (AAC) system with variable (VCC) and fixed (FCC) capacity compressors. The AAC system was equipped with original components and instruments for mechanical measurements. The experiments were conducted for both types of compressors and refrigerants at various compressor speeds, air temperatures entering the evaporator and condenser and air speeds passing over them. The performance parameters of the AAC system have been evaluated by performing energy and exergy analysis based on the experimental data, and the results were presented in the form of comparative graphics. The experimental results show that the VCC compressor limits the refrigerant flow rate when the capacity control system is activated due to the decrease in the evaporator and condenser air inlet temperatures and the increase in the compressor speed. It was found that the coefficients of performance (COPs) of the R1234yf AAC system with VCC and FCC were approximately 13.6% and 20.1% lower than those of the R134a system with VCC and FCC, respectively. For both refrigerants, in the AAC system with VCC, the total exergy destruction rate per unit cooling capacity was 18.2% − 47.5% lower compared to the system with FCC. The R1234yf AAC system experiences lower exergy destruction in the evaporator and condenser compared to the R134a system, while it practices higher exergy destruction in the compressor and expansion device in comparison to the R134a system [ABSTRACT FROM AUTHOR]

The Total Equivalent Warming Impact (TEWI) index is conventionally used to evaluate emissions from heating, ventilation, air conditioning and refrigeration (HVAC&R) systems. However, a more comprehensive indicator, the Expanded Total Equivalent Warming Impact (ETEWI), has been proposed to overcome the limits of TEWI index and to consider additional environmental impacts such as the effects of urban heat island and the natural gas losses along high-pressure pipelines supplying gaseous fuel to natural gas-fired power plants. In this study, TEWI and ETEWI metrics are applied to an air-to-water electric heat pump (EHP) serving a university building in Benevento (Southern Italy). Real data on EHP electricity consumption have been derived from the entire building's electric load and compared to measured data. ETEWI index has been estimated in two scenarios, one considering the impact of refrigerant charge variation on the performance of the EHP and its environmental impact and the other disregarding it. Additionally, carbon dioxide emission factors for electricity production have been forecasted from 2021 to 2033 to determine the indirect term of ETEWI index. Over the lifetime of the EHP, ETEWI increases by 4.8% compared to TEWI when the variation of refrigerant charge level is not considered. However, this percentage growth is equal to 6.5% when the impact of refrigerant charge change is accounted too. In the latter scenario, the indirect term of ETEWI decreases from 22.7 tCO 2 in 2015 to 12.0 tCO 2 in 2033 when the forecast of the carbon dioxide emission factors for electricity production is taken into account. [ABSTRACT FROM AUTHOR]

This article presents the results of a novel concept of heat and cold decoupling from magnetocaloric materials (MCM) by unidirectional fluid flow. An experimental setup was developed to analyse the heat/cold decoupling and determine the optimal process parameters. Three different kinds of magnetocaloric material samples were analysed by using this setup. Comparing the measuring results to those of existing active magnetic regenerator (AMR) systems shows a very good performance and indicates a higher achievable thermal power output when using a unidirectional fluid flow. [ABSTRACT FROM AUTHOR]

Air conditioning (AC) is a key driver to produce electricity consumption, particularly in residential buildings. In Indonesia, the electricity bill during pandemic covid-19 has increased to a high level on hot days. This is because during these periods many consumers applied their AC for a long time at the same time. It is therefore essential to develop an innovative model to control the electricity peak price and keep a comfortable room during hot days. Many previous studies have confirmed that applied evaporative cooling or other technologies can minimize the whole consumption and cost. This research aims to design a pre-cooling model (PM) for AC to avoid high electricity prices at midday during hot days. To achieve this goal a mathematical model was developed to define the energy cost (EC) and total cost (TC) for AC during the hot season. Under numerical optimization, the EC can be minimized when a spike may occur due to increased temperature at midday for a half hour (0.5 h) and one hour (1 h) spike cases. To justify this model, a PM was applied for two different building characteristics. As a result, the benefits of a PM if a spike occurs for 0.5 h and 1 h were achieved, such as IDR 10,061 (30.43 %) and IDR 10,693 (24.44 %) for building-1; IDR 12,071 (37.40 %) and IDR 14,844 (34.97 %) for building-2. In addition, the TC considering the probability of a spike of 0.5 h and 1 h if the spike occurs every five minutes were IDR 45,247 and IDR 38,287 for building-1 and building-2, respectively. [ABSTRACT FROM AUTHOR]

• Almost all the investigated PCMs are compatible with aluminium, copper, stainless steel, and plastic. • Differences in thermal behaviour were observed despite the same operating conditions were applied. • The thermophysical and transport properties deeply affect the thermal performance of PCMs. • The charging time differs from the discharging one despite the same operating conditions. • The presence of metal lattice structures reduces the charging time more than the discharging one. Refrigeration, air conditioning and heat pump sector represents between 25 and 30% of the global consumption of electricity and this figure is expected to rapidly grow due to the current trend of electrification. To increase the efficiency of these systems or to maximize the use of renewable energy, latent thermal storage systems are being studied and recommended. However, there is a lack of reliable design rules based on trustable data that could help the thermal experts to design efficient and cost-effective latent thermal energy storage. This paper follows a previous work recently published (Longo et al., 2022) where the thermo-physical and transport properties of a few low temperature PCMs (i.e. 2–9 °C of melting temperature) were measured and discussed. In the present work, the attention is focused on two other fundamental aspects: the PCMs' compatibility with the most common construction materials and their thermal behaviour during the solid/liquid phase change. The collected results will contribute to add currently unavailable data in the literature and to highlight interesting insights on the performance of the selected PCMs. [Display omitted] [ABSTRACT FROM AUTHOR]

Increasing the Coefficient of Performance (COP) of vapor compression cycles has been a major focus for decades. Significant improvements can be brought by modifying multistage compressor to flooded single-stage compressor to approach isothermal compression. This work presents the comparative analysis of the cycle performance of a flash tank economized system (FTES), multiple refrigerant injection system (MRIS) and an oil flooded system (OFS). Thermodynamic models of each of these systems using ideal mixing models of refrigerants with the flooding agents are presented. Additionally, mixing effectiveness is introduced as a metric to evaluate the non-ideal mixing of the OFS. Results show that in MRIS, an increase in the number of injection ports significantly increases the COP of the cycle between 18% and 51% for air conditioning and refrigeration applications. The OFS shows that increasing the oil mass flow rate increases the COP significantly above the baseline cycle, benefiting higher temperature lift applications. At evaporating temperature of -40 ℃, relative COP for MRIS with 2 injection points is 7.5% higher than FTES and 5.0% higher than OFS. Further, quantification of the influence of the non-ideal mixing model for OFS showed that a mixing effectiveness of 80% results in 21% degradation of system COP suggesting the ideal mixing assumption has significant influence on the potential for an OFS. [ABSTRACT FROM AUTHOR]

• Drop-in comparison of R513A and R516A for R134a were tested in refrigeration and air conditioning conditions. • R516 proved to be more suitable for low. • Compressor volumetric efficiency, pressure ratio and superheating for R516A have a similar behavior to R134a. refrigeration temperatures. • The differences in COP of R516A are reduced by up to 5.4% compared to R134a. This paper presents the experimental energy behavior of R516A and R513A compared to R134a as baseline refrigerant in refrigeration and air conditioning temperatures. The comparative is made in an evaporating temperatures range of 261 K to 285 K with step 4 K increases, taking condensing temperatures of 308 K, 313 K, and 318 K. Results show that the best energy performance was reached by R134a while the worst were for R513A in all experimental tests, here R516A shows the smallest difference respect to R134a being just 5.4%. Also, R134a showed lower values in discharge pressure respect to its replacements, while R516A exhibited the lower discharge temperatures. R513A showed lower useful superheating for refrigeration applications, while R516A achieved the minor useful superheating for air conditioning temperatures only below R134a. Finally, R513A reached the higher value of volumetric refrigeration capacity for air conditioning temperatures at 308 K condensing temperature. All results were obtained considering the optimal refrigerant mass charge which were 682 g, 655 g, and 632 g for R134a, R513A and R516A, respectively. [ABSTRACT FROM AUTHOR]

The scroll compressor is the core component of the air conditioning system. It is important to accurately evaluate the operation status of the air conditioning system. In this paper, the condenser failure is simulated to explore the impact on the scroll compressor by building an air conditioning system experimental platform. The characteristic frequencies and generation mechanisms of vibration and noise signals are discussed through Time-frequency analysis. The characteristic frequencies in the x, y, and z directions are shaft frequency, second harmonic frequency of stator slot and magnet frequency. Abnormal vibration of the scroll compressor caused by changes in pressure and unbalanced electromagnetic force. The modulation characteristic frequency of the signal and the trend of modulation characteristic changes under fault conditions are discussed through signal demodulation methods. The amplitude modulation of the characteristic frequency is enhanced by the unbalanced electromagnetic force on the shaft rotor. The amplitude of the modulation characteristic frequency of the vibration signal in the three directions and the noise signal increases by 45.0%, 17.3%, 71.4% and 123.0%. This study reveals the mechanism and modulation characteristics of vibration and noise of the scroll compressor, and provides support for its fault diagnosis and status recognition. [ABSTRACT FROM AUTHOR]

Rotary compressors are widely used in split air conditioning units and have a significant global market share. However, the atomization of lubricant in the rotary compressor during discharge from the cylinder can cause negative effects on both heat transfer performance and reliability. Therefore, it is crucial to deepen the understanding of the behavior of atomized oil in the form of small droplets in order to improve the system's performance. In this study, lubricant droplets were analyzed at different locations, operating frequencies, and pressures using shadowgraph imaging. The droplets were extracted using the Canny operator and corrected using a Convolutional Neural Network, and their sizes were analyzed statistically. The results reveal that the droplet characteristic mean diameters increase with frequency and pressure, with larger sizes observed in the outer region above the rotor/stator and constant sizes in the radial direction at the discharge tube level. Additionally, the droplet's volume fraction increases with frequency, with higher values observed in the outer region above the rotor/stator and above the rotor/stator clearance at the discharge tube level. These findings provide valuable experimental data for setting up the boundary conditions used in computational fluid dynamics (CFD) simulations. • An algorithm to identify oil droplets from images recorded in the rotary compressor. • Oil droplet size versus frequency, pressure, and locations are measured in-situ. • The volume fraction of oil droplets is experimentally quantified. [ABSTRACT FROM AUTHOR]

• A CFD fluid-solid coupling simulation model to study the temperature distribution of stator coils and inverter of an electric scroll compressor was developed and validated. • The temperature distribution of stator coils and inverter under different refrigerant conditions was simulated and analyzed. • The working reliability of stator coils and IGBT modules under the studied refrigeration conditions was checked. • The heat dissipation of IGBT modules and the proportion of heat exchange amount between different parts of compressor housing and suction gas were analyzed. In the electric scroll compressor for vehicle air conditioning, the heat generated by motor and inverter is mainly taken away by suction gas. It is necessary to maintain the working temperature of motor and inverter within a safe range to void overheat or burnout. The temperature distribution of motor and inverter under refrigeration conditions are studied using computational fluid dynamics (CFD) simulation in this paper. At first, a CFD fluid-solid coupling simulation model is developed and verified by temperature measurement experiment. The maximum deviation between the simulated temperature at three points on the compressor housing and the measured results does not exceed ±3°C. Then the velocity and pressure distribution of fluid domain, and the temperature distribution of solid domains including the compressor housing, the stator coils and insulated gate bipolar transistor (IGBT) modules are analyzed. Next, the effects of operation conditions on the maximum working temperature and temperature distribution unevenness of stator coils and IGBT modules are discussed in detail. In addition, the working reliability of IGBT modules under refrigeration conditions is checked and the heat dissipation of IGBT modules is analyzed. [ABSTRACT FROM AUTHOR]

Fully-dense ZrB 2 and HfB 2 composites were elaborated by Spark Plasma Sintering with 20 vol% AlN to replace SiC or TaSi 2 with the objective to improve the oxidation resistance at very high temperature. This study follows the ones on (Zr/Hf)B 2 -SiC and (Zr/Hf)B 2 -TaSi 2 systems carried out in the same conditions (Pellegrini et al. 2022a; Pellegrini et al. 2022b). Oxidation behavior of several samples in air plasma conditions, at 1000 Pa total pressure and from 1980 K up to 2600 K, was studied using the MESOX facility implemented at the focus of a solar furnace. The mass variation of the samples during oxidation duration of 300 s on a temperature plateau was measured. The characterization of the oxidized samples was done using SEM, EDS, XRD, XPS and Raman. A better oxidation resistance was obtained with these new compositions as, for example, no mass loss up to 2600 K was measured for the ZrB 2 -20 vol% AlN composite due to the protective effect of the aluminum-rich phase formed by oxidation and confirmed by the cross-section analysis. [ABSTRACT FROM AUTHOR]

The air compressor for fuel cell system (FCS) is used to supply air for the cathode of fuel cell whose performance directly affects the efficiency of the whole system. Compared with the traditional air compressor, the special air compressor for vehicle fuel cell needs to meet the requirements of oil-free, high pressure ratio, high efficiency, low noise, low weight, small volume and fast dynamic response. In this study, through comparative analysis of various types of air compressors, it is clear that centrifugal air compressors have the best comprehensive effects on power density, isentropic efficiency, noise, volume and so on, and it will be the mainstream development direction of FCS special air compressors in the future. The current development and problems are systematically reviewed and analyzed, and the future development trend is also proposed. In addition, the durability test for centrifugal air compressors is also discussed, and the life test conditions of centrifugal air compressors are presented. This study is beneficial for the researchers to obtain a holistic view of the overall state of centrifugal air compressor and is of guidance to design a more efficient and commercial fuel cell system. • The performance, noise and cost of centrifugal air compressor for fuel cell are reviewed. • Air compressor efficiency in full operating conditions under the whole system should be optimized. • The noise reduction methods for centrifugal air compressor needs to be further explored. • Its cost needs to be further reduced to meet the target with $40/kWnet. • It is necessary to develop durability test technology with high acceleration coefficient. [ABSTRACT FROM AUTHOR]

This study analyzed the RT8HC melting in a spherical vessel employing air as a heat transfer fluid. The phase change process was followed both visually and by thermal measurements. Photographs and thermographs allow the following phases' evolution and melting mechanisms. We observed that the melting process was not symmetric around the vertical axis; implications of non-symmetric conditions on the melting mechanisms and heat transfer are discussed and analyzed. This work also includes the effects of outer water vapor condensation on heat transfer in the analyses. We proposed a mathematical model to quantify the heat flux that only requires humidity and temperature measurements and considers both heat convection and condensation effects. Results show that condensation significantly affects heat transfer during the initial stage of the melting process. Beside, these effects extend beyond the condensation time due to the liquid film draining from the spherical vessel surface. Regarding thermography, this technique may be a valuable tool for analyzing and following melting processes inside vessels; however, the presence of liquid film over the sphere affects the temperature measurements obtained from the thermograph analysis. This investigation provides relevant information about using phase change materials in cold thermal energy storage applications, latent thermal loads, and humidity control, which are essential aspects of air-conditioning system designs. [ABSTRACT FROM AUTHOR]

In this study, an evaporative cooling device (ED) was developed using the evaporative cooling pad (EP) made of cellulose-based materials with related accessories to actually install on a condenser of the automotive air conditioner (MAC) to improve the operating performance of HR-12 MAC. The ED was used to pre-cool the air entering the condenser by evaporative cooling instead of directly spraying water to cool the condenser. This approach can effectively reduce the risk of condenser corrosion and contamination. The HR-12 MAC performance was assessed at three different outdoor ambient temperatures (T oa : 30 °C, 35 °C, and 40 °C) and EP thicknesses (3 cm, 5 cm, and 7 cm). The configuration of the optimum EP thickness was identified through the results of HR-12 MAC performance experiments. The operating performance of HR-12 MAC with ED improved with the increase in T oa and EP thickness. However, according to most test results, ED could not effectively improve the performance of HR-12 MAC at the T oa of 30 °C. Under optimal conditions, the coefficient of performance (COP) of the refrigeration system and the energy efficiency ratio (EER) of the air conditioning system of HR-12 MAC with ED were respectively 7.76% and 13.09% higher than the original HR-12 MAC at the T oa of 40 °C, and the EP thickness of 7 cm. [ABSTRACT FROM AUTHOR]