Search Results (228)

Modern aircraft increasingly utilizes highly integrated electronic equipment, driving continuously increasing heat dissipation demands. Vapor compression refrigeration systems demonstrate stronger alignment with future aircraft thermal management trends, leveraging their superior volumetric cooling capacity, high energy efficiency, and independence from engine bleed air. This paper reviews global research progress on aircraft vapor compression refrigeration systems, covering performance optimization, dynamic characteristics, control strategies, fault detection, and international development histories and typical applications. Analysis identifies emerging challenges under large-temperature-range cooling requirements, with comparative assessment establishing zeotropic mixture auto-cascade vapor compression refrigeration systems as the optimal forward-looking solution. Finally, recognizing current research gaps, we propose future research directions for onboard auto-cascade vapor compression refrigeration systems: optimizing refrigerant mixtures for flight conditions, achieving efficient gas-liquid separation during variable overloads and attitude conditions, and developing model predictive control with intelligent optimization to ensure reliability. Full article

The worldwide need for energy as well as environmental challenges have promoted the creation of sustainable power solutions. The combination of different working fluids is used for an organic Rankine cycle-powered vapor compression cycle (ORC-VCC) to deliver cooling applications. The selection of an appropriate working fluid significantly impacts system performance, efficiency, and environmental impact. The research evaluates possible working fluids to optimize the ORC-VCC system. Firstly, Artificial Neural Network (ANN)-derived models are used for exergy destruction ( E d t o t ) and heat exchanger total heat transfer capacity ( U A t o t ). Later on, multi-objective optimization was carried out using the acquired models for E d t o t and U A t o t using the Genetic Algorithm (GA) followed by the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS). The optimization results showcase Decane ORC-R600a VCC as the best candidate for the ORC-VCC system; the values of E d t o t and U A t o t were found to be 24.50 kW and 6.71 kW/K, respectively. The research data show how viable it is to implement biogas-driven ORC-VCC systems when providing air conditioning capabilities. Full article

This work investigates the effect of nanoclay addition—specifically natural montmorillonite (MMT) and organo-modified montmorillonite (O-MMT)—on the elastocaloric performance of natural rubber (NR), a promising material for solid-state cooling due to its non-toxicity, low cost, and ability to exhibit large adiabatic temperature changes under moderate stress (~a few MPa). Despite these advantages, the cooling efficiency of NR remains lower than that of conventional vapor-compression systems. Therefore, improving the cooling capacity of NR is essential for the development of solid-state cooling technologies competitive with existing ones. To address this, two series of NR-based nanocomposites, containing 1, 3, and 5 phr nanofiller, were prepared by melt compounding and hot pressing and characterized in terms of morphology, thermal, mechanical, and elastocaloric properties. The results highlighted that the better dispersion of the organoclays within the rubber matrix promoted not only a better mechanical behavior (in terms of stiffness and strength), but also a significantly enhanced cooling performance compared to MMT nanofilled systems. Moreover, NR/O-MMT samples demonstrated up to a ~45% increase in heat extracted per refrigeration cycle compared to the unfilled NR, with a coefficient of performance (COP) up to 3, approaching the COP of conventional vapor-compression systems, typically ranging between 3 and 6. The heat extracted per refrigeration cycle of NR/O-MMT systems resulted in approx. 16 J/cm³, higher with respect to the values reported in the literature for NR-based systems (ranging between 5 and 12 J/cm³). These findings emphasize the potential of organoclays in enhancing the refrigeration potential of NR for novel state cooling applications. Full article

Greenhouses are crucial for maintaining an ideal temperature and humidity level for plant growth; however, attaining ideal levels remains a challenge. Energy-efficient and sustainable alternatives are needed because traditional temperature/humidity control practices and vapor compression air conditioning systems depend on climate conditions and harmful refrigerants. Advanced alternative technologies like evaporative cooling and desiccant dehumidification have emerged that maintain the ideal greenhouse temperature and humidity while using the least amount of energy. This study reviews direct evaporative cooling, indirect evaporative cooling, and Maisotsenko-cycle evaporative cooling (MEC) systems and solid and liquid desiccant dehumidification systems. In addition, integrated desiccant and evaporative cooling systems and hybrid systems are reviewed in this study. The results show that the MEC system effectively reduces the ambient temperature up to the ideal range while maintaining the humidity ratio, and both dehumidification systems effectively reduce the humidity level and improve evaporative cooling efficiency. The integrated systems and hybrid systems have the ability to increase energy efficiency and controlled climatic stability in greenhouses. Regular maintenance, initial system cost, economic feasibility, and system scalability are significant challenges to implement these advanced temperature and humidity control systems for greenhouses. These findings will assist agricultural practitioners, engineers, and researchers in seeking alternate efficient cooling methods for greenhouse applications. Future research directions are suggested to manufacture high-efficiency, low-energy consumption, and efficient greenhouse temperature control systems while considering the present challenges. Full article

The environmental impact of innovative indirect regenerative evaporative cooling (IREC) technology is analyzed using the life cycle assessment. This study compared typical equipment using this technology from Innovative Ideas LLC with available-on-the-market traditional vapor compression ducted air conditioning systems as the closest analogous representatives of the vapor compression technology. For comparison, units with the same cooling capacity (5 kW) were selected. The endpoint indicators demonstrated that the air conditioning systems using IREC technology had lower environmental load compared to the vapor compression system by 29–70%, depending on the scenario and damage category. This advantage resulted from the significantly higher coefficient of performance of the IREC system. The amounts of cooling energy generated and electricity consumption were determined based on temperature and relative humidity data recorded at hourly intervals in the summer seasons of 2023 and 2024. The operation turned out to be a life cycle stage with dominating environmental load. The uncertainty analysis carried out with Monte Carlo simulations indicated significant deviation, particularly for the ecosystem category. The sensitivity analysis showed that the assumed electricity mix did not significantly affect the general conclusions. Full article

This review paper addresses the design and testing of ultra-low temperature (ULT) freezers, highlighting their critical functions in various industries, particularly foods, medicine, and research. ULT freezers operating at temperatures of −86 °C and lower have come a long way with improvements in freezing technology, for instance, from traditional vapor compression systems to new multi-stage refrigeration technologies. This progress has added operational reliability and energy efficiency, essential for preserving delicate samples and facilitating groundbreaking research. The article deeply explores the contribution of refrigerants to ULT freezer efficiency and sustainability. With the use of chlorofluorocarbons (CFCs), previously reliant on them, being prohibited due to environmental concerns, the sector opted for environmentally friendly substitutes like hydrofluorocarbons (HFCs), natural refrigerants, and hydrofluoroolefins (HFOs). Regulatory compliance is ensured by rigid validation protocols to guarantee ULT freezers are safe and meet quality requirements without compromising the integrity of the stored material. In addition to their wide-ranging advantages, ULT freezers also have disadvantages, such as energy efficiency, incorporating automation, the integration of IoT and AI for proactive maintenance, and the development of environmentally sustainable refrigerants. Adequate management strategies, including regular employee training and advanced monitoring systems, are vital to counteract threats from temperature variations and reduce long-term diminished performance. Finally, subsequent innovations in ULT freezer technology will not only aid in research and medical initiatives but also support sustainable practices, ensuring their core role as beacons of innovation in preserving the quality of precious biological materials and increasing public health gains. Full article

This work studies the feasibility of integrating a hydrogen-powered propulsion system in a regional aircraft at the conceptual design level. The developed system consists of fuel cells, which will be studied at three technological levels, and batteries, also studied for four hybridization factors (X = 0, 0.05, 0.10, 0.20). Hydrogen can absorb great thermal loads since it is stored in the tank at cryogenic temperatures and is used as fuel in the fuel cells at around 80 °C. Taking advantage of this characteristic, two thermal management system (TMS) architectures were developed to ensure the proper functioning of the aircraft during the designated mission: A1, which includes a vapor compression system (VCS), and A2, which omits it for a simpler design. The models were developed in MATLAB^® and consist of different components and technologies commonly used in such systems. The analysis reveals that A2, due to the exclusion of the VCS, outperformed A1 in weight (10–23% reduction), energy consumption, and drag. A1’s TMS required significantly more energy due to the VCS compressor. Hybridization with batteries increased system weight substantially (up to 37% in A2) and had a greater impact on energy consumption in A2 due to additional fan work. Hydrogen’s heat sink capacity remained underutilized, and the hydrogen tank was deemed suitable for a non-integral fuselage design. A2 had the lowest emissions (10–20% lower than A1 for X = 0), but hybridization negated these benefits, significantly increasing emissions in pessimistic scenarios. Full article

More efficient energy conversion systems operating with clean energy sources or utilizing waste heat are crucial to minimizing the negative environmental impact associated with conventional systems. This study presents the energy and exergy analysis of a modified heat pump capable of producing cooling and desalinated water using heat dissipated in the condenser. Six refrigerants were analyzed in the theoretical evaluation of the proposed system. These were selected based on their use in vapor compression systems and their thermodynamic properties. A parametric study considering operating temperatures and relative humidities determined that refrigerant R-123 achieved the greatest benefits in terms of the EER, the GOR, and ${\mathsf{\eta }}_{\mathrm{E}\mathrm{x}\mathrm{e}\mathrm{r}\mathrm{g}\mathrm{y}}$. In contrast, the highest benefits in water desalination were obtained with refrigerant R-410a. For operating conditions of T_E = 0 °C, T_C = 34 °C, and T_CA = 14 °C, the system using refrigerant R-123 achieved an EER, GOR, ${\mathsf{\eta }}_{\mathrm{E}\mathrm{x}\mathrm{e}\mathrm{r}\mathrm{g}\mathrm{y}}$, D_W, and I_T of 0.82, 2.51, 0.35, 3.46 L/h, and 0.55 kW, respectively. Additionally, the dehumidifier and the evaporator were the components contributing the highest irreversibilities, accounting for approximately 24% and 19.3%, respectively. Full article

Liquid hydrogen is regarded as a key energy source and propellant for lunar bases due to its high energy density and abundance of polar water ice resources. However, its low boiling point and high latent heat of vaporization pose severe challenges for storage and management under the extreme lunar environment characterized by wide temperature variations, low pressure, and low gravity. This paper reviews the strategies for siting and deployment of liquid hydrogen storage systems on the Moon and the technical challenges posed by the lunar environment, with particular attention for thermal management technologies. Passive technologies include advanced insulation materials, thermal shielding, gas-cooled shielding layers, ortho-para hydrogen conversion, and passive venting, which optimize insulation performance and structural design to effectively reduce evaporation losses and maintain storage stability. Active technologies, such as cryogenic fluid mixing, thermodynamic venting, and refrigeration systems, dynamically regulate heat transfer and pressure variations within storage tanks, further enhancing storage efficiency and system reliability. In addition, this paper explores boil-off hydrogen recovery and reutilization strategies for liquid hydrogen, including hydrogen reliquefaction, mechanical, and non-mechanical compression. By recycling vaporized hydrogen, these strategies reduce resource waste and support the sustainable development of energy systems for lunar bases. In conclusion, this paper systematically evaluates passive and active thermal management technologies as well as vapor recovery strategies along with their technical adaptability, and then proposes feasible storage designs for the lunar environment. These efforts provide critical theoretical foundations and technical references for achieving safe and efficient storage of liquid hydrogen and energy self-sufficiency in lunar bases. Full article

In response to the significant increase in cooling needs for the built environment due to climate change, hybrid air conditioning units can provide energy efficient alternatives to vapor compression systems. This paper reviews the reported energy performance of integrated air conditioning systems consisting of three types of hybrid options: direct expansion (DX) combined with evaporative cooling, DX with desiccant, and evaporative cooling combined with desiccant. In addition, the reported analyses of integrating these hybrid systems with phase change materials (PCMs) and/or photovoltaic (PV) systems are considered. The evaluated analyses generally confirm that integrated air conditioning systems offer substantial energy saving potential compared to traditional vapor compression cooling units, resulting in substantial economic and environmental benefits. Specifically, hybrid systems can reduce the annual energy consumption for space cooling by 87% compared to traditional air conditioning units. This review analysis indicates that hybrid systems can have a coefficient of performance (COP) ranging from 6 to 16 compared to merely 3 to 5 for conventional systems. Additionally, liquid desiccant cooling systems have reported notable improvements in dehumidification efficiency and energy savings, with payback periods as low as three years. Future work should focus more on real-building applications and on conducting more comprehensive cost–benefit analyses, especially when integrating more than two technologies together. Full article

Due to urban expansion and limited heat sources, the heating capacity of heat supply stations is inadequate to meet the growing heat demand. In current heat supply stations, heat from the primary heat network is generally conveyed to the secondary heat network solely via plate heat exchangers, resulting in the return water temperature of the primary heat network being as high as 50 °C, with a substantial amount of recoverable waste heat resources. In this paper, a case study of a heat supply station with insufficient heating capacity in Beijing is conducted to propose supplemental heating systems using vapor-compression heat pumps and absorption heat pumps to further extract waste heat from the primary heat network. Through the TRNSYS platform, simulation models for both systems were developed. Then, based on the bilevel optimization method, the design scheme and operational strategy were co-optimized with the objective of minimizing the lifecycle cost. The performance of the two systems was compared from the perspectives of energy consumption, economy, additional footprint, and regional applicability. The results indicate that the energy consumption of the vapor-compression heat pump supplemental heating system (VCSHS) is 0.85% higher than that of the absorption heat pump supplemental heating system (ASHS), with supplementary heat of 3500 kW. The initial cost of the VCSHS is approximately 1 million CNY lower than that of the ASHS, while the operational costs of both systems are nearly identical, making the VCSHS more cost-effective overall. Additionally, the footprint of new equipment in the VCSHS is nearly 30% smaller than that in the ASHS. Compared with cold regions, it is more economical to adopt ASHSs in severe cold regions due to their lower heat price. Full article

As global environmental consciousness continues to expand, the issue of refrigerant alternatives has increasingly become a focal point for scholarly attention. Using CiteSpace visualization technology, a comprehensive and innovative research framework for refrigerant alternatives has been developed. This framework systematically organizes and analyzes not only the volume of publications related to refrigerant alternatives but also the collaborative relationships among authors and research institutions. By employing keyword co-occurrence maps, clustering diagrams, and timeline charts, an in-depth analysis of the academic literature on refrigerant alternatives has been performed, elucidating the core research themes, evolutionary trajectories, and emerging trends in this field. Research indicates an exponential increase in the number of studies on refrigerant alternatives; however, there is insufficient collaboration and communication among researchers and institutions. Key research hotspots in this field encompass the organic Rankine cycle, vapor-liquid equilibria, pressure drop characteristics, vapor compression refrigeration systems, exergy analysis, alternative refrigerants, and performance evaluation of carbon dioxide systems. In future research, the performance of various low GWP refrigerants in refrigeration cycle systems will continue to be a focal point. To address diverse application requirements, developing blended refrigerants represents a pragmatic technical approach. From a sustainability standpoint, natural refrigerants are anticipated to emerge as the ultimate alternative, with the technical challenges associated with their application constituting a critical area for future investigation. Full article

The concept of integrating mechanical vapor compression (MVC) with direct contact membrane distillation (DCMD) is presented and analyzed. The hybrid system utilizes the DCMD to harvest the thermal energy of the MVC reject brine to preheat a portion of the seawater intake and simultaneously produce additional fresh water. Based on the operating temperature, the hybrid system requires specific energy consumption between 9.6 to 24.3 kWh/m³, which is equivalent to 25 to 37% less than the standalone MVC. Similarly, the freshwater production of the hybrid system can range between 1.03 and 1.1 kg/h, which is equivalent to a 3% and 10% increase relative to the standalone MVC when operating at brine temperatures of 50 and 90 °C, respectively. However, this enhancement is achieved at the expense of an average of 60% larger total surface area. This is partially due to the incorporation of the surface area of the MD modules and mostly to reduced temperature differences. Altering the permeate-to-feed ratio of the DCMD module led to a marginal change in the overall production without any enhancement in the compression power consumption. Increasing the MD module length by 50% resulted in a 3% enlargement in the overall production rate and a 10% reduction in power consumption. A modified hybrid structure that additionally utilizes the distillate heat is sought. A 5% increase in water production at the expense of a 45% rise in the specific compression energy of the modified structure over the original hybrid system is obtained. Full article

Refrigeration is vital in daily life and industries, traditionally relying on single-system cooling. The two predominant kinds of single-system cooling are vapor compression refrigeration (VCR) and thermoelectric cooling (TEC). Each of these two single systems has its own disadvantages, such as higher input energy requirements and lower efficiency. However, the effect of the integration of VCR and TEC for achieving higher cooling performance with lower energy input has not been well studied and reported in the existing literature. Therefore, the aim of this study is to conduct a thorough investigation into an integrated refrigeration system that combines VCR and TEC. This integration allows switching between systems based on specific requirements, leveraging the high coefficient of performance (COP) of VCR and the benefits of TEC. Three configurations have been studied, and each of them has three operating conditions: VCR alone, TEC alone, and TEC hybrid with VCR. Configuration I corresponds to the results from the individual refrigeration test. In Configuration II, the hot end of the thermoelectric cooling module is installed at the insulation layer between the TEC layer and the VCR compartment. In Configuration III, the cold end of the thermoelectric cooling module is positioned at the insulation layer between the TEC layer and the VCR compartment. Configuration III of the integrated system demonstrated good performance by reducing the time required to reach the target temperature. It took 40 min for TEC alone to reach a temperature of 11.1 °C, 13 min for VCR alone, and only 9.6 min for a hybrid system. The hybrid system shows increased versatility and potential for future applications, providing valuable insight into optimizing advanced cooling technologies. Furthermore, from an economic and sustainability standpoint, the proposed hybrid refrigeration system is advantageous and ambitious as it offers superior cooling capacity and greater efficiency than current refrigeration systems. Full article

This study proposes a cogeneration system for the simultaneous production of cooling and freshwater. A double-stage cascade compression cooling system consists of two interconnected vapor compression cycles. The proposed system integrates a double-stage cascade compression cooling system with a water desalination unit, which takes advantage of the heat released by the cascade system. The system performance was evaluated using various refrigerants selected based on their energy efficiency, environmental impact, and widespread use. Multiple combinations of the fluids were used in the high-temperature cycle (HTC) and low-temperature cycle (LTC) to analyze their impact on system performance. A parametric analysis was conducted by developing a mathematical model in MATLAB. The model’s input parameters were the evaporation temperature and the temperature difference between the inlet and discharge of both compressors (ΔLTC and ΔHTC). System performance was assessed from a first-law point of view through the coefficient of performance (COP), the energy utilization factor (EUF), and the gain output ratio (GOR). The results revealed that the maximum (105 °C) and minimum (−13 °C) temperatures, essential for desalination and cooling, respectively, were achieved using R134a in the LTC and R123 in the HTC, with ΔLTC = 65 °C and ΔHTC = 70 °C. However, the best performance was observed with R123 in both cycles, with ΔLTC = 45 °C and ΔHTC = 70 °C. This configuration achieved a COP of 1.06, a GOR of 1.61, and an EUF of 2.74. Full article