Search Results (182)

In sorption cooling systems, an important stage of the thermodynamic cycle is the separation of the refrigerant fluid from the absorbent mixture. This process is called “regeneration” or “desorption,” and it is similar to thermal desalination, where water is separated from an aqueous saline solution. However, since sorption systems utilize high salt concentration solutions, conventional desalination techniques such as reverse osmosis are not suitable. In this regard, membrane devices can enhance heat and mass transfer processes in compact sizes. In the present paper, a membrane device with an air gap membrane distillation configuration was evaluated, operating with the H₂O/LiBr + LiCl solution (with a mass ratio of 2:1, LiBr:LiCl), to assess the produced distilled water flux. Among the operating parameters analyzed (solution temperature, cooling water temperature, salt concentration, and membrane pore size), solution temperature had the highest impact on the distilled water flux, while the membrane pore size had the lowest impact. The maximum distilled water flux was 7.63 kg/h·m² with a solution temperature of 95.3 °C, a cooling water temperature of 25.1 °C, a salt concentration of 44.99% w/w, and a membrane pore size of 0.45 μm. On the other hand, the minimum distilled water flux was 0.28 kg/h·m² with a solution temperature of 80.3 °C, a cooling water temperature of 40.1 °C, a salt concentration of 50.05% w/w, and with a membrane pore size of 0.22 μm. Full article

Two-phase expansion processes have emerged as a promising technology for enhancing energy efficiency in power generation, refrigeration, waste heat recovery systems (for example, partially evaporated organic Rankine cycle, organic flash cycle, and trilateral flash cycle), oil and gas, and other applications. However, despite their potential, widespread adoption is hindered by inherent challenges, particularly energy losses that reduce operational efficiency. This review systematically evaluates the current state of two-phase expansion technologies, focusing on the root causes, impacts, and mitigation strategies for expansion losses. This work used Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). Using the PRISMA framework, 52 relevant publications were identified from Scopus and Web of Science to conduct the systematic review. A preliminary co-occurrence analysis of keywords was also conducted using VOSviewer version 1.6.20. Three clusters were observed in this co-occurrence analysis. However, the results may not be significant. Therefore, the extended work was done through a comprehensive analysis of experimental and simulation studies from the literature. This study identifies critical loss mechanisms in key components of two-phase expanders, such as the nozzle, diffuser, rotor, working chamber, and vaneless space. Also, losses arising from wetness, such as droplet formation, interfacial friction, and non-equilibrium phase transitions, are examined. These phenomena degrade performance by disrupting flow stability, increasing entropy generation, and causing mechanical erosion. Several losses in the turbine and volumetric expanders operating in two-phase conditions are reported. Ejectors, throttling valves, and flashing flow systems that exhibit similar challenges of losses are also discussed. This review discusses the mitigation and the strategy to minimize the two-phase expansion losses. The geometry of the inlet of the two-phase expanders plays an important role, which also needs improvement to minimize losses. The review highlights recent advancements in addressing these challenges and shows optimization opportunities for further research. Full article

This study investigates the significant energy optimization gaps in hotel retrofits in a subtropical climate, quantifying the missed energy-saving opportunities through advanced simulation techniques. Utilizing Design Builder software, the energy consumption of a hotel in Cienfuegos (Cuba) was assessed both before and after renovation, focusing on passive strategies (e.g., replacing single-glazed windows with double glazing) and active interventions (e.g., upgrading the air conditioning system). The results reveal that current retrofit strategies fail to reduce energy consumption substantially. Replacing single-glazed windows with double glazing could reduce annual energy use by 42%. Additionally, upgrading the existing chiller system or implementing a Variable Refrigerant Flow (VRF) system could result in 40% and 59.5% energy savings, respectively. The most significant energy reduction, 71%, is achieved when both interventions—upgrading the chiller and installing double-glazed windows—are implemented, reducing the energy consumption index (ECI) to a quarter of its current value. The life cycle cost (LCC) analysis demonstrates that energy-efficient investments offer considerable economic returns. For instance, an investment of USD 508,600 in a modern chiller system would generate net savings of USD 1,373,500 over its operational lifespan. This study underscores substantial economic and environmental losses from omitting energy efficiency considerations in hotel renovations. It calls for integrating comprehensive energy optimization strategies in retrofit planning, with each dollar invested in energy-saving measures potentially yielding USD 2.5 in life cycle savings. This approach is crucial for global hotel markets facing energy challenges. Full article

The twin-screw compressor exhibits significant application value in the fields of energy, refrigeration, construction, transportation, and related domains. Owing to the benefits of short cycles and low costs, numerical simulation technology has attracted increasing attention. Over recent years, the numerical simulation technology for twin-screw compressors has advanced rapidly, and many important results have been achieved. This paper comprehensively discusses the modeling method of twin-screw compressors, the meshing technique, advances in numerical simulation of internal flow, the research status of numerical simulation research regarding structural operating conditions, and performance optimization. The synergistic potential between these technologies for improving the performance and efficiency of twin-screw compressors is investigated. The numerical simulation research progress of the internal flow and performance optimization of twin-screw compressors is systematically reviewed. Against the background of global energy saving and carbon reduction, this paper offers readers an in-depth understanding of the technical challenges, research hotspots, and development directions in the related field. It fills the relevant gaps within the current literature. The results highlight the role and potential of deep exploration of the intrinsic relationship between local complex flow characteristics and structural optimization for the performance optimization of twin-screw compressors. For conforming to actual conditions and pertinency, mathematical models such as multiphase flow and turbulence models should be further improved. The current research results remain constrained by the lack of comprehensive consideration of multi-field coupling. In the future development of energy-saving and environment-friendly high-performance twin-screw compressors, numerical simulation research should be developed for high precision, multi-physical field coupling, influencing mechanism research, energy-saving, and environmental friendliness, and intelligence. It establishes a theoretical foundation for further enhancing the performance and mechanism theory of twin-screw compressors. Full article

This paper aims to evaluate the feasibility and performances of a novel hybrid solar–gas system, which provides electric power and cooling. By using Ebsilon (V15.0) software, the operation, advanced exergic and economic analyses of this hybrid system are conducted. The analysis results show that the total electric power and energy efficiency of the hybrid system are 96.0 MW and 45.8%. The solar energy system contributes an electric power of 9.0 MW. The maximum cooling load is 69.66 MW. The exergic loss and exergic efficiency of the whole hybrid system are 119.1 MW and 44.6%. The combustion chamber (CC) has the maximum exergic loss (56.5 MW). The exergic loss and exergic efficiency of the solar direct steam generator (SDSG) are 28.5 MW and 36.2%. For the air compressor (AC), CC, heat recovery steam generator (HRSG) and refrigeration system (CSS), a considerable part of the exergic loss is exogenous. The avoidable exergic loss of the CC is 11.69 MW. For the SDSG, there is almost no avoidable exergic loss. Economic analysis shows that for the hybrid system, the levelized cost of energy is 0.08125 USD/kWh, and the dynamic recycling cycle is 5.8 years, revealing certain economic feasibility. The results of this paper will contribute to the future research and development of solar–gas hybrid utilization technology to a certain extent. Full article

This research models a 20 MW PEM hydrogen plant. PEM units operate in the 60 to 80 °C range based on their location and size. This study aims to recover the waste heat from PEM modules to enhance the efficiency of the plant. In order to recover the heat, two systems are implemented: (a) recovering the waste heat from each PEM module; (b) recovering the heat from hot water to produce electricity utilizing an organic refrigerant cycle (ORC). The model is made by ASPEN^® V14. After modeling the plant and utilizing the ORC, the module is optimized using Python to maximize the electricity produced by the turbine, therefore enhancing the efficiency. The system is a closed-loop cycle operating at 25 °C and ambient pressure. The 20 MW PEM electrolyzer plant produces 363 kg/hr of hydrogen and 2877 kg/hr of oxygen. Based on the higher heating value of hydrogen, the plant produces 14,302.2 kWh of hydrogen energy equivalents. The ORC is maximized by increasing the electricity output from the turbine and reducing the pump work while maintaining energy conservation and mass balance. The results show that the electricity power output reaches 555.88 kW, and the pump power reaches 23.47 kW. Full article

This study experimentally analyzes the performance of a passive thermal management system using a three-dimensional (3D) pulsating heat pipe (PHP) designed for pouch cell batteries in electric vehicles. The term “3D” refers to the complex spatial arrangement of the PHP, which features multiple interconnected loops arranged in three dimensions to maximize heat dissipation efficiency and improve temperature uniformity around the battery pack. Lithium-ion pouch cells are increasingly favored for compact and lightweight battery packs but managing their heat generation is crucial to maintaining efficiency and preventing failure. This research investigates the operational parameters of a 3D PHP by testing two working fluids (R134a and Opteon-SF33), three filling ratios (30%, 50%, and 80%), and various condenser conditions (natural and forced convection at 5 °C, 20 °C, and 35 °C). The effectiveness of the PHP was tested using simulated battery discharge cycles, with power inputs ranging from 5 to 200 W. The results show that the 3D PHP significantly improves battery thermal management. Additionally, Opteon-SF33, an environmentally friendly refrigerant, offers excellent heat transfer properties, making 3D PHP with this fluid a promising passive cooling solution for electric vehicle batteries. Full article

Hydrogen (H₂) liquefaction is an energy-intensive process, and improving its efficiency is critical for large-scale deployment in H₂ infrastructure. Industrial waste heat recovery contributes to energy savings and environmental improvements in liquid H₂ processes. This study proposes a comparative framework for industrial waste heat recovery in H₂ liquefaction systems by examining three recovery cycles, including an ammonia–water absorption refrigeration (ABR) unit, a diffusion absorption refrigeration (DAR) process, and a combined organic Rankine/Kalina plant. All scenarios incorporate 2 MW of industrial waste heat to improve precooling and reduce the external power demand. The simulations were conducted using Aspen HYSYS (V10) in combination with an m-file code in MATLAB (R2022b) programming to model each configuration under consistent operating conditions. Detailed energy and exergy analyses are performed to assess performance. Among the three scenarios, the ORC/Kalina-based system achieves the lowest specific power consumption (4.306 kWh/kg LH₂) and the highest exergy efficiency in the precooling unit (70.84%), making it the most energy-efficient solution. Although the DAR-based system shows slightly lower performance, the ABR-based system achieves the highest exergy efficiency of 52.47%, despite its reduced energy efficiency. By comparing three innovative configurations using the same industrial waste heat input, this work provides a valuable tool for selecting the most suitable design based on either energy performance or thermodynamic efficiency. The proposed methodology can serve as a foundation for future system optimization and scale-up. Full article

The cryogenic supercritical hydrogen storage system offers notable advantages including heightened hydrogen storage density and operation under relatively moderate conditions compared to conventional hydrogen storage methodologies. In this study, a cryogenic supercritical hydrogen storage system based on the multi-stage Joule–Brayton refrigeration cycle is presented, analyzed, and optimized. The proposed system employs a five-stage cascade cycle, each stage utilizes a distinct refrigerant, including propane, ethylene, methane, and hydrogen, facilitated by Joule–Brayton cycles, with expanders employed for mechanical work recovery, which is capable of effectively cooling hydrogen from ambient temperature and atmospheric pressure to a cryogenic supercritical state of −223.15 °C (50 K), 18,000 kPa, exhibiting a density of 73.46 kg/m³ and a hydrogen processing capacity of 2 kg_H2/s. The genetic algorithm is applied to optimize 25 key parameters in the system, encompassing temperature, pressure, and flow rate, with the objective function is specific energy consumption. Consequently, the specific energy consumption of the system is 5.71 kWh/kg_H2 with an exergy efficiency of 56.2%. Comprehensive energy analysis, heat transfer analysis, and exergy analysis are conducted based on the optimized system parameters, yielding insights crucial for the development of medium- and large-scale supercritical hydrogen storage systems. Full article

The material in the mold of the injection-molding machine releases significant latent heat of solidification during the cooling process. The efficient recovery and utilization of this waste heat is crucial for improving energy efficiency. A novel integrated energy management system for mold cooling/heat pump/material preheating is proposed in this paper. Taking the symmetrical thermodynamic performance of the heat pump components as the basis and optimizing the system configurations, four system configurations were investigated: MC/BHP/MPCC, MC/RHP/MPCC, MC/HP/MP-IEMS, and MC/DCHP/MP-IEMS, utilizing EBSILON software. The performance of the systems was evaluated through the coefficient of performance (COP) and whole cycle energy efficiency (η). The T-q, T-s, and P-h diagrams were analyzed. It was found that, under comparative operating conditions, both the MC/HP/MP-IEMS and MC/DCHP/MP-IEMS systems exhibited significantly higher COP and η than the MC/BHP/MPCC and MC/RHP/MPCC systems. MC/HP/MP-IEMS achieves a COP of 13.66 and η of 22.09. Similarly, MC/DCHP/MP-IEMS achieves a COP of 14.00 and η of 22.53. The paper optimizes the other three systems using MC/BHP/MPCC as the comparison condition. Optimal cycle performances are achieved with COP and η values of 9, 16, 16, and 9, 26, 25, respectively. A comparison of the thermodynamic performance of five different refrigerants revealed that R123 and R245fa have superior overall performance. This study provides theoretical support for the engineering implementation of integrated energy management systems for injection-molding machines. Full article

In recent years, the use of R744 natural refrigerant has become increasingly popular in a wide range of applications from air conditioning to low-temperature refrigeration. This study focuses on optimizing the thermodynamic parameters of the R744/R134a cascade cycle operating under evaporative temperature varying from −23 °C to −29 °C, operating in tropical climates region. The parameters include the evaporating temperature, the condensing temperature, the subcooling temperature, and the superheating temperature in the low temperature cycle, and the evaporating temperature, the subcooling temperature, and the superheating temperature in the high temperature cycle. The study has given a rating of the influence of thermodynamic parameters on the coefficient of performance (COP) of the system. In addition, the study shows that the optimal dataset for all the above thermodynamic parameters is A₃B₃C₂D₁E₁F₃ with a COP of 2.560 in theory and 2.461 in experiment. Moreover, the ANOVA analysis method for the variances also shows the consistency of the above results with the highest error of 3.54% compared to the experiment. Full article

Demand defrosting is a well-established strategy for improving defrost efficiency in refrigeration systems, and resistive frost-detection sensors provide a cost-effective means of enabling such control. However, copper electrode resistive sensors operating in water-based environments are susceptible to electrolysis, which degrades electrode integrity and compromises measurement reliability. This study investigates the impact of electrolysis on sensor performance and evaluates the effectiveness of an intermittent powering method in mitigating these effects. Two sensor excitation methods were experimentally tested: continuous voltage application and pulsed DC excitation with a 1.7% duty cycle. The results demonstrated that continuous excitation caused erratic measurements and electrode degradation due to ongoing electrochemical reactions. In contrast, the pulsed DC excitation method stopped observable electrolysis effects, leading to stable measurements and improved sensor longevity. These findings highlight pulsed DC excitation as a practical and effective solution for enhancing the accuracy and durability of resistive frost-detection sensors, making them more suitable for long-term use in commercial refrigeration system evaporators. Full article

Recent research in the liquefied natural gas (LNG) industry has concentrated on reducing specific power consumption (SPC) during production, which helps to lower operating costs and decrease the carbon footprint. Although reducing the SPC offers benefits, it can complicate the system and increase investment costs. This review investigates the thermodynamic parameters of various natural gas (NG) liquefaction technologies. It examines the cryogenic NG processes, including integrating NG liquid recovery plants, nitrogen rejection cycles, helium recovery units, and LNG facilities. It explores various approaches to improve hybrid NG liquefaction performance, including the application of optimization algorithms, mixed refrigerant units, absorption refrigeration cycles, diffusion–absorption refrigeration systems, auto-cascade absorption refrigeration processes, thermoelectric generator plants, liquid air cold recovery units, ejector refrigeration cycles, and the integration of renewable energy sources and waste heat. The review evaluates the economic aspects of hybrid LNG systems, focusing on specific capital costs, LNG pricing, and capacity. LNG capital cost estimates from academic sources (173.2–1184 USD/TPA) are lower than those in technical reports (486.7–3839 USD/TPA). LNG prices in research studies (0.2–0.45 USD/kg, 2024) are lower than in technical reports (0.3–0.7 USD/kg), based on 2024 data. Also, this review investigates LNG accidents in detail and provides valuable insights into safety protocols, risk management strategies, and the overall resilience of LNG operations in the face of potential hazards. A detailed evaluation of LNG plants built in recent years is provided, focusing on technological advancements, operational efficiency, and safety measures. Moreover, this study investigates LNG ports in the United States, examining their infrastructures, regulatory compliance, and strategic role in the global LNG supply chain. In addition, it outlines LNG’s current status and future outlook, focusing on key industry trends. Finally, it presents a market share analysis that examines LNG distribution by export, import, re-loading, and receiving markets. Full article

To address the high energy consumption and carbon emissions associated with cold storage operations, a novel refrigeration system is proposed, which utilizes the natural refrigerant CO₂ and integrates an innovative control strategy. Experimental validations were conducted in Changsha (a subtropical monsoon climate) and Changchun (a continental monsoon climate), which are two regions representing typical climatic zones in China, to assess the system’s energy-saving potential, temperature stability, and environmental impacts with the total equivalent warming impact and life cycle carbon performance methods. For Changchun, the total equivalent warming impact reached 78.3 kg CO_2e/kg, reflecting reductions of 99.5% in direct emissions and 58.6% in indirect emissions compared with R410A systems, as mentioned in the reference. The life cycle carbon performance was reduced by 85.1% and 72.2% compared with the two experiment cases, with indirect emissions from energy consumption comprising the largest share. The system maintained exceptional temperature stability, with vertical-layer variations remaining under 1 °C. These findings demonstrate this system’s adaptability to achieve energy and emission reductions across diverse climates, providing a sustainable framework for future cold storage design aligned with global carbon neutrality goals. Full article

In this study, a Reheat Organic Rankine Cycle (ORC) utilizing the cold energy of liquefied hydrogen (LH₂) and liquefied natural gas (LNG) was proposed, and its performance was evaluated by comparing it with the base model, which represented a conventional ORC. The process was simulated using ethane and propane, which were considered as potential refrigerants for the target system. A case study was conducted on the inlet pressure and temperature of the turbine included in the process to determine the optimal operating point. The calculation results indicated that ethane exhibited a higher energy efficiency, and a maximum net power of 34.65 kW was obtained when the inlet pressure and temperature of the turbine were 40 bar and 75 °C, respectively. Additionally, an exergy analysis was conducted to quantitatively analyze the high energy efficiency of the Reheat ORC model. We confirmed that exergy efficiency was up to 2.4% higher than that of the base model. Full article