Efficient Refrigeration Research Articles

ANÁLISE DE RENTABILIDADE DE INVESTIMENTOS EM SISTEMAS DE REFRIGERAÇÃO COM ALTA EFICIÊNCIA ENERGÉTICA

This study analyzes the profitability of investments in high-energy-efficiency refrigeration systems, addressing the economic and environmental impacts of these systems compared to conventional technologies. Energy efficiency is essential for reducing operational costs and promoting sustainability, especially in sectors with high continuous refrigeration demand. The objective is to evaluate the economic feasibility of efficient systems, highlighting variables that influence the return on investment. A descriptive and qualitative literature review was conducted, analyzing studies on energy efficiency, environmental impact, and cost-benefit in commercial and industrial sectors. The findings indicate that, although the initial investment in high-efficiency technologies is high, these systems significantly reduce energy consumption and operational costs over time. It concludes that adopting efficient refrigeration systems is economically viable across various sectors, especially those with high energy demand, and an effective strategy for meeting environmental requirements and reducing emissions.

The reasonableness and feasibility of replacing standing wave vibration with air piston mode vibration in thermoacoustic refrigerator

On the basis of analyzing the longitudinal forced vibration of the gas column in the resonator of a half-wavelength standing wave thermoacoustic refrigerator, the idea of replacing the standing wave vibration with the first-order piston mode vibration of the gas column in the thermoacoustic refrigerator was proposed, so as to increase the vibration amplitude of the gas in the resonator, realize the large alternating flow of gas, and improve the working efficiency of the thermoacoustic refrigerator. At the same time, its rationality and feasibility are discussed from the aspects of modal vibration, pressure distribution of gas column piston, and temperature variation of gas microcluster vibration in equilibrium position. Combined with the existing research results, the superiority of the application of the first-order piston mode vibration of the gas column in the thermoacoustic refrigerator is further explained. The results provide a new research idea and direction for further reducing the cold end temperature of thermoacoustic refrigerator.

Calculation of exergy losses, exergy efficiency and cooling coefficient of refrigerant R22

This study presents a detailed analysis of the exergy losses, exergy efficiency, and cooling coefficient of performance (COP) for the refrigerant R22 in refrigeration systems. Exergy analysis, which considers both the quantity and quality of energy, is used to identify and quantify the irreversibilities within the system. The objective of this analysis is to provide insights into the areas of inefficiency and potential improvements for enhanced energy performance. Results indicate that the exergy losses in R22 systems are primarily associated with the compressor and expansion valve, highlighting these components as key targets for efficiency improvements. The exergy efficiency was found to vary significantly with operating conditions, suggesting that system performance could be optimized through appropriate design and control strategies. Additionally, the cooling COP of R22 was evaluated, demonstrating its effectiveness in converting input energy into cooling capacity under various conditions. This analysis contributes to the broader understanding of R22's thermodynamic performance and offers a foundation for developing more sustainable and efficient refrigeration technologies.

Simulation analysis and optimization of thermoelectric refrigeration and air conditioning

Abstract Thermoelectric refrigeration technology is mainly through the Peltier effect to achieve refrigeration, thermoelectric refrigeration air conditioning needs to be combined with a certain air flow rate to realize the separation of cold and heat, and make full use of the cold end to realize the refrigeration function, or else the refrigeration efficiency is seriously affected. Based on the ICEPAK simulation platform of ANSYS, we analyze the influence of structure and parameter settings on the conversion efficiency of thermoelectric refrigeration air conditioning fan under the established boundary conditions, establish the relationship between air flow rate and temperature drop value, and put forward the optimization of the product structure design scheme, and the results of the optimization scheme show that there is a peak in the operating current at a certain heat dissipation efficiency; and lengthening the length of the air ducts through the optimization of the structure can enhance the refrigeration effect of the air conditioner.

Thermally driven MnCl2[sbnd]NH4Cl resorption cycle for seasonal thermal management of urban buildings

The frequency of extreme weather conditions caused by global greenhouse gas emissions has led to a significant increase in energy consumption for refrigeration and heating supply in urban buildings. However, conventional sensible and latent heat storage technologies hold low thermal energy storage density and short-term energy storage capabilities. Additionally, electrically driven compression refrigeration with non-negligible global warming potential (GWP) is unsuited to high ambient temperatures in summer. We propose an advanced strategy, adopting the MnCl2NH4Cl resorption cycle to achieve efficient desorption refrigeration of NH4Cl and resorption heating supply of MnCl2 under seasonal conditions. Experimental results have demonstrated that our proof-of-concept system can output 70 °C heat with a thermal energy storage density of 166.2 kJ·kg−1, providing continuous heating for 30.5 min under the winter ambient temperature of 10 °C. Moreover, COPref remained at 0.589 for continuous indoor refrigeration lasting 58.5 min under summer ambient and refrigeration temperatures of around 30 °C and 2 °C, respectively. This exceptional adaptability to ambient temperatures enables efficient adjustment of urban building comfort. Our work presents a promising zero-carbon pathway for replacing conventional fossil fuels employed in the thermal management of urban buildings with solar energy.

The DFT prediction of comprehensive properties of antiperovskites Mg6CX4 (X = S, Se, Te) and effects of defects and surface adsorption

It is important to search potential materials to meet ever-increasing demand in various fields. In order to understand the new hexagonal antiperovskites material Mg6CX4 (X=S, Se, Te), their mechanical, electronic and optical properties were studied based on density functional theory (DFT). The structural stability has been confirmed by the elastic constant criteria, formation energy, phonon dispersion spectra and ab-initio molecular dynamics (AIMD) simulation performed at 300K. Besides, the Poisson's ratios over 0.26 demonstrate the ductility of the studied materials. They all have direct electronic band structures with bandgaps of 0.977eV for Mg6CS4, 0.809eV for Mg6CSe4 and 1.274eV for Mg6CTe4, respectively. The calculated melting temperatures are all around 1000K, which indicates the potential for high-temperature application. Therefore, Mg6CTe4 fits most for absorber in solar cells due to its proper bandgap and dispersive band edge. The antiperovskites exhibit high and broad light absorption in visible and near ultraviolet region with absorption coefficient greater than 104cm-1, which inidcates a broad applicable prospect in optoelectronic field. Mg6CTe4 is also a candidate for efficient solid-state refrigeration due to its lowest thermal conductivity as 0.0046W/(K•m). The defect analysis suggest that oxygen defects are the most favorable and have complex effects on bandgaps. The high bandgap sensitivity to surface adsorbates implies potential application in gas detector.

Adaptive control for refrigeration via online identification

Vapor compression refrigeration systems (VCRS) occupy a crucial position in modern society and in the field of thermal sciences. However, the operation of VCRS is subjected to both external disturbances (dynamic-changing environment) and inherent system characteristics (coupling or nonlinear features), leading to issues like reduced refrigeration efficiency and significant fluctuations in cooling capacity. To address these challenges and enhance the adaptability of VCRS in dynamically changing environments, this study establishes a dynamic simulation model for VCRS based on the Switched Moving-Boundary method. The impact of external environmental disturbances on refrigeration performance is investigated, and continuous online identification methods are employed to elucidate its internal coupling characteristics and nonlinear features. The adaptive temperature control method is introduced, benefiting from the developed recursive least squares method with a forgetting factor for online identification, achieving precise model identification which facilities the real-time parameters tuning of adaptive controller. The results indicate that the hybrid paradigm of online identification and adaptive control algorithm not only effectively handles various disturbances but also reduces overshoot and IAE by 2-3 orders of magnitude compared to traditional PID controllers. Adaptive PID control maintains overshoot in the 10-4 order of magnitude and IAE in the 10-5 order of magnitude.

Magnetostructural transformation and magnetocaloric response in Mn(Fe)NiSi(Al) alloys

An efficient magnetocaloric refrigerant must have certain characteristics such as a sharp transition near the desired working temperature, a large cyclic magnetocaloric response, and the use of raw materials with reduced costs and low environmental consequences. In this sense, this work focuses on a series of rare-earth- and Co-free Mn0.5Fe0.5NiSi1-xAlx alloys (x = 0.0525, 0.060, 0.0685) with promising magnetocaloric properties. The alloys were synthesized using combined arc melting and induction melting techniques, as this synthesis route provides improved control on the sample composition and homogeneity. We investigated how the heat treatment temperature and Al content affect the magnetostructural and magnetocaloric properties of the alloys. On the one hand, it is found that annealing at 1173 K for 7 days leads to a sharp magnetostructural transformation with no traces of impurities for the alloy with x = 0.0525. Under these conditions, a large isothermal entropy change of –11.5 J kg−1 K−1 for 1 T is obtained near room temperature, significantly improving the value of the as-cast sample. On the other hand, following this optimal heat treatment, the influence of Al content is studied: upon increasing the Al concentration the magnetostructural transformation shifts to lower temperatures, ranging from 320 K for x = 0.0525 to 220 K for x = 0.0685 (measured upon heating).

Numerical Simulation and Experimental Research on Effect of Flow Regimes for Refrigeration Performance of Wave Rotor

Abstract Wave rotors exchange energy through the interaction of fluids with different pressures to produce a cooling effect without the application of mechanical parts, which makes them suitable for the complex flow field environments. But the flow situation inside the wave rotor is complex, and research on the impact of various flow regimes for the refrigeration efficiency is currently incomplete. This study deals with the numerical simulation and the experimental verification of a four-port fixed rotor gas wave refrigerator. Various typical flow regimes within the wave rotor were obtained through simulation to analyze their impact on the refrigeration efficiency. To further demonstrate the effectiveness of the simulation results, experimental verification was conducted. The simulation results indicate that separation bubbles and vortices will be respectively generated on the upper and lower walls of the wave rotor tube during the gradual opening stage. Vortex affects the airflow flow and causes detachment of separation bubbles as the airflow moves, which results in the loss of pressure energy and kinetic energy of the incident gas. As a result, the loss caused by the gradual opening process leads to a decrease in the self-expansion ability of high-pressure gas during the gradual closing stage, thereby affecting the refrigeration effect. Therefore, reducing the influence of vortices plays an important role in improving the cooling efficiency of wave rotors. Finally, this study analyzes the main factors that affect the cooling effect within the wave rotor through flow regime and provides new insights for improving refrigeration efficiency.

Performance assessment on a modified precision refrigeration cycle using low GWP mixtures

Recently, with the increasing worldwide demand for low-temperature freezers, applying natural working medium hydro-carbon refrigerants for them has been widely concerned. Auto-cascade refrigeration cycle (ARC), as an efficient refrigeration technology, has been widely applications. However, the low separation efficiency of the refrigerant mixtures of the conventional ARC leads to its poor performance. Therefore, this paper presents a modified auto-cascade refrigeration cycle (MARC) using low GWP hydro-carbon refrigerants R170 and R290 for low-temperature freezer applications. In MARC, the two auxiliary separators are applied to make more low-boiling working fluid into evaporator to improve the volumetric cooling capacity (qev) and COP. The characteristics of conventional ARC and MARC are evaluated with theoretical method. The important parameters such as evaporating temperature and intermediate temperature for MARC are also detailed discussed. The theoretical research results suggest the MARC is more energy-saving and feasible. The improved cycle offers significant improvements in qev, COP and exergy efficiency. In detail, for MARC, the qev can be lifted by 40.3–91.3 % and the COP can be improved by 30.6–70.4 % compared with the ARC system. Therefore, the modified MARC shows its potential advantages for low-temperature freezer applications.

Phase modulation analysis on a cavity-structured single-unit thermoacoustic refrigerator

The establishment of traveling-wave-dominated acoustic fields within the regenerator is crucial for developing highly efficient thermoacoustic refrigeration systems. The present work introduces a novel looped, single-unit, direct-coupling thermoacoustic refrigerator, incorporating an optimally dimensioned cavity at a strategic location to maximize system performance. Central to this research is the systematic exploration of the phase modulation mechanism. This exploration involves adjusting the dimensions of the cavity structure, tracking its evolution from initial absence to full integration. The research method includes comprehensive evaluations of steady-state performance, onset characteristics, exergy loss, and axial parameter distribution analysis. The findings are visually depicted through simulations, highlighting the cavity's role in acoustic field modulation and its consequent impact on system efficiency. With the integration of an optimally sized and positioned cavity, the system's cooling efficiency improves by more than 2.5 times compared to the efficiency of a structure without cavities. A prototype replicating the proposed design was then constructed and experimentally tested. The results reveal a close correlation between the simulated and experimental data, affirming the analysis's accuracy and dependability. These studies effectively elucidate the significance of the cavity in looped single-unit thermoacoustic refrigerators and provide valuable insights for the development of more efficient phase modulation structures.

Experimental study on the matching relationship of gas wave oscillation tube under liquid-carrying condition

The gas wave oscillation tube (GWOT) transfers energy directly between gases of varying pressures using non-constant motion waves, and its low rotational speed operation offers a broader application potential in two-phase refrigeration compared to turbomachinery. The GWOTs achieve a high performance by optimizing the relationship between tube length, deflection displacement, rotational speed, and incident excitation wave (S1) velocity. However, under the liquid-carrying conditions, the optimizing matching relationship of the GWOTs deviates, leading to a decline in performance, so it is necessary to explore the matching relationship of the high performance of the GWOTs under the liquid-carrying conditions. This study focuses on "spoon" GWOTs, analyzing the impact of rotational speed, liquid-carrying capacity, and deflection displacement on their refrigeration performance under a fixed tube length through experimental analysis. It is found that the refrigeration efficiency at the design parameters of the GWOTs decreases by a maximum of about 25 % with the increase in the amount of liquid-carrying capacity within the study area of this paper, while the refrigeration efficiency can be improved by a maximum of about 8 % by varying the rotational speed. The findings provide valuable insights for enhancing the liquid-carrying performance of the GWOTs and promoting the application expansion of GWOTs in the field of gas-liquid two-phase.

Experimental correlations to predict the cooling performance and compressor energy consumption of domestic refrigerator with phase change material

ABSTRACT The phase change material technology is continuously evolving in commercial market. In order to develop/design PCM modules of different capacity and different PCM material, it is necessary to develop the equation which will provide required information for development of PCM module. This paper establishes correlations to predict backup time and equivalent energy consumption of domestic refrigerator based on experimental data of testing of PCMs, potassium chloride (KCl), sodium chloride (NaCl), and sodium fluoride (NaF) dissolved in water for PCM masses varying between 0 and 1.75 kg in both closed door and door opening conditions. This paper investigates the impact of incorporating a phase-change material (PCM) on the cooling performance and energy consumption of a domestic refrigerator. The PCM module, filled with potassium chloride (KCl), sodium chloride (NaCl), and sodium fluoride (NaF) dissolved in water, is strategically placed on the contact surface of the refrigerator’s evaporator coil. The utilization of PCM aims to mitigate cabin temperature fluctuations and reduce overall energy consumption. Through experimental evaluation, the study assesses the effectiveness of different phase-change materials in enhancing the cooling performance and energy efficiency of the domestic refrigerator. The findings reveal that the incorporation of phase-change material significantly improves the cooling performance, as evidenced by the extended backup time during power cut-off and a reduction in compressor energy consumption. The tested phase-change materials, including KCl, NaCl, and NaF, demonstrate varying impacts on performance parameters. The backup time for closed-door tests is 1.83 – 1.03 times longer than that for door opening tests, respectively. The backup time of door opening tests is shortened due to heat entered to the cabin for all masses, between 45.45% and 3.23%. The backup time is increased by the masses of PCM KCl between 14% and 155%, the masses of PCM NaCl between 18% and 159%, and the masses of PCM NaF between 27% and 182%. The equivalent energy consumption for door opening tests is 1.12–1.02 times larger than that for the closed-door tests. The correlation equation established based on the existing experimental data can be used to accurately predict the backup time and equivalent energy consumption of refrigerator for tested PCM of any mass within the interval of 0 Kg to 1.75 Kg with ± 10% accuracy.

Experimental comparison of flow boiling heat transfer in smooth and microfin tubes using R134a, R1234yf, and R513A

Addressing the urgent need for environmentally sustainable and efficient refrigeration systems, this study investigates the performance of low-GWP refrigerants R1234yf and R513A in comparison to the high-GWP refrigerant R134a, focusing on the heat transfer coefficient (HTC) and pressure drop during flow boiling in smooth and microfin tubes. The experimental setup involves tubes with a 6.14 mm internal diameter and 500 mm length. Data were collected across a broad range of operating conditions, including mass fluxes from 170 to 495 kg/m² s, heat fluxes from 10 to 40 kW/m², saturation temperatures of 15 °C and 25 °C, and vapor qualities from 0.15 to 1.0. In a specific case with a mass flux of 170 kg/m² s, heat flux of 23 kW/m², and a saturation temperature of 15 °C, the results indicate that the microfin tube achieves an HTC enhancement of up to 64 % compared to smooth tubes. However, R134a exhibits a higher HTC than R1234yf and R513A, approximately 5 % and 3 % higher, respectively. In contrast, R134a presents a higher pressure drop than R1234yf by about 8 %. While the pressure drop for R134a is slightly higher than R513A in the smooth tube, the microfin tube shows similar trends but more pronounced differences. This study comprehensively explores microfin tube performance with these refrigerants, offering critical insights for designing advanced refrigeration systems that balance environmental responsibility with energy efficiency. These findings were validated against predicted correlations, showing good agreement.

Exploring Synergistic GHG Emissions Mitigation Potential and Costs of Room Air Conditioners.

This study explores the potential of synergistically reducing direct (refrigerant) and indirect (electricity) greenhouse gas (GHG) emissions in the global room air conditioning (RAC) sector, based on 80% of global RAC manufactured in China. Three scenarios are evaluated: Business-as-usual (BAU) based on maintaining refrigerant and energy efficiency levels from 2021 China RAC sales shares, Kigali Amendment compliant with 10% energy efficiency improvement by 2025 (KAE), and accelerated refrigerant transition and energy efficiency improvement (ATE). Each scenario considers the costs of refrigerant and efficiency measures for export market groups based on Kigali Amendment classifications. BAU predicts around 1 Gt CO2-eq average annual global RAC emissions (2022-2060). Cumulative emission reductions in China's RAC manufacturing under KAE and ATE are 12.2 and 17.2 Gt CO2-eq A5II and A5I (except China), presenting cost-effective abatement measures, with average costs of -$51.4 and -$68.8/t CO2-eq in KAE and ATE. Cumulative average abatement costs are around $18 and $4/t CO2-eq globally. KAE and ATE scenarios would avoid surface temperature rises of 0.023 (±0.002) °C and 0.027 (±0.003) °C, respectively, versus BAU. Collaboration between China and importing countries is urged to enhance energy efficiency in RACs traded, ensuring sustainable mitigation aligned with the Kigali Amendment.

Engineering Multiphase Phase Transitions for Exceptional Electrocaloric Performance and Ultraweak Electrostrictive Response in Ferroelectrics.

In the pursuit of eco-friendly alternatives for refrigeration technology, electrocaloric materials have emerged as promising candidates for efficient solid-state refrigeration due to their high efficiency and integrability. However, current advancements in electrocaloric effects (ECEs) are often constrained by high temperatures and elevated electric fields (E-field), limiting practical applicability. Informed by phase-field simulation, this study introduces a (1-x)Pb(Yb1/2Nb1/2)O3-xPb(Mg1/3Nb2/3)O3 system, strategically engineered to incorporate highly ordered YN and disordered MN mixtures. The synergistic interplay between E-field/temperature-induced polarization reorientation and cation shift initiates multiple ferroelectric-antiferroelectric-paraelectric phase transitions. Our results demonstrate that under a moderate E-field of 50 kV cm-1, the x = 0.22 composition achieves remarkable performance with a giant temperature change (ΔT) of 3.48 K, a robust ECE strength (ΔT/ΔE) of 0.095 K cm kV-1, and a wide temperature span (Tspan) of 38 °C. Notably, the disrupted lattice structure contributes to ultralow electrostrains below 0.008%, with an average electrostrictive coefficient Q33 of 0.007 m4 C-2. The significantly weakened electrostrictive activity favors enhancing the performance stability of subsequent devices. This work introduces an innovative strategy for developing robust electrocaloric materials, offering substantial ΔT and low electrostrains, presenting promising advancements in ECE applications with an extended lifetime.

Differentiable programming for gradient-based control and optimization in physical systems

This paper presents an exploration of the application of control theory, particularly utilizing a gradient-based algorithm, to automate and optimize the operation of photovoltaic panels and refrigeration systems in warehouse environments. The study emphasizes achieving coordination between energy generation and consumption, specifically harnessing surplus solar energy for efficient refrigeration. The complex interplay between fluctuating solar irradiance, thermal dynamics of the warehouse, and refrigeration needs underscores the significance of control theory in designing algorithms to dynamically adjust PV panel output and refrigeration system operation. The paper discusses foundational control theory principles, proposes a tailored framework for warehouse operations, and highlights the potential for sustainable energy practices. This paper explores the use of data-driven approaches based on NeuralODEs vs classical ones using physics equations.

Dynamic magnetic and magnetocaloric behaviors of a Kagome-like cluster

By utilizing the Monte Carlo simulation, how different physical parameters affect the dynamic magnetic properties and magnetocaloric effects of a Kagome-like cluster with mixed spins (3/2, 2) are explored. The findings show that changing the values of the exchange coupling |J|, |Js|, and |J2| had no impact on the saturation order parameters of the system. Under specific parameter conditions, the magnetization susceptibility curve displays double peaks, and compensation phenomena are noted. The impacts of hbias and hosc on the blocking temperature of the system are opposite. In addition, the effects of various parameters on the magnetization, magnetic entropy change, and relative cooling power of the ferromagnetic system under a static magnetic field are given. The strong exchange coupling is found to negatively affect the magnetic refrigeration efficiency of the material, while a strong magnetic field enhances the system's relative cooling power.

Experimental COP optimization procedure in an air-based reverse Brayton cycle for cryogenic applications

Sustainable and efficient refrigerants are essential due to increasing regulatory constraints on traditional high-GWP refrigerants. This study investigates the potential of natural refrigerants, specifically air, in Reverse Brayton Cycles (RBC) for low-temperature applications. Unlike carbon dioxide and ammonia, which pose limitations and safety concerns below -40°C, air offers a safer and more versatile solution due to its excellent thermodynamic properties and availability. An experimental RBC was constructed using automotive components like centrifugal compressors, a radial turbine, and inter-coolers. These cost-effective and accessible components shift the refrigeration paradigm. The RBC was tested to optimize the Coefficient of Performance (COP) at -100°C while dissipating 2 kW, a typical scenario for whole-body cryotherapy (WBC). Key control parameters included the pressure ratio of the centrifugal compressors and the position of the stator vanes in the variable geometry turbine (VGT). The optimization process resulted in a COP increase of up to 28%. Additionally, a 1D gas-dynamic model validated these results, suggesting that different component selections could enhance performance by 17% compared to the experimental optimum point. Air-based RBC systems using automotive components can effectively achieve temperatures below -40°C, offering a viable, eco-friendly alternative to traditional refrigerants. This advancement addresses regulatory challenges and contributes to the scientific community by providing a sustainable refrigeration solution using commercially available components and demonstrating improvements through experimental data.

Achieving Magnetic Refrigerants with Large Magnetic Entropy Changes and Low Magnetic Ordering Temperatures.

Adiabatic demagnetization refrigeration (ADR) is a promising cooling technology with high efficiency and exceptional stability in achieving ultralow temperatures, playing an indispensable role at the forefront of fundamental and applied science. However, a significant challenge for ADR is that existing magnetic refrigerants struggle to concurrently achieve low magnetic ordering temperatures (T0) and substantial magnetic entropy changes (-ΔSm) at ultralow temperatures. In this work, we propose the combination of Gd3+ and Yb3+ to effectively regulate both -ΔSm and T0 in ultralow temperatures. Notably, the -ΔSm values for Gd0.1Yb0.9F3 (1) and Gd0.3Yb0.7F3 (2) in the 0.4-1.0 K range exceed those of all previously reported magnetic refrigerants within this temperature interval, positioning them as the most efficient magnetic refrigerants for the third stage to date. Although the -ΔSm values for Gd0.5Yb0.5F3 (3) in 1-4 K are less than those of the leading magnetic refrigerant Gd(OH)F2, the -ΔSm values for Gd0.7Yb0.3F3 (4) in 1-4 K at 2 T surpass those of all magnetic refrigerants previously documented within the same temperature range, making it the superior magnetic refrigerant for the fourth stage identified thus far.