Refrigeration Cycle Research Articles

Optimizing Co-generation performance of reactivity controlled compression ignition engines with solar steam reforming of methanol; a thermoeconomic, economic and exergoenvironmental analysis

Reactivity-controlled compression ignition engines have garnered significant interest for their potential to deliver enhanced performance, particularly in environmental aspects. This study investigates the performance of such engines within a co-generation framework for simultaneous power and cooling production. Low reactivity fuel for the engine is derived from solar steam reforming of methanol, with waste heat recovered through a supercritical CO2 cycle and an absorption refrigeration cycle. The designed configuration undergoes comprehensive analysis encompassing thermodynamic, economic, and exergoenvironmental assessments, including parametric analysis. Optimal engine performance is evaluated through computational fluid dynamics, thermodynamic, and exergoenvironmental analyses across various syngas compositions and reforming conditions. Results indicate that a syngas portion of 60% at a reforming temperature and CH3OH to H2O ratio of 200 °C and 1.2 yields optimal engine performance. Besides, the inlet temperature of the CO2 turbine exhibits the greatest impact on co-generation performance. At the optimal state, co-generation's power and cooling load generation reach 467.8 kW and 225 kW, with a unit cost of 53.89 $/GJ, an exergy efficiency of 38.14%, a sustainability index of 1.622, and an exergoenvironmental impact index of 1.607.

Thermodynamic analysis and performance optimization on an ultra‐low‐temperature cascade refrigeration system using refrigerants R290 and R170

AbstractTo meet the strict requirement on whole chain of vaccine production, storage, transportation, and distribution, most researches have been done on cascade refrigeration systems to achieve high operation performance, while a research gap on the performance exploration of eco‐friendly refrigeration systems still exists. In this paper, a comprehensive thermodynamic model was established to analyze the operation performance of a pre‐cooled cascade refrigeration system with eco‐friendly refrigerants propane (R290) and ethane (R170). Based on the present thermodynamic model, the performance optimization on the R290‐R170 cascade refrigerator was made with considerations of degree of subcooling, degree of superheat, evaporation temperature, condensation temperature, cascade condensation temperature, and cascade temperature difference. Variations of the coefficient of performance, exergy destruction, and total exergy efficiency of the refrigeration cycle were analyzed. Two mathematical correlations yielding the optimal cascade condensation temperature and maximized coefficient of performance were developed by multilinear regression analysis. When the evaporation temperature is − 60°C, the maximized coefficient of performance and total exergy efficiency are 1.276 and 49.51%. This paper demonstrates the potential for improving the R290‐R170 cascade refrigeration system and furnishes the basis for further exploration on ultra‐low‐temperature refrigerators.

Energy, exergy, and economic analysis of a novel solar-assisted ejector subcooling CO2 transcritical refrigeration systemt

To further enhance the performance of transcritical CO2 refrigeration cycle (base cycle), a solar-assisted ejector subcooling transcritical CO2 refrigeration cycle (SESRS) is proposed. The base cycle is subcooled utilizing a solar-assisted ejector refrigeration cycle. This research performed energy, exergy, and economic evaluations of SESRS utilizing the eco-friendly refrigerant R152a in the ejector cycle based on the established model. The thermodynamic analysis results demonstrate that SESRS outperform the base cycle. At typical working conditions, the COPm of the SESRS demonstrates a 22.96 % increase compared to that of the base cycle. Although the total cost of the SESRS is 7.98 %–17.9 % higher than that of the base cycle when subcooling degree is 5 °C, the enhancement of COPm is larger and is increased by approximately 18.34 %–26.22 %. The impact of subcooling degree and other parameters on system performance are also investigated. Overall, this study confirms the potential of the SESRS system for utilization in the refrigeration and air-conditioning fields. Considering both the system’s performance and economy, further optimized analysis should be done on key operational parameters, such as subcooling degree and discharge pressure.

Performances Study of Eco-friendly Binary Azeotropic Mixtures Used as Working Fluid in Three Refrigeration Cycles

According to the European (F-gas) regulation, all refrigerants with a global warming potential (GWP) above 150 will be out by 2030. Searching for alternative refrigerants that are environmentally friendly has become an urgent challenge for the refrigeration and air-conditioning sector. Based on their environmental advantages and good thermo-physical properties, azeotropic mixtures have recently gained special interest as substitutes for conventional refrigerants. This study aims to compare the performance of three eco-friendly azeotropic mixtures with the common refrigerant R134a in three refrigeration cycles: the basic cycle (BC), the ejector-expansion refrigeration cycle, and the ejector sub-cooled cycle. The mixtures under study are R1234ze+R600a, R1234yf+R600a, and R1234yf+R290. These mixtures have global warming potential (GWP) of 5.668, 3.8688, and 3.2865 respectively, whereas R134a has a GWP of 1430. To reach this objective a numerical program was developed using MATLAB software to evaluate the coefficient of performance (COP), and the cooling capacity of the three refrigeration cycles using the studied eco-friendly mixtures and were compared with those of the commonly used R134a refrigerant. The entrainment ratio was also compared for the two ejector cycles using these refrigerants. The simulation was realized for condensing temperatures (Tc) selected between 30 and 55°C and evaporation temperatures (Te) ranging between -10 and 10°C. The results have shown that the eco-friendly azeotropic mixture R1234yf+R290 (GWP=3.51) has the best performances compared to the two other mixtures and they are close to those of R134a. On the other hand, the ejector expansion refrigeration cycle has exhibited a high coefficient of performance compared to the basic cycle and ejector sub-cooled cycle, and a high entrainment ratio compared to the ejector sub-cooled cycle for all used refrigerants. However, the ejector sub-cooled cycle gave a better cooling capacity than the other cycles. According to the obtained results, the azeotropic mixture R1234yf+R290 apart from its excellent environmental properties yields better performances in most of cases, this confirms that it could be a suitable substitute for conventional working fluid R134a which has a great global warming potential.

ABSORPTION REFRIGERATION SYSTEMS FOR WASTE HEAT RECOVERY AT THE SILICATE INDUSTRY

The glass, ceramic and cement plants are energy intensive industrial systems, releasing high amounts of greenhouse gases. The dissipation of the waste heat reduces their profitability, energy and ecological efficiency. The absorption refrigeration systems are successful solutions for the recovery of thermal energy at different temperature levels to obtain useful cooling and heating powers for technological needs, and for air conditioning of administrative and industrial buildings. Although the absorption units in a heat pump and refrigeration cycle are currently used in building and industrial systems, they have not yet penetrated widely into the silicate factories. This paper discusses possibilities for the applications of basic types of absorption cycles at heat pump and refrigeration modes to utilize waste energy at different temperature levels in glass, ceramic and cement plants. The examined variants are demonstrated via examples, diagrams and analyses of the possible energy saving.

Multi-objective optimization and exergoeconomic analysis of a novel solar desalination system with absorption cooling

This paper presents a novel design for a solar-powered desalination system utilizing a single-effect absorption refrigeration cycle with a flat-plate solar collector. The NH3-H2O working fluid pair in the refrigeration subsystem produces chilled water while the rejected heat from the condenser drives a humidification-dehumidification (HDH) subsystem for freshwater generation. This cycle has been analyzed thermodynamically and exergetically to understand its key performance parameters. Furthermore, for a detailed examination and optimization, an exergoeconomic analysis was also conducted. Design parameters for this study include the tilt angle of the solar collector, Volume fraction of nanoparticles in the CuO nanofluid, Solar collector area, Base fluid mass flow rate in the collector, Mass flow rate of the strong solution, Absorber and condenser temperatures, Mass ratio and Humidifier effectiveness. The Objective functions used to evaluate the system, performance are the Cooling effect of performance (COP), Energy performance (EP), Exergy efficiency (μExe), and the Total product cost rate of the system (Ċp,Tot). The genetic algorithm optimization is employed to find the best system performance using two sets of three objective functions. The effectiveness of multi-objective optimization using LINMAP, TOPSIS, and Shannon Entropy methods is demonstrated. LINMAP and TOPSIS consistently achieved improvements in COP (32–42 %), exergy efficiency (33–48 %), and reduced total cost (89–90 %) compared to the base point, while Shannon Entropy offered slightly lower gains. These methods consistently identify superior system configurations, achieving significant improvements in performance while minimizing the total product cost rate.

Performance analysis of a novel dual exhaust mixed refrigerant heat pump with large temperature lift

The substantial demand for heat energy, ranging from 70 − 100°C in industrial and commercial sectors, presents a significant challenge when utilizing traditional air source heat pumps. The conventional single-stage air source heat pumps often struggle with low system efficiency and poor operating conditions when tasked with heating with large temperature lift. To address these issues, a novel dual exhaust mixed refrigerant heat pump cycle was proposed. By incorporating an intermediate pressure compression stage in parallel, the proposed system can achieve an optimal temperature match in the recuperator, and lead to a significant enhancement in the coefficient of performance (COP). Compared to a single stage mixed refrigerant heat pump cycle, the novel system improves the COP from 5.063 to 5.756, representing an increase of 13.68 %. Concurrently, the exergy loss proportion of the recuperator decreases from 18.8 % to 13.7 %. The proposed system consistently demonstrates superior COP and exergy efficiency regardless of whether the ambient temperature is within the range of 0 °C to 20 °C or the outlet water temperatures between 80 °C to 100 °C are present. These findings provide theoretical guidance for enhancing the performance of high-temperature heat pumps with large temperature lift.

Advanced Dual Mixed Refrigerant (DMR) Natural Gas Liquefaction Plant with Liquid Air: Focus on Configuration and Optimization

This study introduces a novel approach to integrating LNG cold energy into the dual mixed refrigerant (DMR) process, employing liquid air as a cold energy carrier. The DMR process is chosen for natural gas liquefaction due to its flexibility in adjusting mixed refrigerant compositions when external cold sources are utilized. Two configurations are investigated: the low-pressure liquid air (LPLA) process, which relies solely on heat exchange, and the high-pressure liquid air (HPLA) process, which involves the pressurization and expansion of liquid air. Additionally, two optimization strategies are explored: 'With Composition' (WC) optimization, which includes refrigerant composition as a variable, and 'Without Composition' (WOC) optimization, which does not. Utilizing liquid air reduces the load on the refrigeration cycle, leading to improved performance compared to the conventional DMR process. The air expansion generates additional power and cold energy, while WC optimization further reduces the flow rate of low-boiling-point components, significantly lowering compression energy consumption. As a result, the DMR-HPLA-WC process achieves a 44.17% reduction in energy consumption, an 8.7% improvement in exergy efficiency, and a 37.63% decrease in specific costs.

Thermodynamic and technoeconomic limitations of Brayton refrigeration for air conditioning{fr}Limites thermodynamiques et technoéconomiques de la réfrigération Brayton pour la climatisation

With global cooling demand increasing, there is a need for refrigeration cycles that use low global warming potential (GWP) refrigerants. Researchers have flirted with the idea of using the Brayton cycle for refrigeration over the years, but it has yet to prove competitive in performance or cost when compared to the widely used vapor compression cycle. The recent development of an electrochemical Brayton refrigeration cycle has renewed interest in the thermodynamics of Brayton refrigeration. This work provides a parametric study of the COP of a Brayton cycle air conditioner (either mechanical or electrochemical in nature) as a function of the characteristics of the cycle components (thermal conductances and isentropic efficiencies). When the isentropic efficiencies of the adiabatic components (i.e., the compressor and turbine in the mechanical Brayton cycle) are 90%, the cycle COP is limited to a value of ∼1. Furthermore, a thermodynamic comparison to the vapor compression cycle reveals that the Brayton refrigeration cycle generates ∼8 × more entropy, and that the thermodynamic favorability of the vapor compression cycle is due to the presence of phase change.

Improvement of the properties of ionic liquids for the absorption refrigeration cycle

Ionic liquids (ILs), recognized as environmentally friendly green reagents, have good application prospects in many fields. However, their high viscosity has hindered their widespread application. Currently, an effective solution is to introduce a solvent as an additive. In this work, ethanol with different molar fractions was chosen to form working pairs with three ILs ([emim]BF4, [bmim]BF4 and [hmim]BF4), to reduce their viscosities. The densities and viscosities of the three working pairs were obtained in a temperature range of 293.15∼338.15 K, thereby determining the thermal expansion coefficients. The effects of ethanol on the volumetric and viscometric characteristics of the three ILs are discussed. To further analyze the interactions between ethanol and the ILs, excess mole volume and viscosity deviations were introduced. The interactions between different molecules were stronger than those between the same molecules in the working pairs. This is the main reason why the addition of ethanol reduces the viscosity of the three ILs. Finally, the hard-sphere model was applied to predict the viscosities of the working pairs. Upon introducing an adjustable argument, the average absolute relative deviation of the prediction for the aforementioned three ILs decreased to 4.4%, 5.9%, and 5.0%, respectively.

Binary hydrocarbon mixtures of Joule-Thomson refrigeration cycle based for -70°C freezer: Theoretical and experimental evaluation

Binary hydrocarbon mixtures of Joule-Thomson refrigeration cycle based for -70°C freezer: Theoretical and experimental evaluation

Design and optimization of large-scale natural gas liquefaction process based on triple refrigeration cycles

In large-scale natural gas liquefaction, minimizing specific energy consumption has consistently been a primary objective. This study aims to develop a large-scale natural gas liquefaction process that balances energy efficiency and cost-effectiveness, presenting a viable option for industrial production. By employing a refrigerant strategy of “propane + mixed refrigerant + mixed refrigerant”, a novel large-scale natural gas liquefaction process based on triple refrigeration cycles (TRC) is proposed. To address the challenge of boil-off gas (BOG) re-liquefaction, the TRC process is further refined to integrate BOG re-liquefaction (TRC-BR). Thermodynamic models are built for the proposed TRC and TRC-BR processes, as well as the propane pre-cooled mixed refrigerant (C3MR) and AP-X processes as baseline cases. Global optimization is conducted using the Particle Swarm Optimization (PSO) algorithm, with the specific power consumption (SPC) serves as the objective function. The results reveal that the SPC of the TRC and TRC-BR processes are 0.2726 and 0.2704 kWh/kg-LNG respectively. Compared with the C3MR and AP-X processes, the SPC of the TRC decrease by 1.54% and 4.84%, respectively. The total investments for the TRC and TRC-BR processes are estimated at a similar level compared to the baseline cases, demonstrating their significant potential for industrial application.

Impact of the Capillary Tube Length on the Refrigeration Cycle Exergy

Impact of the Capillary Tube Length on the Refrigeration Cycle Exergy

Analysis of HEM applicability for a subcritical flashing ejector at low motive pressure

Validated CO2 ejector models are essential for developing high-performance refrigeration and heat pump cycles. This study focuses on assessing the Homogeneous Equilibrium Model’s applicability to simulate a CO2 flashing ejector at a reduced pressure of 0.47. The model was implemented in FLUENT, integrating a user-defined real gas model. Simulation results with different boundary condition options were compared to experimental data. The analysis was carried out to evaluate the predictive capabilities of the model and assess the experimental data quality. The results indicate that the developed model accurately estimated the motive mass flow rate, with a maximum relative error of 5.7%, showing better performance than previously reported data. The entrained flow rate, assuming double choking operation, was significantly higher than the experimental measurement, and the CFD-predicted wall static pressure underestimated the experimental profile, suggesting single-choked ejector operation. In contrast, the outflow density was better predicted under the same assumption, with an average error of 8.6%. Nevertheless, the simulated temperature profiles showed good agreement with the experimental data, especially when using the experimental entrained mass flow rate as a boundary condition.

Predicting Performance of Air Source Heat Pump System with Virtual Refrigeration Cycle

Predicting Performance of Air Source Heat Pump System with Virtual Refrigeration Cycle

Performance assessment of solar tower collector based integrated system for the cogeneration of power and cooling

Integrating solar energy systems is an essential measure in advancing worldwide sustainability objectives and offers a sustainable, environmentally friendly approach to reducing greenhouse gas emissions and pollutants. To this direction, the proposed system integrating solar tower collector, supercritical CO2, organic Rankine cycle, and single effect absorption refrigeration cycles shows potential as an efficient and sustainable solution for meeting energy and cooling demands. A detailed thermodynamic evaluation has been performed to gain valuable understanding of the energy and exergy performance, enabling the assessment of thermal and exergy efficiencies, exergy destructions, and heat losses. Results show that this study found the thermal efficiency of the proposed system to be 47.35 % for R245fa, 48.59 % for R123, and 52.32 % for toluene. In addition, the exergy efficiency was obtained at 40.99 % for R245fa, 42.41 % for R123, and 46.67 % when toluene is used as a working fluid. With all investigated working fluids of organic Rankine cycle, toluene achieved the highest thermal and exergy efficiency of the proposed power-cooling cogeneration system, while R245fa achieved the lowest energetic and exergetic performance. Among the various ORC working fluids investigated under operating conditions, toluene demonstrated the highest turbine power output (3202 kW), whereas R245fa exhibited the lowest turbine power output (2804 kW). The refrigeration output for all ORC working fluids studied was found to be 988.8 kW. Additionally, the primary contributor of exergy destruction rate in the proposed system was determined to be the solar tower receiver, contributing 73.24 %, 67.80 %, and 66.19 % to the total for the toluene, R123, and R245fa working fluids, respectively.

Numerical Investigation of Two-Phase Shock Waves in CO2 Flows Using a Modified Hertz–Knudsen Model

Abstract Understanding the complex behavior of two-phase shocks in CO2 flows is essential for a variety of applications, including carbon capture and storage () and transcritical refrigeration cycles. This study presents a comprehensive numerical investigation of two-phase shock waves using the multispecies user-defined real gas model in Ansys Fluent. The simulations are performed for de-Laval nozzles, exploring the two-phase shock features for three-dimensional (3D), two-dimensional (2D), and two-dimensional axisymmetric geometries. The nonequilibrium condensation, subsequent evaporation, and denucleation occurring across the shock are modeled through a set of user-defined scalar transport equations implemented within Ansys Fluent. The two-phase computational fluid dynamics (CFD) simulations are carried out in proximity to the critical point where real gas effects are relevant. The CO2 real gas properties are computed using an in-house Python code and integrated into the solver via user-defined functions as external look-up tables. This study provides valuable insights into the physical processes underlying two-phase shocks in CO2 flows and their sensitivity to geometric variations and thermodynamic conditions. The findings contribute to the development and modification of predictive models and optimized designs for systems involving two-phase CO2 flows. The results highlight the influence of geometry configurations and thermodynamic conditions on shock location and intensity, providing comparisons for shock waves occurring in two-phase flows and supercritical single-phase flows.

Anomalous electrocaloric behaviors in (anti)ferroelectrics: a mini-review.

Solid-state cooling, represented by the electrocaloric effect (ECE) in (anti)ferroelectric materials, has emerged as an alternative green refrigeration technology by virtue of its high efficiency and miniaturization and is expected to substitute conventional vapor-compression. Significant progress has been made in developing high-performance EC materials since its revival. However, anomalous EC behaviors are frequently observed, including asymmetric and negative EC profiles, and the physical mechanism behind this is still under debate. Its rationalization is of great importance since full utilization of anomalous EC behaviors could enhance EC strength and/or cooling capacity. This mini-review gives a brief overview of research advances in EC anomalies in (anti)ferroelectrics with the hope of provoking thought on the design of reconstructed refrigeration cycles and superior EC materials for application in solid-state cooling devices.

Experimental comparison of cycle modifications and ejector control methods using variable geometry and CO2 pump in a multi-evaporator transcritical CO2 refrigeration system

To reduce the direct global warming impact of refrigerants in HVAC&R applications, low-global warming potential (GWP) refrigerants, including natural refrigerants, have been extensively investigated as alternatives to hydrofluorocarbon (HFC) refrigerants. Among the natural refrigerants, Carbon Dioxide (CO2) offers several advantages, such as excellent transport and thermo-physical properties, being neither toxic nor flammable, and having a low price and high availability around the world. However, the high critical pressure and low critical temperature of CO2 often lead to transcritical operation, resulting in lower efficiency due to the additional compressor power necessary to achieve transcritical operation relative to subcritical HFC cycles. Therefore, a number of cycle modifications are used to enhance the coefficient of performance (COP) of transcritical CO2 cycles to meet or surpass those of HFC cycles. This paper provides a systematic experimental investigation of four such cycle architectures by employing the same multi-stage, two-evaporator CO2 refrigeration cycle test stand, 3 of these configurations in transcritical and 1 in subcritical conditions. The four cycles architectures included intercooling, open economization, an internal heat exchanger and two different ejector control approaches. Specifically, a variable-diameter motive nozzle and a variable-speed liquid CO2 pump located directly upstream of the ejector motive nozzle inlet were analyzed. Based on the experimental data, the maximum COP improvements are 4.64 % and 9.47 % when the ejector and the internal heat exchanger are used, respectively. The CO2 pump, once successfully stabilized, can control the ejector, increase its efficiency by up to 15 % and increase the cooling capacity to a maximum of 6.2 %. Nevertheless, a reduction in COP is measured when the pump is in use; however, unlike the other three different configurations, it was only analyzed under subcritical conditions.

Enhancing Semiconductor Chiller Performance: Investigating the Performance Characteristics of Ultra-Low-Temperature Chillers Applying a Liquid Receiver

This study investigates the implementation of a cryogenic chiller utilizing a mixed-refrigerant cascade refrigeration cycle (MRCRC). In this setup, R-404A is employed in the high-temperature circuit (HTC), while a mixture of refrigerants is utilized in the low-temperature circuit (LTC). Unlike a conventional MRCRC that operates without a receiver to maintain the composition ratio, this research explores the impact of receiver installation on system performance. Experiments were conducted with and without a receiver to assess performance improvements and device behavior. With a fixed refrigerant charge of 4 kg, the suction and discharge pressures of the LTC compressor remained low and stable after the receiver’s installation. The addition of a receiver significantly reduced the cooling time, with further reductions observed as the refrigerant charge increased. The system achieved evaporative heat capacities of 0.59, 1.76, and 2 kW for refrigerant charges of 4, 7, and 9 kg, respectively. Notably, at the maximum refrigerant charge of 11 kg, the evaporative heat capacity peaked at 3.3 kW. These findings indicate that incorporating a receiver is crucial for enhancing the cooling performance of cryogenic coolers using mixed refrigerants and stabilizing device operation. This contrasts with previous studies that omitted receivers due to concerns over potential alterations in the composition ratio of the mixed refrigerant.