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• Experimental investigations on the solubility of Propylene and DME in PAG oil. • The form of NRTL and Heil interaction parameters was key to high model accuracy. • Two novel empirical correlations were proposed. • Single coefficient correlation: compact, explicit and robust to low amount of data. • DME most soluble refrigerant followed by Propylene and Propane. This work experimentally investigated the solubility of Propylene and Dimethyl Ether (DME) in polyalkylene glycol (PAG) oil. The solubility experimental data were used to fit different local composition models from the literature, the Wilson and Heil equations, and the Non-Random Two-Liquid (NRTL) model. Two new empirical correlations were proposed to decrease the deviation between experiments and the models. The first correlation used six fitting coefficients and resulted in an average deviation of 1.2 % for Propylene and 2.8 % for DME. The second empirical correlation was proposed with a single solubility coefficient (SSC) and a compact form, which allows solubility to be determined explicitly. The correlation resulted in average deviations from experimental data of 1.6 % for Propylene and 2.5 % for DME. Moreover, the SSC correlation showed performance robustness against the decrease of available data points. The correlation was used to compare the solubility of Propylene and DME with the solubility of Propane. At the same conditions, Propane showed the lowest solubility while DME resulted in the most soluble refrigerant. [ABSTRACT FROM AUTHOR]

Spiral blast freezing is a common unit operation used in food processing facilities for rapidly freezing a variety of foodstuffs. The purpose of a blast freezer is to generate high velocity, low temperature air flow over food products being conveyed within refrigerated enclosures to accomplish the freezing process. However, air flow patterns observed within field operating blast freezers are often suboptimal, resulting in diminished system performance. This paper applies a Monte Carlo simulation technique to a food product freezing simulation in order to identify velocity profiles that optimize the freezing process. A one-dimensional food product model is used to evaluate the interplay between the time variation in the magnitude of the air velocity over food products conveyed through the freezing system and the resulting dwell time needed to achieve a target product core temperature at the blast freezer exit. Temporal heat transfer coefficients derived from field measurements made in a newly installed spiral blast freezer serve as a basis to calibrate the one-dimensional product model. The results of the Monte Carlo analysis show freezing system performance is improved when high and stable air velocities over the product are achieved early in the freezing process dwell time. Air flow patterns within a freezing system that result in high air velocity later in the freezing process dwell time are suboptimal. Field-measured data on a newly installed spiral blast freezer showed this suboptimal air flow pattern and the use of baffling within the spiral enables improved airflow leading to an estimated 10 % increase in production throughput. [ABSTRACT FROM AUTHOR]

This paper analyzes the developing adiabatic two-phase flow after an expansion valve in an air conditioning system. R245fa and POE 32 mixture is used as the working fluid. The developing two-phase flow patterns are visualized in an 8 mm straight tube after the expansion valve from 15 to 595 mm. To explore the effect of fluid properties on the developing two-phase flow, the experimental results from previous research by the same authors are compared with those of R245fa in this paper. An image analysis technique and a one-dimensional developing two-phase flow model proposed in a previous paper by the same authors (Yao & Hrnjak, 2023c) are applied to both R134a and R245fa. The flow patterns near the expansion valve exhibit some similarities when comparing the two refrigerants. However, a significant contrast emerges in the presence of a greater number of droplets suspended within the vapor phase in the case of R245fa flow. This disparity is primarily attributed to R245fa's higher vapor velocity. Furthermore, R245fa exhibits a shorter developing length than R134a. For fully developed flow, R245fa showcases a more pronounced turbulent behavior, and the transition to annular flow happens at a lower vapor quality in comparison to R134a. All of these distinctions can be adequately accounted for by the proposed model. The developed flow patterns of both refrigerants are compared with some existing flow pattern maps. At last, a new flow pattern map is proposed based on the observed flow patterns in this research. [ABSTRACT FROM AUTHOR]

This paper applies an image analysis technique to quantify the two-phase flow videos after an expansion valve. This method first finds the liquid-vapor interface and then estimates the void fraction and velocity of each phase. This paper also proposes a one-dimensional developing two-phase flow model based on the force-momentum balance. The void fraction of the developing flow predicted by the model shows a similar trend to the quantified experiment data from image analysis: void fraction will decrease and then stabilize as flow develops along the tube. In essence, the change in void fraction and flow velocity is a result of unbalanced force in liquid and vapor phase. This model is also capable of estimating the distance to achieve fully developed flow after an expansion valve. The ability to predict two-phase flow behavior is not only important to the theoretical study of two-phase flow, but also critical to two-phase flow system design to optimize heat transfer and pressure drop. [ABSTRACT FROM AUTHOR]

• Precise predictive models for CO 2 frosting temperature were developed. • Machine learning algorithms of GPR and MLP were utilized for modeling. • The novel models showed excellent results for different natural gas mixtures. • The models provided excellent physical trends under different operating conditions. • The most effective operating factors on frosting temperature were identified. In this study, universal and precise predictive models for CO 2 frosting temperature in different natural gas mixtures were developed employing the machine learning algorithms of multilayer perceptron (MLP) and gaussian process regression (GPR). The models were verified by an extensive databank including 430 experimental samples collected from 7 published sources, enveloping a broad range of conditions in methane/CO 2 binary mixtures as well as the ternary mixtures of methane/CO 2 /ethane and methane/CO 2 /nitrogen. Both GPR and MLP models exhibited excellent predictions with total average absolute relative errors (AAREs) of 0.16% and 0.42%, and R2 values of 99.80% and 99.38%, respectively. The novel models use only 4 simple adjusted parameters, and they were found to be applicable for both binary and ternary mixtures with high precisions. In addition, the effects of each operating parameter on frosting temperature were studied, and the new models showed excellent physical trends. Subsequently, in order to provide more insight about the most effective factors on frosting temperature, a sensitivity analysis based on the present databank was performed. [ABSTRACT FROM AUTHOR]

In low-and middle-income countries, the cold chain that supports vaccine storage and distribution is vulnerable due to insufficient infrastructure and interoperable data. To bolster these networks, we developed a convolutional neural network-based fault detection method for vaccine refrigerators using datasets synthetically generated by thermodynamic modeling. We demonstrate that these thermodynamic models can be calibrated to real cooling systems in order to identify system-specific faults under a diverse range of operating conditions. If implemented on a large scale, this portable, flexible approach has the potential to increase the fidelity and lower the cost of vaccine distribution in remote communities. • Thermodynamic simulations can be used to generate datasets of refrigeration faults. • These time-series datasets can be used to train convolutional neural networks. • This approach can support the cold chain for vaccine distribution. [ABSTRACT FROM AUTHOR]

• 3D moving-boundary model for water solidification in ice cubes is presented. • Experiments were performed in a purpose-built closed-loop wind-tunnel facility. • Ice cube of 145 ml with distilled, mineral, and filtered tap water was evaluated. • Ice cube was modeled as a pyramid trunk and Stefan's formulation was applied. • Deviations within a ± 10% error band were observed for all cases. The present work is aimed at putting forward a three-dimensional moving-boundary model to calculate the water solidification in ice trays subjected to operating conditions typically found in household appliances. To better understand the physical phenomena and validate the model, experiments were performed in a purpose-built closed-loop wind tunnel facility at -23 °C and air flow rate of 10 m³ h−1 using a single volume of 145 ml fed with distilled, mineral, and filtered tap water. The end of the solidification process was identified by monitoring the cooling curves with the aid of seven thermocouples placed within the ice cube. In the numerical front, the ice cube was modeled as a pyramid trunk and Stefan's formulation was applied to each of the domain boundaries so that the ice thickness could be calculated over time. Deviations within a ±10% error band were observed for all cases. A good agreement between the model predictions for the time evolution of the ice cube temperature and the experimental counterparts was also verified. In addition, literature data for the position of the solidification front and the remaining liquid fraction were fairly predicted by the model. [ABSTRACT FROM AUTHOR]

This study concerns to model the flow boiling heat transfer coefficient (HTC) in smooth helically coiled tubes. A dataset including 1035 samples was collected from 13 independent studies, enveloping a broad range of geometrical and operating conditions. The predictive capability of the earlier models was assessed for straight and coiled tubes by the analyzed database that they were not precise enough. Accordingly, a new empirical model based on the least square fitting method (LSFM) was constructed using seven input effective dimensionless factors. It was found that LSFM was not able to describe the complex and nonlinear nature of HTC in smooth helically coiled tubes. Furthermore, the intelligent method of genetic programming (GP) was utilized to obtain more accurate explicit correlation for HTC, which produced an acceptable average absolute relative error (AARE) of 17.35%. Finally, the machine learning approaches of multilayer perceptron (MLP), Gaussian process regression (GPR), radial basis function (RBF) was also implemented to model HTC in smooth coiled tubes. Although all intelligent based models provided excellent results, the GPR model outperformed the others with an average absolute relative error (AARE) of 5.93% for the tested dataset. In addition to the proposed models' performance, the most influential factors in controlling the boiling HTC in coiled tubes were also detected. [ABSTRACT FROM AUTHOR]

• A method of inherent capacity modulation for a linear compressor is proposed. • Experimental validation has been conducted. • The modulation characteristics of a linear compressor using R134a were numerically studied. • The inherent capacity modulation can make the linear compressor meet the cooling load. Conventional refrigeration compressors sized for peak cooling load actually operate at partial load mostly which could cause excessive on-off cycling loss. Linear compressor could overcome this challenge by varying the compressor stroke in response to transient cooling load. The present work establishes a numerical model for the capacity modulation of linear compressor using R134a through changing the input voltage to meet the cooling load. The numerical model contains a linear compressor model (including three sub-models describing the in-cylinder thermodynamic process, the piston mechanical dynamic process and the electrical part behaviour, respectively) and an input voltage modulation loop. Experimental data are collected for the validation of the numerical model. The results show that the capacity modulation, aiming to meet the cooling load within the error of 5%, can be achieved through varying the input voltage while fixing temperatures of heat exchangers. An increased voltage brings increased compressor stroke and mass flow rate in a linear trend with the heat exchanger temperature unchanged. Lower input voltage leads to higher motor efficiency due to lower copper loss. At a fixed condenser temperature and cooling load, the inherent capacity modulation can save energy with evaporator temperature increasing as the power consumption decreases. At condenser temperature of 50 °C, 40 °C and 30 °C, the CoP only changes by 1.5%, 0.9% and 2.7% when the cooling load changes from 100 W to 200 W. The inherent capacity modulation will allow the linear compressor to maintain a high annual efficiency for refrigeration. [ABSTRACT FROM AUTHOR]

• New VLE data for HFC/HFO with R1234yf. • VLE data measured by means of static synthetic method. • VLE data correlated with Peng Robinson EoS. • Azeotropic behaviour for R1234yf + R134a and R152a are observed. Isothermal vapour−liquid equilibrium (VLE) for four binary systems involving R1234yf (R1234yf + R134a, R1234yf + R152a, R1234yf + R1233zd(E) and R1234yf + R1233xf) were measured at temperatures from 278.15 to 348.15 K. The experiments were conducted by means of a "static−analytic" apparatus with phase analysis via gas chromatography, with resulting uncertainties of 0.6 K for temperature, 8 kPa for pressure and a maximum of 0.007 for vapour and liquid mole fractions. The main advantage of the equipment is that vapour and liquid samples are taken from vapour and liquid phases by two capillary samplers (ROLSI®). The Peng Robinson Equation of State is considered to represent the experimental data. If possible, comparison between the new experimental data and prediction with REFPROP 10.0 software are realized. [ABSTRACT FROM AUTHOR]

• The critical properties of R1243zf + R1234yf and R1243zf + R245cb are studied based on a novel method • The critical point is determined via modeling vapor-liquid coexistence points to the combined equations of the scaling law and rectilinear diameters law. • Experimental VLE measurement of R1243zf + R1234yf and R1243zf + R245cb by the static-synthetic method. • The R1243zf + R1234yf and R1243zf + R245cb exhibit near-azeotropic behavior within a temperature range of 293.15 to 353.15 K. • Good agreement is obtained between experimental critical points and predictions from the PR-MC-MHV2 EoS. This work studies two binary mixtures of R1243zf + R1234yf and R1243zf + R245cb which can be possibly used as a long-term alternative refrigerant for heat pumps. We present critical property (critical temperature, pressure, density) and vapor liquid equilibrium (VLE) of R1243zf + R1234yf and R1243zf + R245cb two binaries. The maximum extended uncertainties (k=2) are estimated as U(T) = 0.21 K, U(p) = 0.048 MPa, and U(ρ) = 6.4 kg/m3 for critical property measurement, and U(T) = 0.06 K and U(p) = 0.015 MPa for bubble point measurement. The uncertainty of liquid-phase mole fraction is estimated less than 1.8 × 10−4. The critical property is investigated by a novel method that determines the critical point via modeling vapor-liquid coexistence points to the combined equations of the scaling law and rectilinear diameters law. The VLE of R1243zf + R1234yf and R1243zf + R245cb binary mixtures in the range of 293.45 to 353.55 K are studied by the static-synthetic method which determines the bubble point via the variable volume cell technique. The experimental bubble points are correlated by the Peng-Robinson (PR) equation of state (EoS) with vdW and MHV2 mixing rules. The modeling results are in good agreement with the measured data. The high temperature VLE of the two binary systems is predicted up to the critical point line by PR-MC-MHV2 model with the optimal binary parameters. [Display omitted] [ABSTRACT FROM AUTHOR]

This work has focussed on the development of an accurate method for testing and modelling the reaction kinetics involved in ammonia-salt adsorption reactions, something not achieved consistently to date. A Large Temperature Jump (LTJ) test cell has been developed for testing ammonia-salt reactions in real machine conditions. A Large Temperature Jump (LTJ) test cell has been developed for testing ammonia-salt reactions in real machine conditions. This was used to validate a new approach to modelling the behaviour and simulate the performance of chemisorption machines. A derivation of the heat transfer and thermodynamic equations are presented, and a finite difference model described which has been validated for the adsorption and desorption reactions of ammonia into halide salts within a porous matrix. The model is implemented in a MATLAB® program. Large Temperature Jump (LTJ) tests have been conducted on manganese chloride and barium chloride to validate the model and to identify the physical parameters which characterise the dynamic performance of the sorbent. The manganese chloride and barium chloride were impregnated in expanded natural graphite (ENG) (SGL SIGRATHERM®) board. The ENG board gave rise to practicable samples (31.5 mm OD ø over ½" tube) undergoing a desorption reaction in under 250 seconds with the fluid temperature 15°C above the equilibrium temperature, an order of magnitude faster than observed elsewhere. A new test method has been developed enabling an accurate single heat of reaction to be identified due to reduced hysteresis, which is reported for barium and manganese chloride. The model has been validated using experimental data from LTJ tests of two geometric configurations in radial heat transfer: discs heated/cooled from the outside radius ('tube-side') and annuli heated from the inner radius ('shell-side'). The empirical data obtained is a milestone towards designed and optimised salt generators. [ABSTRACT FROM AUTHOR]

• A mechanistic model is developed to predict two-phase flow distribution in BPHEs. • Vapor distribution is predicted by the phase separation models of two flow stages. • Liquid distribution is predicted by the pressure balance. • The developed model is validated by the experimental results. This paper presents a mechanistic model that predicts two-phase refrigerant distribution in brazed plate heat exchangers. The modeling of two-phase distribution is based on the flow visualization in the inlet header, in which the flow regime is identified to be periodic and one cycle includes two or three flow stages, given a fully developed stratified/stratified-wavy flow is present at the heat exchanger entrance. To predict the vapor refrigerant distribution, this model considers two different flow stages in the inlet header: for the top corner vapor flow, the vapor refrigerant distribution is predicted by the balance between the suction force (radial pressure gradient) and the axial momentum of each phase; for the vapor jet flow, the vapor refrigerant is assumed to be distributed evenly among the channels. The time ratio of the two flow stages is estimated by assuming the irregular large-amplitude rolling waves in the feeding tube, which lead to the vapor jet flow in the header, to have the most dangerous wavelength and their traveling time can be related to the liquid slug frequency. The apparent vapor refrigerant distribution is the time average of the vapor distributions at the two stages. For the liquid refrigerant distribution, it is predicted by imposing an equal total pressure drop for each flow path. The proposed model is validated against the experimental results: quantified two-phase refrigerant distribution, heat exchanger capacities, pressure profiles in the headers, and surface temperature of the sidewalls. [ABSTRACT FROM AUTHOR]

• Thermal conductivity, specific heat and surface tension of PVE VG68 oil were measured. • Models of thermophysical properties of PVE oil and R32/PVE mixture were proposed. • Force balance analysis was performed on oil transport in suction line. • An oil retention correlation with satisfactory accuracy was proposed. Advanced PVE was developed as the coupled lubricant oil for the alternative refrigerant R32 and R32/PVE will be a potential working pair of R32 refrigeration systems. This paper presented modeling study of physical properties of PVE lubricant oil with viscosity grade 68 and R32/PVE mixture. Thermal conductivity, specific heat and surface tension of PVE oil were measured experimentally. New calculation models for properties of pure oil were developed based on the experimental data. Moreover, the solubility, miscibility and viscosity of R32/PVE mixture were also well correlated with the new correlations. Further, a parametric analysis was performed to study oil transport and retention characteristics in compressor suction line, based on the force balance method. A new consolidated database for oil retention was amassed from six existing literatures, including 187 data points. A new correlation for oil retention was established by incorporating influence factors derived from the parametric analysis. The validation result showed that the oil retention correlation exhibits satisfactory prediction accuracy, which achieved mean absolute error of 14.43% and 87.70% of data fell within ±30% error bands. The property models and oil retention correlation could serve as tools to accurately predict oil retention amount of suction line with R32/PVE mixture. [ABSTRACT FROM AUTHOR]

• Three different models were developed to predict the oil retention amount in suction line. • Double circle model was proposed to describe the interface behavior of stratified-wavy flow and annular flow. • New correlations of interfacial friction factor and void fraction were established. • The flow-pattern based method displayed MAE of 9.35% and captured 87.83% of data within ±20% deviation. • Two models were utilized to evaluate minimum refrigerant mass flux, which guarantee that oil can successfully return back to compressor. Modeling study for predictions of oil retention and critical refrigerant mass flux in compressor suction line was presented in the current work. Three approaches were developed for prediction of oil retention amount in suction line, namely, annular flow model, flow-pattern based method and empirical void fraction model. The annular flow model assumed that annular flow exists as the flow pattern, while the flow-pattern based method described the flow behavior of refrigerant/oil mixture by the flow pattern classifications and double circle model. Based on the proposed models, new correlations of interfacial friction factor and void fraction were established. The experimental data for R32 with coexistence oil PVE68 inside horizontal, vertical and inclined suction lines were used as the foundation and validation of the models. The results showed that all the models display satisfying prediction for oil retention. The flow-pattern based method exhibited the best results, which yielded the mean absolute deviation of 9.35% and captured 87.83% of the data within ±20% error bands. Moreover, two models for prediction of minimum refrigerant mass flux were recommended in order to ensure successful oil return. These models could serve as tools for operation optimization incorporating the lubricant oil effect. [ABSTRACT FROM AUTHOR]

• Non uniform temperature in tomato crates arranged in a pallet layer was observed. • Simplified thermal and aroma models were developed and linked together. • Statistical analysis on these models showed acceptable Root Mean Square Error. • Aroma losses when temperature < 12 °C and recovers partially when return to ambient. • Product temperature and aroma evolutions in supply chain scenarios were predicted. Convective cooling/heating experiments were carried out using a device representing a half-layer of a pallet with four crates of tomatoes (var. Cauralina, Solanum Lycopersicum). Air and product temperatures were measured at different positions in the crates, which were exposed to several different ambient conditions in order to study the influence of air velocity, warming/cooling regimes, hole opening area and filming. The experimental results show that the product and air temperatures vary with the distance from the air inlet position. Since airflow rate was varied and controlled using fans equipped with electrical power variation, a correlation between the air velocity and the convective heat transfer coefficient was established. A transient state heat transfer model was developed based on a zonal approach, which considers overall thermo-physical properties for each crate. An aroma model was developed based on three hypothetic first order kinetics. The model takes into account the observation reported in several studies that tomato aroma decreases when the product temperature is lower than 12 °C and the aroma is recovered, but only partially, when the product temperature is higher than 12 °C. Finally, the thermal model was linked with the aroma model to predict the product temperature and the aroma evolution in two examples of supply chain scenario from producer cold room to consumption point. These numerical results show that the tomato variety and the product time-temperature history in a supply chain exert a significant influence on the aroma evolution. [ABSTRACT FROM AUTHOR]

• Four different refrigeration machine models are evaluated. • Implementation of the models in the optimization potential index (OPI) is shown. • Acceptable and adequate baseline values for the OPI scale are proposed. • Performance and optimization potential of refrigeration machines is revealed. • Application of the method is shown on a real field plant as a case study. To investigate and optimize a refrigeration system, the behavior at various operating conditions must be known or determined. The performance and improvement possibilities may then be inferred from measurement data and compared with corresponding performance key figures. These values are typically referred to normal conditions and it is usually unknown which ones represent an adequate operation. However, it is relevant for refrigeration plant operators to have reference values for a large range of operation conditions as a baseline for determining the obtainable improvements. The present work proposes the application of steady-state models of refrigeration machines for increasing the range of applicability of the exergy-based optimization potential index method. Four different modeling approaches are evaluated and discussed: equation-fit, physical lumped parameter, refrigeration cycle and artificial neural network based models. The practical usage of the improved evaluation method is shown for the subsystem refrigeration machine on a real field installation as a case study. With the introduced additional limits for the optimization potential index, the interpretability of the results is increased. The distinction between adequate (technical requirements exceeded), acceptable (technical requirements fulfilled) and inadequate (potential for improvement) operation according to the state of the art in technology is straightforward, which is important in practice. [ABSTRACT FROM AUTHOR]

• A linearized model provides insight into electrocaloric cooling thermodynamic cycles. • Derivations for Brayton, Carnot, and Otto cycles are provided. • Modeling results highlight the importance of efficient charge recovery. • Brayton and Otto cycles can be more efficient than Carnot cycles in practical systems. This paper introduces a linearized model of electrocaloric cooling. The model is derived for electrocaloric Brayton, Carnot, and Otto cycles, and a more practical hybrid constant voltage-charge (HCVC) variation of the Otto cycle. It is then parametrized for a benchmark terpolymer material. Model outputs are used to examine the system performance under each cycle as a function of temperature lift. The impact of electrical charge recovery efficiency on performance is then investigated to provide insight into system optimization requirements. Practical limitations of charge recovery circuits are discussed in the context of heat and work transfer in each cycle leg. Results indicate that electrical charge recovery efficiency greater than 95% is needed to achieve competitive system efficiency and that this is challenging with a Carnot cycle, despite its theoretical optimality. The Brayton and Otto cycles, in contrast, can achieve cooling efficiencies that approach the theoretical maximum. [ABSTRACT FROM AUTHOR]

The numerical geometrical configuration and cooling performances of parallel wire geometry have been investigated in one-dimensional active magnetic regenerator. Based on the actual regenerator, the wires in geometries were primarily arranged in square and triangular array, and worked in cross and parallel flow patterns. Regenerators containing wire bundles with three geometries were evaluated by varying utilization at fixed temperature spans between hot and cold reservoirs. The effects of geometrical parameters on heat transfer performance and friction factor of regenerator were firstly discussed here. Two materials, gadolinium and La(Fe,Mn,Si) 13 H y , have been used for simulating the cooling performance of wire geometry. The numerical results showed that the arrangement of wires did not have influence on the cooling power greatly and the wire geometry could provide a higher coefficient of performance in parallel flow. After optimization, the desirable parallel wire geometry had a porosity of 0.40 and wire diameter of 0.15 mm. When the frequency was 2 Hz and temperature span was 10 K, the maximum cooling power could reach 158.40 W and 100.3 W for Gd and La(Fe,Mn,Si) 13 H y wire geometries, whose coefficients of performance were as high as 13.46 and 14.96 respectively. Comparatively, the cooling powers of commonly used Gd and La(Fe,Mn,Si) 13 H y packed bed were one third lower than those of optimized wire geometriesand the coefficients of performance were lower half. [ABSTRACT FROM AUTHOR]

High pressure miniature air compressor plays an irreplaceable role in some areas such as refrigeration and pneumatic ejection in the fighter. But, as a lot of heat is produced during compression, the cooling system consumes relatively more energy and its volume and weight even exceeds the compressor itself. So, how to design cooling system becomes the key factor. A novel self-air-cooling reciprocating compressor (SACRC) is first proposed in this paper, which can continuously cool the compressor through ingenious structural design without any auxiliary equipment. The SACRC's model is established considering of thermal dynamics and heat exchange characteristics of all the units, which regards the spiral groove in the cooling system as a chamber with compressibility and heat exchange. The characteristics of SACRC are studied by comparative simulation and experiment validation with traditional reciprocating compressor (TRC). The research results showed that the volumetric efficiency and temperature characteristics of SACRC are both improved significantly especially at high output pressure and long working time, which is pioneering significance to further improve the miniaturization of high pressure compressor. [ABSTRACT FROM AUTHOR]

• A mathematical method is developed to simulate the processes of an adsorption chiller. • The simulated outlet temperatures are within ± 0.5 °C of experimental data. • The variations of uptake and bed temperature throughout the cycle are investigated. • Optimum mass and heat recovery durations for different operating temperatures are determined. • A nominal mass recovery may be sufficient for low generation temperature lift. A typical commercial two-bed adsorption chiller using silica gel as adsorbent and water as adsorbate is simulated in the current study. Each of the two beds goes through four processes in one cycle, namely, adsorption, mass recovery, heat recovery, and desorption. A transient lumped analytical model is developed, and the governing equations are solved using the MATLAB® platform. The thermophysical properties of the refrigerant are collected from REFPROP®, which is integrated within the MATLAB® codes. The simulation model is validated with the test results of a commercial chiller manufactured by Bry-Air (Asia) Pvt. Ltd. The cooling capacity of the chiller is 40 ton of refrigeration, and in this study, the simulation results are in good agreement with the test results provided by the manufacturer. The simulation model is then utilized in the present investigation to predict the performance of a typical commercial chiller under various working conditions. The recovery times, the temperatures of hot water, cooling water, and chilled water are varied, and their impacts on the cooling capacity and COP of the chiller are analyzed. The optimum recovery durations are reported for different temperatures, and their effects on the bed uptakes are investigated. The model can be used as an effective means to determine the optimal cycle time with necessary recovery durations for a specific cooling load, with a view to providing the maximum efficiency under specified operating conditions. [ABSTRACT FROM AUTHOR]

Sorption compressors are thermally driven, and unlike mechanical compressors, they do not have moving parts, and therefore do not emit vibrations and are highly reliable. There exist different sorption compressor configurations for different operating conditions and various gases. The current research presents a dynamic numerical model of multi-stage sorption compressors, where each compression stage may consist of several sorption cells, which are connected in parallel. The model is based on a single sorption cell model, which determines the fluid pressure and temperature as a function of the cell's operating conditions and design (configuration, dimensions, and materials). The model is suitable for describing sorption cells with various heating and cooling methods, and for any adsorbent-adsorbate pair. An experimental validation of the model is presented, with three experiments at different operating conditions. Then, a numerical investigation of two different sorption cell configurations, and with several compressor structures is demonstrated, to show the capabilities of the model. The main difference between the configurations is their cooling method: one is internally cooled by a heat transfer fluid, and the other is externally cooled through its envelope. The presented model is suitable for developing sorption compressors for different fluids and applications. [ABSTRACT FROM AUTHOR]

• A new DX-SAHP system with subcooling control is formed by adding two components. • A quasi-dynamic mathematical model of the new DX-SAHP system has been developed. • The simulated results are compared with experimental data of the original system. • The maximum heating COP of the new system occurs with degree of subcooling at 4 K. • The system has better performance with degree of subcooling in range of 2–5 K. As an essential operation parameter of a direct-expansion solar-assisted heat pump (DX-SAHP) system, the degree of subcooling has influence on the thermal performance of the system. Based on the original experimental setup, a throttling valve and a liquid receiver are added at the outlet of the condenser to control degree of subcooling, forming a new system. A quasi-dynamic mathematical model of the new system has been developed to analyze the effect of subcooling on the system performance, and the iterative criterions for the model convergence are degree of superheat and degree of subcooling. The simulation results show that, the heating capacity per unit refrigerant mass is sensitive to the variation of degree of subcooling at the lower degree of subcooling, while the compressor power per unit refrigerant mass is sensitive to that at the higher degree of subcooling. The maximum heating coefficient of performance (COP) of the new system occurs when the degree of subcooling remains constant at 4 K. In the four typical days, the heating COP values of the new system with a constant degree of subcooling of 4 K are 9.13%, 14.35%, 9.42% and 5.73% higher than that of the original system, respectively. Moreover, the parametric study shows that the DX-SAHP system can achieve better performance in term of heating COP by controlling the degree of subcooling in the range of 2–5 K. [ABSTRACT FROM AUTHOR]

• Experimental measurement of VLE data for R1243zf + R1234ze(E) by a static analytical method. • The R1243zf + R1234ze(E) system is a zeotropic system within 283.15 to 323.14 K. • Experimental data show good agreement with the predicted results of PR-MC-vdW and PR-MC-MHV2 models. The environmental performance becomes the critical factor of the selection of refrigerant. 3,3,3-trifluoropropene (R1243zf) and trans-1,3,3,3-tetrafluoropropene (R1234ze(E)) are environmental friendly candidates to replace R134a. Whereas, in the consideration of environmental factor, safety, and energetic efficiency at the same time, none of the pure refrigerants has been proved to be a suitable solution. Mixed refrigerants provide an approach to this problem because the characteristics of refrigerant blends can be optimized for particular applications in the way pure component refrigerant alone cannot be. The purpose of this work is to explore an R1243zf/R1234ze(E) blend which can be possibly used as a long-term alternative to replace hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs). We report the measurements of saturated vapor pressures of R1234ze(E) and R1243zf ranging from 273.17 to 353.13 K, and isothermal vapor-liquid equilibrium of R1243zf + R1234ze(E) systems from 283.15 to 323.14 K. The measurements are performed by static-analytic type apparatus coupled with two electromagnetic capillary samplers (ROLSI®, patent of Armines). The experimental data are correlated by the Peng-Robinson (PR) equation of state (EoS) associated with Mathias-Copeman (MC) alpha function and classical mixing rules. For the comparison of conventional mixing rules and excess free energy (GE) mixing rules models, classic van der Waals one fluid mixing rules and modified Huron-Vidal second-order (MHV2) mixing rules are employed respectively to the correlation of experimental VLE data. The modeling results are in good agreement with the measured data, while the PRMC-MHV2 model exhibits better performance in VLE prediction. [ABSTRACT FROM AUTHOR]

• A parametric convective heat transfer term is used to assess t span & cooling power. • Four major magnetocaloric materials are screened. • Optimal fluid velocity depends on the magnetic transition temperature. A 2-dimensional numerical model of a room temperature operating Active Magnetic Regenerator (AMR) that comprises of a regenerator, hot and cold heat exchangers, heat transfer fluid is developed. The regenerator is made of a magnetocaloric material (MCM) which heats up upon applying a magnetic field, H, and cools down when the field is removed; thus, making it the most essential part of an AMR. The model takes experimentally measured ∆T ad (H,T) and the C p (H,T) data as input and provides quantitative performance metrics of the magnetic cooling system, such as ∆T span and the cooling load, as output. With this model, it is possible to assess a wide range of MCMs in an AMR. 4 different MCMs were investigated using this model in terms of their ∆T span and the cooling loads—LaFe 10.96 Co 0.97 Si 1.07 , MnFeP (1-x) As (x) and AlFe 2 B 2 and Gd. During the screening of MCMs, all the important operating conditions of the device were fixed such as the fluid flow rate, ambient temperature, cycle duration, magnetic field strength. Our results indicate that Gd exhibits the maximum ∆T span with respectable cooling load, while AlFe 2 B 2 generates the lowest ∆T span. Even though LaFeCoSi compound did not perform as well as Gd, it could be the MCM choice for the realization of magnetic refrigeration on a global scale due to its much lower cost. [ABSTRACT FROM AUTHOR]

• Generalized method presented to predict heat transfer rate and refrigerant temperature of transcritical gas coolers. • Based on the moving-boundary approach to separate supercritical and supercritical liquid regions. • New method shows higher accuracy in the predictions with extremely low computational efforts. • New model presents improved predictions for micro-channel type gas coolers compared to fin-and tube ones. • Source code of the method is provided in Python programming language as an appendix. This paper presents the development of a CO 2 gas cooler model using the moving-boundary (MB) method. The model aims to separate the gas cooler into two regions, supercritical and supercritical liquid, to predict the steady-state thermal heat transfer rate for air-type CO 2 heat exchanger. The model uses the latest correlations for refrigerant and air-side heat transfer coefficients and pressure drops. The experimental results of fin-and-tube type and micro-channel type gas coolers were used for model validation. The mean absolute error (MAE) of the gas cooler heating capacity predictions was approximately 4%, while the predictions of the outlet temperature of the refrigerant side were within ± 3 K. The present MB model also showed an improved computational time of up to 10 times faster compared to a discretized model, which can reduce the overall computational effort in the simulation of detailed transcritical cycle model. [ABSTRACT FROM AUTHOR]

• New VLE data for 5 binary mixtures of hydrocarbons, HFCs and HFOs. • VLE data measured by means of a static analytic method. • VLE data correlated with a Peng-Robinson EoS with Mathias–Copeman α function and classical mixing rules. • Both temperature dependent and independent kij were used. Performances of systems using refrigerants are highly dependent on the selection of the working fluids. In order to guide this choice, the thermophysical properties of these fluids need to be correctly correlated. Experimental data are required for models to work; The knowledge of thermophysical properties of working fluids is required for designing ORC and High Pump (HP) systems. Isothermal vapor-liquid equilibrium (VLE) data for the HFO-1336mzz(E) (trans-1,1,1,4,4,4-hexafluoro-2-butene) binary mixture with HFC-290 (Propane), HFC-134a (1,1,1,2-tetrafluoroethane), HFC-152a (1,1-difluoroethane), HFC-227ea (1,1,1,2,3,3,3-heptafluoropropane) and HFO-1234ze(E) (trans-1,3,3,3-tetrafluoropropene) were measured at 313 K, 333 K and 353 K. The experimental technique used is based on static analytic methods. All of the data (P-x-y) were well correlated with the Peng-Robinson equation of state, associated with a Mathias-Copeman alpha function and classical mixing rules. The results of such modeling are in good agreement with the measured data. [ABSTRACT FROM AUTHOR]

An improved internal structure is proposed to improve the distribution of cooling capacity in refrigerated container. Firstly, a computational fluid dynamics model was established and the fruit stacks was simplified to be porous medium. The flow resistance coefficient was obtained by combining theory and numerical simulation and then verified. Secondly, three baffles were added to reduce the loss of cold airflow by blocking the airflow through air-gaps. The velocity and temperature of the previous refrigerated container and the improved refrigerated container were obtained and compared. The cold airflow distribution in the improved refrigerated container is more uniform. The improvement of vertical velocity in all stacks is in the range of 5.24% – 425.04%. The cooling performance of the two refrigerated containers were also obtained. The variation of temperature distribution is within ±1 °C and the cooling time is also reduced by at least 22.9% in the improved refrigerated container. Finally, the proposed structure showed good applicability for different fruits and vegetables. For all produce tested, the decrease ratio of temperature rise in the improved refrigerated container relative to the previous refrigerated container ranges from 34.0% to 59.5%. [ABSTRACT FROM AUTHOR]

• Adsorption beds made by finned tube heat exchangers packed by silica-gel grains. • Heat and mass recovery cycles were combined with the system. • A lumped analysis for coupled heat and mass transfer model is carried out. • The effect of various fin configurations on the chiller performance is investigated. Adsorption refrigeration systems are commercially matured due to the need of decreasing electrical power consumption and usage of non-environmental refrigerants, which are the main problems of the conventional refrigeration systems. This paper presents an investigation on the performance of small-scale two-bed adsorption chiller combined with heat and mass recovery cycles with the aid of a lumped analytical simulation technique. This model is applied to analyze the effect of fin design parameters on the heat transfer inside the bed and system performance. The working pair used in the simulations is RD silica gel–water. Defining a base-case for the fin design parameters, fin thickness, fin radius, and fin spacing are changed and the performances of four fin configurations are demonstrated. Decreasing the fin spacing enhances the heat transfer significantly. For optimum operation condition, specific cooling capacity is improved by an average value up to 147.6% by decreasing fin spacing from 4 mm to 2 mm, while increasing the fin radius decreases temperatures of the adsorbent. Specific cooling capacity is improved by an average value up to 44% by decreasing fin radius from 16 mm to 8 mm. The fin thickness has a minor effect on heat transfer in the bed. [ABSTRACT FROM AUTHOR]

Isobutane flows through electronic expansion valves with hydraulic diameters smaller than 0.19 mm are analyzed in this paper. First, three similar valves but with different orifice sizes were tested with nitrogen to establish the operational envelope in terms of volumetric flow rate and opening ratio. Two valves suitable for household refrigeration were then selected and tested with isobutane under conditions typically observed in practice. To this end, a purpose-built set-up capable of operating with condensation and evaporation temperatures between 25 and 45°C and −28 and −10°C, respectively, was constructed. In order to check for choked flow, performance curves for the mass flow rate were obtained for several opening ratios by varying the backpressure up to values closer to the condensation pressure. The nitrogen results revealed that the largest orifice valve can behave similarly as 3 m long capillary tubes with inner diameters between 0.40 and 0.85 mm. Concerning the isobutane tests, it was found that the valves are nearly insensible to the inlet sub-cooling and that the flow is likely to be choked for household refrigeration conditions. It was observed that the choking pressure ratio is not affected by the inlet pressure, being a function basically of the valve opening. Finally, a π-type correlation was proposed for the flow coefficient, putting forward a model for predicting the valve mass flow rate. An agreement between experiments and model predictions was achieved with 94% of the 138 points within 15% error bounds. [ABSTRACT FROM AUTHOR]

This paper comes out with an experimental investigation of the expansion of refrigerant HFC-134a through adiabatic capillary tubes with internal diameters ranging from 0.23 mm to 0.53 mm aiming at the so-called mesocooling applications. To this end, an experimental apparatus was designed and constructed to emulate the operating conditions of mesoscale refrigerating devices, with condensing pressures ranging from 9 to 19 bar, and inlet refrigerant subcooling ranging from 5 to 10 K. The tube length was varied from 1 to 2 m. The tests were carried out following a factorial design. The experimental data were used to assess the mass flow rate prediction capabilities of an explicit, algebraic model for adiabatic capillary tubes devised in a prior work. The results revealed that the model is not suitable for small-bore capillary tubes. Correction factors were proposed, so that the model predictions for more than 90% of the experimental dataset fell within ±10% error bounds. [ABSTRACT FROM AUTHOR]

• Evaporative pads applied to gas cooler are very effective to reduce energy use. • Subcooling by chilled water from HVAC is as effective as parallel compression. • Evaporative gas coolers are a promising solution also in hot and humid climates. Subcooling methods at the exit of the gas cooler in transcritical CO 2 commercial refrigeration systems have been studied in the recent years showing that overall remarkable improvements can be obtained. Another strategy that results efficient is the use of evaporative systems at the gas cooler (adiabatic cooling) as it allows to significantly reduce the refrigerant quality at the liquid receiver and to lower the heat rejection pressure. In this work, a fully instrumented CO 2 transcritical booster system with parallel compression, in operation in a small size supermarket in northern Italy, made available measured data of its performance when subcooling and/or adiabatic cooling are active. The plant operates in a mild climate, where it suffers operation at transcritical conditions for most of the year. Subcooling in this plant is performed by coupling the refrigeration system with the HVAC system. Taking advantage of experimental measurements, a model in the TRNSYS environment is validated and allows the prediction of the annual plant performance when these strategies are adopted. The adiabatic cooling showed to allow a significant reduction (about 10%) in the energy use, and makes unnecessary the use of a parallel compressor. Subcooling by the HVAC gives rise to a reduced saving (2.9%) due to the absence of a dedicated mechanical subcooler, however it is almost comparable to parallel compression. These trends are confirmed in two other hot and humid climates. [ABSTRACT FROM AUTHOR]

• Novel mathematical model to predict the heat transfer rate of skin condensers. • Experimental validation with eigth hot-wall condenser designs. • Adhesive tape has the strongest impact on the heat exchanger performance. This paper comes out with an investigation of the thermal performance of skin-type hot-wall condensers for household refrigeration applications. Eight different hot-wall condensers were manufactured and installed in identical refrigerators. The condenser samples were constructed by varying the following design parameters: (i) adhesive tape (aluminum or polyethylene), (ii) tube O.D. (4.00 or 4.76 mm), (iii) total length (10 or 11.5 m) and (iv) condenser positioning. The refrigerators were placed inside a climate-controlled chamber and tested in steady-state conditions. A mathematical model that takes into account the heat transfer not only to the surroundings but also to the refrigerated compartments was also put forward. The model predictions were compared to the experimental data when deviations within the ±10% bounds were achieved. It was found that the adhesive tape thermal conductivity and the tube-outer sheet contact area have the strongest impact on the condenser performance. It was also found that the polyethylene tape increases the condensing pressure, due to its low thermal conductivity and thus to the smaller useful heat transfer area. It was thus concluded that the refrigerator foaming process must be carried out with an extreme care to avoid any negative impact on the tube-outer sheet contact resistance. Finally, it was noted that the heat transfer to the refrigerated compartments is directly affected by the condenser positioning and the thermal insulation thickness. [ABSTRACT FROM AUTHOR]

• The ejector performance is very sensitive to its dimensions. • Ultimate performance is achieved only if the ejector is double chocked. • Optimum ejector size depends mainly on the system operating conditions. • R1234yf is confirmed to be a promising substitute to R134a in ejector systems. Vapor jet refrigeration system has been a promising research topic by far. This system bears such importance due to using low grade energy instead of the less economical high grade energy necessary for driving the conventional vapor compression refrigeration cycles despite the low COP values. The main purpose of the present work is to introduce a mathematical model to optimally size the single phase supersonic vapor ejector and to give a detailed picture on how the system operating conditions affect the main dimensions of the optimally operated ejectors. On the other hand, this paper is a predesign study of the operating conditions effect on the system performance parameters like the COP, entrainment and area ratios. The model is validated with experimental data mentioned in the literature and it gives high trusted results. Moreover, the model is general as it can be used with any refrigerant. However, the present results belong to the environment friendly hydro-fluoroolefin refrigerant (R1234yf) which will be increasingly adopted and a potential alternative for the currently used hydroflourocarbon (HFC) R134a. [ABSTRACT FROM AUTHOR]

A novel generalized framework is presented that can be used to simulate the quasi-steady-state performance of a wide range of positive displacement compressors and expanders (scroll, piston, screw, rotary, spool, etc.). The complete simulation algorithm is described, and an emphasis is placed on the numerical methods required to obtain robust behavior of the simulation. This formulation has been implemented into an open-source software package entitled PDSim written in the Python language. PDSim is the first open-source generalized compressor and expander simulation package and the complete source code is included in the Supplemental material. A piston expander is used as an example of the utilization of this framework. The framework has been applied to several positive displacement machines in the companion paper in order to demonstrate the flexibility of the approach (Ziviani et al., 2019). [ABSTRACT FROM AUTHOR]

Linear compressor technology is characterized by the absence of a crank mechanism, which has gained increasing attention in vapor compression systems due to its compactness and lower friction losses in comparison to conventional reciprocating compressors. Limited work was found in the open literature related to the development and in-depth validation of a comprehensive linear compressor dynamic model that couples thermodynamic aspects with both mechanical and electrical sub-models. This paper presents a comprehensive and generalized simulation model that is used to simulate the dynamic performance of a linear compressor. The model is based on mass and energy balance equations applied to open control volumes. The overall model is composed of several sub-models including the piston dynamics, electrical motor, valve dynamics, and leakage flows. The thermodynamic model and the sub-models are integrated into a compressor overall energy balance that describes the different heat flows and losses. The linear compressor model is able to predict both transient and steady-state behaviors of the piston movement, internal pressure and temperatures as well as the overall performance. Comparisons of predicted and measured mass flow rates as a function of operating frequency are also presented within this work. [ABSTRACT FROM AUTHOR]

• The aim is at characterizing the performance of small variable-capacity compressors. • The model was built upon the first-principles and calibrated with experimental data. • 35 crankshaft compressors with strokes ranging from 2 to 20 cm³ were modelled. • Prediction errors within 10% bounds were observed for 95% of the dataset. • The approach is also suitable to variable-displacement oil-free linear compressors. This paper presents a semi-empirical modelling approach for predicting the performance characteristics of variable-capacity crankshaft and linear reciprocating compressors for household and light commercial refrigeration applications. The model is built on thermodynamic grounds, and its key parameters are calibrated using experimental data. A total of 33 crankshaft compressors were used for validation purposes, being 26 single-speed and 7 variable-speed, with strokes ranging from 2 to 20 cm³. For conventional single-peed compressors, approximately 97% of the mass flow rate and 93% of the power consumption data presented errors within the 10% thresholds. For variable-speed compressors, more than 95% of the datapoints presented absolute errors lower than 10% for both power consumption and mass flow rate. In addition, the proposed approach was employed to predict the performance of a linear oil-free compressor with variable-displacement capacity control, showing errors for performance characteristics within the range of the experimental uncertainties. [ABSTRACT FROM AUTHOR]

We have published vapor liquid equilibrium data (VLE) for the binary mixture of CO2 + R-1234ze(E) (trans-1,3,3,3-tetrafluoroprop-1-ene) in International Journal of Refrigeration, Volume 98, February 2019, Pages 362-371. In this paper, we presented Gibbs Ensemble Monte Carlo simulation data performed at 293.15 K and 353.02 K. It just so happened that there was a mistake in one of the initial configurations at 353.02 K and the results were not correct. We present here corrected MC values and we compare the results with Peng Robinson EoS calculation and REFPROP predictions. [ABSTRACT FROM AUTHOR]

• Coil model with no cross fin-conduction has increased bias to underpredict capacity. • The addition of cross fin conduction to the model reduces the amount of bias. • Cross-fin conduction is important in coil when its system(s) is inactive. • It increases with increased difference in air and water temperatures at coil inlet. Modeling of heat exchanger coils is an important step of developing predictive simulation platforms which allow for a model-based design of new equipment. These simulation models, if accurate enough, the experimental iterations needed during new product development, will reduce overall development cycle time and cost. Fin-and-tube heat exchanger coils are used extensively in residential and commercial heating, ventilation, and air-conditioning (HVAC) systems. Many of the current state-of-the-art heat exchanger models do not account for cross-fin conduction between tubes and struggle with a predictive accuracy of the coils under a non-uniform air flow and especially with a large temperature difference between the adjacent tubes. This paper presents a detailed segment-by-segment model of a fin-tube heat exchanger that calculates the conduction between all the adjacent tube segments through the fins (e.g. "cross-fin conduction"). The physics of the model includes both refrigerant and air side phase change transitions as well as the ability to account for air and refrigerant flow maldistribution. The model's predictions are compared against experimental results collected from an industrial heat exchanger test facility for an air-to-water heat exchanger. A preliminary set of results confirm that cross-fin conduction between heat exchanger tube segments accounts for significant discrepancies in predicted coil performance, particularly with a large temperature difference between the adjacent tubes. [ABSTRACT FROM AUTHOR]

In order to solve the problem of poor regeneration performance of the solar solution dehumidification air conditioning regeneration system under high temperature and high humidity weather conditions. In this paper, a novel vacuum membrane distillation (VMD) solution regeneration method was proposed for a solution desiccant air conditioning system, and a theoretical study of this novel regenerator is performed. Through the analysis of heat and mass transfer, the mathematical model of VMD regeneration is established, and the mathematical model is verified by experiments. The results indicated that VMD regenerator not only could increase the regenerate rate but also could exhibit higher energy utilization efficiency. At the same concentration, the VMD regenerator has a higher regeneration performance, and the regeneration rate is 1.6–2.4 times that of the internal heat type regenerator, and the 4.5–6 times that of the adiabatic regenerator. [ABSTRACT FROM AUTHOR]

Highligths • Results from field measurements of a fully instrumented integrated CO 2 booster system in a supermarket in northern Italy are given and analyzed. • A comprehensive model of the refrigeration system, display cabinets, cold rooms and refrigerating unit is presented and successfully validated. • Different levels of integration between the actual CO 2 system and the HVAC are compared. • Conversion to a standalone solution, covering full space heating, air-conditioning and DHW requests is feasible and gets slight energy savings. Abstract A fully instrumented CO 2 trans-critical booster system with parallel compression, in operation in a small size supermarket in northern Italy, made available measured data that allowed monitoring its performance. The entire refrigeration system of the supermarket, i.e. the Commercial Refrigerating Unit, the refrigerated display cabinets and cold rooms, have been modeled in TRNSYS with in-house types for all components. The comparison with the field data available from monitoring the plant allowed to thoroughly calibrate the model, spanning the operation conditions of a whole year. The validated model is a reliable and powerful tool, usable to predict the plant performance in several conditions and to evaluate the feasibility and effectiveness of the integration with DHW/HVAC systems. Measurements and simulations show that, at mild climate conditions, it is possible and effective to fully provide HVAC and refrigeration duties with a single all-in-one unit properly designed and operated. [ABSTRACT FROM AUTHOR]

Highlights • VLE data for the CO 2 + R1234ze(E) mixture were experimentally measured. • VLE data for the CO 2 + R1234ze(E) mixture were obtained by molecular simulation (GEMC). • The experimental data were correlated with the Peng–Robinson EoS, with the Wong–Sadler mixing rules involving NRTL activity coefficient model. • Critical phase behavior data were calculated by power laws with asymptotic behavior. Abstract Isothermal Vapor–Liquid Equilibrium (VLE) data for the binary mixture of CO 2 + R-1234ze(E)(trans-1,3,3,3-tetrafluoroprop-1-ene) were measured using a static-analytic method apparatus at seven temperatures between 283.32 and 353.02 K and pressures up to 7.6 MPa. For temperatures over the critical temperature of pure CO 2 , the critical compositions and pressures of binary mixtures were approximated applying power laws with asymptotic behavior at critical point. The data were well correlated using the Peng–Robinson equation of state incorporating the generalized alpha function, with the Wong–Sandler mixing rules involving NRTL activity coefficient model. The experimental and correlated phase compositions were compared with Gibbs Ensemble Monte Carlo simulation data obtained at 293.15 K and 353.02 K. Though the molecular simulation predictions at low temperature (293.15 K) properly match experimental data, a slight shift appeared at high temperature (353.02 K), and the expected convergence of phase compositions near critical point was not fully observed. [ABSTRACT FROM AUTHOR]

Highlights • Economized vapor injection (EVI) investigated for application in extreme hot climates. • A packaged air-conditioner retrofitted and tested with an EVI system. • EVI system reduced the compressor discharge temperature and improved COP. • A detailed implicit EVI cycle model developed, tuned, and validated. • At 51.7 °C, system optimization increased cooling capacity by 22.3% and COP by 17.3%. Abstract Operating packaged air conditioning systems at extremely high temperature ambient conditions result in severe performance degradation. In this paper, vapor injection (VI) with economization is proposed to improve system performance. An Environmental Control Unit (ECU) operating with R-407C has been retrofitted with an economized vapor injection (EVI) system and experimentally characterized in side-by-side psychrometric chambers. The performance of the EVI system for superheated and saturated injection conditions were compared to the case of without injection at different operating conditions. The results showed that the EVI system reduced the compressor discharge temperature by up to 5° C, and improved the cooling capacity and COP by up to 12.7% and 3.1%, respectively. The experimental data have been used to develop, tune, and validate a detailed steady-state cycle model. At last, the model has been employed to optimize the economizer geometry in order to maximize the system COP under such extreme weather conditions. [ABSTRACT FROM AUTHOR]

Highlights • A thermal transient model (Modelica language) is developed for a display cabinet. • Comparison between experimental and numerical results is presented. • Numerical case studies (load configurations, demand response) are considered. Abstract Open display cabinets are widely used in supermarkets and represent an important contribution to their energy consumption. The present study is related to modeling and experimental characterizations of an open display cabinet in a transient state. The model is based on a simplified zonal approach to determine heat transfer by conduction, radiation and convection within the display cabinet using experimental evaporator outlet temperature as input data. It is used to simulate a fully loaded display case with 5 shelves. The model can be used to predict the dynamic behavior during the on-off process, defrost operations and power failure. The comparison with experimental data obtained on an open display shows a good agreement with simulating results and allows the model to be validated. [ABSTRACT FROM AUTHOR]

Highlights • Quality changes in apple tissue were studied during frozen storage. • Temperature fluctuations significantly affect the apple quality during storage. • The quality data were fitted to first order kinetics. • A developed kinetic model can be used to predict the apple quality evolution. Abstract Apple quality after freezing is affected by temperature fluctuations during cold storage. Ice re-crystallization and sublimation occur slowly at a constant temperature over a long period of storage, and more rapidly during fluctuating temperatures. These phenomena impact fruit quality, thus reducing storage life. To this end, apple tissue samples were frozen and subsequently stored in three different freezers set at −12 ± 3 °C, −18 ± 3 °C, and −23 ± 3°C. In each freezer, three different compartments were created to achieve different amplitudes of temperature fluctuations: (i) low (± 0.1 °C), (ii) medium (± 0.5 °C) and (iii) large (± 1.8 °C). Frost formation, drip loss, color changes and vitamin C (ascorbic acid) content were measured during five months of storage. The results revealed that apple quality was strongly affected by the temperature fluctuations during frozen storage. The kinetic models were calibrated using apple quality data collected at low and large amplitudes of fluctuations. The temperature dependency was successfully incorporated using an Arrhenius equation that integrates the temperature fluctuations. The kinetic models were validated using apple quality data gathered at a medium amplitude of fluctuation. In addition to a kinetic model, a physical model was applied to predict frost formation. [ABSTRACT FROM AUTHOR]

Highlights • A dynamic grey box thermodynamic model is used to model the heat pump components. • A zonal model allows to model convection and thermal stratification in the tank. • An experimental set up is used to evaluate the model accuracy in various conditions. • The developed model allows to accurately predict the energy performance and comfort. Abstract Air Source Heat Pump Water Heaters (ASHPWHs) are efficient and fast-developing sanitary hot water production systems for the building sector. However, it was shown that their energy performance can still be improved. Therefore, a dynamic grey box Modelica based model is developed representing a split type ASHPWH with a mantle heat exchanger. The thermal storage model includes a zonal model to model convection during heat-ups and the heat pump is modeled using the TIL® thermal component library. The model is first compared to dynamic experimental data during 9 heat-up tests under various operating conditions, including low temperature defrosting stages. On such heating periods, the overall mean relative error reached is of 2% for the COP and the maximum temperature error over the height of the tank is less than 1°C. The model is reproducible and can be used to conduct further design based optimization studies. [ABSTRACT FROM AUTHOR]

Highlights • New iterative numerical scheme to solve acoustic field and heat flow in thermoacoustic stacks. • Incorporation of iterative numerical scheme with genetic algorithm for optimization. • Optimum stack length and position, relative to specific wavelength, are near constants, about 0.24 and 0.21, respectively. • Non-dimensional optimum stack spacing and porosity are 2.9 and 0.6, respectively for the thermoacoustic refrigerator. • Parato front is obtained for a range of choices of thermoacoustic stack design. Abstract The main focus of this work is the optimization of a thermoacoustic plate stack in a standing-wave thermoacoustic refrigerator using genetic algorithm. A numerical model of the thermoacoustic stack and its iterative solving process are firstly presented. A comparison to DeltaEC modelling shows that the presented method is effective in predicting the acoustic field and the energy flow. Based on the numerical model, the stack is optimized in terms of four and five variables for both single objective and multiple objectives. In the four-variable models, the length and position of the stack, the plate spacing and the stack porosity are investigated. In the five-variable model, the acoustic frequency is considered additionally. In the single-objective optimization, the objective function is either the cooling power or the coefficient of performance of the stack, and the multi-objective model has two objective functions, namely, the coefficient of performance of the stack and the cooling power. For the optimization, genetic algorithm hybridized by pattern search and implemented in Matlab is adopted. The optimal values of the stack length and the stack position, obtained from the single-objective optimization, agree with those in the published work. The extended multi-objective models present the Pareto optimal, which provides more design choices depending on the preference. [ABSTRACT FROM AUTHOR]

A novel design methodology has been proposed based on the equidistant curve approach for constructing the complete meshing profiles (CMPs) of scroll compressors. The CMPs, including the peripheral profiles and central profiles for both the orbiting and fixed scrolls, can be generated simultaneously by offsetting the midline in the convex and concave direction. Three examples of the CMPs, named the circular arc modified wrap, circular arc add line modified wrap and asymmetric circular arc modified wrap, have been designed and illustrated by using the proposed design method. Geometric models of these three CMPs are established. Effects of geometric parameters of the modified wrap on performance of the scroll compressor are analyzed. The discharge pressure under the same suction volume of the scroll compressors with these three modified wraps are compared using numerical simulation. Results show that the discharge pressure of the circular arc modified wrap is bigger than that of the circular arc add line modified wrap with the same conditions, and the symmetric wrap is better than the asymmetric wrap in terms of the compression efficiency. The proposed design method is convenient to design new types of the advanced CMPs with better thermal and mechanical properties for scroll compressors. [ABSTRACT FROM AUTHOR]

The performance of fan-supplied tube-fin evaporators is assessed in the present paper aiming at identifying the key parameters which affect the cooling capacity under frosting conditions and defrost cycle performance. The analysis was carried out by means of a mathematical model comprised of a frost formation submodel, which was developed by the authors in a prior publication, together with an improved defrosting submodel. A performance evaluation criterion to account for the periodic defrosting, the so-called cooling cycle efficiency, was employed as an objective function for the defrost cycle optimization. The results pointed out that there does exist an optimal runtime which maximizes the evaporator performance even for variable air flow rate conditions. Moreover, it was observed that the optimal runtime rises either by increasing the heat transfer surface (while keeping the fin spacing) or the coil surface temperature, and diminishes by either increasing the power supplied to the heater, or the relative humidity of the inlet air. [ABSTRACT FROM AUTHOR]

A thorough literature review indicates that there is a dearth of modeling studies on the defrosting dynamics of air source heat pumps (ASHPs) due to the complex underlying physics and numerous computation details. In an effort to bridge the research gap, this paper first presents a five-stage hot-gas defrost model which is incorporated into a distributed-parameter heat exchange model integrated with a detailed frost growth model proposed in Qiao et al. (2017). Numerical treatments are then proposed to smooth the discontinuous transition between different defrosting stages, resulting in a significant improvement in numerical robustness. The developed models and the component models described in Qiao et al. (2015a) are applied to construct the system model of an air source flash tank vapor injection (FTVI) heat pump. A dynamic simulation is conducted to explore the transient fluid flow and heat transfer phenomena of the system during the reverse-cycle defrosting (RCD). A detailed description of the resulting physical processes is provided. The simulation results indicate that the energy used to melt the frost accounts for 17.7% of the total energy supply from the refrigerant flow, which is consistent with published experimental data for the efficiency of a typical defrosting process. [ABSTRACT FROM AUTHOR]