Search Results (433)

Improving the thermodynamic and economic performance of industrial refrigeration systems is essential for reducing energy consumption and enhancing cold chain sustainability. This study presents an integrated energy, exergy, and exergoeconomic assessment of a full-scale two-stage ammonia (R717) vapor compression refrigeration system operating under real industrial conditions in Türkiye. Experimental data from 33 measurement points were used to perform component-level thermodynamic balances under steady-state conditions. The results showed that the evaporative condenser exhibited the highest heat transfer rate (426.7 kW), while the overall First Law efficiency of the system was 63.71%. Exergy analysis revealed that heat exchangers are the dominant sources of irreversibility (>45%), followed by circulation pumps with a notably low Second Law efficiency of 11.56%. The exergoeconomic assessment identified the circulation pumps as the components with the highest loss-to-cost ratio (2.45 W/USD). An uncertainty analysis confirmed that the relative ranking of system components remained robust within the measurement uncertainty bounds. The findings indicate that, although the existing NH₃ configuration provides adequate performance, significant improvements can be achieved by prioritizing pump optimization, maintaining higher compressor loading, and implementing advanced variable-speed fan control strategies. Full article

This experimental study comparatively investigates flow boiling performance and mechanisms in open and closed rectangular microchannels (ORMs/CRMs) with a high aspect ratio of 4. Fabricated on a copper substrate and sealed with a transparent window for visualization, the systems were tested using refrigerant R245fa. Experiments spanned mass fluxes from 89 to 545 kg/m²·s and heat fluxes from 6.3 to 218.5 W/cm² at an inlet temperature of 14 °C. Flow visualization reveals that the ORM configuration accelerates the transition from bubbly to slug and churn flow regimes and facilitates a unique stratified flow pattern absent in the CRM. Quantitatively, the ORM enhances the heat transfer coefficient by 4.2–14.1% while reducing the system pressure drop by 11.5–58.6% within the low mass flux range (89–269 kg/m²·s). Conversely, at a high mass flux of 545 kg/m²·s, the ORM’s pressure drop increases substantially by 29.9–246.8%, attributed to significant two-phase losses in the top-gap region. As heat flux increases, inertial forces dominate over gravitational effects, shifting the primary heat transfer contribution from nucleate to flow boiling. The figure of merit (FOM) confirms the overall performance superiority of the ORM at low mass fluxes. This work provides valuable insights and design guidelines for high-performance, high-aspect-ratio microchannel heat sinks in advanced thermal management systems. Full article

The demand for efficient dehumidification in evaporators has become one of the key technical challenges restricting the high-quality development of the refrigerated air dryer industry. To investigate the effects of fin structure on the air-side heat transfer and dehumidification performance of finned-tube evaporators applied in refrigerated air dryers under the operating conditions of 50 °C, RH = 85%, numerical heat and mass transfer models for the air side of evaporators with plain fins and wavy fins were established based on the Ansys Fluent software 2022R1. The study found that wavy fins possess superior heat transfer and moisture removal capabilities. Key performance indicators, including the air-side heat transfer rate (Q), moisture removal amount (Δm), friction factor (f), and the nusselt number (Nu), were all higher for wavy fins compared to plain fins. Building upon this, three types of vortex generators (VGs) were introduced to further optimize the performance of the wavy fins, aiming to balance heat transfer enhancement and flow resistance control. At an attack angle of 30°, the comprehensive performance factor (JF) showed the highest improvement, reaching 43% with the Delta Winglet vortex generators. The 15° configuration also showed improvement, while 45° led to the worst performance due to increased flow resistance. The results indicate that for typical high-temperature and high-humidity environments, the wavy fin is recommended as the preferred choice due to its superior overall performance and simple structure. For applications requiring higher dehumidification capacity, wavy fins equipped with vortex generators can be selected to achieve the most efficient dehumidification. This study provides valuable insights for the design and application of finned-tube evaporators in dehumidification systems under high-temperature, high-humidity conditions for refrigerated air dryers. Full article

Amidst the ongoing global energy crisis, environmental deterioration, and the exacerbation of climate change, the development of renewable energy, particularly solar energy, has become a central topic in the global energy transition. This study investigates a solar photovoltaic thermal (PVT) heat pump system that utilizes an expanded honeycomb-channel PVT module to enhance the comprehensive utilization efficiency of solar energy. A simulation platform for the solar PVT heat pump system was established using Aspen Plus software (V12), and the system’s performance impact mechanisms and engineering applications were researched. The results indicate that solar irradiance and the circulating water temperature within the PVT module are the primary factors affecting system performance: for every 100 W/m² increase in solar irradiance, the coefficient of performance for heating (COP_h) increases by 13.7%, the thermoelectric comprehensive performance coefficient (COP_co) increases by 14.9%, and the electrical efficiency of the PVT array decreases by 0.05%; for every 1 °C increase in circulating water temperature, the COP_h and COP_co increase by 11.8% and 12.3%, respectively, and the electrical efficiency of the PVT array decreases by 0.03%. In practical application, the system achieves an annual heating capacity of 24,000 GJ and electricity generation of 1.1 million kWh, with average annual COP_h and COP_co values of 5.30 and 7.60, respectively. The Life Cycle Cost (LCC) is 13.2% lower than that of the air-source heat pump system, the dynamic investment payback period is 4–6 years, and the annual carbon emissions are reduced by 94.6%, demonstrating significant economic and environmental benefits. This research provides an effective solution for the efficient and comprehensive utilization of solar energy, utilizing the low-global-warming-potential refrigerant R290, and is particularly suitable for combined heat and power applications in regions with high solar irradiance. Full article

Maintaining optimal humidity in livestock buildings during winter is a major challenge in cold climate regions due to the conflict between moisture-removing ventilation and the need for heat preservation. To address this issue, a novel condensation dehumidification system is proposed that utilizes the natural low temperature of cold winters. An integrated energy consumption model, coupling moisture and thermal balances, was developed to evaluate room temperature drop, dehumidification rate (DR), and the internal circulation coefficient of performance (IC-COP). The model was calibrated and validated with experimental data comprising over 150 operational cycles under varied operation conditions, including initial temperature differences (ranging from −20 to −5 °C), air flow rates (0.6–1.5 m/s), refrigerant flow rates (3–7 L/min), and high-humidity conditions (>90% RH). Correlation analysis showed that higher indoor humidity improved both DR and IC-COP. Four machine learning models—Extreme Gradient Boosting (XGBoost), Light Gradient Boosting Machine (LightGBM), Random Forest (RF), and Multilayer Perceptron (MLP)—were developed and compared with a stacking ensemble learning model. Results demonstrated that the stacking model achieved superior prediction accuracy, with the best R² reaching 0.908, significantly outperforming individual models. This work provides an energy-saving dehumidification solution for enclosed livestock housing and a case study on the application of machine learning for energy performance prediction and optimization in agricultural environmental control. Full article

Vaginal microbiome composition has been linked to risk of preterm birth (PTB), a persistent global health challenge. 16S rRNA microbial profiling has identified specific vaginal community state types (CSTs) that have been associated with PTB risk. Diagnostic profiling requires standardised pre-analytical protocols. We evaluated two storage methods and validated a curated, vagina-specific 16S rRNA gene database (VagDB) to enhance annotation. Paired Copan FLOQ swabs from 22 women at high PTB risk were processed for either (a) dry/immediate freezing or (b) Amies-stabilisation/refrigeration. Amplicon sequence variants were generated via 16S rRNA gene (V4) PCR and Illumina sequencing. We assessed diversity, composition, and community state type (CST) allocation. Amies-stabilised samples yielded significantly higher DNA (p = 0.003), but this did not alter species richness, evenness, or community structure. VagDB enhanced species-level resolution. PCoA showed robust clustering by participant and CST (p < 0.001), irrespective of storage; CST concordance exceeded 90%. Routinely collected vaginal swabs in stabilisation medium with an 8–72 h refrigeration window yield reliable data, supporting the integration of vaginal microbiome profiling into clinical PTB risk assessment. Full article

This study investigates a Proxy-Calibration method for modeling Variable Refrigerant Flow (VRF) systems in TRNSYS, addressing the absence of a dedicated simulation component. The approach approximates part-load behavior through indoor-unit combination mapping, utilizing empirical data from a public office building in Seoul. Simulation results were compared with one year of monitored data. While indoor temperature trends showed moderate agreement (R² = 0.68), electricity consumption diverged significantly from actual measurements. The coefficient of variation in the root mean square error (CVRMSE) ranged from 95% to 118% for the boiler and 153% to 590% for the VRF system, indicating a substantial discrepancy well beyond standard calibration thresholds. These findings underscore the limitations of using static performance maps without explicit control logic. Consequently, this study defines the proposed method as an exploratory investigation; while it establishes a procedural framework for approximating VRF operation, rigorous energy prediction requires further refinement through empirical curve fitting and detailed control representation. Full article

Replacing electric water heaters with heat pumps significantly lowers energy consumption and greenhouse gas emissions. Among the refrigerants considered, carbon dioxide (CO₂ or R744) has attracted considerable attention from refrigeration specialists. However, the high operating pressures of R744 can exceed safe limits when heat pump components are exposed to intense solar radiation and elevated temperatures. This study develops a mathematical model for the evaporator of a Direct Expansion Solar-Assisted Heat Pump (DX-SAHP) to analyze pressure behavior when the system is inactive but subjected to solar radiation. The model also examines how these pressures affect component integrity, accounting for the mass of R744 trapped inside the evaporator. Meteorological data from Brazil’s four regions, provided by INMET, were used in the simulations. Simulations were conducted using information from five different cities and up to 10 years of climate data. Results show that for a refrigerant mass fraction of 12%, the maximum pressure reached approximately 122 bar, compared to the manufacturer’s specified limit of 132 bar for the evaporator tubes. Full article

Thermally driven heat pumps primarily use thermal energy to drive a compression cycle. The thermal energy can be waste heat, natural-gas combustion, or solar, helping increase efficiency and reduce greenhouse-gas emissions. We study a thermal compressor heat pump (TCHP) in which Stirling-type thermal compressors (TCs) are heat-driven rather than electrically driven, delivering a nominal heat capacity of 8 kW with CO₂ as the refrigerant. Unlike most existing dynamic models of CO₂ cycles, which focus on electrically driven or single-stage systems, this work targets a heat-driven multi-stage configuration and includes transient validation. Like any vapor compression cycle (VCC), a TCHP requires a dynamic model for control and optimization; its predictive reliability must be validated on experimental data. We therefore describe the test bench and performance expressions, collect steady-state and transient datasets, and derive a hybrid dynamic model: finite-volume (FV) differential equations for slow components and quasi-static submodels (linear regressions and correlations) for fast elements. The contribution of this work is the development and experimental validation of a hybrid FV model for a multi-stage heat-driven CO₂ TCHP. Validation against both steady-state and transient datasets shows good agreement. On 15 steady-state operating points, the model reproduces pressures within ∼1 bar mean absolute error (MAE) and system-level performance (total recovered heat, $CO{P}_{\mathrm{th}}$) within ∼6% mean absolute percentage error (MAPE), with $R^2\gtrsim 0.8$; component heat-rate predictions are within ∼20% MAPE. Under transient step tests on expansion valve openings and burner fan speed, the thermal COP and total recovered heat track within $4\%$ MAPE (up to $R^2=0.96$), pressures within $1.5$ bar MAE, and the evaporator heat rate within 14–$22\%$ MAPE. Full article

Objectives: The aim of this study was to evaluate the stability of azacitidine (AZA) under clinical storage conditions (room temperature vs. refrigeration) to identify practical protocols that minimize waste and improve cost-effectiveness. Methods: AZA solutions (1 mg/mL) were stored at 23 ± 2 °C or 4 °C. Stability was assessed using a validated high-performance liquid chromatography (HPLC) method. Chromatographic separation was achieved on a Hypersil ODS C₁₈ column (250 mm × 4.6 mm, 5 μm) using an isocratic mobile phase of 50 mM potassium phosphate buffer (pH 7.0)-acetonitrile (98:2, v/v) at a flow rate of 1.0 mL/min, with UV detection at 245 nm and a 20 μL injection volume. The method demonstrated specificity for AZA and its main degradation product (DP), with LOD and LOQ of 12.56 μg/mL and 62.8 μg/mL, respectively. Linearity (R² = 0.9928), precision (RSD% < 5 for mid/high levels), and accuracy (mean recovery 96%) were established. Results: Azacitidine degraded rapidly at room temperature, with >85% loss within 24 h. In contrast, refrigeration at 4 °C significantly delayed degradation, with only ~26% loss observed over the same 24 h period. Chromatographic analysis confirmed the formation of a primary degradation product (tentatively identified as the open-ring hydrolytic species N-(formylamidino)-N′-β-D-ribofuranosylurea based on its chromatographic behavior and literature data), consistent with the known hydrolytic pathway. The applied HPLC-UV method offered an optimal balance of specificity and practicality for monitoring this main degradation trend under clinical storage conditions, distinguishing it from more complex techniques used primarily for structural elucidation. Conclusions: The pronounced instability of reconstituted AZA underscores the critical importance of strict adherence to immediate-use protocols. Refrigeration provides only a limited stability window. Based on our kinetic data, maintaining the reconstituted solution within an acceptable degradation limit (e.g., ≤10% loss) at 4 °C would require administration within a very short timeframe, supporting current handling guidelines to ensure therapeutic efficacy and minimize economic waste. Full article

The compression–absorption cascade refrigeration cycle (CACRC) has attracted considerable interest due to its advantages of decreasing electricity consumption and enhancing efficiency of energy utilization. To further reduce irreversibility and improve energy efficiency, the ejector was integrated into an absorption refrigeration subsystem (EA1, EA2) and a vapor-compression refrigeration subsystem (EC1, EC2, EC3) in the CACRC, respectively. Six novel ejector-based CACRC systems (EA1-EC1, EA1-EC2, EA1-EC3, EA2-EC1, EA2-EC2, and EA2-EC3 cascade systems) were developed in this work. A comparative analysis was performed to evaluate the performance of the proposed systems and conventional CACRC using NH₃/H₂O and R41 as working fluids. The effects of the evaporator temperature, generator temperature, condenser temperature, absorber temperature, and the temperature difference across the cascade heat exchanger on COP, ECOP, input power, and total exergy destruction of the system were analyzed. Results show that the proposed ejector-based CACRC systems have better performance than that of the conventional CACRC. The EA1-EC1 cascade system has the superior performance, and the improvements of COP and ECOP are about 7.96% and 10.86% compared to the conventional CACRC. The analysis of exergy destruction for each component in the proposed system shows that the main exergy destruction occurs in the generator, compressor, and absorber. Full article

This study undertakes a detailed computational examination of a direct refrigerant cooling approach for a 50 Ah prismatic lithium iron phosphate (LiFePO₄) battery. We conducted a systematic assessment to determine how the cooling plate’s topological layout and flow orientation influenced key performance indicators, namely thermal homogeneity, heat removal efficiency, and hydraulic pressure loss. Utilizing a validated two-phase flow model with 1,1,1,2-Tetrafluoroethane (R134a), simulations were performed on six distinct serpentine channel designs under a wide range of operating scenarios, covering variations in mass flow rate, saturation temperature, and inlet vapor quality. The simulation data revealed a strong correlation between the cooling plate’s geometric parameters and the system’s thermal behavior. In terms of uniformity, the optimized Case 6 configuration significantly outperformed Case 2, achieving a 76% improvement by narrowing the maximum mid-plane temperature difference from 2.02 °C down to 0.48 °C. A trade-off was observed regarding the mass flow rate: while higher rates lowered the peak temperature by approximately 18%, they simultaneously led to increased hydraulic pressure loss and slight non-uniformity. Similarly, decreasing the saturation temperature improved heat extraction but exacerbated flow resistance. Notably, this study identified an inlet vapor quality of 0.1 as the optimal point for maximizing temperature uniformity. These insights provide a robust theoretical foundation for optimizing the design and operation of compact direct refrigerant-based BTMSs. Full article

In the naval sector, hydrofluorocarbons (HFCs) are the primary refrigerants in use. To face global environmental challenges, international treaties have established stringent regulations aimed at transitioning towards more sustainable alternatives. Natural refrigerants are proposed as valid solutions, with a particular focus on carbon dioxide (R744) due to its very low direct environmental impact and high safety. This paper evaluates the potential of using R744 as a refrigerant for refrigeration systems onboard cruise ships; based on the R744 innovative solutions currently proposed in the literature for cruise ship applications, the aim is to assess whether the transition to R744 would provide advantages in terms of energy performance and total environmental impact compared with conventional systems employing HFCs. The analysis includes a description of the conventional provision and air conditioning systems mounted onboard and innovative technologies utilizing R744 as a refrigerant, proposed in the literature. These systems are numerically analyzed and compared. The numerical results show that the exclusive use of R744 in onboard systems would significantly reduce the direct environmental impact compared with the current HFCs-based configurations. However, when considering the total impact, further technological advancements in R744 systems are required to achieve a reduction in indirect emissions as well. While progressing toward full R744 adoption, some promising pathways are proposed to enhance current system efficiency. Full article

Breakdown of cold-chain integrity drives the persistence of foodborne pathogens in poultry supply chains in warm, mountainous climates. This study used Al-Mandaq (Saudi Arabia) as a model to assess genetic diversity and contamination in bacteria from poultry storage units using 16S rRNA sequencing, VITEK 2, selective culturing, and ISSR/RAPD fingerprinting on 150 swabs. The Salmonella enterica complex comprised 15/29 isolates (51.7%), followed by Escherichia spp. 6/29 (20.7%) and Bacillus spp. 3/29 (10.3%). Five Salmonella serovars were identified: Enteritidis (8), Waycross (3), Minnesota (2), Typhimurium (1), and Dublin (1). S. Enteritidis accounted for 8/29 isolates (27.6%) and predominated among Salmonella in supermarket retail samples in Al-Mandaq. Combined ISSR and RAPD cluster analysis revealed highly clonal S. Enteritidis groupings, consistent with cross-contamination and prolonged survival in refrigeration equipment. In resource-limited settings, the combined ISSR and RAPD approach enhanced identification and differentiation of bacterial contamination sources within refrigeration equipment, providing superior strain-level discrimination compared to single-marker systems and improving epidemiological traceability of cross-contamination events. These results highlight the risk of clonal pathogen persistence in poultry cold-chain environments and the value of integrated molecular fingerprinting for surveillance in challenging climates. Full article

Cis-1,1,1,4,4,4-hexafluoro-2-butene (R1336mzz(Z)) is a highly promising alternative refrigerant, particularly in heat pumps with large temperature lifts. To meet the superheat requirement of R1336mzz(Z), the heat pump system typically requires the installation of an internal heat exchanger, which renders system performance more sensitive to the solubility of the refrigerant in lubricant. Dipentaerythritol ester (DiPEC) is one of the main components of POE lubricants. In this study, the solubilities of R1336mzz(Z) in two DiPECs, dipentaerythritol hexaheptanoate (DiPEC7) and dipentaerythritol isononanoate (DiPEiC9), were measured in the temperature range of 293.15 K–343.15 K. The solubility data were correlated using the non-random two-liquid (NRTL) model; the average absolute relative deviation between this work and values from NRTL model is lower than 2%. In addition, the Henry’s constants of R1336mzz(Z) in DiPEC7 and DiPEiC9 were calculated, and the dissolution potential was compared. Moreover, the mixing thermodynamic properties (such as mixing enthalpy change, mixing entropy change, and mixing Gibbs free energy change) of R1336mzz(Z) dissolving in DiPECs were analyzed. Full article