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• Oil retention amount of R32 with PVE oil in compressor suction lines were measured experimentally. • The flow patterns of R32/PVE were observed and the flow mechanism was analyzed. • Horizontal, vertical upward and two inclination pipes were included to investigate the influence of flow configuration. • The existing horizontal flow pattern maps and WWF correlations were not compatible with the flow patterns of R32-PVE mixture. • The effects of mass flux, oil mass fraction and flow orientation on oil retention were discussed. Oil retention characteristic and flow patterns of R32/PVE lubricant oil mixture in compressor suction lines were investigated. Smooth copper tubes with 10.7mm inner diameter and four tube orientations including horizontal flow, vertical upward flow and inclined upward flow with 45° and 60° inclined angles, were utilized as test samples. Saturation temperature and superheat degree were maintained at 7.5°C and 12°C, respectively. The operation conditions of refrigerant mass flux and nominal oil mass fraction covered ranges of 48.5−230 kg•m−2•s−1 and 1−5%, respectively. The oil retention amount was measured by the remove and weight technique. Based on the visualization technique, flow patterns of R32/oil mixture were also observed, identified and analyzed. The characteristic of flow patterns was greatly influenced by the thermophysical properties of refrigerant-oil mixture. Comparisons of existing flow pattern maps and wet wall fraction correlations were conduct to investigate the applicability. The experimental result showed that oil retention in suction lines increased with the decrease in refrigerant mass flux and increase in oil mass fraction. The oil retention amount of 60° inclination suction line was slightly higher than that for 45°. Additionally, the difference of oil retention among the four configurations becomes limited at high mass flux conditions. [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]

• A novel advanced cascade refrigeration system incorporating three-stage is proposed. • Flash tank and suction line heat exchanger implemented in HTC and MTC respectively. • Exergy, Energy and Economic analysis has been conducted under various conditions. • Conventional and proposed triple cascade refrigeration system is compared. Ultra-Low Temperature (ULT) solutions have been researched in response to the rising demand for energy-efficient and environmentally favorable refrigeration systems. This study addresses a significant research void in ULT refrigeration technology by introducing a novel 'Advanced Three-Stage Cascade Refrigeration System' (ATCRS) with a flash tank and suction line heat exchanger. In the high, medium, and low-temperature circuits, respectively, the system employs m-Xylene, Toluene, and 1-Butene as refrigerants. Through a comprehensive thermo-economic analysis and Python simulation model evaluation, the proposed ATCRS demonstrates superior performance in comparison to conventional Triple cascade refrigeration systems (TCRS), thereby demonstrating improved cascade refrigeration efficiency. Under identical operating conditions, the ATCRS obtains a remarkable 19.33% reduction in compressor work input, resulting in a 22% increase in the coefficient of performance (COP) compared to the conventional vapor compression refrigeration (VCR)-based TCRS. In addition, an exergy analysis reveals the significant effect of cascade heat exchangers on system losses, with the ATCRS demonstrating a remarkable 19.35% improvement in exergy efficiency. The economic analysis highlights the critical significance of optimizing condenser temperature to effectively reduce operating costs. This novel ATCRS design holds great promise for achieving energy savings, enhanced performance, and cost-effectiveness in Ultra-Low Temperature refrigeration applications, thereby making a significant contribution to the advancement of the field of ultra-low temperature refrigeration. [ABSTRACT FROM AUTHOR]

This paper discusses the experimental results of oil retention amount and pressure drop in the gas line of refrigerant. R410A and polyvinylether oil were used as refrigerant and lubricant, respectively. The experiment was conducted under various pipe inner diameters of 14.1, 17.3 and 26.0 mm, and refrigerant mass flux and oil circulation ratio (OCR) were varied from 40 to 250 kg m −2 s −1 and 0.5–4.0%, respectively. The oil retention amount tends to increase as refrigerant mass flux decreases and OCR increases. The oil retention amount in vertical pipe was higher than that in horizontal pipe. The empirical expressions for predicting the oil retention amount and pressure drop were suggested. The mean absolute percentage errors of each expression for predicting the oil retention amount in horizontal and vertical pipes were 18.1% and 14.1%, respectively, and those for predicting the pressure drop in horizontal and vertical pipes were 22.2% and 20.1%, respectively. [ABSTRACT FROM AUTHOR]

Pressure drop in the suction line of the turbo compressor will affect the pressure in the inlet section of the compressor. Lower inlet pressure will require higher drive power. As a result, energy consumption for compressed air production will be higher because turbo compressors are machines with continuous operation. [ABSTRACT FROM AUTHOR]

• Oil retention amount and pressure drop of R32 with PVE oil in suction line were measured experimentally. • The influences of refrigerant mass flux, oil mass fraction, transport property and flow direction on oil retention and pressure drop were discussed. • Two consolidated databases of oil retention and pressure drop were amassed to conduct comparison and analysis. • Oil retention impact factor was proposed to reflect the oil transport difficulty and it integrated the influences of geometric dimension, working pairs and operation parameters. R32/PVE oil mixture has become a popular working pair of commercial refrigeration/heat pump systems in recent years. This paper presented experimental study of oil retention and pressure drop characteristics of R32/PVE VG68 mixture in the compressor suction lines. The test samples were two smooth copper pipes of horizontal and vertical flow orientations with 10.7mm inner diameter. The oil retention in suction lines were measured based on remove-and-weight technique (RWT). Three conditions of saturation temperature and superheat degree (7.5/12, 7.5/6 and 10/12°C) were tested, in order to obtain different thermophysical and transport properties. Refrigerant mass flux and nominal oil mass fraction (OMF no) were varied with the ranges of 90−230 kg•m−2·s−1 and 1−5%, respectively. The influences of refrigerant mass flux, oil mass fraction, mixture viscosity and flow configuration on oil retention and pressure drop were investigated. The results showed that the oil retention amount tends to increase with the increases of actual oil mass fraction (OMF act) and mixture kinematic viscosity ratio and the decrease of refrigerant mass flux. Two consolidated databases for oil retention and pressure drop of suction lines, which involved five working pairs, were collected from the existing literatures to perform a comparison. Finally, based on analysis of oil transport mechanism, a new dimensionless parameter called oil retention impact factor was proposed to characterize the difficulty of oil transport, which integrated the influences of geometric dimension, working pairs and operation parameters. It showed relatively satisfactory relationship with the oil retention data from the amassed database and the present study. [ABSTRACT FROM AUTHOR]