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Hydrogen, as a sustainable fuel for transportation sector as well as some other heavy industries, should be stored or transferred in liquid phase. To prevent the evaporation of hydrogen in the tanks and the consequent hazards, it is common to lower its temperature below the saturation point known as subcooling of the fluid. When the subcooled liquid hydrogen flows through pipes with higher wall temperatures, the hydrogen can evaporate and flow boiling occurs, resulting in a complex heat transfer behavior of the fluid. In this study, we propose an advanced intelligent model based on the Cascade Forward Neural Network (CFNN) to predict Heat Transfer Coefficient (HTC) of subcooled liquid hydrogen under various flow conditions. Our model leverages on a dataset that is nearly twice the size of the largest previously used in the literature, significantly enhancing its generalization, reliability, and accuracy. The proposed CFNN model incorporates 19 input features, including crucial dimensionless parameters, orientation and thermodynamic condition of the fluid, and characteristics of the pipe that hydrogen flow through to accurately estimate HTC in unseen fluid conditions. The results demonstrate that the proposed model achieves an R-squared value of 0.9978, substantially outperforming the best empirical methods, which have an R-squared value of only 0.8058 for the same testing data. This innovative approach provides a highly accurate and reliable tool for predicting HTC, offering significant improvements over conventional methods and contributing valuable insights for real-world applications in the energy and transportation sectors. • Subcooling hydrogen seems necessary for safe storing in aircraft. • Modelling of heat transfer of LH2 in the pipes is vital for designing the system. • Use of artificial intelligence enables highly accurate heat transfer predictions. • Cascade Forward Neural Network estimates HTC of subcooled LH2 with 99.78% accuracy. • A comparison of findings is made with existing AI models and empirical correlation. [ABSTRACT FROM AUTHOR]

This research discovered that carboxylated cellulose nanofibrils (CNF) with cations of various structures can significantly reduce the number of nucleation sites for methane hydrate formation when compared to distilled water. The electrokinetic potential of CNF in water slightly affects the concentration of hydrate crystallization centers, but it does alter the work of their formation. The energy barrier increases as the absolute value of the electrokinetic potential of nanoparticles decreases. The study of the effect of various CNF salts on the kinetics of methane hydrate formation expands our understanding of the inhibition mechanism of hydrate formation. It's assumed that a significant negative charge prevents the adsorption of like-charged hydrate nucleation centers on CNF. A decrease in the absolute value of zeta potential of CNF due to a change in cation facilitates this process. As a result, nuclei sorbed on colloidal CNF particles are stabilized on the surface, complicating their coalescence and crystal growth. The design of cellulose-based nanoparticles with varying zeta potential will allow the development of a colloid theory for controlling the formation of gas hydrates. [ABSTRACT FROM AUTHOR]

Phase change materials enhance the thermal comfort of buildings by utilizing stored thermal energy. In large air-conditioning systems, ice storage plays a crucial role in managing peak power loads. This experimental study explores the freezing characteristics of deionized water containing suspended iron oxide nanoparticles in spherical containers for cold storage. The synthesized nanofluid phase change material (NFPCM) was investigated for its freezing behavior under surrounding fluid temperatures of − 2 °C and − 6 °C. The uniformity in charging of NFPCM is the unique feature prevalent in the first quarter of the charging, with 50% mass frozen observed. An increased surface heat flux of 200% was achieved using NFPCM at Tsurr = -6 °C. The chiller operational time is optimally reduced by 75% by considering twice the container design's phase change materials. Adding iron oxide nanoparticles and partial charging is suitable for uniform heat transfer for the shorter freezing duration in cooling applications. The novelty of the present study is that the proposed NFPCM nearly nullifies the subcooling effects of deionized water without using nucleating agents. This NFPCM appreciably enhances power competence, yielding large-scale air-conditioning systems' desired economic impact and sustainability. The reported results align with Sustainable Development Goals (7—Affordable and Clean Energy and 13—Climate Action). [ABSTRACT FROM AUTHOR]

This study focused on the expansion rate of steam; the effect on efficiency was investigated experimentally and numerically by varying the expansion rate of steam in the stage, where condensation occurs by varying the flowrate and inlet temperature using a five-stage model steam turbine. The steam expansion rate of the stator blades in each stage was evaluated from the measured wall pressure and total pressure. In addition, the turbine efficiency was evaluated from the measured torque and mass flowrate, and the effect of flowrate and condensing stage can be taken into account for losses caused by condensation. In addition, numerical calculations to account for the effects of nonequilibrium condensation were performed using ANSYS CFX. The numerical calculations were able to show the details of the nucleation situation and the resulting changes in flow patterns. Numerical evaluation of the subcooling loss showed that there was no difference in subcooling loss between different mass flow rates. The steam expansion rate was evaluated from the measurement results, and it was found that there was no difference in the steam expansion rate due to differences in mass flowrate. This corresponds to the numerical result that the subcooling loss does not vary with flowrate. [ABSTRACT FROM AUTHOR]

When the Covid-19 pandemic occured, most of the industries and public facilities were not used properly, but the cooling machines was still used, resulting in large consumption of power and electrical energy. Along with high energy consumption where the availability of energy is running low, savings are needed. As an alternative so that the cooling machine can save energy is to use the subcooling method, namely the addition of a liquid suction heat exchanger on a spiral portable chiller with 29 spirals. Furthermore, the refrigerant used in the portable chiller is R407c. This study aims to determine the effect and effectiveness of Liquid Suction Heat Exchanger on a portable chiller. The results obtained are the coefficient of performance on the non-Liquid Suction Heat Exchanger portable chiller is 4,699 with a cooling capacity of 6,668 kW and compressor performance of 1,419 kW while the portable chiller with the addition of Liquid Suction Heat Exchanger, the Coefficient Of Performance obtained is 5,197 with a cooling capacity of 6,719 kW and compressor performance of 1,219 kW. From the calculation above, the use of a liquid suction heat exchanger in a portable chiller can increase the cooling capacity by 1,97 %.

• Thermodynamic analysis of absorption cooling-assisted CO 2 systems. • Performance enhancement over simple CO 2 system is analysed. • Simple CO 2 system with IHX coupled with DEDHVARS performs better at high T gc. • Enhanced COP and exergy efficiency. Studies have shown appreciable improvements in system performance by subcooling the working fluid in transcritical CO 2 refrigeration systems. The use of a dedicated vapour absorption refrigeration system (VARS) for subcooling the high side working fluid downstream of the heat rejection device is proved to be a viable option. The heat available in the discharged gas downstream of the compressor in the transcritical CO 2 system is used to drive a LiBr-H 2 O VARS. This study examines the performance of an absorption cooling-assisted transcritical CO 2 system. Three different configurations of the absorption system are considered, namely, single effect (SE), series double effect (DE), and series double effect with dual heat input (DEDH). The performance analysis is carried out for gas cooler exit temperatures (T gc) ranging from 30 to 50 °C and evaporation temperatures ranging from -10 to 5 °C. The average COP improvement of the CO 2 system is found to be 29 and 27% using SE and DEDH systems respectively. [ABSTRACT FROM AUTHOR]

• A novel CO2/NH3 cascade refrigeration system with subcooling in LTC and HTC is proposed. • The proposed system is compared with conventional HFC-404A and CO2/NH3 cascade refrigeration systems. • Mathematical models are based on the actual compressors equations. CO 2 /NH 3 cascade refrigeration system is an all-natural refrigeration option which can be specifically designed and gainfully operated for low temperature applications in warm ambient conditions. In the present study, a novel CO 2 /NH 3 cascade refrigeration system with subcooling is proposed and evaluated as an alternative to the HFC-404A refrigeration system, which is typically used for blast freezer applications in the seafood processing industry. The performance of the proposed system is also compared with a conventional CO 2 /NH 3 cascade refrigeration system without any subcooling arrangement. Real compressor specific equations were used to simulate the performance of the systems under various conditions. The proposed system yields 26% higher performance ratio (COP) than the conventional HFC-404A system at the design condition. In addition, the proposed subcooling arrangement enhances COP of the conventional CO 2 /NH 3 cascade unit by around 5%. The system performance is investigated theoretically under various condensing temperatures and subcooling degrees. The annual energy demand and total equivalent warming impact (TEWI) of the proposed system are 15% and 48% lower than for the conventional HFC-404A system which results in significant economic and environmental benefits. Overall, the proposed system exhibits superior energy efficiency and offers a climate and environmental friendly alternative to the conventional environmentally harmful systems within the seafood industry. Adoption of such energy efficient all natural and clean refrigerant technology is crucial for the future phase out of hydrofluorocarbon (HFC) fluids, as ratified in accordance with the Kigali Amendment to the Montreal Protocol in India and other tropical countries. [ABSTRACT FROM AUTHOR]

The adhesion between a hydrate and a pipe wall is the main cause of hydrate deposition and blockage. In this study, the adhesion strength of semi-clathrate hydrate (tetrabutylammonium bromide hydrate) to four kinds of solid surfaces (E235B carbon steel, E355CC low alloy steel, SUS304 stainless steel, and polytetrafluoroethylene) was measured. This investigation reveals that the adhesion strength of the hydrate to a solid surface is negatively correlated with the wettability of the solid surface, which suggests that hydrophobic materials effectively reduced the hydrate adhesion to the pipe wall. The surface roughness showed different effects on the adhesion of the hydrate to hydrophilic or hydrophobic surfaces. To be specific, when the surface roughness increased from 3.2 µm to 12.5 µm, the hydrate adhesion strength to the hydrophilic surface of SUS304 increased by 123.6%, whereas the hydrate adhesion strength to the hydrophobic surface of polytetrafluoroethylene only increased by 21.5%. This study shows that low wettability and low surface roughness effectively reduce the critical rate required to remove hydrate deposition, which achieves the self-removal of hydrates. At the same time, it was found that the adhesion strength of the hydrate to surfaces increases with increasing subcooling. This investigation holds significant theoretical implications for designing self-cleaning surfaces for oil and gas pipes. [ABSTRACT FROM AUTHOR]

The integration of phase change phenomena through an interface is a numerical challenge that requires proper attention. Solutions to properly ensure mass and energy conservation were developed for finite difference and finite volume methods, but not for Finite Element methods. We propose a Finite Element phase change model based on an Eulerian framework with a Continuous Surface Force (CSF) approach. It handles both momentum and energy conservation at the interface for anisotropic meshes in a light an efficient way. To do so, a model based on the Level Set method is developed. A thick interface is considered to fit with the CSF approach. To properly compute the energy conservation, heat fluxes are extended through this interface thanks to the resolution of a transport equation. A dedicated pseudo compressible Navier–Stokes solver is added to compute velocity jumps with a source term at the interface in the velocity divergence equation. Several 1D and 2D benchmarks are considered with increasing complexity to highlight the performances of each feature of the framework. This stresses the capacity of the model to properly tackle phase change problems. [ABSTRACT FROM AUTHOR]

Phase change material based thermal energy storage has many current and potential applications in the heating and cooling of buildings, battery and electronics thermal management, thermal textiles, and dry cooling of power plants. However, connecting lab scale thermal data obtained with differential scanning calorimetry (DSC) to the performance of large-scale practical systems has been a major challenge primarily due to the dependence of supercooling on the size and temperature gradient of the system. In this work we show how a phase change material's supercooling behavior can be characterized experimentally using common lab scale thermal analysis techniques. We then develop a statistics based theoretical model that uses the lab-scale data on small samples to quantitatively predict the supercooling performance for a general thermal energy storage application of any size, including also allowing for the possibility of temperature gradients. Finally, we validate the modeling methodology by comparing to experimental results for solid-solid phase change in neopentyl glycol, which shows how the model successfully predicts the changes in supercooling temperature across a large range of cooling rates (2 orders of magnitude) and volumes (3 orders of magnitude). By accounting for thermal gradients, the model avoids ~2x error incurred by lumped approximations.

Phase change material based thermal energy storage has many current and potential applications in the heating and cooling of buildings, battery and electronics thermal management, thermal textiles, and dry cooling of power plants. However, connecting lab scale thermal data obtained with differential scanning calorimetry (DSC) to the performance of large-scale practical systems has been a major challenge primarily due to the dependence of supercooling on the size and temperature gradient of the system. In this work we show how a phase change material's supercooling behavior can be characterized experimentally using common lab scale thermal analysis techniques. We then develop a statistics based theoretical model that uses the lab-scale data on small samples to quantitatively predict the supercooling performance for a general thermal energy storage application of any size, including also allowing for the possibility of temperature gradients. Finally, we validate the modeling methodology by comparing to experimental results for solid-solid phase change in neopentyl glycol, which shows how the model successfully predicts the changes in supercooling temperature across a large range of cooling rates (2 orders of magnitude) and volumes (3 orders of magnitude). By accounting for thermal gradients, the model avoids ~2x error incurred by lumped approximations.

Choosing the right phase change material (PCM) for a thermal energy storage (TES) application is a crucial step in guaranteeing the effectiveness of the system. Among a variety of PCMs available, the choice for a given application is established by several key factors, e.g., latent heat, stability, and melting point. However, phenomena such as subcooling—for which PCM cools in a liquid state below its solidification point—can lead to a reduction in the amount of energy stored or released, reducing the TES overall effectiveness, and also in some inaccuracies when modeling the problem. Thus, understanding the effects of subcooling on PCM performance is crucial for modeling and optimizing the design and the performance of TES systems. To this end, this work analyzes the PCM discharging phase in a cold thermal energy storage coupled to a chiller system. A first conduction-based predictive model is developed based on enthalpy–porosity formulation. Subcooling phenomena are encompassed through a control variable formulation, which takes its cue from the operation of a thermostat. Then, thermal properties of the PCM, i.e., the phase change range and specific heat capacity curve with temperature, are evaluated by using differential scanning calorimetry (DSC), in order to derive a second predictive model based on these new data, without including subcooling, for the sake of comparison with the first one. Experimental results from the storage tank confirm both model reliability and the fact that the PCM suffers from subcooling. Between the two numerical models developed, the first one that considers subcooling proves it is able to predict with satisfactory accuracy (RMSE < 1 °C) the temperature evolution on different tank levels. [ABSTRACT FROM AUTHOR]

• Expander-compressor boosted subcooling refrigeration system is proposed. • For different refrigerants optimum increment in COP with respect to conventional system is determined. • Heat transfer surface area of the subcooler is calculated. Many applications have made extensive use of refrigeration systems, which have a high energy requirement. Any improvement on the refrigeration systems can reduce the need for energy demand. A common method to improve the system performance is to subcool the condenser exit temperature and known as subcooling. An expander-compressor booster enhanced subcooling vapor compression cycle is proposed as an addition to the subcooling systems described in the literature. The refrigerant is split into two parts at the condenser exit: one portion expands in the expansion device to reach the necessary subcooling temperature, while the other part goes straight into a separate heat exchanger. Later, this additional refrigerant flows into the other expansion valve, the evaporator, and a booster expander-compressor to increase inlet pressure of compressor. As working fluids, six distinct refrigerants including low global warming potential (GWP) are used (namely R134a, R1234yf, R32, R290, R1270, and R600a) in simulations. The coefficient of performance (COP) and increment in COP values for each refrigerant are computed and graphically displayed for various evaporation temperatures between -10 °C and 5 °C. Furthermore, the heat exchanger analysis of subcooling heat exchanger is performed to compare heat transfer surface area and pressure drop for each refrigerant. Results indicate that R1234yf achieves the greatest performance with an increase in COP by 16.7, 19.1 and 21.8% depending on the mechanical efficiencies of the expander and compressors and as well as isentropic efficiency of the expander. By utilizing an expander-compressor with higher or lower mechanical and isentropic efficiencies, these enhancements can be raised or lowered. Heat exchanger analyses show that the pressure drop in the exchanger does not significantly affect the performance of the system. [ABSTRACT FROM AUTHOR]

In this study, an overview of energy performance was obtained from the comparison of refrigerants (R32 to R1270 and R410a to R1270) in split inverter AC equipment. R32 testing was carried out with temperature settings of 16oC and 27oC while R410a was carried out with temperature settings of 18oC and 27oC. At each temperature setting, the cooling load is carried out under conditions using a heater and without loading. In this analysis, a comparison of energy performance and energy efficiency is carried out using the VDMA 24247-2 standard. The results of this study showed that the refrigeration effect value of R1270 was greater than R32 and R410a in all conditions. For compressor work, R1270 has a lower value than R32 and R410a because the value of ΔP (P2-P1) on R1270 is smaller so that the compressor work in the compression process is lower. In terms of system, the efficiency for R1270 in various conditions for replacing R32 is almost the same while for R1270 for replacing R410a, the highest efficiency is at a temperature setting of 16oC, namely at 100% mass condition. Based on the VDMA 24247-2 standard, the highest total energy efficiency value in R32 is 17.17% while in R1270 with a mass of 90%, 100% and 110% is 18.15%, 21.09% and 21.86%. The highest total energy efficiency value in R410a is 5.44% while in R1270 with a mass of 90%, 100% and 110% is 6.25%, 6.22%, 7.42%. [ABSTRACT FROM AUTHOR]

This paper proposes a NH3/CO2 cascade refrigeration system that sets an auxiliary refrigeration loop in the high-temperature cycle to increase the subcooling degree in the low-temperature cycle (CRSS). Based on the basic principles of thermodynamics, a mathematical model is established and theoretical simulation is carried out to obtain the influence of key parameters on the cycle performance. Compared with the conventional cascade refrigeration system (CCRS), the conclusions find that there exists an optimal condensation temperature of low-temperature cycle (TMC.opt) to maximize COP. The maximum COP of CRSS is 4.58% higher than that of CCRS when the subcooling degree is 10 °C. The maximum exergy efficiency is 0.391, increasing by 4.40%. With the increase of the subcooling degree, both the COP and the TMC.optof CRSS increase. When the subcooling degree increases from 5 °C to 15 °C, the performance increment increases from 2.73% to 6.00%. When the evaporation temperature of the system changes, both the COP and exergy efficiency decreases slightly and it is found that the performance is better when the evaporation temperature is lower when condensation temperature is kept constant. Besides, the discharge temperature of the NH3 compressor in CRSS can be reduced by 9.9 °C when the evaporation temperature is −30 °C.

The current paper presents the design and performance of a high-temperature heat pump (HTHP) integrated in an innovative, sensible, and latent heat storage system. The HTHP has been designed to work between a heat source from 40 to 100 °C and a heat sink above 130 °C. An initial refrigerant analysis has revealed that R-1233zd(E) is the best candidate to meet the required performance and environmental considerations. The first part of this paper deals with the sizing and selection of the main components while discussing the challenges and working limits. A numerical model is also presented and validated. The second part of the paper is dedicated to develop parametric studies and performance maps under different operating conditions. The results show that the current HTHP, at a source temperature of 80 °C, consumes from 3.23 to 9.88 kW by varying the compressor’s speed from 500 to 1500 rpm. Heat production is achieved in the form of latent heat (7.40 to 21.59 kW) and sensible heat (from 6.35 to 17.94 kW). The heating coefficient of performance (COPHTHP) is around 4.

Abstract Exhaust steam condensation equipment is an important component in thermal power generation systems. Direct‐contact condensation offers high heat transfer efficiency, small flow resistance, simple structure, and less scaling; therefore, its application to exhaust steam condensation equipment is conducive to reducing equipment investment and operation costs. In this study, the direct‐contact condensation of subatmospheric pressure steam (exhaust steam) is investigated in a cocurrent flow packed tower. The effects of steam temperature, steam flow, cooling water temperature, and cooling water flow on the condensation rate, subcooling, number of liquid‐phase heat transfer units (NTUL), and total volume heat transfer coefficient (KV) are investigated. The results show that the direct‐contact condensation of exhaust steam can yield a high condensation rate, low subcooling, and good stability in the cocurrent flow packed tower. Lower steam temperature, higher steam flow, higher inlet‐water temperature, and lower water flow are conducive to the increase in NTUL. It is discovered that NTUL and KV can be expressed by dimensionless parameters of flow and temperature, and that the empirical correlations of NTUL and KV agree well with experimental data.

In this work, double rotating active cylinders and slot nanojet impingement are considered for the cooling system of a conductive panel. Colder surface temperatures of the cylinders are used, while different rotational speeds are assigned for each of the cylinders. The impacts of cylinder rotational speeds, size and distance between them on the cooling performance are evaluated. The rotational effects and size of the cylinders are found to be very effective on the overall thermal performance. At the highest rotational speeds of the cylinders, the average Nusselt number (Nu) rises by about 30.8%, while the panel temperature drops by about 5.84 ° C. When increasing the cylinder sizes, temperature drops become 7 ° C, while they are only 1.75 ° C when varying the distance between the cylinders. Subcooling and nanofluid utilization contributes positively to the cooling performance, while 1.25 ° C and 10 ° C temperature drops are found by varying the subcooled temperature and solid volume fraction. An artificial neural network is used for the estimation of maximum and average panel temperatures when double cylinder parameters are used as the input. [ABSTRACT FROM AUTHOR]

Internal, or liquid-suction, heat exchangers are used with the primary goal of ensuring the entry of refrigerant in the liquid phase to the expansion device. The greatest COP gain is primarily determined by the thermodynamic parameters linked to the relative increase in refrigerating effect. Large latent heat of vaporization refrigerants often does not gain as much from condenser subcooling in support of a cooling system. Computational fluid dynamics (CFD) is used to study the effects of the turbulence model, which requires the solution of two transport equations. A technique was developed to study the thermal effect on the heat exchange process between two fluids. To observe the temperature effect on 17 tubes, the diameter was altered twice, first to 6 mm and then to 4 mm. The flow procedure happened in one direction, and the tube that contains the tubes had a diameter of 50 mm. The best-case scenario is the case where the pipe diameter is 4 mm and the heat exchanger are 300 mm in length. Through the results, the enthalpy was improved in the simulated cases to 423.2 h [KJ/M]. The length of the heat exchanger greatly affects the values of the exit temperatures and the temperature difference. For a length of 225 mm, the temperature reached 15.73 °C, and for 300 mm, it reached 13.847 °C. The significant reduction in temperatures helps increase the coefficient in the refrigeration cycle. A high coefficient of cooling in the heat exchanger appears when the length is 300 mm compared to other lengths.

• Optimization of emulsion ice slurry preparation by response surface methodology. • Experimentally prepared emulsions eliminate water supercooling. • Emulsion ice slurry does not stick to the walls of the flash chamber and has a softer texture than pure water. • Pure water ice slurry is flaky in the vacuum flash state, and emulsion ice slurry is spherical. As a cold storage material, emulsion ice slurry is expected to increase the ice slurry's fluidity because of the emulsion's structural characteristics, which does not adhere to the wall of the cooling vessel. In this paper, surfactants were mixed in the water-oil mixture, and the emulsion with small particle size and high stability was optimized by the response surface method. The emulsion ice slurry was also prepared under vacuum flash evaporation by solid adsorption, and we studied the properties of the emulsion ice slurry under vacuum flash evaporation. The microstructures of pure water ice slurry and emulsion ice slurry under vacuum flash evaporation were observed by metallographic microscopy. [ABSTRACT FROM AUTHOR]

• Absorption subcooling CO 2 refrigeration system driven by solar energy & waste heat. • Optimize thermodynamic performance and assess carbon emission of systems. • Effect of maldistribution of solar radiation and ambient temperature is discussed. • Annual performance factor and life cycle carbon emissions are evaluated in cities. • Hybrid absorption subcooling shows better performance in hot and solar rich areas. A novel hybrid solar energy and waste heat driving absorption subcooled carbon dioxide (CO 2 /R744) booster refrigeration system (SE + WH) is proposed to improve the energy efficiency of the traditional CO 2 refrigeration system used in supermarkets. The thermodynamic and energy conversion model of the system is established. Then, the optimization method of the two-dimensional golden section search algorithm is introduced to optimize the system energy efficiency taking the variation of ambient temperature and solar radiation intensity into account. Moreover, considering the maldistribution of solar energy and the influence of meteorological conditions in China, eight typical cities are selected to assess the annual performance factor and life cycle carbon emissions to achieve energy saving and carbon emission potentials. The performance of hybrid solar energy and waste heat driving absorption subcooled CO 2 booster refrigeration system is the best with the COP enhanced by 3.05–42.30 % at the solar radiation intensity of 1200 W/m2 and the temperature of 0–35 °C in contrast to the baseline system. In addition, the discharge pressure of the new proposed hybrid system can be reduced by 7.86 % when the ambient temperature is 34 °C. The annual performance factor of the new proposed hybrid system in Haikou can be increased by 14.47 %, and the life cycle carbon emissions are effectively reduced by 39.54 %. The payback period is also reduced by 4.01 % and 3.37 % for Beijing and Shanghai. Consequently, the novel configuration of the hybrid absorption subcooling subsystem is recommended, particular in hot or warm climate areas with rich solar energy. [ABSTRACT FROM AUTHOR]

The utilization of condensate water as a compressor-discharge cooler results in subcooling on the condenser outlet. On the other hand, a split-type air conditioner (A/C) with R32 as working fluid can provide higher compressor-discharge temperatures than other refrigerants used in the same A/C. Therefore, A/C working with R32, equipped with a heat exchanger by utilizing waste-condensate water as the compressor-discharge cooler, has promising potential to produce the largest subcooling effect in air-conditioning systems. The aim of this study is to investigate the effect of condensate water as the compressor-discharge cooler on the performance of an A/C using R32 as the working fluid with different sizes of heat exchanger. The experimental study was carried out on the A/C with a compressor capacity of 1.1 kW, using three different heat-exchanger lengths, i.e., 18, 20 and 22 cm. The results indicated that longer heat exchangers produced higher degrees of subcooling; the heat exchangers with lengths of 18, 20 and 22 cm produced average degrees of subcooling of 0.9, 1.5 and 4.5 K, respectively. Therefore, increments in the degree of subcooling generate improvements in cooling capacity, lowering the compressor-input power, and enhance the COP of the A/C. The average COP improvement of the A/C with heat-exchanger lengths of 18, 20 and 22 cm were 9.1, 14.4 and 27.3%, respectively. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Henan University of Science & Technology, Natural Science is the property of Editorial Office of Journal of Henan University of Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The integration of phase change phenomena through an interface is a numerical challenge that requires proper attention. Solutions to properly ensure mass and energy conservation were developed for finite difference and finite volume methods, but not for Finite Element methods. We propose a Finite Element phase change model based on an Eulerian framework with a Continuous Surface Force (CSF) approach. It handles both momentum and energy conservation at the interface for anisotropic meshes in a light an efficient way. To do so, a model based on the Level Set method is developed. A thick interface is considered to fit with the CSF approach. To properly compute the energy conservation, heat fluxes are extended through this interface thanks to the resolution of a transport equation. A dedicated pseudo compressible Navier–Stokes solver is added to compute velocity jumps with a source term at the interface in the velocity divergence equation. Several 1D and 2D benchmarks are considered with increasing complexity to highlight the performances of each feature of the framework. This stresses the capacity of the model to properly tackle phase change problems.

• Solutions to boost the COP of low-medium power transcritical CO2 refrigeration cycles • Evaluation of an internal heat exchanger (IHX) and a thermoelectric subcooler (TESC) • Comparative of COP and cooling capacity between the IHX and the TESC • Greater improvements obtained in the COP and cooling capacity with the TESC • Discussion of the strengths and weaknesses of both technologies for transcritical CO2 The use of carbon dioxide in transcritical state has become one of the most used solutions to comply with the F-Gas directive and reduce greenhouse gases emissions from refrigeration systems at high ambient temperatures. For low-medium power units, the commonly used solutions to improve the efficiency such as the ejector, multiple compressor arrangements, mechanical subcooler, etc., add complexity and increase the cost of the refrigeration facility, which is not ideal for small units. In this low-medium power range, two technologies stand out to increase the performance of a carbon dioxide transcritical cycle: the internal heat exchanger and the thermoelectric subcooler. This study brings a complete research in which both solutions have been tested in the same experimental transcritical carbon dioxide refrigeration facility under the same working conditions. It focuses on the real performance of both systems and discusses the strengths and weaknesses of using an internal heat exchanger or a thermoelectric subcooler. The results show that the thermoelectric subcooler outperforms the internal heat exchanger in both the coefficient of performance and the cooling capacity while also being a more controllable and flexible solution. [ABSTRACT FROM AUTHOR]

As an efficient heat and mass transfer technology, falling film evaporation has attracted more and more scholars' attention. In this paper, a falling film evaporation platform was established to discuss the mechanism of two-phase flow in narrow channels. The width of the channel varied from 0.5 to 2.0 mm. We focused on the relationship between heat transfer characteristics with flow patterns, channel width, and pressure loss. Three kinds of flow patterns were observed: bubble flow, restricted bubble flow, and dry area. In channels with the same width, the initial heat flux of subcooled evaporation increased linearly with the growth of flow rate. But at the same flow rate, the initial heat flux of subcooled evaporation decreased when the channel width became larger. The heat transfer coefficient on the wall was influenced by the bubble generation frequency and bubble separation diameter. Higher bubble generation frequency led to smaller bubble separation diameter. Through mathematical analysis, it was found that the heat transfer coefficient changed with the channel size. And a boundary was observed between the strengthening and weakening status. The comparison of theoretical and experimental values showed good agreement. [ABSTRACT FROM AUTHOR]

Exhaust steam condensation equipment is an important component in thermal power generation systems. Direct‐contact condensation offers high heat transfer efficiency, small flow resistance, simple structure, and less scaling; therefore, its application to exhaust steam condensation equipment is conducive to reducing equipment investment and operation costs. In this study, the direct‐contact condensation of subatmospheric pressure steam (exhaust steam) is investigated in a cocurrent flow packed tower. The effects of steam temperature, steam flow, cooling water temperature, and cooling water flow on the condensation rate, subcooling, number of liquid‐phase heat transfer units (NTUL), and total volume heat transfer coefficient (KV) are investigated. The results show that the direct‐contact condensation of exhaust steam can yield a high condensation rate, low subcooling, and good stability in the cocurrent flow packed tower. Lower steam temperature, higher steam flow, higher inlet‐water temperature, and lower water flow are conducive to the increase in NTUL. It is discovered that NTUL and KV can be expressed by dimensionless parameters of flow and temperature, and that the empirical correlations of NTUL and KV agree well with experimental data. [ABSTRACT FROM AUTHOR]

Choosing the right phase change material (PCM) for a thermal energy storage (TES) application is a crucial step in guaranteeing the effectiveness of the system. Among a variety of PCMs available, the choice for a given application is established by several key factors, e.g., latent heat, stability, and melting point. However, phenomena such as subcooling—for which PCM cools in a liquid state below its solidification point—can lead to a reduction in the amount of energy stored or released, reducing the TES overall effectiveness, and also in some inaccuracies when modeling the problem. Thus, understanding the effects of subcooling on PCM performance is crucial for modeling and optimizing the design and the performance of TES systems. To this end, this work analyzes the PCM discharging phase in a cold thermal energy storage coupled to a chiller system. A first conduction-based predictive model is developed based on enthalpy–porosity formulation. Subcooling phenomena are encompassed through a control variable formulation, which takes its cue from the operation of a thermostat. Then, thermal properties of the PCM, i.e., the phase change range and specific heat capacity curve with temperature, are evaluated by using differential scanning calorimetry (DSC), in order to derive a second predictive model based on these new data, without including subcooling, for the sake of comparison with the first one. Experimental results from the storage tank confirm both model reliability and the fact that the PCM suffers from subcooling. Between the two numerical models developed, the first one that considers subcooling proves it is able to predict with satisfactory accuracy (RMSE < 1 °C) the temperature evolution on different tank levels.

Copyright of Journal of China University of Petroleum is the property of China University of Petroleum and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Chinese Journal of Refrigeration Technology is the property of Shanghai Society of Refrigeration and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

• CO 2 transcritical refrigeration plant with different integrated mechanical subcooling systems is analysed experimentally. • Optimum operating conditions of gas-cooler pressure and subcooling degree were determined experimentally. • Cycles are compared at three heat rejection temperatures. • Behaviour of the subcooler and auxiliary compressor has been analysed. • COP of gas-cooler exit configuration is higher with no very significant difference. Subcooling systems are positioned in recent years as one of the best solutions to improve the efficiency of transcritical CO 2 cycles. Specifically, the integrated mechanical subcooling cycle allows the improvement of these systems only using CO 2 as a refrigerant. This integrated cycle can be designed with three different architectures: extracting the CO 2 from the gas-cooler outlet, from the subcooler outlet or from the liquid tank. In this work, the three configurations are experimentally analysed and the main differences between them are studied. An experimental plant has been tested at three heat rejection levels (25.0, 30.4 and 35.1 °C) and a fixed temperature of the secondary fluid at the evaporator inlet of 3.8 °C. The results show that from an energy efficiency point of view, all the configurations have practically the same COP, with certain variations in the cooling capacity and the greatest differences in the cycles are found in the subcooler. [ABSTRACT FROM AUTHOR]

• An NH 3 /CO 2 cascade refrigeration system with ejector subcooling is proposed in this paper. • The proposed system and conventional cascade refrigeration system are compared. • The discharge temperature of the NH 3 compressor decreases obviously. • COP and exergy efficiency increased by 5.4% and 4.8%, respectively. An NH 3 /CO 2 cascade refrigeration system with ejector subcooling (ESCRS) is proposed in this paper. Based on the basic principle of thermodynamics, the mathematical model of the refrigeration system is established and thermodynamic analysis is carried out to obtain the influence of main working parameters on system performance. Compared with the conventional cascade refrigeration system (CCRS), it is concluded that the performance of ESCRS is better than that of the CCRS. Within a certain range, the greater the subcooling degree, the more obvious the decrease of power consumption of low-temperature compressor, the greater the discharge temperature of NH 3 compressor decreases, and the more obvious the increase of system COP and exergy efficiency. Under typical operating conditions, the COP and exergy efficiency of the system proposed in this paper is about 5.4% and 4.8% higher than that of the CCRS. [ABSTRACT FROM AUTHOR]

This study investigated the spray cooling heat transfer performance of Al2O3-water nanofluid given four different subcooling degrees (0 °C, 10 °C, 20 °C, and 30 °C). The results showed that the subcooled nanofluids were ranked in order of a reducing spray cooling heat transfer performance as follows: 20 °C, 10 °C, 0 °C, and 30 °C. On average, the heat transfer coefficient obtained using the nanofluid with 20 °C subcooling was around 8.3%, 8.6%, and 15.6% higher than that obtained with 10 °C, 0 °C, and 30 °C subcooling, respectively. However, the heat transfer performance decreased with an increasing spray operating time. The scanning electron microscopy observations showed that the reduction in the heat transfer coefficient was the result of a gradual increase in the thickness of the nano-adsorption layer on the heated surface as the spray operating time increased. [ABSTRACT FROM AUTHOR]

An experimental investigation has been carried out to find the effect of subcooling of moderator temperature under a Pressure Tube (PT) concentric with Calandria Tube (CT) (e = 0) and PT contact with CT (e = 8.5 mm) at a quasi-steady temperature of a center pin at 750 ℃. The circumferential temperature distribution at different axial positions has been established for the PT and CT. The results demonstrated that a large circumferential temperature gradient was observed in the pressure tube during contact conditions. The maximum and minimum temperatures were measured at the top and bottom nodes of the pressure tube. However, the CT exhibited an opposite trend. The maximum temperature difference between the top and bottom surfaces of the PT and CT is 148 °C and 9.1 °C, respectively. However, no substantial temperature variations were observed between the PT and the CT in concentric conditions. [ABSTRACT FROM AUTHOR]

• The circumferential temperature of PT and CT were recorded for a fuel bundle temperature of 900 °C. • No discernible change in PT temperature is observed with a change in moderator temperature. • The heat transfer coefficient of the annulus varies minimally as a function of moderator temperature. • The moderator temperature of 65 °C results in the highest heat transfer coefficient across CT. • The moderator performs effectively as a heat sink in an accidental situation like LOCA with a change in moderator temperature. During LOCA with ECCS failure, the removal of decay heat from the channel to a moderator plays a significant role in determining the fuel bundle temperatures. An experimental investigation has been carried out to study the effect of change in moderator temperature (65 ℃, 75 ℃, and 85 ℃) on the fuel channel at a steady state of 900 ℃ center pin temperature. The results show that at different moderator temperatures, there is insignificant variation in the temperature of PT, whereas for CT appreciable temperature gradient has been observed. The maximum heat transfer coefficient for CT was attained at 65 ℃ moderator temperature. Even with an increase in moderator temperature, channel integrity is maintained, and the moderator acts as an ultimate heat sink for all three moderator temperatures. [ABSTRACT FROM AUTHOR]

In this work, double rotating active cylinders and slot nanojet impingement are considered for the cooling system of a conductive panel. Colder surface temperatures of the cylinders are used, while different rotational speeds are assigned for each of the cylinders. The impacts of cylinder rotational speeds, size and distance between them on the cooling performance are evaluated. The rotational effects and size of the cylinders are found to be very effective on the overall thermal performance. At the highest rotational speeds of the cylinders, the average Nusselt number (Nu) rises by about 30.8%, while the panel temperature drops by about 5.84 °C. When increasing the cylinder sizes, temperature drops become 7 °C, while they are only 1.75 °C when varying the distance between the cylinders. Subcooling and nanofluid utilization contributes positively to the cooling performance, while 1.25 °C and 10 °C temperature drops are found by varying the subcooled temperature and solid volume fraction. An artificial neural network is used for the estimation of maximum and average panel temperatures when double cylinder parameters are used as the input.

• Describe the four stages of vacuum flash ice production under solid adsorption. • Recording and analysis of flash evaporation phenomena at different initial pressures and different initial temperatures. • Analysis of the effects of factors on the subcooling state of distilled water during vacuum flash evaporation. The paper based on the solid adsorption vacuum flash ice slurry production device, the process of distilled water flashing was recorded with a high-speed CCD camera, and the vacuum flashing state of distilled water at different pressures and different initial temperatures was analyzed by experimental phenomena. The effect of system pressure, different wall temperatures and solution volumes on the subcooling state of the ice slurry formation process under solid adsorption vacuum flash evaporation was also experimentally investigated. The results show that the lower the pressure the more intense the flashing phenomenon in the vacuum flashing state, and the higher the initial temperature the more likely the solution is to produce bubbles. Within 20 seconds after the start of the experiment, distilled water will appear subcooling phenomenon in solid adsorption vacuum flash evaporation ice making system, due to the vacuum flash action water is constantly disturbed subcooling state duration is very short. The lower the pressure, the lower the subcooling degree, the subcooling degree is about 2 °C - 4 °C. The wall temperature has a greater impact on the ice crystal phase change accumulation stage, the higher the initial wall temperature the greater the fluctuations in the subsequent stages of flashing and the lower the ice content. When the volume of the solution is small, the liquid film is prone to flash formation of solid ice. [ABSTRACT FROM AUTHOR]

• Five pure sugar alcohols were selected to obtain eutectic mixtures with melting temperatures between 60 °C and 90 °C. • The sugar alcohols were tested by DSC and investigated by isothermal phase change tests. • The crystallization rate of the eutectic mixtures can be accelerated by mechanical agitation. • The eutectic mixtures obtained at about 80 °C are suitable for heat storage in buildings. • The eutectic sugar alcohols obtained still have good crystallization characteristics after multiple repetitive experiments. Sugar alcohols are suitable for compact and high-density building thermal energy storage systems because of the high enthalpy, low price, and non-toxicity. But most sugar alcohol materials have severe supercooling characteristic, which limits their application as phase change materials (PCMs) in thermal energy storage systems. In this study, xylitol, sorbitol, erythritol, mannitol and dulcitol were selected as PCMs. Based on the five single sugar alcohols, ten multicomponent eutectic sugar alcohols were obtained which melting temperatures is between 60 °C and 90 °C applied to buildings. The thermal parameters of sugar alcohols were tested by differential scanning calorimetry (DSC), the supercooled eutectic sugar alcohols were stimulated by means of mechanical agitation to accelerate crystallization. The crystallization after excitation was monitored by microscope, and the supercooled crystallization phenomenon of eutectic sugar alcohols was investigated by isothermal phase change tests. The results showed that only three eutectic sugar alcohols could crystallize by stirring, and the melting temperatures of three eutectic sugar alcohols are about 80 °C. After multiple repetitive experiments, three eutectic sugar alcohols still have good crystallization characteristics. The results of the research provide a reference value in practical aspects for the design and selection of phase change materials in buildings. [ABSTRACT FROM AUTHOR]

The experimental investigation was carried out for the spiral coiled capillary tube having a spiral pitch of 32 mm, 48 mm, and 64 mm to study the mass flow rate of R32. A wooden spiral pattern was used to get the spiral shape of the capillary tube. Three wooden patterns were prepared for three different spiral pitches. The spiral convolutions are calculated for the capillary tube length of 1000 mm, 1500 mm, and 2000 mm. The variation in mass flow rate for all three spiral pitches was studied, and the results were shown on a graph. The effect of variation of capillary inlet pressure and degree of subcooling were observed. From the data comparison, it can be concluded that if the spiral pitch increases from 32 mm to 48 mm, for all the diameters for similar operating conditions, the mass flow rate increases from 3.89% to 5.05%. If the spiral pitch increases from 32 mm to 64 mm, for all the diameters for similar operating conditions, the flow rate increases from 6.49% to 11.64%. The measured mass flow and predicted mass flow rate is well within the accepted range. The percentage deviation of the mass flow rate is compared with the other researchers and found between +30% and −34%. The mass flow rate was higher for the higher spiral pitch, a higher degree of subcooling, higher capillary inlet pressure, and higher capillary diameter. [ABSTRACT FROM AUTHOR]

Subcooling is the process of bringing down the temperature of liquids lower than that of the boiling point of the corresponding vapor pressure. The performance of subcooling of cryogenic liquids mainly depends on the heat-inleak of the system, the helium injection mass flow rate, helium injection temperature, and helium injection nozzle pattern. This paper presents an alternative method, by making use of the least heat in the leakage of the liquid hydrogen storage container, which is quite possible because containers with excellent thermal insulation are commercially available nowadays. The process involved is rapid evacuation through gas ejectors, thus reducing the effect of temperature. The advantage and the process of evacuation leading to subcooling in a unique manner are the objective of this article. The experimental results are discussed in comparison with the thermophysical process involved in the subcooling operation. A comparative study is also carried out with the theoretical heat exchange process in which helium is used as a medium for the economy of the stated process. It is stated that the current process of subcooling through evacuation is superior to the conventional heat exchange process. [ABSTRACT FROM AUTHOR]

The thermal cycle of the secondary circuit at an NPP with a BREST-OD-300 reactor includes a mixing feed water heater (MFWH) to heat the feedwater at the steam generator's inlet to a minimum of 340°C (to keep the lead coolant temperature above the lead pour point in the shell side of the steam generator) under all operating conditions. To substantiate the design solutions and finalize the procedure for thermohydraulic design of the MFWH at an operating pressure as high as 15 MPa, NPO CKTI conducted bench tests on an MFWH model in versions with one or two heating stages with water distribution by gravity. The experiments have confirmed that the feedwater can be heated as required in a full-scale heater. Generalization of the experimental data has demonstrated the advantage of the droplet model in describing the thermohydraulic processes in the MFWH over the jet model used to calculate the low-pressure mixing heaters (LPMH). The dependences for calculating the average diameter of water droplets and their fall velocity in a steam environment have been updated. It has been established that, at a pressure of 5–15 MPa, the time to heat droplets depends mainly on their size and the thermal conductivity of water in them. The minimum height of the heating section (the zone of free fall of water droplets in a steam environment) in the MFWH should be 0.7 m, which will provide the subcooling of water to the steam saturation temperature of less than 1°C in a heater with two heating stages. [ABSTRACT FROM AUTHOR]