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The current research is conducted with the aim of investigating a multi-generation energy system (MGS) for electricity, hydrogen, heating, cooling and hot water production using SRC, Kalina cycle and proton exchange membrane (PEM) electrolysis as the main subsystems. The thermodynamic analysis namely energy, exergy, and exergo-economic examination carried out. Analysis for each component is done after thermodynamic modeling. The exergy investigation showed that regenerator 2, vapor generator and condenser had the highest exergy destruction rate, respectively. A comparison was made between the current work and the basic system, and according to the results obtained, the system's ability to produce electricity, cooling, heating and hydrogen are calculated as 782 kW, 173.2 kW, 2265 kW and 0.01613 mol/day, respectively. Also, the energy and exergy efficiency of the proposed system increased by 3.13% and 5.37%, respectively. The optimization based on PSO method was carried out. The results of PSO optimization represented that in the case exergy destruction and exergy efficiency will be the optimization target these two outputs can reach the value of 2208 kW and 9.84%, while optimization based on exergy efficiency and production cost rate will lead to 9.86% and 166.6 $/h. • Simulation a CSP based system to design a poly-generation energy system. • Using PEM electrolyzer to generate hydrogen as an energy storage media. • The exergy efficiency of introduced system is 3.13% higher than basic system. • The output power of new plant is 1.54 MW higher than basic cycle. [ABSTRACT FROM AUTHOR]

Generators and condensers are the two vital equipment items that determine the output of vapor absorption refrigeration systems. Arid weather conditions produce a significant reduction in the performance of the vapor absorption refrigeration cycle due to low condenser heat dissipation despite high generator temperatures. Although numerous studies on condenser cooling methods in vapor compression systems have been reported in the literature, solar-operated vapor absorption systems have not been studied. Limitations in generator temperatures of solar-operated vapor absorption systems necessitate a focused study in this area. This study makes the selection of the best choice for condenser cooling from among four different condenser cooling methods which have an impact on the performance of the vapor absorption refrigeration system for effective cooling using solar energy. A solar vapor absorption refrigeration system working with low-grade heat using a compound parabolic collector is considered in this study. Analysis of a vapor absorption refrigeration system for cooling in arid weather conditions is carried out using different condenser cooling methods with Engineering Equation Solver. Initially, the model used in the study is compared with a similar study reported in the literature. Techniques considered are air, water, evaporative, and hybrid cooling techniques. The performance of the vapor absorption cooling system was analyzed using experimental values of a solar compound parabolic collector obtained from real-time measurements for simulating the model. Results show that water cooling can provide suitable condenser cooling and improve the coefficient of performance of the solar vapor absorption refrigeration system using the solar collector. The water-cooled condenser has 1.9%, 3.3%, and 2.1% higher COP when compared to air-cooled condensers for spring, summer, and autumn seasons respectively, whereas the water-cooled condenser cooling recorded 6%, 14%, and 8% higher COP relative to the evaporative cooling method. Cost comparison showed maximum cost for water-cooled condensers and minimum cost for hybrid-cooled condensers. The effect of each cooling method on the environment is discussed. [ABSTRACT FROM AUTHOR]

Nuclear magnetic resonance (NMR) spectroscopy is a powerful analytical tool used in modern science and technology. Its novel incarnation, based on measurements of NMR signals without external magnetic fields, provides direct access to intramolecular interactions based on heteronuclear scalar J-coupling. The uniqueness of these interactions makes each zero-field NMR spectrum distinct and useful in chemical fingerprinting. However, the necessity of heteronuclear coupling often results in weak signals due to the low abundance of certain nuclei (e.g., 15N). Hyperpolarization of such compounds may solve the problem. In this work, we investigate molecules with natural isotopic abundance that are polarized using non-hydrogenative parahydrogen-induced polarization. We demonstrate that spectra of hyperpolarized naturally abundant pyridine derivatives can be observed and uniquely identified whether the same substituent is placed at a different position of the pyridine ring or different constituents are placed at the same position. To do so, we constructed an experimental system using a home-built nitrogen vapor condenser, which allows for consistent long-term measurements, crucial for identifying naturally abundant hyperpolarized molecules at a concentration level of ~1 mM. This opens avenues for future chemical detection of naturally abundant compounds using zero-field NMR. Zero- and ultralow-field (ZULF) nuclear magnetic resonance (NMR) has emerged as a complementary technique to conventional high-field (≳1 T) NMR, however, the ability to distinguish heteronuclear coupling remains challenging due to the low abundance of certain nuclei. Here, the authors apply non-hydrogenative parahydrogen-induced hyperpolarization to identify naturally abundant molecules, and demonstrate the detection of pyridine derivatives at a concentration level of ~1 mM. [ABSTRACT FROM AUTHOR]

This article focuses on evaluating and analyzing the performance of an autocascade refrigeration system with the zeotropic mixture of R600a/R1150/R14 refrigerants using grey correlation theory and response surface methodology (RSM). The correlation degree among various factors is analyzed using grey correlation theory. The interactive influences that have significant impacts on the six output parameters are illustrated, and a regression model is further validated by five confirmation parameters. The results show that the vapor quality of the evaporator outlet is the greatest factor that affecting the refrigerating capacity and coefficient of performance (COP). However, the evaporation temperature has the greatest effect on compressor's discharge temperature, pressure ratio, exergy destruction rates, and exergy efficiency. Lower vapor quality of the condenser outlet and condensation temperature can improve the performances of refrigerating capacity, COP, compressor's discharge temperature, compression ratio, total exergy destruction rate, and exergy efficiency based on the RSM results. The random five groups of validation parameters indicate that the errors between the predicted modeling and calculation results are all less than 5%, demonstrating that the RSM model has good predictability. The results achieved in this work will assist in the optimizing analysis and the application of cryogenic refrigerators. [ABSTRACT FROM AUTHOR]

This study concerns the numerical simulation and the experimental implementation of a low-scale Phase Change Material-based (PCM-based) condenser, to be included in a PCM-based portable cooling systems. In this category of cooling systems, the PCM can be integrated either in the condenser or in the evaporator. In the present study, the PCM is integrated in the condenser of the vapor compression cycle to absorb the heat power released from the refrigerant fluid (R134a) during condensation, thus eliminating the need to transfer heat to the external environment. The main objective of the present study is to realize and validate a numerical model capable of simulating both the refrigerant fluid and the PCM thermofluid dynamics. For this purpose, a commercial solver was used for the implementation of the developed numerical model, and experimental tests were performed to validate the numerical simulations results. The paper reports the details and test results of both the numerical model and the experimental apparatus. The simulation results indicate a good accordance between the numerical and experimental data. [ABSTRACT FROM AUTHOR]

This paper analyses the performance and behavior of water circulation system (WCS) of a thermal power plant in fuzzy environment. For this purpose, fuzzy 1-t technique coupled with petrinet modelling has been used. To address the vagueness in data, trapezoidal fuzzy numbers have been employed in fuzzy 1-t technique. Various reliability indicators of WCS viz. failure rate, repair time, expected number of failures, mean time between failures, reliability and availability have been computed at ±15%, ±25% and ±40% spreads using fuzzy 1-t technique. Further, fuzzy values of reliability indicators have been defuzzified employing COA method and the failure dynamics of WCS have been studied on account of decreasing / increasing trends of reliability indicators. The outcomes of this study are of great importance for plant personnel / management to enhance the availability of WCS. [ABSTRACT FROM AUTHOR]

Two-phase flows are found in almost all areas of technology. For example, tubular evaporators, boiling water reactors, boiler blowdown systems, heaters, boilers, gas lift pumps, oil and geothermal wells, oil and gas pipelines, refrigerators, process pipelines, and condensers. Two-phase flows are classified as mixtures. According to the composition of the mixture are divided: (a) for single-component (or one-component) - vapor-liquid flows; (b) multicomponent - gas-liquid flows. One-component mixtures consist of the same substance in different states of aggregation. This can be not only vapor-liquid, but also a mixture of liquid or vapor with a solid phase, a water-ice mixture, or a vapor flow with ice particles, for example, in sublimation installations. Multicomponent mixtures are a combination of substances of different physical nature. These include not only gas-liquid flows, but also, for example, mixtures of air and sand, water and oil. The paper presents the main attention is paid to the movement of two-phase flows in the pipeline. [ABSTRACT FROM AUTHOR]

An autonomous dilution microrefrigerator manufactured as an insert into a helium cryostat with a superconducting magnet is described. In this refrigerator, the 3He circulation in the circuit filled with a 3He–4He mixture (mixer–heat exchanger–still–condenser–heat exchanger–mixer) is achieved due to the condensation of mixture vapors on the walls of the condenser, which is cooled by the 3He bath pumped out by a sorption pump, as well as entry of the condensate into the mixer under the action of gravity. An 8-mm-range resonator that contains a sample is connected to the mixer via a heat conductor; the sample is located at the center of a superconducting solenoid with a field of up to 80 kOe. Radiation passes from the generator through a waveguide to the resonator, and the signal that passed through the resonator arrives at the detector. The generator and detector are at room temperature. The device is designed for microwave spectroscopy of magnetic materials at temperatures in the range of ~0.09–3 K. The time within which the temperature is maintained at a level of ~0.1 K is 4–6 h. The results of a test experiment on the antiferromagnetic resonance in a MnCO3 single crystal are presented. [ABSTRACT FROM AUTHOR]

Loop heat pipe (LHP) promises great application potential in electronics cooling. However, the selection of environmentally friendly working fluid remains a big issue, especially in commercial applications. Although R134a is a common refrigerant, the R134a-charged LHP is limited by small heat transfer capacity (HTC). In this work, a LHP with R134a as the working fluid is designed and fabricated. In order to enhance its HTC, the structure optimization has been made based on the theoretical analysis of flow resistance where the smaller wick thickness and larger diameter of the vapor and condenser lines are adopted. Experimental results show that the R134a LHP can reach a high HTC up to 250 W at the horizontal orientation with the condenser cooled by air forced convection. With an adverse elevation of 5 cm, the HTC is reduced to about 230 W. In addition, an extensive experimental study on its startup characteristics with the heat loads ranging from 5 to 30 W is conducted. The influence of the initial liquid/vapor distribution in the evaporator on the startup performance is investigated. This work proposes an effective method to enhance the HTC of the R134a LHP, which contributes greatly to its structure optimization and future commercial applications. [ABSTRACT FROM AUTHOR]

This paper proposes a modified auto-cascade refrigeration cycle (MARC) with a self-recuperator. The introduced self-recuperator and associated expansion valve effectively increases the refrigerant enriched with more low-boiling component in the evaporator. This case could improve the cycle performance by further choosing appropriate design-dependent cycle parameters. The energy and exergy analysis methods are used to compare and evaluate the performance of MARC with conventional auto-cascade refrigeration cycle (CARC). The simulation results show that under all given working conditions, the COP and exergy efficiency of MARC are superior to those of CARC. Among R290/R170 and R600a/R1150, R600a/R1150 is much better refrigerant mixture. Under a typical working condition, the COP of MARC using R600a/R1150 is 68.17% higher than that using R290/R170. The performance improvement of MARC is more obvious when R600a/R1150 is used. Under the typical working condition, the COP of MARC is increased by 6.24% and 24.17% using R290/R170 and R600a/R1150, respectively. When initial mass fraction of R1150 is about 0.6, the two cycles have maximum COP and exergy efficiency, and the maximum COP of MARC is 24.26% higher than that of CARC. In addition, the increase in the two-phase flow vapor quality at the condenser outlet can improve the COP, but reduce the refrigeration capacity. The COP of MARC increases by 37.56% when the quality increases from 0.4 to 0.6. It is also found for MARC that COP and refrigeration capacity are positively correlated with intermediate pressure. [ABSTRACT FROM AUTHOR]

This study focused on the optimal production feasibility of distilled water from the concentrate of a reverse osmosis device using an evacuated tube collector basin solar still. The characteristic effect of the device's condenser on the produced freshwater volume was evaluated to improve the performance of the solar still, resulting in productivity enhancement. The direct contact of two faces of the cubic condenser with water vapor results in the doubling of the effective surface area. However, freshwater production was decreased by eight times compared to the case where only one face of the condenser is in contact with water vapor. This reduction was attributed to the shorter path taken by the condensed droplets. At the bottom of the evacuated tube collector, some building mineral pumice was used to prevent the formation of large water vapor bubbles. According to this methodology, the average daily production of distilled water from the concentrate of the reverse osmosis unit with a total dissolved solids of 15200 ppm was achieved at 4.58 ± 0.12 L. m − 2 . The quality of produced distilled water revealed that solar desalination using an evacuated tube collector basin solar still can be a notable and economical solution for the concentrate treatment of reverse osmosis. [Display omitted] • The longer the droplets' path on the glass condenser's surface, the higher the freshwater production rate. • The movement path of liquid droplets to the outlet with angles of θ = 0 ° is equal to the length of the condenser. • The ETC has the potential to transfer part of the salty water by the rise of large water vapor bubbles. • Building mineral pumice can be used to prevent the formation of large vapor bubbles at the bottom of the ETC. • Modified ETC basin solar still can be a considerable solution for the desalination of RO concentrate. [ABSTRACT FROM AUTHOR]

• Use of environment friendly hydrocarbons as working fluids in the system. • Hybrid heat source of the solar collector and the biomass burner system. • Heptane is the most suitable fluid for the higher thermal performance of the system. • Hybrid heat source system contributes 88% to total exergy destruction of the system. In this study, a thermodynamic analysis of the hybrid heat source driven organic Rankine cycle integrated flash tank vapor compression refrigeration (ORC-FTVCR) system is conducted using five different hydrocarbon fluids such as hexane, heptane, octane, nonane, and decane. The hybrid heat source consists of a solar collector and a biomass burner system. The system coefficient of performance (COP s), overall exergetic efficiency (η oex), are taken as the indices of the thermal performance of the system. The impact of the operating parameters such as the intensity of solar radiation, inlet temperatures of expander and VCR evaporator, isentropic efficiencies of the compressor and expander, and the condenser saturated vapor temperature on system performance is also investigated. The results indicate that the system performs better using heptane as the working fluid. The values of COP s , η oex , for ORC-FTVCR system using heptane are 0.551 and 4.21%, respectively. The solar collector and the biomass burner system contribute 88% to the total exergy destruction of the system. [Display omitted] [ABSTRACT FROM AUTHOR]

In the current study, a passive single-slope solar distillation unit has been proposed. An incorporated condenser has been integrated into the system to promote the condensation rate and hence improve the unit productivity. External fins have been used as a means to enhance the condenser performance further. The system performance has been examined experimentally for seven consecutive summer days in Mashhad city located at 36° 18′56.12″ N latitude and 59° 34′4.66″ E longitude. The unit yield and efficiency have been compared to the corresponding data for a conventional solar still tested in Tehran city. The results reveal that using fins increases the distillate in the condenser by 35%. But, there is only a 5% increase in the total unit productivity due to a reduction in distillate on the glass cover by 8%. Compared to the typical solar still tested in Tehran, up to 92.3 and 86% increase in daily productivity can be achieved using the current still with and without fins, respectively. The thermal efficiency of the currently proposed structure is about double than is it for the traditional solar still. The economic feasibility of the current solar still has been compared to some passive and active designs found in the literature, where it has been found not only efficient but less costly as well. The system without fins is the least expensive with C P L = 0.007 $ / l / m 2 , while the one with fins is slightly more expensive with C P L = 0.0117 $ / l / m 2 but still economically outstanding. • The still integrated with a built-in condenser, with or without external fins. • Productivity of single-basin solar still improved by condensing fin wall cavity. • Fins increases distillate in condenser by 35% compare to 5% in total productivity. • System without and with fin has C P L = 0.007 and 0.0117 $ / l / m 2 respectively. [ABSTRACT FROM AUTHOR]

Condensers are flow architectures needed to provide high rates of condensation (or cooling) per unit volume, in enclosures with fixed volume. Their design has not changed from configurations consisting of the banks of horizontal tubes. In this paper, we outline a free path to evolving the design by exploring new features of flow configuration: flattened tubes, multiple tube sizes, arrays of flattened tubes, vertical tubes with turbulent film flow, forced convection condensation instead of gravity driven condensation, and the optimal length of a horizontal tube, i.e., the number of tubes in a column aligned with vapor cross flow. We show that the condensation density can be increased sizably by varying freely and without bias the morphology of the flow system: the shapes and arrangement of the cooled surfaces on which condensation occurs. The evolution of technology is described in terms of the special time direction of the useful (purposeful) changes in the configuration (shapes, arrangements) of surfaces on which flow/condensation occurs. This explains what "evolution" means. It is an important step for physics, not just technology. [ABSTRACT FROM AUTHOR]

Radiative vapor condenser sheds heat in the form of infrared radiation and cools itself to below the ambient air temperature to produce liquid water from vapor. This effect has been known for centuries, and is exploited by some insects to survive in dry deserts. Humans have also been using radiative condensation for dew collection. However, all existing radiative vapor condensers must operate during the nighttime. Here, we develop daytime radiative condensers that continue to operate 24 h a day. These daytime radiative condensers can produce water from vapor under direct sunlight, without active consumption of energy. Combined with traditional passive cooling via convection and conduction, radiative cooling can substantially increase the performance of passive vapor condensation, which can be used for passive water extraction and purification technologies. [ABSTRACT FROM AUTHOR]

The primary cause of unsteadiness in a concentrated solar power (CSP) plant is cloud passing and the subsequent shadowing of its solar fields. The effects of these transients on a condenser pipe of an air-cooled condenser, typical of CSP applications, are numerically investigated. The parameters that are considered to be impacted by unsteadiness are the condenser inlet mass flow rate, the condenser inlet vapor quality and the ambient temperature. These perturbations are represented by downward step functions to reflect the unanticipated change due to cloud passing. Reasonable nominal values and reasonably large drops of 90%, 0.15 and 15 ° C in the steam mass flow rate, vapor quality and ambient temperature, respectively, are identified and implemented into the transient simulations. The transient response of the fluidic and thermal characteristics of the condensing steam flows to the imposed perturbations are examined. Interestingly, prompt responses to the imposed perturbations are observed. The heat transfer coefficient increases sharply by around 160% and 150% upon the imposed perturbations in mass flow rate and ambient temperature, respectively, before reaching their corresponding quasi-steady state values. The findings have, therefore, implications in the design of air-cooled condensers which are subjected to sudden temporal variations in boundary conditions. • Abrupt increases in thermal characteristics appear on initiation of transients. • Transient steam flow is highly sensitive to perturbation in ambient temperature. • Condenser more affected by perturbation in ambient temperature than fouling. [ABSTRACT FROM AUTHOR]

Flooding limit is the most severe limitation in the operation of a two-phase closed thermosyphon (TPCT). However, the effect of condenser length to the critical heat flux (CHF) and the influences of structural and operational parameters to the critical liquid film thickness (CFT) were not universally concerned. In the present study, a comprehensive model for TPCT is developed to predict the CHF and CFT. In particular, the proposed model is validated through three criterions. Based on the validated model, parametric analysis of the structural and operational parameters is comprehensively carried out, and variations in CHF and CFT are illustrated and discussed in detail. Simplified correlations for CHF are finally proposed based on the numerical modeling results. The results indicate that the CHF decreases with increasing absolute length and evaporator length, while increases with increasing vapor temperature, condenser length, and inner diameter. However, the increment due to the condenser length is limited. The CFT has different fluctuation trends in comparison with the CHF. It increases first and then decreases with increasing vapor temperature and inner diameter, while reverses with increasing absolute length and condenser length, and remains unchanged with increasing evaporator length. Meanwhile, the effect of working fluids to the CHF and the effect of aspect ratios to the CFT both indicate that much efforts need to be made to further understanding the TPCT. However, correlations of CHF can be obtained in a good agreement with the numerical modeling results within 30% deviation for the whole limited scope. [ABSTRACT FROM AUTHOR]

In this study, R404A and R452A refrigerants used in refrigeration systems were compared experimentally. The energy performance of the system was investigated for widely used evaporation temperatures (−5, 0, +5 °C) and condenser temperatures (25, 35, 45 °C). It was seen that the coefficient of performance (COP) was higher but the power consumption of the system was lower when using R452A as a substitute for R404A. When R452A was used, the COP was improved by about 3% to 8% compared to R404A. Furthermore, the cooling capacity decreased by about 2% for condenser temperatures of 25 and 35 °C, while it increased at a condenser temperature of 45 °C. The power consumption of the system was also reduced by nearly 5%. The mass flow rate of the refrigerant was lower when the system was operated with R452A. In the middle term, R452A could be a suitable alternative refrigerant for commercial refrigeration applications due to its low global warming potential (GWP) value and better energy performance compared to R404A. [ABSTRACT FROM AUTHOR]

• Design of solar thermal plant in Al Khobar must account for salt, sand and dust. • Enclosed trough, saltwater condenser and thermal energy storage are considered. • Computations suggest annual capacity factor of 38% and LCOE of 0.08 US$/kWh. • The LCOE can be up to 30% more accounting for enclosed trough and technology readiness. • A small pilot plant experience is needed before building a full scale plant. The preliminary design of a concentrated solar power (CSP) plant with thermal energy storage (TES) in Al-Khobar, Kingdom of Saudi Arabia is here presented. The specific conditions, in terms of environment, weather and sun irradiance, sand and dust, humidity, temperature, solar irradiance, clouds coverage, and proximity to the sea, are considered. A CSP parabolic trough (PT) with TES in a glass enclosure and a once-through saltwater condenser is selected to produce solar energy with the added value of dispatchability. The results of the simulation by using the System Advisor Model (SAM) software are proposed in detail. The manuscript presents the supporting experimental data, and the model development, validation, and application. The computation of the operation of a reference CSP PT with TES plant located in a drastically different environment, requiring specific components such as a glass enclosure and a once-through saltwater condenser, is trustworthy. A small-scale pilot plant is however suggested before moving to full-scale plant construction. [ABSTRACT FROM AUTHOR]

In this study, a reactive distillation column for production of isopropanol was investigated. Firstly, a dynamic model was developed for the process. The model of the process was then programmed, and the process simulated using a base case obtained from the literature. Results showed that distillate contained more than 58 mol% propylene-free isopropanol. In the next step, optimization of some operating variables was performed to maximize concentration of isopropanol in distillate with condenser temperature as constraint, which was considered to be above the freezing point of water. Several simulations were performed by changing operating parameters, and finally optimum isopropanol content in distillate was obtained above 58 mol%. Results of using classic controllers showed that PID controller had the best performance for both condenser temperature set-point tracking and disturbance rejection. [ABSTRACT FROM AUTHOR]

Understanding condensation in microchannels is critical for designing optimized and compact microchannel condensers, which have the potential to increase system level efficiency and reduce system size. Analytical and numerical models can yield insights into local condensation phenomena. This study provides a review of models of condensation in microchannels. These models are categorized based on the applicable, typically annular and intermittent, flow regimes. Annular-flow-based models are further subdivided into analytical models with closed-form solutions, analytical models with numerical solutions, reduced-order CFD models, and full-fledged CFD models. Intermittent-flow-based models are subdivided into single-bubble, repeated-unit-cell, and overall-bubble-train models. The characteristics, use, and range of applicability of each of these models is highlighted. A criterion for the film Reynolds number is proposed for internal forced convective condensation in microchannels, to assess the validity of the modeling assumptions. Annular flow models using the laminar film assumption appear to be valid for Re δ0 < ~ 360, beyond which turbulent effects must be modeled. Intermittent flow models using the laminar film assumption, in turn, appear to be valid for Re δ0 < ~ 130. [ABSTRACT FROM AUTHOR]

Hot-spots are a common occurrence in power electronics which become increasingly hotter as chips become denser. Novel cooling technologies are emerging to cope with this increasing heat load, which imbed a condenser to supply cooling drops to the evaporator resting on the hot-spots. Nonetheless, the evaporation process of the drops has been overlooked. Here, we conducted a series of experiments to understand how the evaporation and motion of drops are influenced by the wetting mode of rough hot-spots. We fabricated three different surfaces exhibiting full (Wenzel) or partial (Cassie–Baxter) wetting and the hot-spot is imposed by laser irradiation. We report a direct link between drop motion and wetting mode with the partial wetting drops being highly mobile, attributable to lower pinning energy based on an energy analysis. This study provides a framework for future modifications in hot-spot cooling to account for drop motion which should greatly influence the overall heat removal performance. [ABSTRACT FROM AUTHOR]

We prove that each homeomorphism of Euclidean domains in , , belonging to the Sobolev class , where , and having finite distortion induces a bounded composition operator from the weighted Sobolev space into for some weight function . This implies that in the cases and as well as and the inverse belongs to the Sobolev class , has finite distortion, and is differentiable -almost everywhere in . We apply this result to -homeomorphisms; the method of proof also works for homeomorphisms of Carnot groups. Moreover, we prove that the class of -homeomorphisms is completely determined by the controlled variation of the capacity of cubical condensers whose shells are concentric cubes. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations of miscible and partially miscible binary Lennard-Jones mixtures are used to study the dynamics and thermodynamics of vapor condensation onto a non-volatile liquid drop in the canonical ensemble. When the system volume is large, the driving force for condensation is low and only a submonolayer of the solvent is adsorbed onto the liquid drop. A small degree of mixing of the solvent phase into the core of the particles occurs for the miscible system. At smaller volumes, complete film formation is observed and the dynamics of film growth are dominated by cluster-cluster coalescence. Mixing into the core of the droplet is also observed for partially miscible systems below an onset volume suggesting the presence of a solubility transition. We also develop a non-volatile liquid drop model, based on the capillarity approximations, that exhibits a solubility transition between small and large drops for partially miscible mixtures and has a hysteresis loop similar to the one observed in the deliquescence of small soluble salt particles. The properties of the model are compared to our simulation results and the model is used to study the formulation of classical nucleation theory for systems with low free energy barriers. [ABSTRACT FROM AUTHOR]

The reactive power compensation of large-capacity synchronous condensers in a ultrahigh-voltage direct current (UHVDC) converter station is not yet fully utilised, and there is no method for achieving effective coordination between synchronous condensers and DC systems. To realise their coordinated control of reactive power and voltage, a dynamic reactive power optimisation model that considers the coordination of synchronous condenser and filtering requirements of system is proposed in this study. The model considers the constraints of the variable steady reactive power capacity of synchronous condenser by taking into account its dynamic reserve demand, the minimum filter capacity of the system, and the switching sequence of AC filters and shunt capacitors. The model is solved by a two-stage hybrid intelligent algorithm based on the interior point method and the differential evolution algorithm. Further, the effectiveness of the proposed method is verified by the example of a UHVDC sending converter station in Northeast China. The simulation results show that the proposed model can greatly reduce the number of times discrete devices enter operation in a converter station under satisfying the dynamic reactive power reserve of the synchronous condenser, providing a basis for the coordinated optimal control of synchronous condensers and DC systems. [ABSTRACT FROM AUTHOR]

This article developed a novel numerical model for accurately predicting the thermal performance of fin-and-tube condenser, which coupled heat transfer between the air and refrigerant side. The heat exchange calculation between the air and refrigerant side was alternatively performed by coupling the tube wall temperatures. Meanwhile, the air side flow and heat transfer characteristics among the fin plates were achieved by porous media approach. Based on this model, the numerical studies were conducted for investigating the effects of air inlet temperature and frontal velocity on the thermal performance of such heat exchanger. Results showed that the predicted overall heat transfer rate was within the range of ±10% compared with the experimental data. It indicated that the porous media model was able to predict the thermal and flow characteristics of air side in a fin-and-tube condenser, and furthermore it could be used for the optimal design of such heat exchanger. [ABSTRACT FROM AUTHOR]

This paper presents a comparison of three surface condenser connection setups on the cooling water side. Four connections were considered, namely serial, mixed and two parallel ones. The analysis was conducted based on the calculated heat balances of proposed power unit for nominal and not nominal parameters for tested connections. Thermodynamic justification for the use of more complex configuration was verified. The exhaust steam pressure calculation was presented. Three methods of computing the heat transfer coefficient based on characteristic numbers, namely the Heat Exchange Institute (HEI) method, and the American Society of Mechanical Engineers (ASME) standard, were used. Calculation results were validated with the real data. The most accurate model was indicated and used in heat balance calculations. The assumptions and simplifications for the calculations are discussed. Examples of the calculation results are presented. [ABSTRACT FROM AUTHOR]

Power quality has become major concern these days due to application of power electronic devices. Conventional equipment like passive filter, segregate series and shunt filters and synchronous condenser etc. have become inadequate to mitigate different power quality problems. Since, power quality mainly concerned with voltage quality and the current quality in the system. For voltage quality, series compensator is used and for current quality, shunt compensator is used. Further, when these two power quality problems are mitigated simultaneously, the device, which is used, called unified power quality conditioner (UPQC), in power distribution system. In this paper voltage related power quality problems such as (voltage sag, voltage swell, voltage and current distortion) are discussed and UPQC controller is simulated to mitigate these problems. There are different control techniques available for UPQC. Here one of them i.e., unit vector template generation (UVTG) is used to simulate UPQC controller. The considered system efficiently regulated the DC link voltage using properly tuned PI parameters. The proposed work is also validated using experimental results. [ABSTRACT FROM AUTHOR]

• Solar driven vapor compression refrigeration system was analyzed. • The effect of condenser's pressure on performance of the system is studied. • The effect of evaporator's pressure on performance of the system is studied. Photovoltaic (PV) solar refrigeration system is considered as one of the most vital areas in photovoltaic application. This research work aims to study the effect of operating pressures of evaporator and condenser to the performance of directly coupled variable speed solar refrigeration system. Performance parameters which were considered in the study are compressor speed, power consumption, refrigerant mass flow rate, and cooling capacity. The working pressure of the refrigeration system at evaporator and condenser were expressed with the saturation temperatures. In this study, a sensitivity analysis was performed with two cases. In the first case, the working saturation temperature of the condenser was fixed to 49 °C while the working saturation temperature of the evaporator was varied from −13 °C to −34 °C. In the second case, the saturation temperature of the evaporator was fixed to −24 °C while the saturation temperature of the condenser was varied from 38 °C to 60 °C. In the first case, it was found that all the considered performance parameters were sensitive to variation in saturation temperature of the evaporator. In the second case, compressor speed and power consumption showed negligible sensitivity to variation in saturation temperature of condenser but the other two performance parameters (refrigerant mass flow rate and cooling capacity) showed significant sensitivity to variation in saturation temperature of condenser. [ABSTRACT FROM AUTHOR]

HC-290 is a promising alternative for HCFC-22, which is an ozone depleting substance under Montreal Protocol. However, HC-290 charge is to be reduced because of its flammability. The objective of this study was to reduce the charge quantity of HC-290 in a split air conditioner, which was originally designed for HCFC-22. The effect of charge reduction on the performance of the HC-290 split air-conditioning system was studied experimentally by varying condenser tube diameter, length of capillary tube, and condenser air face velocity. Initially, simulation study was conducted using ART simulation software. In accordance with the simulation results, a 5.25 kW split air conditioner was modified and experimentally tested with HC-290 in a psychrometric test facility under standard test conditions as per IS 1391 part 2. The condenser tube diameter was reduced from 12.7 mm to 6.35 mm, while the length of capillary tube was increased from 650 mm to 820 mm with enhanced condenser air face velocities. It was found that with 300 g of HC-290 charge, the performance parameters such as cooling capacity, power consumption, and coefficient of performance were better than the baseline test with HCFC-22 in all conditions tested. [ABSTRACT FROM AUTHOR]