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Copyright of Transactions the Japan Society of Refrigerating & Air Conditioning Engineers is the property of Japan Society of Refrigerating & Air Conditioning Engineers 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 Transactions the Japan Society of Refrigerating & Air Conditioning Engineers is the property of Japan Society of Refrigerating & Air Conditioning Engineers 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.)

This article proposes an integrated solar PV refrigerator and heat pump (ISPVRHP) for Sub-Saharan African food vendors; the warm chamber would keep prepared food warm until the food is sold, while the cold chamber would minimise food spoilage. The ISPVRHP proposed in this article can cool water or other beverages and be capable of utilising the heat rejected to the atmosphere by the condenser for warming food. The ISPVRHP was modelled using ANSYS software, and the results were validated experimentally. The results show that both systems work well at peak hours, especially under more intense sun rays. The study found that the variation of incident solar radiation and ambient temperature has significant effects on the performance of the ISPVRHP; the wind speed, however, has only a minor impact on the total heat load of the system. In addition, the systems (cooling and heating) reached the desired temperatures and maintained them for long periods. The capacity of the refrigeration system can be increased by increasing the component sizes, including the PV system size. The ISPVRHP performance dropped substantially when the doors remained open for extended periods due to loss of energy through mass transfer.

To investigate the depressurization mechanism of the CO 2 vapor compression refrigeration cycle with an ionic liquid loop, a vapor-liquid equilibrium (VLE) model of CO 2 -[emim][Tf 2 N] in the flow state was established based on Aspen Plus, and the prediction of VLE in the supercritical state was carried out. Furthermore, the effects of CO 2 inlet pressure, absorber temperature, CO 2 inlet mole fraction and CO 2 inlet flow rate on the depressurization amplitude of absorber were analyzed through the absorption-desorption process simulation. The results showed that with the increase of CO 2 inlet pressure in the supercritical state, the depressurization amplitude increased but its growth rate slowed down, which indicated that the effect of pressure as a driving term of mass transfer decreased in the supercritical state. The depressurization amplitude decreased with the increase of absorber temperature, and decreased rapidly with the increase of CO 2 inlet mole fraction. In this sense, adding an auxiliary desorber at the absorber inlet is beneficial to the system depressurization. Due to the limited absorption capacity of quantitative [emim][Tf 2 N] in the absorber, with the continuous increase of CO 2 inlet flow rate, the depressurization amplitude first dropped sharply, then flattened, and later dropped rapidly. Because the CO 2 flow rate in an actual system is proportional to the system cooling capacity, the proper mass flow ratio of CO 2 -[emim][Tf 2 N] should be selected to reconcile the cooling capacity and depressurization amplitude. [ABSTRACT FROM AUTHOR]

Natural refrigerants such as CO2 have become a research hotspot. Under high-pressure conditions, a large throttling loss becomes the primary reason for the low circulation efficiency of the CO2 refrigeration cycle. Therefore, reducing the throttling loss is an effective method to improve efficiency. This study proposes a supersonic two-phase expander with a Laval nozzle as the core component. A CO2 supersonic two-phase expansion refrigeration cycle model is established, and an ideal cycle thermodynamic analysis and simulation investigation are conducted. The results show that the inlet pressure and temperature of the supersonic two-phase expander and the outlet pressure of the cyclone separation section affect the cooling performance of the system. The coefficient of performance (COP) of the CO2 supersonic two-phase expansion refrigeration cycle is 6.69, which is 1.63 times that of the existing CO2 transcritical refrigeration cycle, with relatively optimal refrigeration performance. Additionally, the operating pressure of the system is considerably reduced. The loss of liquid-phase velocity during gas-liquid separation affects the refrigeration performance of the system. The COP of the system decreases from 9.56 to 6.01, and the relative Carnot efficiency decreases from 0.95 to 0.60; however, it still remains at a high level. The preliminary thermodynamic analysis and simulation show that the proposed CO2 supersonic two-phase expansion refrigeration cycle is feasible and exhibits good development prospects.

Liquefaction of unconventional natural gases, such as coalbed methane, synthetic natural gas, coke oven gas, and tail gas from chemical processes, is an effective method for recycling. Owing to the involvement of large amounts of oxygen, nitrogen, or hydrogen, they usually need to be purified by low-temperature distillation. Thus, the unconventional natural gas liquefaction technology is quite different from that for the conventional natural gas. In this paper, the research progress of unconventional natural gas liquefaction in recent years is reviewed. For coalbed methane, large-scale coalbed methane projects abroad employed a cascade process owing to the refrigerant supply, while the research and development in China focused on small-scale or skid-mounted liquefaction devices and specific characteristics of air-bearing coalbed methane liquefaction. For synthetic natural gas, the structure of the liquefaction–distillation processes was employed because of hydrogen removal and the energy integration between the two parts was recommended to increase the system energy efficiency. For coke oven gas, the mainstream technology scheme to produce synthetic natural gas was methanation, followed by liquefaction. The new technology scheme of separating and liquefying coke oven gas to simultaneously produce liquefied natural gas and liquid hydrogen should be analyzed. In addition, the safety, phase equilibrium, and solubility issues related to the unconventional natural gas liquefaction are discussed.

A new type of air refrigeration cycle combined with a dew-point indirect evaporative cooler (IEC) is proposed. Corresponding thermodynamic calculations on the new cycle were carried out. A comparative analysis was carried out with the ordinary air refrigeration cycle and NH3 vapor compression cycle. The influences of operation conditions on the performances of the air refrigeration cycle before and after combining the dew-point IEC as well as the COP of the NH3 vapor compression cycle were analyzed. The results showed that the performance of the new air refrigeration cycle combined with the dew-point IEC was greatly improved. The maximum COP can be increased by 37.8% under the design conditions. In addition, compared to the NH3 refrigeration cycle, it can operate with simpler processes and equipment.

In this study, the working mechanism, performance evaluation indexes, and theoretical models of an ejector are summarized. The effects of the configuration and dimensions of an ejector and its nozzle, suction chamber, constant-area section, and diffuser on the performance are reviewed. Some typical examples of applications of ejector refrigeration systems are described, including single and multi-stage ejector refrigeration, combined compression–ejector refrigeration, combined ejector-absorption refrigeration, and ejector refrigeration systems without pump. Finally, prospective proposals of ejector research are suggested.

This paper aims to provide comprehensive 4E (energy, exergy, exergoeconomic, and exergoenvironmental) and advanced exergy analyses of the Refrigeration Cycle (RC) and Heat Recovery Refrigeration Cycle (HRRC) and comparison of the performance with R744 (CO2) and R744A (N2O) working fluids. Moreover, multi-objective optimization of the systems has been considered to define the optimal conditions and the best cycle from various perspectives. In HRRC, heat recovery is used as a heat source for an organic Rankine cycle. The energy and exergy analysis results show that utilizing HRRC with both refrigerants increases the coefficient of performance (COP) and exergy efficiency. COP and exergy efficiency for HRRC-R744 have been obtained 2.82 and 30.7%, respectively. Due to the better thermodynamic performance of HRRC, other analyses have been performed on this cycle. Exergoeconomic analysis results show that using R744A leads to an increase in the total product cost. Total product cost with R744 and R744A have been calculated by 1.56 $/h and 1.96$/h, respectively. Additionally, to obtain the processes' environmental impact, Life Cycle Assessment (LCA) is used. Exergoenvironmental analysis showed that using R744A increases the product environmental impact by 32%. Owning to the high amount of endogenous exergy destruction rate in the compressor and ejector compared to other equipment, they have more priority for improvement. Multi-objective optimization has been performed with exergy efficiency and total product cost objective functions as well as COP and product environmental impact for both refrigerants, which indicates that HRRC-R744 has better performance economically and environmentally. In optimal condition, the value of exergy efficiency, total product cost, COP, and the product environmental impact have been accounted for by 28.51%, 1.44 $/h, 2.76, and 149.01 mpts/h, respectively. [ABSTRACT FROM AUTHOR]

In this study, COP and heat capacities of evaporator and condenser were calculated by artificial intelligence and machine learning method in a vapor compression mechanical refrigeration cycle using well-known R134a as a refrigerant. Dataset was obtained with CoolPack software to train the model. Evaporating, condensing, superheating and subcooling temperatures are selected as input data. COP, heat capacities of evaporator and condenser are included in the dataset as target values. Artificial Neural Network (ANN) model was created with Matlab R2018b software and validated with target data. The output files obtained were compared with the target files and it was found that the mean square error value was quite close to one. The results of this study show that the ANN method can be used to obtain cycle parameters in one stage refrigeration cycle with high accuracy. [ABSTRACT FROM AUTHOR]

A comparative analysis of refrigeration cycles for supporting actual loads at temperatures around 28–30 K is presented. Within this temperature range, such cryoagents as Ne, He, H2, D2 and Ne-He mixture can be used. Refrigeration cycle simulations using various cryoagents were performed using the Aspen HYSYS V8.8 software package. [ABSTRACT FROM AUTHOR]

Featured Application: Experimental testing of a novel heat exchanger embedded with thermal energy storage material for refrigeration cycles and air-conditioning systems applications. This paper experimentally investigates the direct integration of 3.15 kg of phase change materials (PCM) into a standard vapour compression system of variable cooling capacity, through an innovative lab-scale refrigerant-PCM-water heat exchanger (RPW-HEX), replacing the conventional evaporator. Its performance was studied in three operating modes: charging, discharging, and direct heat transfer between the three fluids. In the charging mode, a maximum energy of 300 kJ can be stored in the PCM for the cooling capacity at 30% of the maximum value. By doubling the cooling power, the duration of charging is reduced by 50%, while the energy stored is only reduced by 13%. In the discharging mode, the process duration is reduced from 25 min to 9 min by increasing the heat transfer fluid (HTF) flow rate from 50 L·h−1 to 150 L·h−1. In the direct heat transfer mode, the energy stored in the PCM depends on both the cooling power and the HTF flow rate, and can vary from 220 kJ for a cooling power at 30% and HTF flow rate of 50 L·h−1 to 4 kJ for a compressor power at 15% and a HTF flow rate of 150 L·h−1. The novel heat exchanger is a feasible solution to implement latent energy storage in vapour compression systems resulting to a compact and less complex system. [ABSTRACT FROM AUTHOR]

PEM Fuel Cells (PEMFCs), fueled by hydrogen, are electrochemical devices that convert hydrogen to useful power and two by-products: heat and water. They cover an important part of power applications namely in the transportation area, and in other practical applications that are either stationary or portable. In particular, the domestic refrigerator is one of the daily and indispensable applications but with a high-energy demand due to the high running time cycles. This work is a technical assessment of the feasibility of building a coupled "PEM Fuel Cell – Refrigerator" system. Real technical data for the refrigerator are collected, processed and evaluated. The obtained results show reasonable flows consumption rates. In fact, the refrigerator requires a flow rate of 1.607 slpm of hydrogen and 8 slpm of air at a pressure of respectively 3 atm and 1 atm. The water is produced at a rate of 1.285 10−3 slpm. The annual amount of hydrogen consumed by the refrigerator is estimated to 28, 47 kg. The energy provided to the refrigerator is about 130 W and the energy needed by the air compressor is 28, 24 W. A technical solution is suggested at the end of this work to reduce the start and stop cycles of the fuel cell. • The possibility to build a coupled PEMFC – Refrigerator system is discussed. • The daily running time cycle of the refrigerator is collected. • The real energy consumed by the refrigerator is evaluated. • The energy balance and the flows consumption are estimated. • An energy storage subsystem is proposed for the stack lifespan enhancement. [ABSTRACT FROM AUTHOR]

In this study, a novel boil-off-gas handling process was proposed to optimize refrigerant mix and flow rate considering different boil-off gas rates under different weather conditions. The proposed design utilizes a nitrogen expander and mixed refrigerant cycle to generate subcooled liquified natural gas to cool the tank, preventing boil-off gas generation. The optimized design in terms of exergy destruction minimization is assessed in a multiple steady-state simulation based on seasonal boil-off gas and heat ingress rates which are predicted by a machine learning algorithm. Furthermore, an economic analysis of the proposed reliquefaction processes was conducted. The result shows that the conventional process has 46% and 8% lower exergy destruction compared to the proposed one for the nitrogen expander and mixed refrigerant cycle respectively. However, the proposed process outperforms the conventional process in terms of investment costs. The proposed process has 36% and 27% lower investment costs for the nitrogen and mixed refrigerant cycle compared to the conventional one. This leads to higher profit for the novel process and performs better in the face of uncertainty of liquified natural gas price. [Display omitted] • This study proposed a novel BOG handling process for minimizing capital costs. • This study offers BOG handling using subcooled LNG refrigerated by MR and N 2 cycle. • Utilizes ML for predicting BOG and heat ingress rates in varying weather conditions. • The study lowers capital costs by 36% and 27% compared to the traditional approach. [ABSTRACT FROM AUTHOR]

In this paper, parametric analysis and optimization of the transcritical ejector refrigeration cycle using different working fluids have been proposed which can be employed in the parts of solar energy processes. The main advantages of using ejector in the refrigeration cycles, which often use instead of the compressor, are simplicity in construction and maintenance, high reliability and low cost. In this study, the transcritical ejector refrigeration cycle is modelled using EES software and the effects of different parameters such as temperature and pressure of different parts of cycle on the coefficient of performance and entrainment ratio are investigated. In continued, the coefficient of performance of the transcritical ejector refrigeration cycle for four different working fluids is optimized using the combination the Artificial Neural Network and Particle Swarm Optimization algorithm.

Faced with a changing about global environmental issues, there are great expectations to optimize energy saving design in home appliance products. For effective energy saving design in Refrigeration System, integrated design method is highly needed to understand detailed physical behavior of a whole product based on careful study of the interactive influence of each device (e.g., Insulator layout design, Heat exchanger, Compressor and FAN flow rate balance, etc.). Although 1D and 3D-CAE tool become a part of engineer's daily routine in recently, effective integrity interface between the Digital tool and real humanistic collaboration process is the most important key to accomplish the innovative synthesis. This paper presents a practical lean development method using set-based design method which combines digital tool with human tacit knowledge for architecture type product having hierarchical interaction between system and subsystems.

An office drinking water cooler is converted to a humidity absorption device. The reservoir-type evaporator of the water cooler is separated, and a finned-tube evaporator is installed. A channel is installed at the inlet of the evaporator. A fan, a cool-mist humidifier, and a heater are installed inside this channel, where the amount of humidity and heat production can be adjusted. Several pressure gauges are installed at different locations of the cycle and monitor cycle performance while working. Pressure variations in different locations of the cycle are measured at various inlet air conditions. The MHI is defined as the ratio of condensation enthalpy to the total given heat. Changes of this index are evaluated by changing the input conditions. Results show that with increasing the air temperature, the condenser and evaporator pressure increases. Results of absorbed water in various MHIs show that with increasing this index, the amount of absorbed water increases. The graph of the absorbed water based on the MHI can be used to estimate the amount of water collected from this device under different climatic conditions. The amounts of collected water from this device for several different cities of Iran are presented. Results show that in high MHIs for a device with a quarter horsepower, the water production rate can reach to 250 g h−1. Also, if the device is working continuously in these conditions, it can produce about 4 kg of water per day. [ABSTRACT FROM AUTHOR]

The efficiency of a system with separate subsystems is compared with that of an integrated system developed by means of an informational approach to system organization. The comparison is based on exergy analysis. As an example, we consider a system for commercial carbon dioxide production from flue gases at a trigeneration power plant. The trigeneration power plant combines two subsystems: a Rankine cycle for flue gas heat recovery (after the removal of sulfur and nitrogen oxides); and a refrigeration cycle with an expander for the capture and extraction of carbon dioxide as a commercial product. The exergy efficiency of the integrated system is more than twice that of the system with the components operating independently of each other. This indicates a synergetic effect, in which the overall efficiency of the system exceeds the efficiency of either subsystem. [ABSTRACT FROM AUTHOR]

• A modified vapor compression refrigeration cycle using R170/R290 is presented. • Energy and exergy analysis are applied to explore the system performance. • The presented cycle outperforms the conventional cycle in terms of COP and exergy efficiency. This study presents a modified vapor compression refrigeration cycle (MVRC) with zeotropic mixture R170/R290 for freezers. Different from the conventional vapor compression refrigeration cycle (CVRC), two separators and corresponding capillary tubes are employed into MVRC to achieve partial-condensation separation and flash separation for a composition shift effect, respectively. MVRC can provide the cycle performance improvement due to the composition shift effect of zeotropic mixture. The mathematical model based on energetic and exergetic methods is developed to evaluate the cycle operating performance of MVRC and compare with that of CVRC. The results show that MVRC is more promising for low-temperature cooling system over CVRC. Under the given operation condition, the cycle performance improvement of MVRC over CVRC in terms of coefficient of performance (COP), volumetric cooling capacity and exergy efficiency can reach up to 12.7%, 32.6% and 20%, respectively. The performance characteristics of the proposed cycle demonstrate its potential advantages for application in the freezers. [ABSTRACT FROM AUTHOR]

In this study, a modified ejector-expansion refrigeration cycle (MERC) is proposed for applications in small refrigeration units. A vapor bypass circuit is introduced into the standard ejector expansion refrigeration cycle (ERC) for increasing the ejector pressure lift ratio, thereby lowering the compressor pressure ratio in the MERC. A mathematical model has been established to evaluate the performances of MERC. Analysis results indicate that since a two phase vapor-liquid stream is used to drive the ejector in the MERC, a larger ejector pressure lift ratio can be achieved. Thus, the compressor pressure ratio decreases by 21.1% and the discharge temperature reduces from 93.6°C to 82.1°C at the evaporating temperature of -55°C when the vapor quality of two phase vapor-liquid stream increases from 0 to 0.2. In addition, the results show that the higher ejector component efficiencies are effective to reduce the compressor pressure ratio and the discharge temperature. Actually, the discharge temperature reduces from 91.4°C to 82.1°C with the ejector component efficiencies increasing from 0.75 to 0.85 at the two phase stream vapor quality of 0.2. Overall, the proposed cycle is found to be feasible in lower evaporating temperature cases. [ABSTRACT FROM AUTHOR]

In solid-state COB (chip on board) LED (light-emitting diode), the process technology is enhanced, brightness of light per power is improved, and optical performance is increased. However, the COB LED chip junction temperature, Tj, is still a disadvantage in critically high hot spots and high temperatures. These disadvantages can shorten life and reduce efficiency. Therefore, Tj must also be solved. From a single-crystal silicon chip packaging LED to multichip COB packaging LED, this tool has become the most mainstream item in the market development of high brightness. Therefore, investigating the research approach and techniques needed to solve the high temperature Tj is necessary. In this study, the system can be used an environment-friendly refrigerant as R407C and R134a systems for a thermal cooling temperature and constant flow compression refrigeration cycle system that cool ultra-high-power multichip COB and high-brightness gallium indium nitride LED heat source. To reduce the COB LED chip, Tj, temperature needs to reach the following specifications: < 125 °C to maximum 150 °C and Tcase < 50 °C to maximum 85 °C. This temperature will maintain good luminous efficiency and long life. In addition, this approach aims to solve the maximum power of thermal dissipation Tj. [ABSTRACT FROM AUTHOR]

In this study, a refrigeration cycle was simulated with different refrigerants in a petrochemical plant in Iran. Using Aspen HYSYS Software, necessary modifications were checked as much as possible and optimum values for important parameters affecting cycle of the optimized simulators in the Aspen HYSYS were found. Having found the most economical refrigeration cycle, financial expenses were reduced in the refrigeration cycle. Then, results from the simulation by Aspen HYSYS and Icarus software were compared with actual values of the petrochemical plant under study, and the most efficient and economical strategies to achieve the desired cycle were suggested. Energy consumption of the compressors was optimized by creating a Joule–Thomson balance between VLV-100 and the compressor power of the refrigeration cycle, which reduces the cost of utilities in the refrigeration cycle. The aim of this study is process optimization of the refrigeration cycle economically and also use of the environmental friendly refrigerants. [ABSTRACT FROM AUTHOR]

• Theoretical models, solving and optimizing techniques have been highlighted. • Different experimental and visualization techniques have been reviewed. • Ejector and combined ejector refrigeration systems have been reviewed. • Workless boiler, micro and combined ejector systems should be given a special attention. • Variable component efficiency assumption should be imposed in future studies. The objective of this work is to provide a literature survey on the research attempts made in the field of ejector refrigeration systems and the studies made on the ejector as a component. The review is to be structured four parts. In the first part, the focus is on the effect of different geometrical aspects affecting the performance of the ejector in terms of entertainment ratio, pressure ratio and other flow related features, where various geometrical aspects are reviewed including primary nozzle position, area ratio, mixing suction length. The second part is dedicated to reviewing the attempts made in proposing different mathematical models to investigate the behavior of the ejector. In addition, experimental flow visualization attempts are also presented. In the third part, the study focus is on the main ejector refrigeration systems proposed. Finally, the effect of using different working fluids on the performance of the ejector refrigeration system will be reviewed. [ABSTRACT FROM AUTHOR]

This study focuses on the thermal performance analysis of an organic Rankine cycle powered vapor compression refrigeration cycle for a set of working fluids for each cycle, also known as a dual fluid system. Both cycles are coupled using a common shaft to maintain a constant transmission ratio of one. Eight working fluids have been studied for the vapor compression refrigeration cycle, and a total of sixty-four combinations of working fluids have been analyzed for the dual fluid combined cycle system. The analysis has been performed to achieve a temperature of −16 °C for a set of condenser temperatures 34 °C, 36 °C, 38 °C, and 40 °C. For the desired temperature in the refrigeration cycle, the required work input, mass flow rate, and heat input for the organic Rankine cycle were determined systematically. Based on the manifestation of performance criteria, three working fluids (R123, R134a, and R245fa) were chosen for the refrigeration cycle and two (Propane and R245fa) were picked for the organic Rankine cycle. Further, a combination of R123 in the refrigeration cycle with propane in the Rankine cycle was scrutinized for their highest efficiency value of 16.48% with the corresponding highest coefficient of performance value of 2.85 at 40 °C.

An ejector is a simple mechanical device that can be integrated with power generation or the refrigeration cycle to enhance their performance. Owing to the complex flow behavior in the ejector, the performance prediction of the ejector is done by numerical simulations. However, to evaluate the performance of an ejector integrated power cycle or refrigeration cycle, the need for simpler and more reliable thermodynamic models to estimate the performance of the ejector persists. This research, therefore, aims at developing a single mathematical correlation that can predict the ejector performance with reasonable accuracy. The proposed correlation relates the entrainment ratio and the pressure rise across the ejector to the area ratio and the mass flow rate of the primary flow. R141b is selected as the ejector refrigerant, and the results obtained through the proposed correlation are validated through numerical solutions. The comparison between the analytical and numerical with experimental results provided an error of less than 8.4% and 4.29%, respectively.

This paper experimentally investigates the direct integration of 3.15 kg of phase change materials (PCM) into a standard vapour compression system of variable cooling capacity, through an innovative lab-scale refrigerant-PCM-water heat exchanger (RPW-HEX), replacing the conventional evaporator. Its performance was studied in three operating modes: charging, discharging, and direct heat transfer between the three fluids. In the charging mode, a maximum energy of 300 kJ can be stored in the PCM for the cooling capacity at 30% of the maximum value. By doubling the cooling power, the duration of charging is reduced by 50%, while the energy stored is only reduced by 13%. In the discharging mode, the process duration is reduced from 25 min to 9 min by increasing the heat transfer fluid (HTF) flow rate from 50 L·h−1 to 150 L·h−1. In the direct heat transfer mode, the energy stored in the PCM depends on both the cooling power and the HTF flow rate, and can vary from 220 kJ for a cooling power at 30% and HTF flow rate of 50 L·h−1 to 4 kJ for a compressor power at 15% and a HTF flow rate of 150 L·h−1. The novel heat exchanger is a feasible solution to implement latent energy storage in vapour compression systems resulting to a compact and less complex system.

Highlights • The working mechanism of imposing a DC flow on the regenerator is investigated. • The real gas losses are reduced significantly with an optimized DC flow. • The coefficient of performance of the refrigeration cycle is improved exponentially. • The mechanism of improving the liquefaction rate is further revealed. • The entropy loss of this approach and reduction possibilities are analyzed. Abstract Improving efficiency is an enduring effort for all refrigeration cycles. Real gases cause "intrinsic" heat losses in the regenerator and degrade the coefficient of performance (COP) of the regenerator of the refrigeration cycle. Previous experimental and numerical studies found that the COP of the regenerative refrigerator can be improved by imposing a direct-current (DC) flow, and the liquefaction rate can be improved by several times when the gas is precooled by the regenerator that works down to the temperatures close to or below the critical point. However, the working mechanism of such improvements has not been fully explored. In this paper, the working mechanism of imposing a DC flow on the regenerator working with a real gas is revealed based on thermodynamic analyses. The theoretical value of the DC flow and its influence on the COP of the regenerator are analyzed. The results show that the COP of the regenerator can be improved by over 10 times with a DC flow. An even higher relative Carnot COP of around 80% is possible to obtain in some specific temperature ranges. The enthalpy loss and the entropy loss of this approach has been estimated. This approach provides a potential way to improve the refrigeration COP and the liquefaction rate significantly. Measured liquefaction results found in the relevant literature have been analyzed to demonstrate the effectiveness of this approach. [ABSTRACT FROM AUTHOR]

Highlights • A model for a three refrigerant cascade LNG liquefaction plant is presented. • Several control structures are investigated to minimize the operational loss. • The exact local method finds the best controlled variables for SOC. • The optimal subset of n measurements is selected using a branch and bound method. Abstract In this paper we apply self-optimizing control (SOC) to a cascaded LNG liquefaction plant. We first introduce the model, and then define the operational objective, which is to achieve minimal energy consumption while satisfying operational constraints. Four control structures are compared; a "standard" temperature control structure, an SOC structure with two plant measurements, an SOC structure that uses a combination of plant measurements as controlled variable, and an SOC structure where we also include measurements of disturbances in addition to the plant measurements. We find that the SOC structures significantly reduce the average steady-state loss when the operating conditions change. We furthermore find that using more plant measurements in the SOC structure results in lowered losses. In particular, for the disturbances considered, the steady-state loss becomes acceptably low, such that there is no need for a supervisory real-time optimization layer. Finally, it has been found that including disturbance measurements results in somewhat reduced losses, although the improvement was insignificant for the studied case. The effectiveness of the SOC framework is shown by closed-loop step responses to selected disturbances. [ABSTRACT FROM AUTHOR]

Abstract Solar energy assisted heat pump systems (SAHP) have been used in this application. SAHP system with solar collectors and the heat pump are combined into one unit so as to convey the solar energy to the refrigerant. The solar collector is used as the evaporator, where the refrigerant is directly vaporized by solar energy input. Due to the complicated technical issues associated with a combined system that provides air for space heating and domestic hot water, most of the previous studies have concentrated on water heater heat pump mechanism. The current work is aimed at examining the use of a new multi-functional heat pump (DX-SAMHP) , air for space heating mutually with solar for domestic hot water without employing an auxiliary heater. Comprehensive experimental and analytical studies in the first of its kind have been performed on the new system. The novel system with ternary panels and the thermal performance of the collector has been examined in this study. Results indicate that the DX-SAMHP using solar inner and outer panels for space and water heating is a promising substitute for the existing DX-SAHP water heater. Compared to the conventional solar-assisted SAHP heat pump systems, the coefficient performance of the new design doubles that of the conventional DX-SAHP systems. Highlights • Developed design for heating system using solar assisted-heat pump cycle and R-407C as working fluid is proposed. • Positive influence of using indoor collector in absorbing wasted heat. • Comparison of experimental and mathematical modelling for predicting cycle process and measuring COP's. [ABSTRACT FROM AUTHOR]

For more than a decade, there is a great demand for finding environmentally-friendly refrigerants obeying the global warming potential value restrictions of the tough environmental legislation. Among the candidate working fluids, R744 (carbon dioxide or CO2), R170 (ethane), and R41 (fluoromethane) are selected to be investigated parametrically in this paper. Performance comparison is made for these three working fluids individually in both transcritical (supercritical) refrigeration cycle and modification of this cycle with ejector expansion. As the first step, the effects of the gas cooler outlet temperature, evaporator temperature, and evaporator outlet superheat temperature difference on the overall performance and percentage expansion losses are investigated within a specific gas cooler pressure range. Evaporator outlet superheat temperature difference is found to be the least effective parameter on the performance; hence, secondly, the transcritical ejector expansion refrigeration cycle is analyzed considering only evaporator temperature and gas cooler outlet temperature based on the same gas cooler pressure ranges. Thermodynamic models are constructed in Matlab® and the ejector equations for the ejector expansion refrigeration cycle are established with reference to constant pressure mixing assumption. Comparisons of the performance, percentage expansion losses, and performance improvement potential through the implementation of the ejector instead of the expansion valve among these three refrigerants having low critical temperatures represent the main objective of the paper in order to make contributions to the previous researches in the literature. [ABSTRACT FROM AUTHOR]

Summary: In a recent perspective paper, Dincer's 6‐step approach in teaching thermodynamics was explained with reference to Bryton and refrigeration cycles. In the present study the benefits of this approach was assessed with nutrition, as a distant example. One of the best advantages of using this guided tool was found as its functionality in avoiding the analogy mistakes and pointing the spots where further research is needed. [ABSTRACT FROM AUTHOR]