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The Kigali Amendment to the Montreal Protocol officially calls for a global phase-down of conventional hydrofluorocarbon refrigerants to reduce the climate impact of the refrigeration, heating, ventilation and air-conditioning industry. Several Asian countries, such as China, Japan and Singapore, have ratified the Kigali Amendment. Among the various options, CO₂ is recognized as a viable solution to replace conventional refrigerants, especially in supermarket applications. However, current CO₂ refrigeration systems suffer from significant throttling loss due to their high operating pressure which makes CO₂ systems less efficient as compared to conventional systems. This paper introduces different CO₂ refrigeration systems for supermarkets as well as the latest technology development to improve energy efficiency and the global refrigeration market landscape. Supermarket CO₂ refrigeration systems have already been widely adopted in Europe and several Asian countries, but China has been slow in adopting this technology despite having a tremendous and potentially expanding refrigeration market. A summary of the constraining factors and corresponding proposition of future development strategies is provided with a focus on China which can be also applied to other Asian countries.

Due to their large latent heats, pseudoelastic Ni–Ti-based shape memory alloys (SMAs) are attractive candidate materials for ferroic cooling, where elementary solid-state processes like martensitic transformations yield the required heat effects. The present work aims for a chemical and microstructural optimization of Ni–Ti for ferroic cooling. A large number of Ni–Ti-based alloy compositions were evaluated in terms of phase transformation temperatures, latent heats, mechanical hysteresis widths and functional stability. The aim was to identify material states with superior properties for ferroic cooling. Different material states were prepared by arc melting, various heat treatments and thermo-mechanical processing. The cooling performance of selected materials was assessed by differential scanning calorimetry, uniaxial tensile loading/unloading, and by using a specially designed ferroic cooling demonstrator setup. A Ni${}_{45}$Ti${}_{47.25}$Cu₅V${}_{2.75}$ SMA was identified as a potential candidate material for ferroic cooling. This material combines extremely stable pseudoelasticity at room temperature and a very low hysteresis width. The ferroic cooling efficiency of this material is four times higher than in the case of binary Ni–Ti.

This paper provides a comprehensive review of ejector technology for refrigeration applications, combining an understanding of basic fluid flow fundamentals within the ejector with application in cycle-level development. An ejector is a passive device that requires no external mechanical input or moving parts. A high-velocity motive stream produces a low-pressure region into which a suction flow is entrained, resulting in a pressure rise of the suction flow and mixing between the two streams to provide a pumping effect. The first part of this review addresses the progression from experiment-based analytical models to computational modeling of the ejector itself from the early 1950s to 2009. Included is an assessment of the most recent work in CFD modeling, and an exploration into what is needed to develop these models further. Suggestions for future research include better modeling of shock phenomena and the effects of two-phase flow in ejectors. The second part of this review focuses on ejector applications in refrigeration cycles with special emphasis on the vapor-jet refrigeration cycle. Important connections are made between ejector component and system level studies, an understanding of which would enable improvement of system level performance to the extent where they could be used in some niche applications instead of conventional refrigeration systems.

A refrigeration system exhibits a dynamic behavior on which the variables are interdependent and subjected to oscillation, hence, implicating necessity of changes on operating conditions and undesirable energy expenses. These characteristics ratify the importance of adequate dimensioning and equipment selection to find pre-defined operating conditions such as, the maximum cooling capacity and the evaporating and condensing temperatures. The application of fuzzy control in industrial processes is growing fast in the last decades, mainly in processes whose first principle models require complex methods to be simulated. In these cases, the fuzzy controllers’ capacity of acting correctly based only on expert knowledge and on the capacity of inter-relating all the variables of the process are attractive features. This work presents the experimental development and evaluation of fuzzy-PID controllers for the maintenance of the evaporating temperature in a chiller. The system was submitted to load and set-point disturbances accomplishing an analysis based upon error parameters and transient response. The results showed that fuzzy controllers were adapted satisfactorily.

Carbon dioxide (CO₂) is one of the natural refrigerants which can be used as working fluid in various refrigeration applications along with the ammonia and hydrocarbons due to its eco-friendliness, higher volumetric capacity, good heat transfer properties, etc. The present article consists of two parts: A detailed comparative study of CO₂-based transcritical refrigeration systems with conventional refrigerants-based systems in terms of both thermodynamic and heat transfer performances, and review of both theoretical and experimental researches on transcritical CO₂ vapor compression cycle for various refrigeration applications including commercial product status. Suitability of the CO₂ system in specific refrigeration application is also discussed.

An analytical investigation on the performance of adsorption–compression hybrid refrigeration systems with two different cycle configurations, cascade type and subcool type has been performed. In the former type, a cascade condenser is used which works as a condenser for mechanical compression cycle and evaporator for adsorption cycle. In the latter type, an evaporative subcooler is used which subcool the fluid of mechanical compression cycle. The refrigerants examined for the mechanical compression cycle are R134a, R152a, R1234yf and R1234ze whereas ethanol is the refrigerant for the adsorption cycle. The main feature of the proposed system is the capability to significantly reduce work input for the mechanical compressor which results up to 30% energy saving potential depending on the selection of refrigerant and system configuration. Based on the thermodynamic properties and laws the study analyzed the effect of the major design parameters such as evaporation temperature, compressor discharge pressure and desorption temperature on the system performances.

The impact of transient conditions along with varied capillary tube length and charge quantity over the performance of a simple refrigeration system under all time transient operations has been investigated in a specially designed experimental setup. A maximum drop of 75% in the coefficient of performance (COP) of the system was recorded by the end of the transient cooling period. The continuous deterioration in performance from start to end of the transient cooling job can be well minimized by the optimum selection of capillary tube length and charge quantity. This paper refers some of the existing methods to determine the appropriate length of the coiled capillary tube and charge quantity for a newly designed refrigeration machine working under steady state conditions and compares the experimental results of transient operation with these. Optimum charge quantity for transient operation in the present study is 3.5% to 5% less than that calculated by the existing analytical and numerical methods. The optimum length of coiled capillary tube for transient operation as found in this experimental study matches approximately with the length predicted by the existing dimensionless correlation on the basis of design parameters as estimated towards the end of the transient cooling period.

Alcoholic fermentation is one of the most important stages in industrial ethanol production process, involving a biochemical and exothermic reaction. Sometimes cooling towers are not capable of supplying a cold utility with a temperature low enough to maintain the fermentative medium temperature in a desirable range. Absorption Refrigeration Systems (ARS) appears to be a good alternative to obtain the necessary refrigeration for the fermentation process. The aim of the present paper was to carry out a thermodynamic analysis of ARS, evaluating their performance through the First and Second Laws of Thermodynamics. ARS with different configurations were studied (single-effect and double-effect with series, parallel and reverse parallel flows), all of them operating with water/lithium bromide mixture as working pair, under different operating conditions in order to satisfy the cooling load required by an industrial alcoholic fermentation process. Another objective of this paper was to investigate the risk of LiBr crystallization, which can result in scaling formation, with the aid of the solid–liquid phase equilibrium curve of H₂O/LiBr mixture. Among the double-effect configurations studied, it was observed that series flow presents the more significant crystallization risk, which represents a limit to improve its First and Second Law performances. It was verified that the Second Law performance for the single-and double-effect ARS analyzed are similar, but their First Law performance are considerably different. This is due to the amount and quality of the heat consumed in the first effect generators of these systems. For a base case studied, First Law performance measured by coefficient of performance (COP) of double-effect ARS is 72% greater than the one for single-effect, while for Second Law performance, measured by exergetic efficiency, an increase of 5% was observed.

The aim of this paper is to develop a complete, precise and simple numerical model based on the thermophysical properties of an adsorptive cooling system (using activated carbon–methanol pair), analyze and discuss the heat and mass transfer processes and identify the parameters which influence the system performance. In the design of adsorption refrigeration system, the characteristics of both adsorbate–adsorbent pairs and system operating conditions are very important. So in this model, different thermophysical properties of working pair such as, specific heat, density, isosteric heat of adsorption and desorption, and different temperatures of the system are considered. A simulation code, written in FORTRAN, is carried out. The performance of the system is assessed in terms of refrigeration effect and coefficient of performance (COP).

Applications of advanced control algorithms are important in the refrigeration field to achieve low-energy costs and accurate set-point tracking. However, the designing and tuning of control systems depend on dynamic mathematical models. Approaches like analytical modeling can be time-consuming because they usually lead to a large number of differential equations with unknown parameters. In this work, the application of system identification with the fast recursive orthogonal least square (FROLS) algorithm is proposed as an alternative to analytical modeling to develop a process dynamic model. The evaporating temperature (EVT), condensing temperature (CDT) and useful superheat (USH) are the outputs of interest for this system; covariance analysis of the candidate inputs shows that the model should be single-input–single-output (SISO). Good simulation results are obtained with two different validation data, with average output errors of 0.0343 (EVT model), 0.0079 (CDT model) and 0.1578 (USH model) for one of the datasets, showing that this algorithm is a valid alternative for modeling refrigeration systems.

The adequate and efficient performance of HVAC systems are signs of luxury and human comfort, and the improvement of their performance has been the target of continuous researches. Choosing the suitable refrigerant is the main parameter in matching the system components, selecting the type of heat exchangers, the compressor, the expansion device and the suitable lubricant. The theoretically ideal refrigerant is the one having zero ozone depletion potential (ODP), low global warming potential (GWP), nontoxic, nonflammable, has appropriate thermodynamic and heat transfer properties and is compatible with any type of lubricating oil. Chlorinated, fluorinated refrigerants, zeotropic and azeotropic mixtures satisfy many requirements, but have high ODP and GWP and are not compatible with all types of oil. Hydrocarbons (HCs) satisfy all the requirements except being highly flammable. This work reviews previous research aiming to find substitutes for the environmentally harmful refrigerants by other environmentally friendly ones and compare their performance in various HVAC appliances.

Thermal systems of buildings in the tropics are highly energy intensive. In this study, a novel integrated solar photovoltaic–thermal–refrigeration (PVTR) system used to produce hot water and air-conditioning in the tropical climate conditions of Singapore was analyzed. A dynamic simulation model was formulated for the analysis. Mathematical models were developed for the PV sandwich attached with a solar flat plate collector and for the main components of the refrigeration system. Thorough investigation of the electrical and thermal performances of the system were conducted through the analysis of coefficient of performance (COP), cooling capacity, water temperature and heat capacity in water heater, photovoltaic (PV) module temperature and PV efficiency. The results show that attractive electrical and thermal performance can be achieved with a maximum annual cooling COP of 9.8 and a heating COP of 11.3. The PV efficiency and power saving were 14% and 53%, respectively. The annual cooling, heating and PV energy produced were 9.7, 15.6 and 1.6MWh, respectively. The financial payback period of the system was 3.2 years and greenhouse gas (GHG) emission reduction annually was 12.6 tons of CO₂ equivalents (tCO₂e).

An experimental performance study is performed on a refrigeration system equipped with a scroll compressor and tested with R22 using an electronic expansion valve (EEV) as an expansion device and controlled by proportional-integral-derivative (PID) control method. The system is tested at $-12^{\circ }$C, $-8^{\circ }$C, $-4^{\circ }$C, 0${}^{\circ }$C and 4${}^{\circ }$C evaporator air temperature and 20${}^{\circ }$C, 25${}^{\circ }$C and 30${}^{\circ }$C condenser inlet water temperature at 50Hz compressor driving frequency and 50Hz evaporator fans driving frequency. R22 reached the set point at all temperatures except $-12^{\circ }$C evaporator temperature with 30${}^{\circ }$C condenser temperature due to the severe increase in the compressor discharge temperature that could result in the lubricating oil burnout. Then, the system is retrofitted with a reciprocating compressor especially designed to be used with R290 and tested with R290 at the same evaporator and condenser temperatures using EEV as an expansion device. R290 reached all set points at all evaporator and condenser temperatures. Also, R290 was able to reach all evaporator temperatures at higher condenser temperatures, 35${}^{\circ }$C and 40${}^{\circ }$C, and this will be discussed in future work. The results show that using R290, the pulldown time decreases by 30.3–71.4%, the ON time ratio decreases by 1–23.6%, the compressor discharge temperature decreases by 46.6–81${}^{\circ }$C, the refrigerant mass flow rate decreases by 28.8–50.4%, VRC decreases by 15.2–32.5%, the compressor power consumption decreases by 34.4–44.3% and coefficient of performance (COP) increases by 35–115.5%.

The heat transfer characteristics of R134a flow boiling in a horizontal tube of an evaporator section for a refrigeration system of 310-W capacity are investigated experimentally and numerically. The experimental work was conducted using an evaporator tube test section of inner diameter 5.8mm and length 600mm. The ranges of investigated experimental data for heat flux, mass flux, saturation temperature and vapor quality were 13.8–36.6kW/m², 52–105kg/m²$\cdot$s, $-15$–$-3.7^{\circ }$C and 0.2–1, respectively. Numerical analysis was based on two-phase flow turbulent model and this model was solved using the Ansys-18 code. The results showed that the effects of heat flux, mass velocity and saturation temperature on local heat transfer coefficient and pressure drop were greater compared to that of the refrigerant vapor quality. The enhancements in local heat transfer coefficient due to the increase in heat flux, mass and saturation temperature were 38%, 57% and 64%, respectively, within the prescribed test conditions. The influence of mass flux variation on pressure drop along the evaporator channel was higher in the range of 27% compared to the heat flux effect. The average deviations between experimental and numerical results of heat transfer coefficient and pressure gradient were 14% and 17%, respectively, while the same between the experimental and predicted results were 16% and 33%, respectively.

In this study, energy and exergy analysis was used to evaluate the performance of a vapor compression refrigeration system with a flooded evaporator and the causes of high temperatures of beverage during the production process determined. Subsequently, the components of the operation that require modification were identified in order to improve the system performance. The actual operating parameters related to energy and exergy analysis of the investigated beverage manufacturing plant were measured, the thermal properties of the beverage were determined from a calorimeter experiment, and mathematical models were developed based on the first and second laws of thermodynamics from the literature. The system energy and exergy efficiencies were 57.46% and 21.17%, respectively, whereas the system exergy destruction was 695.71kW. The highest exergy destruction among the components of the refrigeration system occurred at the cooling plate, followed by the ammonia compressor. The cooling plate also experienced a loss in the refrigerating effect of 43.59kW. Therefore, the cooling plate is the area with the highest potential for improvement. The ammonia compressor presents another potential area of improvement, which includes operating the compressor at a high compression ratio and high superheated temperature. However, the reduction of beverage inlet mass flow rate at the cooling plate offers the best opportunity to achieve a low beverage temperature between 1.00^∘C and 2.00^∘C and decreasing the system exergy destruction without incurring additional investment costs.

Ordinary refrigeration systems such as vapor-compression refrigerators are the commonly used devices in industry, mostly for their high efficiencies. However, they make a significant contribution to the depletion of Ozone and global warming due to their operational refrigerants. Hence, thermoacoustic refrigeration can be a great alternative candidate which uses inert gases such as air, helium and nitrogen as the primary refrigerant. Thermoacoustic refrigerators convert the acoustic power (sound waves) into a thermal effect (cooling power). Thermoacoustics can be counted as a new technology that has a strong potential toward the development of the thermal applications. This study aims to design and fabricate miniaturized traveling wave thermoacoustic refrigerator which can be driven by an ordinary loudspeaker. The optimized numerical design of the refrigerator shows an overall efficiency (cooling power over input electricity) of nearly 66% at a temperature difference of 25K (between cold and ambient heat exchangers). The maximum estimated cooling power is 65W at coefficient of performance (COP) of 2.65.

This paper presents the analysis of a modified vapor compression cooling system which uses an ejector as an expansion device. Expanding refrigerant in an ejector enhances the refrigeration effect and reduces compressor work. Therefore, it yields a better coefficient of performance. Thermodynamic analysis of a constant area ejector model has been done to obtain primary dimensions of the ejector for given condenser and evaporator temperature and cooling capacity. The proposed model has been used to design the ejector for three refrigerants; R134a, R152a and R1234yf. The refrigerant flow rate and the diameters at various sections of the ejector have been obtained by doing numerical modeling in Engineering Equation Solver (EES). Refrigerant R1234yf demanded the highest diameter requirements at a fixed 5^∘C evaporator temperature and 40^∘C condenser temperature for a given range of cooling load. Both primary and secondary refrigerants flow rates are higher for R1234yf followed by R134a and then R152a.

The world is now living in an energy crisis. Refrigeration and air-conditioning systems have become the basics of daily life in various fields and accordingly, it cannot be dispensed. Refrigeration machines and air-conditioning systems are the most energy-consuming systems, independent on the application whether it is domestic, commercial, industrial or medical. Therefore, using cooling systems which are powered by thermal energy, e.g., solar energy, can save a lot of electrical energy. Absorption refrigeration system is an example of a refrigeration system powered by heat energy. However, the system problem here is that it has low coefficient of performance (COP). The objective of this research is to improve the COP of the ammonia absorption cycle. This is done in the absorber unit by improving the absorption of the refrigerant ammonia into the ammonia–water solution. The absorption efficiency is improved by using (1) a stirrer pump to improve mixing, (2) sprayers to increase the contact area between ammonia and ammonia–water solution and (3) continuous cooling of the solution during the absorption process via an external heat exchanger. The COP of the ammonia absorption cycle has increased from 0.48 to 0.715, i.e., by 49%. This is due to the improvement of the absorption of the ammonia into the ammonia–water solution.

The rising need for thermal comfort has resulted in a rapid increase in refrigeration systems’ usage and, subsequently, the need for electricity for air-conditioning systems. The ejector system can be driven by a free or affordable low-temperature heat source such as waste heat as the primary source of energy instead of electricity. Heat-driven ejector refrigeration systems become a promising solution for reducing energy consumption to conventional compressor-based refrigeration technologies. An air-conditioning system that uses the ejector achieves better performance in terms of energy-saving. This paper presents a study on the combined driven refrigeration cycle based on ejectors to maximize cycle performance. The experimental setup is designed to determine the coefficient of performance (COP) with ejector nozzle sizes 1.8, 3.6, and 5.4mm, respectively. In this system, the R-134a refrigerant is considered as a working fluid. The results depict that the efficiency is higher than that of the conventional refrigeration method due to comparing the performance of the conventional refrigeration cycle and the combined driven refrigeration cycle. The modified cycle efficiency is better than the vapor compression cycle below 0^∘C, which implies sustainability at low temperatures by using low-grade thermal energy. For the improvement of mechanical efficiency, proposed cycle can be easily used.

The Natural Gas Liquids (NGL) recovery unit is one of the processes that requires cooling. The sweetened gas enters this unit after the dehydration stage, and the final product called NGL Product is stored and ready for consumption or export. In this research, the first, one of the NGL units, is simulated with HYSYS software. Three types of processes with different cooling systems are studied using the exergy analysis method. Joule–Thomson’s combination with the expander is selected for its high exergy efficiency, and the exergy efficiency function has been selected as the objective function 1 to optimize this process mathematically based on this study’s findings. The critical term in this objective function is the work of the compressors and turboexpanders in the process. After defining the optimization problem, the problem is optimized by two genetic algorithms and SQP, considering the process constraints and the process’s initial conditions. Finally, using the genetic algorithm’s data application to the simulated process, a 15% increase in the plant’s exergic efficiency was observed.