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According to the characteristics of variable operating conditions and high exhaust temperature of the refrigeration system of the refrigerator truck, the change of the superheat at the outlet of the evaporator is adjusted by a new electronic expansion valve, and a performance test-bed using the R404A refrigerant is built to study the influence of the superheat at the outlet of the evaporator on the performance of the refrigeration system of the refrigerator truck. The results show that in the process of increasing the superheat at the outlet of the evaporator, the outlet temperature of the evaporator increases and the evaporation temperature decrease, the cooling capacity of the system is reduced by 8.4%, and the COP of the system increases first and then decreases; At this time, the optimal superheat at the evaporator outlet is 6 °C, and the system COP reaches the optimal value of 2.856. [ABSTRACT FROM AUTHOR]

n this research, an experimental investigation was conducted on a dual-evaporator ejector system (DEES). The experiments were conducted under two distinct configurations, known as condenser outlet split (COS) and diffuser outlet split (DOS), across varying compressor inlet pres-sures. The system was initially operated in accordance with the COS configuration followed by operation under the DOS configuration. The comparison revealed a 9% reduction in the compressor work within the DOS configuration relative to the COS configuration. Evaporator#2 cooling capacity was 14% higher in the DOS compared to the COS. Moreover, the total cooling capacity achieved in the COS mode exhibited a 16% increase in comparison to the DOS mode. Furthermore, research findings indicate that by operating the DEES in the DOS configuration, full refrigerant separation can be achieved, leading to enhanced operational efficiency. [ABSTRACT FROM AUTHOR]

The performance of an ejector-assisted condenser outlet split dual-evaporator cycle is compared with a conventional dual-evaporator cycle albeit consisting a pressure reducing valve. The cycles do not employ any separator due to its inability to efficiently separate the liquid and the vapor phases. The comparison of both the cycles has been made for the same cooling capacity in low-temperature evaporator and unit flow rate of R134a and R1234yf as refrigerants. The impacts of changing the operating temperatures of evaporator and condenser have been examined in the current investigation. The study reveals that with the increase in temperature of the high-temperature evaporator, the cooling capacity of the high-temperature evaporator yields, while that of the low-temperature evaporator plummets in both the cycles. Further, the compressor work is allayed in the ejector-assisted cycle; thus, the COP is enhanced considerably. The percentage COP improvement over the basic cycle is obtained from 14.7 to 17.53% for the refrigerant R1234yf and from 14.45 to 17.32% for R134a; however, the COP of both the cycles with R12134yf is slightly lower than with R134a. The ejector has been modeled assuming a constant pressure theory. The observed trend indicates that the entrainment ratio is improved with the rise in the temperature of low-temperature evaporator, whereas it is decreased with the rise in the temperature of high-temperature evaporator. [ABSTRACT FROM AUTHOR]

CO2 booster refrigeration systems have higher energy efficiency and are more environmentally friendly. Therefore, the CO2 booster refrigeration cycle with flooded evaporators and parallel compressors (BFP), BFP with mechanical subcooling (BFP-MSC), and BFP with evaporative cooling (BFP-EVC) are investigated for supermarkets in this study. For the first time in the literature, these systems are analyzed to present which system performs better in terms of energy and environmental performance for Türkiye. According to the results of the investigation, BFP-MSC has a better coefficient of performance (COP) values than BFP, with up to a 16.67% increase at equivalent dry bulb temperatures. Meanwhile, BFP-EVC has the lowest annual energy consumption (AEC) in each city, followed by BFPMSC and then BFP. Annual savings obtained by BFP-EVC over BFP vary between 10.81% to 25.47%. Additionally, BFP-EVC offers more substantial savings in cities with lower humidity levels, as it was analyzed with respect to wet bulb temperatures. [ABSTRACT FROM AUTHOR]

When a brazed plate heat exchanger is used as an evaporator, the working mass in the channel may undergo solidification, thereby hindering the refrigeration cycle. In this study the liquid solidification process and its optimization in a brazed plate heat exchanger are investigated numerically for different inlet velocities; moreover, different levels of corrugation are considered. The results indicate that solidification first occurs around the contacts, followed by the area behind the contacts. It is also shown that dead flow zones exist in the sharp areas and such areas are prone to liquid solidification. After optimization, the solidification area attains its smallest value when a corrugation spacing λ = 4.2 mm is considered. [ABSTRACT FROM AUTHOR]

• Influence of heat sink temperature on PWM ejector and system performance is studied. • Influence of compressor speed and evaporator overfeeding is also studied. • PWM ejector with overfed evaporator shows COP increases up to 15.1% over basic unit. • PWM ejector shows COP enhancements up to 10.2% compared to passive ejector. • PWM ejector offers higher COP improvements than its currently available competitors. Ejector-equipped transcritical R744 condensing units are believed to lead to a low-to-zero commercial refrigeration sector. In order to overcome the persisting barrier to their wider adoption represented by the lack of an affordable ejector control technique, the novel pulse-width modulation (PWM) ejector, being low cost, simple and invulnerable to clogging was recently implemented. However, additional experimental evaluations are needed. Therefore, in this experimental work the performance of two PWM ejector-equipped transcritical R744 condensing units, i.e. with and without overfed evaporator, was carried out. The experimental assessment was implemented at the medium temperature (MT) of about -5 °C, heat sink temperatures from 30 °C to 40 °C and compressor speeds from 40 Hz to 60 Hz. The outcomes obtained revealed that the PWM ejector can effectively control the high pressure in transcritical operating conditions, regardless of the selected heat sink temperature and compressor speed. In addition, at the same cooling capacity, the PWM ejector-equipped R744 system was found to permit energy savings between 7.0% and 11.1% without overfed evaporator and between 11.5% and 16.3% with overfed evaporator compared to the standard R744 unit (i.e. with vapour by-pass valve and without ejector), respectively. Finally, higher values of coefficient of performance (COP) were found to be offered by the PWM ejector compared with its today's available competitors. [ABSTRACT FROM AUTHOR]

Micro and nanostructures can delay frost and ice buildup, improve defrosting efficiency, and reduce water retention. Here, we examine the impact of nanostructures on aluminum evaporators during frosting and defrosting inside of a 20.5 ft3 commercial food refrigerator. We use scalable manufacturing methods to generate structures on the external surfaces of the heat exchangers using bohemitization and chemical vapor deposition, rendering them superhydrophilic or superhydrophobic. Our results demonstrate a 93% reduction in water retention for the superhydrophobic heat exchanger compared to its uncoated and superhydrophilic counterparts. We conduct frosting and defrosting visualization experiments in the refrigerator to show frost pattern growth and droplet distributions on the heat exchangers. Frost was fluffier and less dense on the superhydrophobic heat exchanger compared to its counterparts which resulted in sparse droplets that are easily removed during defrosting. Furthermore, we show that the superhydrophobic heat exchanger can decrease energy consumption by 13.6% during defrosting when compared to its uncoated and superhydrophilic counterparts. We also comment on the durability of the applied coating on the heat exchangers. This study provides guidelines for the broader integration of micro and nanostructured surfaces with refrigeration and cooling appliances to create energy savings. [ABSTRACT FROM AUTHOR]

DWSIM is an open-source chemical process simulator. For educational purpose, its capabilities are comparable to commercial simulators such as Aspen Plus, Aspen HYSYS, ChemCAD, ProSim, etc. The objective of this paper is to present a model of NH3-H2O vapor absorption refrigeration system in DWSIM. Simulation results of this model are compared with those of Aspen HYSYS. NH3-H2O vapor absorption refrigeration system consists of absorber, evaporator, pump, generator, rectifier, condenser, evaporator, and valves. It provides examples of common chemical engineering processes such as heat transfer, mass transfer, condensation, evaporation, throttling, gas-vapor separation, absorption, and desorption. Sensitivity and optimization analyses can be performed using the DWSIM model presented in this paper. Therefore, it is expected that this model will not only teach a student about chemical engineering in general and vapor absorption refrigeration in particular, but also enhance the student's skill in using DWSIM. [ABSTRACT FROM AUTHOR]

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This study presents an experimental rig of a multi-evaporator refrigeration system, in which the pressure difference between two evaporators can be maintained by using both the pressure-regulating valve (PRV) and electronic expansion valve (EEV)-based ejector. The proposed EEV-based ejector that is used to partially recover the throttling losses of the PRV consists of an EEV and the main body of an ejector. The established experimental system can work in both PRV-based mode and ejector-based mode by switching the valves. Via experimental means, the performances of both modes were evaluated by varying the cooling loads. Moreover, the effects of the spindle-blocking area percentage of the EEV-based ejector and the condensing temperature on the system performance were identified. The results showed that: (1) the system performance of the ejector-based mode was 3.6% higher than the PRV-based mode; (2) both entrainment ratio and coefficient of performance dropped along with the increase in ejector spindle-blocking area percentage; (3) compared to ejector spindle-blocking area percentage, the condensing temperature had a more evident influence on the system performance. [ABSTRACT FROM AUTHOR]

The refrigeration system can be utilized with dual or multi-evaporator to meet the cooling needs at several vapor pressures with a single compressor refrigeration system. The evaporators utilized in these systems can take water or air to the desired low temperatures. The energy consumption of the compressor can be decreased and the system can be made more efficient by including an ejector in refrigeration systems with dual evaporator. Within the scope of this study, an experimental refrigeration system with an ejector and two evaporators, the first one (evaporator#1) sourced by air, and the second one (evaporator#2) sourced by water, were installed. The performance of the experimental dual-evaporator ejector system (DEES) was tested depending on the water temperature and mass flow rates passing through evaporator#2. The performance parameters of the system at several mass flow rates and water temperature were analyzed, and the ejector's impact on the system was determined. As a refrigerant in DEES, low GWP (global warming potential) R516A refrigerant was utilized. System performance was calculated for three different water mass flow rate values at several water temperatures passing through evaporator#2. As a result, it was determined that when the water temperature increased from 10°C to 30°C and the water mass flow rate was the maximum, the power of the compressor increases by 7.2%, while the total refrigeration capacity rises by 25.9%. The results showed that the coefficient of performance (COP) increased by 9.1%, 15.2%, and 16.5%, respectively, at m1, m2, and m3 mass flow rates with the increase in water temperature from 10°C to 30°C. Additionally, evaporation temperatures in the evaporator increased with the decrease of entrainment ratio (ER). Finally, it was determined that the impact of the change in ER values on the superheating degree temperatures was higher than the mass water flow rate values. [ABSTRACT FROM AUTHOR]

This paper presents an evaluation of the energetic, exergetic, and exergoeconomic performances of a modified auto-cascade refrigeration (MACR) cycle integrated with a dual evaporator refrigerator (DER) to determine optimum operating conditions. DER facilitates a reduction in the compression ratio, allowing the low-boiling-point component to release more heat before entering the evaporator. In this study, the R170/R290 refrigerant mixture, which has a low global warming potential but an explosion risk, was used. The main purpose of this study is to eliminate the risk of explosion by reducing the compressor discharge temperature and at the same time to enhance the overall cycle performance. To achieve this, DER is used instead of air-cooled coils, which have limited cooling performance. Despite an ambient temperature of 35 °C , the MACR cycle achieved a remarkable 51.29 % reduction in compressor discharge temperature when the separator inlet temperature was reduced to 10 °C by the DER. It also results in a 72.73 % reduction in compression work rate and a significant 137.02 % increase in cooling effect compared to the conventional auto-cascade refrigeration cycle. Furthermore, the MACR cycle exhibits notable improvements in total exergy destruction rate and exergy destruction cost rate with a 75.23 % and a 76.07 % reduction, respectively. Simultaneously, the exergy efficiency and the exergoeconomic factor increased by 266.67 % and 179.15 % , respectively. The MACR cycle achieves optimum energy and exergy performance with a 60 % R170 mass fraction and 0.50 vapor quality, resulting in 1.429 k W compression work rate, a COP of 0.70, and an exergy efficiency of 26.66 %. The optimum exergoeconomic performance is achieved with a 40 % R170 mass fraction and 0.50 vapor quality. [Display omitted] • Energy, exergy, and exergoeconomic analyses have been conducted for the MACR cycle. • Optimum operating conditions have been identified. • Significant improvements are observed in discharge temperature and exergy destruction cost rate. • There is a notable enhancement in exergy efficiency and a substantial 179.2 % rise in the exergoeconomic factor. [ABSTRACT FROM AUTHOR]

This paper proposes a novel two-stage compression transcritical CO 2 dual-evaporator refrigeration cycle with an ejector. The ejector and flash tank introduced in the novel system is used to reduce the flashed vapor flowing through the low-temperature evaporator and thus reduce the input power of the low-temperature compressor, rather than traditionally reducing the compressor input power by lifting the compressor suction pressure. Thermodynamic analysis results indicate that under all given operating conditions, the performances of novel system are better than those of conventional system. Compared with the conventional system, the COP and exergy efficiency of the novel system under a typical operating condition is increased by 19.6% and 15.9% respectively, and the discharge temperature of high-temperature compressor in the novel system is reduced by 10.5 °C. In addition, the optimum gas cooler pressure of the novel system is 10.3 MPa, which is lower than that of the conventional system. Moreover, exergy analysis results display that the overall exergy destruction in all expansion devices for both systems accounts for the largest part of the total exergy destruction, but its proportion of the novel system is smaller than that of the conventional system. [ABSTRACT FROM AUTHOR]

Part load performance analysis on simple VCR system using selected refrigerant mixture at different loading conditions is completed to identify the economic mode of loading in the evaporator. In this research work, evaporator has been loaded at different loading (thermal loading – cooling of liquid substance in the evaporator) conditions like 25, 50, 75 and 100% of its capacity based on its volume and water is considered as a substance to be cooled in the evaporator for analyzing the performance of the refrigeration system at different loading conditions. The cooling temperature C and the condensation process has range of water is considered from 26 to 2 been carried out by Atmospheric Air Circulation (AAC) mode. The various performance indexes of refrigeration systems namely work input to the compressor, condenser heat rejection rate, refrigerating effect and COP are obtained based on unit mass flow rate of the refrigerant in this analysis. Experimental results suggest that 75% loading condition is the significant one among other loading conditions in the evaporator.Experimental analysis has been carried out with 3oC of subcooling in the VCR system with thermoelectric subcooling and various performance indexes are investigated with reference to water temperature in the evaporator at different loading conditions. Significant improvements in various performance indexes have been obtained for VCR system with thermoelectric subcooling. The experimental results clearly state that 75% loading condition gives the highest COP at lowest temperature of evaporator substance. Among various loading conditions, COPof 75% loading condition is about 6.7, 3.9 and 25.13% higher than that of 25, 50 and 100% loading conditions respectively. [ABSTRACT FROM AUTHOR]

Domestic refrigerators have become an indispensable part of the modern life. Since they are connected to the electric mains and operate throughout the day and year, they consume a lot of energy. Several experimental studies show that the addition of phase change material in the refrigerators at various locations improves the energy efficiency of the refrigerators. In this work, an experimental study was conducted to explore and reveal the improvement in energy efficiency of a small-scale refrigeration system when PCM was applied between the evaporator coil and the insulation. It was observed that the addition of PCM for a thickness of 0.03 m could reduce the heat ingress inside the evaporator by 15-19%. Moreover, the compressor ON cycle time and the temperature fluctuation inside the freezer cabinet were also relatively lesser. The per day energy consumption was reduced by 15.7-17.3% and the improvement in COP was found to be 17.4% with the addition of PCM. The refrigeration system was able to retain its desired temperature level for a period of 5 h even after the power supply was switched OFF. This idea of incorporating PCM between coil and insulation could be extended to household refrigerators so as to reduce the energy consumption. This would come handy in case of power outages which are very common in places having low grid reliability. [ABSTRACT FROM AUTHOR]

The parallel dual-evaporator system has energy-saving potential in frost-free refrigerator-freezers, since it can provide proper evaporating temperature difference for the refrigerator and the freezer, respectively. However, energy loss is generated during the transition period of switches between refrigerating (R-) and freezing (F-) cycles in actual use. In this article, switch loss of a frost-free refrigerator-freezer with parallel dual-evaporator refrigeration system is studied experimentally. Results show that the transition process after F- to R-cycle switch takes 7.17 min and consists of three stages according to R-evaporator's feeding: short feeding (1.83 min), no feeding (2 min), and continuous feeding (3.34 min). The starvation in R-evaporator during the first two stages leads to switch loss for the refrigerator-freezer, by consuming 23.3% electric energy but yielding only 6.9% capacity for an entire R-cycle. The pump-down (P/D) action before R-cycles accelerates refrigerant's pumping from F-evaporator and feeding to R-evaporator, thus recovering part of the capacity loss. However, the introduction of P/D is not necessarily energy-efficient because P/D itself consumes considerable electric energy. By contrast, R- to F-cycle switch has little effect on refrigerator-freezer performance due to instant feeding. Dynamic simulation on the transition process will be provided in the future. [ABSTRACT FROM AUTHOR]

Highlights • Thermodynamic performance of a FTVI refrigeration cycle was investigated. • Binary mixtures of hydrocarbon refrigerants were used in simulations of a FTVI cycle. • Mixed refrigerants allow a better thermodynamic performance than pure fluids. • Mixed refrigerant R290/R600 60/40 wt% presented the greatest COP. • R170/R290 and R290/R600 presented the best temperature glide matching in the evaporator. Abstract Refrigeration systems are major consumers of electrical energy in many process industries. Hydrocarbons have regained interest as refrigerants because of the increasing restrictions applied to halogenated fluids. In this work, the use of hydrocarbons mixed refrigerants and an alternative flash tank with vapor injection (FTVI) refrigeration cycle were combined. Five different binary mixed refrigerants involving R170 (ethane), R290 (propane), R600 (n-butane) and R600a (isobutane) were studied. Using different refrigerant compositions, the cycle was simulated and optimized for maximum COP, considering a fixed refrigeration capacity in the evaporator to reduce the temperature of a secondary thermal fluid from 281.55 K to 269.15 K. Parameters analyzed were: coefficient of performance, temperature glide in the evaporator and refrigerant mass flow rate. The use of a FTVI led to a COP improvement from 4% to 36% when compared to the traditional vapor compression cycle (VCC). The pair R290/R600 with 60/40 wt% presented the maximum COP of 4.88. [ABSTRACT FROM AUTHOR]

This study aims to make a comparative investigation on performance analysis of cascade refrigeration systems using R744/R717, R744/R134a, and R744/R1234yf refrigerant pairs. Artificial Cooperative Search methaheuristic algorithm is put into practice to obtain the optimal values of eight design parameters including Condenser and evaporator temperature, R744 condensing temperature, temperature difference in the cascade condenser, and amount of subcooling and superheating at the bottom and the top of the cascade cycle. Second law efficiency and total annual cost of the cascade refrigeration system are chosen as design objectives to be optimized individually and concurrently in order to obtain the optimal operating conditions of the system. Single optimization results show that R744/R1234yf system has the lowest operating cost while having the highest second law efficiency compared to other cycle configurations. A set of non-dominated solutions obtained through multi objective Artificial Cooperative Search algorithm is represented in the form of Pareto front and the best result is chosen from the well-reputed decision makers of TOPSIS and LINMAP for each cycle configuration. Multi objective optimization results reveal that design variables of the refrigeration system can create a trade off between problem objectives. A sensitivity analysis is performed to investigate the influences of varying values of design variables upon problem objectives while the system is operated under optimal conditions. [ABSTRACT FROM AUTHOR]

With great requirements of ice in handling, storage, and supply of food products, it is significant to investigate the operation performance of ice making machine and improve the efficiency of refrigeration system. This paper presents an experimental investigation on a vapor compression refrigeration cycle with a subcooler applied in an ice-making machine. A multichannel evaporator is selected to generate ice cubes. To investigate the basic operation performance of refrigeration system in an ice-making machine, the fluid temperature distribution in multichannel evaporating coils and the dynamic variation in each cooling loop are measured in detail with a multichannel data acquisition instrument. Moreover, the ice generating and thawing phases are investigated. Parts of main conclusions are arrived at based on the analysis of the collection data. Meanwhile, some potential operational issues are also detected. To improve the operation performance of the ice machine, some suggestions and improvements are proposed. [ABSTRACT FROM AUTHOR]

Highlights • A numerically efficient but accurate model for frosting evaporators is developed. • The enthalpy-based reformulation and linearization method are employed • Simulation results on flat plate and finned-tube heat exchangers are provided. • It is 8 to 20 times faster than reference models but withcomparable accuracy. Abstract Growth of a frost layer on an evaporator surface due to low evaporator temperature as well as moisture contained in surrounding air deteriorates performance of a refrigeration system significantly and requires significant energy for defrost. Many studies have been performed to model the heat and mass transfer phenomena in an attempt to have insight and accurate prediction. However, many models form nonlinear algebraic differential equations which require iterative numerical solvers. Computationally efficient but accurate models are needed in order to evaluate overall system performance. The objective of this paper is to introduce a modeling approach to overcome the problem. A solution strategy based on an enthalpy-based reformulation and linearization method will be presented. Comparisons of the proposed and detailed model results for both flat plate and finned tube heat exchangers are provided. The proposed modeling approach is around 10 times faster than reference models while maintaining comparable accuracy. [ABSTRACT FROM AUTHOR]

Highlights • An improved 1-D model of an ejector refrigeration system has been developed. • The model accounts for ejector performance in both the critical and subcritical modes. • Performance investigation with environmentally benign working fluids was undertaken. • R1234Ze(Z) and R1233Zd(E) have been identified as suitable replacements for R141b. • Optimal operating conditions have been determined for different ejector geometries. Abstract Ejector systems are receiving considerable attention due to their simplicity, lower maintenance requirements, use of low grade heat, longer lifespan and low cost. In this paper an improved model to predict the performance of an ejector refrigeration system under both the critical and subcritical modes of operation was developed and validated. The model predicts ejector performance more precisely compared to studies following the same modeling approach in the literature. Using the developed model, performances with environmentally benign refrigerants, including R1233zd(E), HFO1336mzz(Z), R1234ze(Z), R600, RE245fa2, and RE245fa2 as alternatives to R141b and R245fa were investigated. Furthermore, for ejector area ratios between 4.45 and 12.98, evaporator temperatures between 0 °C and 16 °C and condenser temperatures between 20 and 40 °C, the optimal performance of the ejector system was determined. Results show that for each refrigerant, higher area ratios give higher coefficients of performance, but require higher generator temperatures for better critical condensing temperatures. R600 showed the best performance followed by R1234Ze(Z) and R1233Zd(E) for the entire range of parameters considered. Results further show that there is an optimum generator temperature at each area ratio that maximizes performance. The optimal generator temperature increases as the area ratio and the condensing temperature increase. An alternative and more convenient approach to optimize ejector performance has been suggested in this work. [ABSTRACT FROM AUTHOR]

Highlights • A two-stage ejector-based multi-evaporator refrigeration system was presented. • Effects of key geometries on two-stage ejector performances were investigated. • Optimum values of the key geometric parameters were obtained. Abstract A three-evaporator and dual-ejector refrigeration system was presented in this paper. By combining two single ejectors as a whole, the authors attempted to discuss the effects of key geometric dimensions of each stage on both stage performances with two-dimensional CFD simulation method. First, the CFD models were validated by experimental data. Then, the primary nozzle diameters of both stages were determined by the cooling load demands of the refrigerating and air-conditioning chambers. Next, the detailed effects of key geometric parameters such as the length of constant-pressure mixing section, the length of constant-area mixing section and area ratio of each stage on two-stage performances were identified with simulations. Finally, the optimum values of the key geometric parameters were obtained, and the results showed that the area ratio had the most significant influences on the entrainment ratio of both stages as compared to other parameters. [ABSTRACT FROM AUTHOR]

Highlights • A thermal transient model (Modelica language) is developed for a display cabinet. • Comparison between experimental and numerical results is presented. • Numerical case studies (load configurations, demand response) are considered. Abstract Open display cabinets are widely used in supermarkets and represent an important contribution to their energy consumption. The present study is related to modeling and experimental characterizations of an open display cabinet in a transient state. The model is based on a simplified zonal approach to determine heat transfer by conduction, radiation and convection within the display cabinet using experimental evaporator outlet temperature as input data. It is used to simulate a fully loaded display case with 5 shelves. The model can be used to predict the dynamic behavior during the on-off process, defrost operations and power failure. The comparison with experimental data obtained on an open display shows a good agreement with simulating results and allows the model to be validated. [ABSTRACT FROM AUTHOR]

This study is developed to evaluate the possibility of R1234yf to be a drop-in replacement for a pre-designed system with R134a, including the characterization of control system in a vapor compression system. The control algorithms are required for regulating the refrigerant flow rate into the evaporator and their control parameters depend intrinsically on refrigerant fluid. This paper presents a comparison of the effects of R134a and R1234yf refrigerants on the transient response of an evaporator operating with water as secondary fluid (counter-flow). The dynamic heat exchanger distributed model combines principles of thermodynamics, heat and mass transfer with empirical correlations, which are proposed in the literature, in order to compute the void fraction, pressure drop and heat transfer in two-phase flow. Experimental tests are carried out on a fixed refrigeration system for cooling capacity less than 3 kW, with constant condensation conditions, variable evaporating temperature and compressor speed to validate the model. The results demonstrated that a good agreement between simulation results and experimental data was achieved. The evaporation temperature data were within ± 1   °C error band. Furthermore, comparative simulations between the refrigerants R-134a and R-1234yf exhibited a similar dynamic behavior during a step at the inlet mass flow rate, and the gain and time constant for superheat control were not considerably modified. Therefore, the refrigerant changing does not demand many changes in the expansion device control strategy. [ABSTRACT FROM AUTHOR]

Heat removal is the most extended method for food preservation in food manufacturing industry by lowering food temperatures to stop microorganisms growing, which might spoil the product and could cause toxicity. Therefore, walk-in freezers are used for that purpose consuming a relevant part of the energy on service sector. The compression refrigeration system of the walk-in freezers can be blocked by the frost accumulated on the evaporator. For that reason a defrost process, which requires an important part of the energy consumption, has to be launched from time to time. In this paper, the schedule which manages the defrost process is investigated to limit its activation only when it is necessary. Moreover, different fan operation strategies were tested regarding the energy efficiency of the whole refrigeration system. This study has provided a system control strategy both for defrost and fans operation, depending on the frost built up on the evaporator. The control improves the energy performance of the whole refrigeration system. [ABSTRACT FROM AUTHOR]

With the arrival of electrified vehicles, the air-conditioning system has to be reconsidered. Battery cooling management system and high level of comfort for passengers make the single evaporator air-conditioning system a multi-evaporator one. In a multi-evaporator air-conditioning system, evaporating pressures are equal in each evaporator so that evaporators are coupled dynamically. However, the demand in cooling capacity and temperature target can vary from each other. For an operating point with a first evaporator working at high load and a second at low partial load, thermal interaction can occur from the superheated refrigerant coming from a first evaporator to the outlet of a second evaporator. This phenomenon makes the second evaporator sleeping since its expansion valve bulb misreads the superheat and closes. Furthermore, sleeping evaporator looks like an extreme case of refrigerant maldistribution in the evaporator. Refrigerant maldistribution is then investigated to show some drawbacks and advantages multi-evaporator air-conditioning systems (MEAC) have to face or can benefit by comparing two types of expansion valve: thermostatic and electronic ones. In this paper, sleeping evaporator and refrigerant maldistribution phenomena are experimentally investigated in order to propose in the future a robust control of an automotive MEAC. A test bench was built to compare two types of expansion valves (thermostatic/electronic) and study their behaviours in steady and transient state to tackle sleeping evaporators and benefit from refrigerant maldistribution. [ABSTRACT FROM AUTHOR]

The suitability of nanosuspensions as secondary heat transfer fluids in refrigeration systems has been assessed aiming at the external irreversibilities of the heat exchangers of the refrigeration cycle. The results suggested that, in the case where the heat exchangers are optimized to minimize the rate of entropy generation, water-based nanofluids do not perform as well as pure water. Nanofluids enthusiasts, however, might advocate that nanosuspensions would allow the refrigerator to operate with lower condensing and higher evaporating temperatures, thus increasing the system COP. The present paper is therefore aimed at assessing both the internal and external irreversibilities of the refrigeration cycle when nanofluids are used as secondary coolants. The analyses have pointed out that despite most of the nanofluid research and development has been focused on the transfer properties (viscosity, conductivity), the transport properties related with the thermal capacity (specific heat, density) showed to be the most influential factors on the total system COP. In the case of water-based nanofluids, the nanoparticles have twice the density but only a quarter of the specific heat of pure water, suggesting that such nanosuspensions are not likely to perform better than the base fluid in HVAC-R applications. [ABSTRACT FROM AUTHOR]

Performance of a frost-free refrigerator may be deteriorated by frost accumulation on its evaporator surface. The objective of this study is to investigate the feasibility of using an enthalpy exchanger (EE) to reduce the frost accumulation on evaporator surface in frost-free refrigerator. The influence of EE on air circulation and the change process of air humidity is analyzed, and it is indicated that the application of EE is capable to decrease the amount of water vapor entering the evaporator and consequently reduce the frost accumulation on evaporator surface. The design process of EE in frost-free refrigerator is illustrated, and an optimal type of EE is presented. An experiment on a frost-free refrigerator shows that the application of EE decreases the frost accumulation by 18.8%. In addition, effects of EE on other main performances of frost-free refrigerator besides the frost accumulation are evaluated. [ABSTRACT FROM AUTHOR]

In this work, the experimental examination was carried out using a mixture of R134a and LPG refrigerant (consisting of R134a and LPG in a proportion of 28:72 by weight) as a replacement for R134a in a vapor compression refrigeration system. Exergy and energy tests were carried out at different evaporator and condenser temperatures with controlled environmental conditions. The results showed that the exergy destruction in the compressor, condenser, evaporator, and a capillary tube of the R134a / LPG refrigeration system was found lower by approximately 11.13-3.41%, 2.24-3.43%, 12.02-13.47% and 1.54-5.61% respectively. The compressor exhibits the highest level of destruction, accompanied by a condenser, an evaporator and a capillary tube in refrigeration systems. The refrigeration capacity, COP and power consumption of the compressor of the R134a /LPG refrigeration system were detected higher and lower compared to the R134a refrigeration system by about 7.04-11.41%, 15.1-17.82%, and 3.83-8.08% respectively. Also, the miscibility of R134a and LPG blend with mineral oil discovered good. The R134a and LPG refrigerant mixture proposed in this study perform superior to R134a from component-wise exergy and energy analyses under similar experimental conditions. [ABSTRACT FROM AUTHOR]

Refrigeration and air conditioning (RAC) system Multi-evaporator structures are popularly applied in for efficient temperature and humidity control of multi-zone in underground buildings, light commercial and residential buildings, cold stores, et al., which can also attract and/or release heat from and/or to renewable sources. The increase on the system complexity makes it difficult to analyze the performance and to optimize its design and control. In this paper, a novel method, performance chart, is presented for the performance analysis and system optimization of multi-evaporator and RAC systems. The performance chart is generated by superimposing the performance curve of different evaporators of the indoor unit (IDUs), which can be applied to describe the performance of the whole RAC system by superimposing with the performance curve of outdoor units (ODUs). Based on the performance chart, the performance of multi-evaporator systems are analyzed at different conditions such as varying indoor temperatures, varying indoor air volumes, and varying IDUs’ capacities. The performance chart can give the reasonable and quantitative trends of multi-evaporator RAC system performance and guide the system design. These results showed that the performance chart can be used as a convenient tool for performance analysis and system optimization of multi-evaporator RAC systems. [ABSTRACT FROM AUTHOR]

According to Kyoto protocol, R134a must be phased out soon due to its high global warming potential of 1430. In this work, an experimental investigation is carried out with R134a and LPG refrigerant mixture (composed of R134a and LPG in the ratio of 28:72 by weight) as an alternative to R134a in a vapor compression refrigeration system. Performance tests were performed under different evaporator and condenser temperatures with controlled ambient conditions. The results showed that the R134a and LPG refrigerant mixture has a higher coefficient of performance and lower compressor discharge temperature and pull down time as compared to R134a by about 15.1–17.82%, 2.10–13.86% and 1.01–5.90% respectively. Furthermore, the miscibility of R134a/LPG with mineral oil as a lubricant was also found good. In conclusion, the mixing refrigerant R134a/LPG proposed in this study seems to be an appropriate long-term candidate to replace R134a as a new generation refrigerant of VCRS, because of its well environmentally acceptable properties and its favorable refrigeration performances. [ABSTRACT FROM AUTHOR]

• Novel condenser outlet split cycle with the presence of two ejectors working in different temperatures has been investigated. • Exergy and energy analysis has been performed. • COP enhancement of the proposed cycle at different condenser temperature has increased from 8.3 to 14.1%. In this paper, the possibility of performance enhancement of a new Condenser Outlet Split (COS) cycle with the presence of two ejectors working in different temperatures is investigated. In order to enhance the cycle performance, an auxiliary ejector-expansion refrigeration cycle equipped with a separator and a secondary ejector has been employed, resulting in further performance improvement on both exergy and energy analyses on the different condenser and evaporator temperatures. The thermodynamic equations of each component in the standard and proposed cycles have been solved in EES software. The auxiliary cycle boosted the pressure at the inlet of the secondary nozzle of the main ejector leads to a better performance of the proposed cycle. Through energy analysis, compressor work recovery increased by 12% and the coefficient of performance showed up to 14.1% enhancement. Through exergy analysis, our proposed cycle have been produced 6.8% reduction in exergy destruction compared to the standard cycle, and the total exergy performance of the given system can be increased from 8.2 to 14%. [ABSTRACT FROM AUTHOR]

This paper presents a new concept for air-conditioning systems in Liquefied Petroleum Gas (LPG) fuelled vehicles, a ½ cycle refrigeration system. Prior to being used in an engine as a fuel, LPG serves as a refrigerant. Harvesting of cooling from LPG was carried out by an auxiliary evaporator. Initially, to evaporate LPG in an Original Equipment Manufactured (OEM) vaporizer, water coolant is used. In these systems, the thermal energy to evaporate LPG is obtained from air driven by an electric blower. Cold air exiting from the evaporator may then be supplied to the cabin. The test results show that the actual cooling effect produced is as high as 1.2 kW for an LPG flow rate of more than 3 g/s and an air mass flow rate of 16 g/s. In conclusion, the ½ cycle air conditioning system is a promising application for LPG-fuelled vehicles to reduce the load on air-conditioning systems. [ABSTRACT FROM AUTHOR]

Finned tube evaporators are used in a wide range of applications such as commercial and industrial cold/freezed storage rooms with high traffic loading under frosting conditions. In this case study, an evaporator with an integrated fan was manufactured and tested under frosting conditions by only changing the air flow rate in an ambient balanced type test laboratory compared to testing in a wind tunnel with a more uniform flow distribution in order to detect the effect of air flow rate on frosting. During the test, operation was performed separately based on three different air flow rates. The parameters concerning test operation such as the changes of air temperature, air relative humidity, surface temperature, air-side pressure drop and refrigerant side capacity etc. were followed in detail for each air flow rate. At the same time, digital images were captured in front of the evaporator; thus, frost thicknesses and blockage ratios at the course of fan stall were determined by using an image-processing technique. Consequently, the test and visual results showed that the trendline of air-side pressure drop increased slowly at the first stage of test operations, then increased linearly up to a top point and then the linearity was disrupted instantly. This point speculated the beginning of defrost operation for each case. In addition, despite detecting a velocity that needs to be avoided, a test applied at minimum air velocity is superior to providing minimum capacity in terms of loss of capacity during test operations. [ABSTRACT FROM AUTHOR]

This paper presents the evaluation of the ejector refrigeration system from three levels: energy analysis, conventional exergy analysis and advanced exergy analysis, in light of introducing the thermal conductance and the objective function, the exergy efficiencies, the exergetic rehabilitation ratio and the exergetic improvement potential ratio, respectively. Five environmentally friendly working fluids, namely R600, R600a, R601a, R1233zd(E) and R1234ze(E), are used to compare their performance and working characteristics in the system. At the normal condition, it is found that these candidates have different orders of highest performance by different analysis, but agree that the ejector has the highest priority of improvement. The parametric study shows that these candidates have the same optimum pinch temperature differences in the condenser (7 °C and 3 °C) and in the evaporator (3 °C and 2 °C) to minimize the thermal conductance and the objective function, while they are different in the generator. The ejector efficiencies have considerable influence on the system performance, and a 0.1 increase in ejector efficiency could lead to the increase of system exergy efficiency from 1.38% to 10.33%. The pump efficiency has insignificant influence the system performance, but a 0.1 increase in the pump efficiency results in a 7.37% decrease in exergetic improvement potential ratio of the pump. By comprehensive comparisons, R1233zd(E) has generally higher system performance than the other four candidates, it is therefore recommended as the good working fluid for the ejector refrigeration system. [ABSTRACT FROM AUTHOR]

Combined use of heat and mass recovery processes in adsorption refrigeration is an efficient way to improve the system performance. Several kinds of heat and mass recovery processes have been proposed. In this study, a serial heat recovery process between two adsorbers and a mass recovery-like process between two evaporators is selected. Their operating features in a practical silica gel-water adsorption refrigeration system are experimentally studied. Operating features and performances of heat and mass recovery process can be presented in terms of inlet and outlet temperatures and transferred heat of two adsorbers and two evaporators. The results show that residual heat transfer fluid in the adsorbers and evaporators significantly influences the heat and mass recovery processes, respectively. In the case of this study, optimal ranges of heat and mass recovery time is 25–45 s and 5–50 s, respectively. Heat recovery process can produce negative effect when heat recovery time is beyond 45 s and it is inefficient when heat recovery time is below 25 s. Cooling effect is remarkably yielded when mass recovery time is within the range of 5–50 s. [ABSTRACT FROM AUTHOR]

We present in this paper an experimental study of a commercial diffusion-absorption refrigeration machine (DAR) operating on the Platen and Munters cycle. The temperatures at the inlet and outlet of every component of the machine, as well as the cabinet and ambient temperature are measured continuously. The tests are repeated for various electric power inputs to the refrigerator. The global heat transfer coefficient of the cabinet ( UA ) cab is determined using both theoretical and experimental methods. This coefficient is found equal to 0.2 W/°C. The global heat transfer coefficient of the evaporator ( UA ) evap is deduced using dynamic and steady state methods. This global heat transfer coefficient ( UA ) evap is found equal to 0.3 W/°C. Finally the cooling capacity of the unit and the coefficient of performance are evaluated. The heating power supply to the generator necessary to ensure the desired state of this machine is found to be in the range of 35 W–45 W. [ABSTRACT FROM AUTHOR]

In this work, a new dual-evaporator CO2 transcritical refrigeration cycle with two ejectors is proposed. In this new system, we proposed to recover the lost energy of condensation coming off the gas cooler and operate the refrigeration cycle ejector free and enhance the system performance and obtain dual-temperature refrigeration simultaneously. The effects of some key parameters on the thermodynamic performance of the modified cycle are theoretically investigated based on energetic and exergetic analysis. The simulation results for the modified cycle indicate more effective system performance improvement than the single ejector in the CO2 vapor compression cycle using ejector as an expander ranging up to 46%. The exergetic analysis for this system is made. The performance characteristics of the proposed cycle show its promise in dual-evaporator refrigeration system. [ABSTRACT FROM AUTHOR]

This paper reports the results of an experimental and numerical study of the use of a minichannel coil and a fin-and-tube coil in an air/water heat pump working as evaporator when the system is working in heating mode. The experimental installation developed to test the heat pump unit is briefly described and then the experimental results are presented. Alternatively, the heat pump is modelled using a refrigeration system design program. The results obtained using this model are compared to experimental results allowing the validation of the model. Once the model is validated, it is used to numerically determine the distribution of refrigeration charge and other interesting parameters not experimentally measured. Finally, an analysis of the numerically obtained results is presented in order to study the influence of several operating conditions on refrigerant charge, system COP and heating power for both types of evaporators tested. [ABSTRACT FROM AUTHOR]

To analyze the influence of liquid spraying flow rate on the performance of a falling-film evaporator with R134a, the finite difference model of the horizontal-tube falling-film evaporator is established, and a falling-film air-cooled water chiller with ejector liquid recirculation system (LRS) is presented; then the comparison between numerical simulation and experimental tests are performed. The analysis results show that the experimental and numerical evaporating capacities increase 9.5% and 6.7%, respectively, when the liquid recirculating ratio R l increases from 1.0 to 1.21; and the deviation between the experimental and numerical capacities of the evaporator is about 3.3%. And that the evaporated liquid flow rate rises quickly at first and then increases slightly as R l increases. Moreover, the results show that the optimum value of R l is about 1.2, the corresponding value of integrated falling-film factor φ with about 0.85. This suggests that attempting to eliminate completely the dryout patch outside of tubes is unadvisable. [ABSTRACT FROM AUTHOR]