Despite its good environmental properties, the application of 1,1-Difluoroethane (R152a) is hindered by its flammability. So, an accurate instrument is required to solve the safety issues of R152a. In this study, the combustion characteristics of R152a mixtures with non-flammable CF3I/C3F6 were measured using the vertical tube method by ISO-817. It could be found that the maximum burning velocity (Su,max) of R152a decreased from 21.163 cm/s to 7.805 cm/s (with R13I1) or 7.675 cm/s (with R1216) at concentration of 15.403%(with R13I1) and 11.508%(with R1216) at an ambient temperature. By adding non-flammable retardants to R152a from volumetric concentration of 10% to 40%, the flammability of the mixtures was lowered. And Su,max of both were reduced by more than 60%, leading the mixture to reach A2L. According to the Su,max data, the dilution effect of the three refrigerants is: R1216 > R13I1 > R227ea. Meanwhile, the density functional analysis theory was used to study the relationship between the molecular bonds of these refrigerants. The results showed that the refrigerants containing higher F/H ratio and the molecules with -CF3 and -I groups were more prone to inhibit combustion.

The dedicated mechanical subcooled (DMS) refrigeration system is examined in the current study, based on the configuration of energy and exergy. The performance of a simple vapor compression refrigeration system (VCRS) and dedicated mechanical subcooled system are evaluated while maintaining the same cooling capacity (i.e. 100 kW). The results of comparative study showed an improvement of 8.2% in the coefficient of performance (COP) of the DMS system. Additionally, it has been discovered that the exergetic efficacy of the VCRS and DMS systems is 32.8% and 35.2%, respectively. The above results proved that, the suggested system perform better with more efficient cooling technology, which proves it to be a better option for design engineers in water chilling application in the foreseeable future.The coefficient of structural bond (CSB) and advanced exergy analysis (AEA) methodologies along with environmental benefits of the DMS system are also looked into in light. The value of CSB for conderser-1 is observed to be highest (2.08), with total irreversibility rate of 22.7%. However, in case of compressor-1 the highest irreversibility rate of 34.8% is observed but its CSB value is only 1.09. Therefore, by enhancing the performance of system components, it is possible to avoid 42.9% of the overall irreversibility rate of the dedicated mechanical subcooled system using enhanced exergy analysis.

This study introduces an improved methodology to evaluate with accuracy the performance of a conventional system with R404A and a Booster system with R744. Reciprocating and scroll compressors are modeled with improved semi-empirical approaches, and their operation is ideally controlled to maintain the required refrigerant mass flow rate with an On/Off and variable speed control system. The R744 gas cooler is modeled with a four-zones model and the R404A condenser with a three-zones model. The R744 condenser is modeled with the superheated zone discretized into eight zones to avoid unrealistic results due to the variation of its thermophysical properties and the two-phase and subcooled zones with one zone respectively. In line with the design, the Booster condenser enters into the pseudo-critical zone at an ambient temperature of 23°C, while the gas cooler is activated after 31°C. The compressor models present errors lower than 10%, while the Booster model presents mean deviations lower than 2.3%. The Booster system presents better COPs than the conventional at ambient temperatures lower than 15ºC. At higher ambient temperatures, the COPs of both systems are similar: the conventional system overperforms the Booster up to 6%, being in disagree with the literature results where these differences increase up to 30%. The proposed methodology allows to reduce the overall model error by 3% with respect to a thermodynamic cycle-based model; allowing to improve the comparison between the Booster system with R744 and the conventional one with R404A, which leads to more transparent results than the reported common comparisons.

This work focuses on the exploration of binary mixtures as alternative to isobutane (R-600a) from a theoretical and experimental point of view. To predict the most energy efficient blends, a theoretical model was used that analysed 5445 different blends consisting of 11 pure refrigerants. Three blends were selected for experimental testing in a commercial cabinet: R-1234ze(E)/R-600 (8/92) %mass, R-152a/R-600 (8/92) %mass and R-32/R-600 (2/98)%mass. The results of the 16-hour tests showed that, at their optimum refrigerant charge, the R-1234ze(E)/R-600 (8/92)%mass and R-152a/R-600 (8/92)%mass blends achieved energy consumption reductions of -2.69% and -5.04%, respectively, while the R-32/R-600 (2/98)%mass blend showed an increase of +0.36%. All blends reduced compressor consumption, but increased duty cycles. The results demonstrate the existence of alternative blends that can significantly reduce isobutane energy consumption with similar thermodynamic properties.

The present work includes an in-depth performance analysis in fixed-speed reciprocating compressors. The industry standard for compressor characterization is the AHRI-540, which uses a 10-term and third-degree polynomial to characterize mass flow rate and energy consumption. However, the suitability of such a high-degree polynomial is unclear, and the potential for overfitting and extrapolation errors cannot be ignored. This work analyzes the response surfaces of mass flow rate and energy consumption in reciprocating compressors to determine if more concise models with lower degrees are more suitable. For that purpose, a massive experimental dataset with multiple compressors using different refrigerant and suction conditions was analyzed to obtain overall conclusions in the compressor field. The results of the present work showed that mass flow rate modeling requires lower-degree polynomials. However, the energy consumption characterization is more complex, and the model reported in the standard may be justified. Additionally, it was found that, if the specific energy consumption is selected as the modeling variable, it is possible to use a compact polynomial expression, which can also be extended to scroll compressors and also has the advantage of reducing the experimental data necessary for the model fit. Finally, by selecting the mass flow rate and the specific energy consumption as response variables, this work also explores other critical issues related to the experimental points’ location and minimum sample sizes required in order to minimize the experimental costs and increase the model accuracy.

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.

This study visualized the evaporation flow regime of a non-azeotropic mixture R32/R1234ze(E) inside multiple vertical-upward and horizontal rectangular minichannels with a hydraulic diameter of 2 mm. The effects of the mass flux, vapor quality, heat flux, flow direction, and test refrigerant on the flow regime characteristics were explored. The flow regimes of the mixture were compared to those of R1234ze(E). The effect of flow direction on the flow regime was examined under low mass flux conditions. In the vertical-upward flow, three flow regimes: slug, slug-annular, and annular flow regimes were observed. The flow regime transition boundary of R1234ze(E) shifted to lower mass flux and vapor quality conditions compared to the mixture because of the higher vapor velocity of R1234ze(E). Boiling bubbles were generated in the liquid slug and channel corners around the vapor plug, and the number of boiling bubbles increased with an increasing heat flux. The size of the boiling bubble of the mixture was smaller than that of R1234ze(E), which is attributed to the mass transfer resistance of the non-azeotropic mixture. Only in the vertical-upward flow, the reverse flow was observed in some channels, where the slug flow was observed, because of the effect of gravity. The number of channels with reverse flow decreased with increasing vapor velocity. The annular flow did not appear in the horizontal flow, and the flow regime was observed only in two regimes: slug and slug-annular flow regimes. No difference in flow regime transition boundary between R1234ze(E) and R32/R1234ze(E) was observed.

Innovative approach for electronics cooling was proposed, i.e. heat generated by a part of electronic equipment, e.g. CPU, is absorbed by heat driven micro-ejector refrigeration system that can provide cooling of other electronic components, e.g. GPU. It was demonstrated the procedure of design, fabrication, and experimentation on the supersonic micro-ejectors for the case of isobutane as a working fluid for such system. It was demonstrated that it possible to design and fabricate the micro-ejector of cooling capacity in the range 3 W suitable for cooling of electronic equipment. For the discussed micro-ejector entrainment ratio obtained was app. 0.20 under conditions of the motive heat source temperature app. 60 °C and evaporation temperature app. 22 °C. There were demonstrated difficulties in fabrication of the supersonic ejector due to small dimensions of the motive nozzle as well as mixing chamber. Required throat diameter of the motive nozzle was less than 200 μm and the diameter of the mixing chamber was 260 μm. For reported tests conditions the boundary temperature of the on-design operation condition was between 21 – 25 °C. However, the operation of the micro-ejector under off-design operation regime was stable and repeatable. Micro-ejector tests required an indirect method of measurement of critical motive mass flow rate to be applied. The performance line of tested ejector fits to ejectors theory and meet the basic assumptions in terms of thermal capacity and operating temperature. CFD technique used for numerical predictions of the ejector performance fits to experimental measured values with acceptable accuracy.

Generally, the central air conditioners are centralized in a refrigeration room in public buildings. The proportion of energy consumption of the refrigeration room is about 40 % of entire building. This paper aims to propose an energy plus and self-designed simulator to reduce the energy consumption of a large electronic factory in Zhuhai City, Guangdong province, China. In this paper, the real data collected from the electronic factory in February and the group control method used in the refrigeration room based on the kernel ridge regression algorithm. The correctness of the kernel ride regression algorithm was verified with the experimental results. Compared to traditional PID control method, the kernel ridge regression algorithm could dynamically adjust those parameters, such as temperature and frequency to match the high efficiency zone of each device. The overall average COP of the system is increased from 4.17 to 7.04. The electricity of the refrigeration room could save 64 MWh with the cooling load forecast error being below 7% in February. The power consumption is expected to reduce by 8.2 % and 562.3 MWh in 2022.

Using the distilled water as the heat transfer fluid, this paper built an active magnetic regenerator test bench to investigate the influence of crucial parameters on the cooling performance of the active magnetic regenerators with different geometries, including the relative angle between the Gd plates and magnetic field, the utilization factor, the temperature at the hot side of the regenerator, and the operating frequency. In addition, the performance enhancement potential of the newly proposed perforated parallel-plate regenerator was experimentally studied. The impacts of the perforation ratio and perforation on different thicknesses of plates were discussed. For the parallel-plate active magnetic regenerator with a thickness of 0.4 mm and a plate spacing of 0.35 mm, the 3.4% perforation ratio increases the temperature span between the hot and cold ends of the regenerator by 14.7%∼24.7% at no load condition from the baseline none-perforated parallel-plate regenerator.

This study analyzed the RT8HC melting in a spherical vessel employing air as a heat transfer fluid. The phase change process was followed both visually and by thermal measurements. Photographs and thermographs allow the following phases' evolution and melting mechanisms. We observed that the melting process was not symmetric around the vertical axis; implications of non-symmetric conditions on the melting mechanisms and heat transfer are discussed and analyzed. This work also includes the effects of outer water vapor condensation on heat transfer in the analyses. We proposed a mathematical model to quantify the heat flux that only requires humidity and temperature measurements and considers both heat convection and condensation effects. Results show that condensation significantly affects heat transfer during the initial stage of the melting process. Besides, these effects extend beyond the condensation time due to the liquid film draining from the spherical vessel surface. Regarding thermography, this technique may be a valuable tool for analyzing and following melting processes inside vessels; however, the presence of liquid film over the sphere affects the temperature measurements obtained from the thermograph analysis. This investigation provides relevant information about using phase change materials in cold thermal energy storage applications, latent thermal loads, and humidity control, which are essential aspects of air-conditioning system designs.

The re-liquefaction of BOG is a necessary part of the safety and security of LNG cargo ships. And the volatility of BOG will fluctuate with the sea conditions of ship transportation, so how to deal with the fluctuation of the re-liquefaction system and improve the liquefaction capacity is a problem that cannot be ignored in the operation of the liquefaction system; In this paper, a BOG buffer tank is added to the Reverse Brayton Process. Moreover, a control strategy is proposed to optimize the liquefaction process. The proposed four possible operating conditions' efficiency,the specific energy consumption (SEC), liquefaction rate and main heat exchanger parameters were simulated and analyzed by using Aspen HYSYS software. According to the results, the specific energy consumption of the basic re-liquefaction process is 1.329 kWh/kgLNG, which is 5.7% less than that of the reference process; In the study of flow fluctuation, after adopting the control strategy, the specific energy consumption of the whole process is 1.29 kWh/kgLNG, with 15.6% efficiency and 99.5% liquefaction rate. The whole system can be maintained at a low specific energy consumption level when the feed gas volume is fluctuating. The analyses of various BOG composition and the parameters of the main heat exchanger show that the regulation of the inlet gas volume can make the primary re-liquefaction process flexible and maintain the heat exchanger in a good working condition; Even if the system is in a worse working condition, the inlet gas volume can be improved by 12.2% compared with the reference process.

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

This study focused on investigating the annual performance of a novel hybrid solar-driven cooling system that can be used on refrigerator vehicles. The cooling system is mainly driven by a DC compressor which is powered by a PV array, while an AC compressor which is powered by the car alternator assists the cooling system when the cooling load is higher than the capacity of the DC compressor. Detailed electrical modeling of the PV panels in the array is performed based on an algorithm that comprises a set of mathematical equations and is validated against the manufacturer's test data. The detailed transient electrical power generation of the PV array is analyzed. The effect of solar irradiation and ambient temperature on the performance of the PV modules is presented. Considering the refrigeration cycle, detailed thermodynamics and heat transfer analysis on the cycle are carried out. The effect of ambient temperature and refrigerator compartment temperature on the performance of the refrigeration cycle is investigated. It is concluded that an increase in ambient temperature decreases the performance of both the PV panel and the refrigeration cycle. While an increase in refrigerator compartment temperature increases the performance of the refrigeration cycle.

Electrochemical (EC) energy conversion has a critical role to play in the future of clean energy. As the world transitions away from fossil fuel energy sources, EC compression emerges as a promising technique for energy storage, specifically energy stored in the form of pressurized ammonia. The present study examines the performance of an ammonia EC compressor stack under steady-state operating conditions to demonstrate the technology's utility in such applications. Using hydrogen as a carrier gas, we examined the effect of pressure and current on the operation of an EC ammonia compressor stack. We found the total voltage increased significantly with increasing current but increased marginally with increasing pressure. We measured the flow rate leaving the cell and analyzed the composition of the effluent gas stream with gas chromatography. While the device provided useful compression work in all observed cases, back diffusion of ammonia hampered the performance, reducing the flow rate of the effluent fluid by as much as 67%. The maximum observed single-cell efficiency was 40% with respect to ideal isentropic compression. The ohmic losses associated with high current and the back diffusion effect are likely responsible for the low cell efficiency.

Berries are highly perishable fruits and require both low storage temperature and suitable packaging throughout the supply chain to preserve their organoleptic qualities. However, the energy consumption of refrigerated equipment and the use of packaging materials, plastic in particular, might generate important environmental impacts. Besides, there is a strong commitment to reduce the use of plastic in the food industry.The aims of the current work are first to assess the energy consumption of refrigerated equipment and second to analyze the environmental performance of the strawberry supply chain. Various stages of the supply chain from transport from growers to retail storage were modeled using data from field measurement and interviews with professional stakeholders. Life Cycle Assessment (LCA) was performed for the strawberry supply chain. Different packaging materials, plastic (PET, RPET) and alternatives (molded pulp, recycled paper, cardboard), were used. The processes that generated the most important environmental burden were the packaging production and the long-distance refrigerated transport. To limit the impact related to packaging production, it is necessary to consider not only the type of packaging material but also the processes and energy consumption used in their manufacturing.

Suitable low global warming potential (GWP) refrigerants that conform to F-gas regulations are fundamental to the operation and future development of high-temperature heat pumps (HTHPs) used for industrial processes and waste heat recovery. This paper presents the results of a theoretical simulation to investigate a range of low-GWP refrigerants and their suitability to supersede refrigerants HFC-245fa and HFC-365mfc. A steady-state thermodynamic model of a single-stage HTHP with an internal heat exchanger (IHX) was developed to assess system cycle characteristics and performance at temperature setpoints at 60 and 70°C heat source, 90 and 140°C heat sink, at 30 and 70 K lift. This study focuses on energetic and exergetic efficiencies within the system and the impact of regulating superheat to optimise performance. Based on energetic and exergetic theoretical results, a trade-off between COP, VHC, and exergetic efficiency indicates HCFO-1233zd(E) and HFO-1336mzz(Z) as the most likely replacements for HFC-245fa and HFC-365mfc respectively. The refrigerant HC-601, followed by HFO-1336mzz(Z) and HCFO-1233zd(E), exhibited the lowest exergetic destruction within test conditions. Mapping the minimum superheat indicated optimum performance for HCFO-1233zd(E) between 5 to 8 K and HFO-1336mzz(Z) between 17 to 22 K, depending on temperature lift. Validation of the theoretical results with experimental data indicates that simulated COP closely matches empirical values. This work provides a method to optimise refrigerant selection in HTHPs based on operational indicators to maximise overall system performance.

The ejector, as one of the core components of the CO2 trans-critical ejection refrigeration system, plays an important role in improving refrigeration capacity and reducing compressor power consumption. Although the ejector can be optimized by experiment and Computational Fluid Dynamics (CFD) simulation to improve its performance, these methods are time-consuming and complicated. This study aims to propose a method to improve the performance of the CO2 trans-critical two-phase ejector assisted by using CFD, artificial neural network (ANN), and genetic algorithm (GA). Firstly, the influence of geometric parameters on ejector efficiency was analyzed by using CFD technology, and the database was generated. Next, the complex and time-consuming CFD model was replaced by the ANN surrogate model established to predict the ejector performance. Finally, the GA method was used to optimize the ejector to maximize the ejector efficiency. The results show that the efficiency of the optimized ejector is 35.39%. The optimized ejector increases the secondary flow velocity and eliminates the vortex in ejector, and the efficiency of the optimized ejector is raised by more than 8% on average than that of initial ejector under different primary and secondary flow conditions. The research shows that the combination of CFD, ANN, and GA has higher reliability and better performance in the optimization design of CO2 two-phase ejector.

The static performance of an Active Magnetic Regenerator Refrigerator (AMRR) can be evaluated using various indicators, such as the refrigeration capacity, coefficient of performance, and efficiency, for a given temperature span (that is, the hot-to-cold heat source temperature difference). The two main control parameters (cycle frequency and fluid mass flow rate) must be adjusted according to the imposed temperature span to achieve optimum performance. However, in real-world operations, heat exchangers at both ends of the regenerator thermally connect the device to the surroundings, and the hot and cold temperatures are no more imposed quantities. Under these heat transfer constraints, the device performance, in terms of refrigeration capacity, could be suboptimal, even after adjusting the two control parameters. Indeed, to provide optimal performance, heat exchangers must have precise values of the overall heat transfer coefficient, depending on the desired operating temperature difference. So, if a single pair of heat exchangers are used, it is impossible to characterize the performance of the magnetic refrigerator at different temperature spans. This work contrasts the systematic procedure for evaluating the performance of a magnetic refrigeration device with heat exchangers at the cold and hot ends to the procedure with an imposed temperature span. Both procedures can be used to obtain the optimal AMRR performance curves. However, this work highlights the necessity to use different (or variable heat transfer coefficient) heat exchangers when the first procedure is adopted. The needed overall heat transfer characteristic of both heat exchangers will be lower for a higher temperature span.

The thermal and flow resistance properties of wetting pads play a key role in how effective direct evaporative cooling (DEC) systems Perform. To make an informed decision, it's crucial to study the heat transfer properties and airflow resistance manifested in pressure drop for various types of wetting media. An experimental study was conducted to determine pressure drop and heat transfer correlation constants at three airflow rates for palm fruit mesocarp fibres (PFMF) wetting media. Heat transfer and pressure drop equations were fitted with generated data to obtain correlation constants. The wetting media were effective to lower the ambient temperature at an average depression of 6.6 to 8.2°C and increase the relative humidity of the inlet air at an average value of 25.54 to 39.32 %. PFMF had a low-pressure drop per unit length, ranging from 5.29 to 7.62Pa/m, which makes it an appealing alternative to other wetting media. New correlation constants generated for pressure drop and heat transfer data fit well with high coefficient of determination (R2) values. The average cooling efficiency ranged from 56.43 to 65.27%, while the average Merkel number was 0.16 to 0.19. The Nusselt number increased with the Reynolds number and showed a laminar flow. Amaranths stored in DEC produced respiratory heat ranging from 290.86 to 336.53mg/kg/h for all air velocities. Considering the respiratory rate within the range of cooler temperatures, it is recommended to use the DEC only for short periods or for pre-cooling of vegetable storage.