Conventional Refrigeration Research Articles

Thermodynamic Analysis of an NH3/CO2 Cascade Refrigeration System with Subcooling in the Low-Temperature Circuit Utilizing the Expansion Work

NH3/CO2 cascade refrigeration system is recognized one of the most promising technologies in low-temperature application. In this paper, a NH3/CO2 cascade refrigeration system with subcooling in low-temperature circuit driven by recovery expansion work has been proposed. The aim of this study is to investigate the proposed cascade refrigeration system compared with conventional cascade refrigeration system. Mathematical models based on energy conservation and exergy balance are established. The selection of different refrigerants in auxiliary subcooling system is discussed. The effects of operating parameters such as the condensation temperature of the low-temperature circuit, evaporation temperature, and expander efficiency on system performance are evaluated. The results show that the coefficient of performance and exergy efficiency of the proposed system are about 7.56% and 7.98% higher than that of conventional cascade refrigeration system. The discharge temperature of NH3 compressor can be significantly reduced by 18.33%. The isentropic efficiency of the expander has a large impact on the system performance.

Numerical simulation of CO2 two-stage compression refrigeration system with external intercooler

The CO2 two-stage compression refrigeration system is a feasible alternative to conventional refrigeration systems for logistics cold storage cooling that provides high efficiency and environmental protection. In a previous study, we proposed a two-stage compression refrigeration cycle with an external intercooler and performed a thermodynamic analysis. Based on that, a more comprehensive simulation analysis is performed herein using the validated models. The performance, optimal discharge pressure, and intermediate pressure are investigated using a high-pressure compressor with both fixed and variable speeds. The results show that the cooling-water temperature has a significant positive linear correlation with the optimal discharge pressure, whereas the evaporator-inlet air temperature has little effect at a fixed high- pressure compressor speed. When the high-pressure speed is adjusted to achieve the optimal intermediate pressure and discharge pressure simultaneously, the coefficient of performance increases by 4.5% compared with that of the fixed-speed system, while the cooling capacity decreases by 8.4%. The correlation of optimal discharge pressure and optimal intermediate pressure is given.

Performance assessment of novel solar still regenerated liquid desiccant-based evaporative air-conditioning system for an office in India

A liquid desiccant-based evaporative air-conditioning system (LDeACS) is one of the excellent alternatives to conventional vapour compression refrigeration system. The liquid desiccant (LD) requires less thermal energy at low temperatures for regeneration, therefore, the use of renewable (solar) energy is a promising source for the regeneration of LD. The prime motive of the research is to assess the applicability of novel solar still (SS) regenerated LDeACS for an office located at tropical savanna humid climate using numerical simulation. The novel solar still provides the combined function of a regenerator and LD heater. The simulation was carried out to evaluate the performance of sub-components of proposed LDeACS by varying the various input operating conditions (inlet mass flow rate of LD; inlet temperature of LD; temperature of absorber plate of SS) of SS. For the simulation, the mathematical model of sub-components of the proposed LDeACS is interlinked using commercial equation solver software. Simulated results indicated that the proposed LDeACS is capable to provide the required human comfort conditions. The parametric analysis of the system revealed that variations in performance parameters of sub-components of LDeACS are more sensitive to the inlet mass flow rate of LD at SS. An increment in the inlet temperature of LD at SS indicates an adverse effect on the performance indices of LDeACS. An increase in absorber plate temperature of SS enhances performance of SS, contrary to expectations, it degrades the performance of the dehumidifier.

Natural refrigerants are favored by the future

BACKGROUND: Reducing the harmful impact on the environment is a promising way to the development of low-temperature technology. According to the amendment to the Montreal Agreement, approved by the Russian Federation, the use of hydrofluorocarbons should be reduced by 85% by 2036.
 AIMS: To justify the use of hydrocarbons as refrigerants in terms of their effectiveness.
 MATERIALS AND METHODS: Here, we have studied the losses of refrigeration plants at different temperature levels (refrigerant boiling points of 25 С, 18 С, and 13 С), while working with the refrigerants R134a, R404A, R1270, and R290 using the entropy-statistical method of thermodynamic analysis.
 RESULTS: Experimental results revealed that the natural refrigerants, R1270 and R290 have higher efficiency than the conventional refrigerants R134a and R404A. The values of the cooling coefficient under adiabatic compression are higher by 16.28%, 1.81%, and 1.14% compared to R404A, R1270, and R290, respectively, for installation with a boiling point of 13 C. Similarly, for installation with a boiling point of 18 C, these values are higher by 16.84%, 1.13%, and 0.58% compared to R404A, R1270, and R290, respectively. Furthermore, for installation with a boiling point of 25 C, the values of the cooling coefficient under adiabatic compression are higher by 18.53%, 0.8%, and 0.43% compared to R404A, R1270, and R290, respectively.
 In addition, the degree of thermodynamic perfection for R290 is higher by 27.99%, 19.2%, and 14.79% compared to R134a, R404A, and R1270, respectively, for a boiling point of 13 C. Similarly, for R290 and a boiling point of 18 C, it is higher by 21.25%, 14.71%, and 9.9% compared to R134a, R404A, and R1270, respectively.Furthermore, for R290 and a boiling point of 25 C, it is higher by 27.94%, 11.44%, and 3.61% compared to R134a, R404A, and R1270, respectively.
 In this study, data on the production of hydrocarbon refrigerants, in particular R1270 and R290, under the Russian Federation are presented. Moreover, quality indicators and the main areas of application for the same are provided here.
 CONCLUSIONS: The results of the analysis showed the prospects of using natural refrigerants (R1270 and R290) and allowed us to assess different ways to improve the refrigeration plants.

Magnetic field delays the senescence of strawberries by maintaining energy state and regulating respiratory metabolism

Strawberries are prone to rapid quality deterioration after harvest. Research has confirmed that a magnetic field can improve fruit quality during postharvest storage. However, how the magnetic field impacts the postharvest physiology of strawberries is far from being explored. In this study, the magnetic field (MF, 4 mT, and 50 Hz) was employed during the storage of strawberries at 4 °C for 1, 3, 5, 7, 10, and 15 d, and conventional refrigeration (CR) was used as the control. The results showed that the MF maintained better fruit quality, as indicated by lower decay incidence, declined weight loss, and greater firmness retention. The decrease in soluble solids content and titratable acidity of strawberries caused by respiratory depletion was also alleviated by MF. Furthermore, an improvement in the adenosine triphosphate level, energy charge, activity of enzymes (H+-ATPase, Ca2+-ATPase, succinate dehydrogenase, and cytochrome oxidase) involved in the respiratory metabolism, as well as primary respiratory metabolites (D-glucose, succinic acid, fumaric acid, and citric acid) were observed for the strawberries of MF group. Accumulations of hydrogen peroxide, superoxide anion, and malondialdehyde were suppressed with the application of MF. Overall, the MF contributed to maintaining higher energy and membrane integrity and function, regulating the levels of energy metabolism enzymes, and mitigating reactive oxygen species accumulation, which might be a part of the mechanism involved in retarding the senescence and decay of harvested strawberries.

Development of Conventional Refrigeration Control System Learning Media, Automatically Cooling and Defrost System

Development of Learning Media aims to design a Conventional Automatic Refrigeration Control System Design for Refrigeration and Defrosting Systems so that it can assist the learning process in Class XI Refrigeration Engineering. This research is a type of R&D level 3. This study used a questionnaire as an instrument to collect data from content experts, media experts, and students. The results of the material expert trial obtained a percentage value of 93.33%, with very decent qualifications, the media expert trial results obtained a percentage of 97.64%, with very decent qualifications, the small group trial results obtained a percentage value of 90.25% , with very decent qualifications, the results of the large group trial data obtained a percentage of 90.04%, qualifications Based on the research results, the media is feasible and good to be used as a learning medium in the subject of Refrigeration Systems and Installation in class XI TP majoring in Electrical Engineering, package refrigeration and air conditioning engineering expertise at SMK Negeri 1 Denpasar

Current perspective in magnetocaloric materials research

Magnetocaloric refrigeration has remained a promising alternative to conventional refrigeration for the last few decades. The delay in reaching the market is significantly based on materials’ related issues, such as hysteresis/reversibility, mechanical stability, or formability. This perspective paper shows the current trends in magnetocaloric materials research, highlighting the families of alloys and compounds that are gaining attention in the recent years. It also includes an overview of novel approaches that can be used to analyze these properties that could improve the applicability of magnetocaloric materials.

Simulation of refrigerant-lubricant two-phase flow characteristics and performance test in space compressor

The vapor-compression heat pump allows for lightweight heat-control systems and efficient heat emissions. It is considered to be the best choice for future space thermal control systems. To solve the problem of separation and compression deterioration of conventional positive-displacement refrigeration compressors in a microgravity environment, an innovative microgravity solution, mixing refrigerant and lubricant without oil separation, is proposed. A flow model in the compression chamber was developed and simulations were performed to investigate the effects of gravity and lubricant volume fraction on the flow characteristics of the refrigerant-oil mixture in a rolling rotor compressor. A modified compressor performance test bench was built and the effect of compressor speed on parameters such as power and heat dissipation was investigated experimentally. The results showed a maximum difference between the simulated and experimental values of compressor discharge temperatures of 9.16 %. Under microgravity conditions, a lubricant-refrigerant mixture with a volume fraction of less than 5 % can serve as the system working medium. The lubricant volume fraction at the outlet of a compressor cycle in normal gravity was 4.9 %, while it was 3.34 % in microgravity. As the compressor speed increased from 1500 to 5000 rpm, the compressor power increased from 15.5 to 64.5 W and the system heat discharge rate increased from 115.2 to 164.1 W. The system refrigeration coefficient of performance (COPc) decreased from 6.4 to 1.5, while that of heat dissipation, COPh, decreased from 7.4 to 2.5.

Single-phase air parallel ejectors: An experimental and numerical study

Ejector-based refrigeration systems (ERS) raise a lot of interest, given their lower electrical consumption compared to conventional refrigeration systems. However, a single ejector suffers from a lack of capacity flexibility, while the commercial success of this technology often relies on its ability to handle the fluctuating heating load availability and cooling load requirements. To that end, this work proposes the use of multiple ejectors having similar performance curves that could operate individually or simultaneously, according to the needs. To investigate the suitability of the proposed solution, a test bench equipped with two ejectors having different capacities, and a turbulence model, are used. The results show that the performance of the two ejectors is exactly the same, whether they are used separately or simultaneously. To the best of the author’s knowledge, it is shown here for the first time that, when several ejectors are used simultaneously, they each retain their performance, without any disturbance of their entrainment ratio or critical outlet pressure. This important new finding paves the way for the design of ERS for variable capacity applications, such as solar cooling systems.

A Systematic Review of Thermoelectric Peltier Devices: Applications and Limitations

Conventional refrigeration processes release ammonia and freon into the atmosphere, which results in global warming. These problems may be overcome by using thermoelectric modules because of the absence of coolants or refrigerants in these systems. However, the cooling performances of such modules are relatively small in comparison to those of conventional refrigerators. In this paper, the working principles of thermoelectric modules are discussed together with a review of different relevant aspects, namely: the thermoelectric materials, and their mechanical properties used to build thermoelectric devices, different types of thermoelectric devices available on the market, mathematical modeling of thermoelectric materials, and various applications of thermoelectric materials in different fields.

A concise review on the Suitability of Nano-Refrigerants for Residential Refrigeration Systems (RRS)

Nanoparticles have recently attracted huge attention as an engineering alternative in various fields. This is not unconnected with its established ability to perform better when used to replace some conventional systems or used as an enhancement for the system. Hence, this study reviewed the viability of nanofluids developed from nanoparticles as a possible replacement for conventional refrigerants available. In this review, focus was placed on refrigerants and refrigeration types, Nanoparticles and Nanofluids, Synthesis, Characterization and properties of Nanoparticles and finally on Nano-refrigerants and their viability. Conclusions were reached based on findings of the review.

Energy and exergy study of the integrated adsorption-absorption system driven by transient heat sources for cooling and desalination

The scarcity of clean water and the lack of sustainable cooling systems are continuously pressing. Although many technologies are well-established, such as vapour compression for refrigeration and reverse osmosis for desalination, they are energy-intensive and conventional refrigeration technology utilising working fluids of long-lasting ozone-depleting and greenhouse effects. Alternatively, adsorption and absorption technologies can meet such demands, and they are the most feasible to utilise the waste and renewable heat abundant in many locations. Therefore, this paper computationally studies the emerging integrated adsorption-absorption system for cooling cum desalination employing transient waste heat sources of various waveform characteristics. A previously validated computational model for the adsorption subsystem was coupled with a thermodynamic model for the absorption subsystem and experimental heat profiles obtained from an internal combustion engine. The energy and exergy analysis of the integrated system utilising the actual heat source from an internal combustion engine and predefined waveforms were undertaken and benchmarked against that operated under steady heat sources. The integrated system operated with a relatively low exergy efficiency in the absorption cycle of up to 15.33%. The adsorption bottoming cycle successfully utilised the heat from the absorption subsystem at a relatively higher exergy efficiency of up to 42.69%. The execution of a transient heat source of sinusoidal waveform enhanced the water production by up to 30% and the cooling of absorption and adsorption subsystems by 24% and 15%, respectively. However, admitting realistic waveforms of an internal combustion engine showed marginal differences compared to the steady heat sources owing to their high frequencies and small amplitudes.

Proposal and performance study on a component-based double-stage compression auto-cascade refrigeration cycle

It is difficult for the conventional single-stage compression auto-cascade refrigeration cycle to achieve higher refrigeration efficiency and lower refrigeration temperature, because the stream rich in high boiling point component from the phase separator bottom undergoes a single-stage compression process of high pressure lift ratio. Based on the concept of the evaporating temperature of the high/low boiling point component matching the grade compression of two streams from the phase separator, a component-baseddouble-stagecompressionauto-cascaderefrigeration (CDACR)cycle using R170/R600a is proposed in this paper. In the novel cycle, one dedicated compressor with two suction ports is used as the substitute for a conventional compressor with the sole suction port to realize grade compression process of the component of the refrigerant mixtures, and the stream enriched with high boiling point component from the separator bottom is sucked into the high-pressure suction port and undergoes the low-pressure-lift-ratio compression process, while the stream rich in low boiling point component from the separator top is sucked into the low-pressure suction port and executes the high-pressure-lift-ratio compression process, so as to cut down the compressor power consumption and obtain a lower refrigeration temperature. The mathematical model of the proposed cycle is developed to evaluate the thermodynamic performance of the system and comparisons with the conventional single-stage compression auto-cascade refrigeration (SCACR) cycle are also discussed. The results indicate that application of the component-based grade compression to the conventional auto-cascade refrigeration cycle dramatically improves the performance of the CDACR cycle, and there is optimum composition ratio of refrigerant mixtures for the CDACR cycle to obtain the highest coefficient of performance (COP). It is also shown that the performance of the CDACR cycle is significantly better than that of the SCACR cycle. As compared with those of the SCACR cycle, the compressor power consumption of the CDACR cycle decreases by 44.83%-53.17%, and its COP increases by 0.34–0.43, as the evaporating temperature at the evaporator outlet ranges from −60°C to −40°C. In addition, at the condenser outlet temperature in the range of 26°C- 40°C, the compressor power consumption for the proposed cycle is 37.74%-47.03% lower than that for the SCACR cycle, while COP of the CDACR cycle is 0.29–0.42 higher than that of the SCACR cycle.

Experimental optimization of replacing R22 with R417A without any other changes in configuration of residential air‐conditioning systems based on energy and exergy analysis

AbstractIn this paper, the optimal refrigerant mass charge amount of R417A, as a substitute for R22, was experimentally investigated in a split‐type air‐conditioner with no changes in system configuration. Experiments were conducted for both refrigerants over a range of mass charge from 500 to 850 g in a 12,000 Btuh−1 split air‐conditioner as the case study which is a conventional refrigeration system in residential sector of Iran. In order to study the effect of refrigerant mass charge on performance of refrigeration cycle, energy and exergy analysis were performed to determine cooling capacity, energy efficiency ratio (EER) and exergy efficiency. Results showed that the maximum EER for R22 and R417A are 2.48 and 2.41, and the maximum exergy efficiencies obtained for R22 and R417A are around 7.3% and 7%, respectively. Based on both EER and exergy efficiency, the optimum mass charge for R22 and R417A refrigerants are around 640 g and 650 g, respectively. In addition, it was found that under optimal charge conditions, the cooling capacity, EER and exergy efficiency of the system while working with R417A are lower than R22, just by 2.5%, 3%, and 4.5% respectively. Comparison results indicate that R417A can be considered as a suitable substitute for R22, which can almost provide the same performance without need to change the system components.

Energy and exergy analysis of a modified three-stage auto-cascade refrigeration cycle using low-GWP refrigerants for sustainable development.

This study proposed a modified three-stage auto-cascade refrigeration cycle (MTARC) operating with environmentally benign zeotropic mixture of R1234yf/R170/R14 at the refrigeration temperature level of - 80°C. Compared with the conventional three-stage auto-cascade refrigeration cycle (CTARC), MTARC incorporates an additional pressure regulator between the condenser and separator to realize phase separation at a lower pressure and temperature. A comprehensive evaluation of energy and exergy performance of the two cycles was conducted theoretically. Under a typical working condition, the cooling capacity, COP and exergy efficiency of the MTARC are improved by 15.85%, 11.69% and 7.65% in comparison with the CTARC, respectively. In addition, a lower evaporating temperature was also obtained by the MTARC under the same operating condition. When the intermediate pressure drops from 2 to 1MPa, the cooling capacity, COP and exergy efficiency are improved by 35.43%, 25.25% and 16.74%, respectively, for the MTARC, meanwhile the compressor outlet temperature increases 19.93°C from 92.27 to 112.20°C. Therefore, the selection of the intermediate pressure should be comprehensively considered to ensure a desirable cycle performance and a proper working condition for the compressor. The proposed modified cycle offers new pathways for designing innovative cryogenic refrigeration systems, thereby potentially improving the energy economy in a myriad of modern energy applications for sustainability concerns.

Additive manufactured thermoplastic elastomers for low-stress driven elastocaloric cooling

Exploiting the strain-induced crystallization of soft elastomeric polymers elastocaloric cooling has recently been explored as an environmental-friendly alternative to conventional refrigeration. Elastomers require a much lower applied stress to induce the elastocaloric effect compared to shape memory alloys. Several prototype coolers employing these soft polymers have been demonstrated to achieve a moderate temperature span under lower stresses. Here, we investigate the elastocaloric properties and potential cooling performance of five thermoplastic elastomers that can be 3D printed, both in the form of filaments and as Additive Manufactured (AM) parts. The materials were first characterized as filaments to screen for the elastomers with the highest elastocaloric effects. A large adiabatic temperature change of 17.8 K was obtained in the Ultimaker98A filament. AM parameters were optimized to achieve parts with satisfactory functional stability while maintaining their elastocaloric effect. As a printed part, NinjaFlex achieved a high material coefficient of performance (COPmat) of 3.2 with 1.74 J/g input work at ∼0.1 Hz, driven by a stress of 5.7 MPa. Implementing AM elastocaloric elastomers creates opportunities for the development of full-scale low-activation-stress regenerative elastocaloric cooling components that enable optimizing flow structures and enhanced heat-transfer performance.

Evaluation and Analysis of an Agro-Based Nano Refrigerant to Improve the Performance of a Domestic Refrigeration System

The use of nanoparticles along with the conventional refrigerant in a vapor compression cycle is relatively a new idea, where nano-refrigerants are found to have improved thermo-physical properties over the conventional refrigerants. Nano-refrigerant is the combination of nanoparticles with the refrigerant to improve the performance of the refrigeration process. In this study, a developed nanofluid from agricultural source (rice husk) was applied in a domestic refrigerator and its performance investigated. The pre-developed nanofluid which was prepared using the synthesis, centrifugation and calcinations processes was administered in the compressor of the refrigerator at concentrations of 0.2wt%, 0.3wt%, 0.5wt% and 0.6wt% to form a mix with refrigerant R600a used in the compressor (as control) and allowed to run for 4 hours. Performance evaluation was measured using parameters such as pull down time, discharge temperature and coefficient of performance (COP). Results show an increase in the COP by 31, 23 and 35% compared to the control sample for the 0.2wt%, 0.3wt% and 0.5wt% concentrations respectively. The sample 0.6wt% and 0.5wt% showed the best pull down time with temperatures of -6.1 and -3.1℃ at 240 minutes respectively and a reduced discharge temperature of 7-16% by the 0.2wt%, 0.3wt% and 0.5wt% concentrations in respect to the control sample. Hence, the use of rice husk based nanofliud resulted in an enhanced performance for the domestic refrigerator.

Can user reviews on online shopping websites contribute to user-involved green product innovation: a case study of household refrigerators

ABSTRACT User reviews (URs) have been regarded as a novel way of promoting user-involved green product innovation (GPI) in theory. However, the actual relationships between URs and GPI are still underexamined. This study adopted the method of content analysis to exemplify the effectiveness of user reviews on online shopping websites (OSURs) in user-involved GPI. Specifically, 62,909 effective OSURs on 24 green household refrigerators and 43 conventional refrigerators were collected and analyzed. The results show that 8.41% of all the pre-processed OSURs contain green information, which cannot be a dominant information source for promoting GPI. Yet, the identified green reviews (GRs) are still valuable for developing and diffusing GPI. On the one hand, three green topics related to energy efficiency, environmental friendliness, green materials and technologies are intensively generated, massive user experiences can objectively reflect the actual environmental performance of existing products. On the other hand, GRs account for 12.62% and 6.19% of all the OSURs on green refrigerators and conventional refrigerators, respectively. Users prefer to generate positive rather than negative GRs on green refrigerators. The implementation of GPI has a positive impact on OSURs in return. Firms can actively collect and analyze OSURs of extant green products, thus promoting the green innovation of their own products. This study adds to the literature of user-involved GPI by exploring the actual relationships between OSURs and GPI. A practical analysis framework and valuable implications are also proposed to advance GPI, green growth at firm level and sustainable development at social level.

Thermal performance analysis of a passive hybrid earth-to-air heat exchanger for cooling rooms at Mexican desert climate

This research incorporates two passive technologies selected to offer thermal comfort conditions in a room exposed to extreme desert climatic conditions (Hermosillo, Sonora, Mexico). On the one hand, a rectangular earth-air heat exchanger assisted with PCM (REAHE + PCM) is implemented. Its job is to supply cooled air to the room at temperatures below the comfort temperature. On the other hand, a room with PCM on its ceiling (room + PCM) is proposed, to reduce the thermal load towards the room and shift the thermal peak load, acting as thermal insulation. Hoping that the benefits of this combination of passive technologies provide the thermal comfort conditions required in a building in this region and thereby eliminate or reduce the consumption of electrical energy in conventional refrigeration systems. This article reports a detailed transient study of the thermal behavior of a passively cooled room. The effect of position, thickness, latent heat, and phase change temperature of the PCM in the room was investigated. Also, the different room configurations reported the time evolution of heat fluxes, temperatures, coefficient of performance (COP), and liquid fraction. A comparison between the proposed system and a room without PCM was made. Adding PCM to the roof can drop the peak heat flux in the ceiling by up to 33%. It was found that the most favorable system was with the PCM placed on the top of the room with a thickness between 1.5 cm and 2.0 cm. The best configuration kept an average room temperature of 0.6 K below the comfort temperature. The maximum temperature in the room only exceeded the comfort temperature by 0.33 K. The average COP varied between 264 and 288 for the room systems, while the average COP for the REAHE-PCM was 307. This combination of technologies is satisfactory for the climatic conditions studied.

Experimental and numerical investigation of the transient thermal characteristics of twisted nitinol wires in a continuous torsional refrigeration system.

Twistocaloric cooling technology is a novel solid elastocaloric refrigeration to be promising alternatives to conventional compression refrigeration. The transient thermal characteristics of the twistocaloric-effect material and its cooling capacity are critical for this technology. A test rig of the continuous torsional refrigeration system (CTRS) using nitinol wires twisted by a stepping motor was built. The experimental tests show that, the surface temperatures increased as the stepping motor twisted the nitinol wires clockwise, and decreased by untwisting them counterclockwise under the stepping motor speed of 40, 45 and 45rpm. The maximum temperature rise and drop relative to the ambient temperature for the two-twisted-nitinol-wire combinations were 7.1 and 2.6°C, higher than those of 1.4 and 0.6°C for the single nitinol wire, respectively. An optimization program based on a heat conduction model was constructed to attain the potential cooling and heating capacities (PHCCs) of the nitinol wires. Then, PHCCs were introduced into the coupled flow and convective heat transfer model to predict the actual cooling and heating capacities of the CTRS. They were discovered to increase as the number of nitinol wires, the stepping motor speed, and the air velocity. The results can be referred in developing a continuous torsional refrigeration prototype.