Conventional Refrigeration Research Articles

Substantially Enhanced Electrocaloric Effect in Ba(Zr0.2Ti0.8)O3 Lead-Free Ferroelectric Ceramics via Lattice Stress Engineering.

As an alternative to conventional vapor-compression refrigeration, cooling devices based on electrocaloric (EC) materials are environmentally friendly and highly efficient, which are promising in realizing solid-state cooling. Lead-free ferroelectric ceramics with competitive EC performance are urgently desirable for EC cooling devices. In the past few decades, constructing phase coexistence and high polarizability have been two crucial factors in optimizing the EC performance. Different from the external stress generated through heavy equipment and inner interface stress caused by complex interface structures, the internal lattice stress induced by ion substitution engineering is a relatively simple and efficient means to tune the phase structure and polarizability. In this work, we introduce low-radius Li+ into BaZr0.2Ti0.8O3 (BZT) to form a particular A-site substituted cell structure, leading to a change of the internal lattice stress. With the increase of lattice stress, the fraction of the rhombohedral phase in the rhombohedral-cubic (R-C) coexisting system and ferroelectricity are all pronouncedly enhanced for the Li2CO3-doped sample, resulting in the significant enhancement of saturated polarization (Ps) as well as EC performance [e.g., adiabatic temperature change (ΔT) and isothermal entropy change (ΔS)]. Under the same conditions (i.e., 333 K and 70 kV cm-1), the ΔT of 5.7 mol % Li2CO3-doped BZT is 1.37 K, which is larger than that of the pure BZT ceramics (0.61 K). Consequently, in cooperation with the great improvement of electric field breakdown strength (Eb) from 70 to 150 kV cm-1, 5.7 mol % Li2CO3-doped BZT achieved a large ΔT of 2.26 K at a temperature of 333 K, which is a competitive performance in the field of electrocaloric effect (ECE). This work provides a simple but effective approach to designing high-performance electrocaloric materials for next-generation refrigeration.

Theoretical performance studies on environment friendly refrigerants used in refrigeration units

European Union regulations stipulate that household refrigeration systems must operate with fluid refrigerants that possess low global warming potential (GWPs). In this work, theoretical performance of six binary and one ternary mixture (which consists of R13I1, R290, R161, R32, R1234yf, and R1234ze(E)) was investigated. The performance parameters such as coefficient of performance (COP), refrigeration effect (RE), volumetric cooling capacity (VCC), discharge temperature, pressure ratio, and specific power consumption of all considered refrigerant mixtures is studied with respect to the evaporator temperature range of -18 to 180C and the condenser temperature range of 40 to 550C. The properties corresponding to different operating conditions for the refrigerants considered in this study are estimated using REFPROP 10. The findings demonstrated that, when compared to R134a, all the investigated refrigerants exhibited very low specific power consumption (apart from M9, M10, and M14-M16), and high volumetric cooling capacity (VCC) (apart from M11 and M13) under the operating conditions of evaporator temperature -180C and condenser temperature 400C. M1-M3 and M11-M13 gave similar and within 10% deviation in coefficient of performance, while M3 and M11-M13 refrigerant mixtures offer significantly low discharge temperatures when compared to R134a. Refrigerant mixtures M2 and M11 consistently exhibited a better performance in comparison to R134a in the aspect of majority of the performance parameters considered in this study. Finally, it is understood that M2 and M11 are two possible alternative refrigerants to conventional refrigerants used in small refrigeration units (R134a and R22). Further, it is also identified that these mixtures are non-flammable, possess zero ODP and low GWP values.

Highly efficient grooved NiTi tube refrigerants for compressive elastocaloric cooling

Elastocaloric (eC) cooling without environmental issues has been a promising substitute for the conventional vapor-compression refrigeration. Commercial superelastic NiTi shape memory alloy tubes show large elastocaloric cooling capacity and ultrahigh fatigue life under cyclic compression but suffer from the limited specific heat transfer area (Aht) and insufficient cooling performance. Up to now, compressive NiTi tube eC refrigerant with Aht larger than 1 m2 Kg−1 has not been available due to the easy buckling problem. In this work, the buckling-free vertically and spirally grooved NiTi tubes (VGT and SGT) with Aht of 1.04 m2 Kg−1 and 1.25 m2 Kg−1 respectively are developed as the compressive eC refrigerants. The VGT and SGT are fabricated by the slow-feeding wire electric discharge machining based on the bared NiTi tubes. Then a compressive eC refrigeration prototype (ERP) is built to experimentally characterize the specific cooling power (SCP) and system temperature span (ΔTspan) of the grooved tubes. Under the regenerative flow configuration, the VGT and SGT achieve large zero-ΔTspanSCP of 2.18 W g−1 and 2.61 W g−1 at the operation frequency (fERP) = 0.5 Hz. Besides, the VGT and SGT produce maximum no-cooling-load ΔTspan of 25.2 K and 27.7 K respectively at fERP = 0.417 Hz. The experimental SCP and ΔTspan exceed most of the reported eC regenerators and there are still rooms for enhancing the cooling results by improving the ERP in future. Overall, the developed VGT and SGT with large Aht records and excellent cooling performance show big potentials of heat transfer structure design in developing highly efficient eC devices.

Preservation of high pressure pasteurised milk by hyperbaric storage at room temperature versus refrigeration – Effect on natural microbiota and physicochemical properties

Compared to refrigeration (RF), hyperbaric storage (HS) has been applied as a preservation methodology to increase foods shelf-life. The aim of this study was to compare HS at naturally variable uncontrolled room temperature (RT) to RF and evaluate its feasibility to preserve high pressure pasteurised milk (HPP milk), using different pressure levels (50, 75 and 100 MPa), by testing microbial and physicochemical parameters.While RF merely inhibited microbial growth over 40 days, HS/RT (75/100 MPa) maintained pH and gradually reducing all endogenous microorganisms tested to below the detection limit (< 1.0 log CFU/mL) corresponding to at least 2.60 log CFU/mL reduction on total aerobic mesophiles. Additionally, total soluble solids and apparent viscosity could both be kept using HS/RT for at least for 21 days. For 40 days, the total colour difference showed a small but discernible change for RF and HS/RT conditions, being also observed an increase on soluble protein for HS/RT samples, which may have resulted by pressure leading to aggregation of micelle caseins and whey proteins.In conclusion, the present work showed the potential of HS to preserve HPP milk with longer microbial shelf-life compared to RF and with a minor impact on physicochemical properties, being more environmentally friendly and sustainable than conventional RF.

Design methodology of standing-wave thermoacoustic refrigerator: theoretical analysis

Thermoacoustic refrigeration systems are one of the best alternative solutions for conventional refrigeration systems that are harmful to the environment and humans due to global warming and ozone layer depletion issues. Thermoacoustic technology can be considered a renewable and clean technology with a promising future for its many advantages. A thermoacoustic refrigerator converts acoustic energy to thermal energy (creating a cooling effect). In the present research, the focus is on the design of a standing-wave thermoacoustic refrigerator driven by an ordinary loudspeaker using the numerical simulation program DELTAEC with the concern of building the apparatus at a low cost. In addition, investigating the influence of some crucial parameters on cooling power and thermal/overall performance. Hence, the designed thermoacoustic refrigerator performed well in respect of cooling power and coefficient of performance. It has achieved a cooling power of 134.34 W with a temperature difference between the ambient and cold heat exchangers of 25 K at a COP of 1.956 and the overall efficiency (electrical power converted into cooling power) amounted to 113.43%. The achieved cooling power and COP could be significant when compared to others’ results.

Landau theory-based relaxational modeling of first-order magnetic transition dynamics in magnetocaloric materials

The magnetocaloric effect is often largest within the neighborhood of a first-order phase transition. This effect can be utilized in magnetocaloric refrigeration, which completely eliminates the need for the greenhouse gases utilized in conventional refrigeration. However, such transitions present unique dynamical effects and are accompanied by hysteresis, which can be detrimental for such refrigeration applications. In this work, a Landau theory-based relaxational model is used to study the magnetic hysteresis and dynamics of the first-order magnetic transition of LaFe13−x Si x . Fitting the experimental magnetization data as a function of applied magnetic field under different field sweep rates with this model provided the Landau parameters (A, B, and C) and the kinetic coefficient of the studied material. We demonstrate the tendency of the magnetic hysteresis to increase with the magnetic field sweep rate, underlining the importance of studying and minimizing the magnetic hysteresis in magnetic refrigerants at practical field sweep rates. While evaluating the temperature dependence of the time required for a complete transition to occur, a nonmonotonic behavior and a sharp peak were found for temperatures near the transition temperature. Such peaks occur at the same temperature as the peak of the magnetic entropy change for low fields, whereas for higher fields the two peaks decouple. This information is critical for technological applications (such as refrigerators/heat pumps) as it provides guidelines for the optimization of the magnetic field amplitude in order to reduce the transition timescale and consequently maximize the machine operational frequency and amount of heat that is pumped in/out per second.

Improving the Efficiency of a Conventional Vapor-Compression Refrigeration System used for Geothermal and Evaporative Cooling Techniques: Case Study in Iraq

A conventional vapor compression refrigeration cycle is among the most effective technology in refrigeration systems. In the present experimental study, thermal performance and the effect of the condenser temperature have been analyzed. With the decrease in the condenser temperature, the overall performance of the refrigeration cycle is increased. However, the cooling power and efficiency of conventional vapor pressure air conditioning units can experience a significant reduction when operating in extreme weather (hot and dry). This drop is mainly affected by the increase in the temperature (and pressure) of the condenser with an increase in the ambient air temperature. Unfortunately, Iraq experiences the most extreme summer seasons especially in the months of June and July when the temperature reaches or exceeds 50° C. So, ground cooling has been used in areas with a hot environment for split system air conditioners. Evaporative cooling was also performed to lower the coolant temperature of the AC unit used inside the condenser area. Experimental results showed that when using a geothermal heat exchanger, the temperature of the condenser is reduced from 116 to 110 ° C and the coefficient of performance (COP) is improved by 41%. In addition to this when the system uses evaporative cooling the temperature of the condenser is reduced from 110 ° C to 88° C. Moreover, a 65% improvement was made in the COP of the conventional vapor compression refrigeration cycle. Furthermore, with a decrease in the evaporator temperature from 6 to 3.5 °C there was an increase in refrigeration capacity by an average of 52%.

Thermal Performance Evaluation of a Novel Ejector-Injection Cascade Refrigeration System

In this article, a novel cascade refrigeration system is proposed for moderately low temperature applications. An ejector expansion vapor compression cycle (EEVCC) and a vapor injection cycle with the flash tank (VICFT) are coupled together through a cascade heat exchanger to develop the novel ejector injection cascade refrigeration system. The goal of this study is to investigate the potential improvement scope of a conventional cascade refrigeration system by integrating EEVCC and VICFT. A detailed energy and exergy balance analysis are conducted on the novel proposed system by considering the following three design parameters: (1) evaporator temperature; (2) pressure drop at the ejector; and (3) lower circuit condensation temperature. The results reveal that the performance of the proposed system is sensitive to pressure drop at the ejector and lower circuit condensation temperature for each evaporator temperature. Therefore, it is necessary to determine the optimal values of these factors in order to conduct an accurate performance analysis. Furthermore, a comparative study between the proposed system and the conventional system is conducted based on the first and second laws of thermodynamics. The results show that at −60 ℃ of evaporator temperature, the proposed system has 8.571 % COP improvement and 7.241 % exergy efficiency improvement over conventional cascade refrigeration system. This study also explores the suitable pair of refrigerants for this proposed system to minimize environmental impact. Among seven pairs of refrigerants investigated, R170 and R601 at LTC and HTC respectively shows the best performance. The proposed system was found to be more sensitive to change of LTC refrigerant than HTC.

Exergy and performance analysis of low GWP and Non-flammable HFO based refrigerant mixtures as alternatives to R134a

R1234yf and R1234ze(E) can be potential retrofits for the conventional refrigerants used in domestic refrigerator provided their flammability is controlled. In this study, the inerting effect of the dilutants R125, R134a, R227ea and R245fa on R1234yf and R1234ze(E) based ternary mixtures is studied theoretically. R152a, R161 and RE170 are used as the secondary refrigerants with R1234yf and R1234ze(E) based ternary mixtures. Minimum inerting concentration (most important parameter that decides the flammability of the mixture) is estimated with thermal balance method (TBM) and modified thermal balance method (MTBM) for the selected mixtures. The calculated MIC values are compared with 86 experimental data points (both binary and ternary) available in the literature. It is calculated that TBM and MTBM predicted the minimum inerting concentration values (for a majority of the mixtures) within ±30% and ±8% respectively when compared with the experimental data. The COP ratios of the non-flammable mixtures (that are proposed with MTBM) are estimated and is found to be maximum at a volumetric cooling capacity ratio close to 0.8. It is also calculated that the exergy efficiency varied between 0.54 to 0.64 for the low GWP mixtures (M1 to M5) proposed in this study.

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.&#x0D; AIMS: To justify the use of hydrocarbons as refrigerants in terms of their effectiveness.&#x0D; 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.&#x0D; 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.&#x0D; 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.&#x0D; 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.&#x0D; 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&amp;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.