Efficient Refrigeration Research Articles

Magnetic Refrigeration Design Technologies: State of the Art and General Perspectives

Magnetic refrigeration is a fascinating superior choice technology as compared with traditional refrigeration that relies on a unique property of particular materials, known as the magnetocaloric effect (MCE). This paper provides a thorough understanding of different magnetic refrigeration technologies using a variety of models to evaluate the coefficient of performance (COP) and specific cooling capacity outputs. Accordingly, magnetic refrigeration models are divided into four categories: rotating, reciprocating, C-shaped magnetic refrigeration, and active magnetic regenerator. The working principles of these models were described, and their outputs were extracted and compared. Furthermore, the influence of the magnetocaloric effect, the magnetization area, and the thermodynamic processes and cycles on the efficiency of magnetic refrigeration was investigated and discussed to achieve a maximum cooling capacity. The classes of magnetocaloric magnetic materials were summarized from previous studies and their potential magnetic characteristics are emphasized. The essential characteristics of magnetic refrigeration systems are highlighted to determine the significant advantages, difficulties, drawbacks, and feasibility analyses of these systems. Moreover, a cost analysis was provided in order to judge the feasibility of these systems for commercial use.

Thermodynamic and Comparative Analysis of Ejector Refrigeration Cycle and Absorption Refrigeration Cycle Integrated Wet Ethanol-Fueled HCCI Engine for Cogeneration of Power and Cooling

Abstract This study attempted for the proposal and analysis of a combined cycle that consists of a wet ethanol-fueled and turbocharged homogeneous charge compression ignition (HCCI) engine coupled to ejector refrigeration cycle (ERC) and absorption refrigeration cycle (ARC) for the simultaneous generation of two distinct outputs, namely, power and refrigeration. Both first and second laws of thermodynamics were employed to develop a thermodynamic model, which has been applied to investigate the performance of combined cycle. Furthermore, performance of the combined cycle for ERC versus ARC was compared and assessed after altering operating parameters (turbocharger pressure ratio, turbocharger compressor efficiency, ambient temperature, and the entrainment ratio of ERC and generator temperature of ARC) to study their effect on engine power output, refrigeration load, exergy of refrigeration, and energy and exergy efficiencies of the cooling-power cogeneration cycle. Results show that the elevated pressure of turbocharger results in the enhancement of HCCI engine power and increase of the refrigeration of thermal load, simultaneously. However, the increasing ambient temperature shows the decline of HCCI engine efficiencies and energy efficiency of cogeneration, while the cogeneration cycle exergy efficiency is found increasing. Furthermore, the results are reported for the refrigeration performed by lithium bromide–water (LiBr–H2O)-operated ARC, and R134a- and R290-operated ERC, respectively. Mapping of exergy destruction for the presented cogeneration cycle discovered HCCI engine, boiler of ERC, generator of ARC, and catalytic convertor as the components of significant exergy destruction. Entrainment ratio and type of refrigerant employed in ERC and the generator temperature of ARC show a marginal impact on the COPs of these cycles.

Multi-objective optimisation of thermodynamic performance parameters of a Gifford-McMahon refrigerator

The maximisation of cooling capacity and thermodynamic efficiency of a Gifford-McMahon refrigerator is a tedious task due to the occurrence of complex thermo-physical mechanisms inside its expander. Thus, in this paper, a hybrid simulation approach is introduced by using a combination of the numerical model, response surface model, and non-sorted genetic algorithm to maximise its cooling capacity and relative Carnot efficiency. The selected design factors are length and diameter of the regenerator, its porosity, stroke length of the displacer, and the delay angle of the displacer motion. A Box–Benhken design approach is adopted to create a robust design matrix by using the aforementioned design variables and responses. The correctness of the model is detected through the analysis of variance. Finally, a non-sorted genetic algorithm is utilised to maximise both responses. The numerical analysis at optimal parameter suggests that a major portion of expansion work loss takes place at the regenerator.

Study on solar-ground source heat pump and combined heating system in severe cold area

This paper studies the operation strategy and economy of solar-ground source heat pump gas heating system in severe cold region. Two operation modes of the system are introduced: series operation and parallel operation, and the two operation modes are simulated. This paper compares and analyses the heat exchange of the ground pipe, the change of the water temperature at the inlet and outlet of the ground pipe heat exchanger, the heating efficiency coefficient cop and the refrigeration efficiency coefficient EER of the heat pump unit during the five-year operation of the combined heating system, and studies the change of the soil temperature, Finally, the economic analysis is made from the initial investment cost and operation cost of two different heating schemes. The results show that the maximum heat transfer efficiency of the parallel system is 2.5 times that of the serial system, and the total heat transfer between the parallel system and the heat network is 83.2 % higher than that of the serial system. The inlet and outlet water temperature of the buried pipe decreased under both operation modes. After five years of operation, although the operation cost of the parallel combined heating system is higher than that of the serial combined heating system, the parallel combined heating system has more advantages than the serial combined heating system in terms of the overall heating effect of the system and the influence degree of the system on soil temperature.

Modeling and Optimizing the Parameters of Condensers in Split Type Room Air Conditioners

Split type room air conditioners (RACs) are very common nowadays. In Bangladesh, RAC manufacturers employ trial-error prototyping techniques in their design to increase the efficiency of RACs and the profitability of the plant. Computer modeling can be a great help to reduce the cost in the R&D stage to find the optimum design of RACs. In this study, modeling of heat transfer in the condenser of split type RACs employing the techniques of Computational Fluid Dynamics (CFD) was performed. To reduce the computational load the geometry was divided into small sections and geometric symmetries were also taken into account. For the simulation, the geometry and other relevant data were set in such a way so that they commensurate closely with real industrial data. An example data set for validation of simulation results were obtained from an AC manufacturer company, Elite Hitech Industries Ltd. The geometry was built using meshing techniques. Copper and aluminum were selected as materials for tubes and fins, respectively. R-22 was chosen as the refrigerant. Heat transfer and fluid flow were modeled using non-isothermal flow in a multi-physics environment. The main assumptions employed are laminar flow, extra coarse mesh size, constant air inlet temperature, perfect insulation between system and surroundings, and thin layer fins. The temperature distribution and heat transfer efficiency in the condenser, the impact of different refrigerant flow arrangements in the tubes have been studied in detail. This study leads to the finding of efficient refrigerant flow arrangements from the viewpoint of maximum heat transfer.
 Chemical Engineering Research Bulletin 21(2020) 20-25

Performance Analysis of a PV Powered Variable Speed DC Fridge Integrated with PCM for Weak/Off-Grid Setting Areas

This paper investigates the transient performance of a DC compressor fridge incorporated with Phase Change Material (PCM) for weak/off-grid setting regions. A photovoltaics (PV) module is directly connected to the DC compressor without use of batteries and inverter, in order to simplify the system and reduce its cost. The DC compressor speed can be adjusted according to the radiation intensity for an optimum match between PV output and the efficiency of refrigeration. During the daytime, the PCM is charged for cold storage by refrigeration; when solar radiation is weak or during the night, the PCM releases cooling to maintain the required cabinet temperature. A transient mathematical model is built for the whole system including PV module, DC compressor refrigeration system, fridge cabinet and PCM packs. The model is coded and solved in MATLAB while CFD method is used to produce some additional information. The simulations are conducted to evaluate the effect of solar radiation intensity, thermostat setting and the number of PCM packs on the fridge refrigeration performance. Moreover, the study aims to investigate and present benefits of incorporating PCM with a direct PV powered DC compressor fridge in weak/off-grid setting areas. When the fridge cabinet temperature varies between 4℃ and –2℃, the average COP of the fridge refrigeration system was found 1.7 for high solar radiation day due to the high rotation speed of the compressor, but for low solar radiation day, the average COP was calculated as 1.95. The analysis also shows that a variable speed DC compressor can keep the foods in the desired temperature range for two days of power outage by using 1 m² PV module and 3.6 kg of thin PCM packs.

A sustainable syngas cryogenic separation process combined with ammonia absorption refrigeration pre-cooling cycle

With the goal of effectively utilising low-grade waste compression heat by investigating potential improvements in energy efficiency, this study proposed a novel syngas liquefaction process combined with an ammonia absorption refrigeration cycle driven by available low-grade compression heat. The systems were evaluated from thermodynamics, as well as techno-economic aspects, to reduce the energy consumption and greenhouse gas emission. This study attempted to tackle two vital issues: how to effectively convert low-grade compression heat to cooling capacity to improve energy efficiency and design refrigeration cycles (both ammonia absorption refrigeration cycle and main refrigeration cycle) tailored with Heat Integration. The process was modelled, simulated, and optimised, aiming to reduce refrigerant and energy. The case study results demonstrated that the syngas liquefaction process with ammonia absorption cycle dramatically reduced the refrigerant consumption by 15.3%, contributing to a 7 MW reduction in electricity consumption. The specific energy consumption was decreased from 3.2 to 2.36. The coefficient of performance increased from 0.11 to 0.14. As for the environmental effect, the total greenhouse gas emissions were decreased from 0.12 Mt CO2-eq to 0.09 Mt CO2-eq. The exergy analysis showed that the new process decreased the total exergy destruction by 6.7 MW, leading to a higher exergy efficiency of 54.5%. In view of the economic performance, the total capital investment and total product cost were lowered by 10.8% and 20.1%. The proposed syngas liquefaction process exhibited the significant potential to improve environmental, thermodynamic, and techno-economic performances. The sensitivity analysis showed that the product cost of the new process was less sensitive to the variation of the electricity price.

Повышение энергоэффективности холодного хранилища

Saving resources and energy in refrigeration systems is one of the main vectors of development of the national economy of our country. One of the promising ways to solve these problems is the use of energy efficient refrigeration machines. The article discusses the main issues on the organization of energy efficient storage. In particular, the main recommendations for the design of the storage building are given; an analysis of the energy efficiency of refrigeration machines with and without VFD (variable frequency drive) is given; the main aspects of the operation of the condenser of the refrigeration unit are considered. Keywords: ANNUAL ENERGY CONSUMPTION, REGULATION, ENERGY EFFICIENCY

The Data Mining Technique Using RapidMiner Software for New Zeotropic Refrigerant

This research presents the development of environmentally-friendly and energy efficient refrigerant for medium temperature refrigeration systems that new azeotropic refrigerant mixture of hydrofluorocarbons and hydrocarbon that can retrofit in the refrigeration system using R404A. The medium back pressure refrigeration testing standard that follow CAN/ANSI/AHRI540 standard air-conditioning, heating, and refrigeration institute (AHRI) and The properties of refrigerants and refrigeration simulation system that used national institute of standards and technology (NIST) reference fluid thermodynamic and transport properties database (REFPROP) software and NIST vapor compression cycle model accounting for refrigerant thermodynamic and transport properties (CYCLE_D-HX) software. The methodology uses decision tree function in datamining by rapid minor software that first of KDnuggets annual software poll that showed new azeotropic refrigerant mixture had cooling capacity, refrigerant effect, GWP and boiling point were lower than R404A but work and pressure for medium temperature refrigeration system of azeotropic refrigerant mixture were higher than R404A. The artificial intelligence (AI) by data mining technic can predictive environmentally-friendly and energy efficient refrigerant for medium temperature refrigeration. The result of refrigerant mixed by R134A, R32, R125 and R1270 and is consistent with the evolution of fourth-generation refrigerants that contain a mixture of HFCs and HCs which are required to produce a low-GWP, zero-ozone-depletion-potential (ODP), high-capacity, low-operating-pressure, and nontoxic refrigerant.

Colossal Barocaloric Effect: Colossal Barocaloric Effect by Large Latent Heat Produced by First‐Order Intersite‐Charge‐Transfer Transition (Adv. Funct. Mater. 25/2021)

In article number 2009476, Yuichi Shimakawa and co-workers present an A-site-ordered quadruple perovskite NdCu3Fe4O12 that releases significant latent heat at the intersite-charge-transfer transition temperature near room temperature. The transition is first-order and accompanied by an unusual magnetic ordering and a large volume change, and thus, it causes a large entropy change, which is utilized through a colossal barocaloric effect. Efficient refrigeration can be realized through this effect.

Maximum efficiency of absorption refrigerators at arbitrary cooling power.

We consider absorption refrigerators consisting of simultaneously operating Carnot-type heat engine and refrigerator. Their maximum efficiency at given power (MEGP) is given by the product of MEGPs for the internal engine and refrigerator. The only subtlety of the derivation lies in the fact that the maximum cooling power of the absorption refrigerator is not limited just by the maximum power of the internal refrigerator, but, due to the first law, also by that of the internal engine. As a specific example, we consider the simultaneous absorption refrigerators composed of low-dissipation (LD) heat engines and refrigerators, for which the expressions for MEGPs are known. The derived expression for maximum efficiency implies bounds on the MEGP of LD absorption refrigerators. It also implies that a slight decrease in power of the absorption refrigerator from its maximum value results in a large nonlinear increase in efficiency, observed in heat engines, whenever the ratio of maximum powers of the internal engine and the refrigerator does not diverge. Otherwise, the increase in efficiency is linear as observed in LD refrigerators. Thus, in all practical situations, the efficiency of LD absorption refrigerators significantly increases when their cooling power is slightly decreased from its maximum.

Thermodynamic analysis and parametric optimization of ejector heat pump integrated with organic Rankine cycle combined cooling, heating and power system using zeotropic mixtures

Schematic diagram of ejector heat pump integrated with organic Rankine cycle combined cooling, heating and power (ORC-CCHP) system and mass fractions of (R141b/R134a) in ORC and heat pump loop, merits: great temperature glides in the high-temperature evaporator and high-temperature condenser, beneficial to generate plentiful refrigeration capacity in the heat pump loop. • Comprehensive thermal efficiency is proposed to achieve energy utilization potential substantially. • Mass fractions of zeotropic mixture, generator temperature and entrainment ratio are optimized. • R141b/R134a(55%/45%) achieves optimum mass fractions in ORC and heat pump loop. • Comparative analysis of basic ORCs, ORC with post ejector, ORC with ejector heat pump, EORC is conducted. • Ejector heat pump integrated with ORC-CCHP system is thermodynamiclly feasible and economically attractive. To improve the coefficient of performance ( COP ) of ejector refrigeration cycle (ERC), a novel ejector heat pump integrated with organic Rankine cycle combined cooling, heating and power system (ORC-CCHP) using zeotropic mixtures is established in this study. The comprehensive thermal efficiency is proposed considering exergy efficiency and heat recovery efficiency simultaneously. Results show that the entrainment ratio can be determined with the objective of exergy efficiency, while generator temperature and mass fraction of zeotropic mixture are optimized with the comprehensive thermal efficiency. With the optimized entrainment ratio of 0.2 and generator temperature of 351.15 K, R141b/R134a (55%/45%) achieves the power efficiency of 4.21%, refrigeration efficiency of 14.6% and COP of 1.12, which are considerably higher than those of pure R141b or R134a. Meanwhile, R141b/R134a with optimum mass fractions in ORC and heat pump loop can generate plentiful refrigeration capacity, great temperature glides in the high-temperature evaporator and high-temperature condenser. The comparative analysis of basic ORCs, ORC with post ejector, ORC with ejector heat pump, ORC combined with ejector (EORC) is carried out. The ejector heat pump integrated with ORC-CCHP system is thermodynamically feasible and economically attractive, thanks to optimized system parameters and optimum compositions of zeotropic mixture, giving support of new applications of ERC coupled with positive and reverse Carnot cycles.

Analysis of Aqueous Lithium Bromide Absorption Refrigeration Systems

Abstract Aqueous lithium bromide absorption refrigeration systems have been studied in recent years and their advantages such as environmental safety and utilization of low-grade energy have been proved. Research on improving their performance has been increasing lately. In this paper, single effect and parallel flow double-effect aqueous lithium bromide absorption refrigeration systems have been studied. Mass, energy, entropy, and exergy balances have been used to model the absorption refrigeration systems. Parametric studies have been done to investigate the effects of cooling load, evaporator exit temperature, condenser exit temperature, generator vapor exit temperature, absorber exit temperature, and solution energy exchanger effectiveness on the performance of the system. The analyses show the coefficient of performance, and exergetic efficiency of double-effect absorption refrigeration is higher than those of single-effect refrigeration. The effect of other parameters on the performance of both single- and double-effect systems has been described in detail in this article.

Experimental and numerical study of a PV/T direct-driven refrigeration/heating system

A photovoltaic/thermal (PV/T) direct-driven refrigeration/heating system was proposed in this paper. This system had the functions of off-grid refrigeration and hot water supply without using batteries. The solar refrigeration efficiency could also be improved by means of PV cell cooling in PV/T modules and compressor speed controlling. In this paper, performance of this system was investigated by experiments and numerical simulations. The influences of the total capacity of PV cells and water temperature in the ice storage tank were also studied. When the number of PV cells increased, the daily cooling capacity per cell increased first, then decreased. This revealed that the capacities of the compressor and PV cells should be designed to improve the PV utilization efficiency. Total cooling capacity of the system increased with the increase of initial water temperature in the ice storage tank. This revealed that high initial water temperature was benefit for system cooling capacity.

Thermal Analysis of Paraffin-Embedded Tissue Blocks for Anatomic Pathology Processes.

We analyze temperature dynamics in anatomic pathology samples to identify the most efficient refrigeration method and to predict the time available for optimal sectioning before sample heating, thus getting appropriate information for a correct diagnosis by anatomopathologists. A thermal finite element (FE) analysis was carried out with comsolmultiphysics to evaluate temperature variations in paraffin-embedded tissues, i.e., muscle, bone and fat, and the corresponding thermal stresses. Experiments with different tissues and thermocouple-based measurements allowed validating the FE simulations. Simulations allowed to estimate the time needed to bring the sample at the optimal temperature for sectioning (-8 to -4 °C) in different conditions: refrigeration on a cold plate, refrigeration in a cooled environment, and refrigeration in an environment with forced convection. Among the three cooling methods tested, the forced convection at -20 °C and with an air-flow speed of 5 m/s resulted in the shortest cooling time. As compared to the other methods, thermal stresses can be modulated by varying the air-flow speed. For the different conditions, the time needed for the surface of the tissue block to exit from a temperature corresponding to an optimal cutting, when leaving the sample exposed to room temperature after refrigeration, ranged from 12 to 310 s. We quantify the time needed to adequately refrigerate paraffin-embedded tissue samples and the time available before they leave the optimal temperature window for sectioning. We also evaluate the maximum stress attained in the paraffin block during the cooling and the heating transients. This information will help optimize anatomic pathology processes.

Giant low-field actuated caloric effects in a textured Ni43Mn47Sn10 alloy

In this work, based on composition adjusting and texture control, we demonstrate giant elastocaloric and magnetocaloric effects in a directionally solidified Ni43Mn47Sn10 polycrystalline with strong <001>A texture. On removing a low compressive stress of 210 MPa, giant adiabatic temperature change up to −17.3 K is achieved. Such value is much higher than those in some elastocaloric materials reported previously. Besides, giant magnetic field induced entropy changes of 23.5 Jkg−1K−1 and 37.1 Jkg−1K−1 are also obtained under the magnetic field changes of 2 T and 5 T, respectively. Simultaneously achieving giant elastocaloric and magnetocaloric effects actuated by relatively low external field is of great importance to explore multi-caloric or coupled caloric effects in developing efficient and eco-friendly solid-state refrigeration technology.

Performance optimization and comparison towards compact and efficient absorption refrigeration system with conventional and emerging absorbers/desorbers

Absorption refrigeration system (ARS) is significant for renewable/waste energy utilization to mitigate global warming. To select the best-performing ARS, four systems, namely falling-film horizontal tube ARS, falling-film vertical tube ARS, plate heat exchanger ARS, and microchannel membrane-based ARS, are compared systematically. System models have been established with validated accuracies to evaluate the coefficient of performance (COP) and volumetric cooling effect (qv). The results show that under a design driving power of 0.5 kW, the COP increases with the tube outer diameter/length in falling-film ARS and channel width in plate heat exchanger ARS and microchannel membrane-based ARS. qv decreases with tube outer diameter/length in falling-film ARS and channel width/height in plate heat exchanger ARS and microchannel membrane-based ARS. With geometry optimization, microchannel membrane-based ARS provides the highest COP of 0.855 with qv = 385 kW/m3, followed by plate heat exchanger ARS of 0.846, falling-film horizontal tube ARS of 0.832, and falling-film vertical tube ARS of 0.801. Meanwhile, microchannel membrane-based ARS also produces the maximum qv of 1147 kW/m3 with COP = 0.840, followed by plate heat exchanger ARS of 714 kW/m3, falling-film horizontal tube ARS of 391 kW/m3, and falling-film vertical tube ARS of 197 kW/m3. Thus, microchannel membrane-based ARS is advantageous in both efficiency and compactness among four ARSs. This work aims to facilitate absorbers/desorbers structure design towards compact and efficient ARS.

A novel cryogenic condensation system based on heat-driven refrigerator without power input for volatile organic compounds recovery

Volatile organic compounds (VOCs) are important precursors of pollutants such as PM2.5 and ozone, and the development of their treatment technologies is of great significance to environmental protection and economic development. The current VOCs destruction technology, such as the combustion method, has low operating costs, but there is a large waste in the treatment of high-value gas; while the current VOCs recovery technology, such as the condensation method based on refrigerator cooling, can recover high-value gas, but it still has some unsatisfactory aspects in terms of emission concentration, refrigerant use, and power supply. In this paper, a novel cryogenic condensation system based on a heat-driven refrigerator without power input for oil gas VOCs recovery was proposed. The heat obtained by burning part of the oil gas VOCs is employed to drive a thermoacoustic refrigerator using helium as working gas to realize the recovery of the remaining oil gas VOCs, which has the advantages of not relying on external power supply, using natural working fluid, and zero-emission of oil gas. A thermodynamic calculation model was established to quantitatively calculate the recovery efficiency. The results show that the remaining 91.0% of the oil gas VOCs can be recovered by burning 9.0% of the oil gas VOCs when the refrigeration temperature is 200 K, the heat source temperature is 873 K and the concentration is 33.5% at 100 kPa. And compared with the method of burning part of the liquefied VOCs, the method of burning part of inlet gaseous VOCs to drive the refrigerator has a higher recovery efficiency (around 10%). The effects of the refrigeration temperature, the heat source temperature, VOCs concentration, VOCs inlet pressure, and refrigerator efficiency on the system were also analyzed.

Performance of Commercially Open Refrigerated Showcases with and without Ice Storage—A Case Study

This study examines the applicability of the ice storage systems in the small commercial refrigerated showcases through experimental analysis. R-404A is used as the working fluid and various influence of parameter settings and improvements, are discussed in details. In the ice storage system, the condenser is changed from air-cooling (refrigeration mode) to an immersion type that is placed in an ice storage tank, the corresponding condensing temperature and pressure are reduced appreciably. This increased the efficiency and can effectively reduce the peak power consumption. The reduction of the condensing temperature and pressure increased the coefficient of performance (COP) from 3.6 (refrigeration mode) to 6.35 (melting mode), effectively enhancing the refrigeration efficiency. The results indicated that the ice storage system could effectively increase the coefficient of performance from 3.6 to 6.35 during ice melting when compared to the conventional refrigeration system. It also can shift approximately 35% of the power during peak hours and lower the energy cost by USD$ 17.13 per month.

Integrated Design of Working Fluid Mixtures and Absorption Refrigeration Cycles

This work presents a CAMD (computer-aided molecular design) approach for the design of working fluid mixtures used in ABR (absorption refrigeration) cycles. Compared to previous works, the proposed approach introduces two major improvements. It employs for the first time an ABR process model in the course of CAMD, hence enabling the evaluation of the generated mixtures considering process performance indicators. It enables for the first time the simultaneous generation and evaluation of molecular structures for both refrigerants and absorbents. The employed model and CAMD optimization problem formulation incorporates major ABR operational driving forces pertaining to efficient refrigeration, sufficient solubility of mixture components and ease of separation in the generator. The approach employs a multicriteria assessment methodology both during CAMD and for the evaluation of selected mixtures using a more rigorous ABR model at a second stage. The work identifies novel mixtures, with Acetaldehyde/2-Methoxyethyl acetate and Acetaldehyde/Methanediol exhibiting the highest performance. The latter exhibits 3% higher COP (coefficient of performance) and cooling output than the reference mixture NH3/H2O, whereas it operates at 87 and 89% lower high and low cycle pressures. The novel mixtures are also compared with novel mixtures previously identified through a heuristic approach by the authors. The latter mixtures indicate overall higher ABR performance but similar or worse performance in safety, health and environmental impact indices. Further performance improvements may be achieved by including into CAMD additional chemical groups to be able to simulate the complex absorbent structures available in published works.