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The temperature rapid rise phenomenon often happens in the side-by-side frost-free refrigerators during the damper-off cycle, which leads to a decrease in damper-off duration and an increase in energy consumption. A three-dimensional transient model of natural convection during the damper-off cycle is established and experimentally validated to analyze the refrigerating compartment (RC) temperature rapid rise phenomenon. The results show that the violent natural convection airflow driven by the non-uniform temperature distribution will lead to the significant variation of RC temperature. The hot air rises from bottom into top layer along the three passages, which include the front gap (FG) between shelves and door boxes, the side gap (SG) between the right-side wall and door boxes and the rear gap (RG) between shelves and the rear wall. The air enthalpy along FG into the first layer is the dominant factor of the temperature rapid rise, accounting for almost 64.4% of the total inflow air enthalpy. The net air enthalpy flow along FG is larger than other passages in the first 15s and decreases rapidly as the temperature distribution becomes uniform.

Helical condenser coiled tube is widely used in refrigeration machines for water heating due to its higher heat transfer, compact structure, high energy efficiency, ease of manufacture and arrangement. In addition, developing and optimizing the helical condenser coil designs are considered a sustainable solution for improving the performance of the system. Based on this vision, a particular difference of this study with other studies performed on similar researches is the influence of different shapes of condenser coil designs on heat transfer and temperature distribution during heating process. Therefore, the main objective of this paper is to improve the thermal performance of a helical coil by modifying the coil shape. Based on the results, the average heat transfer coefficient and average COP of variable pitch coil were increased by 36.48% and 16.17%, respectively, compared with normal coil. Moreover, the obtained results indicated that the water temperature, the water velocity, the heat transfer and the performance of the helical condenser with variable pitch coil were improved in comparison with that of normal coil. However, this investigation could provide some guidance to obtain the optimum coil structure of refrigeration machines for domestic hot water production.

Solid-state refrigeration technology has become a promising candidate to replace the traditional low-efficiency and environment-harmful vapor compression refrigeration. However, the narrow temperature region becomes a critical problem which hinders the practical applications of caloric materials to a refrigerator. Here, we report a potential way to solve this problem by combining different caloric effects in one refrigerant. A multiferroic ferromagnetic shape memory alloy Ni45Co5Mn37In13 can exhibit large inverse magnetocaloric effect and elastocaloric effect in adjacent working temperature regions. Thus a broad refrigeration temperature span can be realized in Ni45Co5Mn37In13 alloy by applying magnetic field or external stress at different temperature. Moreover, we propose a potential equipment schematic drawing to achieve it. The system can facilitate the multiferroic materials to produce useful cooling at a much larger temperature range. This combined caloric effect and the concept system proposed in this study would inspire researchers working in this field.

The typical domestic refrigerator employs a blind and periodic defrost strategy that leads to the clogging of the evaporator between the consecutive defrost cycles. The clogging of the evaporator causes a loss in performance which can be minimized using the demand defrost technique. The demand defrost systems proposed in the literature rely on the detection of frost as the defrost triggering criterion, rather than the real-time quantification of the thickness of frost. The initial frost layer improves the performance and therefore, the thickness of frost must be taken into consideration. Frost becomes detrimental only after it crosses a critical threshold. Defrosting the system at lower thicknesses may lead to frequent defrosting cycles which in turn increases the defrost energy. Therefore, the defrost triggering criterion must be selected tactfully to utilize the benefit of the initial frost layer along with the minimization of the defrost energy. In this article, a novel real-time thickness of the frost-based demand defrost technique is presented for a domestic refrigerator. A hybrid system comprised of a frost detection and defrosting modules is employed to quantify the thickness of frost in real-time and to defrost the evaporator using a 12 W heater. The effect of the thickness of the frost-based defrost threshold on the energy consumption of the refrigerator is evaluated. The defrost threshold of 6 mm yields the maximum energy conservation of 10% as compared to the default blind and periodic defrost strategy of the test refrigerator.

A few researchers recently reported the presence of vapor bubbles of R600a at the inlet of the capillary tube of refrigerators under subcooled conditions. However, the effect of a non-equilibrium two-phase state on the refrigerant mass flow rate has not yet been addressed. The aim of this study was firstly to investigate the effects of ambient temperature and R600a charge amount on the refrigerant state at the inlet of the capillary tubes and, secondly, to examine the ability of empirical correlations for prediction of the refrigerant mass flow rate under a non-equilibrium two-phase state. A transparent tube was installed at the inlet of the capillary tubes of a parallel two-circuit cycle refrigerator-freezer for visualization of the refrigerant flow. The visualization results demonstrated the presence of a non-equilibrium state under subcooled conditions. The experimental mass flow rates were compared with predictions by empirical correlations of Rasti et al. and Wolf and Pate. Both correlations predicted the mass flow rate with a large deviation under a non-equilibrium state and acceptable deviation under a fully liquid state. Results showed that the mass flow rate under a non-equilibrium two-phase state significantly decreased compared to the fully liquid condition. Finally, a new empirical parameter was introduced to consider the non-equilibrium two-phase flow. The new parameter was applied to previous empirical correlations and the modified version of Rasti et al.’s correlation showed good agreement with the experimental data under a non-equilibrium two-phase state.

Thermoelectric refrigerating systems (TER) are environment-friendly technologies. They have several advantages such as low maintenance costs, are less cumbersome and long lifetime. However, these systems have low coefficient of performance and are limited in achieving low temperature levels. This study investigates a new configuration of TE refrigerator employing a novel arrangement of heat sinks with integrated flat and finned heat pipes. A mathematical model is firstly developed to predict transient temperatures and cooling limit time. An experimental characterization is then performed and it includes optimization of energy consumption, cooling time, temperature levels and TE refrigerator related COP. TE module coefficient of performance (COPTEC) is evaluated at 0.74 while the hot and cold sides temperature difference ΔT is equal to 32.7 °C. The coefficient of performance of the TE refrigerator (COPTER) is evaluated at 0.297 with an inside/outside temperature difference ΔTi/o = 13 °C and an energy consumption rate of 42.7 Wh. Multiple experiment's results lead to a specific characterized chart adapted for this TE refrigerator. An empirical equation for transient temperature prediction is established and presents a novel contribution in this work.

Nowadays, research has been focused on refrigerants from Hydrofluorocarbons (HFCs), which are not harmful to the ozone layer. Because of replacing refrigerants from chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs). HFCs are used in many applications, including refrigerants, aerosols, solvents, and blowing agents for insulating foams. However, some HFCs have relatively high global warming potential (GWP) and are subject to further examination due to growing concerns about global climate change. The present work’s main objective is to select eco-friendly refrigerants from AC5, R430A and R440A, combining two or more refrigerants from HC, HFC and HFO groups as a direct substitute HFC-134a in a household refrigerator. The performance of the domestic refrigerator with liquid suction heat exchanger (LSHX) was compared in terms of compressor discharge temperature, coefficient of performance (COP), volumetric cooling capacity (VCC), and power consumption of a compressor. It was found that the average COP of R440A and R430A was higher by approximately 2.5% and 1.47% than HFC-134a. However, the COP of AC5 was 6.1% lower than that of HFC-134a. The VCC of R430A is almost equal to HFC-134a. The results also show that AC5, R440A and R430A consume less power than HFC-134a. The compressor outlet temperature with R440A, AC5 provide higher values than HFC-134a, which affects the compressor life. The best overall performance was achieved with the refrigerant R430A in the household refrigerator and suggested an alternative to HFC134a, which also has a very low GWP from the environmental safety perspective.

This work is aimed at investigating the effects of the refrigerant charge, expansion device restriction, compressor speed, and their interactions on the performance of a household refrigerator. To this end, a micrometric valve was installed in series with the capillary tube of a frost-free refrigerator to vary the expansion restriction within a range equivalent to capillary tubes with inner diameters spanning from 0.55 to 0.85 mm. The refrigerant charge was manually changed from 35 to 65 g whereas the compressor speed was adjusted between 2500 and 4500 rpm. In total, 294 steady-state energy consumption tests were conducted, being 147 at a surrounding temperature of 32 °C, and the rest at 16 °C. It was noticed that low energy consumptions can be achieved for several combination of refrigerant charge and expansion restriction, albeit the minimal energy consumption figures were always achieved for the highest charges and restrictions. It was also verified that the refrigerator operates in a sub-optimum region so that increasing the charge from 42 g to 52 g while decreasing the capillary tube diameter from 0.64 mm to 0.60 mm led to a 3% decrease on the energy consumption. It was also found that a single combination of refrigerant charge and equivalent diameter provided satisfactory performance levels regardless of the compressor speed. Finally, a method to reduce the number of tests was proposed, in such a way that only 9 datapoints are required to generate a full energy consumption map for a given compressor speed and surrounding temperature.

A key issue in the optimal designing of a Stirling machine is to develop a precise thermodynamic numerical model that could predict the performances and provide means for further optimization. In this paper, a non-ideal second-order numerical model called modified simple analysis model has been presented for the Stirling cycle refrigerating machine. The model incorporates effects of shuttle heat loss to the expansion space and mass leakage to the crankcase in the differential equations of pressure change, rate of change of mass of gas in compression and expansion spaces, and mass flow rates across these working spaces. The model was simulated using MATLAB code for Beta configuration FEMTO 60 Stirling engine operating as a refrigerator and validated with an experiment. The validation of the numerical model with experimental work showed that the results of the simulation are consistent with the results of the experiment. Hence, the numerical model could be used to design a Stirling cycle refrigerating machine for moderate temperature applications with reasonable accuracy especially if optimization is performed further. The effects of incorporating shuttle heat loss in the differential equations on the temperature of working gas and the overall performance of the Stirling refrigerator have been analyzed. Lastly, parametric investigations have also been performed to evaluate the effect of operating parameters (temperature, pressure, and frequency) on the performances of the refrigerating machine. Better performance could be achieved at relatively lower frequency or higher pressure.

The infiltration of warm and humid air from the outside into a freezer results in frost accumulation around the evaporator in household refrigerators. This can significantly reduce the cooling capacity of refrigerators. In this study, the pressure, temperature, and frost around a proposed drain tube were monitored through in-situ measurements until the first defrost process (about 54 h). The proposed drain tube has 220 times higher hydraulic resistance and shows 55 times lower inflow in computational fluid dynamics (CFD) analysis. Once the door of the freezer compartment is opened and closed, external warm air replaces the cold air in the freezer. Negative pressure is produced by the shrinkage of this external air under low-temperature conditions. The other role of the drain tube is to vent air between the outside and inside of the refrigerator under negative pressure. To release the negative pressure, the proposed drain tube has a movable shutter. In the CFD results, the secondary inlet increases the inflow by 3.2 times compared to the inflow in an I-type tube. To determine the design, the weight and inner diameter of the drain tube were changed. The performance of the proposed tube was validated by the lack of blockage of discharge until the first defrost process. The movable shutter did not allow the negative pressure to exceed -100 Pa by facilitating air venting after opening the door for 10 seconds and then closing it.

Single and multi-stage Joule-Thompson refrigerators operating with natural nitrogen-hydrocarbon mixtures are marketable for creating refrigeration equipment for freezing and cryopreservation of biomedical materials, liquefaction of certain gases, high-temperature superconductors cooling, conducting climate tests without using cryogenic liquids. One of the main objectives of the development of such refrigerators is to determine the optimal weight of mixed-refrigerant charge with the known geometry of the refrigeration circuit and to ensure the optimal “circulating” composition in the steady-state mode. This article proposes an analytical method for solving this problem and presents the experimental results. The accuracy of the method is determined by the validity of calculating thermodynamic properties of the mixed refrigerants forming solutions with limited solubility in the liquid phase and by taking into account the shift of the “circulating” working body composition relative to the “charge” composition in the steady-state mode due to structural specifics of real refrigerators. The application of the method will allow reducing the time and cost of experimental development of new refrigeration equipment.

In this study, an experimental determination of the refrigerant charge and the operating conditions in a vertical display refrigerator using R134a, R513A, and R1234yf is presented. The three refrigerants' energy inputs under ambient temperatures of 24, 32, and 40°C are compared. The refrigerator is instrumented with a mass flow meter, thermocouples, and pressure transducers. The evaluations are carried out inside a room with controlled temperature and air recirculation. For each analysis, the refrigerator is operated for a period long enough until differences among operation on/off cycles are negligible. Batch loads of 15 g are used for determining an adequate refrigerant charge. The results show a recommended charge of 175g for the three refrigerants and the range of temperatures. The electric energy consumption increase on average 20 kJ per hour of operation for every degree the ambient temperature increases. Compared with R134a, the R513A results in lower energy input in 3.8, 3.9, and 0.3% for 24 and 32 and 40°C, respectively. The experimental determination of EER values does not give accurate guidance for the adequate refrigerant charge. The assumption of isobaric heat exchange results in a maximum deviation of the actual cooling duty of 13, 18.7, and 16.6% for R134a, R1234yf, and R513A, respectively.

This work provides an analysis of the thermal flow and behavior of the (load-free) refrigerator compartment. The main goal was to compare the thermal behavior inside the refrigerator cavity to the freezer door (home refrigerator) effect and install a fan on the freezer door while neglecting the heat transmitted by thermal radiation. Moreover, the velocity distribution, temperature, and velocity path lines are theoretically studied. This was observed without affecting the shelves inside the cabinet and the egg and butter places on the refrigerator door as they were removed and the aluminum door replaced with a glass door. This study aims to expand our knowledge about the temperature and flow fields of this refrigerator model. Finally, the development of this work highlights the importance of numerical simulation in the search for improvements in the design of this refrigerator model, which may assist refrigerator manufacturers.

Vegetables lose quality after harvest mainly due to water-related weight loss. In households, vegetables are usually stored in refrigerators, typically providing temperatures from 0 – 14°C and relative humidity ranges from 20 – 100 %. Weight loss is related to the storage humidity conditions. As a consequence, storage systems providing humidity-controlled conditions are decisive for the evaluation of the freshness performance of refrigerators. To evaluate the impact of storage zones on the fresh weight loss of stored goods, the international standard IEC 63169:2020 “Electrical household and similar cooling and freezing appliances – Food preservation” has been released. It uses a cellulose based food simulant, overcoming influences of cultivar and post-harvest handling conditions of real vegetables. This publication compares the weight loss of spinach and the food simulant in chilled storage conditions at three ranges of relative humidity. Different cultivars and pre-handling modifications of the spinach were used to determine the impact of product parameters on weight loss. A round robin test was performed to analyse the applicability of the IEC 63169:2020. The results prove the applicability of the standard to analyse the impact of humidity controlled storage on weight loss: It is shown that pre-handling has an impact on spinach's weight loss, which is overcome by the food simulant. For all tested conditions, the weight loss behaviour from spinach and the food simulant is correlating in test durations up to 72 h. The round robin test shows that the test method of IEC 63169:2020 provides repeatable and reproducible results.

This study aims to find the effect of variations in the capillary tube winding on the suction line on achieving optimal temperature and room cooling rate. This study uses three variations: the capillary tube without being wrapped around the suction line, the capillary tube wrapped in half on the suction line, and the capillary tube fully wound on the suction line. Specifically, the purpose of this study was to determine the effect of variations in the capillary tube wrapped around the suction line, which led to efforts to maintain the performance of the refrigerator trainer prototype. The method used in this study uses an experimental method where the data collection process is carried out through observation and documentation. The data analysis technique used in this study uses quantitative descriptive research techniques where the research data will be tabulated and displayed in the form of tables and graphs, and data analysis is carried out to find out how much influence the achievement of the optimal room temperature and the cooling rate of the prototype trainer refrigerator room itself. From the research that has been carried out, it is obtained that the highest optimal room temperature achievement occurs in the variation of the capillary tube fully wound on the suction line, where there is an increase in the optimal room temperature achievement of 16.17% when compared to the room cooling rate using standard variations or without being wrapped. And the result in the form of the highest room cooling rate is the variation of the capillary pipe fully wound on the suction line.

The Kyoto protocol emphasized the need of replacement of HFC refrigerant due to their high GWP values that causes pollution in the environment. So in this paper the refrigerants R1234yf, R152a and HFOs/HFCs mixtures of R134a/R152a/R1234yf such as ARM42 (in the ratio of 8.5/14 /77.5 by mass), ARM42a (in the ratio of 7/11/82 by mass) with a view of replacement of the refrigerant HFC-134a in a domestic refrigerator were analyzed theoretically. Volumetric cooling capacity, compressor discharge temperature, coefficient of performance, compressor energy consumption and refrigeration capacity are the main parameters to estimate the performance of the refrigerator. The results are revealed that HFC-152a had gave a superior performance as compared to HFC-134a in terms of COP and equal cooling and volumetric cooling capacities. However, the refrigerant HFC-152a was flammable and runs with high compressor outlet temperature which may restrict its usage. The HFO refrigerant R1234yf showed an almost equal volumetric cooling capacity, compressor energy consumption, refrigerating effect and COP when compared with HFC-134a. Among the refrigerants ARM42 and ARM42a, the refrigerant ARM42a was selected as a good alternative for HFC-134a because the Volumetric cooling capacity and COP of ARM42a were almost equal to HFC-134a. Therefore ARM42a had better choice of direct substitute to HFC-134a in a domestic refrigerator when the corresponding safety requirements are adopted. So on overall comparison of every property of refrigerants we can conclude that R1234yf can be treated as best alternative to HFC-134a in a domestic refrigerator.

Cool storage has been considering an efficient and cost-effective means to enhance the behavior of a refrigerator. However, its drawback in temperature control of the refrigerator compartment has not received enough attention. The controllable two-phase loop thermosyphon has the prospect of solving this problem. In this study, a novel cool-storage refrigerator integrated with a controllable two-phase loop thermosyphon is built to investigate its precise temperature control capacity. The phase change material is optimized by the orthogonal experiment method. The controllable two-phase loop thermosyphon presents the optimal cooling performance for the fresh food compartment when the filling ratio is 27.0%. As the average temperature of the fresh food compartment increases, the one on–off cycle of the controllable two-phase loop thermosyphon maintains at 32.0 min, and the operation ratio varies from 86.3% to 13.6%. The temperature control accuracy can be improved from 2.1 °C to 0.6 °C and the overall time of one on-off cycle decreases from 49.8 min to 22.4 min. The operation ratio gradually increases from 7.2% to 38.6% as the ambient temperatures increase. The results demonstrate that the controllable two-phase loop thermosyphon is a feasible and effective way to improve the temperature control performance of the cool-storage refrigerator.

The present paper is focused on development of the thermodynamic model and a heat-driven Vuilleumier refrigerator. Thermodynamic properties and performance are predicted by thermodynamic model. On the other hand, a prototype Vuilleumier refrigerator with crank drive mechanism is built and the performance is measured. In the thermodynamic model, the refrigerator is divided into five working spaces for analysis, including hot chamber, hot regeneration chamber, middle chamber, cold regeneration chamber and cold chamber. Also, the influence of clearance leakage between middle chamber and buffer chamber is investigated. The effects of geometrical parameters, charged pressure, rotating speed, heating temperature, cooling temperature and heat loading on the cold head temperature are evaluated. In addition, the numerical results and the experimental data under different operating parameters are compared for model validation. As the Vuilleumier refrigerator operated at 22 bar pressure, 600 rpm rotating speed, 900 K heating temperature and 276 K cooling temperature, the cold head can reach a zero-load temperature of 221 K. When a 0.7 W heating load is applied on the cold head, cold head temperature of 252.6 K and coefficient of performance of 0.0068 can be obtained.

In this research, the performance of serial two-stage compression (STC) cycle and bypass two-stage compression (BTC) cycle on the household refrigerator-freezers is tested in the laboratory. Then, based on the results of the experiments, exergy, exergoeconomic analyses, and cycle optimization are carried out. Considering that replacing refrigerants in household refrigerator-freezers is one of the approaches to increase the performance and environmental impact of these systems, R436A refrigerant (46% Isobutene and 54% Propane mixture) is used and analyzed to replace previous refrigerants. Finally, the multi-objective optimization of the mentioned cycles is performed with both refrigerants. For analyses, two models of refrigerator-freezers with different cycles are used (STC cycle with R134a refrigerant and BTC cycle with R-600a refrigerant). In both models, two evaporators for refrigerator-freezer compartments are used. International standards (IEC 62552) are used to test refrigerator-freezers. MATLAB and REFPROP 9.1 software are used to model the systems. According to the results of the analyses, the STC cycle with R436A refrigerant has more total exergy destruction rate (0.727 kW) compared to R134a refrigerant. In the BTC cycle, in which the fresh food compartment (FFC) and freezer compartment (FZC) operate, the total exergy destruction rate with R-600a refrigerant (0.422 kW) is less than with R436A refrigerant. In the case of the BTC cycle in which only the FZC operates, the total exergy destruction rate with R-600a refrigerant (0.455 kW) is less than with R436A refrigerant. The most exergoeconomic factor among cycle equipment is related to the compressor (about 98%). The highest COP value between cycles is related to the STC cycle with R134a refrigerant.

In the present study, numerical analysis of coiled tube heat exchanger used in J-T refrigerator is carried out. A computer code is developed to estimate the length of the heat exchanger by giving mass flow rate, diameter of tube and shell as input parameters. This code is verified against experimental data. Two different configurations are considered in this study viz., heat exchanger with wire fin wound around the inner tube of heat exchanger and without wirefin. Three different refrigerant mixtures are used to evaluate the performance of heat exchangers. The variations of temperature and heat transfer coefficient are brought out as result. Significant reduction in the length of heat exchanger is observed in all the cases. Mixture-1 causes 33% reduction in length of heat exchanger with wirefin. Similarly, for mixture-2 and mixture-3 the length is reduced by 15% and 30%. Additionally, heat transfer coefficient (HTC) values are also estimated for heat exchanger with wirefin and without wirefin. Considerable increase in HTC values is observed in the heat exchanger with wirefin.

The article describes the implemented system of pneumatic lifting of the bell of the state primary standard gas volume and volume flow rate units. The system is composed of unified elements of industrial air preparation. There are elements for air purification in front of the compressor, dehumidifier, refrigerator dryer. With the use of a pneumatic system, the bell can be filled with prepared air with different values of excess pressure. The system is installed as a backup to the current to increase security. Pneumatic lifting of the bell allows you to connect a set of cylinders with pure inert gases or mixtures thereof to determine the impact on the gas meters metrological characteristics.

The frost-free refrigerator typically has three compartments, i.e. refrigerating, variable-temperature and freezing ones. The temperature and humidity (T&H) inside each compartment vary dramatically, leading to non-uniform T&H distribution in the overall return air. Therefore, frost maldistribution occurs on the evaporator and further induces airflow redistribution. In this article, the quasi-static 3–2–1–1 frosting model is built considering 3D evaporator, 2D T&H of frontal airflow, 1D frost growth and 1D non-uniform fin spacing. The model is verified by the experiment data in the open literature. Results show that frost mass is similar with non-uniform and uniform T&H distribution in frontal airflow, but frost distribution is much different. The evaporator capacity for non-uniform airflow is lower at the early stage of frosting process than that for uniform airflow, but higher later due to the airflow transverse redistribution when the airflow transfers transversally from higher to lower T&H areas owing to frost maldistribution. The transverse redistribution results in the air velocity increment and heat transfer compensation effect. Moreover, the fan stall for non-uniform airflow arises later and results in the larger airflow rate and evaporator capacity at later frosting process.

Stirling / pulse tube hybrid refrigerator (SPR) has attractive prospects due to its high reliability, high efficiency and compactness around 30 K. As the typical characteristics of the SPR, the inter-stage cooling capacity allocation characteristics allows the refrigerator to shift cooling capacity of both stages by adjusting the movement of the displacer, which enables the SPR to meet the demand of time-varying heat loads at different cooling temperatures and makes it a competitive choice in complicated space applications. In this paper, a SPR designed by our lab is adopted to study the typical characteristics. A one-dimensional thermoacoustics-based numerical model is adopted to optimize the structure parameters and the operating parameters. The cooling capacities, relative Carnot efficiencies at different displacer phases are given. The axial distributions of gas temperature and wall temperature in SPR are drawn. In addition, axial distributions of pressure amplitude, phase difference between volume flow and pressure wave and acoustic power are presented and compared. Experimental results operating at different mean pressures and frequencies are given. Compared the experimental results with the corresponding simulation results, a good consistency is revealed. The experimental results show that the SPR can obtain cooling capacities of 8.8 W at 80 K plus 0.81 W at 30 K with an input electric power of 245 W, which indicates an overall relative Carnot efficiency of 12.85%.

In this work, Computational Fluid Dynamics (CFD) analysis was conducted considering three different turbulence (viscous) models for a fresh food compartment of a domestic refrigerator (DR), in order to not only gain idea on cooling down time rate of fresh food compartment but also present air and temperature distribution inside the compartment when it is loaded. The refrigerator composes of three compartments: Fresh food (FFC), chill (CC) and freezer (FC). The FFC compartment is cooled by a thermoelectric/Peltier cooler (TEC) while the other compartments are handled by a vapour compression (VC) system. To measure cooling times, tests were conducted according to new IEC62552:2015 standard in climatic chambers and the cooling time was measured as 146.5 min. The predictions of developed CFD model clearly visualize the airflow and temperature fields inside the FFC. Concerning numerical predictions for the packages in the upper regions were in better agreement (below 10%) with measurements than the predictions for the packages in the lower regions mainly due to convective heat transfer behaviour. (C) 2020 The Author(s). Published by Elsevier Ltd.

Variable displacement compressor technology can achieve high steady-state efficiency, non-start/off operation thus high seasonal efficiency and capacity modulation. A comprehensive thermal-economic-environmental analysis of a household refrigerator with variable displacement compressor using three refrigerants (R134a, R152a and R1234yf) was presented using CoP and normalized CoP, set-up and running cost and Life Cycle Climate Performance, respectively. The results indicate that with the application of variable displacement technology, the compressor stroke can be tuned in response to heat load so that the power consumption is reduced thus the running cost and CO2 emissions. When the compressor stroke using R134a drops from 13 mm to 10 mm, the power consumption, total cost and life cycle CO2 emissions decrease by 86.3%, 56.7% and 59.9%, respectively. Running cost accounts for 89% of the total cost while indirect emissions accounts for 98% of the total CO2 emissions. Replacement of R134a by R152a will decrease the CoP by 10% but also reduce the cost and CO2 emissions by 5% and 8.6% respectively. This is comparable to increasing the R134a system CoP by 0.9. It is indicated that by adopting variable displacement technology, more CO2 emissions could be reduced given that part load represents over 80% of operating hours for refrigerators.

In this paper, a novel looped heat-driven thermoacoustic refrigerator with direct-coupling configuration is proposed to realize high coefficient of performance and high specific power for room temperature cooling. The novel system comprises three identical thermoacoustic engine-refrigerator units with direct coupling configuration, connected end-to-end by resonance tubes to form a closed loop. Detailed simulation and analysis about the internal operating mechanism is presented firstly. The theoretical results indicate the optimum entrance acoustic phase between pressure and velocity waves for the thermoacoustic engine and the thermoacoustic refrigerator operating in room temperature range are lagging and leading, respectively. In addition, the optimum heating temperature is 300 °C for the direct-coupling looped heat-driven thermoacoustic refrigerator with a cooling temperature of 10 °C and an ambient temperature of 50 °C. Upon extensive calculations and analysis, an experimental setup was designed and built for achieving 3–5 kW, which is aiming at for a waste heat driven air-conditioning application of heavy trucks. The experimental system can be thermally self-excited operation with a resonance frequency of about 56 Hz and an onset temperature of about 80 °C. The total cooling capacity of 4.0 kW with a coefficient of performance of 0.28 is obtained under the heating temperature of 300 °C and the cooling temperature of 10 °C. Compared with previously reported heat-driven thermoacoustic refrigerators, this work exhibits a substantial improvement in cooling efficiency and cooling capacity, showing good prospects for medium-temperature heat-driven refrigeration applications.

In this study, a method to evaluate the environmental effects of household refrigerators is newly developed in terms of life cycle climate performance (LCCP). The energy consumption model of the refrigerator is developed with three types of typical single evaporator refrigerators. The operation ratio of the evaporators, which is critical for calculating the energy consumption of dual evaporator refrigerators, is determined using experimental results of serial, bypass, and parallel-circuit cycle refrigerators. The LCCP results show that the system performance and equipment manufacturing emissions are dominant factors in lifetime CO2 emissions. Therefore, energy- and material-related factors, such as refrigerator cycle options, refrigerator material, insulation, and power sources, are primarily investigated. For cycle options, CO2 emissions can be reduced by 14.7% using a two-stage cycle. For condenser materials, CO2 emissions can be reduced by 2% to 2.5% using aluminum instead of steel. For insulation, the total emissions can be reduced by up to 7.7% by applying vacuum insulation panels on each side of the refrigerator. When 20% renewable energy is supplied, the total emissions are expected to be reduced by 13% in the baseline, 19.9% in the parallel-circuit cycle, and 26% in the two-stage cycle.

Improving the performance of the household refrigerator plays a major role in the rate of electricity consumption which involves mostly the efficiency of the compressor refrigerators, the thermal load, the ambient temperature and the refrigerant used. The aim of this work is to increase the efficiency of the household refrigerator by attaching phase change materials (PCM) at different locations such as at freezer, fridge and condenser. The PCM used in this analysis is commercial (OM32, OM29, OM03 and HS3N). The PCM is used in the form of slab in both the freezer and fridge section. In condenser, the PCM is arranged in a descending order of their melting temperature in the direction of flow of refrigerant in the form of packets surrounded by aluminum foil. The refrigerator is tested with no PCM, with PCM in freezer and fridge compartment, with PCM in condenser and with PCM in freezer, fridge and condenser. The test results showed that the efficiency of the refrigerator with PCM at all three locations is improved i.e. freezer, fridge and condenser.

The air forced convection is utilized to cool foods in frost-free refrigerator, and it offers uniform temperature field and the fast cooling rate. But the air forced convection also accelerates the water evaporation from foods surface, which leads to foods dehydration. Numerical model of water evaporation process inside refrigerating compartment was validated by experimental results including the evaporated water mass, air temperature and relative humidity during compressor on /off cycle. The air supply modes have effects on velocity and temperature fields inside refrigerating compartment, and three air supply modes were compared: annularly blowing air (ABA) supply, upward blowing air (UBA) supply and forward blowing air (FBA) supply modes. The results show that the water evaporation rate during compressor-on cycle is 20 times of that during compressor-off cycle. The effect of air velocity on water evaporation process is greater than that of vapor partial pressure difference. The water evaporation rate for FBA supply mode is the largest due to its highest air velocity. The water evaporation rate of ABA supply mode is the least because of both its smaller air velocity and vapor partial pressure difference, and it is the best mode to decrease water loss.

As a new type of refrigeration technology, the traveling-wave thermoacoustic refrigerator offers advantages that include high efficiency, reliability and environmental friendliness. To date, because of problems such as low power utilization and high power recovery losses, traveling-wave thermoacoustic refrigerators for use in room temperature applications have not been widely studied. In this paper, following an investigation of the traditional single-stage traveling-wave thermoacoustic refrigerator, a multi-stage traveling-wave thermoacoustic refrigerator is proposed and the working mechanism of this refrigerator is studied numerically using SAGE software. The calculation results show that the proposed multi-stage traveling-wave thermoacoustic refrigerator can enhance the utilization of the input acoustic work effectively, thereby improving the cooling power of the refrigerator with high cooling efficiency. As a result, the cooling power increases from 2.17 kW for a single-stage refrigerator to 6.42 kW for a seven-stage refrigerator, while the acoustic work utilization rate increases from 0.26 to 0.82, and the coefficient of performance changes from 2.60 to 3.19. The calculation results also indicate that three to five stages may be most suitable for the multi-stage traveling-wave thermoacoustic refrigerator when working within the temperature range of interest here by striking a balance between cooling efficiency and cooling power.

A mathematical model is proposed for predicting the air-side pressure drop and heat-transfer rate of straight fin-tube heat exchangers of a household refrigerator under nofrosting conditions. The six-sigma method is employed to optimize the preliminary critical-to-quality (CTQ). The proposed model is consistent with the experimental data with an error of less than 15 %. The numerical results agree well with the experimental data. It can be applied to evaluate the thermal-hydraulic performance of a fin-tube heat exchanger with varying fin pitch along the airflow direction.

The influence of latent heat storage elements on the cooling performance and the temperature rise time of household refrigerating appliances is studied experimentally in the context of the “new global refrigerator standard” IEC 62552:2015 (IEC 62552:2015, 2015). In addition to the daily energy consumption, this international standardization introduced performance tests for cooling capacity and temperature rise time. While the cooling capacity has long been anchored in various test procedures of consumer organizations, the temperature rise time, which has only been tested on freezers so far, will be a decisive factor in the future. Moreover, the need for so-called "smart appliances" that may balance power consumption compensate the volatility of renewable energies and thus stabilize the power grid is increasing. Against this background, eight commercial household refrigerators and refrigerator-freezers are equipped with polymer-bound phase change materials (PCM) and their performance is determined under the new standard test conditions. The results show that the introduction of PCM increases the cooling capacity by up to 33 % and also increases the temperature rise time by up to 145 %, without affecting power consumption, as compared to the unmodified refrigeration appliances.

The aim of this work is at investigating the applicability of electronic expansion valves (EEVs) in domestic refrigerators. To this end, a valve with an orifice of 0.19 mm of hydraulic diameter was installed in a conventional refrigerator to correlate the flow restriction with the overall energy consumption spanning different operating conditions. Tests with the same refrigerator mounted with a capillary tube were also performed. Also, a mathematical model was devised to simulate the effect of the refrigerant charge and the expansion device restriction on the system performance. More than a thousand different conditions were simulated. The results revealed that zero superheating is not necessarily the best-case scenario in terms of energy consumption. In addition, it was noticed that the lowest energy consumptions were achieved for the highest refrigerant charges and expansion restrictions. Furthermore, it was observed that, when the surrounding temperature or the compressor speed were changed, the energy consumption could be reduced by varying the restriction of the expansion device. The system with the EEV, nonetheless, presented higher energy consumptions than the system with the capillary tube for most conditions, which was mostly related to the extra thermal load generated by the valve. Nevertheless, by increasing the internal heat exchanger length and mitigating the heat dissipated by the EEV, it was found that the system with the EEV consumed between 4 and 9% less energy than the system mounted with capillary tube under operating conditions different from that the capillary tube has been sized for.

Dehumidifier with Polymer electrolyte membrane (PEM) is suitable for high-accuracy, limited-space humidity control in refrigerators. This study experimentally investigated the performance of PEM-based dehumidifier under the temperature range of -10~10°C. Empirical equations of PEM water content at refrigerator temperatures were developed. Results showed that although the low-temperature performance of electrolytic dehumidifier is not as good as that of room temperature, the efficiency (~1.3 × 10−2 g·J−1·m−2) is still competitive to desiccant or electrochemical methods. The dehumidifier has a starting voltage, and the voltage is higher at lower air temperatures (i.e. 1.3V for 26.1°C and 2.3 V for -3.9°C). During dehumidification, the operating current first increases significantly and then drops as the applied voltage increases, leading to a first increase and then steady dehumidification rate. The peak of current occurs at a smaller voltage as the air temperature decreases, i.e. 1.8V for 0°C and 2.5V for 26°C. Furthermore, the dehumidification rate increases as the air temperature and flow rate increases, while the changing rate with operating conditions was lower at sub-zero temperatures. Dehumidification has little effect on the oxygen concentration or temperature increment of the supply air. Characterizations also indicated that there was no obvious physical change on the PEM surface after operating at low temperatures. However, there exists a starting temperature for the dehumidifier, i.e. -9.5°C for the 3V applied voltage, which is due to the possible icing and swelling problem within the membrane. This study provided a new method, and proved its feasibility for dehumidifying at refrigerator temperatures.

In the first part of this work an experimental apparatus was designed and constructed to map the energy consumption of a household refrigerator subjected to several combinations of refrigerant charge and expansion restriction. In the second part, the expansion restriction imposed by the pair metering valve-capillary tube was converted into an equivalent tube diameter applying two different procedures: dry nitrogen flow and mathematical modeling. An empirical correlation to estimate the energy consumption based on the capillary tube inner diameter and refrigerant charge was also developed and used during the minimization process. Different strategies were also explored in order to reduce the amount of experiments to a minimum. It was found that at least 14 data points, collected with three different refrigerant charges, are required to ensure the convergence of the energy consumption minimization process.

The Stirling cycle machines have many applications as prime mover and cooling purpose. A review is presented for the development of regenerative Stirling cycle machines in the refrigeration area. The Stirling cycle refrigerators of gas cycle machines, which are the counterparts of the Stirling engines. They can operate from low temperature to moderate temperature applications. The present paper describes an overview of the Stirling refrigerating machine and its associated researches carried out in this area.Initially, the review explains the general working principle, the configuration and the drive mechanisms as well as the research findings within the range from low-temperature cryocoolers to moderate temperature cooling applications. Furthermore, this review points out and discusses the various models and methods of optimization to improve the performance of the Stirling cycle refrigerator.

We propose a novel cooling and power cogeneration system based on duplex free-piston thermoacoustic-Stirling cycles and an oscillating linear alternator. In such a cogeneration system, a free-piston Stirling heat engine produces acoustic power via the thermoacoustic power cycle, and a free-piston Stirling refrigerator produces cooling power via the thermoacoustic refrigeration cycle; an oscillating linear alternator is used to couple the free-piston heat engine and refrigerator and simultaneously produces electricity. The configuration and operating principles of the cogeneration system are described along with the thermoacoustic energy transformations and transmission mechanisms. An experimental prototype system was designed, built and successfully operated for the first time. In the preliminary experiments, thermoacoustic oscillation startup typically occurred at heating temperatures around 50 to 60 °C, and a cooling power of about 230 W at -20 °C and an electrical power of more than 6 W were obtained at a heating temperature below 190 °C. The alternator-coupled system has potential applications in heat-driven cogeneration systems for low-grade waste heat recovery and solar energy utilization.

This paper presents an experimental research on configuration optimization of a frost-free refrigerator-freezer with the parallel circuit cycle based on the analysis of circuit switching characteristics. Through combination optimization of R-fan voltage, F-fan voltage, R-capillary tube flow capacity, refrigerant charge, structure of suction pipe, F-compressor speed and R-compressor speed, the system could save 9.27% energy consumption compared with the initial condition. The experimental results also showed that the larger the R-capillary tube flow capacity, the larger the flow rate of the RC, resulting in the quickly temperature drop in R-cabinet and slowly temperature drop in R-cabinet based on “R-cabinet temperature priority” control strategy. Additionally, the R-cabinet temperature drop rate decreased with the increase of ambient temperature but the F-cabinet temperature drop rate was almost unaffected by the ambient temperature.

The objective of this study is to investigate the effects of hot-wall condenser geometry on domestic refrigerator-freezers (RFs) in terms of refrigerant charge reduction. A transient simulation model for an R600a domestic RF is developed and validated to capture the dynamic performance at various operating conditions. The hot-wall condenser in the domestic RF is determined to store excess refrigerant charge. The effects of the hot-wall condenser geometry on the performance of the RF are analyzed according to the total refrigerant charge. The coefficient of performance (COP) decreases with decreasing hot-wall condenser length and diameter; however, the decrease in the COP of the RF is compensated by the decreased energy consumption. Based on the global minimum energy consumption, the optimum hot-wall condenser design is achieved when the tube length is reduced to 70% of its original size and the tube outer diameter is decreased to 3.75 mm. Furthermore, the total refrigerant charge in the RF corresponding to the optimized hot-wall condenser geometry is shown to be 14% lower compared to the rated charge amount.

Thermodynamic analysis of a volatile organic compounds (VOCs) condensation recovery system combined with mixed-refrigerant J-T (MRJT) refrigeration is illustrated in this paper, which provides an effective and economical choice for petroleum plants. VOCs is compressed, cooled by its recuperation process and separated in two simple rectification columns with 3–5 stages. The cooling powers for condensers at column top are provided by a high efficiency dual MRJT refrigerator at 100 K and 232 K, respectively. The cooling and separation characteristics of petroleum VOCs are also analyzed comprehensively. It is indicated that most of VOCs condensation load locates in high temperature region (≥ 235 K approximately). It might be feasible to cool VOCs from 235 K to 110 K by cold purified air through recuperation. For a typical petroleum VOCs, non-methane hydrocarbon residual of 56 mg Nm−3 is achieved with specific power consumption (SPC) of 0.1289 kWh Nm−3, free of additional purifying units. According to the analysis on the effects of variable VOCs composition and pressure, the cooing loads of top condensers are close related to the performance of VOCs recuperation. C1 and C2 are key components to enhance recuperation at low temperatures and reduce SPC. Exceed C3 could enlarge cold stage condenser load and SPC due degraded cold stage recuperation; while exceed C4-C6 could reduce condenser loads and SPC. Higher VOCs pressure could also decrease SPC.

This paper in refrigeration analyses the effects of internal and external irreversibilities on the steady-state of a double irreversible absorption refrigeration system powered by a waste wood boiler. At the optimal steady-state of the maximum coefficient of performance, expressions of relaxation times of a double irreversible absorption refrigerator are derived. The influence of internal irreversibility parameters, heat leakage coefficient and heat transfer coefficients on relaxation times are discussed. Phase portraits for the trajectories are presented. The results of our analysis show that the eigen-values of the generator-absorber assembly are real with opposite signs while those of the evaporator-condenser are real and both negative. From these results, it follows that internal and external irreversibilities parameters have a draconian effect on the steady-state of the generator-absorber assembly which leads to the disturbance of the absorption system and consequently to its instability. The result can provide some theoretical guidelines for the designs of real absorption refrigerators.

This article provides a detailed design and a CAD model of a new moving magnet linear compressor for the household refrigerator. A comprehensive electromechanical analytical model is provided to quantify the dynamic parameters necessary for the estimation of a compressor's performance. Additionally, the frequency response functions of the prototype at different input power conditions are investigated in order to evaluate the effect of excitation frequency on the dynamic parameters. The developed compressor is rigorously evaluated on a test-rig to validate all the presented analytical models. This article also provides a methodology to calculate the actuator's back-emf and motor constant which performs a vital role in the analytical model developed for any linear compressor. Furthermore, performance of the proposed compressor is evaluated with R600a to validate the pressure–volume curves and frequency response functions.

Compared with double inlet type two-stage pulse tube refrigerator, step displacer type has higher efficiency. The step displacer has two functions, input power distribution function and phase shifting function, which are fundamental issues of this type refrigerator. The two functions are discussed by an ideal model, and are investigated by a numerical simulation. Theoretically, the exergy flow ratio to the first stage over the second stage depends on the refrigeration temperature ratio and step ratio, the dead volume at the hot end of the pulse tube can be an additional parameter for adjusting the phase angle difference at the cold end of the regenerator.

The frost-free refrigerator typically uses a bottom-placed calrod heater to remove frost on evaporator surface. However, the mismatch between full coverage of frost and bottom-up heat transfer extends defrost duration, and warm air intrusion into freezing cabinets (FCs) during defrosting leads to increased FC-temperature rise and overall energy consumption. Therefore, comprehensive measures were applied in this article to enhance defrost performance of the frost-free refrigerator. A special fan cover was adopted which opened during cooling cycles to supply cold air into cabinets normally, but closed during defrosting to block warm air intrusion passage. Moreover, an extra heater (60 W) was inserted in the middle height of the evaporator besides the original bottom one (180 W) to form better frost-heat match. Results show the fan cover and dual heaters altogether reduced defrost duration by 4.5 min and FC-temperature rise by 2.7 °C. Lower FC-temperature after defrost further declined energy consumption for the subsequent recovery cycle, which compensated for its increase for the defrost cycle and dominated the 1.2% reduction in overall energy consumption of the refrigerator. Both measures proved effective in enhancing defrost performance. However, the middle heater may affect cooling cycle performance of the refrigerator, necessitating further investigation.