Comparison of R-290 and two HFC blends for walk-in refrigeration systems

To help provide a clear understanding of the relative performance potential of HFCs (R-404A and R-410A) as compared to R-290 for walk-in refrigeration systems representing direct expansion commercial refrigeration systems with small charge, an experimental evaluation of the three refrigerants was investigated. To compare the environmental impact of refrigerants over the entire life cycle of fluid and equipment, including power consumption, the life cycle climate performance (LCCP) of the three refrigerants were evaluated based on measured data. The estimated LCCPs at various emission rates indicate that the LCCP of R-290 is always lower than that of R-404A. The LCCP of R-410A is lower than that of R-290 as long as the annual emission is kept below 10%. It was concluded that R-410A has less or equivalent environmental impact as compared to R-290 when safety (toxicity and flammability), environmental impact (climate change), cost and performance (capacity and COP) are considered.     

Measurements of the air flow field in the freezer compartment of a top-mount no-frost refrigerator: the effect of temperature

The energy consumption of a household refrigerator is closely related to the distributions of temperature inside its compartments. Since, such distributions are dependent on the chilled air circulating inside the refrigerator, its energy consumption can be reduced and its efficiency improved through optimization of the air flow fields inside the compartments. In this work, particle image velocimetry (PIV) was used to measure velocity fields inside the freezer compartment of a commercial top-mount no-frost refrigerator at two critical vertical sections at three different temperatures levels. To perform the tests, a commercial unit was equipped with two specially constructed insulated windows which enabled clear visualization of the flow field under real operating conditions. The results show that significant changes in the air flow distribution occur when the temperature is reduced.     

Contribution to the gas chromatographic analysis for both refrigerants composition and cell gas in insulating foams – Part II: Aging of insulating foams

In part I, a simple analysis protocol for refrigerant substances has been proposed for use in refrigerating plants or as blowing agents for insulating foams. The present work proposes original results obtained with that method to study the aging of insulating foams. The characteristics of insulating foam panels have been studied including the initial composition and heterogeneity of cell gases, as well as the aging of both unprotected and protected insulating panels. A special focus has been laid on aging at the junctions in refrigerated trucks panels. Indeed, insulation boxes for refrigerated trucks are usually made of various foam panels covered by a single gas-tight facing. A quicker aging was observed under the facing in the foam panels' junction areas, and we could assert that the global aging of the refrigerated trucks box mainly results from the aging of the assemblies (sides and junctions).     

Performance enhancement of a household refrigerator by addition of latent heat storage

This paper studies the effect of adding a phase change material (PCM) slab on the outside face of a refrigerator evaporator. A dynamic model of the vapour compression cycle including the presence of the phase change material and its experimental validation is presented. The simulation results of the system with PCM show that the addition of thermal inertia globally enhances heat transfer from the evaporator and allows a higher evaporating temperature, which increases the energy efficiency of the system. The energy stored in the PCM is yielded to the refrigerator cell during the off cycle and allows for several hours of continuous operation without power supply.     

Analysis of an air cycle refrigerator driving air conditioning system integrated desiccant system

This study presents theoretical investigation on the performance of air cycle refrigerator driving air conditioning system integrated desiccant system. Total system performance is evaluated and the system feasibility is examined. The system has such characteristics that (1) safe material of air and water are used as a refrigerant, (2) waste heat from air cycle refrigerator performs the regeneration of desiccant material for energy saving. It has been clarifying that (1) controlling the evaporative cooling process in air washer, the system can operate for a wide range of cooling loads, (2) the total coefficient of performance on air conditioning system is better than the conventional vapor compression system with reheating coil, and (3) the system performance highly depends on the ratio of the amount of outdoor intake air to the supply air.     

LCCP evaluation on various vapor compression cycle options and low GWP refrigerants

Reducing environmental impacts from the energy conversion systems has been an important research topic due to recent severe global climate changes. In residential buildings, the space heating and cooling are main energy consumers, which are mainly relying on a vapor compression cycle. In an effort to better understand the environmental impacts of these systems, life cycle climate performance (LCCP) evaluation method was developed, which considers the direct and indirect emissions of the system over the course of its lifetime from manufacturing to disposal. Based on the developed LCCP evaluation method, five cycle options and seven low GWP refrigerants are evaluated for air conditioning applications.     

Numerical analysis and experimental investigation into the performance of a wire-on-tube condenser of a retrofitted refrigerator

The present paper discusses (a) the analysis of a wire-on-tube condenser under varying operating conditions of free convection using FEM, and (b) experimental verification of the performance of two wire-on-tube condensers in a retrofitted domestic refrigerator using refrigerant R-134a. The study is motivated by the desire to investigate if the wire-on-tube condensers used in R-12 based refrigerators could be used in a modified refrigerator using R-134a refrigerant. Experiments were conducted in a climate chamber under controlled and varying ambient temperatures and mass flow rates to determine the locations where phase change occurs and the degree of subcooling achieved. In terms of initial and final phase change point locations the predicted results agree with the experimental results to within ±10%. The analysis and the experiments also lead to the information about the adequacy of the number of tubes for complete condensation of the refrigerant vapour under given operating conditions. The methodology can be used as a design tool for the design of wire-on-tube condenser of a small refrigerator as well as the suitability of specific decommissioned condensers for use in a retrofitted refrigerator. It also indicates that R-12 based refrigerators using wire-on-tube condensers retrofitted with R-134a compressor and refrigerant deserve and warrant further studies for adoption.     

Performance of a domestic refrigerator under influence of varied expansion device capacity, refrigerant charge and ambient temperature

This paper reports experimental results of an on/off cycling domestic refrigerator at varied expansion device capacity (EDC), quantity of charge and ambient temperature. It was found that the energy consumption is insensitive to varied EDC and charge within a wide range of settings. For the charge this is explained by the low side accumulator, which buffers over- and undercharge. It was also found that the optimum charge increased at lower ambient temperature. The paper describes an experimental procedure on how to determine the capillary tube length and the quantity of charge for a domestic refrigerator/freezer. This procedure is recommended since it takes different thermal masses and loads into consideration and since the potential for energy saving with a more sophisticated method appears to be limited.     

Numerical optimisation of a two-stage ejector refrigeration plant

Jet-refrigeration cycles seem to provide an interesting solution to the increasing interest in environment protection and the need for energy saving due to their low plant costs, reliability and possibility to use water as operating fluid. A steam/steam ejector cycle refrigerator is investigated introducing a two-stage ejector with annular primary at the second stage. The steady_state refrigerator, exchanging heat with the water streams at inlet fixed temperatures at the three shell and tube heat exchangers, evaporator, condenser and generator, is considered as an open system. Heat transfer irreversibilities in the heat exchangers and external friction losses in the water streams are considered, ignoring the internal pressure drop of the vapor. A simulation program numerically searches the maximum COP at given external inlet fluid temperatures as a function of mass flows, dimensions and temperature differences in the heat exchangers. The code gives the ejector and heat exchangers design parameters.     

电冰箱节能潜力的研究

本文首先简要讨论了一些用于电冰箱的节能措施。然后通过ERA软件及自行编制的软件计算了使用这些措施后电冰箱的能耗情况。为了分析这些措施的可行性。继而进行了回收期和生命周期成本计算。分析结果表明，这些节方法不仅技术上能够实现，而且在经济上也具有可操作性。     

Characteristics of Voorhees refrigerating machine with hermetic piston compressor producing refrigeration at one or two temperature levels

Research on the operation of the refrigerating machine working on the Voorhees cycle which permits two-stage compression in a single-cylinder compressor has been carried out. The purpose of this research was to study the possibilities of using the Voorhees machine in a domestic refrigerator for production of refrigeration at one or two temperature levels. The experiments were carried out on the basis of a small hermetic lubricated compressor with a low refrigerating capacity operating on a commonly used R12 and natural refrigerant isobutane R600a. The improved refrigerating capacity in the Voorhees cycle with isobutane makes the latter an alternative substitute for conventional refrigerants. Some peculiarities in the operation of a hermetic piston compressor as part of the Voorhees refrigerating machine have been revealed. They require the use of a compressor developed specially for the Voorhees cycle. The method of optimizing the cycle parameters for a one temperature refrigerating system is suggested in this paper. The research carried out proved that the optimum intermediate pressures of the Voorhees refrigerating machine producing refrigeration either at one or two temperature levels are different.     

Endogenous Particle Stabilization During Magnesium Integral Foam Production

The production of magnesium integral foam components with a dense shell and a porous core is investigated. High pressure casting methods are used where liquid magnesium mixed with a blowing agent is injected into a permanent steel mould. A compact shell develops due to fast cooling at the walls. Larger cooling times in the core allow the decomposition of the blowing agent and the evolution of a foam structure. The resulting integral foams show a high weight‐specific stiffness combined with high energy absorption capability. For the first time, foam stabilizing without additives is realized. Stabilization is by foaming during solidification with the primary α‐phase particles acting as obstacles slowing down cell wall thinning.     

Testing of propane/isobutane mixture in domestic refrigeratorsEtude sur un mélange propane/isobutane dans les réfrigérateurs domestiques

The performance of a propane/isobutane (R290/R600a) mixture was examined for domestic refrigerators. A thermodynamic cycle analysis indicated that the propane/isobutane mixture in the composition range of 0.2 to 0.6 mass fraction of propane yields an increase in the coefficient of performance (COP) of up to 2.3% as compared to CFC12. For the actual tests, two commercial refrigerators of 299 and 465 l were used. For both units, all refrigeration components remained the same throughout the tests, except that the length of the capillary tube and amount of charge were changed for the mixture. Each refrigerator was fully instrumented with more than 20 thermocouples, two pressure transducers, and a digital watt/watt-h meter. For each unit, both ‘energy consumption test’ and ‘no load pull-down test’ were conducted under the same condition. The experimental results obtained with the same compressor indicated that the propane/isobutane mixture at 0.6 mass fraction of propane has a 3–4% higher energy efficiency and a somewhat faster cooling rate than CFC12. The mixture showed a shorter compressor on-time and lower compressor dome temperatures than CFC12. In conclusion, the proposed hydrocarbon mixture seems to be an appropriate long term candidate to replace CFC12/HFC134a from the viewpoint of energy conservation requiring minimal changes in the existing refrigerators.     

X-ray investigation of a domestic refrigerator. Observations at 25°C ambient temperature

In this study, the transient behavior of a domestic refrigerator is investigated by the use of an X-ray system. The studies are made on a two-door upright freezer with a volume of 435 liters, and which has an automatic defrost feature. The refrigerant is R134a. During the experimental study, ambient temperature is held at 25±2 °C. Real time X-ray video images of the refrigeration circuit are taken during the pull-down (cooling down of the refrigerator from ambient temperature) and cyclic periods as well. X-ray images are recorded by focusing to on the dryer, capillary exit, evaporator inlet, and accumulator regions specifically. In order to watch evaporator and dryer sections continuously, two identical experiments are made while the probe is focused on either the evaporator or dryer sections each time. By matching the video images and temperature data, the flow regimes, charge inventory, accumulator functioning, and changes of subcooling degree at dryer inlet are explained. Possible flow induced noise mechanisms are identified.     

Modelling and simulation results for a domestic exhaust-air heat pump heating system

Energy consumption in residential buildings has gained an increasing interest the latest years due to the rising demand for efficient energy use and higher comfort standards. In tight building constructions with controlled ventilation, heat recovery with exhaust-air heat pump connected to floor heating is regarded as energy efficient heating system that optimises the energy use in buildings while maintaining an acceptable level of thermal comfort. In this study, we use the computational tools TRNSYS and EES to model and analyse the performance of a residential house, its ventilation system and its floor heating system based on an exhaust air heat pump. The system analysis focuses particularly on the influence of internal and solar gains on the operation of the heating system and the thermal comfort of the house. Furthermore, the way that gains influences the performance of the floor heating system is examined. Overall, the results bring to light the impact of factors that are not easy to predict on the indoor climate and the thermal comfort.     

Study of domestic refrigerator temperature and analysis of factors affecting temperature: a French survey

A survey was carried out in France from April to June 1999. Temperatures were recorded at three levels (top, middle and bottom) of the refrigerator compartment using a data logger. A questionnaire was filled in, enabling the following information to be obtained: characteristics of the family, characteristics of the refrigerator and the use conditions. One hundred and forty-three domestic refrigerators were surveyed, but due to various technical problems, only 119 sets of recorded temperatures were exploitable. The temperatures of the surveyed refrigerators were: average 6.6 °C, minimum 0.9 °C and maximum 11.4 °C. Statistical analysis such as clustering and segmentation were used. It was found that the heterogeneousness of temperature inside each refrigerator seems to be dependent on the type. This study shows the influence of the use conditions on the temperature. No one factor exerts a single direct effect; a combination of the effects of all factors is observed.     

Modeling of a domestic frost-free refrigerator

In the present study, a comprehensive thermo-fluidic model is developed for a domestic frost-free refrigerator. The governing equations, coupled with pertinent boundary conditions, are solved by employing a conservative control volume formulation, in the environment of a three-dimensional unstructured mesh. Experiments are also conducted to validate the results predicted by the present computational model. It is found that the computational and experimental results qualitatively agree with each other, although certain discrepancies can be observed in terms of the exact numerical values obtained. For the freezer compartment, the computationally predicted temperatures are somewhat higher than the experimental ones, whereas for the refrigerating compartment, the computed temperatures are lower than the corresponding experimental observations. The difference between experimental and computational results may be attributed to the lack of precise data on the airflow rates and the unaccounted heat transfer rates through the door gaskets and the compressor. From the heat transfer and fluid flow analysis, certain modifications in the design are also suggested, so as to improve the performance of the refrigerator.     

HFC134a/HC600a/HC290 mixture a retrofit for CFC12 systems

The environmental concerns with the impact of refrigerant emissions lead to the importance in identifying a long-term alternative to meet all requirements in respect of system performance and service. Even though HFC134a and HC blend (containing 55.2% HC600a and 44.8% HC290 by weight) have been reported to be substitutes for CFC12, they have their own drawbacks in respect of energy efficiency/flammability/serviceability aspects of the system. In this present work, experimental investigation has been carried out on the performance of an ozone friendly refrigerant mixture (containing HFC134a/HC blend) in two low temperature systems (a 165 l domestic refrigerator and a 400 l deep freezer) and two medium temperature systems [a 165 l vending machine (visi cooler) and a 3.5 kW walk-in cooler]. The oil miscibility of the new mixture with mineral oil was also studied and found to be good. The HFC134a/HC blend mixture that contains 9% HC blend (by weight) has better performance resulting in 10–30% and 5–15% less energy consumption (than CFC12) in medium and low temperature system, respectively.     

A quel point est-il difficile de réaliser un réfrigérateur miniaturisé?

This paper describes how the entropy generation rate changes at each component in a vapor compression refrigerator as the system scale is decreased. A so-called micro refrigerator composed of all components in micro scale is inherently difficult to work according to the second law of thermodynamics. Although the quantitative evaluation of the entropy generation is not made here, it is clearly revealed that the mechanical compressor is the most difficult component to be miniaturized in a micro refrigerator. If a micro vapor compression refrigerator is to be successfully operated, a great deal of efforts must be made to develop a workable micro compressor and to minimize internal heat leak to the evaporator of the refrigerator.     

制冷剂回收再生的碳排放评估及经济性分析

我国已进入HCFCs制冷剂淘汰末期,并即将于2024年启动HFCs的产量和消费量削减.本文以制冷剂的回收再生过程为主要研究对象,基于LCCP气候性能模型,构建了制冷剂回收再生过程的碳排放量评估模型;分析了制冷剂回收再生的经济性;并对所构建模型,以汽车空调制冷剂R134a的回收再生为案例,计算其碳排放量及回收再生经济性....