Comprehensive approach to predicting the circulation composition of zeotropic refrigerants

The problem of composition shift in zeotropic fluid circulation, which is encountered in modern air conditioning and refrigeration systems, is studied. It reveals that the composition shift phenomena is contributed by fractionation related to four mechanisms. This paper concentrates on the modeling of component fractionation in heat exchangers. Element approach is employed, and the amount of each component holdup is calculated element by element with a proper void fraction model. The circulation concentration is determined from the refrigerant differential holdup in heat exchangers. Simulations are carried out to prove the validity. The results can improve the reliability and efficiency in zeotropic refrigerant applications.

Mixed refrigerant composition shift due to throttle valves opening in auto cascade refrigeration system

Auto cascade refrigeration(ACR) cycle with phase separators is widely used in the cryogenic system. The composition of mixed refrigerant has a great effect on the performance of the system. Based on the assumption of infinite volume of phase separator, ACR system with one phase separator is simulated in this paper. The variation of refrigerant composition under different valves opening is obtained. A related experimental system is set up to verify the variation. The result shows that when the valve opening connected to the evaporator increases or the valve opening under the phase separator decreases, the low-boiling component concentration of the working mixture passing through the compressor and condenser increases, while the high-boiling component concentration decreases. Furthermore, the variations of condensation pressure and evaporation pressure under different valves opening are also observed. This paper is helpful to deepen the understanding of ACR system.

Table-like shape magnetocaloric effect and large refrigerant capacity in dual-phase HoNi/HoNi2 composite

Nowadays,magnetic cooling(MC) technology by using the magnetocaloric effect(MCE) has attracted extensive research interest for its promising practical applications.A constant large/giant MCE covers wide refrigeration temperatures(denote as table-like shape) is beneficial for obtaining high efficiency performance for MC.In this paper,the HoNi/HoNi2 composite was successfully synthesized by arc-melting method and proved to be composed of HoNi and HoNi2 crystalline phases with weight ratios of 52.4 wt.% and 47.6 wt.%,respectively.The maximum magnetic entropy change(-ΔSMmax)is 18.23 J/(kg·K),and the refrigerant capacity values RC1,RC2,and RC3 are 867.9 J/kg,676.4 J/kg,and 467.8 J/kg with ΔH=0-70 kOe,respectively.The table-like shape MCE and large refrigerant capacity values make the composite attractive for cryogenic MC using the Ericsson cycle.

Optimization Mechanism of Mechanical Properties of Basalt Fiber-Epoxy Resin Composites by Interfacially Enriched Distribution of Nano-Starch Crystals

Fibre reinforced polymer composites have become a new generation of structural materials due to their unique advantages such as high specific strength,designability,good dimensional stability and ease of large-area monolithic forming.However,the problem of interfacial bonding between the resin matrix and the fibres limits the direct use of reinforcing fibres and has become a central difficulty in the development of basalt fibre-epoxy composites.This paper proposes a solution for enhancing the strength of the fibre-resin interface using maize starch nanocrystals,which are highly yield and eco-friendly.Firstly,in this paper,corn starch nanocrystals(SNC)were prepared by hydrolysis,and were deposited on the surface of basalt fibers by electrostatic adsorption.After that,in order to maximize the modification effect of nano-starch crystals on the interface,the basalt fiber-epoxy resin composite samples were prepared by mixing in a pressureless molding method.The test results shown that the addition of basalt fibers alone led to a reduction in the strength of the sample.Deposition of 0.1 wt%SNC on the surface of basalt fibers can make the strength consistent with pure epoxy resin.When the adsorption amount of SNC reached 0.5 wt%,the tensile strength of the samples was 23.7%higher than that of pure epoxy resin.This is due to the formation of ether bond homopolymers between the SNC at the fibre-epoxy interface and the epoxy resin,which distorts the originally smooth interface,leading to increased stress concentration and the development of cracks.This enhances the binding of basalt fibers.The conclusions of this paper can provide an effective,simple,low-cost and non-polluting method of interfacial enhancement modification.

Exergy Analysis of a Solar Vapor Compression Refrigeration System Using R1234ze(E)as an Environmentally Friendly Replacement of R134a

Refrigeration plays a significant role across various aspects of human life and consumes substantial amounts of electrical energy.The rapid advancement of green cooling technology presents numerous solar-powered refrigeration systems as viable alternatives to traditional refrigeration equipment.Exergy analysis is a key in identifying actual thermodynamic losses and improving the environmental and economic efficiency of refrigeration systems.In this study exergy analyze has been conducted for a solar-powered vapor compression refrigeration(SP-VCR)system in the region of Gharda颽(Southern Algeria)utilizing R1234ze(E)fluid as an eco-friendly substitute for R134a refrigerant.A MATLAB-based numerical model was developed to evaluate losses in different system components and the exergy efficiency of the SP-VCR system.Furthermore,a parametric study was carriedout to analyze the impact of various operating conditions on the system’s exergy destruction and efficiency.The obtained results revealed that,for both refrigerants,the compressor exhibited the highest exergy destruction,followed by the condenser,expansion valve,and evaporator.However,the system using R1234ze(E)demonstrated lower irreversibility compared to that using R134a refrigerant.The improvements made with R1234ze are 71.95%for the compressor,39.13%for the condenser,15.38%for the expansion valve,5%for the evaporator,and 54.76%for the overall system,which confirm the potential of R1234ze(E)as a promising alternative to R134a for cooling applications.

Study of Rice Husks and Expanded Polystyrene Composites for Construction Applications

In the current context of environmental challenges, this study focuses on developing innovative and eco-friendly composites using rice husk and recycled expanded polystyrene. This dual-responsibility approach valorizes a by-product like rice husk, often considered waste, and reuses polystyrene, a plastic waste, thereby contributing to CO2 emission reduction and effective waste management. The manufacturing process involves dissolving recycled polystyrene into a solvent to create a binder, which is then mixed with rice husk and cold-compacted into composite materials. The study examines the impact of two particle sizes (fine and coarse) and different proportions of recycled polystyrene binder. The results show significant variations in the mechanical characteristics of the composites, with Modulus of Rupture (MOR) values varying from 2.41 to 3.47 MPa, Modulus of Elasticity (MOE) ranging from 223.41 to 1497.2 MPa, and Stiffness Coefficient (K) from 5.04 to 33.96 N/mm. These characteristics demonstrate that these composites are appropriate for various construction applications, including interior decoration, panel claddings, and potentially for furniture and door manufacturing when combined with appropriate coatings. This study not only highlights the recycling of agricultural and plastic waste but also provides a localized approach to addressing global climate change challenges through the adoption of sustainable building materials.

Recent Trends in Preparation and Applications of Biodegradable Polymer Composites

This review efficiently covers the research progress in the area of polymer bio composites in perspective of the modern-day renewable materials.In the last decade,attraction towards the bio-composite based systems has been the topic of interest due to their potential as a substitute of conventional materials produced in important manufacturing industries.Recently,preparation of biocompatible and biodegradable polymer composites is an important achievement as an alternative of petrochemical based renewable products.Successful production of eco-friendly bio-composite materials have been achieved with natural fibers viz jute,bamboo,hair,flex,wool,silk and many others instead of synthesized fibers like carbon,glass dispersed in synthesized resins viz poly vinyl alcohol,epoxy and etc.Biomaterials based on natural fibers dispersed in natural matrix like natural rubber or polyester have also been obtained with endless applications for the mankind.The utilization of such materials for the good well of mankind is attributed to their ease of disposal and being renewable.The last but not the least,the extraordinary mechanical properties of bio-composites make them superior to many other conventional materials.This review paper addresses the recent trends,mechanical and chemical properties,synthesis,and application of bio-composites in the recent years.

Experimental Testing of Composite Panels Reinforced with Cotton Fibers

A research project has been carried out at the National Technical University of Athens, Greece, to develop composite panels reinforced with cotton fibers. The primary aim of the project is to examine the mechanical properties of such panels for use in secondary structural members such as wall or door systems. The use of natural fibers such as cotton, flax or sisal fibers has the primary advantage of being eco-friendly, low cost and low weight compared to glass fibers on the expense of lower structural properties. This paper presents results from experimental work on composite plates made from polyester resin reinforced with cotton fibers, with special attention given to the effect of the fiber type on the structural properties of the plates. The results from this study showed that the structural performance of cotton fiber composites is satisfactory for structural parts with low requirements, such as wall panels or doors. The present results for cotton fiber composites are also compared to testing results from previous studies on composites with flax/sisal fibers.

微酸性电解水处理对兔肉冷藏期间品质及微生物菌群的影响

为探究微酸性电解水(slightly acidic electrolytic water,SAEW)对兔肉贮藏品质的影响,将新鲜兔肉分别使用SAEW浸泡处理5 min(SWa)、SAEW浸泡处理10 min(SWb)、无菌水浸泡处理5 min(PW)和未经浸泡处理为对照组(CK)。处理后样品使用托盘覆膜,置于4℃冷藏。每2 d检测样品的总挥发性盐基氮(total volatile base nitrogen,TVB-N)含量、硫代巴比妥酸(thiobarbituric acid,TBA)含量、pH值、色度、感官及微生物菌群结构的组成及变化。结果表明,SAEW浸泡处理兔肉在冷藏期间pH值、TVB-N值、TBA值上升速率明显低于CK组和PW组,且能够更好地保持兔肉原有色泽以及感官品质,当贮藏到第8天时,发现TVB-N值在CK组[(14.98±0.42)mg/100 g]和PW组[(14.76±0.40)mg/100 g]显著高于SWa组[(13.58±0.40)mg/100 g]和SWb组[(12.66±0.43)mg/100 g]。结合16S rDNA测序分析,SAEW可抑制兔肉冷藏期间腐败菌拟杆菌属(Bacteroides)、假单胞菌属(Pseudzaomonas)的生长繁殖,有效延缓冷藏兔肉腐败变质且SAEW处理10 min减菌效果更佳。该研究结果为SAEW在兔肉贮藏保鲜中的应用提供了理论参考。

制冷剂复合强化流动沸腾传热研究进展

单一的传热强化技术对于传热性能和传热效率的提升有限,大力发展复合强化传热技术对提高资源利用率、节能减排具有重要意义。制冷剂作为一种应用广泛的热力学介质,其物理性质很大程度上会影响制冷系统的能量传输效果。基于制冷系统小型化、轻量化及节能高效换热的发展趋势,制冷剂复合强化传热可以有效改善系统的制冷能效,近年来受到专家学者的广泛关注。综述了制冷剂复合强化流动沸腾传热的最新研究进展,分别从纳米颗粒、泡沫金属、外场(超声/磁场/电场)以及绿色混合制冷剂4个角度进行系统的讨论和总结,指出制冷剂复合强化技术应用的前景和存在的问题,展望了多场协同作用下的纳米颗粒-泡沫金属-制冷剂复合强化传热是今后的重点发展方向,可为建立新型的多元制冷剂复合强化体系提供一定的思路和参考。

预挂浆草鱼片冷藏过程中食用品质及菌群变化规律

为探究预挂浆草鱼片(grass carp fillets with sizing,GCFS)在冷藏条件下的品质变化规律及货架期,对4℃和10℃贮藏期间样品的菌落总数、菌相变化、持水力(water holding capacity,WHC)、挥发性盐基氮(total volatile basic nitrogen,TVB-N)、硫代巴比妥酸(thiobarbituric acid reactive substances,TBARS)、生物胺、ATP-关联化合物及K值等进行分析。结果表明,4℃和10℃贮藏样品的菌落总数分别于7 d和3 d接近或超过腐败阈值,说明低温会明显影响微生物生长和菌群组成,尤其是延缓不动杆菌属、希瓦氏菌属及气单胞菌属等生长。贮藏期内,样品间持水力变化差异不显著(P>0.05),pH在3 d时达到最低值,TBARS、TVB-N及特定生物胺(尸胺、腐胺、组胺、酪胺)含量逐渐升高。此外,核苷酸降解情况受贮藏温度的影响较大,4℃贮藏7 d和10℃贮藏3 d的样品K值超过推荐限值(60%),此时样品进入不新鲜状态。感官评价结果表明,鱼肉感官品质与贮藏时间呈负相关,且4℃贮藏5 d和10℃贮藏3 d的生/熟样品出现不同程度的质地软烂、红肉暗红及腥臭味加重等现象。综合各指标测定结果,为保证良好的食用品质,预挂浆草鱼片在4℃和10℃下的推荐货架期分别为3 d和1 d。

Table-like magnetocaloric effect and large refrigerant capacity of composite magnetic refrigerants based on LaFe_(11.6)Si_(1.4)H_y alloys

Composite magnetic refrigerants were prepared by physical mixing LaFeSiHalloys with different Curie temperatures(Tc). The phase structures of these LaFeSiHalloys were analyzed by X-ray diffraction(XRD) and the magnetocaloric effect(MCE) and refrigerant capacity(RC) of these composite magnetic refrigerants were investigated by experiment and calculation in this paper. The magnetocaloric effect(MCE) and refrigerant capacity(RC) of these composite magnetic refrigerants were investigated by experiment and calculation in this paper. The results indicate the experimental magnetic entropy change(-△S)-Tcurve corresponds reasonably with the(-△S)-Tcurve calculated by the linear combination of(-△S)-T curves of the single material. An optimal mixing ratio can make the composite magnetic refrigerant possess a table-like(-△S)-Tcurve which is beneficial to magnetic Ericsson cycle. When three LaFeSiHalloys with different Tare mixed, the full width at half maximum(△T) of(-△S)-T curves is about 48.7 K and the RC is about 177.76 J/kg under a magnetic field change of 2 T. The composite magnetic refrigerants based on LaFeSiHalloys can be promising candidates for near room temperature magnetic refrigeration and the work will be helpful to develop novel composite magnetic refrigerants with table-like MCE and large RC.

电卡制冷技术:器件发展现状与高熵铁电材料前瞻

电卡制冷技术是一种基于电场调控的固态制冷技术,该技术利用电卡材料在电场作用下产生的温度变化来实现制冷效果。该技术因无直接碳排放、高效率等优点,在全球变暖和碳减排目标的背景下,受到广泛关注。自2006年巨电卡效应发现以来,电卡制冷技术经历了快速发展,尤其是在电卡材料和器件的改进方面取得了显著进展。从电卡制冷器件研究、电卡聚合物纳米复合材料和电卡材料高熵优化方面展开分析与讨论。介绍了电卡效应的基本原理和当前主动回热式电卡制冷器件的研究进展,总结了电卡聚合物纳米复合材料的研究进展以及高熵优化策略和界面极化增强策略,展望了电卡制冷技术在工质和系统领域的未来研究方向。

浸泡法制备吸附制冷用复合吸附剂

以分子筛为基材通过浸泡C aC l2和S rC l2溶液的方法制备复合吸附剂.在模拟制冷条件下,对以不同浓度溶液制备的复合吸附剂的吸附、解吸性能进行了测定,并将吸附解吸性能最好的复合吸附剂在自制的模拟制冷装置上进行了制冷实验.结果表明,复合吸附剂具有良好的吸附、解吸性能,最大吸附量达51.6%,解吸率可达69.3%,在模拟制冷装置上系统的制冷系数达0.25,单位吸附剂的制冷功率为0.072 W/g,符合太阳能吸附制冷的要求.

自复叠制冷系统混合工质配比研究

分析了混合工质组分选择时必须考虑的几个选配原则。针对一种五级自动复叠制冷循环混合工质的配比,分析了相关制冷工质的性能及非共沸混合工质的特性。根据所要达到的温度,选择了R22、R23、R 4、R740和R728五种制冷工质作为系统循环工质,应用制冷工质性能商业计算软件Refprop,对混合工质的配比进行了模拟计算,得到了可以接受的一种混合工质配比。

混合制冷剂泄漏试验研究与模拟分析

Alternative refrigerants have been used in refrigerating and air-conditioning systemsdue to the phase out of CFC-12, HCFC-22 and R502 etc. Most of them are mixtures.The composition fractionation and thermal performance change during refrigerant leakedout from system must be paid attention. The compositions of mixture THR02 were mea-sured by gas chromatographic analysis. Then we developed a general model to calculate thecomposition fractionation of zeotropic, near-azeotropic and azeotropic mixtures. The max-imum deviations between the calculated compositions and experimental results are within5% for the mixture THR02, R4O7C, R404A and R507. THR02 is a near-azeotropic mixture,it is remain unflammable under the worst case, and the change of system performance onlyresulted from composition fractionation during refrigerant leakage can be neglected.

制冷用凹土-氯化钙复合吸附剂的制备和吸水性能

制备了凹土-氯化钙复合吸附剂,通过静态称重法测定了其吸水性能。考察了制备方法、焙烧温度和时间以及原料比例等制备工艺条件对复合吸附剂性能的影响,优化了制备工艺。采用X射线衍射和低温氮吸附对复合吸附剂进行了表征。结果表明:焙烧温度对复合吸附剂吸水性能影响较大,较佳的制备工艺条件是采用溶解-混合法、焙烧温度300℃、焙烧时间2h。低相对湿度时(<20%)吸附剂吸水受微孔和氯化钙含量共同作用,高相对湿度(>30%)时吸水性能主要和氯化钙含量有关。20%氯化钙含量的凹土吸附剂,在相对湿度为20%,吸水量为0.30kg·kg-1;相对湿度80%,吸水量超过0.65kg·kg-1;该吸附剂可反复再生。

CMC与抑菌草制剂复合涂膜对冷藏南丰蜜桔的保鲜效果

为了开发南丰蜜桔贮藏保鲜新技术,该文以"杨小-2,6"南丰蜜桔为试材,研究了凤仙透骨草提取液与羧甲基纤维素(CMC)复合可食性涂膜对冷藏期间果实品质及采后生理生化变化的影响。结果显示:与对照相比,复合涂膜处理显著抑制了果实的采后腐烂及水分损失,延缓了可溶性固形物、可滴定酸及抗坏血酸含量的下降,对可溶性糖的含量影响不大;复合涂膜处理还能保持较高超氧化物歧化酶、过氧化物酶、几丁质酶、β-1,3-葡聚糖酶和苯丙氨酸解氨酶的活性,对多酚氧化酶活性影响不大。与CMC涂膜相比,复合涂膜可显著降低果实的腐烂,对果实品质无不良影响,同时可以诱导几丁质酶和β-1,3-葡聚糖酶活性的上升,说明复合涂膜用于南丰蜜桔的保鲜切实可行。

硅胶及其混合吸附剂-水吸附工质对性能测试

测试了硅胶-水吸附制冷工质对的等量吸附线,且利用各类吸附方程对实验测量数据进行拟合以用于硅胶-水冷水机组的整体系统的数值模拟。实验还通过在纯硅胶颗粒中添加黏结剂或膨胀石墨形成混合吸附剂来提高传热性能。研究表明混合吸附剂(黏结剂的含量为1.1%)在解吸过程中前5min的解吸量相对于纯硅胶颗粒吸附剂提高了13.8%;解吸15min时,混合吸附剂的解吸量相对于纯吸附剂仅提高2.5%。表明混合吸附剂有利于缩短吸附循环周期。在添加剂质量分数相同的情况下,利用膨胀石墨作添加剂形成的混合吸附剂与通过浸泡于黏结剂溶液中形成的混合吸附剂的吸附性能相同,但有其各自的优缺点。

吸附制冷用复合吸附剂的吸附性能

Adsorption performance of adsorbents for the adsorption cooling cycle was discussed. Adsorption isotherms and adsorption rate of water or ethanol on composite adsorbents prepared by the authors (named M4-0132, M1- 0001, M1-9906 and M2-0003 respectively), were tested. The results of fitting to the micro-pore filling theory equation and calculation of characteristic ads orption work based on these pairs were presented. The results showed that the a mount of water adsorbed by composite adsorbents was as high as 2 times that by s ilica gel and 2.5 times that by 13X molecular sieve, respectively, and characte ristic adsorption work calculated was 2.55～4.78 kJ·mol-1, only 12%～29 % of that on 13X molecular sieve. The values of adsorption rate of water on com posite adsorbents were higher than that on silica gel. Analysis for ethanol ads orption on composite adsorbent, M1-0001, showed occurrence of capillary condens ation, which resulted in a considerably higher ethanol uptake than on activated carbon at higher relative vapor pressure. The characteristic adsorption work of ethanol on composite sorbents was 2.55～4.78 kJ·mol-1, merely 10%～20% of that on activated carbon. Based on comprehensive estimate of adsorption pro perties, including adsorption loading, characteristic adsorption work and adsorp tion rate etc., M4-0132 and M1-0001 composite adsorbents were more prefer red for the adsorption cooling process, and the preferable type of isotherm for adsorption cooling cycle appeared to be the Ⅴ type of Brunauer classification.