回热对跨临界CO2喷射制冷系统的影响

目的：研究回热对跨临界CO₂双级压缩/喷射制冷系统性能的影响。方法：采用仿真模拟软件建模，分析在不同气体冷却器出口温度（25～45 ℃）、高压侧排气压力（7.4～9.5 MPa）、蒸发温度（-40～-15 ℃）和中间压力（3～5 MPa）的情况下，回热对低压压缩机吸气温度、排气温度、比功率增量以及系统性能系数的影响。结果：在特定的回热度下，随着中间压力的增加，低压压缩机排气温度和比功率增量升高；但随着蒸发温度升高，低压压缩机排气温度和比功率增量逐渐降低。在标准工况下，回热系统的性能系数低于不带回热系统的，同时随着回热度的增加，回热系统的能效降低。结论：随着回热度的增加，低压压缩机吸气温度、排气温度和比功率增量显著升高。但回热改善跨临界CO₂双级压缩/喷射制冷系统性能效果不佳。     

CO2热泵最优排气压力理论分析与试验

目的:优化热泵系统性能,探讨二氧化碳系统在不同工况下的最优排气压力。方法:通过建立CO₂跨临界热泵模型,分析了排气压力和制热量、吸气过热度、制冷剂质量流量及系统能效的关系,深入研究了进出水温度和环境温度对最优排气压力的影响,再利用搭建的CO₂热泵试验台验证模型的可靠性。结果:3种出水温度下,制热量随排压的升高而增大,质量流量随排压的升高而减小,循环性能系数和过热度随排压的升高呈先增大后减小趋势,最优排气压力随着进出水温度和环境温度升高而升高,但进出水温度的升高会降低系统循环性能系数,据此拟合了出水温度60℃下的最优排气压力关联式,并设计了5组试验证明了其具有可靠性。结论:通过大量的仿真数据确定了系统的最优排气压力,并与试验值对比发现,误差值均小于5%,满足试验及设计需求。     

R404A/R23复叠式超低温制冷系统试验

依托自建的R404A/R23复叠式超低温制冷试验台,采用控制单一变量的方法,研究蒸发温度与冷凝温度对复叠式制冷循环中压缩机压缩比、排气温度、吸气压力、制冷剂流量和制冷系数的影响。结果表明:当蒸发温度从-50℃降至-55℃时,系统制冷系数下降最快,达到2.1%;当冷凝温度从28℃升至30℃时,系统制冷系数下降最快为1.7%,且蒸发温度下降1℃比冷凝温度上升1℃对系统性能系数影响更大。另外,当蒸发温度为-55℃,冷凝温度为36℃时,压缩机排气温度达到最高90℃,此时,系统性能系数最低为1.5,所以,有效控制压缩机排气温度对系统安全和高效运行至关重要。     

循环加热式空气源热泵热水器运行性能的试验研究

以套管式换热器作为热回收元件对循环加热式空气源热泵热水器的运行性能进行试验研究,指出:水箱水温从15℃升高到55℃时,系统参数如吸、排气压力,进、出水温度等随着水箱水温的变化而升高,同时系统的能耗也增大,而系统性能系数有所降低,在3.69左右,但与传统热水器相比系统还是节能的,是可行的.     

R410A机组在变进水温度下制冷和制热运行的特性

文章主要对R410A机组的物理性质进行简要分析,在出水温度为5~20°C(制冷工况)和35~55°C(制热工况)范围之内进行吸气压力、排气温度以及吸气温度等新性能测试,继而得出R410A机组在变进水温度之下制冷和制热的运作特点,再分析其变化规律。实验研究结果表明,在水源热泵空调机组中,一旦未设计好地源埋管系统,势必会耗损更多能量。     

热压工艺对对位芳纶纸强度性能的影响

探讨了热压压力、热压温度以及热压次数对对位芳纶纸强度性能的影响,并利用扫描电镜对热压前后的纸张结构进行观察。结果表明:与芳纶原纸相比,热压后对位芳纶纸的紧度、抗张指数和撕裂指数显著提高,但随热压工艺参数的变化有不同的规律。固定热压温度为160℃,在热压压力为2~5MPa的范围内提高压力,紧度和抗张指数增加不明显,而撕裂指数有下降趋势;固定热压压力为2MPa,在温度120~180℃范围内提高温度,紧度增加幅度不大,而抗张指数和撕裂指数则随温度的升高呈现出先升高后降低的趋势,在温度为140℃时达最大值。较佳的热压工艺为:热压压力2MPa、热压温度140℃、热压次数5次,此时纸张的抗张指数和撕裂指数分别为43.8N.m/g和30.9 mN.m2/g。     

多效冷凝制冷机组的冷凝机理与工况分析

分析了多效冷凝制冷机组的传热和传质过程及风量、水量对机组冷凝效果的影响:空气与喷淋水交叉流动的结构可使多效冷凝制机组水泵的功耗更低;合理的风量及喷淋水量可强化水膜传热传质性能,同时使制冷量和能效比达到最大.以10 t保鲜冷库(0～3 ℃)为实验库,进行多效冷及风冷2种冷却方式下压缩机系统运行特性的对比实验研究.实验表明:多效冷凝机组很好地解决了高温环境下风冷机组排气压力、排气温度过高的问题,最高气温36 ℃时使排气压力和排气温度分别降低了0.73 MPa,28.23 ℃,节能效果显著.     

对脱溶粕结块问题的探讨

蒸脱机排粕结块,结块内溶剂、水分、尿素酶和胰蛋白酶的含量均超标,严重影响成品粕质量,应当设法加以解决.研究发现,脱溶粕结块的主要原因是蒸脱机排气温度变化过大,排气压力过高,混合气体在脱溶层内结露,物料吸收大量结露水造成的;蒸汽带水,料坯软化、蒸炒不佳等都不是根本原因.为了减少结块,蒸脱机排气温度应控制在85～90℃,排气压力应控制在-118～-245 Pa.     

制冷剂R32吸气状态对变频转子式压缩机的影响

吸气带液作为一种既不增加系统成本又能降低压缩机排气温度的方法,需要进一步了解其对核心部件压缩机性能的影响,课题组利用变流量水冷冷水机组实验台,R32作为循环系统冷媒,模拟实际运行工况进行实验,研究频率、吸气干度和过热度对滚动转子式压缩机性能的影响。实验研究结果表明:相同工况下,频率越高,系统压比越高;在吸气饱和状态下,同频率下,压比越高,压缩机等熵压缩效率和容积效率越低;相同压比下,频率越高,等熵压缩效率和容积效率越高。吸气带液时,压缩机排气温度急剧下降,综合效率系数达到最大;吸气过热度对压缩机效率几乎无影响,吸气带液时,压缩机效率只有小幅度的下降。得出了R32滚动转子式压缩机适合进行少量吸气带液压缩的结论。     

回火工艺对碳钢薄板组织和性能的影响

对碳钢薄板进行810℃淬火后分别进行200,400,540℃回火,研究回火温度对试验钢显微组织和力学性能的影响;通过对试验钢薄板施加100,200,300 N的压力,并在不同温度下回火不同时间,研究回火压力、温度和时间同钢板平面度、硬度之间的关系。结果表明:随着回火温度的升高,组织结构逐渐转变为回火马氏体、回火屈氏体和回火索氏体,强度和硬度逐渐下降;同一温度下,随着压力的增加,平面度逐渐提高。当回火温度为400℃、回火时间2 h、压力为200 N时,硬度与平面度综合性能最好。     

Reliable identification of grapevine rootstock varieties using RAPD PCR on woody samples

Since grapevine ( Vitis spp .) rootstock material is being traded increasingly as disbudded woody material a lack of distinctive morphological features on such material necessitates an alternative and reliable means of identification. Methods described here were developed for rapid and efficient extraction of DNA from woody samples rich in phenolic compounds and polysaccharides, and for subsequent identification of varieties by RAPD PCR. Using these methods, and with the application of only one selected RAPD primer, we were able to differentiate sixteen rootstock varieties, including the seven varieties most commonly used in Germany. Problems commonly encountered with reproducibility of RAPD patterns were avoided by choosing primers with a dinucleotide sequence and a high G/C content that allowed a rather high annealing temperature of 45°C. Methods described here should also be useful for other horticultural crops, especially those with woody tissues rich in phenolic compounds and polysaccharides.     

Aroma characterization of various apricot varieties using headspace–solid phase microextraction combined with gas chromatography–mass spectrometry and gas chromatography–olfactometry

The characterization of the aromatic profile of several apricot cultivars with molecular tracers in order to obtain objective data concerning the aromatic quality of this fruit was undertaken using headspace–solid phase microextraction (HS–SPME). Six apricot cultivars were selected according to their organoleptic characteristics: Iranien, Orangered, Goldrich, Hargrand, Rouge du Roussillon and A4025. The aromatic intensity of these varieties measured by HS–SPME–Olfactometry were defined and classified according to the presence and the intensity of grassy, fruity and apricot like notes. In the six varieties, 23 common volatile compounds were identified by HS–SPME–GC–MS. Finally, 10 compounds, ethyl acetate, hexyl acetate, limonene, β-cyclocitral, γ-decalactone, 6-methyl-5-hepten-2-one, linalool, β-ionone, menthone and (E)-hexen-2-al were recognized by HS–SPME–GC–O as responsible of the aromatic notes involved in apricot aroma and considered as molecular tracers of apricot aromatic quality which could be utilized to discriminate apricot varieties.     

Tests of potential functional barriers for laminated multilayer food packages. Part I: Low molecular weight permeants

The advent of the functional barrier concept in food packaging has brought with it a requirement for fast tests of permeation through potential barrier materials. In such tests it would be convenient for both foodstuffs and materials below the functional barrier (sub-barrier materials) to be represented by standard simulants. By means of inverse gas chromatography, liquid paraffin spiked with appropriate permeants was considered as a potential simulant of sub-barrier materials based on polypropylene (PP) or similar polyolefins. Experiments were performed to characterize the kinetics of the permeation of low molecular weight model permeants (octene, toluene and isopropanol) from liquid paraffin, through a surrogate potential functional barrier (25 μm-thick oriented PP) into the food simulants olive oil and 3% (w/v) acetic acid. These permeation results were interpreted in terms of three permeation kinetic models regarding the solubility of a particular model permeant in the post-barrier medium (i.e. the food simulant). The results obtained justify the development and evaluation of liquid sub-barrier simulants that would allow flexible yet rigorous testing of new laminated multilayer packaging materials.     

Textural Properties of Cold-set Gels Induced from Heat-denatured Whey Protein Isolates

A 9% whey protein (WP) isolate solution at pH 7.0 was heat-denatured at 80°C for 30 min. Size-exclusion HPLC showed that native WP formed soluble aggregates after heat-treatment. Additions of CaCl2 (10–40 mM), NaCl (50–400 mM) or glucono-delta-lactone (GDL, 0.4–2.0%, w/v) or hydrolysis by a protease from Bacillus licheniformis caused gelation of the denatured solution at 45°C. Textural parameters, hardness, adhesiveness, and cohesiveness of the gels so formed changed markedly with concentration of added salts or pH by added GDL. Maximum gel hardness occurred at 200 mM NaCl or pH 4.7. Increasing CaCl2 concentration continuously increased gel hardness. Generally, GDL-induced gels were harder than salt-induced gels, and much harder than the protease-induced gel.     

Occurrence of bisphenol-F-diglycidyl ether (BFDGE) in fish canned in oil

The levels of bisphenol-F-diglycidyl ether (BFDGE) were quantified as part of a European survey on the migration of residues of epoxy resins into oil from canned fish. The contents of BFDGE in cans, lids and fish collected from all 15 Member States of the European Union and Switzerland were analysed in 382 samples. Cans and lids were separately extracted with acetonitrile. The extraction from fish was carried out with hexane followed by re-extraction with acetonitrile. The analysis was performed by reverse phase HPL C with fluorescence detection. BFDGE could be detected in 12% of the fish, 24% of the cans and 18% of the lids. Only 3% of the fish contained BFDGE in concentrations considerably above 1mg/kg. In addition to the presented data, a comparison was made with the levels of BADGE (bisphenol-A-diglycidyl ether)analysed in the same products in the context of a previous study.     

Analysis of benzo[a]pyrene in spiked fatty foods by second derivative synchronous spectrofluorimetry after microwave-assisted treatment of samples

A simple, rapid and inexpensive method has been developed for the determination of benzo[a     

The development of reference materials for paralytic shellfish poisoning toxins in lyophilized mussel. II: Certification study

This paper describes the second part of a project undertaken to develop certified mussel reference materials for paralytic shellfish poisoning toxins. In the first part two interlaboratory studies were undertaken to investigate the performance of the analytical methodology for several PSP toxins, in particular saxitoxin and decarbamoyl-saxitoxin in lyophilized mussels, and to set criteria for the acceptance of results to be applied during the certification exercise. Fifteen laboratories participated in this certification study and were asked to measure saxitoxin and decarbamoyl-saxitoxin in rehydrated lyophilized mussel material and in a saxitoxin-enriched mussel material. The participants were allowed to use a method of their choice but with an extraction procedure to be strictly followed. The study included extra experiments to verify the detection limits for both saxitoxin and decarbamoyl-saxitoxin. Most participants (13 of 15) were able to meet all the criteria set for the certification study. Results for saxitoxin.2HCl yielded a certified mass fraction of <0.07 mg/kg in the rehydrated lyophilized mussels. Results obtained for decarbamoyl-saxitoxin.2HCl yielded a certified mass fraction of 1.59+/-0.20 mg/kg. The results for saxitoxin.2HCl in enriched blank mussel yielded a certified mass fraction of 0.48 +/- 0.06 mg/kg. These certified reference materials for paralytic shellfish poisoning toxins in lyophilized mussel material are the first available for laboratories to test their method for accuracy and performance.     

Contribution of European research to risk analysis

The European Commission's, Quality of Life Research Programme, Key Action 1—Health, Food & Nutrition is mission-oriented and aims, amongst other things, at providing a healthy, safe and high-quality food supply leading to reinforced consumer confidence in the safety of European food. Its objectives also include the enhancing of the competitiveness of the European food supply. Key Action 1 is currently supporting a number of different types of European collaborative projects in the area of risk analysis. The objectives of these projects range from the development and validation of prevention strategies including the reduction of consumers risks; development and validation of new modelling approaches; harmonization of risk assessment principles, methodologies, and terminology; standardization of methods and systems used for the safety evaluation of transgenic food; providing of tools for the evaluation of human viral contamination of shellfish and quality control; new methodologies for assessing the potential of unintended effects of genetically modified (genetically modified) foods; development of a risk assessment model for Cryptosporidium parvum related to the food and water industries; to the development of a communication platform for genetically modified organism, producers, retailers, regulatory authorities and consumer groups to improve safety assessment procedures, risk management strategies and risk communication; development and validation of new methods for safety testing of transgenic food; evaluation of the safety and efficacy of iron supplementation in pregnant women; evaluation of the potential cancer-preventing activity of pro- and pre-biotic ('synbiotic') combinations in human volunteers. An overview of these projects is presented here.     

Announcing a new international peer-reviewed journal:Food Science and Human Wellness now accepting manuscript submission in English

<正>We are pleased to announce the launch of a new international peer-reviewed journal-Food Science and Human Wellness,ISSN 2213-4530,which is an open access journal,produced and hosted by Elsevier B.V.on behalf of Beijing Academy of Food Sciences.Food Science and Human Wellness is an international peer-reviewed English journal that provides a forum for the dissemination of the