关于结球白菜在真空预冷实验中温度分布影响因素的探讨

以天津产结球白菜作为实验对象,探讨复压阶段的温度回升,以及在真空室内不同摆放形式和不同包装方式对蔬菜最终温度分布的影响,对比分析试验数据,为今后真空预冷技术的推广应用提供参考.     

真空预冷中捕水器与真空泵的优化匹配研究

真空预冷过程中捕水器能力与真空泵抽气能力匹配决定着预冷过程的质量。通过对预冷过程中水蒸汽为理想气体的假定，分别计算了捕水器和真空泵在匹配时所需要的能耗。在这基础上，对真空预冷系统所需要的能耗进行了计算，并在一台真空预冷实验台上对装载率为60％时的白菜了实验研究，并和理论结果进行了比较。结果表明，在确定的工作条件下，单位时间内的能耗只是与抽气量有关，而整体能耗则取决于所需要预冷的果蔬，与系统参数无关。     

集合包装水果的差压预冷研究进展

目的综述国内外关于集合包装水果差压预冷的研究,并分析了存在的问题。方法从差压预冷技术在果品保鲜领域的应用背景出发,分析预冷的基本原理、特点及意义,归纳了目前差压预冷果品在理论和实验两方面的研究内容及成果。结果水果差压预冷的研究主要集中在包装箱内水果预冷的数值模型、送风工艺参数及通气包装结构设计等方面,包装箱上的开孔对调节预冷气流,促进热质交换具有重要的作用。结论果品预冷数学模型的系统性、可靠性及新型实验验证技术的精准性有待进一步研究,送风工况、预冷包装系统的结构及适用性须兼顾经济、强度因素进行优化。     

包装材料的透湿与计算

探讨了包装薄膜透湿的基本规律,并通过一些实验数据和现象,推导出各种膜透湿性的计算公式,以及同一膜材不同因数之间的换算公式,为包装整体设计提供了适用的计算方法。     

数据采集处理系统在真空预冷实验中的应用

在真空预冷实验中,数据的采集处理非常重要.本文介绍了VAC-0.2型真空预冷实验机的数据采集处理系统,以白菜、生菜和黄瓜三种蔬菜作为实验对象,得到了这几种蔬菜的真空预冷实验数据,为真空预冷技术的推广应用提供参考.     

果蔬预冷风速与风机能耗和预冷效果的实验研究及分析

果蔬预冷中,预冷风速是决定风机能耗及预冷效果的重要因素之一.通过对风机能耗和预冷效果与预冷风速之间的分析,分别建立了风机能耗和预冷终止温度与预冷风速关系的模型.在这基础上分别进行了预冷风速为1m/s和2m/s及它们之间3种不同组合的苹果预冷实验.理论及实验结果表明,在预冷过程中,进行变风速预冷能取得较好的节能效果,同时可以达到相似的预冷效果.在实验中,基于2m/s实验数据,最小的节能率达到12%,而预冷效果相差2℃.     

对易腐货物在运输中干耗的研究分析

本文深入探讨了冷藏运输中易腐货物的干耗问题,提出了根据货物降温的不同阶段计算干耗的新方法,获得了干耗的理论计算模型,并进行了仔细的实际计算与分析。结果表明,尽管快速降温的时间仅占运输时间的１０％ 左右,但此期间的干耗量却占运输过程中总干耗量的５０ ％ 左右。运输中的平均总干耗量约占货物重量的３ ％ ,平均每天０３ ％ 。影响干耗的主要因素是货物的初始温度、货物的暴露面积、车内的相对湿度、制冷系统的制冷能力和运输时间或速度等     

白菜真空预冷热质迁移模型及实验研究

以柱状白菜为研究对象,建立了热质迁移数学模型,并对该模型采用实验的方法加以验证。在设定真空压力状况下,就真空室内的压力变化,白菜自身温度变化,真空室内相对湿度变化以及白菜质量损失情况,模拟与试验进行了对比,其结果相接近。文章分析了试验过程参数变化的机理及误差产生的原因,模型对柱状蔬菜真空预冷的理论研究有参考价值。     

低温LNG罐箱预冷介质用量及其过程控制的研究

通过实验方法,探索低温LNG罐箱预冷操作过程中,各细节的控制要求,探索进液量、预冷静止时间、最低温度及最终效果之间的相互关系,并结合经验公式进行比较,分析得出可靠进液量和预冷效果的关系,满足工业化产品的要求。     

集预冷杀菌多功能气调包装机的设计

在集成预冷、杀菌、气调包装三功能基础上,对当前气调保鲜包装机一般为补偿式气调而置换率较低,基于压力配气方式而气体混合精度差,半自动化而生产效率低,冷却不到位并存在二次污染等问题进行了改进,设计了一种集预冷、杀菌、气调包装一体化的全自动设备。此外,就不同包装盒及不同产品所需冷量的不同,设计了2种预冷系统模式:将半导体制冷技术应用于预冷预置气体,适用于小型冷量的包装产品,并可相应地提高其配气精度;采用制冷压缩机真空预冷系统,适用于需较大冷量的包装产品。同时对制冷模式的选择及所需冷量进行了简单的理论计算和分析。     

多功能果蔬保鲜装置的研制及大白菜真空预冷实验

本文介绍了一种兼具"真空预冷、减压贮藏、冰温真空干燥"三个功能于一体的果蔬保鲜装置及其工作原理,并对该装置的真空系统、制冷系统、加湿换气系统、控制系统的组成及工作过程进行了详细介绍与分析。利用该装置做了大白菜真空预冷及减压贮藏实验,结果表明,随着舱内压力的降低大白菜真空预冷过程可分为三个阶段:温度缓降、温度骤降及温度持平阶段;以大白菜失水率3.34%等实验数据分析了此装置的技术特点和独特优势。该装置可以从预冷、贮藏两个阶段缩短冷链物流的运转周期,减少果蔬搬运造成的机械损伤,从而将在商业化普及应用中创造更多的经济效益。     

Effect of aluminium evaporation loss on pore characteristics of porous FeAl alloys produced by vacuum sintering

This study investigated the effect of aluminium evaporation loss on the pore characteristics of a porous Fe–Al alloy. The porous Fe–Al alloy samples were produced through pressureless reaction synthesis from powder compacts of elemental Fe and Al powder mixture under vacuum. Cellular characteristics were analysed by X-ray diffraction, scanning electron microscopy and energy dispersive spectrometry. The maximum open-cell pore size, open-cell porosity and permeability increased with increasing sintering temperature. Based on the Miedema model and Langmuir equation, the evaporation weight losses were calculated and in good agreement with the experimental measurements. The relationship between the evaporation weight losses and the cellular morphology and physical properties of the porous Fe–Al samples is also discussed.     

Effect of pre-treatment with carbon monoxide and film properties on the quality of vacuum packaging of beef chops

Beef chops (longissimus dorsi) were pre-treated with 5% carbon monoxide (CO) − 95% N₂ for 24 h, vacuum packed in thermo-contractile bags and stored at 0 ± 2°C. Shelf life, as determined by the viable aerobic bacterial load, was 11 weeks. Vacuum-packed chops with heat-contractile film produced a smaller drip loss, had a more intense red colour and higher colour stability under storage than chops with non-heat-contractile film. Chops pre-treated with CO were redder during all the storage period than controls without CO. The pre-treatment did not affect pH, water-holding capacity, drip loss or rancidity of the meat stored in vacuum. Copyright © 2008 John Wiley & Sons, Ltd.     

Factors affecting the carriage of meat in containers

Changes in trading patterns call for some reappraisal of currently accepted design criteria. The effects of packaging, including vacuum packaging, on the required temperature distribution, and its effect on handling and weight loss are discussed. Proposals are made to improve temperature control and air distribution in integral containers. Examples are quoted covering both in-service and controlled test conditions.     

甜椒真空冰温保鲜贮藏实验研究

本文将真空贮藏和冰温保鲜这两大第三代保鲜贮藏技术相结合,提出了真空冰温保鲜贮藏的概念。以甜椒为研究对象,对不同贮藏压力、贮藏温度及处理方式下的样品进行真空冰温保鲜贮藏实验研究。测得贮藏过程中的失重率、腐烂指数及商品率,并根据大量的实验数据,进行对比分析,得到真空冰温保鲜贮藏条件下,甜椒的最佳贮藏参数。     

DyAl薄膜真空扩散渗及时效处理对烧结NdFeB磁性和耐蚀性的影响

采用直流磁控溅射的方法,在烧结NdFeB磁体表面制备DyAl合金薄膜,对镀膜样品进行了真空扩散渗(800℃×6h)和时效处理(900℃×2.5h+490℃×5h),研究其耐热性和耐蚀性。经过真空扩散渗及时效处理,磁体的内禀矫顽力Hcj提高14.7%,磁体PCT失重从26.155 mg/cm2降低为1.731 mg/cm2,动态极化曲线显示Dy、Al元素的扩散改变了基体的腐蚀电位和腐蚀电流。结果表明,DyAl薄膜扩散进入NdFeB表层基体中,提高了磁体的耐热性和耐蚀性。     

去皮山药的护色保鲜包装研究

为了解决去皮山药易褐变的问题,利用糖或碱溶液对去皮山药进行浸泡处理,根据山药的褐变度分别得出最佳的浸泡液组成;根据单因素试验结果制成糖碱复合浸泡液对去皮山药进行预处理,再分别选用生物气调保鲜膜、百合保鲜膜、普通PE保鲜膜对其进行包装,通过对山药的色差、硬度、失重率及菌落总数的测定,研究不同保鲜膜对山药的保鲜效果。研究表明：质量分数为9%的糖溶液、pH值为9的碱溶液对山药的护色效果较好;生物气调保鲜膜对山药的保鲜效果较好。     

不同终压对火龙果切片真空预冷效果的影响

研究了不同终压(400～800Pa)下真空预冷对火龙果切片降温速率、失水率以及预冷后在4℃冷藏温度下72h内的持水性、pH值、硬度和色泽指标的影响。结果表明:终压变化对降温速率和失重率的影响都不大,然而,适当的升高终压却可以延缓持水性、pH值、硬度及色泽的变化。综合比较得知,预冷终压在700～800Pa时火龙果切片在4℃冷藏温度下产品货架期最长,为60h。     

Active packaging technology to retain storage quality of pear cv. “Bartlett” during shelf-life periods under ambient holding after periodic cold storage

Response of “Bartlett” pears harvested at commercial maturity (104.29-N firmness and 3.15 starch iodine rating) to various active packaging conditions using O₂ (Fe powder) and ethylene (KMnO₄) scavenger sachets in low-density polyethylene (LDPE) film bags (25.4 and 50.8 μm), cold storage (2 ± 1°C with 95 ± 2%), and shelf-life holding periods under ambient conditions (24 ± 3°C; 68 ± 5% relative humidity [RH]) was recorded as changes in physic chemical parameters. The fruits were packed in 25.4- and 50.8-μm LDPE film bags containing 5%, 10%, and 15% Fe and KMnO₄ powder incorporated on silica as inert carrier in form of sachets. After packaging the fruits airtight in film bags, they were placed in corrugated fiber board (CFB) boxes (29 × 23 × 14 cm; L × B × H). Fruits packed in 50.8-μm LDPE film bags with sachets containing 15% Fe powder recorded maximum fruit firmness, total soluble solids (TSS), titratable acidity, and ascorbic acid with minimum spoilage, weight loss (physiological loss of weight [PLW]), pectin methylesterase (PME), polygalacturonase (PG) activity, and respiration rate and increase in fruit calcium content and highest level of overall acceptability (color, taste, aroma, and texture) after periodic cold storage and ambient shelf-life periods. The effect of different treatments was compared by post hoc analysis using Tukey's test, which also revealed significant differences among different treatments. Our findings also revealed that pear fruit retains edible quality until fruit firmness > 30.89 N, TSS > 10.0%, and weight loss < 9.00%.