银、铝、锌和锡凝固点的高精度复现

我们成功复现了90国家温标定义的固定点：银、铝、锌和锡凝固点。本文介绍了这些凝固点的是现方法和实验结果，表明能满足建立0－961．78范围内90国际温标的高精度复现系统的要求。     

中温区定点炉自动控温装置的设计

一、引言根据ITS-90温标的规定,从平衡氢三相点（13.8033K）到银凝固点（961.78℃）之间,T90用铂电阻温度计来定义。它使用规定的内插方法以及相应的定义固定点组来分度。通常,每个固定点都有相应的固定点炉来复现固定点的温度。本文中,笔者主要讨论的是比较常用的一段温区（0℃～419.527℃）,即第八温区定点炉的自动控温装置的设计问题。     

三段控温固定点炉复现铝凝固点研究

固定点炉垂直温场均匀性是影响ITS-90国际温标固定点温坪质量的重要因素。为了提高铝凝固温坪的复现水平,设计了三段控温固定点炉,利用金属外壳铝固定点容器,研究了垂直温场均匀性及其影响因素;在此基础上,采用连续热流密度法高精度复现了铝凝固点。实验结果表明:通过调整上部、中部、下部炉温的设置,可改善固定点炉温场均匀性,铝凝固温坪4h内的温度变化在1mK以内;此外,在实验条件下,高纯铝相变的过冷度约为0.14℃。     

快速复现水三相点温度的一种方法

水三相点是指水的三相（固、液、汽）共存时的温度。水三相点是国际实用温标中一个极其重要的定义固定点。它也是用来定义热力学温度单位——开尔文的基本点。在国际实用温标（ITS-90）中，通过各温区和分温区来定义T90，在第二温区即从平衡氢三相点（13．8033K）到银的凝固点（961．78℃），T90是由铂电阻温度计来定义的。它使用一组规定的定义固定点及利用规定的内插方法来分度。温度值T90是由该温度计的电阻R（T90）与水三相点时的电阻R（273．16K）之比来求得的。[第一段]     

新型退火炉的研制

研制了新型的退火炉,建立了ITS-90温标定义标准铂电阻温度计检定分度中必须的退火装置.采用先进的加热和控温技术及合理有效的加热器绕制方式,使用铠装加热丝保证绝缘电阻符合要求且无漏电,绕制后加热丝牢固不脱落,杜绝长期使用后温场变化不稳定的现象.炉温呵达700℃,稳定性好,垂直温场优于1.0℃,可用于标准铂电阻温度计的退火,或者用于提供较为稳定的温度源.     

在0～660.323℃温区标准铂电阻温度计的两个二次偏差函数

给出了在0～660．323℃温区标准铂电阻温度计(SPRT)的两个二次偏差函数：一个是由水三相点、锡凝固点和铝凝固点的检定值来确定;另一个由水三相点、锌凝固点和铝凝固点来确定。这两个二次偏差函数是ITS-90温标在0～660．323℃温区标准铂电阻温度计偏差函数的一个很好的近似。使用70支标准铂电阻温度计检验了这两个偏差函数,其误差一般不超过2．4mK,最大不超过4．7mK。     

中温标准铂电阻温度计测温误差的计算方法

本文介绍按照１９００年国际温标（ＩＴＳ－９０）分度，在０￣４２０℃温度范围内提出两种有关分度误差传递分布的计算方法；并且分析了分度误差用外推法传递到６００℃时的测量不确定度大小，说明中温标准铂电阻温度计经过水三相点、锡凝固点和锌凝固点三个固定点上检定后，可作为０￣６００℃扩展温度量程的量值传递标准的可行性。     

标准铂电阻温度计在0—30—℃范围内的不确定度评定

本给出了0-30℃分温区内基于ITS-90温标定义的固定点——镓熔点复现装置的标准不确定及坟展不确定度评定,以及由此引起的0-30℃范围内工作基准铂电阻温度计分度的各温度点上的不确定度。本的分析结果可用于该温区内使用标准铂手工电阻温度计测温结果的不确定度分析。     

对基准铝凝固点扩展不确定度评定

铝凝固点是ITS-90国际温标新增的一个定义固定点.本文对铝凝固定点进行了扩展不确定度评定.     

锡固定点的凝固点与熔点研究

介绍了锡凝固点的特点,锡熔点及锡凝固点的比较,操作及使用。     

Influence of the Freezing and Annealing Conditions on the Realization of Cryogenic Triple Points

As a basis for evaluating the results of an international star comparison of sealed fixed-point cells, dedicated investigations have been directed to the dependence of the melting temperature on different conditions concerning the preparation of the solid phase, i.e., fast and slow freezing, refreezing without supercooling, or annealing at a temperature of only a few mK below the melting temperature. Differences in the typical thermophysical behavior of the four fixed-point substances hydrogen, neon, oxygen, and argon have been found. In the case of hydrogen and oxygen, the quality of the crystal lattice has little influence on the melting temperature. This enables temperature widths of the melting curves of only a few tens of μK, if there are no additional influences. On the contrary, argon samples frozen after supercooling with different velocities of freezing typically melt within a range of 0.3 mK. The melting-curve width can be reduced only by refreezing. A broader melting range of a few tenths of mK has been typically observed for neon cells. Unlike argon, an improvement of the crystal quality by a slow refreezing does not decrease the width of the melting-curve.     

The Comparison of MTDATA with the Melting/Freezing Point Curves of ITS-90 Metal Fixed Points

The International Temperature Scale (ITS-90) is defined in part by a series of metal freezing points between 156 °C and 1,084 °C. These freezing-point cells provide reference temperatures with an uncertainty of realization claimed to be in the range of several tenths of a millikelvin. The impurities in the nominally 99.9999 % pure metals make a major contribution to the uncertainty of realization of the fixed-point temperature. Recently, a new method to correct for the influence of the impurities by summing the individual contributions of each impurity has been suggested. This method is referred to as the “sum of individual estimates” (SIE). NPL is a partner in a Euromet project to improve the realization of ITS-90 metal fixed points. As part of this project, NPL is particularly interested in the fixed-point cells of tin (231.928 °C) and aluminum (660.323 °C). This article describes the use of a thermodynamic model, embodied in NPL’s MTDATA software, to estimate the initial drop in the freezing temperature and the temperature decrease during freezing using both equilibrium and “Scheil” approaches. Calculations of this type establish the effect of single elements, and with the chemical analysis of the metal, enable an estimation of the whole freezing curve. This has been done for a sample of tin from this laboratory, and thereafter, the theoretical curves are compared with previously published experimental data on impurity-doped aluminum, with good agreement, e.g., better than 1 mK over most of the curve for 76 μg · g⁻¹ Ag in Al.     

Intercomparison of the Realization of the ITS-90 at the Freezing Points of Al and Ag among European NMIs

The EUROMET.T-K4 comparison is the regional extension of CCT-K4, an intercomparison of the realizations of the freezing points of Al (660.323°C) and Ag (961.78°C). The intercomparison was organized in four loops. Long-stem standard platinum resistance thermometers (SPRTs) were used as traveling standards: 25 Ω thermometers to be used only at the Al freezing point and two high-temperature standard platinum resistance thermometers (HTSPRTs) to be used only at the Ag freezing point in each loop. Parallel to the measurements with thermometers, the pilots and sub-pilots organized an internal intercomparison using an Ag fixed-point cell. Most HTSPRTs showed a strong drift which is mainly due to mechanical stress and poisoning of the sensor by impurities. This drift can be partially compensated by a correction based on Matthiessen’s rule. An evaluation of the data taking into account both HTSPRTs in each loop, the linkage of the sub-pilots by measurements at the Ag freezing point, and a possible compensation according to Matthiessens’s rule, allows calculation of the results of the participants’ measurements at the Ag freezing point. The results of the participating laboratories are summarized, and proposals for key comparison reference values and linking of the results to CCT-K3 and CCT-K4 are presented.     

草莓液氮速冻工艺研究

采用喷雾式流态化液氮速冻及缓冻,探讨了在选用不同的筛板、风速和食品层高,以及不同的冻结温度下草莓的流化状态,冻结速率与解冻后冻品汁液流失率之间的关系等.结果表明选用开孔率为50%,孔径为5mm的筛板,用3.0m·S-1循环风速对床层高度为4cm的新鲜草莓进行流态化速冻效果最佳;建议采用-50℃以下温度进行冻结,冻品在-26℃冰箱中.贮藏9个月后,解冻时的汁液流失率低于5.8%.     

超声辅助冷冻技术在食品浸渍式冷冻中的研究进展

目的 概述超声辅助冷冻技术在食品浸渍式冷冻中的研究进展,为今后新型技术辅助浸渍式冷冻提供研究方向.方法 研究超声辅助冷冻的成核机理和对冰晶生长的影响,以及超声对溶液性质的影响,并对超声辅助冷冻技术在食品浸渍式冷冻中的应用进行综述.结论 超声辅助浸渍式冷冻技术可以广泛应用在各类食品加工中,有很大的研究和发展空间.超声辅助冷冻技术能够进一步加快食品浸渍式冷冻的冻结速率,减小食品内部冰晶尺寸,较好地改善了冷冻食品的品质和风味,在食品加工中具有广阔的应用前景,可以高效应用于食品工业.     

The Lyophilization of Dispersed Systems: Influence of Freezing Process,Freezing time,Freezing Temperature and RBCs Concentration on RBCs Hemolysis

ABSTRACT

In this work, we studied the influence of different parameters controlling cooling stage on biological dispersed system injury. The human red blood cell (RBCs) was chosen as work model. The study examined the influence of two freezing processes on RBCs hemolysis, one process producing big crystals, the other producing small crystals. Using both processes, we examined the effect of freezing temperature, freezing time, and RBCs concentration on injuries to RBCs. Freezing damage was assessed by the hematocrite measure before freezing and after thawing. The process producing a small number of big ice crystals (Pa) seems—in relation to the one producing a large number of small ice crystals (Pb)—to be less traumatic for the RBC, although the two are not statistically different. Freezing temperature and freezing time influence the preservation of RBCs. At 0 and ?20°C there were high preservation and total hemolysis, respectively. At ?5°C and ?10°C, the RBC hemolysis depends on freezing temperature and freezing time. The RBCs hemolysis rates increases when freezing time increases and when freezing temperature decreases. The rates of RBCs preserved decreases with RBCs concentration some with either the freezing process used (Pa or Pb). More, an accentuation of the difference between the two used freezing processes on RBCs hemolysis was retrieved. The analysis of the conductivity evolution within the RBCs suspension frozen showed that the destruction of the RBCs is had essentially to the solution effects. When the crystallization eutectic takes place, the RBCs are already completely destroyed.     

带喷嘴的连续冻结隧道装置的设计及其冻结效果分析

本文以一个冻结能力为800 kg/h的网带速冻装置为原型,对现有连续冻结隧道装置增设喷射结构,经过静压箱均混的气流再经喷嘴射流后,吹风速度加快,食品冻结时间缩短.理论计算表明:本设计的冻结时间减少到原来的65.3%,单位时间内冻结量提高了53%.     

浸渍冷冻用多元载冷剂的凝固点实验研究

通过实验手段测试了乙醇、氯化钠、水构成的多元载冷剂的凝固点温度,分析了各组分彼此间的影响以及葡萄糖、蛋白质作为添加剂对混合溶液凝固点的影响。通过实验得到了适合不同温度区间使用的载冷剂质量浓度组成:-20℃以上区域:乙醇5%~15%,氯化钠5%~20%;-20℃~-30℃区域:乙醇23%~25%,氯化钠14%~18%;-30℃~-40℃区域:乙醇37%~40%,氯化钠12%~14%;-40℃~-46℃区域:乙醇40%~55%,氯化钠9%~12%。实验结果表明:乙醇溶液加入氯化钠后,溶液的凝固点都有大幅下降;同等浓度的氯化钠溶液,随着乙醇加入的浓度增大,凝固点降低;氯化钠在乙醇水溶液中的溶解的饱和度随着乙醇水溶液质量浓度增加而减小;加入蛋白质可以使溶液凝固点降低1~2℃,葡萄糖对溶液凝固点的影响不明显。     

Freezing processes in high-pressure domains

Experimental freezing of water in high-pressure domain is studied considering temperature reduction (TRF) as well as high-pressure-assisted freezing (HPAF). The most important advantage of HPAF is that the whole volume of the sample is subcooled when an expansion is made, so a rapid and uniform nucleation and growth of ice crystals are produced. In this work through mathematical modelling the amount of ice appearing instantaneously in the latter freezing, is predicted.