共查询到19条相似文献,搜索用时 484 毫秒
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本文介绍了两种不同的冰套冻制方法--固态干冰法和低温热管法.采用这两种方法分别在两个水三相点容器内冻制冰套,通过实验研究冻制方法对水三相点温度的影响.实验结果表明这两种冻制方法对水三相点温度的影响非常小,即两个水三相点容器所复现的水三相点温度在±0.04mK范围内一致. 相似文献
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不同来源的水三相点容器的比对 总被引:1,自引:0,他引:1
本文介绍了水三相点在开尔文热力学温度和ITS-90国际温标中的重要地位.重点介绍了麦克劳式水三相点容器内冰套的冻制方法及水三相点的复现.同时,NIM与ISOTECH同种结构的水三相点容器进行比对.比对结果表明,不同来源的水三相点容器复现的水三相点值在±0.04mK范围内一致. 相似文献
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液氮冻制冰套法对水三相点温度的影响 总被引:3,自引:2,他引:3
介绍了液氮作为冷却剂在水三相点容器内冻制冰套的方法。利用该方法同时在两个不同真空度的水三相点容器内分别冻制冰套。通过实验,研究了此方法对所复现的水三相点温度的影响。实验结果表明:冻制过程中产生的应力以及开始生成的小冰晶引起水三相点温度偏低;并且,其对水三相点温度的影响随着水三相点容器内真空度的降低而增大。随着应力慢慢消除,小冰晶逐渐长大为大冰晶,所复现的水三相点值逐渐回升并趋于稳定。因此,为了高精度复现和准确测量水三相点,采用该冻制方法时,必须将冰套老化至少5天以后,才可以消除其对水三相点温度的影响。 相似文献
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介绍一种使用精密液体低温槽的水三相点瓶冻制和保存方法。冻制过程简单安全,易于操作,不易损坏水三相点瓶。此种方法冻制水三相点瓶,在实际检测工作中具有较好的实用价值。 相似文献
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水的三相点是热力学温度的唯一基准点,也是1990年国际温标(ITS-90)定义的最基本的、及其重要的固定点.水三相点的复现是通过水三相点瓶的冻制和保存来实现的,本文介绍了一种快速且实用的水三相点瓶冻制方法,并阐述了此种方法的优点. 相似文献
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水三相点的高精度复现及准确测量是保证国际温标ITS-90实施的关键。水三相点容器内高纯水的同位素组成会影响复现的水三相点温度值。为了提高水三相点复现水平,减小氢氧同位素的影响,研制了带有氢氧同位素分析的石英及硼硅玻璃高准确度水三相点容器。为了评价容器的性能,开展了硼硅玻璃和石英水三相点容器的比对。实验结果表明:同位素修正前,石英玻璃和硼硅玻璃水三相点容器复现的水三相点在0.058mK范围内一致;同位素修正之后,容器之间的差异在0.017mK范围内一致。采用高准确度水三相点容器复现水三相点的扩展不确定度为0.066mK(k=2)。 相似文献
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K. Kodaira 《International Journal of Thermophysics》2011,32(11-12):2261-2268
The effect of differences in the amount of ice mantle on the realization temperature of the triple point of water (TPW) was investigated. Three TPW cells were used in the experiment as the TPW cell under test. These TPW cells were manufactured at different times. An ice mantle was prepared for each cell, and the amount of these ice mantles was changed when the ice mantle was re-prepared. Comparison measurements were carried out between a standard TPW cell and the three cells under test, and the temperature difference was measured. As a result, although an identical TPW cell was used, a change in the temperature difference was observed when the amount of ice mantle was different. In the case of the TPW cell that was manufactured 30 years ago, the observed temperature change was larger than 0.1 mK. It is considered that the principal cause is the dissolution of glass elements from the TPW cell. 相似文献
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To investigate an ideal container material for the triple point of water (TPW) cell and to reduce the influence to the triple-point
temperature, due to the deviation of the isotopic composition of the water, both borosilicate and fused-quartz glass shelled
TPW cells with isotopic composition substantially matching that of Vienna Standard Mean Ocean Water (VSMOW) were developed
and tested. Through a specially designed manufacturing system, the isotopic composition, δD and δ18 O, of the water in the TPW cell could be controlled within ±10‰ (per mil) and ±1.5‰, respectively, resulting in control of
the isotopic temperature correction to better than ± 8 μK. Through an ampoule attached to the cell, the isotopic composition
of the water in the cell could be individually analyzed . After manufacture, the initial triple-point temperatures of the
two types of cell were measured and compared to assess the quality of the cells and manufacturing process. Cells fabricated
with the new system agree within 50 μK. Two innovatively designed borosilicate and fused-quartz TPW cells were made, each
with six attached ampoules. One ampoule was removed every 6 months to track any changes in purity of the water over time. 相似文献
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In 2005, the National Institutes of Standards and Technology (NIST) and Fluke’s Hart Scientific Division initiated a study
to validate the isotopic correction algorithm applied to the realization temperature of triple point of water (TPW) cells.
Additionally, the study quantified the impact of water sample impurities on the TPW cell realization temperature. For this
study, eight TPW cells containing water of the same nominal isotopic concentration as Vienna Standard Mean Ocean Water (VSMOW)
were used. Five of the cells were manufactured with fused-quartz envelopes and the remaining three with borosilicate envelopes.
One TPW cell of each type was uniquely designed so that water samples could be periodically removed to analyze the isotopic
composition and to monitor any changes in water purity with time and thereby correlate changes in composition with changes
in realization temperature. The borosilicate TPW cells gave an average drift of −13 μK · yr−1 and the more stable fused-quartz TPW cells gave an average drift of −2 μK · yr−1. 相似文献
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Three comparisons of different triple-point-of-water (TPW) realizations in Europe have been organized under the auspices of
EUROMET (EUROMET Projects 278, 549, and 714). Thirty European national metrology institutes were involved in these three comparisons
that took place from 1994 to 2005. The aim of these successive projects was to assess the uncertainties associated with the
practical realization of the triple point of water in Europe. Fifty-four TPW local cells were compared to a traveling standard
cell (ref 679) circulated with an isothermal enclosure. The same equipment was used for the three projects, and LNE-INM regularly
checked the stability of the TPW standard cell. Recently, LNE-INM has devoted efforts to bring the French standard at the
triple point of water into close agreement with CIPM Recommendation 2 (CI-2005). The isotopic fractionation between water
and ice when the cell is in use was experimentally studied. Several new TPW cells delivered by the manufacturer with water
samples were added to our batch of reference cells. A French laboratory analyzed the isotopic compositions of these samples.
These actions allow the French national definition of temperature at the triple point of water to be changed. A new temperature
was associated with TPW cell 679 in agreement with the CIPM recommendation. In this presentation, the latest TPW cell measurements
carried out by LNE-INM are presented. The results from EUROMET Projects 278, 549, and 714 are investigated in light of these
changes. 相似文献
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K. D. Hill 《International Journal of Thermophysics》2014,35(3-4):611-619
Contamination of triple-point-of-water (TPW) cells by the chemical components of the borosilicate glass that contains the water is now widely recognized as the principal contributor to long-term drift of the cell temperature. To add to the available experimental data, a comparison of 24 TPW cells of various ages (from 10 years to 59 years), manufacturers (NRC, Jarrett, Isotech), and materials (borosilicate glass and fused quartz) was undertaken in 2013. Twelve cells from this group were compared to one another in 1997. By comparing the current inter-cell temperature differences to those determined 16 years earlier, it was found that some cells have remained stable, others have become colder (as might be expected from ongoing dissolution of the glass), and one or two show an apparent increase in temperature that seems anomalous. Also included among the 24 cells are five cells of borosilicate glass and five of fused quartz that were purchased 10 years ago. By comparing the relative temperature differences among this group of borosilcate and fused-quartz-encapsulated cells to the values obtained when they were last compared 6 years ago, it was found that the average temperature of the borosilcate group of cells decreases by \(-6\,\upmu \mathrm{K}\,{\cdot }\,\mathrm{year}^{-1}\,({\pm }2\,\upmu \mathrm{K}\,{\cdot }\,\mathrm{year}^{-1})\) , in reasonable agreement with an average drift of \(-4\,\upmu \mathrm{K}\,{\cdot }\,\mathrm{year}^{-1}\) suggested 12 years ago. It was concluded that fused quartz is the superior container for TPW cells. 相似文献
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In order to investigate mechanisms of phase transitions of supercooled water in a triple-point-of-water (TPW) cell when a mush method was used to create an ice mantle, an automated apparatus using small TPW cells was developed to obtain the TPW. In this article, the design principle, the apparatus, and the procedure for an automated formation of ice mantles in small TPW cells are described. Supercooled water in small TPW cells spontaneously transformed into uniform metastable dendritic crystals throughout the cells at supercoolings ranging from 5.85 °C to 8.77 °C and then changed into stable hexagonal closed-packed cellular crystals, forming an outer ice mantle from the outside inward. Some pertinent explanations based on thermodynamic solidification theory were used to describe the phase transition process in the mush method. In addition, the experimental results indicated that the realized temperatures of water in the small TPW cells were in good agreement within 0.1 mK approximately 6 h after the initial spontaneous crystallization had occurred. Finally, the small TPW cells (s/n 008 and s/n 001) were directly compared with a conventional TPW cell (s/n NIM-1-211); the temperature differences between the small TPW cells and the regular TPW cell were less than 0.21 mK. 相似文献
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Miruna Dobre 《International Journal of Thermophysics》2008,29(3):799-807
The definition of the kelvin is based on the triple-point temperature of highly pure water having the isotopic composition
of ocean water (more specifically, the isotopic composition is equivalent to that of VSMOW). Belgian national metrology realizes
the triple point of water (TPW) as the mean of temperatures measured in three sealed cells. In order to take into account
the isotopic composition effect on TPW temperature, the ensemble of cells was replaced in 2006. Three new cells, with isotopic
analysis of the contained water, were bought from different manufacturers. The new group of cells was compared to the old
TPW national realization in order to quantify the effect of moving towards a new reference. Two different standard thermometers
were used in all the cells to take 10 daily measurements on two different ice mantles. The measured resistances were corrected
for hydrostatic head, self-heating, and isotopic composition (when available) before calculating the difference. A difference
of about 87 μK was found between the old and the new national references. This difference is transferred to customers’ thermometers
and cells through calibrations, and the change has to be documented in each new calibration certificate. An additional consequence
of the new ensemble cell implementation is the significant reduction in the spread of deviations of individual cells from
the mean temperature. The maximum difference between two cells of the ensemble is 96 μK for the old reference cells and 46 μK
for the new reference cells corrected for isotopic composition effects. 相似文献