Triple Point Of Water Research Articles

Thermodynamic Simulation of Cascade Cooling System for Vacuum Freeze Drying

Vacuum freeze drying (VFD) is a drying method carried out at pressures and temperatures below the triple point of water. Drying occurs by sublimation. The results of the VFD method are able to maintain the quality of dry ingredients (taste, colour, nutrient, etc.). To achieve a condition below the triple point of water, it is conditioned so that the pressure is under a partial pressure of 6.11657 mbar at a temperature of 0.01°C. The refrigeration system is simulated using refrigerants R-134a and R-22. The purpose of the simulation is to obtain the optimum system conditions. The variables varied were the saturated temperature of the LTC (Low-Temperature Circuit) evaporator, the saturation temperature of the HTC (High-Temperature Circuit) evaporator, the difference in the temperature of the pinch point between the LTC condenser and the HTC evaporator and the temperature of the HTC condenser. The simulation results are the saturated temperature of the LTC evaporator -30°C, the saturation temperature of the HTC evaporator -15°C, the difference in the temperature of the pinch point between the LTC condenser and the HTC evaporator 10°C and the temperature of the HTC condenser 40°C. The highest Coefficient of Performance (COP) of the cascade cooling system with these parameters is 2.55 using a combination refrigerant R22 in HTC and R134a in LTC.

A new interpolation equation in the ITS-90 subrange from the triple point of water to the freezing point of indium

For all the subranges above 0.01 °C, other than the interpolation between the triple point of water (TPW) to the melting point of gallium, temperatures on the international temperature scale of 1990 (ITS-90) are specified without the melting point of gallium. This study suggests a new interpolation equation in the subrange from the TPW to the freezing point of indium which is a polynomial of fractional third order with two coefficients to be determined by the measuring values of standard platinum resistance thermometers (SPRTs)’ resistance ratios at the melting point of gallium (W Ga) and at the freezing point of indium (W In). A sample set of 30 SPRTs from various countries and laboratories is used to quantify the comparisons between this new interpolation and the ITS-90. Analyses show that the reproducibility is significantly improved compared with the ITS-90 in the same subrange. The peak value of overlapping subrange inconsistencies (SRI) from TPW to the melting point of gallium is reduced from 0.91 mK to 0.21 mK. Both the mean and standard deviation of the SRI peak values for the new equation decrease by approximately a factor of four compared to those of the ITS-90 (mean decreasing form 0.20 mK to 0.05 mK and standard deviation decreasing form 0.32 mK to 0.07 mK). Type 3 non-uniqueness (NU3) determinations of the same subrange have also been looked into with a data set of four SPRTs compared in thermostatic baths using a copper block and the results show that NU3 scales down from a range −0.15 mK–0.25 mK of the ITS-90 to −0.10 mK–0.15 mK of the new interpolation equation. Propagation of Uncertainties investigation shows that the new equation inflates merely 7% the measurement uncertainties of fixed points in a relatively short interval from 30 °C to 60 °C.

SIM.T-K9.3: Standard platinum resistance thermometer ITS-90 realizations from the Hg triple point to the Zn freezing point

Main textThis report shows the results of a bilateral comparison of temperature standards between Instituto Nacional de Metrologia, Qualidade e Tecnologia (Inmetro, Brazil), and Trinidad and Tobago Bureau of Standards (TTBS, Trinidad and Tobago), carried out between January and July of 2020. The measurands of this comparison were the W(t90) ratios of two Standard Platinum Resistance Thermometers (SPRTs), used as transfer standards, measured at the zinc freezing point (Zn FP, 419.527 °C), tin freezing point (Sn FP, 231.928 °C), gallium melting point (Ga MP, 29.7646 °C), triple point of water (TPW, 0.01 °C) and mercury triple point (Hg TP, -38.8344 °C).To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/.The final report has been peer-reviewed and approved for publication by the CCT, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Surface premelting of ice far below the triple point

Premelting of ice, a quasi-liquid layer (QLL) at the surface below the melting temperature, was first postulated by Michael Faraday 160 y ago. Since then, it has been extensively studied theoretically and experimentally through many techniques. Existing work has been performed predominantly on hexagonal ice, at conditions close to the triple point. Whether the same phenomenon can persist at much lower pressure and temperature, where stacking disordered ice sublimates directly into water vapor, remains unclear. Herein, we report direct observations of surface premelting on ice nanocrystals below the sublimation temperature using transmission electron microscopy (TEM). Similar to what has been reported on hexagonal ice, a QLL is found at the solid-vapor interface. It preferentially decorates certain facets, and its thickness increases as the phase transition temperature is approached. In situ TEM reveals strong diffusion of the QLL, while electron energy loss spectroscopy confirms its amorphous nature. More significantly, the premelting observed in this work is thought to be related to the metastable low-density ultraviscous water, instead of ambient liquid water as in the case of hexagonal ice. This opens a route to understand premelting and grassy liquid state, far away from the normal water triple point.

Expansivity of Fused Quartz Glass Measured with 6 x 10-10/K

Thermal expansion sometimes dominates uncertainty in a precision measurement. A cell-based refractometer has been designed at NIST which targets 10−6 relative uncertainty in the measurement of helium refractivity; in terms of absolute refractive index at ambient conditions, the accuracy goal is 3 × 10−11. To achieve this level of accuracy, the length of a 0.5 m gas cell would need to be known within 100 nm. This is achievable when cell length is measured by coordinate-measuring machine at 20 °C. However, the refractometer will operate at the thermodynamically known fixed-points of water and gallium, near 0 °C and 30 °C, respectively. The cell is made from fused quartz glass, which has a nominal thermal expansion coefficient of 0.4 (μm/m)/K. Therefore, to scale the accuracy of the dimensional metrology across 20 °C to the triple-point of water requires that the thermal expansion coefficient of fused quartz glass is known within 10 (nm/m)/K, or 2.5 %. A method is described to measure the thermal expansion coefficient of fused quartz glass. The measurement principle is to monitor the change in resonance frequency of a Fabry–Perot cavity as its temperature changes; the Fabry–Perot cavity is made from fused quartz glass. The standard uncertainty in the measurement was less than 0.6 (nm/m)/K, or 0.15 %. The limit on performance is arguably uncertainty in the reflection phase-shift temperature dependence, because neither thermooptic nor thermal expansion coefficients of thinfilm coatings are reliably known. However, several other uncertainty contributors are at the same level of magnitude, and so any improvement in performance would entail significant effort. Furthermore, measurements of three different samples revealed that material inhomogeneity leads to differences in the effective thermal expansion coefficient of fused quartz; inhomogeneity in thermal expansion among samples is 24 times larger than the measurement uncertainty in a single sample.

Novel tribological test rig prototype and primary results of experiments for additively manufactured test samples

This paper presents a new design of tribological test rig - (TTR), reciprocating type, with a ramp characteristic typical of computer numerical control drives. The guide temperature is measured by a series of sensors, calibrated using the triple point of water and gallium melting point methods. The uncertainty of wear measurements is provided. Experiments showed that TTR gives repeatable results of measurements with respect to wear and temperature. Each experiment was performed under different conditions: dry sliding, dry sliding with intermissions, dry sliding with a temporarily increased payload, and sliding with lubrication and with silicon oil residue. Wear rate was determined to predict the wear and compare it with established methods. Normal force and payload were predicted for a set distance and assumed wear. A set of micro-photographs helped to determine the contact surface position.

Gullies on Mars could have formed by melting of water ice during periods of high obliquity.

Gullies on Mars resemble water-carved channels on Earth, but they are mostly at elevations where liquid water is not expected under current climate conditions. It has been suggested that sublimation of carbon dioxide ice alone could have formed Martian gullies. We used a general circulation model to show that the highest-elevation Martian gullies coincide with the boundary of terrain that experienced pressures above the triple point of water when Mars' rotational axis tilt reached 35°. Those conditions have occurred repeatedly over the past several million years, most recently ~630,000 years ago. Surface water ice, if present at these locations, could have melted when temperatures rose >273 kelvin. We propose a dual gully formation scenario that is driven by melting of water ice followed by carbon dioxide ice sublimation.

Effect of ultrasound pretreatment and microwave vacuum drying in the production of dried poniol fruit

AbstractThis study suggested a combination of microwave and vacuum drying to meet the requirements of preserving the nutritional content of fresh poniol fruit, consuming lower energy, and having a faster drying rate. In this study, the influence of microwave power, vacuum level, and citric acid pretreatment level on the product quality of dried poniol was analyzed. The citric acid pretreatment was conducted in an ultrasonicator bath. The pretreated was dried by changing the microwave power () from 400 to 800 W and the vacuum level () from 300 to 600 mmHg. The quality of the dried product was analyzed in terms of total phenolic content (), antioxidant activity (), total change in color (), and rehydration ratio () of dried poniol fruit. The response range in the sequence was between 22.219–38.361 mg GAE/g, 69.037–92.578 %DPPH inhibition, 23.451–40.148, and 1.38–3.81, respectively, at various combinations of independent variables. The optimal combination of independent variables for maximal recovery of total phenolic content, antioxidant activity, rehydration ratio, and minimal color changes was obtained at 440 W power level, 600 mmHg vacuum, and pretreated with citric acid of concentration .8%. Under the optimum combination of independent variables, the total phenolic content, antioxidant activity, rehydration ratio, and total color change values were 37.904 mg GAE/g, 92.973%, 23.906, and 3.307, respectively. Because of the low temperature in the vacuum process combined with the rapid heating time of microwaves, the results indicate that microwave vacuum drying might be a viable alternative method for improving the quality of dried food products.Practical ApplicationsMicrowave vacuum drying is a technology that uses microwave radiation to generate heat in the absolute pressure range between the triple point of water and atmospheric pressure. Heat is generated in microwave vacuum drying by directly converting electromagnetic energy into kinetic molecular energy. Hence, heat is generated deep inside the product being dried. Because interior temperatures are greater than exterior temperatures, evaporating water is driven to the surface, resulting in higher partial pressure. As a result, the moisture evaporating within the product is released through the pore structure of the macro‐capillary system of the solid material, resulting in a faster drying rate. Since the superficial layer does not dry out completely, the surfaces remain porous. This method results in a superior end product that is also very nutritious with enhanced sensory properties. As a result, this approach is used in the chemical, pharmaceutical, and food industries.

Stability of silicon resonator temperature sensors with the Pound-Drever-Hall technique.

In this paper, we research the temperature stability of silicon-based ring resonator thermometers utilizing the Pound-Drever-Hall (PDH) technique. A slight temperature fluctuation of 12.2 mK in 200 s was experimentally detected by immersing the sensor in the triple point of water (TPW) system with ultrahigh precision. Additionally, factors that affect temperature stability, including fundamental thermal noise, laser frequency drift, and power fluctuation were analyzed and calculated theoretically. This shows high consistency with experimental results. Moreover, it is proved that the laser drift can be suppressed from 11.3 pm to 0.013 pm with the developed experimental system based on the PDH technique. The silicon-based ring resonator as a potential platform for precise temperature monitoring is proved based on this work.

Early Microjet Experimentation with Liquid Water in Vacuum.

ConspectusIn this brief look at the history of liquid microjets, I recollect some personal reminiscences on initial challenges for introduction of this method, as well as unexpected problems and exemplary results using this new tool for liquid evaporation and photoelectron spectroscopy studies.Many efficient and direct, atomic level diagnostic instruments in use at solid state surfaces and in gas-phase atom or cluster studies require high vacuum. They have therefore not been applied to investigations of aqueous solutions because liquid water both strongly evaporates and rapidly freezes in vacuum. Only fairly recently, over the past three decades, have liquid microjets been considered as practicable targets for research on liquid-water interfaces in vacuum. The working principle is analogous to the functioning of a free molecular beam source, where molecules enter through a small aperture into a vacuum without being disturbed by subsequent collisions in their original Maxwellian velocity distribution. Similarly, above a microjet surface in vacuum, water vapor molecules do not interact with each other, or with different probe particles, as long as the liquid jet diameter is small in relation to the mean free path of the liquids' vapor at equilibrium conditions. For pure liquid water, this constraint is Djet < λvap < 10 μm for 6.1 mbar vapor pressure at the triple point of water. A high streaming velocity of the liquid jet, >50 m/s, delays freezing and exposes a steadily renewed fresh vacuum surface for experiments.For experimental verification of the microjet free surface concept, H2O vapor velocities were measured in a molecular beam time-of-flight experiment. These studies showed Maxwellian velocity distributions with the expected local water-jet temperatures for 5 and 10 μm jets, whereas larger liquid jet diameters of 50 μm exhibit narrowed vapor velocity profiles. This narrowing is the known signature of incipient, collision dominated, supersonic hydrodynamic expansions in nozzle beam sources. As a completely unexpected new result in evaporation studies of carboxylic acid solutions, freely evaporating acetic acid dimers showed apparent non-equilibrium liquid surface source temperatures several hundred kelvin above the simultaneously measured monomer temperatures, a phenomenon shown to be correlated with surface tension.Continuing with improvements, the vacuum water microjets were implemented inside a photoelectron spectroscopy apparatus that was modified for handling large amounts of water vapor. After initial complications with liquid jet charging phenomena, the first partial liquid-water photoelectron spectra were recorded using 21 eV photons from a He I discharge lamp. In the next step, the equipment was taken to a synchrotron radiation beamline at BESSY II, resulting in substantial improvements of signal intensity and in photon tunability for narrow band monochromatic soft X-rays up to 1 keV. Two early examples of these continuing experiments are considered, briefly, for aqueous alkali halide salt solutions and for the pH-value dependent protonation of an NH2/NH3+ group in an amino acid directly in a photoelectron spectrum of a solution.In conclusion, liquid microjets have opened up a completely new approach to studies of arbitrary liquids with chemical and biological relevance.

The Kelvin Redefinition and Practical Primary Thermometry

In May 2019 four of the seven base units of the International System of Units (the SI) were redefined and are now founded on defined values of fundamental physical constants. One of these was the kelvin which is no longer defined by the triple point of water but instead through a fixed value of the Boltzmann constant. In this paper the kelvin redefinition is introduced and the implications for temperature traceability and practical temperature sensing discussed. This will include outlining new approaches for temperature traceability, as well as discussing the rise of in-process calibration through practical primary temperature sensing approaches (where, in principle, no sensor calibration is required). These forthcoming changes are likely to have significant impact on everyone in the temperature calibration chain, whilst the advent of in-process temperature calibration should lead to step change improvements in process control, energy efficiency and product quality consistency and will help facilitate autonomous production.

A triple point of water cell-based fixed-point blackbody for radiation thermometry

The radiation temperature metrology above 150 °C relies heavily on the use of physical interpolation equations and known reference temperature (provided by solid–liquid phase transition of high-purity metals and metal-carbon eutectic alloys) fixed-point blackbodies. Recent achievements in thermal infrared detector technologies triggered the extension of the scale interpolation below this temperature down to 0 °C by using the reference temperatures provided by Sn, In, Ga fixed-points and ice-point, where the reference temperature of the later is dependent on external parameters. In this work, we demonstrate that the triple-point of water (TPW) based fixed-point blackbody is the metrologically grounded alternative to the ice-point. For this purpose, a fixed-point blackbody, incorporating only a cavity and large area TPW (LATPW) cell was designed, constructed, and validated for the precise calibration of radiation thermometers (RTs) and thermal cameras at the thermodynamic temperature of TPW. The conceptual design of the LATPW cells is similar to the ones used in contact thermometry, where a thermometer well of the cell is employed as a borehole for a cavity, where the cavity is easily detachable. Four different cavities (two different designs with aperture sizes of 40 mm and 50 mm) and three LATPW cells with two distinct well geometries were comparatively studied in several combinations. The largest absolute temperature difference observed between the primary level reference TPW cell (used in contact thermometry) and the LATPW cells is measured to be only 0.37 mK. Radiometric measurements demonstrate that all radiators maximally reflect the blackbody condition including emissivity close to unity, high uniformity across the aperture and high temporal stability. The simplicity of maintenance and easy in-field usage (only distilled water and dry ice are required) make the TPW blackbodies very versatile for the in-situ calibrations of RTs and thermal cameras, allowing its application in many areas including clinical environments.

No country for old borosilicate triple-point-of-water cells

Temperature calibration labs all around the world typically maintain a set of several triple-point-of-water (TPW) cells for regular measurements using the International Temperature Scale of 1990 (ITS-90). This set often includes more-than-10-year-old TPW cells made from a borosilicate glass. In this paper we summarize the problems with old borosilicate TPW cells, using the available literature data, the results of CCT.K7-2021 key comparison and NRC TPW measurements, and highlight the solution to these issues—vitreous-silica TPW cells. The latter have an exceptional long-term stability, as we demonstrate by using: (a) comparative measurements of the same-age, same-manufacturer vitreous-silica and borosilicate TPW cells at NRC in a period from 2007 to 2021, and (b) inductively coupled plasma-mass spectrometry (ICP-MS) analysis of impurities present in the 18 year-old vitreous-silica outlier, cell Q325. Remarkably, not only all NRC vitreous-silica TPW cells remained stable over a 15 years time period, unlike their borosilicate counterparts, but the amount of impurities in the ‘coldest’ cell Q325 (−31 μK from the intercomparison reference value) is comparable to that in the newly purchased vitreous-silica cells. We argue that the most accurate TPW measurements, such as for defining the national TPW references and for the international key comparisons, should rely exclusively on vitreous-silica TPW cells.

NRC measurement set-up and preparatory work for CCT-K7.2021 key comparison of triple-point-of-water cells

This paper describes the NRC measurement set-up and the preparatory work for the CCT-K7.2021 key comparison (KC) of triple-point-of-water (TPW) cells. The preparatory work at NRC (charged with piloting the KC) included a comprehensive testing of the measurement set-up, the definition of the new NRC national standard for the TPW temperature, and the evaluation of the uncertainty budgets relevant for this KC. The new NRC TPW national standard is composed of an ensemble of ten fused silica TPW cells, characterized in both their isotopic composition and impurity content. Three uncertainty budgets were evaluated, corresponding to three different cases involved in the measurements at the pilot laboratory: (a) the temperature difference between two TPW cells, which amounted to 26 μK (k = 2), (b) the temperature difference between a TPW cell and NRC national reference, which amounted to 35 μK (k = 2) and (c) the temperature difference between a comparison participant’s transfer cell and the comparison reference, composed of the average of two NRC national reference cells, which amounted to 19 μK (k = 2).

Photonic and Optomechanical Thermometry

Temperature is one of the most relevant physical quantities that affects almost all processes in nature. However, the realization of accurate temperature standards using current temperature references, like the triple point of water, is difficult due to the requirements on material purity and stability of the environment. In addition, in harsh environments, current temperature sensors with electrical readout, like platinum resistors, are difficult to implement, urging the development of optical temperature sensors. In 2018, the European consortium Photoquant, consisting of metrological institutes and academic partners, started investigating new temperature standards for self-calibrated, embedded optomechanical sensor applications, as well as optimised high resolution and high reliability photonic sensors, to measure temperature at the nano and meso-scales and as a possible replacement for the standard platinum resistant thermometers. This article presents an overview of the results obtained with sensor prototypes that exploit photonic and optomechanical techniques for sensing temperatures over a large temperature range (5 K to 300 K). Different concepts are demonstrated, including ring resonators, ladder-like resonators and suspended membrane optomechanical thermometers, highlighting initial performance and challenges, like self-heating that need to be overcome to realize photonic and optomechanical thermometry applications.

Vacuum Frying Below the Triple Point of Water (VFBTPW) of Frozen Unmarinated Beef Slices

Vacuum Frying Below the Triple Point of Water (VFBTPW) of Frozen Unmarinated Beef Slices

Experimental demonstration of the thermodynamic temperature unit kelvin

This study focuses on the experimental demonstration of the definition of kelvin using a triple point of water (TPW) cell and estimates the measurement uncertainty. The first part of this article is to construct the measurement setup and perform the measurements. The second stage is related with the calculation of uncertainty according to guides to the expression of uncertainty in measurement. The experiment in this study can be a practical and convenient method to show the unit as the fraction 1/273.16 of the thermodynamic temperature of the TPW, 273.16 K.

Metrological Evaluation of Deep-Ocean Thermometers

An accurate metrological investigation was performed on several units of the two de facto standards for deep-ocean temperature measurements—the SBE35 (the reference thermometer) and the SBE3 (the working thermometer) from SeaBird Scientific. Four SBE35 units were repeatedly calibrated against state-of-the-art fixed-point cells (triple point of water at 0.01 °C and melting point of gallium at 29.7646 °C), with calibration uncertainties of approximately 0.2 mK and 0.5 mK, respectively. Three SBE35 units and one SBE3 unit were calibrated in the temperature range 0 °C to 30 °C, again with sub-millikelvin calibration uncertainties, in a recently-developed water–bath calibration facility. All these calibrations evidenced (1) the deviation of each unit from its original manufacturer’s calibration (up to 1.7 mK), which were found to be inconsistent with the manufacturer’s uncertainty claims and (2) unexplained irreproducibilities, which could not be attributed to the calibration system of up to 1.5 mK. The effect of high pressures (up to 60 MPa) on the response of two SBE35 units was investigated by pressurizing the SBE35 units inside a purpose-built compact pressure enclosure. The results of the pressure investigation confirmed the existence of a small device-dependent pressure effect (approximately 0.3 mK at 60 MPa) and the need for individual temperature–pressure calibration of each SBE35 unit.

On the long-term stability of the triple-point-of-water cells

Slow dissolution of the borosilicate container of triple-point-of-water (TPW) cell is widely recognized as the main cause of long-term drift in observed triple point temperature. We add to the available experimental data a comparison of two large batches of TPW cells (67 cells in total) of various ages (from 1 year to 64 years), manufacturers (NRC, VSL, Fluke, Isotech, etc), and materials (borosilicate glass and fused-silica) which was undertaken in 2018. After measuring the TPW temperatures realized by all 67 cells, 12 borosilicate cells were opened and their water was analyzed by Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) in order to correlate their impurity content with their respective age and their realized TPW temperature. No direct correlation was observed between the TPW cells age/impurity content and their measured triple-point temperature for neither borosilicate cells nor fused silica cells (Pearson’s correlation coefficient rxy is within the range −0.60 ≤ rxy≤ +0.40 for all the pairs considered). For fused-silica cells, the results indicate that after the isotopic variation in the water source is taken into account, the long-term drift due to the dissolution of glass envelope, if any, is negligibly small: (+0.4(±0.6) µK·yr−1 reported herein). Given that all the fused-silica cells realize the TPW temperature within 100 µK of NRC and VSL national reference cells and since the analyzed time period of 15 years is equal to the average lifespan of a TPW cell, we conclude that fused-silica TPW cells are superior to those made from borosilicate glass.

The physics of temperature

Heat: a measure of the total kinetic energy of a body. Measured in joules (J). It depends on the mass of the body and the specific heat capacity of the body. Temperature: a measure of the average kinetic energy within a body. It describes the potential for heat energy to move from one body to another down a gradient from an area of high temperature to an area of lower temperature. It is measured using a temperature scale which is defined against fixed physical events such as absolute zero or the triple point of water. Heat capacity: the amount of heat energy necessary to be added to an entire body to increase the temperature by one degree Kelvin (J/K). Specific heat capacity: the amount of heat energy necessary to be added to one kilogram of a body to increase the temperature by one degree Kelvin (J/K/kg). Absolute zero: a hypothetical temperature at which all molecular movement stops (zero kinetic energy). This is not possible in reality. The ice point: this is the temperature at standard pressure (101.3 kPa) at which water exists in both a solid (ice) and a liquid form. Designated as 0 oC or 32 oF. The steam point (boiling point): the temperature at standard pressure (101.3 kPa) at which water exists in botha liquid and a vapour form. Designated as 100 oC or 212 oF. Triple point of water: the temperature at a pressure of 611 Pa (0.006 atm) at which water exists in a solid (ice), liquid and a vapour form. Designated as 0.01 oC.