Measurement of the Thermodynamic Properties of Single Phases (eBook)

Anthony Goodwin, KN Marsh, WA Wakeham (Autoren)

eBook Download: EPUB

2003 | 1. Auflage
576 Seiten
Elsevier Science (Verlag)
978-0-08-053144-1 (ISBN)

Infos

"This title is a revision of Experimental Thermodynamics Volume II, published in 1975, reflecting the significant technological developments and new methods introduced into the study of measurement of thermodynamic quantities.

The editors of this volume were assigned the task of assembling an international team of distinguished experimentalists, to describe the current state of development of the techniques of measurement of the thermodynamic quantities of single phases. The resulting volume admirably fulfils this brief and contains a valuable summary of a large variety of experimental techniques applicable over a wide range of thermodynamic states with an emphasis on the precision and accuracy of the results obtained. Those interested in the art of measurements, and in particular engaged in the measurement of thermodynamic properties, will find this material invaluable for the guidance it provides towards the development of new and more accurate techniques.

?Provides detailed descriptions of experimental chemical thermodynamic methods
?Strong practical bias and includes both detailed working equations and figures for the experimental methods
?Most comprehensive text in this field since the publication of Experimental Thermodynamics II"

Inhalt

Front Cover 1
Measurement of the Thermodynamic Properties of Single Phases 4
Copyright Page 5
Contents 8
List of Contributors 12
Foreword 14
Acknowledgments 16
Chapter 1. Introduction 20
Chapter 2. Temperature 26
2.1 Thermodynamic Origin of Temperature 27
2.2 International Temperature Scales 29
2.3 Realising the Unit 31
2.4 Fixed Points 36
2.5 Platinum Resistance Thermometry 41
2.6 Radiation Thermometry 50
2.7 Cryogenic Thermometry 53
2.8 ITS-90 and the Thermodynamic Scale 56
2.9 Temperatures below 1 K 57
2.10 Temperatures above 2000 K 59
2.11 Special Thermocouples 60
Chapter 3. Pressure 62
3.1 Electronic Pressure Gauges 64
3.2 Piston Gauges 77
3.3 Pressure Measurements in a Diamond Anvil Cell 87
3.4 Low Pressure 91
Chapter 4. Mixture Preparation and Sampling Hydrocarbon Reservoir Fluids 116
4.1 Preparation of Fluid Mixtures 117
4.2 Sampling Hydrocarbon Reservoir Fluids 124
Chapter 5. Density 144
5.1 Hydrostatic Balance Densimeters with Magnetic Suspension Couplings 146
5.2 Measurement of Density with Vibrating Bodies 168
5.3 Bellows Volumetry 187
5.4 Piezometer 193
5.5 Isochoric Methods 204
5.6 Absolute Density Standards 210
5.7 In Situ Density Measurements 227
Chapter 6. Speed of Sound 256
6.1 Measurement of the Speed of Sound 257
6.2 Thermodynamic Properties from the Speed of Sound 319
Chapter 7. Calorimetry 344
7.1 Flow Calorimetry 346
7.2 AC Calorimetry 355
7.3 Differential Scanning Calorimetry 367
7.4 Nano-Calorimetry 387
Chapter 8. Properties of Mixing 406
8.1 Properties of Gas Mixtures 407
8.2 Mixtures of Liquids 423
8.3 Experimental Techniques for the Determination of Energetic Properties of Inorganic Solids 427
Chapter 9. Relative Permittivity and Refractive Index 452
9.1 Relative Permittivity 453
9.2 Refractive Index 471
9.3 Relative Permittivities of Electrolytes 474
Chapter 10. Extreme Conditions 494
10.1 Low Temperatures 495
10.2 High Temperatures 507
10.3 Molten Metals 523
Index 556

Textauszug

2

Temperature

J.V. Nicholas; D.R. White    Measurement Standards Laboratory of New Zealand
Industrial Research
Lower Hutt, New Zealand

The measurement of temperature is fundamental to thermodynamic measurements and, since publication of Experimental Thermodynamics Volume II, the temperature scale has been updated from the International Practical Temperature Scale of 1968 (IPTS-68) to the International Temperature Scale of 1990 (ITS-90). This chapter covers the implementation of ITS-90 and recent determinations of the fundamental fixed points, which are essential to the practical determination of temperature using secondary thermometers. In addition, the temperature scale at T < 1 K and T > 2000 K are discussed. The use of primary acoustic thermometry for the establishment of the fixed-point temperatures is described in Chapter 6.

2.1 Thermodynamic Origin of Temperature

The scientific meaning for temperature is at the heart of thermodynamics. It arises from the Zeroth Law of thermodynamics that states that if two systems are in thermal equilibrium and one of those systems is in thermal equilibrium with a third system, then all three systems are in thermal equilibrium with each other. Thus, temperature is the property of a system that conveys information about the thermal equilibrium of the system. The Zeroth Law only establishes equality of temperatures and permits the use of any single valued function as an empirical temperature scale. In order to establish a metric scale for temperature, one that allows meaningful ratios of temperature, the Second Law of thermodynamics is used to define an absolute temperature, T, by expressing the law as

S≥δQ/T

  (2.1)

where dS is the change in entropy and δQ is the change in heat. There are other thermodynamically equivalent ways of defining the temperature scale as described in, for example, reference [1].

Equation (2.1) gives a metric temperature scale but requires, in addition, a definition of magnitude and sign in order to define the unit. To establish the thermodynamic temperature scale the Système International d’unités (SI), defines the kelvin, symbol K, by fixing the temperature of the triple point of water, T(H2O, s + 1 + g) = 273.16 K. Over time a variety of other temperature scales have been developed but they are no longer useful for reporting scientific data. The exception is the Celsius temperature scale. The Celsius temperature, t, is related to the absolute temperature by

/∘C=T/K−273.15

  (2.2)

and the unit is the degree Celsius, symbol °C. On this scale the ice point is 0 °C and the triple point of water is 0.01 °C.

In principle, any suitable thermodynamic equation may be used as the basis for a thermometer. However, with the exception of the radiation thermometers used at high temperatures, thermodynamic thermometers cannot achieve the highest precision desired, and are complex and time consuming to use. To overcome these difficulties, an International Temperature Scale, ITS, is defined by the Comité International des Poids et Mesures (CIPM) under the Convention du Mètre, the founding treaty for the SI, and is regularly revised with the current version agreed to in 1990 and known as ITS-90 [2,3]. The ITS are empirical temperature scales giving a close approximation to the known thermodynamic scale, but are more precise and easier to use. All temperature measurements should be traceable to the current ITS. Some earlier ITS were known as International Practical Temperature Scales (IPTS).

Because of the differences between the various temperature scales and because they have the same name for their units, it is often necessary to distinguish between scale temperature and thermodynamic temperature. The symbols T90 and t90 are used for the kelvin and Celsius temperatures on the current scale, ITS-90, and previous scales are similarly denoted, for example, on the International Practical Temperature Scale of 1968 (IPTS-68), T68 and t68 are used for the kelvin and Celsius temperatures.

There are three provisos concerning the scientific use of ITS. Firstly, while the scale is more precise, it does not guarantee thermodynamic accuracy; it is very dependent on the accuracy of the thermodynamic data used to establish the scale as discussed in Section 2.8. For example, recent data indicates that near 300 K the ITS-90 differs from the thermodynamic scale by about 5 mK. Secondly, ITS varies with time because it is updated approximately every 20 years. This means that older thermodynamic data may not be in agreement with recent data. For example, under the IPTS-68 the normal boiling point of water, T68(H2O, 1 + g, p = 0.101 325 MPa), was 373.15 K but under ITS-90 T90(H2O, 1 + g, P = 0.101 325 MPa) = 373.124 K, a difference of 26 mK. Thirdly, the ITS-90 is not strictly single valued; it exhibits non-uniqueness because of both the way it is defined and the properties of real thermometers. For example, two laboratories’ temperature measurements may differ by as much as 2 mK around 400 K, yet both comply with the ITS-90, assuming other uncertainties are negligible. Therefore, at this level of accuracy, measured thermodynamic properties may not appear to be smooth functions.

This chapter introduces high precision thermometry for those requiring a close match to the thermodynamic temperature. To achieve the highest accuracies close adherence to the published guidelines [2] is necessary. Lower accuracy thermometry is covered in other publications and guidelines [4–7]. Since it is not possible to cover all thermometry applications for all possible environments; in this chapter the emphasis is on making measurements traceable to the ITS-90. In particular, the limits on accuracy and precision are examined in detail. Unless otherwise stated, all uncertainties are reported as the standard uncertainty or one standard deviation.

At the extremes of temperature, the use or ITS-90 may not always be appropriate because new techniques for realising the temperature scale are constantly developed. Extensions of thermometry to very high and very low temperatures are outlined.

2.2 International Temperature Scales

ITS-90 covers the temperature range from 0.65 K up to the highest temperature practicably measurable in terms of the Planck radiation law discussed in Section 2.6. The official text for the ITS-90 is published by the Bureau International des Poids et Mesures (BIPM), and an English version is included in the Supplementary Information for ITS-90 [2], where more detailed and practical information is given. Figure 2.1 outlines the main features of ITS-90: the fixed points, the interpolating thermometers, and the ranges for which interpolation formulae are defined.

Figure 2.1 An outline of the main features of ITS-90.

There are three basic stages in establishing the scale. First, the fixed points, that is the melting-points, freezing-points and triple-points of various substances, are constructed in accordance with the BIPM Supplementary Information. Secondly, the readings of thermometers of approved types are determined at one or more fixed points. Finally, any unknown temperature is calculated from the thermometer readings by interpolation using the readings at the fixed points and the specified interpolation equations.

Fixed points are physical systems whose temperatures are determined by a physical process and are therefore universal and repeatable. The most successful systems for temperature references have been phase transitions involving major changes of state, for example, liquid to solid or vapour to liquid. Under the proper conditions, in a fixed-point apparatus, the phase transition will occur at a single temperature determined by the properties of the substance used and not on the apparatus. As the change involves the enthalpy of a phase transition, good temperature stability is possible. When the fixed point apparatus is properly constructed, a small amount of heat transfer between the substance and its surroundings will not cause a temperature change in the substance during the phase transition.

Triple-point systems of many substances make excellent fixed points since they represent an equilibrium between the three phases of the substance: solid, liquid and vapour, which occurs at a single temperature and pressure. Freezing temperatures of pure metals are also highly repeatable but exhibit a pressure dependence, which must be understood and controlled. Normal boiling points are no longer used for defining temperatures because of their very high dependence on the pressure. Table 2.1 lists the ITS-90 fixed points with their defined values. Section 2.4 examines the main types of fixed points.

Table 2.1

The defining fixed points of the ITS-90. The reference resistance ratio Wr(T90) for SPRTs is defined in...

Produkt-Details

• Erscheint lt. Verlag: 3.7.2003
• Sprache: englisch
• Themenwelt: Naturwissenschaften ► Chemie ► Physikalische Chemie
• Themenwelt: Naturwissenschaften ► Physik / Astronomie ► Thermodynamik
• Themenwelt: Technik ► Maschinenbau
• ISBN-10: 0-08-053144-X / 008053144X
• ISBN-13: 978-0-08-053144-1 / 9780080531441