Transport property

The transport properties, particularly viscosity and diffusion, of a perfect gas are discussed and the concepts of gas dynamics are briefly mentioned. Such methods can be applied to flowing gas in, for example, pipework or nozzles and jets. 

Typical vacuum processes and plants can be classified according to the pressure regions in which they operate. These regions are shown overleaf. 

The term vacuum is applied to pressures below, often considerably below, atmospheric pressure. 

The object of vacuum technology is to reduce the number density of gas particles in a given volume of a system. At constant temperature, this 

Rough Chemical technology (unit operations such as degassing, drying, filtration) 

For the transport properties, we must resort to some other method. These methods are usually specific to the phase, but there are those that are applicable regardless of the phase. 

For example, the viscosity of low pressure gases can be estimated by the following combining rule  

Most correlations use this approach, and the problem becomes one of estimating the parameters 0. For example, Wilke (Reid et al., 1987) gives the following expression  

On the other hand, for liquids, the mixing rule is logarithmic in the pure component viscosity  

- interaction parameter, which requires some experimental data for the mixture 

In this section the transport properties are determined by use of the empirical method suggested by Maxwell [95], on the basis of Clausius mean free path concept. That is, instead of determining the transport properties from the rather theoretical Enskog solution of the Boltzmann equation, for practical applications we may often resort to the much simpler but still fairly accurate mean free path approach (e.g., [20], Sect. 5.1 [48], Sect. 9.6 [119], Chap. 20). Actually, the form of the relations resulting from the mean free path concept are about the same as those obtained from the much more complex theories, and even the values of the pre-factors are considered sufficiently accurate for many reactor modeling applications. 

The overall aim in this analysis is to determine a rough estimate of the transfer fluxes in dilute one-component gases using the elementary mean free path concept in kinetic theory. In this approach it is assumed that the only means for transport of information in the fluid is via molecular collisions. Due to the physical similarity 

At each collision it is assumed to be an equalizing transfer of properties between the two molecules, so in consequence is determined by the relative location of the last collision experienced by a molecule before it crosses the plane at z = zi. This particular distance is thus expected to be related to the mean free path, 1. It is supposed throughout this analysis that the mean free path is small compared to the dimensions of the vessel containing the gas. 

It may be expected that on the average molecules crossing the plane z = zi from the z 1 - / side will transfer the property and those crossing from the zi -1- / side 

The properties iP)m zi-i and iP)m zj+i in (2.596) may then be expanded in a Taylor series about z = zi, since the mean free path is small compared to the distance over which (iP)m changes appreciably. Neglecting terms of order higher than one the result is  

In all cases the flow, the amount of the physical quantity transported in unit time through a unit of area perpendicular to the direction of flow, is proportional to the negative gradient of some other physical property such as temperature, pressure, or electrical potential. Choosing the z-axis as the direction of flow, the general law for transport is 

In these equations, /c j- is the thermal conductivity coefficient, k is the electrical conductivity, C is a frictional coefficient related to the viscosity, and D is the diffusion coefficient. 

Consider the flow of heat from one end of a metal bar to the other. If the hot end is at z = 0 and the cold end is at Z, then in the steady state the temperature as a function of z appears as shown in Fig. 30.1. The value of dT/dz is negative, so that (— dT/dz) is positive. The heat flow is in the positive direction (from the hot to the cold end). If we define 

Electrical conduction and other transport properties of oxides, such as oxygen diffusion, are mainly determined by the presence, concentration and mobility of 

The names and symbols recommended here are in agreement with those recommended by IUPAP [4] and ISO [5.n]. Further information on transport phenomena in electrochemical systems can also be found in [32]. 

The following symbols are used in the definitions of the dimensionless quantities mass (m), time (t), volume (V area (A density (p), speed (u), length (/), viscosity (rj), pressure (p), acceleration of free fall (p), cubic expansion coefficient (a), temperature (T surface tension (y), speed of sound (c), mean free path (X), frequency (/), thermal diffusivity (a), coefficient of heat transfer (/i), thermal conductivity (/c), specific heat capacity at constant pressure (cp), diffusion coefficient (D), mole fraction (x), mass transfer coefficient (fcd), permeability (p), electric conductivity (k and magnetic flux density ( B)  

The behavior of ionic liquids as electrolytes is strongly influenced by the transport properties of their ionic constituents. These transport properties relate to the rate of ion movement and to the manner in which the ions move (as individual ions, ion-pairs, or ion aggregates). Conductivity, for example, depends on the number and mobility of charge carriers. If an ionic liquid is dominated by highly mobile but neutral ion-pairs it will have a small number of available charge carriers and thus a low conductivity. The two quantities often used to evaluate the transport properties of electrolytes are the ion-diffusion coefficients and the ion-transport numbers. The diffusion coefficient is a measure of the rate of movement of an ion in a solution, and the transport number is a measure of the fraction of charge carried by that ion in the presence of an electric field. 

The diffusion coefficients of the constituent ions in ionic liquids have most commonly been measured either by electrochemical or by NMR methods. These two methods in fact measure slightly different diffusional properties. The electrochemical methods measure the diffusion coefficient of an ion in the presence of a concentration gradient (Pick diffusion) [59], while the NMR methods measure the diffusion coefficient of an ion in the absence of any concentration gradients (self-diffusion) [60]. Fortunately, under most circumstances these two types of diffusion coefficients are roughly equivalent. 

There are a number of NMR methods available for evaluation of self-diffusion coefficients, all of which use the same basic measurement principle [60]. Namely, they are all based on the application of the spin-echo technique under conditions of either a static or a pulsed magnetic field gradient. Essentially, a spin-echo pulse sequence is applied to a nucleus in the ion of interest while at the same time a constant or pulsed field gradient is applied to the nucleus. The spin echo of this nucleus is then measured and its attenuation due to the diffusion of the nucleus in the field gradient is used to determine its self-diffusion coefficient. The self-diffusion coefficient data for a variety of ionic liquids are given in Table 3.6-6. 

Transport numbers are intended to measure the fraction of the total ionic current carried by an ion in an electrolyte as it migrates under the influence of an applied electric field. In essence, transport numbers are an indication of the relative ability of an ion to carry charge. The classical way to measure transport numbers is to pass a current between two electrodes contained in separate compartments of a two-compartment cell. These two compartments are separated by a barrier that only allows the passage of ions. After a known amount of charge has passed, the composition and/or mass of the electrolytes in the two compartments are analyzed. Erom these data the fraction of the charge transported by the cation and the anion can be calculated. Transport numbers obtained by this method are measured with respect to an external reference point (i.e., the separator), and, therefore, are often referred to as external transport numbers. Two variations of the above method, the Moving Boundary method [66] and the Hittorff method [66-69], have been used to measure cation (tn+) and anion (tx-) transport numbers in ionic liquids, and these data are listed in Table 3.6-7. 

The measurement of transport numbers by the above electrochemical methods entails a significant amount of experimental effort to generate high-quality data. In addition, the methods do not appear applicable to many of the newer non-haloalu-minate ionic liquid systems. An interesting alternative to the above method utiHzes the NMR-generated self-diffusion coefficient data discussed above. If both the cation and anion (Dx ) self-diffusion coefficients are measured, then both the cation and anion (tx-) transport numbers can be determined by using the following Equations (3.6-6) and (3.6-7) [41, 44]  

Ionic Liquid System Cation D, + (10 s- ) Anion(s) Dx- (10 s- ) Temperature (K) Methodl l Ref. 

Thermal conductivity, viscosity (internal friction), and diffusion are referred to collectively as transport properties. For gases, they are all molecular properties. (See Table 3-4). 

In the case of diffusion, different concentrations of a gas in a given volume are equalized as the molecules strive to disperse uniformly. This dispersion is slowed by intermolecular collisions. 

Because the molecular speed and collision frequency increase with temperature, the intensity of the transport processes generally increases with temperature. 

When the pressure changes, the corresponding changes in both the mean free path between collisions and the collision frequency nullify each other. Thus, the trans- 

Intermolecular potential is directly related to the interaction of molecules of different gases, which affects the thermal conductivity of a given gas mixture. Caution should be observed when calculating the thermal conductivity of gas mixtures because a simple proportioning ( weighting ) of the components thermal conductivities can lead to considerable error if those conductivities are substantially different. 

In general the charge carriers in mixed proton-electron conducting materials could be protons, oxygen ions (or oxygen vacancies), hydroxyl ions, electronic-holes and electrons. To determine the nature of the charge carriers and their transport numbers, various defect structure models have been presented [36-38]. These defect models were fitted to the total electrical conductivity data measured 

The direct evidence for protonic conduction was confirmed primarily by studying the emf of the following gas concentration cell at high temperatures using the specimen ceramics as the electrolyte diaphragm [44—47]  

N2 and H2 were used as gas 1 or gas 2, in wet or dry states. The relevant ionic transport number is then obtained by comparing the measured emf with the predicted emf from the Nernst equation. 

Material Total electrical conductivity (Scm-i) at900°C Activation energy kj mol (eV molecule-3) Ref. 

Electrolyte Ref. Cas1/Cas2 Total conductivity S cm Transference number at 600°C 

In addition to mechanical properties, other physical properties of polycrystaUine materials, such as electrical and thermal conduction, are also affected by microstmcture. Although polycrystals are mechanicaUy superior to single crystals, they have inferior transport properties. Point defects (vacancies, impurities) and extended defects (grain boundaries) scatter electrons and phonons, shortening their mean free paths. Owing to 

The exponent pi is called a scaling exponent. It depends on the dimensionality of the system. For two-dimensional transport, /r= 1.30 and for three-dimensional transport, pu = 2.0 (Stauffer and Aharony, 1994). 

In the following section molecular collisions are discussed briefly in order to define the notation appearing in the exact expressions for the transport coefficients. Diffusion is treated separately from the other transport properties in Section E.2 because it has been found [7] that closer agreement with the exact theory is obtained by utilizing a different viewpoint in this case. Next, a general mean-free-path description of molecular transport is presented, which is specialized to the cases of viscosity and heat conduction in Sections E.4 and E.5. Finally, dimensionless ratios of transport coefficients, often appearing in combustion problems, are defined and discussed. The notation throughout this appendix is the same as that in Appendix D. 

The exact kinetic theory of dilute gases leads to expressions for transport coefficients in terms of certain quantities called collision integrals, which depend on the dynamics of binary intermolecular collisions. These integrals are defined in this section. 

Since the collisions of predominant importance in transport processes are elastic and do not involve chemical reactions, a potential cp may be defined, the negative gradient of which is the force between the two interacting molecules. The interaction may accurately be treated classically for all molecules at room temperature and above. Consideration is restricted to central forces, for which cp depends only on r, the distance between the mass centers of the molecules cp = (r)]. Useful results for more general potentials (which, rigorously, are required to describe interactions of polar molecules) have not been obtained. The arbitrary constant in the potential is defined by (p(co) = 0. 

It is easily seen from classical mechanics that the binary collision problem is mathematically equivalent to a one-body problem in which a body with the reduced mass 

FIGURE E.l. Schematic diagram of the equivalent one-body collision. 

All of the applications of cubic and non-cubic equations of state presented so far refer to equilibrium thermodynamics. Cubic equations of state have been also used for the calculation of transport properties of pure components and mixtures, including viscosity, diffusion coefficient and thermal conductivity. Some recent viscosity calculations will be presented here. 

The viscosity of a liquid mixture, y, can be calculated from the Eyring s absolute rate theory  

Quinones-Cisneros et al. proposed the friction theory (the so called f-the-ory) to predict viscosity using an equation of state. According to f-theory, the viscosity of dense fluids is a mechanical property rather than a transport property. Consequently, the total viscosity of a dense fluid can be written as the sum of a dilute-gas term y q and a friction term t]f through  

Comparison of viscosity rj estimated from the cubic equation of state + NRTL correlation and measured values for (methanol + water) at P = 0.1MPa. , r=285K A, r=300K , 7 =315K T, 

The dilute gas term can be calculated from empirical models based on the kinetic theory of gases, while for the friction term a theory that accounts for repulsive and attractive intermolecular interactions in dense fluids is invoked so that  

The lower carrier density of the 80-nm nanowires compared to bulk bismuth is due to the smaller band overlap in the former. For the 40-nm bismuth nanowires, the carrier density has a temperature dependence similar to bulk bismuth at high temperatures, but it drops rapidly with decreasing temperature at low temperatures. Because the carrier density is highly dependent on wire diameter, the transport properties of bismuth nanowires are expected to be highly sensitive to wire diameter, as will be shown experimentally in the section temperature-dependent resistivity of nanowires.  

Point (microscopic) defects in contrast from the macroscopic are compatible with the atomic distances between the neighboring atoms. The initial cause of appearance of the point defects in the first place is the local energy fluctuations, owing to the temperature fluctuations. Point defects can be divided into Frenkel defects and Schottky defects, and these often occur in ionic crystals. The former are due to misplacement of ions and vacancies. Charges are balanced in the whole crystal despite the presence of interstitial or extra ions and vacancies. If an atom leaves its site in the lattice (thereby creating a vacancy) and then moves to the surface of the crystal, it becomes a Schottky defect. On the other hand, an atom that vacates its position in the lattice and transfers to an interstitial position in the crystal is known as a Frenkel defect. The formation of a Frenkel defect therefore produces two defects within the lattice—a vacancy and the interstitial defect—while the formation of a Schottky defect leaves only one defect within the lattice, that is, a vacancy. Aside from the formation of Schottky and Frenkel defects, there is a third mechanism by which an intrinsic point defect may be formed, that is, the movement of a surface atom into an interstitial site. Considering the electroneutrality condition for the stoichiometric solid solution, the ratio of mole parts of the anion and cation vacancies is simply defined by the valence of atoms (ions). Therefore, for solid solution M X, the ratio of the anion vacancies is equal to mJn. 

Usually the concentration of Frenkel and Schottky defects is relatively small. The maximum mole part of these defects does not exceed several tenths of a percent. Thus, the electroconductivity of such solid solutions is minimal even at the temperatures close to their melting point. 

Apart from the point defects, there are impurity defects in ionic crystals due to some impurities in raw materials. The impact of impurity segregation on ionic conductivity of the solid electrolytes will be considered in detail in section 1.4 of this chapter. The vacancies, developed in the solid solutions during the substitution of the main ion (M in the solid solution M(Mi)02 x) by the ion substituent (Mj) of the different valence, have special meaning for solid electrolytes among impurity defects. In this case, the vacancies must appear from one of the solid-state sublattices 

These solid solutions have several types of charge carriers. They can be represented by anions, cations, electrons, and holes. The Ohm law is fair for each of them. The full current represents itself as a summary of the partial currents by n particles  

The flow of the charged particles in the chemical (p) and electrical (tp) fields can be described by the Wagner equation  

The technology of making the NR/modified EPDM blends has been shown to be suitable for a number of applications such as extruded profile weather strips 

Another major utility of these blends are for making diving suits. A few examples are shown in Fig. 15.18. Pro-Am (Fig. 15.18a) is a rubber suit made from NR/EPDM blend. The main features are good stretch characteristics for comfort and three layer construction for durability. It is ideal for sports, military, rescue, and light commercial applications. The Pro-hd (Fig. 15.18b) is tough NR/ EPDM blend rubber suit made to endure the harshest conditions.USIA(Fig. 15.18c) is also a vulcanized rubber suit made from NR/EPDM blend and it is ideal for sports, military, rescue, and light commercial applications. 

NR/EPDM blends are also used for making rubber boots for agriculture. These boots will have more resistance against cracks caused by ozone. A ratio of 25 75 to 40 60 parts by wt of NR/EPDM is used for preparing these kinds of boots. 

NR/EPDM-based sidewalls of radial tires are also prepared to get more durability and appearance. These blends with an EPDM content varying from 30 to 70 phr are used for making cables and conductors. 

A new method known as reactive mixing has developed recently to increase the cure rate of EPDM by modifying the EPDM phase to make it more reactive toward curatives, using commercially available sulfur donors such as bis-alkylphe-noldisulphide (BAPD), in combination with dithiocaprolactam (DTDC) and/or dithiomorpholine (DTDM). The refinement of reactive mixing process with cost effective sulfur donors is one of the challenges in the maximum utilization of these elastomer blends. 

It can be seen that a reduction in charge carrier can be obtained in materials with a low differential - Nj. This lowering can be achieved, for instance, by adding donors to p-type semiconductors. Such a material is called compensated intrinsic. 

Zeolites are essentially cationic conductors having temperature dependence of resistivity typically displayed by ionic conductors (higher mobility of ions at higher temperatures). By appropriate modifications of the zeolite composition, the conductivities of zeolites can be altered to allow their use as solid electrolytes, membranes in ion-selective electrodes, and as host stmctures for cathode materials in battery systems [84M1, 95A1]. 

The ionic conductivities of the Sn-ferrierites and Sn-silicalites, prepared by treatment of H-zeolite with tin chloride dihydrate, were mentioned in literatrrre [93K1]. The ac birlk corrductivity of Sn-ferrierite is higher than that of H-ferrierite and depends on the water content - Fig. 57. The bulk conductivities are almost indeperrdeirt on temperature in the range between 298 and 388 K. 

Near room temperature, a thermal conductivity X = 0.180 mW-cm -K has been measured by the hot-wire method [1,2]. This was used to evaluate a viscosity r] = 2x 10 P [1]. For X and T] up to 5000 K calculated from a Lennard-Jones potential with potential constants estimated from the molar volume at the boiling point and from the critical temperature, see [3]. 

The conductivity of well-purified solvents is very low and generally can be ignored. Values of the specific conductance, k, have been reported by Riddick et al. [1] for many of the solvents listed here, Table 3.7, but those that are 1 Sm are suspect, in that they are possibly due to the presence of impurities, not least of which is CO absorbed from the air. The true conductivity of a solvent is proportional to the number of charge carriers, that is, ions resulting from self-ionization (autoprotolysis for protic solvents, see Section 3.3.3) and to its fluidity (the reciprocal of its viscosity, see below). 

Of more consequence is the self-diffusion ability of the solvent molecules, D, obtained from isotopically labeled solvent molecules or from the band widths of NMR signals. The values thus determined are shown in Table 3.7. The self diffusion coefficient follows an Arrhenius-type expression with regard to the temperature  

A relationship has been found by Marcus [28] between the viscosities of solvents and their relative free molar volumes, (V-V )IV = (1-V IV), on the one hand, and their molar enthalpies of vaporization, ATT, on the other. The former describes the space available for the movement of the solvent molecules and the latter measures the tighmess of the mutual binding of the molecules. These values have to be modified by the number of hydroxyl groups, pertinent to the hydrogen bonding in solvents containing such groups  

TABLE 3.7 Transport Properties of Solvents at 25°C their Specific Conductance k [1], their Self-diffusion Coefficient D [27], their Dynamic Viscosity tj, and its Temperature Derivative ( 9j//oT)  

There is a relationship between the viscosity and the diffusion coefficient for those solvents, the molecules of which have a more or less globular shape  

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The viscosity, themial conductivity and diffusion coefficient of a monatomic gas at low pressure depend only on the pair potential but through a more involved sequence of integrations than the second virial coefficient. The transport properties can be expressed in temis of collision integrals defined [111] by... 

The theory coimecting transport coefficients with the intemiolecular potential is much more complicated for polyatomic molecules because the internal states of the molecules must be accounted for. Both quantum mechanical and semi-classical theories have been developed. McCourt and his coworkers [113. 114] have brought these theories to computational fruition and transport properties now constitute a valuable test of proposed potential energy surfaces that... 

Infomiation about interatomic potentials comes from scattering experiments as well as from model potentials fitted to the themiodynamic and transport properties of the system. We will confine our discussion mainly to... 

The alternative simulation approaches are based on molecular dynamics calculations. This is conceptually simpler that the Monte Carlo method the equations of motion are solved for a system of A molecules, and periodic boundary conditions are again imposed. This method pennits both the equilibrium and transport properties of the system to be evaluated, essentially by numerically solvmg the equations of motion... 

If these assumptions are satisfied then the ideas developed earlier about the mean free path can be used to provide qualitative but useful estimates of the transport properties of a dilute gas. While many varied and complicated processes can take place in fluid systems, such as turbulent flow, pattern fonnation, and so on, the principles on which these flows are analysed are remarkably simple. The description of both simple and complicated flows m fluids is based on five hydrodynamic equations, die Navier-Stokes equations. These equations, in trim, are based upon the mechanical laws of conservation of particles, momentum and energy in a fluid, together with a set of phenomenological equations, such as Fourier s law of themial conduction and Newton s law of fluid friction. When these phenomenological laws are used in combination with the conservation equations, one obtains the Navier-Stokes equations. Our goal here is to derive the phenomenological laws from elementary mean free path considerations, and to obtain estimates of the associated transport coefficients. Flere we will consider themial conduction and viscous flow as examples. 

Wakeham W A, Nagashima A and Sengers J V (eds) 1991 Experimental Thermodynamics Measurement of Transport Properties of Fluids yo III (Oxford Blackwell)... 

Mason E A and McDaniel E W 1988 Transport Properties of Ions in Gases (New York Wiley)... 

Atomistically detailed models account for all atoms. The force field contains additive contributions specified in tenns of bond lengtlis, bond angles, torsional angles and possible crosstenns. It also includes non-bonded contributions as tire sum of van der Waals interactions, often described by Lennard-Jones potentials, and Coulomb interactions. Atomistic simulations are successfully used to predict tire transport properties of small molecules in glassy polymers, to calculate elastic moduli and to study plastic defonnation and local motion in quasi-static simulations [fy7, ( ]. The atomistic models are also useful to interiDret scattering data [fyl] and NMR measurements [70] in tenns of local order. 

Alternatively, the mass transport properties in tire solution can become rate detennining—tire reaction is tlien said to be diffrrsion controlled. 

Wlrile quaternary layers and stmctures can be exactly lattice matched to tire InP substrate, strain is often used to alter tire gap or carrier transport properties. In Ga In s or Ga In Asj grown on InP, strain can be introduced by moving away from tire lattice-matched composition. In sufficiently tliin layers, strain is accommodated elastically, witliout any change in the in-plane lattice constant. In tliis material, strain can be eitlier compressive, witli tire lattice constant of tire layer trying to be larger tlian tliat of tire substrate, or tensile. 

This database provides thermophysical property data (phase equilibrium data, critical data, transport properties, surface tensions, electrolyte data) for about 21 000 pure compounds and 101 000 mixtures. DETHERM, with its 4.2 million data sets, is produced by Dechema, FIZ Chcmic (Berlin, Germany) and DDBST GmhH (Oldenburg. Germany). Definitions of the more than SOO properties available in the database can be found in NUMERIGUIDE (sec Section 5.18). 

Einstein relationships hold for other transport properties, e.g. the shear viscosity, the bu viscosity and the thermal conductivity. For example, the shear viscosity t] is given by ... 

The relationship between heat transfer and the boundary layer species distribution should be emphasized. As vaporization occurs, chemical species are transported to the boundary layer and act to cool by transpiration. These gaseous products may undergo additional thermochemical reactions with the boundary-layer gas, further impacting heat transfer. Thus species concentrations are needed for accurate calculation of transport properties, as well as for calculations of convective heating and radiative transport. 

Supercritical Extraction. The use of a supercritical fluid such as carbon dioxide as extractant is growing in industrial importance, particularly in the food-related industries. The advantages of supercritical fluids (qv) as extractants include favorable solubiHty and transport properties, and the abiHty to complete an extraction rapidly at moderate temperature. Whereas most of the supercritical extraction processes are soHd—Hquid extractions, some Hquid—Hquid extractions are of commercial interest also. For example, the removal of ethanol from dilute aqueous solutions using Hquid carbon dioxide... 

Fluoroacetic acid [144-49-OJ, FCH2COOH, is noted for its high, toxicity to animals, including humans. It is sold in the form of its sodium salt as a rodenticide and general mammalian pest control agent. The acid has mp, 33°C bp, 165°C heat of combustion, —715.8 kJ/mol( —171.08 kcal/mol) (1) enthalpy of vaporization, 83.89 kJ /mol (20.05 kcal/mol) (2). Some thermodynamic and transport properties of its aqueous solutions have been pubHshed (3), as has the molecular stmcture of the acid as deterrnined by microwave spectroscopy (4). Although first prepared in 1896 (5), its unusual toxicity was not pubhshed until 50 years later (6). The acid is the toxic constituent of a South African plant Dichapetalum i mosum better known as gifirlaar (7). At least 24 other poisonous plant species are known to contain it (8). 

In preparation of permselective hoUow-fiber membranes, morphology must be controUed to obtain desired mechanical and transport properties. Fiber fabrication is performed without a casting surface. Therefore, in the moving, unsupported thread line, the nascent hoUow-fiber membrane must estabUsh mechanical integrity in a very short time. 

Tables 2,3, and 4 outline many of the physical and thermodynamic properties ofpara- and normal hydrogen in the sohd, hquid, and gaseous states, respectively. Extensive tabulations of all the thermodynamic and transport properties hsted in these tables from the triple point to 3000 K and at 0.01—100 MPa (1—14,500 psi) are available (5,39). Additional properties, including accommodation coefficients, thermal diffusivity, virial coefficients, index of refraction, Joule-Thorns on coefficients, Prandti numbers, vapor pressures, infrared absorption, and heat transfer and thermal transpiration parameters are also available (5,40). Thermodynamic properties for hydrogen at 300—20,000 K and 10 Pa to 10.4 MPa (lO " -103 atm) (41) and transport properties at 1,000—30,000 K and 0.1—3.0 MPa (1—30 atm) (42) have been compiled. Enthalpy—entropy tabulations for hydrogen over the range 3—100,000 K and 0.001—101.3 MPa (0.01—1000 atm) have been made (43). Many physical properties for the other isotopes of hydrogen (deuterium and tritium) have also been compiled (44).

Membranes and Osmosis. Membranes based on PEI can be used for the dehydration of organic solvents such as 2-propanol, methyl ethyl ketone, and toluene (451), and for concentrating seawater (452—454). On exposure to ultrasound waves, aqueous PEI salt solutions and brominated poly(2,6-dimethylphenylene oxide) form stable emulsions from which it is possible to cast membranes in which submicrometer capsules of the salt solution ate embedded (455). The rate of release of the salt solution can be altered by surface—active substances. In membranes, PEI can act as a proton source in the generation of a photocurrent (456). The formation of a PEI coating on ion-exchange membranes modifies the transport properties and results in permanent selectivity of the membrane (457). The electrochemical testing of salts (458) is another possible appHcation of PEI. 

NISTELUIDS NIST STN programs for calculating thermophysical and transport properties of cryogenic fluids... 

Relations for transport properties such as viscosity and thermal conductivity are also required if wall friction and heat-transfer effects are considered. 

Ideal gas properties and other useful thermal properties of propylene are reported iu Table 2. Experimental solubiUty data may be found iu References 18 and 19. Extensive data on propylene solubiUty iu water are available (20). Vapor—Hquid—equiUbrium (VLE) data for propylene are given iu References 21—35 and correlations of VLE data are discussed iu References 36—42. Henry s law constants are given iu References 43—46. Equations for the transport properties of propylene are given iu Table 3. 

An excellent review of composite RO and nanofiltration (NE) membranes is available (8). These thin-fHm, composite membranes consist of a thin polymer barrier layer formed on one or more porous support layers, which is almost always a different polymer from the surface layer. The surface layer determines the flux and separation characteristics of the membrane. The porous backing serves only as a support for the barrier layer and so has almost no effect on membrane transport properties. The barrier layer is extremely thin, thus allowing high water fluxes. The most important thin-fHm composite membranes are made by interfacial polymerization, a process in which a highly porous membrane, usually polysulfone, is coated with an aqueous solution of a polymer or monomer and then reacts with a cross-linking agent in a water-kniniscible solvent. 

Roland W. Oshe, ed.. Handbook of Thermodynamic and Transport Properties of Alkali Metals, lUPAC, Blackwell Scientific Publications, Oxford, U.K., 1985. 

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