Determination of temperature and pressure

Techniques for accurate and reproducible measurement of temperature and temperature differences are essential to all experimental studies of thermodynamic properties. Ideal gas thermometers give temperatures that correspond to the fundamental thermodynamic temperature scale. These, however, are not convenient in most applications and practical measurement of temperature is based on the definition of a temperature scale that describes the thermodynamic temperature as accurately as possible. The analytical equations describing the latest of the international temperature scales, the temperature scale of 1990 (ITS-90) [1, 2] 

Chemical Thermodynamics of Materials by Svein St0len and Tor Grande 2004 John Wiley Sons, Ltd ISBN 0 471 492320 2 

Between the triple point of equilibrium hydrogen (13.8033 K) and the freezing point of silver (1234.93 K), Tgo is defined by means of platinum resistance thermometers calibrated at specific sets of defining fixed points. The temperatures are given in terms of the ratio of the resistance of the thermometer at temperature Tgo to the resistance at the triple point of water  

The temperature Tgo for a specific resistance thermometer is calculated from the equation 

Type of transition Compound T in K Type of transition Compound T in K  

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He also gives formulas for determination of temperature and pressure of detonation of such mixtures... 

In the preceding section, which on p. 13 was lieaded Chemical Equilibrium viewed in its External Aspects, we were concerned, on the chemical side with determinations of relative masses, and on the physical with determinations of temperature and pressure, and sometimes of volume. 

Tracy R. J., Robinson P., and Thompson A. B. (1976) Garnet composition and zoning in the determination of temperature and pressure of metamorphism, central Massachusetts. Am. Mineral. 61, 762-775. 

Leardini, L, Cadeddu, M. and Schiavoni, M. (1961) Tests on a cavern for the determination of temperature and pressure transients in a case simulating a major Loss of Coolant-type reactor accident , Energia Nucleare, February. 

Mainly, the Q-branches of simple molecules, like di-, tri-, and four-atomic as well as spherical XY4 top molecules have been studied. As an example Figure 10 shows the Q-branch of methane. The complicated rotational structure seen there has been resolved by applying this powerful nonlinear Raman technique. This very high resolution of the order of 10 cm i allows us to study in detail colli-sional effects, which is of particular importance as a basis for the determination of temperatures and pressures. 

Regnault s method Obsolete method for determining gas densities by direct weighing of a known volume of gas under known conditions of temperature and pressure. 

The general problem is to determine at given conditions of temperature and pressure, the quantities and compositions of the two phases in equilibrium starting from an initial quantity of material of known composition and to resolve the system of the following equations ... 

Surface Area. Surface area is measured by determining the quantity of nitrogen gas that adsorbs on the particle/crystal surfaces of a dry sample. Determination of surface area by measuring adsorption at gas—soHd interfaces is covered extensively in the Hterature (84). Instmments such as the FlowSorb 2300 are used to control the adsorption/desorption within specific conditions of temperature and pressure. 

Reactive System Screening Tool (RSST) The RSST is a calorimeter that quickly and safely determines reactive chemical hazards. It approaches the ease of use of the DSC with the accuracy of the VSP. The apparatus measures sample temperature and pressure within a sample containment vessel. Tne RSST determines the potential for runaway reactions and measures the rate of temperature and pressure rise (for gassy reactions) to allow determinations of the energy and gas release rates. This information can be combined with simplified methods to assess reac tor safety system relief vent reqiiire-ments. It is especially useful when there is a need to screen a large number of different chemicals and processes. 

A useful concept in determining stability in the atmosphere is potential temperature. This is a means of identifying the dry adiabat to which a particular atmospheric combination of temperature and pressure is related. The potential temperature 0 is found from... 

When determining pressure rehef requirements, one should calculate capacities of control valves for the relieving conditions of temperature and pressure, since these are in many cases significantly different from capacities at normal operating conditions. Downstream equipment must be analyzed imder relieving conditions. 

The experimental values of the critical diameter were determined over a wide range of temperatures and pressures. 

Molecules in high-pressure areas flow into regions of lower pressure, generating wind. This continual interplay of temperature and pressure plays a major role in determining our planet s weather. 

Adiabatic calorimetry. Dewar tests are carried out at atmospheric and elevated pressure. Sealed ampoules, Dewars with mixing, isothermal calorimeters, etc. can be used. Temperature and pressure are measured as a function of time. From these data rates of temperature and pressure rises as well as the adiabatic temperature ri.se may be determined. If the log p versus UT graph is a straight line, this is likely to be the vapour pressure. If the graph is curved, decomposition reactions should be considered. Typical temperature-time curves obtained from Dewar flask experiments are shown in Fig. 5.4-60. The adiabatic induction time can be evaluated as a function of the initial temperature and as a function of the temperature at which the induction time, tmi, exceeds a specified value. 

For saturated steam pj = f(Tj), where Tj = f(Pj). Thus the knowledge of density permits the determination of temperature and from this the pressure. 

The key point here is to determine if flammable or combustible materials are being processed under conditions of temperature and pressure such that, if a release occurs, a significant quantity of the material may be released into the air as either a gas, vapor, mist, or aerosol. If such conditions are present, the user should assume that the potential for a vapor cloud explosion exists. Otherwise, VCE hazards can be ignored. 

Enthalpy is a function of temperature and pressure. Values for the more common substances have been determined experimentally and are given in the various handbooks (see Chapter 8). 

For this last stage, the one-at-a-time procedure may be a very poor choice. At Union Carbide, use of the one-at-a-time method increased the yield in one plant from 80 to 83% in 3 years. When one of the techniques, to be discussed later, was used in just 15 runs the yield was increased to 94%. To see why this might happen, consider a plug flow reactor where the only variables that can be manipulated are temperature and pressure. A possible response surface for this reactor is given in Figure 14-1. The response is the yield, which is also the objective function. It is plotted as a function of the two independent variables, temperature and pressure. The designer does not know the response surface. Often all he knows is the yield at point A. He wants to determine the optimum yield. The only way he usually has to obtain more information is to pick some combinations of temperature and pressure and then have a laboratory or pilot plant experimentally determine the yields at those conditions. 

An infinitesimal change in internal energy is an exact differential and is a unique function of temperature and pressure (for a given composition). Since the density of a given material is also uniquely determined by temperature and pressure (e.g., by an equation of state for the material), the internal energy may be expressed as a function of any two of the three terms T, P, or p (or v = 1/p). Hence, we may write ... 

Temperature and pressure affect the operation of fluid-particle systems because they affect gas density and gas viscosity. It is the variation in these two parameters that determine the effects of temperature and pressure on fluid-particle systems. Increasing system temperature causes gas density to decrease and gas viscosity to increase. Therefore, it is not possible to determine only the effect of gas viscosity on a system by changing system temperature because gas density is also changed and the resulting information is confused. Very few research facilities have the capability to change system pressure to maintain gas density constant while the temperature is being changed to vary gas viscosity. 

The effects of temperature and pressure on fluidized-bed systems cannot be considered independently of particle size. Whether temperature and pressure have an effect (and indeed, even the direction of that effect) on a system, depends strongly on particle size. In addition, the type of interaction between gas and solids, i.e., whether the interaction is due to momentum or drag, determines if gas viscosity has an effect upon the system. As will be shown, gas viscosity is not important in systems in which momentum is important, but is important in systems dominated by drag. 

One of the basic parameters to be determined when designing bubbling fluidized-bed systems is the minimum fluidization velocity, Ump The effect of temperature and pressure on IJhas been investigated by many researchers (Botterill and Desai, 1972 Botterill and Teoman, 1980 ... 

Where mobility data are available over a considerable range of temperature, the activation energy is often found to be temperature-dependent. Thus, in n-pentane the activation energy increases with temperature whereas in ethane it decreases (Schmidt, 1977). Undoubtedly, part of the explanation lies in the temperature dependence of density, but detailed understanding is lacking. In very high mobility liquids, the mobility is expected to decrease with temperature as in the case of the quasi-free mobility. Here again, as pointed out by Munoz (1991), density is the main determinant, and similar results can be expected at the same density by different combinations of temperature and pressure. This is true for LAr, TMS, and NP, but methane seems to be an exception. 

Phase solubility analysis is a technique to determine the purity of a substance based on a careful study of its solubility behavior [38,39]. The method has its theoretical basis in the phase mle, developed by Gibbs, in which the equilibrium existing in a system is defined by the relation between the number of coexisting phases and components. The equilibrium solubility of a material in a particular solvent, although a function of temperature and pressure, is nevertheless an intrinsic property of that material. Any deviation from the solubility exhibited by a pure sample arises from the presence of impurities and/or crystal defects, and so accurate solubility measurements can be used to deduce the purity of the sample. 

Here a, b, c, d etc. are coefficients that in general are functions of temperature and pressure. The equilibrium behaviour of r through the phase transition is determined by minimizing AtrsG with respect to r. Furthermore, at equilibrium the AtrsG(T) surface is concave upwards (discussed thoroughly in Section 5.2), hence... 

The Reactive System Screening Tool (RSST), marketed by Fauske and Associates, is a relatively new type of apparatus for process hazard calorimetry [192, 196-198]. The equipment is designed to determine the potential for runaway reactions and to determine the (quasi) adiabatic rates of temperature and pressure rise during a runaway as a function of the process, vessel, and other parameters. 

Process temperature for the Inherent Safety Index (ISI) is determined on the basis of the maximum temperature in the process area under investigation. This is feasible since in the early stage of process design preliminary estimates of temperatures and pressures are available. 

We look once more at the phase diagram of C02 in Figure 5.5. The simplest way of obtaining the data needed to construct such a figure would be to take a sample of C02 and determine those temperatures and pressures at which the liquid, solid and gaseous phases coexist at equilibrium. (An appropriate apparatus involves a robust container having an observation window to allow us to observe the meniscus.) We then plot these values of p (as y ) against T (as V). 

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