Thermodynamics Joule-Thomson coefficients

Thus the change is at constant H, and the Joule-Thomson coefficient is (dT/dP)H. But this can be evaluated easily from our Table of Thermodynamic Relations in Chap. II. It is... 

The denominator on the right side of Eq. (4) is the heat capacity at constant pressure Cp. The numerator is zero for an ideal gas [see Eq. (1)]. Accordingly, for an ideal gas the Joule-Thomson coefficient is zero, and there should be no temperature difference across the porous plug. Eor a real gas, the Joule-Thomson coefficient is a measure of the quantity [which can be related thermodynamically to the quantity involved in the Joule experiment, Using the general thermodynamic relation ... 

Joule-Thomson coefficients for substances listed in Table 2-184 are given in tables in the Thermodynamic Properties section. 

Equation (11.6) is quite general and should apply to any gas/ for its derivation is based entirely on the first la>y of thermodynamics without assuming any specific properties of the system. However, for an ideal gas, (dE/dV)r is zero, as seen earlier, and since PV = /2T, it follows that td PV)/dP ]T is also zero hence, since Cp is finite, it is seen from equation (11.6) that for an ideal gas mj.t. must be zero.f The Joule-Thomson coefficient of an ideal gas should thus be zero, so that there should be no change of temperature when such a gas e.xpands through a throttle. J... 

This expression is based upon thermodynamic considerations only, and hence is exact the Joule-Thomson coefficient, at any temperature, may thus... 

The Joule-Thomson coefficient juj can be related to other thermodynamic derivatives by application of the formula of implicit differentiation [Eq. (A-10)]. Thus we may write... 

The following experimental data are generally considered essential in developing an accurate equation of state ideal gas heat capacities Cf,% expressed as functions of temperature T, vapour pressure and density p data in all regions of the thermodynamic surface. Precise speed of sound w data in both the liquid and vapour phases have recently become important for the development of equations of state. The precision of calculated energies can be improved if the following data are also available Cy,m p, T) (isochoric heat capacity measurements), Cp,m(p, T) (isobaric heat capacity measurements), T) (enthalpy differences), and Joule-Thomson coefficients. 

Din was the editor of a series of books designed to provide reliable thermodynamic data for industrially important gases. Temperature-entropy diagrams were chosen as the most generally useful graphical presentations and these are supplemented by tables of entropy, enthalpy, volume, heat capacity at constant pressure and at constant volume, and Joule-Thomson coefficients. Unfortunately, there is no consistency in the choice of units, although the thermochemical calorie is employed. The report on each substance (i.e. ammonia, carbon dioxide, carbon monoxide, air, argon, acetylene, ethylene, and propane) consists of a brief introduction, a survey of experimental data, a description of methods used for the thermodynamic calculations, and a set of tables. 

NIST/ASME Steam Properties Database versiou 2.21 http //www.nist.gov/srd/nistlO.cfm (accessed November 10, 2010) (purchase required). Thermophysical properties include in the STEAM Database temperature, Helmholtz energy, thermodynamic derivatives, pressure, Gibbs energy, density, fugacity, thermal conductivity, volume, isothermal compressibility, viscosity, dielectric constant, enthalpy, volume expansivity, dielectric derivatives, internal energy, speed of sound, Debye-Hlickel slopes, entropy, Joule-Thomson coefficient, refractive index, heat capacity, surface tension. The STEAM database generates tables and plots of property values. Vapor-liquid-solid saturation calculations with either temperature or pressure specified are available. 

Thermodynamic information is given in Table 1, from which the data required for working with gaseous and liquid chlorine can be obtained [42]. The Joule-Thomson coefficient is 0.0308 KAPa at STP. 

Develop a relationship for the Joule-Thomson coefficient in terms of only the thermal expansion coefficient, the heat capacity at constant pressure, and measured thermodynamic properties. 

---