Joule-Thomson expansion coefficient

Joule-Thomson expansion cycle, 8 42-43 Joule-Thomson expansion coefficients, for hydrogen, 13 764 Journal bearing, 15 211 Journal of Biotechnology and Bioengineering, 11 10 Journal of Physical and Chemical Reference Data, 15 141, 769 Journal of Research of the National... 

Thus, the initial and final states of a Joule-Thomson expansion he on a curve of constant enthalpy (isoenthalp) and the Joule-Thomson process occurs at constant enthalpy. The Joule-Thomson coefficient, pJT, is defined as... 

The Joule-Thomson expansion process was introduced earlier in this book. However, the Joule-Thomson coefficient is a measure of the change in temperature due to a change in pressure. It is defined by Equation (A7). 

Most practical refrigeration and liquefaction systems obtain a reduction in temperature with the aid of an expansion valve (Joule-Thomson valve), an expansion engine, or a combination of the two devices. In the case of the expansion valve, the flow within the valve is irreversible as well as non-isenthalpic. However, the inlet and outlet conditions have the same enthalpy. The change in temperature of a fluid obtained with an isenthalpic change in pressure is represented by the Joule-Thomson (IT) coefficient, defined as... 

Define Joule-Thomson expansion and the Joule-Thomson coefficient. Explain how Joule-Thomson expansion is used in liquefaction. 

Joule-Thomson expansion results from the unrestrained, free expansion of real gases. Such a process occurs at constant enthalpy and is termed isenthalpic. We can determine the change in temperature that results as the pressure decreases in the isenthalpic throtthng process if we know the Joule-Thomson coefficient, fijr — dT/dP)h- Joule-Thomson expansion is the basis for liquefaction processes, such as those shown in Figure 5.11. 

The Joule-Thomson coefficient p.jx, is positive when a cooling of the gas (a temperature drop) is observed because dP is always negative, p.j x, will be positive when dT is negative. Conversely, p.j x, is a negative quantity when the gas warms on expansion because dT then is a positive quantity. Values of the Joule-Thomson coefficient for argon and nitrogen at several pressures and temperatures are listed in Table 5.5. 

The Joule-Thomson coefficient is the slope of the isenthalpic lines in the P-T projection. In the region where iJt<0, expansion through the valve (a decrease in pressure) results in an increase in temperature, whereas in the region where pJt >0, expansion results in a reduction in temperature. The latter area is recommendable for applying the PGSS process. 

USEFUL MEASURABLES THERMAL EXPANSIVITY, HEAT CAPACITY, JOULE-THOMSON COEFFICIENT... 

The Joule Thomson coefficient is the ratio of the temperature decrease to the pressure drop, and is expressed in terms of the thermal expansion coefficient and the heat capacity... 

For most gases under ordinary conditions, 2a RT > b (the attractive forces predominate over the repulsive forces in determining the nonideal behavior) and the Joule-Thomson coefficient is therefore positive (gas cools on expansion). At a sufficiently high temperature, the inequality is reversed, and the gas warms on expansion. The temperature at which the Joule-Thomson coefficient changes sign is called the inversion temperature Tj. For a van der Waals gas,... 

The liquefaction of helium by a controlled expansion process necessitates preliminary cooling because its Joule-Thomson coefficient is negative (spontaneous expansion heats the gas) down to an inversion temperature of 40 All the gases have C /C ratios very close to 5/3, the theoretical value for an ideal monatomic gas. The elements are liquid over very small temperature ranges. Plelium can be solidified only under pressure under 26 atmospheres it solidifies at 0.9 °K. 

Because of the variation of the Joule-Thomson coefficient with both temperature and pressure it is not easy to calculate the change of temperature resulting from a given throttled expansion, even when such data as in Table IV are available. This can be done, however, by a series of approximations. By estimating a rough average for the Joule-Thomson coefficient, some indication of the fall of temperature can be obtained. 

During the expansion the gas does not exchange heat with its environment. However, it exchanges work because of the expansion against the nonzero pressure P2. It is then a simple matter to demoiLstrate that the gas expands isenthalpically [26, 199-203]. This makes it convenient to discuss the Joule-Thomson process quantitatively in terms of a Joule-Thomson coefficient... 

Temperature, pressure, volume, amount, energy, enthalpy, heat capacity, expansion coefficient, isothermal compressibility, and Joule-Thomson coefficient. 

E2.29(b) The Joule-Thomson coefficient fi is the ratio of temperature change to pressure change under conditions of isenthalpic expansion. So... 

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