Processes isenthalpic

The process of reducing gas pressure with an expander is an isen-tropic process, which is able to recover both the energy from the gas pressure and also the gas temperature. A conventional gas regulator station is an isenthalpic process, which only reduces pressure. As a result, an expander system produces much lower gas temperatures downstream compared to a pressure regulator operating under the same pressure conditions. 

Thus, the Joule-Thomson expansion is an isenthalpic process. 

A throttle does not change the enthalpy of the fluid throttling is an isenthalpic process. For a given input state and a specified outlet pressure, one finds the outlet temperature by conducting a one-dimensional search for a temperature at which the enthalpy is equal to the input enthalpy. An enthalpy chart provides a convenient means for the search. Another method of solution is to apply the Joule-Thompson coefficient, defined by... 

An excellent review or LLE applications in the food industry is given by Hamm,17 Since solvent toxicity is a major consideration, supercritical solvents, such as CO, which are nomoxic and LLE from an aqueous leachate are two popalar means of deriling with this problem. Figure 7.8-11 is a cooceptual supercritical extraction flowsheet. Because Tc is much lower than either 7 or rB, the solvent (e.g., C02) simply is flashed from the solute by throttling (an isenthalpic process). Then the vapors are compressed (an isentropic process) and cooled (an isobaric step) to complete the solveni recycle. Usually, costs are determined by the compressor requirearerUs. Several potential applications of supercritical or near-critical solvents are discussed in more datail else where,... 

For an isenthalpic process in a closed homogeneous system of constant composition... 

The temperature at the exit of the vent is given by the isenthalpic condition. In the ideal-gas state, an isenthalpic process is also isothermal, therefore,... 

Throttling. As shown in Figure 9.14. superheated steam is throttled adiabatically across a valve from 600°F and 250 psia to 100 psia. Using the steam tables, for this isenthalpic process, its temperature is reduced to 578°F and its entropy is increased from 1.6502 Btu/lb- R to 1.7483 Btu/lb-°R. Substituting in Eg. 19.191 ... 

One of the classic examples in thermodynamics is the expansion of a fluid across a valve (or a porous plug), which is a constant enthalpy process. The process is shown in Figure 1. The specification of this process is given the temperature and the pressure of the inlet (state 1) and the pressure at the outlet (state 2), calculate the temperature of the outlet stream. Since this is an isenthalpic process, we also know that ... 

Because the enthalpy of the gas does not change, the process is called isenthalpic. What are some consequences of this isenthalpic process ... 

Although the change in enthalpy is zero, the change in temperature is not. What is the change in temperature accompanying the pressure drop for this isenthalpic process That is, what is (dT/dp). We can actually measure this derivative experimentally, using an apparatus like the one in Figure 2.10. 

For an ideal gas, /jlj-j- is exactly zero, because enthalpy depends only on temperature (that is, at constant enthalpy, temperature is also constant). However, for real gases, the Joule-Thomson coefficient is not zero, and the gas will change temperature for the isenthalpic process. Remembering from the cyclic rule of partial derivatives that... 

Now, when the temperature on the left, Ty is measured and the temperature on the right, T2, is measured, we can evaluate at such instant in the process the quantity (T2 - T])/(P2 - Pj)- If the experiment is repeated with a decreasing difference between the pressure on the left and the pressure on the right, this quantity will approach 3T/9P. The variable that is held constant in this derivative quantity is H because the setup insures an isenthalpic process. This derivative is called the Joule-Thomson coefficient ... 

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