Enthalpy processes

Both v and Av are obtained for each increment for a constant stagnation enthalpy process satisfying Eq. (23-113). 

Assume a process each for the eight devices (1) turbines as adiabatic with 80% efficiency, (2) splitters as nonisopar-ametric devices, and (3) condensers as isobaric processes. Notice that throttling devices are automatically constant enthalpy processes. 

As in Example 7.4, Eq. (6.93) is applied to this constant-enthalpy process. If the final state at 1.2 bar is assumed an ideal gas, then Eq. 

Solution Applying Eq. (6.62) to this constant-enthalpy process gives ... 

The Joule-Thomson expansion is a constant-enthalpy process (Section 2,12). Hence,... 

Enthalpy of input Enthalpy of products Process enthalpy Process entropy -1.2193E-H10 J -1.2412E-H10 J -2.1951E-h08 J + 6.8608E + 06-X J/K ... 

Assuming that the expansion is a Joule-Thomson constant-enthalpy process, we have... 

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 ... 

The deuteration experiment shows that hydrogen abstraction does occur but the long lifetime of the radicals indicates that transfer of the radical sites by subsequent abstraction of tertiary H-atoms (which is a zero-enthalpy process) must be rather restricted. Otherwise the radicals would terminate each other rapidly. The transport of radical sites at room temperature is obviously limited to distances shorter than the average distance between trapped radicals (10-14 nm at a radical concentration of (3 1.5) 10 M). 

Flashing. The flash from a superheated liquid released to atmospheric pressure can be estimated in a number of ways. If the initial and final state of the release is quiescent, then the initial and final enthalpies are the same (this does not imply a constant enthalpy process). For pure materials, such as steam, a Mollier entropy-enthalpy diagram or a thermodynamic data table can be used. 

In this analysis, a further simplification is made by assuming that the expansion is a constant enthalpy process rather than a constant entropy process. It is then possible to show a heat balance between the cooled liquid and the evaporation process, which is ... 

For heat balance calculationsfor a system, the energy or heat input in the form of enthalpy processed by materials in, plus any heat added, should be equal to heat out. 

Notice that if the choice of piston pressures is such that gas moves from the left to the right, then AVi < 0 and AV2 > 0. Since the process is carried out adiabatically, q = 0, and therefore, AU = w. The enthalpy change for the entire system is zero this is an isenthalpic (constant enthalpy) process. 

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