Enthalpy, stagnation

Since pipe flow is more nearly isenthalpic, the flash fraction x is found from an enthalpy balance between the stagnation point and a point z downstream. Accounting for changes in potential energy, kinetic energy, and heat added or removed from the pipe Q, x is given by ... 

The velocity term can be considered part of the enthalpy if the enthalpy is defined as the stagnation or total enthalpy. The equation can be simplified to... 

Change in stagnation enthalpy (or temperature) through an open cooled blade row... 

It has already been shown that (stagnation) pressure losses have an appreciable effect on cycle efficiency (see Section 3.3), so as well as obtaining the enthalpy change, it is important to determine the stagnation pressure change in the whole cooling proce.ss. 

A homogeneous flow basis must be used when thermodynamic equilibrium is assumed. For furtl er simplification it is assumed there will be no reaction occurring in the pipeline. The vapor and liquid contents of the reactor are assumed to be a homogeneous mass as they enter the vent line. The model assumes adiabatic conditions in the vent line and maintains constant stagnation enthalpy for the energy balance. 

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

When gas flows from stagnation conditions through a nozzle, thereby undergoing an isoentropic change, the enthalpy change is represented by Eq. (1.23). The flow velocity is obtained by substitution of Eq. (1.14) into Eq. (1.24) as... 

Dunkle remarked (Ref 114) that the energy equation expresses the fact that any decrease in enthalpy in the detonation must be balanced by an increase in kinetic energy and vice versa so that the sum of the two, the stagnation enthalpy, is conserved (Compare with.eq 43r in Ref 93, p 34). This relationship can be expressed by writing ... 

This sum often is called the stagnation enthalpy flux and includes thermal enthalpy, chemical enthalpy, and kinetic energy. 

As was pointed out by Spalding [15], some aspects of the analysis of combustion waves in which kinetic energy is of importance can be simplified by using the stagnation enthalpy (CpT + v /2) as a variable. A normalized dimensionless measure of the stagnation enthalpy is... 

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