Stagnation enthalpy

About: Stagnation enthalpy is a research topic. Over the lifetime, 655 publications have been published within this topic receiving 9816 citations.

Estimation of heats of formation of organic compounds by additivity methods

Abstract: In the present manuscript describing traditional, macroscopic thermochemical properties, the authors` language will be that of molecular structure. Enthalpies (or heats of formation) are the subject of this article, and since the most important practical application of enthalpies is to explore reactivities and/or equilibria, they take a kineticist`s perspective in answering the question, what is a ``sufficiently accurate`` prediction of an enthalpy of formation. In a general reaction, A + B {yields} C + D, a shift in {Delta}{sub r}H (enthalpy of reaction) of 1 kcal/mol will generally result in a change in the equilibrium constant, K{sub eq}, of exp({minus}500/T) where T is the temperature in Kelvins. At room temperature, this means a factor of over 5 in K{sub eq}; the difference between, say, 90% and 64% reaction yield. Or, in terms of the time required for reaction completion, it could also mean an increase of a factor of 5. This factor of 5 is the same whether the total enthalpy of reaction is 5 kcal/mol or 500 kcal/mol. Thus, while theoreticians have struggled to attain the stage where they can with pride calculate enthalpy quantities with 2--4 kcal/mol uncertainty, they are not solving the practical problems at hand.

Analysis and design of numerical schemes for gas dynamics. 2: Artificial diffusion and discrete shock structure

Abstract: The effect of artificial diffusion on discrete shock structures is examined for a family of schemes which includes scalar diffusion, convective upwind and split pressure (CUSP) schemes, and upwind schemes with characteristics splitting. The analysis leads to conditions on the diffusive flux such that stationary discrete shocks can contain a single interior point. The simplest formulation which meets these conditions is a CUSP scheme in which the coefficients of the pressure differences is fully determined by the coefficient of convective diffusion. It is also shown how both the characteristic and CUSP schemes can be modified to preserve constant stagnation enthalpy in steady flow, leading to four variants, the E and H-characteristic schemes, and the E and H-CUSP schemes. Numerical results are presented which confirm the properties of these schemes.

Analysis and design of numerical schemes for gas dynamics, 2: artificial diffusion and discrete shock structure

Abstract: The effect of artificial diffusion on discrete shock structures is examined for a family of schemes which includes scalar diffusion, convective upwind and split pressure (CUSP) schemes, and upwind schemes with characteristics splitting. The analysis leads to conditions on the diffusive flux such that stationary discrete shocks can contain a single interior point. The simplest formulation which meets these conditions is a CUSP scheme in which the coefficients of the pressure differences is fully determined by the coefficient of convective diffusion. It is also shown how both the characteristic and CUSP schemes can be modified to preserve constant stagnation enthalpy in steady flow, leading to four variants, the E and H-characteristic schemes, and the E and H-CUSP schemes. Numerical results are presented which confirm the properties of these schemes.

The absorption of axial acoustic waves by a perforated liner with bias flow

Abstract: The effectiveness of a cylindrical perforated liner with mean bias flow in its absorption of planar acoustic waves in a duct is investigated. The liner converts acoustic energy into flow energy through the excitation of vorticity fluctuations at the rims of the liner apertures. A one-dimensional model that embodies this absorption mechanism is developed. It utilizes a homogeneous liner compliance adapted from the Rayleigh conductivity of a single aperture with mean flow. The model is evaluated by comparing with experimental results, with excellent agreement. We show that such a system can absorb a large fraction of incoming energy, and can prevent all of the energy produced by an upstream source in certain frequency ranges from reflecting back. Moreover, the bandwidth of this strong absorption can be increased by appropriate placement of the liner system in the duct. An analysis of the acoustic energy flux is performed, revealing that local differences in fluctuating stagnation enthalpy, distributed over a finite length of duct, are responsible for absorption, and that both liners in a double-liner system are absorbant. A reduction of the model equations in the limit of long wavelength compared to liner length reveals an important parameter grouping, enabling the optimal design of liner systems.