Volume Chemical Reaction Research Articles

발전용 대형 엔진 적용을 위한 천연가스-디젤 혼소에 대한 수치 해석적 연구

Recently KEPCO, KOGAS and other institutions are jointly conducting an R&D for the development and demonstration of the power generation system based on a natural gas/diesel engine on an island. As a preliminary study, co-combustion in the dual fuel engine, which is expected to produce a few mega-watts of electricity, was modeled and calculated using computational fluid dynamics (CFD). The applied key assumptions are 2-dimensional axisymmetric, transient and static volume chemical reaction. Based on the selected blending ratio, which is the key operating condition, natural gas is substituted instead of diesel fuel (basis of high heating value). Results showed that as the blending ratio increases, the reaction rate of the combustion increases and thus maximum temperature is reached more rapidly. For the optimal performance, various geometric or operational studies will further be conducted.

Exact solutions to differential-difference heat and mass transfer equations with a finite relaxation time

Certain exact solutions to the linear differential-difference heat and mass transfer equations with a finite relaxation time are specified. The exact solution to the one-dimensional Stokes problem with the periodic boundary condition when a first-order volume chemical reaction occurs is given. A wide class of exact solutions to the nonlinear differential-difference heat-conduction equation with the following source is described: $$\Theta _t = div[f(T)\nabla T] + g(\Theta ), = T(r,t + \tau ),$$ where T = T(r, t) is temperature and τ is the relaxation time. Certain more complex heat conduction models with a variable relaxation time that can depend on time and a temperature gradient are also considered.

The asymptotic expansions of the solution for the boundary value problem to a convective diffusion equation with volume chemical reaction near a spherical drop

The paper deals with a boundary value problem for a quasilinear partial elliptical equation. The equation describes a stationary process of convective diffusion near a spherical drop and takes into account the value of a chemical reaction for large Peclet numbers ( Pe). For the problem considered, an asymptotic expansions (AE) of solution on the small parameter ( ε = Pe −1/2) is obtained near a spherical drop.

EC mechanism of an adsorbed redox couple. Volume vs surface chemical reaction

A theoretical model of a complex electrode mechanism coupled by adsorption of the redox couple and followed by two different types of irreversible chemical reactions is developed: Ox ( ads) +n e − ⇆ Red ( ads) → k s P ⇅ ⇅ ( Ox ( aq) ) x=0+n e − ⇆ ( Red ( aq) ) x=0 → k v P The theoretical consideration for this specific type of EC mechanism comprises all relevant phenomena such as diffusion mass transport, adsorption equilibria and kinetics of the following irreversible chemical reactions. The adsorbed electroactive product Red (ads) decays to the final inactive product P through a chemical reaction occurring exclusively on the electrode surface. It is designated as a surface chemical reaction associated by the rate constant k s, whereas the dissolved Red (aq) form transforms independently via a volume chemical reaction taking place in the solution layer adjacent to the electrode surface and is characterized by the rate constant k v. Adsorptions of both species of the redox couple are assumed to obey a linear adsorption isotherm law. The solutions obtained with the aid of Laplace transforms for the surface concentrations for both oxidized and reduced species are presented as integral equations, thus they are valid for any chronoamperometric technique. The numerical solution is adopted for square-wave voltammetry and both reversible and quasireversible cases were studied. Special attention is paid to revealing discrepancies between the surface and volume chemical reactions. It has been demonstrated that for a reversible case the influence of both chemical reactions is rather similar disabling a simple distinguishing of the reaction type. For the quasireversible case, clear and simple criteria for distinguishing the type of chemical reaction can be established utilizing the properties of split SW peaks and a quasireversible maximum.

Square-wave voltammetry of an EC reaction of a partly adsorbed redox couple

The theory of an EC mechanism with partial adsorption of the redox couple is developed. The theoretical response is studied under conditions of square-wave voltammetry (SWV). The theoretical treatment comprises all the relevant phenomena such as diffusion mass transport, adsorption equilibrium and the kinetics of the following irreversible chemical reaction. It is presumed that the following chemical reaction occurs in the vicinity of the electrode rather than on the electrode surface itself. The adsorption of both species of the redox couple obeys a linear adsorption isotherm law. The solutions for the surface concentrations for both oxidized and reduced forms of the redox couple are presented as integral equations, thus they are valid for any chronoamperometric technique. A comparative study between the voltammetric properties of the reaction studied and the other type of EC mechanisms as well as the simple redox reaction of a partly adsorbed redox couple is presented. Special attention is paid to revealing discrepancies between the surface EC mechanism and the EC mechanism of a partly adsorbed redox couple aiming to establish criteria for distinguishing the following chemical reactions occurring on the electrode surface (surface chemical reaction) and in the bulk solution (volume chemical reaction).

The E-DIM reaction with adsorption of the reactants surface vs. volume chemical reaction

A theoretical study of the E-DIM reaction with adsorption of the reactants is presented. The electrochemical reaction E can have a heterogeneous (Eh) or surface (Es) character, whereas the dimerization can occur in a volume near the electrode (DIMv) or on its surface (DIMs). Four paths are possible: EhDIMv, EhDIMs, EsDIMh or EsDIMs. The dependence of the variations of the characteristic parameters (e.g.E1/2 in polarography or RDE voltammetry,Ep in LSV), the measurement time (τ,RT/Fv), the concentrationcT or the surface concentrationГT is different in each case, and can thus be used to determine the nature and the sequence of the paths and to calculate the dimerization reaction rate constant.

Mass transfer between particles and a flow in the presence of a volume chemical reaction

The exterior problem of the mass transfer between a spherical drop and a linear shear flow in the presence of a first-order volume reaction is solved in the diffusion boundary layer approximation. A simple approximate expression for calculating the average Sherwood number for a drop or solid particle of arbitrary shape is proposed. At large Peclet numbers this expression is applicable to any type of flow over the entire range of variation of the reaction rate constant. The problem of diffusion to a spherical drop in a translational Stokesian flow in the presence of a first-order volume reaction was investigated in [1].

Unsteady convection mass transfer inside a drop in the presence of volume chemical reaction

Unsteady diffusion inside a moving drop of material dissolved in a stream of viscous liquid is investigated at high Peclet numbers. The diffusing material in the drop volume may take part in a first-order chemical reaction. The case is considered, when the concentration of the dissolved substance in the liquid surrounding the drop is uniform, and its transport inside the drop depends on the velocity field distribution and the concentration only in that region (the internal problem). The flow in the drop is assumed to be steady and to correspond to a spherical Hill vortex (at low Reynolds number).

II. Double Layer Corrections in the Evaluation of Rate and Equilibrium Constants of Fast Homogeneous Reactions, Coupled with Electrode Reactions. ‐ Some Potentialities of the Galvanostatic Method

AbstractThe influence of the double layer on the overall rate of electrochemical processes controlled by a prior volume chemical reaction is discussed in terms of the ratio between the equivalent thicknesses of the reaction layer and of the diffuse part of the double layer. The influence of potential and ionic strength on the polarographic waves of Cd(CN)4− and Ni++ has been interpreted by the proposed theory.