Mass decomposition model

Kempter50 studied the thermal decomposition of 88% dense NbC cylinders from 2273 to 3473 K in 1 atm of He. Data at 3273 K will be used to test our diffusion-coupled vaporization mass loss model. We transposed the cylindrical geometry into an equivalent slab by dividing the volume by the average vaporizing area. One face of the cylinder was not included in the calculation because it rested on a NbC pedestal in the furnace. Table 3.13. summarizes analytical X-ray data for average C/Nb compositions. 

In studies of mass loss through time decomposition rate constants are not measured directly, necessitating the modeling of mass loss versus time to calculate a k value. The simplest model for this relationship is a zero-order decomposition model where mass loss progressively decreases with time. However, this model often does not capture observed trends and will yield unrealistic predictions as time gets large (Andren and Faustian, 1987). Most often, decomposition dynamics are represented as a first-order process—i.e., decomposition is proportional to the amount of material present ... 

After the determination of the decomposition model, the mass transfer during decomposition can be obtained according to Eq. (4.16) ... 

At a specified temperature, the thermal conductivity of FRP composite materials depends on the properties of the constituents at this temperature, as well as the content of each constituent As a result, if the temperature-dependent thermal conductivity is known for both fibers and resin, the property of the composite material can be estimated. During decomposition, however, decomposed gases and delaminating fiber layers will influence significantly the thermal conductivity (trae against effective thermal conductivity). An alternative method to determine the effective thermal conductivity is to suppose that the materials are only composed of two phases the undecomposed material and the decomposed material. The content of each phase can thereby be determined from the mass transfer model introduced above. As a result, the effects owing to decomposition can be described [12]. 

The temperature-dependent thermal conductivity was estimated by the inverse rule of mixture with reference to the physical series model. Again the volume fraction of each phase (undecomposed and decomposed) was directly obtained from the decomposition model and mass transfer model. The rapid decrease of thermal conductivity during the decomposition process was also well described in this way in the modeling of effective thermal conductivity. The modeling approach was compared with previous models and validated by experiments using the hot disk method. 

The true specific heat capacity of a composite material was obtained by the mle of mixture and the mass fraction of each phase was determined by the decomposition and mass transfer model. The true specific heat capacity of resin or fiber was derived based on the Einstein or Debye model. The effective specific heat capacity was obtained by assembhng the trae specific heat capacity with the decomposition heat that was also described by the decomposition model. The modeling approach for effective specific heat capacity is useful in capturing the endothermic decomposition of resin and was further verified by a comparison to DSC curves. 

The thermal decomposition process of HMX was studied by time-of-flight mass spectrometry (Model Zhp-6 spectrometer) [71]. It is suggested that the decomposition of HMX involves three stages, i.e. initial decomposition of the solid phase at about 160 C, decomposition with melting and decomposition of the liquid phase. The products which have been confirmed are NOj, NO, HCN and CHO. 

Dong W, Wang W, Li J A multiscale mass transfer model for gas-soHd riser flows part II— sub-grid simulation of ozone decomposition, Chem Eng Sci 63 2811—2823, 2008b. 

Where large samples of reactant are used and/or where C02 withdrawal is not rapid or complete, the rates of calcite decomposition can be controlled by the rate of heat transfer [748] or C02 removal [749], Draper [748] has shown that the shapes of a—time curves can be altered by varying the reactant geometry and supply of heat to the reactant mass. Under the conditions used, heat flow, rather than product escape, was identified as rate-limiting. Using large ( 100 g) samples, Hills [749] concluded that the reaction rate was controlled by both the diffusion of heat to the interface and C02 from it. The proposed models were consistent with independently measured values of the transport parameters [750—752] whether these results are transfenable to small samples is questionable. 

The UASB tractor was modeled by the dispensed plug flow model, considering decomposition reactions for VFA componaits, axial dispersion of liquid and hydrodynamics. The difierential mass balance equations based on the dispersed plug flow model are described for multiple VFA substrate components considaed... 

BATCH DECOMPOSITION OF ACETYLATED ACETIC ACID CONSTANT MASS MODEL... 

A unified gas hydrate kinetic model (developed at ARC) coupled with a thermal reservoir simulator (CMG STARS) was applied to simulate the dynamics of CH4 production and C02 sequestration processes in the Mallik geological zones. The kinetic model contains two mass transfer equations one equation transfers gas and water into hydrate, and a decomposition equation transfers hydrate into gas and water (Uddin etal. 2008a). 

The effects of the steady-state situation and the effect of the peak load can be described using a model. When the caustic concentration is low, either through initial concentration effects or by mass transfer limitations, the reaction of chlorine with chlorite can occur and chlorine dioxide (Equations 25.3 and 25.8) is formed near the gas-liquid interface. The concentration of chlorite seems quite important and is influenced by temperature (decomposition) and the hypochlorite concentration. A higher chlorite concentration will give, according to the reactions of Equations 25.3 and 25.8, a higher chlorine dioxide content in the presence of chlorine and/or hypochlorous acid. 

Photochemical decomposition can also be carried out in the presence of a suspension of photoactive material such as Ti02 where substrate absorption onto the uv activated surface can initiate chemical reactions e. g. the oxidation of sulphides to sul-phones and sulphoxides [37]. This technology has been adapted to the destruction of polychlorobiphenyls (PCB s) in wastewater and is of considerable interest in environmental protection. Using pentachlorophenol as a model substrate in the presence of 0.2 % TiOj uv irradiation is relatively efficient in dechlorination (Tab. 4.5) [38]. When ultrasound is used in conjunction with photolysis, dechlorination is dramatically improved. This improvement is the result of three mechanical effects of sonochemistry namely surface cleaning, particle size reduction and increased mass transport to the powder surface. 

For combustion applications and for accurate modeling of the processes involving melting, decomposition, and subsequent oxidation, it is necessary to determine whether or not the fuel undergoes chemical decomposition when it is liquefied and, subsequently, converted to the vapor state. Mass spectral analyses were performed to provide information about the substances in the vapor phase as the fuel is heated. 

The experimental inaccessibility of the configurational entropy poses no problem for the LCT, apart from a consideration of whether to normalize the configurational entropy per lattice site or per monomer in order to provide a better representation of experiment within the AG model. Once the appropriate normalization of Sc has been identified, t can be calculated from Eq. (33) as a function of temperature T, molar mass Mmoi, pressure P, monomer structure, backbone and side group rigidities, and so on, provided that Ap is specified [54]. The direct determination of Ap from data for T > Ta is not possible for polymer systems because Ta generally exceeds the decomposition temperature for these systems. Section V reviews available information that enables specifying Ap for polymer melts. 

TGA. Thermogravimetric analysis (TGA) and differential thermal analysis (DTA) are other means to confirm the above structural models. Figure 4.4.8 shows the thermal analysis data for sample I. Curve (a) shows a TG datum of a mass loss about 22% after heating over 350°C. The derivative curve (b) of mass loss curve (a) clearly shows that there are at least four steps during the decomposition of the sample. This finding was further confirmed by the DTA data curve (c) shown in the same figure. It is clearly seen that there are four endothermic peaks. The DTA and TGA curves were similar for all samples. Note that the relative ratios of mass... 

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