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Theoretical analysis of superadiabatic combustion for non-stationary filtration combustion by excess enthalpy function.

ABSTRACT: The superadiabatic combustion for non-stationary filtration combustion is analytically studied. The non-dimensional excess enthalpy function (H) equation is theoretically derived based on a one-dimensional, two-temperature model. In contrast to the H equation for the stationary filtration combustion, a new term, which takes into account the effect of non-dimensional combustion wave speed, is included in the H equation for transient filtration combustion. The governing equations with boundary conditions are solved by commercial software Fluent. The predictions show that the maximum non-dimensional gas and solid temperatures in the flame zone are greater than 3 for equivalence ratio of 0.15. An examination of the four source terms in the H equation indicates that the thermal conductivity ratio (?s) between the solid and gas phases is the dominant one among the four terms and basically determines H distribution. For lean premixed combustion in porous media, the superadiabatic combustion effect is more pronounced for the lower ?s .

SUBMITTER: Shi J

PROVIDER: S-EPMC7657896 | biostudies-literature | 2020 Oct

REPOSITORIES: biostudies-literature

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Theoretical analysis of superadiabatic combustion for non-stationary filtration combustion by excess enthalpy function.

Shi Junrui J Mao Mingming M Liu Yongqi Y Lv Jinsheng J

Royal Society open science 20201007 10

The superadiabatic combustion for non-stationary filtration combustion is analytically studied. The non-dimensional excess enthalpy function (H) equation is theoretically derived based on a one-dimensional, two-temperature model. In contrast to the H equation for the stationary filtration combustion, a new term, which takes into account the effect of non-dimensional combustion wave speed, is included in the H equation for transient filtration combustion. The governing equati ...[more]

PMID: 33204465

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Project description:Calculations using the density-functional theory (DFT) in combination with the single defect method were carried out to determine the heat of mixing behaviour of mineral solid solution phases. The accuracy of this method was tested on the halite-sylvite (NaCl-KCl) binary, pyrope-grossular garnets (Mg3Al2Si3O12-Ca3Al2Si3O12), MgO-CaO (halite structure) binary, and on Al/Si ordered alkali feldspars (NaAlSi3O8-KAlSi3O8); as members for coupled substitutions, the diopside-jadeite pyroxenes (CaMgSi2O6-NaAlSi2O6) and diopside-CaTs pyroxenes (CaMgSi2O6-CaAlAlSiO6) were chosen for testing and, as an application, the heat of mixing of the tremolite-glaucophane amphiboles (Ca2Mg5Si8O22(OH)2-Na2Mg3Al2Si8O22(OH)2) was computed. Six of these binaries were selected because of their experimentally well-known thermodynamic mixing behaviours. The comparison of the calculated heat of mixing data with calorimetric data showed good agreement for halite-sylvite, pyrope-grossular, and diopside-jadeite binaries and small differences for the Al/Si ordered alkali feldspar solid solution. In the case of the diopside-CaTs binary, the situation is more complex because CaTs is an endmember with disordered cation distributions. Good agreement with the experimental data could be, however, achieved assuming a reasonable disordered state. The calculated data for the Al/Si ordered alkali feldspars were applied to phase equilibrium calculations, i.e. calculating the Al/Si ordered alkali feldspar solvus. This solvus was then compared to the experimentally determined solvus finding good agreement. The solvus of the MgO-CaO binary was also constructed from DFT-based data and compared to the experimentally determined solvus, and the two were also in good agreement. Another application was the determination of the solvus in tremolite-glaucophane amphiboles (Ca2Mg5Si8O22(OH)2-Na2Mg3Al2Si8O22(OH)2). It was compared to solvi based on coexisting amphiboles found in eclogites and phase equilibrium experiments.

Project description:PurposeIn previous work, a theoretical model of the point spread function (PSF) for oblique x-ray incidence in amorphous selenium (a-Se) detectors was proposed. The purpose of this paper is to develop a complementary model that includes two additional features. First, the incidence angle and the directionality of ray incidence are calculated at each position, assuming a divergent x-ray beam geometry. This approach allows the non-stationarity of the PSF to be modeled. Second, this paper develops a framework that is applicable to a digital system, unlike previous work which did not model the presence of a thin-film transistor (TFT) array.MethodsAt each point on the detector, the incidence angle and the ray incidence direction are determined using ray tracing. Based on these calculations, an existing model for the PSF of the x-ray converter (Med Phys. 1995;22:365-374) is generalized to a non-stationary model. The PSF is convolved with the product of two rectangle functions, which model the sampling of the TFT array. The rectangle functions match the detector element (del) size in two dimensions.ResultsIt is shown that the PSF can be calculated in closed form. This solution is used to simulate a digital mammography (DM) system at two x-ray energies (20 and 40 keV). Based on the divergence of the x-ray beam, the direction of ray incidence varies with position. Along this direction, the PSF is broader than the reference rect function matching the del size. The broadening is more pronounced with increasing obliquity. At high energy, the PSF deviates more strongly from the reference rect function, indicating that there is more blurring. In addition, the PSF is calculated along the polar angle perpendicular to the ray incidence direction. For this polar angle, the shape of the PSF is dependent upon whether the ray incidence direction is parallel with the sides of the detector. If the ray incidence direction is parallel with either dimension, the PSF is a perfect rectangle function, matching the del size. However, if the ray incidence direction is at an oblique angle relative to the sides of the detector, the PSF is not rectangular. These results illustrate the non-stationarity of the PSF.ConclusionsThis paper demonstrates that an existing model of the PSF of a-Se detectors can be generalized to include the effects of non-stationarity and digitization. The PSF is determined in closed form. This solution offers the advantage of shorter computation time relative to approaches that use numerical methods. This model is a tool for simulating a-Se detectors in future work, such as in virtual clinical trials with computational phantoms.

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Theoretical analysis of superadiabatic combustion for non-stationary filtration combustion by excess enthalpy function.

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Theoretical analysis of superadiabatic combustion for non-stationary filtration combustion by excess enthalpy function.

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