Discretized pressure Poisson algorithm for the steady incompressible flow on a nonstaggered grid

In the aspect of numerical methods for incompressible flow problems, there are two different algorithms: semi-implicit method for pressure-linked equations (SIMPLE) series algorithms and the pressure Poisson algorithm. This paper introduced a new discretized pressure Poisson algorithm for the steady incompressible flow based on a nonstaggered grid. Compared with the SIMPLE series algorithms, this paper did not introduce three correction variables. So, there is no need to implement the guess-and-correct procedure for the calculation of pressure and velocity. Compared with the pressure Poisson algorithm, there is no need to calculate unsteady Navier¿Stokes equations for steady problems in the new discretized pressure Poisson algorithm. Meanwhile, as the finite volume method and cell-centered grid are used, the governing equation for pressure is obtained from the continuity equation and the boundary conditions for pressure are easily obtained. This new discretized pressure Poisson algorithm was tested at the lid-driven cavity flow problem on a nonstaggered grid and the results are also reliable

Calculation of critical parameters for spontaneous combustion for some complex geometries using an indirect numerical method

In the theory of spontaneous combustion, identifying the critical value of the Frank- Kamenetskii parameter corresponds to solving a bifurcation point problem. There are two different numerical methods used to solve this problem—the direct and indirect numerical methods. The latter finds the bifurcation point by solving a partial differential equation (PDE) problem. This is a better method to find the bifurcation point for complex geometries. This paper improves the indirect numerical method by combining the grid-domain extension method with the matrix equation computation method. We calculate the critical parameters of the Frank-Kamenetskii equation for some complex geometries using the indirect numerical method. Our results show that both the curve of the outer boundary and the height of the geometries have an effect on the values of the critical Frank-Kamenetskii parameter, however, they have little effect on the critical dimensionless temperature. doi:10.1017/S144618111700057

Calculation Of Critical Parameters For Spontaneous Combustion For Some Complex Geometries Using An Indirect Numerical Method

In the theory of spontaneous combustion, identifying the critical value of the Frank-Kamenetskii parameter corresponds to solving a bifurcation point problem. There are two different numerical methods used to solve this problem-the direct and indirect numerical methods. The latter finds the bifurcation point by solving a partial differential equation (PDE) problem. This is a better method to find the bifurcation point for complex geometries. This paper improves the indirect numerical method by combining the grid-domain extension method with the matrix equation computation method. We calculate the critical parameters of the Frank-Kamenetskii equation for some complex geometries using the indirect numerical method. Our results show that both the curve of the outer boundary and the height of the geometries have an effect on the values of the critical Frank-Kamenetskii parameter, however, they have little effect on the critical dimensionless temperature

A study on the thermal decomposition temperature (TDT) and critical ambient temperature (CAT) of cotton

Cotton is a flammable material and some cottons would decompose or even self-ignite at bad storage and transport conditions. This paper studied the spontaneous combustion of cotton from the aspect of thermal decomposition temperature (TDT) and critical ambient temperature (CAT). From Fourier transform infrared spectroscopy analysis and chromatographic and mass spectrometric analysis, significant thermal decomposition was detected at the temperature of 210 ° C, which indicated that the TDT of cotton was around 210 ° C. From TG analysis and small-scale CAT test, activation energy of cotton and CAT of small cotton stack were obtained. Then, CATs of the cotton stacks with different dimensions were calculated based on Frank-Kamenetskii theory. With the dimensions l increased from 0.2 to 3.2 m, the CATs of cotton decreased from 195.0 to 137:9° C. The TDT of cotton was higher than these CATs, and the differences between TDT and CAT of cotton varied from almost 15-70 ° C (with the dimensions l increased from 0.2 to 3.2 m). As the experiments and calculation of the CATs were very complicated and time-consuming, the CATs of cotton can be estimated if the TDT was known. The result of this paper was especially meaningful for evaluating the risk of spontaneous combustion of cotton and speculating the reason of cotton fire

Comparison of thermal hazards of sodium dithionite and thiourea dioxide from thermal analysis (DSC-TG), small-scale self-heating experiments and FTIR smoke gas analysis

Sodium dithionite and thiourea dioxide are two typical reducing agents commonly used in industry. This paper compared the thermal hazards of sodium dithionite and thiourea dioxide based on DSC-TG (Differential Scanning Calorimetry and Thermogravimetry) thermal analysis, small-scale self-heating experiments and FTIR smoke gas analysis. From the thermal analysis (DSC-TG), sodium dithionite starts to lose crystal water at the temperature around 60 °C which makes the sodium dithionite very unstable at relatively lower temperature. The decomposition of sodium dithionite has a close correlation with oxygen while the decomposition of thiourea dioxide has little relationship with oxygen. Small-scale self-heating experiments were designed to reflect the self-heating and spontaneous combustion properties of the characteristic dimension 20 cm. The small-scale self-heating experiments show that there is a little gap between the Critical Ambient Temperature (CAT) of sodium dithionite and thiourea dioxide. From FTIR smoke gas analysis, the smoke of thiourea dioxide (decomposition or combustion) is far more dangerous than sodium dithionite. Although the risk of spontaneous combustion for sodium dithionite is higher than thiourea dioxide, the thermal hazards of thiourea dioxide are far higher than sodium dithionite as the decomposition and combustion of thiourea dioxide would release far more heat and dangerous smokes

The Thermal Properties of Nitrocellulose: From Thermal Decomposition to Thermal Explosion

Nitrocellulose is an extremely dangerous explosive substance, which will decompose at a relatively low temperature. This article studied the thermal properties transformed from thermal decomposition to thermal explosion for a less violent nitrocellulose sample (nitrogen content: 10.92%). Four experiments were implemented: XPS analysis and SEM analysis, DSC-TG analysis, and small-scale thermal explosion experiment. From XPS analysis and SEM analysis, high temperatures led to the decrease of N1s and O1s (O-NO2 bond) and the break or even melt of the nitrocellulose fibers. The results demonstrated that nitrocellulose would become more unstable if it was exposed to high temperature. From the DSC-TG analysis and small-scale thermal explosion experiment, the upper critical ambient temperatures (UCATs) of the nitrocellulose were calculated. The UCATs of the nitrocellulose sample would decrease from 132.5ºC to 96.4ºC with the dimensions increased from 0.1 m to 1.6 m. The results demonstrated that the risk of spontaneous combustion and thermal explosion increased significantly with the increase of the volume of nitrocellulose

The spontaneous combustion mechanism of sawdust from the aspect of biochemical components

Cellulose, hemicellulose and lignin are generally recognized as the main components of sawdust. In this paper, the spontaneous combustion mechanism of sawdust was studied from the aspect of these components. The thermogravimetry analysis and biochemical component analysis showed that the lignin decomposed evidently at the induction period of thermal decomposition of sawdust, and the lignin contents of sawdust also presented positive correlation with their spontaneous combustion risk. Scanning electron microscope, fourier transform infrared spectroscopy and X-ray photoemission spectra were implemented further. The results showed that: the cellulose remained stable at the induction period; for hemicellulose, the oxidation reaction took place, but it was very weak. However, for lignin, the dehydration reaction (loss hydroxyl group of alcohols) took place evidently so that the lignin exhibited an apparent porous structure. Therefore, the dehydration reaction of lignin might greatly affect the spontaneous combustion of sawdust

The influence of soluble components on spontaneous combustion risk of sawdust samples

Sawdust is a common by-product of wood processing industry. Spontaneous combustion would even take place under unfavorable conditions of storage and transportation. In this study, self-heating substances test experiments, Thermogravimetry (TG) experiments and Frank-Kamenetskii (FK) theory were used to compare the spontaneous combustion risk of three sawdust samples (DCP, CFE, and LOH). The results revealed that the Critical Ambient Temperatures (CATs) of DCP, CFE and LOH were 81.2 (±0.3), 96.0 (±0.4) and 125.9 (±0.3)°C respectively when the stack dimension reached 1.6 m. Lower CAT for sample indicated that it had a higher spontaneous combustion risk. On the other hand, the relationship between spontaneous combustion risk and soluble components of three sawdust samples was studied with Gas Chromatographic and Mass Spectrometric (GC-MS) experiments. The results found that if a sawdust sample contained more soluble components than other sawdust samples, the spontaneous combustion risk of this sample would also higher than other sawdust samples, and vice versa

Polymer solar cells spray coated with non-halogenated solvents

Using spray-coating technique, we successfully fabricated conventional ITO-based and inverted ITO-free polymer solar cells (PSCs) based on a conjugated polymer poly[2,3-bis-(3-octyloxyphenyl) quinoxaline-5,8-diyl-alt-thiophene-2,5-diyl] (TQ1) as the donor and [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) or [6,6] -phenyl-C71-butyric acid methyl ester (PC71BM) as the acceptor. Environment-friendly non-halogenated solvents were used to process the active layers. The influence of substrate temperatures and processing solvents on the photovoltaic performance of the ITO-based TQ1:PC61BM PSCs was systemically investigated. A higher substrate temperature can accelerate the solvent evaporating rate and afford a micro-textured rougher surface, which efficiently reduced light reflectance and enhanced absorption. Furthermore, finer phase separation was observed when using this high substrate temperature, which led to enhanced photocurrent due to the reduced bimolecular recombination. The device performance of spray-processed PSCs using the non-halogenated solvent mixtures was comparable to that of spray-processed PSCs using the halogenated o-dichlorobenzene (oDCB), which demonstrates that the non-halogenated solvents are very promising in spray-processed PSCs. This work sheds new light on developing efficient roll-to-roll compatible spray-coated PSCs with environment-friendly solvents