In this work, the effect of spatial distribution and values of the turbulent kinetic energy on the pressure-time history and then on the explosion parameters (deflagration index and maximum pressure) was quantified in both the standard vessels (20 L and 1 m3).The turbulent kinetic energy maps were computed in both 20 L and 1 m3 vessels by means of CFD simulations with validated models. Starting from these maps, the turbulent flame propagation of cornstarch was calculated, by means of the software CHEMKIN. Then, the pressure-time history was evaluated and from this, the explosion parameters.Calculations were performed for three cases: not uniform turbulence level as computed from CFD simulations, uniform turbulence level and equal to the maximum value, uniform profile and equal to the minimum value. It was found that the cornstarch in the 20 L vessel get variable classes (St-1, St-2, St-3) with respect to the 1 m3 (St-1). However, simulations performed on increasing the ignition delay time, shown that the same results can be attained only using 260 ms as ignition delay time in the 20 L vessel. 相似文献
Blast wave and fragment are two main types of physical damage effects representing a significant threat to storage tank structures in chemical industrial parks. Compared with the effect of only blast wave or fragment, the coupling effect of them may cause more severe consequences and is worthy of study. A numerical study of the dynamic responses and damage of a vertical storage tank subjected to the coupling effect of blast wave and fragment is conducted based on a typical accident. The simulation results reveal that stress-concentration and rapid increase of the stress exist in the impacted region of the storage tank under the coupling effect, which leads to the structural damage of the tank exhibiting different failure modes. The coupling effect is significantly apparent following a dramatic increase of the plastic strain, and the damage of the storage tank is further aggravated. From the displacement response and energy absorption, the overall damage of the storage tank subjected to the coupling effect is more severe than that caused by blast wave and fragment separately, which also indicates that the coupling effect is an enhanced damage effect. Besides, the contribution of blast wave and fragment to the coupling effect depends on scaled distance. The results of the study help reveal the coupling effect of blast wave and fragment and prevent domino accidents caused by the coupling effect. 相似文献
A multiphase box model for a remote environment of the troposphere has been developed with an explicit chemistry for both gas and aqueous phase. The model applied to a set of measurements performed by Voisin et al. (2000) during the European CIME experiment for a cloud event on 13th December 1997 at the top of the Puy de Dôme (France). The results of the simulation are compared to the measurements in order to follow the evolution of the ambient chemical composition as a function of the pH and of the varying water content. After verifying that the model retrieves the main features observed in the behavior of species in the cloud droplets, a detailed analysis of the simulated chemical regime is performed. It essentially discusses the sources and sinks of radical in aqueous phase, the relative importance of the oxidation pathways of volatile organic compounds by the main radicals and the conversion of S(IV) into S(VI) which seems to be influenced by the presence of peroxonitric acid, HNO4, in aqueous phase in the environmental conditions that are considered with low H2O2. These numerical results are then compared with the theoretical study from Herrmann et al. (2000), who proposed a slightly different mechanism, including C2 chemistry and transition metal chemistry whereas they neglect some reaction pathways, such as the one involving OHCH2O2 radical. This double confrontation between model results and both real experimental data and numerical results from Herrmann et al. (1999c) underlines limitations of such modeling approach that does not include any dynamical or microphysical coupling but also demonstrates its capability to identify the main oxidants or reactants in aqueous phase in real environmental conditions more realistic than a purely theoretical approach. The originality of this study resides in the explicit and exhaustive ways the chemical reactions are treated in aqueous phase and in a first attempt to compare such a detailed chemical scheme to real environmental conditions. 相似文献
The calibration of scintillation detectors for gamma radiation in a well characterized setup can be transferred to other geometries using Monte Carlo simulations to account for the differences between the calibration and the other geometry. In this study a calibration facility was used that is constructed from bricks of well-known activity concentrations of 40K and of radionuclides from the 238U- and 232Th-series. Transfer of the calibration was attempted to a Marinelli beaker geometry with the detector inside a lead shield and to an in situ application with the detector positioned on a sand bed. In general this resulted in good correspondence (within 5-10%) between the activity concentrations derived using the transferred calibration and activities that were derived by independent measurements. Some discrepancies were identified that were attributed to coincident summing in the natural decay series and interference of radon. 相似文献
The injection of CO2 at the Ketzin storage site and the chemical detection of its arrival in the observation well allowed testing of different numerical simulation codes. ECLIPSE 100 (E100, black-oil simulator), ECLIPSE 300 (E300, compositional CO2STORE) and MUFTE-UG were used for predictive modelling applying a constant injection rate of 1 kg s?1 CO2 and for a history match applying the actual variable injection rate which ranged from 0 to 0.7 kg s?1 and averaged 0.23 kg s?1. The geological model applied, is based on all available geophysical and geological information and has been the same for all programs.The results of the constant injection regime show a good agreement among the programs with a discrepancy of 21–33% for the CO2 arrival times. However, it is determined from the comparison of the cumulative mass of CO2 at the time of CO2 arrival that the injection regime is an important factor for the accurate prediction of CO2 migration within a saline aquifer. Comparing the actual variable injection regime with the simulations applying a constant injection rate the results are relatively inaccurate.Regarding the actual variable injection regime, which was evaluated using all three simulators, the computational results show a good agreement with the data actually measured at the first observation well. Here, the calculated arrival times exceeded the actual ones by 8.1% (E100), 9.2% (E300) and 17.7% (MUFTE-UG).It can be concluded that irrespective of the deviations of the simulations, due to combinations of different codes and slight differences in input parameters, all three programs are well equipped to give a reliable estimate of the arrival of CO2. Deviations in the results mainly occur due to different input data and grid size choices done by the different modelling teams working independently of each other. Deviations of the simulations results compared to the actual CO2 arrival time result from uncertainties in the implementation of the geological model, which was set up based on well log data and analogue studies. 相似文献
Colloid-facilitated transport has been recognized as a potentially important and overlooked contaminant transport process. In particular, it has been observed that conventional two phase sorption models are often unable to explain transport of highly sorbing compounds in the subsurface appropriately in the presence of colloids. In this study a one-dimensional model for colloid-facilitated transport of chemicals in unsaturated porous media is developed. The model has parts for simulating coupled flow, and colloid transport and dissolved and colloidal contaminant transport. Richards' equation is solved to model unsaturated flow, and the effect of colloid entrapment and release on porosity and hydraulic conductivity of the porous media is incorporated into the model. Both random sequential adsorption and Langmuir approaches have been implemented in the model in order to incorporate the effect of surface jamming. The concept of entrapment of colloids into the air-water interface is used for taking into account the effect of retardation caused due to existence of the air phase. A non-equilibrium sorption approach with options of linear and Langmuir sorption assumptions are implemented that can represent the competition and site saturation effects on sorption of multiple compounds both to the solid matrix and to the colloidal particles. Several demonstration calculations are performed and the conditions in which the non-equilibrium model can be approximated by an equilibrium model are also studied. 相似文献
A mathematical model is presented which allows one to treat the combined phenomena of heat, mass and species transfer by diffusion as they occur within smouldering fires in accumulations of dust or other solid bulk materials. The model was applied to predict self-ignition temperatures of five different dusts, where it could be shown that computed and experimental self-ignition temperatures coincide within an error margin of ±5%.
For smouldering fires, if initiated by either self-ignition or an ignition source, it could be shown that the temperature and the velocity at which the reaction front propagates both depend on the volume of the dust accumulation. In addition, the propagation velocity increases when the initial temperature of the dust accumulation is increased and decreases when the initial moisture content of the dust accumulation is increased.
Comparisons of the numerical model with experiments show that the smouldering propagation is mirrored qualitatively, while the accuracy of the computations strongly depends on the accuracy of the input parameters, namely on the apparent activation energy. 相似文献