Numerical modeling of unsteady compressible gas flow around a projectile

In this project, an attempt to calculate the characteristics of compressible gas flow around a projectile during the motion of the projectile in the gun barrel is undertaken. The flow is considered axisymmetrical, nonstationary, nonisothermal, compressible, and turbulent. For calculating the compressible gas flow around a projectile, the finite volume method was employed. An h-adaptive mesh refinement scheme based on elemental flow feature gradients is utilized for greater solution accuracy. For modeling flow around the moving projectile both sliding and dynamic meshes were used; The application of the calculations is in support of the Joint Actinide Shock Physics Experimental Research (JASPER). The JASPER facility utilizes a two-stage light gas gun to conduct equation of state experiments. The gun has a launch tube bore diameter of 28 mm, and is capable of launching projectiles at a velocity of 7.4 km/s using compressed hydrogen as a propellant. A numerical study is conducted to determine what effects, if any, launch tube exit geometry changes have on attitude of the projectile in flight. A comparison of two launch tube exit geometries is considered. The first case is standard muzzle geometry where the wall of the bore and the outer surface of the launch tube form a 90 degree angle. The second case includes a 26.6 degree bevel transition from the wall of the bore to the outer surface of the launch tube. For both cases, solutions are calculated for several positions downstream of the launch tube exit. The effect of beveled muzzle geometry on flight attitude of projectile is studied by using numerical modeling and results are compared with standard design, which is 90° of exit angle. (Abstract shortened by UMI.)

Numerical study of high temperature heat exchanger and decomposer for hydrogen production

This dissertation deals with three-dimensional computational modeling of a high temperature heat exchanger and decomposer for hydrogen production based on sulfur-iodine thermochemical water splitting cycle, a candidate cycle in the U.S. Department of Energy Nuclear Hydrogen Initiative. The conceptual design of the shell and plate decomposer is developed by Ceramatec, Inc. The hot helium from a nuclear reactor (T=975°C) is used to heat the SI (sulfuric acid) feed components (H2O, H2SO4 , SO3) to get appropriate conditions for the SI decomposition reaction (T\u3e850°C). The inner wall of the SI decomposition part of the decomposer is coated by a catalyst for chemical decomposition of sulfur trioxide into sulfur dioxide and oxygen. The proposed material of the heat exchanger and decomposer is silicon carbide (SiC); According to the literature review, there is no detailed information in available publications concerning the use of this type of decomposer in the sulfur-iodine thermochemical water splitting cycle. There is an urgent need for developing models to provide this information for industry. In the present study, the detailed three-dimensional analysis on fluid flow, heat transfer and chemical reaction of the decomposer have been completed. The computational model was validated by comparisons with experimental and calculation results from other researchers; Several new designs of the decomposer plates have been proposed and evaluated to improve the uniformity of fluid flow distribution in the decomposer. To enhance the thermal efficiency of the decomposer, several alternative geometries of the internal channels such as ribbed ground channels, hexagonal channels, and diamond-shaped channels are proposed and examined. It was found that it is possible to increase the thermal efficiency of the decomposer from 89.5% (baseline design) up to 95.9% (diamond-shaped channel design); The calculated molar sulfur trioxide decomposition percentage for the baseline design is 64%. The percentage can be increased significantly by reducing reactants mass flow rate and with increasing channel length and operation pressure. The highest decomposition percentage (∼80%) for the alternative designs was obtained in the diamond-shaped channels case; The sulfur dioxide production (throughput) increases as the total mass flow rate of reacting flow increases, regardless of the fact that the decomposition percentage of sulfuric trioxide decreases as total mass flow rate of reacting flow increases

Numerical modeling of high temperature bayonet heat exchanger and decomposer for decomposition of sulfur trioxide

Motivation Hydrogen is an attractive energy carrier in the future energy technology. Hydrogen is produced from splitting of water through various process namely electrolysis, photo-electrolysis, photo-biological production and thermochemical water-splitting. The aim of this study is to numerically investigate fluid flow, heat transfer and chemical reaction in bayonet high temperature heat exchanger and decomposer. Parametric studies are performed to achieve maximum decomposition with less pressure drop

Modeling and Parametric Study of a Ceramic High Temperature Heat Exchanger and Chemical Decomposer”.

ABSTRACT It is proposed to use ceramic high temperature heat exchanger as a sulfuric acid decomposer for hydrogen production within the sulfur iodine thermo-chemical cycle. The decomposer is manufactured using fused ceramic layers that allow creation of channels with dimensions below one millimeter. A three-dimensional computational model is developed to investigate the fluid flow, heat transfer, stresses and chemical reactions in the decomposer. Fluid, thermal and chemical reaction analyses are performed using FLUENT software. Temperature distribution in the solid is imported to ANSYS software and used together with pressure as the load for stress analysis. Results of this research can be used as a basis for investigation optimal design of the decomposer that can provide maximum chemical decomposition performance while maintaining stresses within design limits

Numerical Modeling of Unsteady Gas Flow Around the Projectile in the Light Gas Gun

In this study, an attempt to calculate the characteristics of gas flow around a projectile during the motion of the projectile in the Joint Actinide Shock Physics Experimental Research (JASPER) light-gas gun is undertaken. The flow is considered as axisymmetric, nonstationary, nonisothermal, compressible, and turbulent. For calculating the flow around the projectile, the finite volume method was employed. A comparison between two launch tube exit geometries was made. The first case was standard muzzle geometry, where the wall of the bore and the outer surface of the launch tube form a 90 degree angle. The second case included a 26.6 degree bevel transition from the wall of the bore to the outer surface of the launch tube. The results of the calculations are represented in figures depicting the flow at different moments of time. The figures show the fields of velocity, pressure and density, as well as the appearance of shock waves inside the geometry. Some comparisons with calculations of the same problem but using finite-element method were made. The obtained results can be further used for optimization JASPER geometry. The results also can be used for calculating the gun barrels for the strength and the oscillatory stability. In our future study we will couple structural analysis of the gun barrel material with the gas dynamic calculation of motion of the projectile in the gun barrel with the use of advanced computational methods

Numerical Modeling of High-Temperature Shell-and-Tube Heat Exchanger and Chemical Decomposer for Hydrogen Production

Numerical simulations of shell-and-tube heat exchanger and chemical decomposer with straight tube configuration and porous media were performed using FLUENT6.2.16 to examine the percentage decomposition of sulfur trioxide. The decomposition process can be a part of sulfur–iodine (S–I) thermochemical water splitting cycle, which is one of the most studied cycles for hydrogen production. A steady-state, laminar, two-dimensional axisymmetric shell-and-tube model with counter flow and parallel flow arrangements and simple uniform cubical packing was developed using porous medium approach to investigate the fluid flow, heat transfer and chemical reactions in the decomposer. As per the investigation, the decomposition percentage of sulfur trioxide for counter flow arrangement was found to be 93% and that of parallel flow was 92%. Also, a high pressure drop was observed in counter flow arrangement compared to parallel flow. The effects of inlet velocity, temperature and the porous medium properties on the pressure drop across the porous medium were studied. The influence of geometric parameters mainly the diameter of the tube, diameter of the shell and the length of the porous zone on the percentage decomposition of sulfur trioxide in the tube was investigated as well. A preliminary parametric study of the mentioned configuration is conducted to explore effects of varying parameters on the decomposition of sulfur trioxide. From the performed calculations, it was found that the Reynolds number played a significant role in affecting the sulfur trioxide decomposition. The percentage decomposition decreases with an increase in Reynolds number. Surface-to-volume area ratio and activation energy were also the important parameters that influenced the decomposition percentage. A high surface-to-volume area ratio enhances the rate of the chemical reaction and high activation energy decreases the decomposition percentage. The decomposition of sulfur trioxide is calculated and compared for both counter and parallel flow arrangements

Flow Distribution on the Tube Side of a High Temperature Heat Exchanger and Chemical Decomposer

Numerical simulations of a high temperature shell and tube heat exchanger and chemical decomposer (thereafter — heat exchanger) with straight tube configuration have been performed using Fluent 6.2.16 code to examine flow distribution on the tube side. The heat exchanger can be a part of sulfur iodine thermochemical water splitting cycle which is one of the most studied cycles for hydrogen production. Uniformity of the flow distribution in the heat exchanger is very critical because the flow maldistribution among the tube or shell sides can result in decreasing of chemical decomposition and increasing of pumping power. In the current study the flow rate uniformity in the heat exchanger tubes has been investigated. Simulations of the straight tube configuration, tube configuration with baffle plate arrangement and with pebble bed region inside the tubes were performed to examine flow distribution on the tube side. It was found the flow maldistribution along the tube direction is very serious with the simple tube configuration. An improvement of the header configuration has been done by introducing a baffle plate in to the header section. With the introduction of the baffle plate, there was a noticeable decrease in the flow maldistribution in the tubes. Uniformity of flow was also investigated with catalytic bed inside the tubes. A significant decrease in flow maldistribution was observed with this arrangement. But if the catalytic bed zone is created on the shell side, then the improved header configuration with a baffle plate is best suitable to avoid flow maldistribution

Computational Model of Airflow in Upper 17 Generations of Human Respiratory Tract

Computational fluid dynamics (CFD) studies of airflow in a digital reference model of the 17-generation airway (bronchial tree) were accomplished using the FLUENT® computational code, based on the anatomical model by Schmidt et al. [2004. A digital reference model of the human bronchial tree. Computerized Medical Imaging and Graphics 28, 203–211]. The lung model consists of 6.744×106 unstructured tetrahedral computational cells. A steady-state airflow rate of 28.3 L/min was used to simulate the transient turbulent flow regime using a large eddy simulation (LES) turbulence model. This CFD mesh represents the anatomically realistic asymmetrical branching pattern of the larger airways. It is demonstrated that the nature of the secondary vortical flows, which develop in such asymmetric airways, varies with the specific anatomical characteristics of the branching conduits

Calculation of Fluid Flow Distribution Inside a Compact Ceramic High Temperature Heat Exchanger and Chemical Decomposer

Numerical analysis of flow distribution inside a compact ceramic high temperature heat exchanger and chemical decomposer (thereafter, heat exchanger), which will be used for hydrogen production, wherein the sulfur iodine thermochemical cycle is performed. To validate the numerical model, experimental investigation of the heat exchanger is accomplished. The study of the flow distribution in the base line design heat exchanger shows that the design has large-flow maldistribution and the reverse flow may occur at poor inlet and outlet manifold configurations. To enhance uniformity of the flow rate distribution among the heat exchanger internal channels, several improved designs of the heat exchanger manifolds and supply channels are proposed. The proposed designs have a sufficiently uniform flow rate distribution among the internal channels, with an appropriate pressure drop

Transient Analysis of a Ceramic High Temperature Heat Exchanger and Chemical Decomposer

Ceramics are suitable for use in high temperature applications as well as corrosive environment. These characteristics were the reason behind selection silicon carbide for a high temperature heat exchanger and chemical decomposer, which is a part of the Sulphur-Iodine (SI) thermo-chemical cycle. The heat exchanger is expected to operate in the range of 950°C. The proposed design is manufactured using fused ceramic layers that allow creation of micro-channels with dimensions below one millimeter. A proper design of the heat exchanges requires considering possibilities of failure due to stresses under both steady state and transient conditions. Temperature gradients within the heat exchanger ceramic components induce thermal stresses that dominate other stresses. A three-dimensional computational model is developed to investigate the fluid flow, heat transfer and stresses in the decomposer. Temperature distribution in the solid is imported to finite element software and used with pressure loads for stress analysis. The stress results are used to calculate probability of failure based on Weibull failure criteria. Earlier analysis showed that stress results at steady state operating conditions are satisfactory. The focus of this paper is to consider stresses that are induced during transient scenarios. In particular, the cases of startup and shutdown of the heat exchanger are considered. The paper presents an evaluation of the stresses in these two cases