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Particle drag is a very important factor in reactor simulation. The complex physical properties of supercritical water (SCW) prevent some modeling methods of reactor simulation from being able to accurately simulate an SCW reactor. Therefore, in this work, the effects of particle interaction on single particle drag within a multi-particle system in SCW are investigated. The results show that the variation in the drag coefficient in SCW is special. This work indicates a control mechanism for the Reynolds number, volume fraction, temperature, and pressure on drag specificity of a single particle. This mechanism essentially exhibits an interaction of viscosity and velocity gradient. Furthermore, through a comparison of SCW and constant property flow, a drag specificity model can be initially developed. The results for SCW can be obtained by calculating the constant property flow, coupled with a drag specificity model. This model can be applied to modeling methods of reactor simulation after further improvement. [ABSTRACT FROM AUTHOR]

The interaction between the fluid and particles is the key to obtain accurate flow and heat transfer rules. For a reactive particle, the Stefan flow will affect the mass, momentum, and energy transfer between the particle and the fluid. The Stefan flow on the coal particle surface cannot be neglected in supercritical water gasification technology. In this paper, the influence of different Stefan flow intensities on the drag coefficient (Cd) and the Nusselt number (Nu) of supercritical water (SCW) cross flowing around a fixed spherical particle with Re in the range of 10–200 is studied; at the same time, the velocity and temperature boundary layers and the flow field around the particle are analyzed. For the influence of the dramatic change of the thermophysical properties of SCW near the pseudo-critical point, simple analysis of the drag coefficient and heat transfer of the particle with Stefan flow is conducted. The results show that with the increase in Stefan flow intensity, Cd and Nu decrease and the thickness of velocity and temperature boundary layers increases. A model of the particle with Stefan flow is constructed, and the Cd and Nu correlation formulas of the particle with Stefan flow are obtained. [ABSTRACT FROM AUTHOR]

Supercritical water fluidized bed is a novel gasification reactor which can achieve efficient and clean utilization of coal. The rough surface of particle produced during grinding and thermochemical conversion processing will deeply affect supercritical water-particle two-phase flow and heat transfer characteristics. In this paper, fully resolved numerical simulation of supercritical water flow past single rough sphere particle with the Reynolds number ranging from 10 to 200 was carried out to investigate the effect of surface roughness. The simulation results show that as roughness increases, the separation bubbles generated in the dimple enhance the flow separation but has no significant effect on the drag coefficient. Particle surface-average Nusselt number decreases with an increase of roughness and surface enlargement coefficient due to the isolation effect at low Re and local separation bubbles in the dimple at high Re. Furthermore, the effect of surface enlargement coefficient on heat transfer efficiency factor for supercritical water near the critical point is greater than that under constant property condition and has a higher dependence on Re. [ABSTRACT FROM AUTHOR]

Abstract Supercritical water fluidized bed (SCWFB) is a novel reactor which can achieve efficient and clean gasification of biomass. The study of supercritical water (SCW)-solid two-phase flow characteristics in SCWFB is of great significance for biomass conversion and optimization of the reactor. However, the work on the drag coefficient of single biomass particle and biomass particle cluster has limitations to describe the interactions between particles accurately. In this paper, two-particle model was used to study the drag coefficient and flow characteristics of supercritical water flow past biomass particle cluster in the range of 10 < Re < 200. The simulation results show the interactions between particles can transmit larger distances perpendicular to the flow field at low Re. Drag coefficient of particles is mainly affected by the wake zone generated behind the upstream particles and nozzle effect between particles. Nozzle effect which is significant at high Re will promote flow separation and make form drag and friction drag increase. And the wake zone generated behind the upstream particles has the opposite effect. Highlights • Momentum of SCW flow past two biomass spherical particles were studied. • Effects of Re and relative position of biomass particles were discussed. • The influence factors for C D and fluid field were discussed. [ABSTRACT FROM AUTHOR]

The drag of particle cluster within a high void fraction environment in supercritical water (SCW) is investigated by numerical simulation. The results show that the description pattern of particle drag in SCW is the same as that in constant property flow (CPF). The diffusion of pressure in the phenomenon of fluid flow around particle cluster caused that the variation pattern of drag coefficient is contrary to the classical conclusion. The normalized drag coefficient is mainly depending on the thermal properties. The internal flow characteristics of the particle cluster further confirm the effects of fluid flow around it. After separating the effects of thermal properties, the exponent - β representing the effects of void fraction in SCW is similar to that in CPF. A correlation for calculating the particle drag in SCW is developed based on this result. [Display omitted] • Effects of pressure diffusion in the bypass flow phenomenon on particle drag. • Analysis of interactions between particles under effects of thermal properties. • Distribution of normalized drag coefficients under effects of thermal properties. • A new drag model based on the momentum transfer coefficients. [ABSTRACT FROM AUTHOR]

• Numerical study on flow and heat transfer of SCW flow around particle pair with Stefan flow. • The fluid-particle interactions with different particle pair configurations under the Stefan flow. • The analysis of flow field, force, and heat transfer process around particles. For any flow process of mixtures containing dispersed reactive particles, especially highly concentrated particles, the particle-particle, and fluid-particle interactions are very complex and affect the overall flow. Supercritical water gasification technology is a complex multiphase-flow process that occurs in high-temperature reactors. Under these conditions, the components of the particle surface are heated and gasify to form a Stefan flow (i.e., a mass flow), which modifies fluid-particle interactions. The interaction between particles and the influence of Stefan flow cannot be ignored. In this work, we consider the simplest case of two identical spherical particles with different relative orientations and particle distances and discuss the flow and fluid-particle heat-transfer characteristics by numerical simulation of supercritical water flowing around the fixed two-particle system. We are particularly interested in the fluid-particle interactions with different particle configurations under the influence of Stefan flow. Three particle configurations are possible: tandem, cross, and parallel. The flow field, Nusselt number, drag coefficient, and temperature distribution around the particles are all analyzed. In comparison with a single particle, the two-particle configurations significantly affect the drag coefficient, Nusselt number, and vortex structure and Stefan flow strongly affects the wake vortex structure of two particles with small particle distance, reducing the drag coefficient and Nusselt number. [ABSTRACT FROM AUTHOR]