The diagram you've shared looks like a graph from a scientific study or a technical analysis. It appears to be a plot of a quantity referred to as "solids fraction" on the y-axis against another parameter on the x-axis. The graph contains three curves, each representing a different scenario:
ideal particles ndwalls2: This curve might represent a scenario where both particles and walls are considered ideal, likely referring to ideal behavior in the context of physics or chemistry, where interactions and other complicating factors are ignored.
non-ideal particles ndwalls2: This curve represents a non-ideal scenario for particles and walls, which suggests that this curve takes into account more realistic interactions or behaviors that deviate from the idealized model.
ideal particles, non-ideal ndwalls2: This line shows a situation where the particles are considered ideal, but the walls are non-ideal. This might indicate a mixed scenario where one aspect of the system is simplified while the other is treated more realistically.
The notation could refer to a squared distance or radius, potentially relevant in a context like particle packing, diffusion, or reaction kinetics, depending on the specific field of study.
The "solids fraction" could be a measure of the volume fraction occupied by solid particles in a given space, which is a relevant parameter in materials science, physics, and engineering, particularly in the study of granular materials, colloids, or composite materials.
The curves suggest that the solids fraction behaves differently under ideal and non-ideal conditions. Both the ideal and non-ideal cases show a U-shaped curve, but the non-ideal curve lies above the ideal curve, indicating a higher solids fraction for the same value of when non-ideal behaviors are considered.
Without additional context or information, it's challenging to provide a more detailed interpretation. The specific nature of the particles and walls, the physical meaning of the x-axis variable, and the context of the study or analysis would significantly affect the interpretation of this graph.
In fluidized bed simulations, the notation on the x-axis is less likely to represent particle size directly, as particle sizes are typically represented with a linear dimension rather than a squared term. The notation more commonly represents a squared distance or radius, which could be related to:
Location of the cell in the simulation: In computational fluid dynamics (CFD) simulations of fluidized beds, the domain is often divided into cells or control volumes where the properties of the fluid and particles are calculated. The could represent the location of the cell in a dimensionless form, where might be the radial position from the center or a reference point within the bed, and squaring it could be a way to normalize or account for geometrical effects.
Distance from the wall: Considering the context of fluidized beds and the mention of "walls" in the legend, could also denote the squared distance from the wall of the bed. In this case, the graph would show how the solids fraction changes as you move away from the wall. The squaring of the distance may relate to how the effect of the wall on the fluidization behavior decreases with the square of the distance, which is a common relationship in diffusion or field effect analyses.
Given the context of fluidized bed simulations and the notation, the x-axis likely represents a spatial dimension related to the position within the bed, rather than particle size. It is most probably indicating the distance from the wall, especially given the different behaviors depicted for ideal and non-ideal walls in the legend of the graph.
To be certain, you would need to refer to the specific article by Hoomans in 2000, as the exact meaning of would be defined there. If you have access to the article or the specific section that describes the graph, I could help interpret the details further.