Generally, there are recommended flow rates for liquids and gases in process manuals. Is there a recommended flow rate for solids (artesian flow)?

The self-flow of solids depends on experience, and it is still related to the characteristics of the solid.

I have never heard of the concept of self-flowing for solids. Generally, it must be considered in terms of conveying equipment.

Generally a screw conveyor or a belt conveyor is required

The flow rate of gas and liquid is used to calculate the pipe diameter. If you only use it to calculate the pipe diameter, you can generally estimate it this way. For the type of feed pipe you mentioned, the slope is generally set to 60°, and the minimum angle cannot be lower than 55°. The finer the particle size of the solid material, the larger the angle. As for the unloading speed, because solids have to consider friction, the surface roughness of different materials is different, and the friction is also different. Generally, a test is done, and then the volume of the plastic in the pipe diameter is calculated according to the material bulk density, and then the final unloading pipe diameter is estimated based on the material filling degree of 40%. Of course, there are also empirical formulas, but after trying them, we found that these formulas are often ideal. Designing according to these formulas may cause blockage in actual operation. You can check some papers on powder conveying, Beverloo discharge diameter, Brown powder discharge diameter