code: def particle_number_concentration(ConcMat, material):
      
      return ConcMat.to(material.Density.units) / ((material.Density * np.pi * material.Diameter**3) / 6)
docs: Return the number of particles in suspension.
  
      :param ConcMat: Concentration of the material
      :type ConcMat: float
      :param material: The material in solution
      :type material: floc_model.Material