that the particle is lost once it comes in contact with the wall the particle tracking models used in cfd ace u00ae also account for stochastic transport using the well known brownian model design analysis has shown that the concentrator design is capable of achieving concentration ratios gt 1 000 u00d7 while maintaining high sample retention efficiencies at sampling rates of u02dc 5 l min for aerosol particles in the range of 1 10 u03bcm in diameter concentration ratios of u02dc 10 000 u00d7 are attained when the aerodynamic and electrostatic forces are balanced through careful design of the air particle flow rate and voltage the performance of concentrator designs can be characterized using two different performance metrics concentration ratio cr and retention ratio rr the cr is the ratio of the particle concentration at the concentrator outlet to that at the inlet and the rr is defined as the ratio of the particle number at the outlet to that at the inlet as shown below where subscripts u201c in u201d and u201c out u201d represent the quantities at the inlet and outlet of the concentrator chamber n is the number of particles q is the airflow rate enclosed by the particle furthest from the axial chamber centerline in addition an index of power expenditure pe can be defined as the sum of the mechanical power and the electrical energy needed to supply the focusing potential where q and u03b4p is the sampling airflow rate and pressure drop through the concentrator u03b4v is the potential difference across the adjacent electrodes a e is the area of the electrodes and i represents the current.