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March 2020 / 29 the rate or amount of conveying line buildup can be decreased by reducing the effective air velocity. Power consumption. The nature of air compression dictates that the energy to drive a compression device is proportional to both the volume being compressed and the differential pressure it achieves. If you can reduce either the volume or the pressure, then a reduc- tion of energy power is accomplished. However, if you can reduce both the volume and the pressure simul- taneously, then the two factors will have an additive effect and attain an even greater power savings. Dilute- phase conveying systems will naturally have lower pressure and volume when the conveying velocity is reduced. The equation in Figure 2 describes adiabatic compression where η is the compression efficiency, Q is the mass airflow rate, P 1 and P 2 are the pressures before and after compression, respectively, and ɣ is the adiabatic constant for air. This equation establishes the power needed to drive a rotating compression device. Let's apply the information in the table in Figure 2 to the adiabatic compression equation. If a 10 percent reduction in airflow simultaneously caused a 5 percent reduction in the system's pressure, then the additive effect on the compression device would be a 14 percent reduction in power. In this way, velocity control can significantly affect the dilute-phase system's power < Airflow < Pressure < Power 5% 5% 9% 10% 5% 14% 10% 10% 18% 15% 10% 22% 20% 15% 30% p = η Q * P 1 P 2 γ −1 γ P 1 FIGURE 2 Power equation for air-movement device and additive effect FIGURE 3 Zenz plot for fiberglass-filled polyethylene pellets Zenz diagram Pressure drop/distance (mbar/m) Conveying velocity (m/s) 10 15 20 25 30 10 9 8 7 6 5 4 3 2 1 0 Pressure minimum �������� �� ����������������� ������������������������� ����������� ����������������� �������������� �!�"#!�$%��&� !'�()(*+(,-./01 �'�()(*+(,-./,2 %'�����3�������4��� '����4�������4��� $����5��������������6�$�����������$���������4