The object of the present work was to design, construct and evaluate a cylindrical tri-axial charger for charging of submicron aerosol particles by unipolar ions. The corona discharge characteristics, the intrinsic and extrinsic particle charging efficiencies, and the losses of aerosol particles were experimentally evaluated for particle diameters in the range between 50 nm and 500 nm under different operating conditions. The conditions included the corona voltages of about 7.0 to 8.0 kV, the

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... sh screen voltages of about 100 to 300 V and the aerosol flow rate was set at 1.5 L/min. It was found that the ion current increased from 2.90´10-10 to 3.66´10-8 A and 2.40´10-10 to 1.36´10-7 A and the number concentration of ions increased from 7.50´109 to 5.92´1011 ions/m3 and 6.21´109 to 2.19´1012 ions/m3 when the corona voltage increased from 5.5 to 8.0 kV at the mesh screen voltage between 100 and 300 V, respectively. The intrinsic charging efficiency of particles introduced a constant value of about 99% for particle diameter in the range between 50 nm and 200 nm and decreased with particle diameter in the range between about 300 nm and 500 nm at a given corona voltage. The best extrinsic charging efficiency of the studied charger occurred between 1.32% and 38% for particle diameter in the range from 50 nm to 500 nm at corona and ion trap voltages of about 7.0 kV and 300 V respectively. The highest electrostatic loss of particles was observed at 50 nm particles and it was about 89.08, 90.73 and 91.91% at a mesh screen voltage of about 300 V for corona voltages of about 7.0, 7.5 and 8.0 kV, respectively. Finally, the highest diffusion losses were at about 28.88, 23.03 and 11.15% for singly charged, neutralized and non-charged particles of 500, 500 and 50 nm, respectively.