The objective of the present work is to develop and calibrate a novel, vertical solid particle injector that uses the pressure drop in the air flow across an orifice plate in a circular pipe, to naturally entrain micron-sized solid particles such as coal dust. The particles continuously drop from a feeder located outside the pipe into the orifice plate through peripheral (side) openings in the pipe, where they are carried upwards by the air flow accelerated near the orifice exit. Three types of designs for the peripheral openings, in terms of the shape, size and number are evaluated by testing which one of them results in maximum particle entrainment. The device is calibrated by recording the mass loss rate of the powder as a function of volumetric flow-rate of air. The results show that there is an optimum area for the side openings, at which the injector performance will be the best for the given pipe and orifice-hole sizes. The entrainment rate is found to be a non-linear function of the flow-rate for low air flow-rates (till around 9.4. g per minute) and for higher air flow-rates it becomes an almost linear function. © 2011 Elsevier B.V.