Thermal water service processes are invariably, to some extent, prone to deposit formation. Cleaning projectiles are among environmentally-friendly approaches that are utilized in tubular heating/cooling devices to mitigate fouling. This study investigates the impact of injection rate and multiple injections of two structurally different projectiles on their cleaning action in tubular heat exchangers. Fouling experiments are performed in which CaSO4 was used as foulant. The rate of projectile injection is varied to discern its impact on fouling mitigation. The results show that increasing the injection rate, i.e. decreasing the time between injections, increases the cleaning efficiency of the attempted projectiles such that it decreases the asymptotic fouling resistance. However, the injection rate is practically limited by the time needed for the projectiles to make a complete cycle around the tubes of the heat exchanger to be cleaned. It has also been found that multiple injections of projectiles improve cleaning. Multiple injections retard the fouling process significantly such that the asymptotic fouling resistance is much lower to that of a single injection. (C) 2014 Elsevier B.V. All rights reserved.