A coiler drum cleaner for cleaning the drum of a coiler furnace is disclosed. The method is preferably used in an estimator for channel coefficients in a base station or in a mobile station in a mobile radio system. The coated substrates possess both hydrophobic and oleophobic properties. The stream of gas surrounded by the liquid in the pressure chamber flows out of an exit orifice of the chamber into a liquid thereby creating a monodispersion of bubbles with substantially uniform diameter.