WATERJET USE IN DECONTAMINATING SURFACES

摘要

Decontamination of surfaces with complex geometry requires that all the surfaces are contacted and cleaned. Not only must each point be reached, but the cleaning mechanism must have sufficient energy to dislodge and remove the contaminating material. The most common method for removing dirt and a number of chemicals is through the use of fan shaped waterjet nozzles operated in much the same way as those found in a conventional car wash. However the structures of many of these jets forming nozzles is poor, and they rapidly erode under use. As a result the jets which are produced rapidly disintegrate into a mist of fine droplets which rapidly decelerate and become ineffective. Common stand-off distances for such nozzles are in the range from 15 to 30 cm, for example and yet many nozzles which have been tested do not produce an effective jet stream beyond around 10 cm. Typical results from a comparative test program are included, along with a simple method for evaluating nozzle performance. Rapidly rotating round jet streams, inclined outwards so that they cover a conic path provide a more coherent structure, which carries a greater level of energy down onto the target surface over a much greater stand-off distance. However there is a trend to use higher and higher pressures, with concomitantly smaller jet diameters, in order to conserve power and water use. This can result in a decrease in the range of the cleaning tool, which may not be evident to the untrained operator, given the structure of the jet stream and plume. Relatively effective operating ranges are discussed and the benefits of different regimes in different circumstances are reviewed.