Numerical analysis of supersonic flow through dry-ice blasting nozzles: Comparative study of nozzle designs and particle transport efficiency

Abstract

Dry ice blasting is an effective method for industrial dirt removal. This cleaning technique is based on treating contaminated surfaces with a high-speed mixture of dry-ice and air. The dry ice blasting mechanism operates through three main phenomena: thermal effects (cooling), abrasion due to kinetic energy, and sublimation. The final force impacting the cleaning surface is the sum of three components: the force of compressed air, the force exerted by solid CO₂ particles due to their velocity, and the sublimation force resulting from a sudden phase change accompanied by rapid volume expansion. One of the critical factors related to this cleaning mechanism are the blasting mixture parameters. The primary system component influencing these parameters is the nozzle. This study aimed to compare different nozzles’ geometries, particularly in the terms of their effect on dry-ice particle behaviour. To achieve this, a mathematical model of supersonic, two-phase flow with particle–wall collision and mass consumption was developed and implemented in the Ansys CFX numerical environment. A key aspect of the modelling process was accurately simulating dry-ice particles, as their behaviour in a supersonic nozzle has not been thoroughly described in the literature to date. Particle transport efficiency depends on the nozzle geometry, inlet pressure, and particle size. Typical efficiency values for the nozzles considered in this study exceed 85 %, with a maximum efficiency of 91.1 % achieved using nozzle A at an inlet pressure of 4 bar. The lowest efficiencies (highest loses) were observed for particles with a diameter of 250 µm in all cases. The cleaning zone was defined as the region 15–30 cm from the nozzle outlet. In this section, particle velocities range from 50 to 150 m/s depending on the distance, particle diameter, and nozzle geometry. The developed model can serve as a valuable tool for assessing new nozzle geometries.