Small-sized aerodynamic stand for determining the efficiency of ice-forming aerosol generatorsPURPOSE
The aerodynamic stand is intended for testing full-size generators of ice-forming aerosols in ground conditions. The stand allows to determine the ice-forming efficiency — the number of active particles per unit weight of the composition or solution — at different temperatures of the supercooled cloud when the generators operate in conditions of blowing them with an air flow at a speed of up to 20 m/s.
COMPOSITION OF THE STAND
Fig.1. General view of the installation: wind tunnel (left), aerosol cube (middle) and cloud chamber (right)
The aerodynamic stand consists of:
• wind tunnel;
• cloud camera;
• aerosol dilution systems;
• aerosol sampling systems;
• systems of fastening and ignition of the aerosol generator;
• ice crystal registration systems.
The wind tunnel is designed to create an air flow blowing around the aerosol generator and includes:
• high pressure fan;
• working part with a diameter of 0,3 m and a length of 1,5 m;
• exhaust pipe with a diameter of 1,0 m and a length of 6 m;
• turbulator with a diameter of 0,1 m;
• generator fastening system in the working part.
The cloud chamber is designed to create a model fog with a given supercooling temperature. The working volume is 125 liters. The cloud chamber is equipped with a fan, an illuminator, a fog temperature meter and a steam generator.
The aerosol dilution system is designed to dilute the initial aerosol concentration in the wind tunnel and includes:
• sampler with a volume of 0,5 to 2 l;
• an aerosol cube with a volume of 1000 l, inside of which there are fans for air mixing.
The aerosol sampling system consists of:
• intake comb located perpendicular to the direction of the air flow;
• samplers with a volume of 50 ml up to 2000 ml.
The registration system is designed to capture and further count ice crystals formed in the cloud chamber and includes:
• optical microscope with digital camera.
Fig. 2. The working volume of the cloud chamber with thermostats, a thermometer, a fan, and a clarifier located in it
• Diameter of the section of the working part of the installation – 0,3 m;
• Air flow speed — up to 20 m / s;
• Supercooled fog temperature range — from -1°С to -25°С;
• Aerosol concentration dilution factor — up to 70;
• The minimum and maximum measured values of the output: ice-forming particles — 107 and 1017 g-1;
• The duration of one measurement is about 40 minutes;
• Root-mean-square error of one measurement of the yield of ice-forming particles from 1 gram of a pyrotechnic composition at a temperature of minus 10°C is not more than ± 120%;
• Power consumption — no more than 1 kW / h.
PRINCIPLE OF MEASURING THE ICE FORMING OUTPUT
The measurement principle is to determine the number of ice crystals formed when a known sample of aerosol produced by the operation of an ice-forming aerosol generator in an air stream is introduced into a supercooled water mist. An air flow with specified characteristics is created in a wind tunnel.
Fog is created in the working volume of the cooled cloud chamber by launching a jet of hot water vapor. The number of ice crystals formed is estimated from the number of crystals that fell per unit area of the cloud chamber floor. The capture of crystals is carried out in a microthermostat, which keeps ice crystals for a time sufficient for their counting with a microscope.
EFFICIENCY OF ICE-BREAKING COMPOSITIONS DEVELOPED IN RUSSIA WITH PARTICIPATION OF THE AGENCY