Gas Dilution With the Equal Capillaries Technique
The advantages of the equal capillaries technique are surprising and leads to reach accuracy values of one order of magnitude better than all the other dynamic dilution techniques. This comparison will be supported by analyzing the accuracy available with two different techniques.
Nozzles (sonic or non-sonic) technique
With this technique, a series of different size nozzles is used to provide, applying a constant pressure, a flows series complying with the 2 n progression. That means if the smaller nozzle is involved by a flow q, the flow through the next is 2•q, through the next again is 4•q, and so on. Combining in parallel different nozzles combinations, all of the integer multiples of q may be obtained. Supplying one part of the nozzles with the gas to be diluted and the remaining with the diluting gas, all the possible dilutions are obtained at intervals whose distance depends upon the number of used nozzles.
For example, with 3 nozzles 8 dilutions are possible (0, 1/7, 2/7, 3/7….6/7, 7/7) , with 4 are possible 16 and so on, complying with the progression 2 n . The advantage of this technique is in the fact that using few nozzles many dilution ratios are possible.
It’s important to verify how much the selection of the nozzles may be accurate before they are installed in the diluter in a way that the wanted flows progression be complied. The series of four targets shown here gives an idea of the proportions between the required flows measurements : Having 4 nozzles, 4 flows must be measured and the targets diameters are proportional to the relevant flows.