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Aerosol propellant selection

Aerosol propellant selection

2015-06-24
Aerosol propellant role has several aspects, which the most basic role is the product pressure, in actuation of the valve the liquid to spray out. At the same time, propellant also played a diluent, solvent and foaming agent, viscosity regulator or turbidity agent role, in some special occasions. It can also used in refrigerants, blowing dust agent, alarm agent (such as for ship flute) and special dewaxing agent, cold catalyst, fire agents and microbial statistics etc..
Agent is the most commonly used projectile is a lower alkyl size; propane, isobutane and n-butane, followed by dimethyl ether (DME), l, 1 - 2 ethyl fluoride (HFC-152a), high pressure CO2 gas, pair, N, and compressed air (4n2 / I, left several less commonly used, such as 1, 1, 1, 2 - four fluorine oxide (HFC - 114A), 2 - H heptafluoropropane (HFC - 227ca) and for fire extinguishing HCFC-124 / HFC - 23 etc.. And some of the vaporization of a liquid, like three pentane actually disdain in propellant, but due to the highly volatile, for safety reasons, sometimes it is the them as propellant.
If the propellant can be dissolved in liquid (or matrix). It is easy to make liquid in spray were smashed, to produce a spray. Interaction with liquid propellant will decide can produce fog and mist, the average particle size and size distribution. But when only the propellant is not to produce a spray can use a variety of mechanical crushing nozzle, the pressure in the tank can provide sufficient energy to produce
Raw eddy current or spray.
To produce a spray, the propellant must be large enough for the dispersion energy to break the surface tension of the liquid and other cohesion, if only a small amount of propellant dissolved in the liquid is not enough to do this. For example a saline spray, although o.69MPa hyperactivity of nitrogen, but can only produce a shares strong fluid flow, even at pressures up to 1.6s MPa of pure water and nitrogen system is the same, without the use of mechanical crushing nozzle.
O, 69 MPa pressure, carbon dioxide in each distillation range of petroleum hydrocarbon fractions in the solubility of up to 2.6% a 2.9%. Using common valves, using solvent oil liquid can produce the rough but fairly dispersed evenly spray: but when alkane carbon number distribution of up to 10 to 16. The spray becomes very rough, fog type with a dense core; and liquid materials for N.P. mineral oil spray effect is poor, the fog type dignified and almost form a piece. When using the USP mineral oil, the use of conventional with conical or straight pipe orifice of nozzle, will not result in a spray, but with inverse taper nozzle nozzle, only with a slight fluctuations in the surface of the jet or the stream a little ejecta. Therefore, the former is not enough to extend the flame in the flame extension test, while the latter is used as a result of the small mist particles, so that the whole jet can be ignited.
Propellant energy dispersion is a complex role. It connected with the pressure and molecular weight, high-pressure ejection agent more prone to fine spray particles. A simple example can illustrate the system of this 90% ethanol and 10% of the 102 propane (a I08), can produce a spray; and 90% ethanol and 10% isobutane system has strong radiation 6R: ethanol and n-butane system, almost no pressure and can only produce a fine liquid flow.
Ejection agent dispersion properties can thermostatic to 21 DEG C for standard and to the following simple test were measured: in accordance with the "DOT-2Q standard 57mm diameter tank filling in is 70% of the volume of ethanol, to have alcohol and valve tank weighing, and then get the capping machine side, with an excess of gasification ejection agent flush tank in the air of the air, well immediately add valve and sealing, thus increasing the quality of is the mass of the propellant.
Add ejection agent propellant accounted for 5% of the overall quality, in water bath shaking the whole pot temperature balance in 21'C, then pressure table (5.73 kPa pressure determination, absolute pressure) is 5% propellant pressure. At low concentration, pressure decreases with the concentration propellant into linear increase, according to the atmospheric pressure (10.122 kPa absolute pressure) and tank pressure can easily calculate the content of propellant. For low or liquefied propellant, the concentration (mass fraction) is usually in the range of 1.5% ~ 5.o%, for CO2, is about this concentration of 1 / 5 and nitrogen for concentration of 1 / 15. The concentration is lower, that the propellant better dispersion, and high pressure gas is usually better dispersion, but there are exceptions. The propellant with low molecular weight also showed good dispersion performance, but there are exceptions, for example, in ethanol or acetone, HCFC 22 than HF~12 or isobutane dispersion much. For the sake of safety, the formula workers often should consider the use of propellant as little as possible, but also make the formula in many contain active ingredients as possible. But sometimes, this rule may not work, because of low pressure propellant in a little sometimes to produce a relatively smooth, not too violent. The spray enables the use of a large diameter of the valve, and has more reserves to compensate the side hole or use after the loss, but also can reduce the viscosity, reduce the foaming tendency. Industrial production, with reference to the "standards, can be obtained by comparison of similar products, such as analysis, testing and consulting vendor or technology services company or query relevant literature, for example, isobutane almost entirely for sizing agent or fabric finishing. Volume fraction was 20% and 80% of propane, isobutane is still commonly used in paint products, if the propellant emulsion dispersed in aqueous phase products, to promote the development of the nozzle valve when.

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