Investigation into continuous spray and metered spray using compressed gas propellant

Miguel, M

Abstract

In general all the domestic aerosol products use hydrocarbon propellants (i.e. butane and propane) in which a high flash vaporisation provides a good atomisation. However, according to the 2015 United Nations Climate Change Conference agreed in Paris, these propellants have the adverse climatic effects due to the level of VOC’s (Volatile Organic Compound) which can lead to greenhouse gases. The agreement has given an impetus to industry to significantly reduce these harmful gases by 2020. Therefore, an alternative energy is required to replace the corresponding hydrocarbon compositions by utilising safer propellant such as compressed gas (i.e. Nitrogen or air). Although the energy of the compressed gas is about 70 times lower than the hydrocarbon propellants. The new valving arrangement which was used in this study, is however introducing the propellant into the valve stem to create ‘bubbly flow’ thus increasing the turbulence prior to the atomiser insert of the actuator. The domestic aerosol products are generally based on either spraying continuously (i.e. airfreshners, body spray, hairspray, insecticide, polish and disinfectant) or on spraying on metered liquid dosage.

This investigation has focused on two different aerosol products: (i) Continuous spraying aerosol with matching valve_actuator using compressed gas propellant (ii) Metered aerosol product for airfreshners, using a specially design compressed gas valve with ‘L’ shape actuator and MBU (Mechanical Breakup Unit) inserts which are normally used as wall-mounted devise.

The new valve design for continuous spray is performing similar to the current commercial products with hydrocarbon propellants in terms of spraying discharge rate and drop size through the packlife. Nevertheless, due to the nature of the compressed gas which contains significant level of moistures, as the main propellant, the applied sprays could inevitably be wetter with an increase dryness time which are not acceptable by the consumers. The challenge of this study therefore was to identify a robust solution to reduce the discharge rate to about 0.30 g/s to 0.50 g/s and average particle size, Dv50, 30 µm to 40 µm through the can life. The results found here showed that the low discharge rates with conforming droplet sizes are achievable and thus providing substantive reduction in the wetness of approximately 50% compared to the high discharge rates (i.e. 1.4 g/s – 1.1 g/s).

Although the novel metered valve design which was used in this investigation, has been developed successfully to employ compressed gas as a propellant. However, the design needed to be diligently modified since the valve had presented an acceptable double actuation (or liquid dosage) after each pulse. Moreover, the valve appeared to cause some liquid leakages which were deposited around the stem and around the mounting cup after each actuation. This study presented a modified design of the metered valve stem that prevents the liquid droplet leakage which could have otherwise led to dysfunctionality of the valve and the mounting wall devise. This was carried out by redesigning and relocating the stem liquid holes on the upper chamber of the stem together with the reduction of the stroke of the stem. These modifications were thus prevented the double actuation of liquid dosage on each pulse using the metered valve_‘L’ shape actuator_MUB insert. The results presented the constant discharge rate of 50 µL to 120 µL through the packlife of the can with average drop size, Dv50, of 60 µm – 70 µm using the relevant wall mounting devises.

Citation

Miguel, M. Investigation into continuous spray and metered spray using compressed gas propellant. (Dissertation). University of Salford

• Thesis Type: Dissertation
• Deposit Date: Jan 19, 2018
• Publicly Available Date: Jan 19, 2018