Andrew J. Yule

Drop size and velocity measurements in an electrostatically produced hydrocarbon spray

Liquid hydrocarbons are difficult to atomize electrostatically at practical flow rates due to their high resistivities and low concentration of charge carriers. However special “charge injection” techniques have been used in this investigation to produce combustible sprays of oils. An experimental investigation of the drop size and velocity distributions within a charged kerosine spray is presented, using a PDA system and photographic methods. Bimodal size distributions are found with a central core of larger drops or ligament formations near the nozzle surrounded by a sheath of smaller drops. Because of the bimodal character the concept of average diameter for the spray is difficult to apply so that there is little practical use defining a relationship between mean drop diameter and mean specific charge without a knowledge of a relationship between charge and size of individual drops. Examination of the velocity component distributions showed the processes which control the two-zone characteristics of the spray. The larger drops have a high inertia and were less deflected by the space charge force within the spray and it is argued that the larger drops possess a smaller specific charge compared with the smaller drops which reinforces the tendency for the large drops to remain along the spray centreline. For the smaller drops the converse is the case, to the extent that at low flow rates their trajectories have a negligible axial velocity component and recirculation toward the earthed injector body is observed.

A new fine spray, low flowrate, spill-return swirl atomizer

A novel high liquid pressure fine spray swirl atomizer has been developed, which incorporates a spill-return orifice into the rear face of the swirl chamber with the aim of giving a significant reduction in flowrate while maintaining the droplet size. The initial work modified a commercial atomizer to add spill return. However, drop sizes were considered to be too large and a new design was constructed based on an earlier work on efficient high-pressure (up to 120 bar) swirl atomization. The resulting fine sprays can be used for various applications such as humidification, cleaning, coating, cooling, and decontamination. The atomizer has been characterized for different geometries, supply pressures, and spill-return orifice sizes using a Laser Particle Sizer and Phase Doppler Anemometry. For an exit orifice of 0.3mm diameter and spill orifice 0.5mm diameter, the drop size (Sauter mean diameter) is less than 20m for flowrates as low as 0.1litre/min and with a mean axial drop velocity of approximately 12m/s. An average liquid volume flux of 0.014(cm3/s)/cm2 is obtained in the spray at 150mm downstream.

The utilisation of fine sprays for Chemical, Biological, and Radiological or Nuclear (CBRN) Decontamination

The risk of exposure to hazardous materials, in many industrial environments and in everyday life due to the possibility of terrorist attacks, is widely recognised. It is therefore pertinent to have robust decontamination equipment to limit the effects of hazardous materials and in turn protect human life and assets. This can be done by the application of neutralisation (coverage) and rinsing techniques to the hazardous materials. The overall aim of this paper is to describe an investigation utilising fine sprays for coverage/deposition on the human body, in conjunction with standard safety showers for rinsing of a victim during decontamination of CBRN materials. As a novel feature miniature high pressure spill-return atomiser are used. It was found that fine sprays decrease the consumption of decontamination liquid that is normally used in practice which has many advantages in practice.

Novel metered aerosol valve

The design and performance of a new valving mechanism for portable pressurized spraying devices is described, where the propellant in the device is a safe gas (so-called compressed gas) propellant rather than the current liquefied gases all of which are either volatile organic compounds or greenhouse gases. The valve sprays a fixed volume of liquid when the spraying actuator is depressed, as is essential used medical sprays, such as pressurized metered dose inhalers and nasal sprays, and also for automatic (wall-mounted) aerosol delivery systems for air-fresheners, insecticides and disinfectants. For ‘compressed gas’ aerosol formats, there is no flash vaporization of propellant so that pumping liquid from a metering chamber and atomization to form a spray must be achieved entirely by designing some means of using the pumping action of the gas in the container to act upon the liquid in the metering chamber. The new design utilizes a loosely fitting spherical piston element and a simple arrangement of a concentric housing and a moveable valve stem, such that liquid flow paths between the different elements are automatically closed and opened in the correct time sequence when the valve stem is depressed and released. Spraying data show excellent repeatability of liquid sprayed per pulse throughout the lifetime of device and drop sizes that are acceptable for devices such as air-fresheners and nasal sprays. The valve has only one additional component compared with liquefied gas metered valves and can be straightforwardly injection moulded. As will be explained, previous attempts failed due to expense, complexity and unreliability.

Fine Sprays for Disinfection within Healthcare

Problems exist worldwide with Hospital Acquired Infections (HAIs). The Spray Research Group (SRG) have been working with relevant industries in developing a product which can provide a delivery system for treatment chemicals for surfaces, including the design and testing of a novel Spill-Return Atomiser (SRA) for this purpose. A comprehensive description of this atomiser has already been given. This paper reports on a new application of this atomiser and discusses the problem of spray coating for disinfection that has been considered very little in previous work. The related spray coating performance tests in developing the product are thus provided. The experimental work includes determining the required spray duration and the coverage area produced by different sprays, including the analysis of the effects of atomiser positions, configurations, and the required number of atomisers. Comparison is made with the efficacy of an ultrasonic gas atomiser that is currently used for this purpose. The investigat...