Fluid sprinkling – spraying – and diffusing – Processes – Vibratory or magneto-strictive projecting
Patent
1996-05-16
1998-10-20
Weldon, Kevin
Fluid sprinkling, spraying, and diffusing
Processes
Vibratory or magneto-strictive projecting
2391022, 239558, 239601, B05B 1706
Patent
active
058234284
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to apparatus and methods for the production of sprays of liquid or of liquid emulsions or suspensions (hereinafter called `liquids`) by means of an actuator.
It is known to produce fine droplet sprays by the action of high frequency mechanical oscillations upon a liquid at its surface with ambient air. Prior art of possible relevance includes: EP-A-0 432 992, GB-A-2 263 076, EP-A-0 516 565, U.S. Pat. No. 3,738,574, EP-A-0 480 615, U.S. Pat. No. 4,533,082 & U.S. Pat. No. 4,605,167.
In some instances (e.g. U.S. Pat. No. 3,738,574) the liquid is introduced as a thin film formed on a plate excited in bending oscillation by the transmission of ultrasonic vibrations from a remote piezoelectric transducer through a solid coupling medium structure.
In some instances (e.g. U.S. Pat. No. 4,533,082) the mechanical oscillations are propagated as sonic or ultrasonic vibrational waves through the liquid towards a perforate membrane or plate (hereinafter referred to as a membrane) that otherwise retains the liquid. The action of the vibrational waves in the liquid causes the liquid to be ejected as droplets through the perforations of the membrane. In these cases, it has been found advantageous to make the pores decrease in size towards the `front` face (herein defined as that face from which liquid droplets emerge) from the `rear` face (herein defined as the face opposite the `front` face).
In other instances (e.g. EP-A-0 516 565) which may be regarded as an amalgamation of the two cases cited above, the mechanical oscillations pass through a thin layer of the liquid towards a perforate membrane that otherwise retains the liquid. In EP-A-0 516 565 there is no teaching of any advantages or disadvantages for particular geometrical forms of perforation.
In yet other instances (e.g. GB-A-2 263 076, U.S. Pat. No. 4,605,167 and EP-A-0 432 992) the source of mechanical oscillations is mechanically coupled to a perforate membrane that otherwise retains the liquid. The action of the oscillations causes the liquid to be ejected as droplets through the perforations of the membrane. In these cases, it again has been found advantageous to make the perforations decrease in size from the `rear` face towards the `front`, droplet-emitting, face of the membrane.
The devices above can be classified into two types: Pat. No. 3,378,574 and EP-A-0 516 565, transmit the vibration through the liquid to the liquid surface from which the spray is produced, but they describe no geometrical features at that surface which influence droplet size. They either have no perforate membrane to retain the liquid in the absence of oscillation (as in U.S. Pat. No. 3,378,574) or they do possess a perforate membrane, but the perforations do not influence droplet size (as in EP-A-0 516 565, eg column 6, line 21). Pat. No. 4,605,167, U.S. Pat. No. 4,533,082, EP-A-0 432 992 and GB-A-2 263 076, have a perforate membrane bounding or defining the liquid surface at which droplets are produced and the membrane perforations do have an influence upon droplet size. In these cases the present inventors have observed that a substantially cylindrical fluid jet emerges from the `small-orifice` opening in the front face of the membrane and that this jet oscillates towards and away from the membrane once per cycle of vibration. When the excitation is sufficiently strong the end portion of the jet breaks off to form a free droplet. This behaviour is represented in FIG. 1. In both cases, the droplet diameter typically lies in the range 1.5 to 2 times the diameter of the small-orifice opening in the `front` face of the membrane. This relationship is also well known in ink jet printing, and has been found in many studies of the instability of liquid jets. The benefit to spray production of having orifices that reduce in size towards the `front` face is common to all these devices and is also known from ink jet technology. See, for example, U.S. Pat. No. 3,683,212.
The first type of device is relatively inefficient in use of electr
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Humberstone Victor Carey
Sant Andrew Jonathan
The Technology Partnership PLC
Weldon Kevin
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