Fluid sprinkling – spraying – and diffusing – With system fluid relief or return to supply – Return from liquid pump outlet to supply holder
Patent
1996-05-15
1998-07-07
Weldon, Kevin
Fluid sprinkling, spraying, and diffusing
With system fluid relief or return to supply
Return from liquid pump outlet to supply holder
239463, B23K 2700
Patent
active
057755884
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD OF THE INVENTION
The present invention concerns a whirl chamber nozzle for atomizing a liquid which is introduced tangentially into the chamber at its outer periphery, comprising a bypass which extends away from the whirl chamber via a central discharge orifice.
BACKGROUND OF THE INVENTION
There has been a long-felt need for the possibility of using whirl chamber nozzles with bypass in connection with spray drying systems, where solid particles remain when an atomized liquid solution or suspension is ejected into a container at a particularly high temperature, causing the liquid portion to evaporate and the solid particles to remain. Such spray drying processes find widespread use for the production of powders in chemical, pharmaceutical, food and related industries.
In particular, the need is present when operation of a spray drying system is initiated and stopped, where the flow of the ejected atomized liquid amount from the known whirl chamber nozzles without bypass can be changed only by changing the pump pressure, resulting in undesired changes in the atomization state and in particular the particle size.
In relation to whirl chamber nozzles without bypass, whirl chamber nozzles with bypass involve the great advantage that the flow of the ejected, atomized liquid amount can easily be controlled by changing the flow of the liquid amount which flows back via the bypass, without it being necessary to change the pressure in the conduit from the feed pump, as is the case with whirl chamber nozzles without bypass, where the feed pump pressure has to be changed when the flow of the ejected, atomized liquid amount is to be changed. This provides the great advantage that the liquid ejection velocity and thereby the atomization degree, i.e. the drop size remain substantially unchanged when the flow of the ejected, atomized liquid amount is changed. This is not the case with whirl chamber nozzles without bypass, where the flow of the ejected, atomized liquid amount can be changed only by changing the pump pressure, which undesirably causes also the atomization degree and thus the drop size to be changed.
To a person skilled in the field of nozzles, the maximum, so-called turndown ratio is defined as the ratio of the maximally acceptable flow to the minimally acceptable flow of atomized liquid amount ejected. This ratio is very small, i.e. less than 2:1, for whirl chamber nozzles without bypass. Whirl chamber nozzles with bypass frequently have a turndown ratio above 5:1, which may be assumed to be advantageous for use in spray drying systems.
On the other hand, it is a great problem of whirl chamber nozzles with bypass that the total flow of liquid to the nozzle increases substantially when the amount of liquid passing through the bypass increases, i.e. when the turndown ratio is increased. This phenomenon is called flow growth. In the known whirl nozzles with bypass a flow growth of 30-50% is not unusual at a turndown ratio of 3:1. When the flow of the ejected, atomized liquid amount is reduced by opening a valve in the bypass, the total liquid flow supplied to the nozzle thus increases (assuming constant pressure at the nozzle). The feed pump must hereby be undesirably overdesigned in capacity.
Another problem making it impossible to use the known whirl chamber nozzles with bypass directly in connection with spray drying systems, is that the liquid whirls in the whirl chamber create an air core which extends through the nozzle orifice and axially through the whirl chamber. When the bypass valve opens, air from the air core will be drawn into the bypass conduit in an uncontrolled manner. This is extremely unfortunate in connection with spray drying systems for several reasons. It should be mentioned that there are also systems for controlled injection of air.
If the bypass conduit extends back to the feed pump, the entering air may cause mechanical problems and fluctuations in the pump pressure. If the bypass conduit extends back to the liquid feed container, entering air may cause foaming o
REFERENCES:
patent: 2567818 (1951-09-01), MacCracken
patent: 3019990 (1962-02-01), Campbell
patent: 3547093 (1970-12-01), Sherman
patent: 4121085 (1978-10-01), Diemer et al.
patent: 4186877 (1980-02-01), Wilcox et al.
Hallstrom Anders
S.o slashed.nderby Henrik
Stahnke Nicolaj
APV Anhydro AS
Weldon Kevin
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