Gas and liquid contact apparatus – Contact devices – Liquid tank
Patent
1996-04-05
1998-09-08
Miles, Tim R.
Gas and liquid contact apparatus
Contact devices
Liquid tank
264257, B01F 304
Patent
active
058041052
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/GB94/02195, Oct. 7, 1994.
This invention relates to a fluid diffuser, for diffusing a first fluid into a second fluid, for example for delivering air or another liquid or gaseous fluid in finely divided form to a surrounding medium.
A common use of a fluid diffuser is in the aeration of polluted mediums, for example sewage or polluted lakes or waterways. In each case, air bubbles are passed through the diffuser into a medium to be treated. Oxygen in the air bubbles then dissolves in the medium, whereupon it is taken up by aerobic bacteria that digest polluting organic matter and thereby clarify the medium.
It is well known that the smaller the air bubble size, the faster it dissolves its oxygen in the medium to be treated. Ideally, the air bubble size should not exceed 1 mm in diameter and should preferably be of the order of 50 to 100 .mu.m in diameter. Such air bubbles can be generated using very fine ceramic diffusers, for example in the form of ceramic tubes having a nominal pore size of 3 to 10 .mu.m. However, disadvantageously, such ceramic tubes are brittle, expensive, can only be produced in short lengths and require a high internal air pressure to function. Furthermore, the pores of the tubes remain permanently open and will allow back leakage of effluent, if the internal air pressure is removed.
International application number PCT/GB 93/01196 describes a fluid diffuser which comprises an elongate flexible member having opposed walls defining a fluid delivery tube. The walls include a multiplicity of minutes valves formed by non-ablative perforation of the material of the flexible member. The valves are arranged to seal tight (and thereby prevent back-leakage of effluent), when the air pressure within the tube is below a threshold pressure. At the threshold pressure, the valves are arranged to emit tiny air bubbles into the medium surrounding the tube.
The material of the walls of the tube of the aforementioned fluid diffuser must have some resilience so that the valves can be self-sealing. This may lead to a problem in that, as air pressure within the tube increases, the tube extends radially outwardly and valve dilation increases. The increased valve dilation leads to the emission of the larger air bubbles which are less efficient at oxygen transfer than small bubbles.
It is an object of the present invention to provide a fluid diffuser which may alleviate problems associated with known diffusers.
According to a first aspect of the present invention, there is provided a device for diffusing a first fluid into a second fluid, the device comprising:
a porous member which includes pores arranged to be self-closing when a fluid is not flowing therethrough; and
restraining means arranged to cooperate with said porous member thereby to restrain an increase in pore size as the pressure of fluid flowing through said pores is increased.
In the context of this specification the term "diffuser" (or like term) includes any device for passing a first fluid into a second fluid.
Thus, if, for example, the device is used for diffusing air into a liquid, increasing the air pressure within the device may advantageously not affect, to any significant degree, the pore size or the emitted air bubble size. The device may function in a manner similar to ceramic diffusers whilst obviating problems associated therewith.
The restraining means is preferably arranged so as to restrain lateral expansion of the pores of the porous member. Preferably, an area of the porous member around each pore is covered by said restraining means. Preferably, said restraining means covers substantially the entirety of said porous member. Preferably, each of a multiplicity of said pores is restrained by a respective part of said restraining means. Preferably, each of a multiplicity of said pores is individually restrained by said restraining means. Preferably, each of said multiplicity of pores is restrained to substantially the same extent; that is, said restraining means is preferably arranged to exert a
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