Patent Application: US-4656402-A

Abstract:
a fluid transport apparatus , comprising a transport channel including a fluid inlet ; and an evaporator including at least one evaporator channel arranged to receive fluid , each evaporator channel having at least one open fluid outlet operable to evaporate fluid at the at least one fluid outlet so as to cause the flow of fluid thought the transport channel .

Description:
in a capillary channel , liquid therein is moved by the capillary force towards the gas / liquid interface , where the liquid evaporates continuously , due to the liquid vapour pressure . this lowers the volume of liquid infinitesimally and is counterbalanced by refilling of the capillary through capillary force . important factors are that the capillary force essentially depends on the contact angle between tee liquid and inner capillary wall , the circumferences of the channels and the ability of the liquid to transmit the pressure differential . unlike the channel geometry , the contact angle and the viscosity are material properties , which cannot be altered for a given system . as illustrated in fig1 in order to enhance the capillary force , the circumference may be scaled up for a given cross section by changing the shape of the channel . therefore , the channel geometry is of significant importance . for maximum capillary force , the circumference has to be increased for a given channel cross section . since wide and shallow channels have a tendency to collapse , the determination of an optimal channel geometry is quite complex . channels of a small scale , typically a few micrometers , can be produced quite readily and are stable in height . furthermore , the concept of open tubular ( ot ) channels is ideal for channels of very small dimension , and , in a preferred embodiment , the present invention is directed to an open tubular - hplc ( ot - hplc ) system . the efficiency of chromatographic systems depends on several parameters , such as the column geometry ( length and inner diameter ), column material , applied driving force , etc . in the 1950s , aris and golay founded the basic equations , which describe open tube chromatography ( otc ). in comparison to a packed column , an open tubular system has at most a coating on the inner capillary wall . according to theory , channels with very small dimensions are ideally suited for open tube chromatography and efficiencies in excess of 1 million theoretical plates can be achieved ( 7 ). one of the first attempts to run ot - hplc on chip was ten years ago , the so called “ hitachi - chip ” ( 8 ). [ 0051 ] fig2 illustrates a schematic of a micro - fabricated liquid transport system in accordance with a first embodiment of the present invention . the micro - fabricated chip - based fluid transport system 1 includes a liquid inlet 2 , in this embodiment a three - point inlet , a transport channel 3 , in this embodiment a separation channel or column , and an evaporator 5 . [ 0052 ] fig3 illustrates the fluid transport system of fig2 mounted in a chip holder 6 . in this embodiment the evaporator 5 includes a fan 8 for maintaining an air flow over the fluid outlets of the evaporator 5 and conditioning the air thereat . [ 0053 ] fig4 illustrates a schematic of a micro - fabricated liquid transport system in accordance with a second embodiment of the present invention . the micro - fabricated chip - based fluid transport system 1 includes a liquid inlet 2 , in this embodiment a two - point inlet , a transport channel 3 , in this embodiment a separation channel or column , and an evaporator 5 . fig5 ( a ) to ( d ) illustrate preferred inlet configurations . fig6 ( a ) to ( d ) illustrate preferred separation channel configurations . fig7 ( a ) and ( b ) illustrate preferred single channel evaporator configurations . fig8 ( a ) to ( d ) illustrate preferred multi - channel configurations . [ 0058 ] fig9 illustrates a chip design in accordance with a first preferred embodiment . [ 0059 ] fig1 illustrates a chip design in accordance with a second preferred embodiment . [ 0060 ] fig1 illustrates a chip design in accordance with a third preferred embodiment . [ 0061 ] fig1 illustrates a chip design in accordance with a fourth preferred embodiment . [ 0062 ] fig1 illustrates a chip design in accordance with a fifth preferred embodiment . fig1 ( a ) and ( b ) illustrate a chip design in accordance with a sixth preferred embodiment . fig1 ( a ) and ( b ) illustrate a chip design in accordance with a seventh preferred embodiment . fig1 ( a ) and ( b ) illustrate a chip design in accordance with an eighth preferred embodiment . fig1 ( a ) and ( b ) illustrate a chip design in accordance with a ninth preferred embodiment . in a preferred embodiment the micro - fabricated devices are fabricated using the direct - write laser lithography process . this process can be used to etch large , complex structures , typically up to around 10 × 10 cm , with very narrow channels , typically a few microns , in a glass or silicon without the need for a mask . the process can also be used to create moulds for polymer devices , for example in pdms , and masks which can be used for more convention forms of lithography . as illustrated in fig1 , the micro - fabrication process is as follows : a ) the first step in the micro - fabrication of a device is to design the chip layout using a cad package , such as autocad . this design is then converted into the machine data format used by the lithography system via special conversion software . b ) a direct - writing laser exposes a commercially available glass substrate / wafer , which contains a metal layer and photo resist . c ) after exposure , the substrate is then developed to remove the exposed photo - resist , leaving an image of the design in the photo - resist . d ) the metal layer is then etched away using a suitable etching solution to reveal the glass . e ) the glass is then etched to produce the channels of the device . the amounts of hydrofluoric acid ( hf ) and ammonium fluoride ( nh 4 f ) for glass etching differ depending on the required etch rate . f ) after etching , the photo - resist and any metal layer are removed and a glass cover - plate is thermally bonded on top of the substrate to complete the device . holes are drilled in the cover - plate before bonding to interface the device with the necessary pumps and injection systems . in order to enable visualisation of the movement of tide liquid in the fluid transport system of fig1 , latex beads of 10 μm in diameter were introduced into the channel 3 . measurements were obtained by estimating the travel time for a given distance ( see fig1 ). the velocity of the liquid within the device for 10 μm beads was ≧ 350 μm / s . the measurements show little difference in the velocity regardless of air condition . however , significantly , with no air conditioning , some beads changed their velocity ( increasing as well as decreasing ) occasionally by a significant amount . moreover , it has been established that the liquid velocity is due to the evaporation and not height effects . fluorescence experiments were also performed . fluorescine ( 5 mm in sodium phosphate buffer ph 8 . 08 ) was passed through the channel 3 from the inlet . these experiments show smearing at the inlet cross - section into the channel 3 . modified inlets have been developed , including the inlet of fig5 ( c ) in which the sample is injected from first to second angled inlets by an electro - generated current . in a preferred embodiment liquids other than water , such as acetonitrile and methanol , organic solvents or standard mixtures for liquid chromatography can be used as the operating medium . in preferred embodiments the channels of the transport system have sub - micron dimensions . in terms of lithographic techniques , channel widths of less than 1 μm can be achieved . there is an upper limit to the channel width where the channel is unsupported , as , if the channels are too wide , then the upper substrate layer can deform or fracture . therefore , wide channels require support structures . the channel depth is limited by the overall substrate thickness . the channel length is for practical purposes not limited as channels having a 30 m meander can be achieved even on a small chip . generally , the longer the channel , the greater the separation , the longer the travel times and the greater the band broadening . also , the longer the channel , the higher the backpressure created therewithin . this said , although pumps capable of generating over 400 bar are available , those pumps cannot be readily coupled to a chip . for channels with sub - micron dimensions in either depth or width , the pressures required to transport liquid therethrough can easily be several thousand bar . these pressures are not obtainable in pumped systems and can only be achieved by the evaporative system of the present invention . length [ cm ] 1 - 3 . 1 suitable for ce and synthesis chips , very fast 5 - 30 suitable for ce , synthesis and chromatography chips , still fast 30 - 100 suitable for gc and lc chips 100 - 500 suitable for gc and lc chips 500 - 3000 lc chips width [ μm ] 0 . 2 - 2 suitable for inlets or in splitter areas as part of a mixing device 2 - 10 suitable for inlets and small separation channels , high pressure being required to transport the liquid through long channels 10 - 50 suitable for all devices 50 - 200 suitable for all devices 200 - 1000 where shallow , two - dimensional analysis can be performed depth [ μm ] 0 . 1 - 1 suitable for open tubular chromatography , allows fabrication from silicon with a glass cover plate 1 - 10 suitable for all applications 10 - 50 suitable for all applications 50 - 250 suitable for biological applications 250 - 1000 suitable for high volume applications the accompanying claims set out various aspects of at least preferred embodiments of the invention . although illustrative embodiments of the invention have been described in detail herein with reference to the accompanying drawings , it is to be understood that the invention is not limited to those precise embodiments , and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope and spirit of the invention as defined by the appended claims . 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