WO2017055093A1

WO2017055093A1 - An in-flow fluid purification system and method

Info

Publication number: WO2017055093A1
Application number: PCT/EP2016/071848
Authority: WO
Inventors: Merlijn Antonius Petrus Maria JANSSEN
Original assignee: Philips Lighting Holding B.V.
Priority date: 2015-09-28
Filing date: 2016-09-15
Publication date: 2017-04-06

Abstract

An in-flow fluid purification system uses a purification tube which remains at least partially filled when a fluid flow through the system is ceased. A UV radiation source at one end of the purification tube is used to implement UV purification, and the UV radiation source is thermally coupled to the fluid in the purification tube to provide effective heat dissipation.

Description

An in-flow fluid purification system and method

FIELD OF THE INVENTION

The invention relates to the field of in-flow fluid disinfection, and more specifically to ultraviolet (UV) fluid disinfection, for example using UV-C radiation.

BACKGROUND OF THE INVENTION

The importance of fluid disinfection for providing a fluid that contains fewer harmful bacteria has widely been recognized. This becomes even more prescient when the fluid in question is, for example, water that is being prepared for human or animal consumption, although UV radiation is widely known for use in the disinfection other fluids such as air.

Fluid disinfection with UV radiation was first used in the 1980's; it has numerous advantages over other methods such as chlorination, especially when the fluid is water that is to be consumed.

UV radiation does not affect the PH, composition, taste or odor of the fluid that has been disinfected. The disinfection of the fluid is achieved by deactivating the DNA of bacteria, viruses and microbes. Further advantages of the use of UV to disinfect fluids are simple installation, less maintenance requirements and space efficiency.

The use of UV to treat a fluid eliminates the need to use a chemical process thus removing the risk of a chemical smell or taste in the fluid after disinfection has been completed.

Current UV water disinfection technologies mainly use mercury discharge lamps to provide the UV radiation that disinfects the water. Generally these systems provide UV radiation to fluids flowing past them. The level of disinfection depends on the total UV dose that the water receives. The higher the dose, the higher the level of disinfection, or the lower the amount of remaining pathogens.

Ultraviolet radiation disrupts the DNA of microbes and thereby prevents reproduction. Without reproduction, the microbes become far less of a danger to health. As such, UV radiation is a mutagen, that is to say, UV radiation creates mutations within the structure of DNA. UV-C radiation in the short wavelength range of 100-280 nm acts on thymine, one of the four base nucleotides in DNA, when a UV photon is absorbed by a thymine molecule that is adjacent to another thymine within a DNA strand, a covalent bond or dimer between the molecules may be created, this is different to the normal structure of DNA wherein the bases always pair up with the same partner on the opposite strand of DNA. This causes a bulge to occur between the two bases, the bulge prevents enzymes from "reading" the DNA and copying it, thus neutering the microbe.

Recently, UV-C LEDs have become available. Their UV-C output power is still low compared to mercury lamps, but LEDs have the advantages of a small size and the ability to generate directional radiation. Providing a higher power output from UV-C LEDs gives rise to problems of thermal management, as a large amount of excess heat needs to be dissipated. There is however a desire for this increased power output. For example, some pathogens are hundreds of times less sensitive to UV radiation and will therefore undergo fewer mutations than others. For example, viruses may require a 10-30 times greater dose of UV light than Giardia or Cryptosporidium which are protozoa.

There is therefore a need for a UV purification system which provides improved thermal management.

SUMMARY OF THE INVENTION

The invention is defined by the claims.

According to examples in accordance with an aspect of the invention, there is provided an in- flow fluid purification system, comprising:

a purification tube having an inlet end and an outlet end;

a fluid inlet at the inlet end of the purification tube;

a UV radiation source at one end of the purification tube, wherein the UV radiation source is thermally coupled to the fluid in the purification tube; and

a fluid outlet at the outlet end of the purification tube,

wherein the purification tube is sloped with respect to the horizontal such that the inlet end is lower than the outlet end such that the purification tube remains at least partially filled when a fluid flow through the system is ceased.

This arrangement uses the fluid being purified as a heat transfer medium to provide heat dissipation for the UV radiation source. By ensuring the tube remains at least partially filled when there is no fluid flow, the purification can be conducted even with no flow. The use of a tubular design enables a long path of the UV radiation in the fluid, thereby improving the purification for a given UV radiation intensity. The UV radiation source is preferably at the inlet end.

In one arrangement, the purification tube is sloped with respect to the horizontal such that the inlet end is lower than the outlet end. This means the tube remains filled or partially filled when flow is interrupted. The UV radiation source is then preferably at the inlet end, which will have fluid present. This slope can vary from, for example, 5° from the horizontal to 70° from the horizontal. In some embodiments it may be preferable to arrange the tube at a low angle with respect to the horizontal, for example, 5° to 15°. In some embodiments it will be sufficient to angle the tube with respect to the horizontal such that, if an imaginary line is drawn from the top of the UV radiation source(s) parallel to the horizontal, then the fluid outlet from the purification tube remains higher than this imaginary line. An alternative is to provide a valve arrangement which prevents fluid flow when a pressure difference drops below a threshold, and the threshold is exceeded when fluid is driven through the system.

The UV radiation source for example comprises a UV LED arrangement. The thermal coupling arrangement combined with the tubular design enable higher power LEDs to be used as well as utilizing the available UV radiation intensity as effectively as possible.

The UV LED arrangement may comprise a substrate and one or more LEDs over the substrate, wherein the LEDs face into the purification tube. This provides a direct thermal coupling of the LEDs with the fluid in the purification tube. The substrate may for example comprise a heat conductive PCB, such as an aluminum PCB, to improve the heat transfer to the fluid.

The LEDs for example comprise a protective coating to enable them to be placed in the fluid path. This coating may comprise a UV transparent coating or else a coating may be used with a UV exit window.

In some designs, there is no air gap between the light output surface of the LED and the fluid in the purification tube. In the case of a liquid purification system, this means that there is a higher refractive index material at the outside of the LED, which tends to bend the light output towards the normal. This provides a beam shaping function which tends to increase the collimation of the output radiation.

The purification tube for example has a transparent wall design which provides total internal reflection of at least part of the UV radiation from the UV radiation source. By improving the collimation, the proportion of the UV radiation which is totally internally reflected is increased. The purification tube may have a wall design which includes a UV reflecting surface. This may be on the inside or the outside, and it may function in conjunction with the total internal reflection mentioned above.

The purification tube may comprise a narrowing and a bend at the outlet end. This assists in maintaining a filled purification tube when the flow is ceased, by interrupting a syphoning effect.

The purification tube may have a length between 50 mm and 250 mm.

A UV detector may be provided at the outlet end of the purification tube. This may be used to determine the transmittance of the fluid and/or verify correct functioning of the UV radiation source. The system may also comprise an integrated fluid valve for controlling the flow through the system.

The system may comprise a liquid purification system, such as a water purification system.

According to examples in accordance with another aspect of the invention, there is provided an in-flow fluid purification method, comprising:

providing fluid to a purification tube at an inlet end;

providing UV radiation into the purification tube from one end using a UV radiation source;

thermally coupling the UV radiation source to the fluid in the purification tube; and

providing purified fluid from the purification tube at an outlet end,

wherein the method comprises maintaining the purification tube at least partially filled when the fluid flow is ceased. BRIEF DESCRIPTION OF THE DRAWINGS

Examples of the invention will now be described in detail with reference to the accompanying drawings, in which:

Fig. 1 shows a purification system;

Fig. 2 shows a first example of UV LED for use in the system of Fig. 1 ;

Fig. 3 shows a second example of UV LED for use in the system of Fig. 1 ;

Fig. 4 shows a third example of UV LED for use in the system of Fig. 1 ;

Fig. 5 is used to explain the benefit of direct contact between the UV LED and a liquid flowing through the system; and

Fig. 6 shows a method of the invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

The invention provides an in-flow fluid purification system which uses a purification tube which remains at least partially filled when a fluid flow through the system is ceased. A UV radiation source at one end of the purification tube is used to implement UV purification, and the UV radiation source is thermally coupled to the fluid in the purification tube to provide effective heat dissipation.

Figure 1 shows an in-flow purification system 10 which comprises a purification tube 12 having an inlet end 14 end and an outlet end 16. A fluid inlet 15 is at the inlet end of the purification tube and a fluid outlet 17 is at the outlet end.

By "at" in this context is meant near the end, for example nearer to that end than the other end, for example the fluid inlet may be within 10% of the length of the tube 12 from the absolute end of the tube.

A UV radiation source 18 is at the inlet end of the purification tube, and the UV radiation source 18 is thermally coupled to the fluid in the purification tube 12.

The system is designed to allow a flow along the tube between the inlet and outlet ends 14,16 to purify the flow. The purification tube is adapted to remain at least partially filled when a fluid flow through the system is ceased.

In the example shown in Figure 1, the purification tube 12 is sloped with respect to the horizontal such that the inlet end 14 is lower than the outlet end 16.

The tube may be at any non-zero angle to the horizontal, for example up to an including 90 degrees (vertical), but in other arrangements, the angle of the slope is for example in the range 10 degrees to 45 degrees.

This means the tube remains filled or partially filled when flow is interrupted. An alternative is to provide a passive valve arrangement either at or near the inlet or at or near the outlet which prevents fluid flow when a pressure difference drops below a threshold, and the threshold is exceeded when fluid driven through the system.

Line A is an imaginary line drawn from the top of the UV radiation source 18 parallel to the horizontal. If the fluid outlet 17 remains higher than this imaginary line A, then the tube will remain at least partially filled when the flow is interrupted.

Directional radiation from the UV radiation source 18 is coupled into the stream of fluid (e.g. water), and the tube 12 is transparent to the UV (e.g. UV-C) radiation. The UV radiation source for example comprises a UV LED arrangement. This generates heat, but the maximum temperature needs to be maintained below for example 60 degrees. The thermal coupling arrangement combined with the tubular design enable higher power LEDs to be used as well as utilizing the available UV radiation intensity as effectively as possible.

With a reasonably UV transparent fluid, the radiation is not absorbed, but travels long distances due to total internal reflection. The tube 12 thus acts as light guide. This ensures a long path for photons in the fluid.

The tube may be perfectly straight, but this is not essential. A more compact arrangement may have a curvature, as long as the angles are such that total internal reflection is preserved. The shape (and/or a valve arrangement) is however designed so that the tube remains filled when flow is interrupted.

By placing the LED arrangement and the substrate on which it is mounted in thermal contact with the fluid, efficient heat dissipation is provided. In this way, more power can be input to the LED arrangement without overheating. It has been found that with this tubular design and thermal coupling arrangement a 60 mW UV-C LED can achieve similar performance to existing 3000 mW UV-C reactors.

The UV LED arrangement may comprise a substrate and LEDs over the substrate, wherein the LEDs face into the purification tube as shown in Figure 1. The substrate defines the end of the tube, so that the tube itself is open-ended. This provides a direct thermal coupling of the LEDs with the fluid in the purification tube 12 because the LED substrate defines an inner end wall of the tube. The substrate may for example comprise a heat conductive PCB, such as an aluminum PCB, to improve the heat transfer to the fluid.

With a total internal reflection arrangement, there may be a significant portion of photons which are emitted at angles that do not ensure total internal reflection. These photons can be reflected with a (partial) internal or external reflective coating. An internal coating may for example comprise a coating with adhesion to glass together with a UV-C reflective coating which is able to be in contact with the fluid. Not all materials are certified to have contact with drinking water, for example. An external coating may for example comprise a coating with adhesion to glass and a wider choice of UV-C reflecting layers, such as aluminum.

The UV-LED arrangement may comprise optics to focus the radiation emitted from the LED so that a narrower range of angles is provided to the tube 12.

The outlet 17 of the purification tube 12 is shown with a narrowing and a bend. This ensures that the system becomes filled with fluid upon first usage and stays filled once the flow is interrupted, for example by closing an upstream valve. A full tube means a long resident time of the fluid in the tube and a maximized received dose, i.e., a maximized performance. By maintaining the purification tube filled, it is possible to use the system at times when the fluid is not flowing. This may be used to maintain a clean system, whereby microorganisms entering from the outside into the tube are de-activated.

By providing the outlet 17 as the direct outlet from the system, there is no possibility of contamination downstream of the purification tube. This is generally referred to as a Point of Dispense solution.

The length of the tube 12 may be adjusted to trade off performance against size of the solution. The length may for example be in the range 50 mm to 250 mm. As one example, an active length of 120 mm is possible, and simulations indicate that a UV-C dose of 16 mJ/cm² in a water flow of 2 liters/minute may then be achieved when a UV-C power of 60 mW is used. Thus, the output power of the UV-C LED arrangement is for example in the range 50 mW to 500 mW.

A UV detector 20 is shown at the outlet end 16 of the purification tube 12. This may be used to determine the transmittance of the fluid and/or verify correct functioning of the UV-C LED arrangement. If the fluid has a transparency which is too low, this means the penetration depth into the fluid may not be sufficient to provide the desired level of purification.

Figure 1 also shows an integrated fluid valve 22 for controlling the flow through the system. In one example the valve comprises a coil 24 placed around the inlet pipe. A metal ball 26 in combination with an orifice keeps the inlet normally closed. When a current is applied to the coil, the metal ball is lifted, and the valve is opened. By integrating the valve, an equipment manufacturer does not need to implement the valve function as a separate component, saving space and cost.

As explained above, the LED arrangement is preferably thermally coupled to the fluid so that the fluid acts to transport heat away from the LED arrangement. This allows for effective heat dissipation, lower LED die operating temperatures, a longer lifetime for the LED, and the possibility to overdrive the LED at higher currents to improve disinfection performance, or any combination of these benefits. Depending on the LED design and the nature of the fluid, the LED arrangement may need to be protected from the fluid.

The LEDs may for example comprise a protective coating to enable them to be placed in the fluid path. This coating may comprise a UV transparent coating or else a coating may be used with an exit window. Figure 2 shows a first example of a single UV LED for use in the system of Figure 1 in which no coating is needed.

A substrate 30 is thermally conductive, such as an aluminum printed circuit board to conduct the heat from the LED to the fluid. A ceramic housing 32 is provided over the substrate in which the LED 34 is mounted. The LED 34 comprises an LED die over a carrier substrate. A cap 36 is provided over the LED 34, for example implementing a beam shaping function or simply providing a UV transparent output window while enclosing the LED in a chamber. The PCB surface or the ceramic LED housing surface can be enlarged (either the inherent shape, or by adding components like rims or rods) to improve contact with the fluid and improve heat dissipation.

The LED may use any known (or future) technology for creating a UV output (i.e. 100 nm to 400 nm wavelength), such as a UV-C output (200 nm to 280 nm). UV-C LEDs for disinfection and for air or water purification are commercially available from many different suppliers.

For a gas purification system, no additional protection may be needed so that the design of Figure 2 may be used.

The ability to conduct heat away is much greater with a liquid purification system, but additional protection may then be needed. In particular, the liquid can cause a short circuit, and may penetrate the ceramic structure and damage the LED die.

Figure 3 shows a second example in which the structure of Figure 2 is supplemented with a protective cover layer 40 which has an exit window 42 over the LED. The cover layer improves the sealing around the LED, for example covering the edge of the exit window 36. The cover layer 40 does need not be transparent for UV-C. This has an advantage because certified conformal food grade coatings are more readily available which are not UV-C transparent.

The cover layer may for example comprise a food grade exoxy resin.

Figure 4 shows a third example in which the structure of Figure 2 is supplemented with a protective cover layer 44 which is formed of a UV transparent material and therefore does not need an exit window over the LED.

The cover layer may for example comprise a food grade silicone, PTFE or

FEP.

A further advantage of having the LED arrangement in optical contact with the fluid is that the radiation is less divergent, i.e., partially collimated and therefore better contained in the fluid. This means more radiation will undergo total internal reflection. Figure 5 is used to explain this benefit of direct contact between the UV LED and a liquid flowing through the system. The top image shows air 50 over the LED arrangement, which gives a diverging beam. The greater refractive index of a liquid such as water 52 gives a narrower beam divergence as shown in the lower image.

In the lower image, there is no air gap between the light output surface of the

LEDs and the fluid in the purification tube.

The performance of the system has been simulated by modeling fluid flow and UV-C radiation. Fluid flows through the tube with a non-uniform cross sectional profile: the speed of the fluid near the tube walls is lower than in the center of the tube. The position and orientation of the UV-C LEDs may be used to optimize the radiation so there is a uniform dose distribution across the entire cross section of the tube.

It has been estimated that a total UV-C power of 60 mW (at 265 nm) is sufficient to deliver a dose of 16 mJ/cm² in a fluid (95%/cm UV-C transparent) with a flow of 2 liters/minute.

The performance of the system has also been confirmed by microbiological tests.

The UV-C LED is driven by a constant current driver in known manner, which can be installed on the same PCB as the LEDs to allow for a wide range of voltage input. The PCB with LED is coated to provide electrical insulation and render the PCB and LED water tight.

Figure 6 shows a method of the invention.

In step 60, fluid is provided to the purification tube at an inlet end.

In step 62, UV radiation is provided into the purification tube from the inlet end using a UV radiation source. The UV radiation source is thermally coupled to the fluid in the purification tube.

In step 64, purified fluid is provided from the purification tube at the outlet end. The purification tube remains at least partially filled when the fluid flow is ceased.

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

CLAIMS:

1. A tubular fluid purification system, comprising:

a purification tube (12) having an inlet end (14) and an outlet end (16);

a fluid inlet (15) at the inlet end of the purification tube;

a UV radiation source (18) at one end of the purification tube, wherein the UV radiation source is thermally coupled to the fluid in the purification tube; and

a fluid outlet (17) at the outlet end of the purification tube,

2. A system as claimed in claim 1, wherein the UV radiation source (18) comprises a UV LED arrangement.

3. A system as claimed in claim 2, wherein the UV LED arrangement comprises a substrate and LEDs over the substrate, wherein the LEDs face into the purification tube and the substrate defines an end wall of the tube.

4. A system as claimed in claim 3, wherein the substrate is a heat conductive PCB (30), such as an aluminum PCB.

5. A system as claimed in claim 3 or 4, wherein the LEDs comprise a protective coating, which comprises:

a UV transparent coating (44); or

a coating (42) with an exit window.

6. A system as claimed in any one of claims 3 to 5, wherein there is no air gap between the light output surface of the LED and the fluid (50,54) in the purification tube.

7. A system as claimed in any preceding claim, wherein the purification tube has a transparent wall design which provides total internal reflection of at least part of the UV radiation from the UV radiation source.

5 8. A system as claimed in any preceding claim, wherein the purification tube has a wall design which includes a UV reflecting surface.

9. A system as claimed in any preceding claim, wherein the purification tube comprises a narrowing and a bend at the outlet end.

10

10. A system as claimed in any preceding claim, wherein the purification tube has a length between 50 mm and 250 mm.

1 1. A system as claimed in any preceding claim, further comprising a UV detector 15 (20) at the outlet end of the purification tube.

12. A system as claimed in any preceding claim, further comprising an integrated fluid valve.

20 13. A system as claimed in any preceding claim, comprising a water purification system.

14. A tubular purification method, comprising:

providing fluid to a sloped purification tube at an inlet end, the slope being 25 with respect to the horizontal such that the inlet end is lower than the outlet end;

30 providing purified fluid from the purification tube at an outlet end,

wherein the method comprises maintaining the purification tube at least partially filled when the fluid flow is ceased.