WO2017060088A1

WO2017060088A1 - Flow cell for reducing viable microorganisms in a fluid

Info

Publication number: WO2017060088A1
Application number: PCT/EP2016/072422
Authority: WO
Inventors: Franklin David Chandra; Venkataraghavan Rajanarayana
Original assignee: Unilever NV; Conopco Inc
Current assignee: Unilever NV; Conopco Inc
Priority date: 2015-10-05
Filing date: 2016-09-21
Publication date: 2017-04-13
Anticipated expiration: 2018-04-05

Abstract

The invention relates to a flow cell for purification of a fluid. It is thus an object of the present invention to provide a flow cell that allows for better circulation of the fluid inside the body of the cell. It is another object of the present invention to provide a flow cell with improved performance with respect to reduction in the number of viable bacteria and virus. We have now determined that performance of the flow cell (202) can be markedly improved by providing an inlet port (205) which is configured to direct the fluid emanating from the inlet port (205) in a direction within a cone having a semi-conical angle a (alpha) of 85°, with the cone axis parallel to the shortest geometric path between the inlet port (205) and the outlet port (207) wherein the cone extends in a direction away from the shortest geometric path; and, the direction is at an angle β (beta) of not more than 15° relative to the wall (213) adjoining the inlet port (205) of the vessel (202).

Description

FLOW CELL FOR REDUCING VIABLE MICROORGANISMS IN A FLUID Field of the invention

The invention relates to a flow cell for reducing the number of viable microorganisms in a fluid.

Background of the invention

Ultraviolet (UV) radiation is one of the most reliable agents for disinfecting water. Conventional lamps generally used in domestic UV water purifiers consume about 10 to 20 W of power. UV lamps also need to warm up sufficiently to radiate light of sufficient intensity. Heretofore, conventional UV lamps were widely used in such devices.

UV LED (Ultraviolet Light Emitting Diodes) is a new generation alternative to conventional UV lamps. The mechanism by which they act against microbes is the same as conventional lamps but they consume lesser power, can be switched-on instantly and are mercury-free.

A typical UV LED flow cell has a coaxial design built around cylindrical UV lamps which are secured within end caps. UV LEDs are relatively smaller in size therefore fewer lamps, typically arranged in the form of an array are needed. The LEDs are generally fitted inside end caps of the flow cell but they may also be arranged inside the body of the cell thereby providing for contact between the fluid which flows through the cell with the UV light.

US20100314551 A1 (CRYSTAL IS INC) discloses an in-line fluid treatment device with LEDs. The system includes a source of UV radiation directed into the flow; a computation unit for determining, based on at least one flow parameter, a configuration of the UV source to achieve germicidal effect in the fluid; and a mechanism for controlling the UV source in response to the determined configuration. US20060131246 A1 (RANCO INC) discloses a water purification system with plurality of ultraviolet light emitting diodes. This includes an inlet, an ultraviolet radiation chamber, and an outlet wherein the inlet is connected in fluid relationship to the ultraviolet radiation chamber. The outlet is connected in fluid relationship to the ultraviolet radiation chamber to allow water to flow between the inlet and the outlet through the ultraviolet radiation chamber, wherein the ultraviolet radiation chamber is positioned adjacent to a plurality of ultraviolet light emitting diodes. The UV LEDs are arranged in the form of an array. The UV radiation chamber is a transparent tube with the plurality of ultraviolet light emitting diodes positioned on the outside of the transparent tube or positioned within the transparent jacket.

US2010/0237254 A1 (PW CIRCUITS LTD) discloses a water purifying apparatus which has a pipe for conveying a fluid, a series of UV LEDs and a control circuit for controlling operation of the LEDs. Conduit means allows constant circulation of the water. Additional purification means like baffles or plates coated with a metal within the pipe are also disclosed.

US2004/0226893 A1 (Kamimura et al.) discloses a water treatment apparatus which has an ultraviolet radiation part and an oxidizer mixing part disposed adjacent to and upstream of the ultraviolet radiation part, said oxidizer mixing part includes a conical part having a tapered configuration that expands from a minimum cross-sectional area to a large passage part.

Baffles are also disclosed in US 20100025337 A1 (Yencho) and CN201777914U (Harbin Institute of Technology).

In such devices, the water must remain in contact with UV radiation for as long a period as possible. The object of UV LEDs is to kill or deactivate bacteria and virus. However, sometimes even recommended power fails to provide appreciable reduction in the number of microbes generally indicated with the help of log value of the microbes. According to U.S. EPA (United States Environmental Protection Agency) standards, any water purification method should provide 6-log reduction of bacteria and 4-log reduction of virus but this is not achievable at all times. Consumers desire such devices/methods which are able to provide log reduction, as close as possible to the standards set by USEPA, but at highest possible flow rate. In other words, the water should be purified as quickly as possible. It is believed that channeling adversely affects the average flow rate and residence time as some portion of input water containing microbes gets short-circuited between input and output thereby leading to insufficient purification. This problem may be solved by increasing the wattage of the UV radiation but this is not practical and sustainable solution.

US2012138545 A (RANCO INC) discloses a system having LED source and photo- catalytic material disposed therein. In some embodiments this conduit also has flow disturbing elements, flow reflectors as well as heat sinks. The reflector may be in the form of continuous helix about the inner surface of the pipe and its shape and positioning is intended to create turbulent fluid flow through the pipe. It is further disclosed that the reflector may also be shaped and positioned as a flow-disturbing element to promote turbulent flow of fluid through the pipe.

Therefore the prior art fails to disclose an embodiment providing a solution for shorter residence time, thereby making it imperative that such devices should be used at higher power consumption and lower flow rate.

It is thus an object of the present invention to provide a flow cell that allows for better circulation of fluid inside the vessel of the flow cell.

It is another object of the present invention to provide a flow cell with improved performance with respect to reduction in the number of viable bacteria and virus.

It is another object of the present invention to provide a flow cell that allows for prolonging the residence time within the flow cell.

Summary of the invention We have now determined that performance of a flow cell (201 ) can be markedly improved by providing an inlet port (205) which is configured to direct the fluid emanating from the inlet port (205) in a direction within a cone having a semi-conical angle a (alpha) of 85°, with the cone axis parallel to the shortest geometric path between the inlet port (205) and the outlet port (207) wherein the cone extends in a direction away from the shortest geometric path; and, the direction is at an angle β (beta) of not more than 15° relative to the wall (213) adjoining the inlet port (205) of the vessel (202). According to a first aspect of the invention disclosed is a flow cell (201 ) for reducing the number of viable microorganisms in a fluid, said flow cell having:

(i) a vessel (202), delimited by a wall, said vessel comprising an inlet port (205) and an outlet port (207) defining a path (203) there between for flow of fluid, and,

(ii) at least one ultraviolet light emitting source capable of illuminating the fluid flowing through the path;

characterised in that the inlet port (205) is configured to direct the fluid emanating from the inlet port (205) in a direction wherein:

(i) said direction is within a cone having a semi-conical angle a (alpha) of 85° with the cone axis parallel to the shortest geometric path between the inlet port

(205) and the outlet port (207) wherein the cone extends in a direction away from the shortest geometric path; and,

(ii) said direction is at an angle β (beta) of not more than 15° relative to the wall (213) adjoining the inlet port (205) of the vessel (202).

According to a second aspect of the invention disclosed is a process for reducing the number of viable microorganisms in a fluid by a flow cell of the first aspect having the steps of:

(i) illuminating said path between the inlet port (205) and the outlet port (207) of the flow cell with one or more ultraviolet light emitting source;

(ii) passing a fluid through the inlet port (205) of the flow cell;

characterised in that the inlet port (205) is configured to direct the fluid emanating from the inlet port (205) in a direction wherein: (i) said direction is within a cone having a semi-conical angle a (alpha) of 85° with the cone axis parallel to the shortest geometric path between the inlet port (205) and the outlet port (207) wherein the cone extends in a direction away from the shortest geometric path; and,

Brief description of the figures

Figure 1 is longitudinal sectional view of a conventional flow cell.

Figure 2 is transverse sectional view of the flow cell of Figure 1 at the point of inlet of water.

Figure 3 is longitudinal sectional view of a preferred embodiment of flow cell.

Figure 4 is transverse sectional view of the preferred embodiment of Figure 3 at the point of inlet of water.

Figure 5a is a longitudinal sectional view of the preferred embodiment showing the semi-conical angle a (alpha).

Figure 5b is a transverse sectional view of the preferred embodiment at the point of inlet of water showing the angle β (beta).

Detailed description of the figures

In the description of the figures, in order to distinguish between features of conventional flow cell and the preferred embodiment, numerals 101 onwards are used for the Figure 1 and 2 and numerals 201 onwards are used in connection with the preferred embodiment in Figure 3, 4 and 5. Figure 1 is a longitudinal sectional view of a conventional flow cell (101 ). The flow cell (101 ) has an elongated tubular vessel (102) which is circular in a transverse cross section. Inside the vessel is a path (103) for flow of fluid. The elongated vessel (102) has a sheath (104) around it. The vessel (102) is made of stainless steel while the sheath (104) is made of Teflon. Dimensions of the vessel (102) are 0.12 meters length and 0.04 meters diameter.

The vessel (102) has an inlet port (105) for entry of untreated water through the inlet pipe (106). The inlet port (105) is preferably directed towards the region of maximum energy density. Similarly, at the opposite end of the tubular vessel (102), an outlet port (107) is provided for exit of treated fluid or fluid after reduction of the number of viable microorganisms through the outlet pipe (108). Between the inlet port (105) and outlet port (107) is the shortest geometric path for flow of the fluid (shown with broken lines). At either ends of the tubular vessel (102) is an end cap (109, 1 10), each provided with five UV LEDs arranged radially approximately 72° apart and one at the centre (not seen in this view). Each end cap (109, 1 10) is made of quartz enclosed in stainless steel frame. The cross sectional area of the cell was 1 .25 x 10^"3 m² and the volume was 1.5 x 10^"4 m³. A gasket is also provided for making the assembly watertight. Figure 2 is transverse sectional view of the flow cell of Figure 1 at the point of inlet of water (region marked at A— A' in Figure 1 )

Figure 3 is longitudinal sectional view of a preferred embodiment of flow cell (201 ). The preferred embodiment is identical in construction to the conventional flow cell (101 ). A difference is that in this preferred embodiment, the inlet (205) is configured to direct the fluid emanating from the inlet port (205) in a direction within a cone having a semi- conical angle a (alpha) of 85° and in which said direction is at an angle β (beta) of not more than 15° relative to the wall adjoining the inlet port (205) of the vessel (202), providing a tangential flow of fluid in the path between the inlet port (205) and the outlet port (207). Another difference is that midway between the inlet port (205) and outlet port (207) is a quartz baffle (21 1 ) having an opening (212) positioned remote from the inlet (205). Figure 4 is transverse sectional view of the flow cell (201 ) of Figure 3 at the point of inlet of water (region marked at A— A' in Fig. 3). This provides the best view of the configuration of the inlet which shows the angled configuration of the inlet port (205) that facilitates the inlet to direct the fluid emanating from it in a specific direction wherein the direction is within a cone having a semi-conical angle a of 85° and the direction is at an angle β (beta) of not more than 15° relative to the wall adjoining the inlet port of the vessel (202), this configuration of the inlet port (205) preferably provides the water emanating from the inlet port a tangential flow through the path between the inlet port (205) and the outlet port (207).

Figure 5a is a longitudinal sectional view of the preferred embodiment of the flow cell (201 ) showing the semi-conical angle a (alpha). This figure shows a cross section of a portion of the cone having semi-conical angle a of 50° within which the fluid emanating from the inlet port (205) is directed to flow. The axis OZ of the cone is parallel to the shortest geometric path (shown by broken line OZ') between the inlet port (205) and the outlet port (207). The apex of the cone (O) is positioned at the mouth of the inlet port (205) from which the water emanates and the cone extends in a direction away from the shortest geometric path. In Figure 5a the cone extends towards the end cap (209) provided with five UV LEDs arranged radially approximately 72° apart and one at the centre (not seen in this view).

Figure 5b is a transverse sectional view of the preferred embodiment of the flow cell (201 ) at the point of inlet of water showing the angle β (beta) which is approximately 15° relative to the wall (213, shown by the dashed line) adjoining the inlet port (205) of the vessel (202).

Details of the invention will now be explained.

Detailed description of the invention

Disclosed flow cell for reducing the number of viable microorganisms in a fluid includes a vessel, an inlet port, an outlet port and an ultraviolet light emitting source. The fluid may be a gas or liquid, whatever can be purified by exposing it to ultraviolet radiation and usually it is water.

Vessel

Disclosed flow cell includes a vessel delimited by a wall. The vessel includes an inlet port and an outlet port defining a path there between for flow of fluid.

Preferably the wall of the vessel is at least partially curved, linear or curvilinear in a transverse cross section. It is preferred that in a transverse cross section, the wall of the vessel is circular or is an n-sided polygon, wherein n is at least 3. Preferably the wall of the vessel is an n-sided polygon where n is 3 to 18, more preferably n is 3 to 8 still more preferably 3 to 6.

The vessel is preferably elongated and having two opposing ends. There is no restriction on the size and dimensions of the flow cell. However, keeping in mind the commercial use and the size of ordinary flow cells for residential applications, it is preferred that the vessel of the flow cell is from 0.08 to 0.2 meters, preferably 0.1 to 0.15 meters long and it has diameter of 0.02 to 0.08 meters, more preferably 0.03 to 0.05 meters. Preferably the cross-sectional area of the vessel is 1.0 x 10^"4 m² to 1.0 x 10^"2 m², preferably 3.0 x 10^"4 m² to 5.0 x 10^"3 m². Further preferably the volume of said vessel is 1 x10^"5 to 1 x10^"3 m³. These principles may be used to scale up or down for larger or smaller applications.

When the vessel of the flow cell is elongated, it is preferred that the length of the vessel is greater than its maximum width, so that the UV radiation is substantially uniform across the cross section of the flow cell over the majority of the length of the flow cell. It is also preferred that the cross section profile and area of the vessel of the flow cell are substantially constant along the length of UV illuminated region. The vessel may be made of any known material which is suitable for construction of a flow cell. A preferred material is stainless steel. It is preferred that the vessel has a sheath, which preferably is made of Teflon or similar material. It is also preferred that the body has reflective surfaces for example polished or coated stainless steel. Preferably the vessel has an end-cap at an end of the vessel for sealing the vessel, more preferably at each end of the vessel. When the vessel is elongated with two opposing ends, the end cap may be present at one end or both the ends of the vessel for sealing the vessel. It is also preferred that the flow cell has a heat sink adjacent an end-cap, preferably adjacent each end-cap.

Preferred embodiments of flow cell includes one or more baffles positioned in the path for the flow of fluid inside the vessel. Function of the baffles is to create additional turbulence and thereby prolong residence time. Preferably the baffles are positioned substantially midway between the inlet port and the outlet port. It is preferred that in the case of a single baffle, it is positioned midway between the inlet and said outlet. In this case it is further preferred that the baffle has an opening for water to pass there through where the opening is positioned remote from said inlet port. When present, the baffle(s) is made of UV transparent material such as quartz glass or silica glass.

Inlet port

Disclosed flow cell includes an inlet port. In a preferred embodiment of the flow cell in which the vessel is elongated with two opposing ends, it is preferred that the inlet port is adjacent to one end and the outlet port is adjacent to an opposing end of the vessel. As shown in Figure 3, it is preferred that the inlet port and the outlet port is on the same side of the longitudinal axis of the vessel.

Direction of flow of fluid emanating from the inlet port

The inlet port of the disclosed flow cell is configured to direct the fluid emanating from the inlet port in a direction which is within a cone having a semi-conical angle a (alpha) of 85°. Preferably the cone has an angle a of 80°, more preferably of 75° and still more preferably of 70°, further preferably of 65° and most preferably of 60° but preferably the angle a is at least 20° still preferably at least 30°, further preferably at least 40° and most preferably at least 50°. The axis of said cone is parallel to a shortest geometric path between the inlet port and the outlet port. In Figure 3, the shortest geometric path is shown with broken lines between the inlet port and outlet port. The cone extends in a direction away from the shortest geometric path, and preferably extends towards a region in which the ultraviolet light density is maximum. Without wishing to be bound by theory, we believe that this configuration of the inlet port which directs the fluid emanating from the inlet port in a specific direction (as disclosed in the present invention) that is away from the shortest geometric path, causes the fluid entering the flow cell to flow through a path which provides the fluid increased residence time inside the flow cell. It is also believed that when the fluid is directed away from the shortest geometric path, the fluid is better circulated inside the vessel of the flow cell, thereby providing improved performance with respect to reduction in the number of viable bacteria and virus, more so in a flow cell operating at lower power consumption and higher flow rates. In addition, the direction of flow of the fluid emanating from the inlet port is at an angle β (beta) of not more than 15° relative to the wall (213) adjoining the inlet port of the vessel. Preferably the angle β is not more than 12°, still preferably not more than 10°, still more not more than 8° and most preferably not more than 3°. Without wishing to be bound by theory, we believe that this configuration of the inlet port which directs the fluid emanating from the inlet port in a direction which is at an angle β of not more than 15° relative to the wall (213) adjoining the inlet port of the vessel, causes the fluid entering the flow cell to flow through a tangential flow path and the fluid is better circulated inside the vessel of the flow cell and thereby providing improved performance with respect to reduction in the number of viable bacteria and virus, more so in a flow cell operating at lower power consumption and higher flow rates.

Outlet port

Disclosed flow cell includes an outlet port. The inlet port and the outlet port defines a path there between for flow of fluid.

Ultraviolet light emitting source Disclosed flow cell includes at least one ultraviolet light emitting source capable of illuminating the fluid flowing through the vessel. The UV light emitting source may be placed suitably anywhere in the path or away from the path whilst ensuring that the fluid is contactable by the UV light emitted therefrom. It is highly preferred that the UV light emitting source is a diode.

Preferably the ultraviolet light emitting source is capable of illuminating the fluid flowing through the vessel with an energy of at least 4 x 10²J/m². Further, in order that there is maximum interaction between the fluid and the ultraviolet radiation, the inlet port is preferably directed towards a region of maximum energy density.

Preferably the vessel has an end-cap at each end of the vessel for sealing the vessel. The LED may be placed in the path of flowing fluid or may, and preferably are, placed within end caps disposed at either ends of the tubular vessel of the flow cell. Each end cap provides air tight fitment to the vessel. The end caps are also preferably made of stainless steel and they also, preferably, contain a gasket for better fit. When the LEDs are arranged inside the end caps, they preferably are arranged along extremities of the end caps and radially in the case of circular end caps. For example, in the case of a circular end cap having six LEDs, the LEDs are arranged at angle of 72° with respect to each other and one at the center. The end caps have quartz windows which are transparent to UV light. Preferably there is a heat sink adjacent each end-cap. The heat sink is preferably cooled by making use of the water which flows in and out of the flow cell.

Process for purification of fluid

According to a second aspect of the present invention disclosed is a process for reducing the number of viable microorganisms in a fluid by a flow cell of the first aspect having the steps of (i) illuminating said path between the inlet port and the outlet port of the flow cell with one or more ultraviolet light emitting source and (ii) passing a fluid through the inlet port of the flow cell characterised in that the inlet port is configured to direct the fluid emanating from the inlet port in a direction which is within a cone having a semi-conical angle a (alpha) of 85° with the cone axis parallel to the shortest geometric path between the inlet port and the outlet port wherein the cone extends in a direction away from the shortest geometric path; and, the direction is at an angle β (beta) of not more than 15° relative to the wall adjoining the inlet port of the vessel.

Preferably said path between the inlet port and the outlet port of the flow cell is illuminated with one or more ultraviolet light emitting diode, and when in operation, the fluid flowing through the path is exposed to at least 4 x 10²J/m² of energy. Preferably the ultraviolet light emitting diode is placed suitably anywhere in the path or away from the path whilst ensuring that the fluid is contactable by the light emitted therefrom.

Examples

The invention will now be explained in further detail with non-limiting examples. Example 1 : Conventional flow cell

The conventional flow cell of Figure 1 was used for this experiment. The flow cell (0.12 m length x 0.04m diameter) was made of stainless steel and encased in a sheath of Teflon. The ends of the flow cell were enclosed by two circular quartz windows of 0.05 m diameter and 0.005 m thickness in a stainless steel frame. Each end cap had six UV LEDs (five radial and one at the centre). Total UV energy density in the cell was 2.2 x 10³ J/m² and it was greater than dosage of 1.0 x 10³ J/m² of UV radiation

recommended for achieving log 6 and log 4 reduction of bacteria and virus.

The results are shown in Table 1.

TABLE 1

Observed log reduction Observed log at flow rate of water reduction at flow rate

Organism Time/minutes

100 ml/minute of water 50

ml/minute

bacteria 2 5.5 7.1

5 6.7 7.1

10 7.0 7.1

virus 2 4.0 3.7

5 3.6 3.9

10 3.7 4.0 Data in table 1 indicates that log reduction values were met only at very low flow rate (50 mL/minute). It is evident that residence time is not sufficient especially for virus even at 50 mL/minute flow rate. At 100 mL/minute flow rate, there was hardly any removal.

Example 2: Preferred flow cell

The preferred flow cell of Figure 3 was used for this experiment. The flow cell (0.12 m length x 0.04m diameter) was made of stainless steel and encased in a sheath of Teflon. The ends of the flow cell were enclosed by two circular quartz windows of 0.05 m diameter and 0.005 m thickness in a stainless steel frame. Each end cap had six UV LEDs (five radial and one at the centre). Total UV energy density in the cell was 2.2 x 10³ J/m² and it was greater than dosage of 1.0 x 10³ J/m² of UV radiation

recommended for achieving log 6 and log 4 reduction of bacteria and virus. The inlet port was configured to direct the water emanating from the inlet port in a direction which is within a cone having a semi-conical angle a of approximately 50° (as shown in Figure 5a). The axis of the cone was parallel to the shortest geometric path between the inlet port and the outlet port and the cone extends in a direction away from the shortest geometric path as shown in Figure 5(a). The direction of flow of fluid emanating from the inlet port was also at an angle β (beta) of 15° relative to the wall adjoining the inlet port of the vessel (as shown in Figure 5b). This data is summarized in table 2.

TABLE 2

Observed log reduction

Observed log reduction for

for Fig.3 with quartz Fig.3 without baffle

Organism Time/minutes baffle

Flow rate in ml/minute Flow rate in ml/minute

200 100 50 200 100 50

2 6.3 6.5 6.6 6.1 6.1 6.0 bacteria 5 6.4 6.6 6.6 6.2 6.1 6.0

10 6.3 6.6 6.7 6.3 6.3 6.2

2 3.2 3.4 3.8 3.0 3.5 3.6 virus 5 3.2 3.4 4.0 3.0 3.7 3.7

10 3.2 3.5 4.0 3.1 3.7 3.8 The microbiological performance improved marginally but did not meet 6-4 log removal criteria however the difference in log values between tables 1 and 2 was appreciable considering even at higher flow rate of 200 mL/minute. Example 3: Greater power and heat sink

This Example 2 was repeated by increasing the power by approximately 50% and flow rate up to 200 mL/minute. Heat sinks were provided at each end cap. Results are shown in Table 3.

TABLE 3

The data in table 3 shows beneficial effect of higher power.

Claims

1 A flow cell (201 ) for reducing the number of viable microorganisms in a fluid comprising:

(i) a vessel (202), delimited by a wall, said vessel (202) comprising an inlet port (205) and an outlet port (207) defining a path (203) there between for flow of fluid, and,

(i) said direction is within a cone having a semi-conical angle a (alpha) of 85° with the cone axis parallel to the shortest geometric path between the inlet port (205) and the outlet port (207) wherein the cone extends in a direction away from the shortest geometric path; and,

2 A flow cell as claimed in claim 1 wherein the wall of the vessel is at least partially curved, linear or curvilinear in transverse cross section.

3 A flow cell as claimed in claim 2 wherein the wall of the vessel in a transverse cross section has a circular shape or is an n-sided polygon where n = 3 to 18.

4 A flow cell as claimed in claim 1 , 2 or 3 wherein the vessel (202) is elongated and comprises two opposing ends.

5 A flow cell as claimed in Claim 4 wherein the inlet port (205) is adjacent to one end and the outlet port (207) is adjacent to an opposing end of the vessel (202).

6 A flow cell as claimed in Claim 4 or 5 wherein the inlet port (205) and the outlet port (206) are on the same side of longitudinal axis of vessel (202). A flow cell as claimed in any one of the preceding claims wherein the ultraviolet light emitting source is capable of illuminating the fluid flowing through the vessel (202) with an energy of at least 4x10²J/m². A flow cell as claimed in any one of the preceding claims comprising one or more baffles (21 1 ) inside the vessel (202). A flow cell as clamed in claim 8 wherein each baffle (21 1 ) has an opening (212) positioned remote from the inlet port (205), for passage of said fluid there through. A flow cell as claimed in any one of the preceding claims comprising an end-cap (209, 210) at each end of the vessel for sealing said vessel (202). A flow cell as claimed in claim 10 wherein each end cap (209, 210) comprises one or more of the ultraviolet light emitting source. A flow cell as claimed in any one of the preceding claims 10 or 1 1 comprising a heat sink adjacent each end-cap (209, 210). A flow cell as claimed in any one of the preceding claims wherein the ultraviolet light emitting source is a diode. A flow cell as claimed in any one of the preceding claims wherein cross-sectional area of said vessel is 1.0 x 10^"4 m² to 1.0 x 10^"2 m². A process for reducing the number of viable microorganisms in a fluid by a flow cell as claimed in any one of the preceding claims comprising the steps of:

(i) illuminating said path between the inlet port (205) and the outlet port (207) of the flow cell (201 ) with one or more ultraviolet light emitting source;

(ii) passing a fluid through the inlet port of the flow cell,

characterised in that the inlet port (205) is configured to direct the fluid emanating from the inlet port (205) in a direction wherein: said direction is within a cone having a semi-conical angle a (alpha) of 85° with the cone axis parallel to the shortest geometric path between the inlet port (205) and the outlet port (207) wherein the cone extends in a direction away from the shortest geometric path; and,

said direction is at an angle β (beta) not more than 15° relative to the wall (213) adjoining the inlet port (205) of the vessel (202).