WO2021250414A1

WO2021250414A1 - Led array

Info

Publication number: WO2021250414A1
Application number: PCT/GB2021/051446
Authority: WO
Inventors: David Armitage; Patrick Keogh
Original assignee: Baldwin Technology Limited
Priority date: 2020-06-10
Filing date: 2021-06-10
Publication date: 2021-12-16
Also published as: GB2596062A; GB2596062B; GB202008816D0

Abstract

The present invention provides a LED array configured to be cooled by a dual-phase cooling system, the LED array comprising: a plurality of LEDs; a refrigerant path, adjacent the plurality of LEDs, comprising a plurality of sections, at least one section of the plurality of sections comprising a control valve configured to control a flow rate of a refrigerant to said section, wherein each one of the plurality of sections is configured to cool a portion of the LED array. A LED cooling system, a UV radiation source, and a method of cooling a LED array are also provided.

Description

LED array

The present invention relates to a LED array comprising a plurality of LEDs. The LED array is configured to be cooled by a dual-phase cooling system, and comprises a refrigerant path having a plurality of sections, each section configured to cool a portion of the LED array. In particular, the LED array of the present invention finds application in the controlled cooling of LEDs or LED modules of the LED array using a dual-phase refrigerant.

As is well-known, electronics require cooling in many applications. For example, during operation, a light-emitting diode (LED) emits heat as a result of the recombination of electrons and holes at a p-n junction. T o achieve improved performance and lifetime, the p-n junction inside the LED requires cooling to avoid overheating.

LEDs have become ubiquitous in many applications, including low-power applications such as lighting and displays, as well as high-power applications such as UV curing. While passive or active air cooling of LEDs is sufficient for many low-power applications, the practical limits of air cooling have been reached in high-power application.

Therefore, for high-power applications, other heat transfer systems are often required. In particular, water cooling is most often used. However, in recent years, increasing power requirements and increasing miniaturisation of LED arrays, e.g. for UV curing, have resulted in water cooling reaching the limits of its practicality. In particular, miniaturisation requires micro channel heatsinks which creates potential corrosion issues if water is used as a refrigerant. The heat capacity of water is also limited compared to some refrigerants.

As such, other heat transfer systems, such as thermoelectric cooling, direct expansion cooling, and on chip cooling have been developed. However, thermoelectric cooling is neither reliable nor efficient enough for high-power application. On chip cooling is expensive and more often used for high-value computing chips, and as such not suitable for low-cost LEDs.

Therefore, dual-phase cooling for high power applications of LEDs is considered to be promising. Dual-phase cooling has various advantages over water cooling, in particular lower required flow rates (of the refrigerant), energy savings, compatibility with smaller micro fluid passages, more compact light sources, more uniform temperature across an LED array to maintain more consistent light output, and overall higher efficiency and reliability.

The term “dual-phase cooling” is used herein to refer to cooling methods using a refrigerant such as R134a, R1234yf, etc., which evaporates and/or partially boils when removing heat from a heat source.

The term “efficiency of cooling” is used herein to describe both efficiency of the removal of heat and the energy efficiency of the overall system. In particular, this involves controlling a flow rate of a refrigerant to a section dependent on a setting of the plurality of LEDs, e.g. reducing a flow rate of the refrigerant when no or less cooling of said section and the plurality of LEDs adjacent said section is not required. However, dual-phase cooling is often more complex and expensive to install. In particular, the use of dual-phase cooling has often been hindered by practical issues of cooling control and maintenance.

Because of the increasing power requirements and progressing miniaturisation of LED arrays for UV curing, the inventors have appreciated the need for a LED array suitable for being cooled by a dual-phase cooling system which overcomes the practical issues that have resulted in a lack of use of LED arrays with dual-phase cooling.

It would be particularly desirable to provide a LED array having means for controlling the cooling rate of at least a portion thereof.

According to a first aspect of the invention, there is provided a LED array configured to be cooled by a dual-phase cooling system, the LED array comprising a plurality of LEDs and a refrigerant path adjacent the plurality of LEDs. The refrigerant path comprises a plurality of sections, and at least one section of the plurality of sections comprises a control valve configured to control a flow rate of a refrigerant to said section. Each one of the plurality of sections is configured to cool a portion of the LED array.

The LED array of the invention allows for direct control of cooling of at least one of the sections of the LED array, and as such the invention allows for more efficient and more precise cooling. In particular, a flow rate of a refrigerant to said section may be controlled responsive to a setting of the plurality of LEDs, which influences how much cooling is required. Cooling of a portion of, multiple portions of, or all of the plurality of LEDs may thus be controlled. This enables improved control and efficiency of cooling.

In particular, providing at least one control valve to control a flow rate of a refrigerant to at least one section of a cooling channel, enables the cooling of an individual LED module, or parts of an individual LED module, to be controlled.

The LED array according to the first aspect may be a LED array configured for a high-power application, i.e. a high-power LED array. The LED array according to the first aspect may be configured for at least one of: curing, in particular UV curing; heating; and drying.

Preferably, the LED array comprises a plurality of modules, each module comprising a sub set of the plurality of LEDs and at least one of the plurality of sections of the refrigerant path.

In preferred embodiments, at least one of the plurality of modules comprises at least two of the plurality of sections of the refrigerant path, at least one of the at least two of the plurality of sections of the refrigerant path comprising a control valve. Advantageously, one module having at least two of the plurality of sections, at least one comprising a control valve, enables more precise control of the cooling of a portion of a LED module dependent on heat generation of the plurality of LEDs.

In preferred embodiments, each module comprises an inlet manifold and an outlet manifold, said inlet manifold connected to a or each upstream end of said module’s at least one section of the refrigerant path, said outlet manifold connected to a or each downstream end of the said module’s at least one section of the refrigerant path.

Preferably, at least two of the plurality of sections are arranged in series. Advantageously, arranging at least two of the plurality of sections in series enables a flow rate of a refrigerant to the at least two sections to be controlled from a single inlet.

In preferred embodiments, at least two of the plurality of sections are arranged in parallel. Advantageously, arranging at least two of the plurality of section in parallel enables precise control of a flow rate of refrigerant to the at least two sections individually for improved control and efficiency.

In preferred embodiments, at least two of the plurality of sections comprises a control valve. Advantageously, a plurality of sections comprising a control valve enables precise control of the flow rate of a refrigerant to said plurality of sections individually, thus enabling improved control and efficiency.

Preferably, each of the plurality of sections comprises a control valve. Advantageously, each section comprising a control valve allows the most detailed control of the flow of the refrigerant, enabling improved control and efficiency by controlling the flow rate of refrigerant to each section individually.

In some embodiments, at least one of the plurality of sections comprises a flow restrictor. A flow restrictor may be e.g. a fixed orifice. Such a flow restrictor may allow relative control of a flow rate of a refrigerant to said at least one section comprising the flow restrictor relative to a flow rate of the refrigerant to other sections. As will be appreciated, the plurality of sections of refrigerant path of the LED array may comprise a combination of sections having a control valve, and sections comprising a flow restrictor.

Preferably, each of the plurality of sections of the refrigerant path is configured such that the cross-sectional area of said section increases from an upstream end to a downstream end. Advantageously, this accommodates for expansion of a refrigerant as it removes heat from the LED array, reducing control issues due to pressure changes.

In preferred embodiments, the LED array further comprises a controller configured to control the or each control valve. Advantageously, this allows for direct control of a flow rate of a refrigerant to at least one of the plurality of sections via a central controller. Advantageously, this allows for precise control of a flow rate of a refrigerant to each one of the plurality of sections having a control valve.

Preferably, the controller is configured to control the or each control valve responsive to an operating state of the LED array. More preferably, the operating state is at least one of: a power setting; a duty cycle; and a proportion of the LED array in use. Advantageously, controlling the control valve responsive to an operating state of the LED array may allow for the required flow rate of a refrigerant to be determined without the need for measuring a temperature or a pressure of the refrigerant in at least one section of the LED array. This may allow for more efficient and more effective cooling, or to act as a check on the pressure loop and/or temperature loop described below.

In preferred embodiments, the LED array further comprises at least one of: a pressure sensor configured to measure the pressure within at least one of the plurality of sections of the refrigerant path; and a temperature sensor configured to measure the temperature within at least one of the plurality of sections of the refrigerant path, and wherein the controller is configured to control the or each control valve responsive to at least one of: a pressure measurement of the pressure sensor; and a temperature measurement of the temperature sensor. Advantageously, measuring either a temperature or a pressure of the refrigerant in one section of the LED array enables direct control of a flow rate of a refrigerant responsive to a parameter of the LED array, and therefore enables improved control and efficiency, thus creating a feedback loop between the flow rate of the refrigerant to said section and the operating state of the LEDs adjacent that section.

Preferably, the controller is a pulse width modulation controller. Alternatively, any standard method of providing variable control demand may be used, such as a voltage loop or a current loop may be used.

In preferred embodiments, the controller is further configured such that controlling at least one of the control valves of the plurality of sections is linked to controlling another one of the control valves of the plurality of sections. Advantageously, controlling at least two of the control valves together may reduce the required computing power of the controller, the required amount of operating state information of the LED array, or the required number of temperature or pressure sensors.

Preferably, at least one of the plurality of sections comprises a surface coating for promoting flow boiling of the refrigerant. Advantageously, promoting flow boiling of the refrigerant enables more efficient cooling as the evaporation of the dual-phase refrigerant is controlled to occur adjacent the LEDs to be cooled, thereby maximising the heat being removed.

In preferred embodiments, the LED array comprises circuitry to drive at least a portion of the LED array, wherein at least one of the plurality of sections is configured to enable cooling of the circuitry. Advantageously, cooling of a circuitry using the same refrigerant path allows for reduced complexity.

Preferably, the refrigerant path comprises a first portion which is closer to the centre of the LED array and a second portion which is further from the centre of the LED array. More preferably, the first portion of the refrigerant path is configured to be upstream of the second portion of the refrigerant path. Advantageously, such an arrangement mitigates condensation. To maximise performance, the refrigerant is typically run as cold as practical. However, exposed outer surfaces of the refrigerant path adjacent electronic components may be problematic because of condensation around the cold refrigerant. As such, the cold, lower pressure side of the cooling circuit is arranged innermost to mitigate condensation.

In preferred embodiments, the LED array comprises at least one quick-release coupling having a two-stage sealing process, configured to couple said refrigerant path to a cooling system. The LED array when used for UV curing may be moved between different positions. In some systems, the refrigerant must be removed from the system and then dosed back into the system once the LED array is in the new position, making the process work intensive. Advantageously, a quick-release coupling allows for easier movement of the LED array and reduces the risk of contamination of the refrigerant path, with air or otherwise.

According to a second aspect of the present invention, there is provided a LED cooling system comprising at least one LED array as described herein. The LED cooling system further comprises a compressor and a condenser in fluid communication with each other and the refrigerant path.

In preferred embodiments, at least one of the compressor and the condenser is water- cooled. Advantageously, water-cooling the compressor or the condenser may improve efficiency of cooling. Preferably, the LED cooling system comprises at least one of a receiver vessel and a filter dryer.

According to a third aspect of the present invention, there is provided a UV radiation source comprising at least one of a LED array as described herein, or a LED cooling system as described herein.

According to a fourth aspect of the present invention, there is provided a method of cooling a LED array according to the previous summary, the method comprises the steps of obtaining at least one of: a pressure measurement of the refrigerant; a temperature measurement of the refrigerant; an operating state of the LED array. The method further comprises instructing the control valve of at least one of the plurality of sections to control a flow rate of said refrigerant to said at least one of the plurality of sections of the refrigerant path responsive to at least one of: the pressure measurement of the refrigerant; the temperature measurement of the refrigerant; and the operating state of the LED array. The operating state may be at least one of: a power setting; a duty cycle; and a proportion of the LED array in use

Any feature in one aspect of the invention may be applied to other aspects of the invention, in any appropriate combination. In particular, method aspects may be applied to apparatus aspects, and vice versa. Furthermore, any, some and/or all features in one aspect can be applied to any, some and/or all features in any other aspect, in any appropriate combination.

It should also be appreciated that particular combinations of the various features described and defined in any aspects of the invention can be implemented and/or supplied and/or used independently.

The invention will now be further described with reference to the figures in which: Figure 1 shows a flow diagram of a conventional water-cooled LED array of the prior art;

Figure 2 shows a flow diagram of a dual-phase refrigerant-cooled LED array in accordance with the present invention;

Figure 3 shows a schematic diagram of a LED array in accordance with the present invention;

Figure 4 shows a schematic diagram of a LED array in accordance with a preferred embodiment of the present invention;

Figure 5 shows a schematic diagram of a LED array in accordance with a preferred embodiment of the present invention;

Figure 6 shows a schematic diagram of a LED array in accordance with a preferred embodiment of the present invention;

Figure 7 shows a schematic diagram of a LED array in accordance with a preferred embodiment of the present invention;

Figure 8 shows a schematic diagram of a further LED array in accordance with a preferred embodiment of the present invention;

Figure 9 shows a schematic diagram of a yet further LED array in accordance with a preferred embodiment of the present invention;

Figure 10 shows a perspective view of a module for a LED array in accordance with the present invention;

Figure 11 shows a perspective view of a LED array in accordance with the present invention;

Figure 12a shows a perspective view of a cross-section of the LED array of Figure 11 ;

Figure 12b shows a side view of the cross-section of the LED array in Figure 12a;

Figure 13a shows a perspective view of a cross-section of an LED array in accordance with the present invention;

Figure 13b shows a side view of the cross-section of the LED array of Figure 13a;

Figure 14a shows a perspective view of a cross-section of an LED array in accordance with the present invention;

Figure 14b shows a side view of the cross-section of the LED array of Figure 14a;

Figure 15 shows a block diagram of a method of controlling the LED array in accordance with the present invention.

Reference numeral 100 in Figure 1 identifies a conventional water-cooled circuit of a LED array 102, which is known in the art. The LED array 102 dissipates heat to a water-cooled heatsink 104. The LED array 102 may be coupled to the water-cooled heat-sink 104 using thermal grease, mechanical clamping, or a chip-on-board assembly. The conventional water- cooled circuit 100 further comprises a heat exchanger 106, a water reservoir 108, a pump 110, and a water flow path 112. Although such a water-cooled system is sufficient for many low-power, and some high-power, applications, the practical limits have, in effect, been reached in high-power applications, and in particular in applications such as print-curing where miniaturisation of components may be required.

As a result of this requirement, a dual-phase refrigerant cooled LED array has been developed. Reference numeral 200 in Figure 2 identifies such a dual-phase refrigerant-cooled circuit of a LED array 202 according to the present invention. The refrigerant partially boils/evaporates inside an evaporator 204 which is integral to the LED array 202 to remove heat from the LED array 202 which, when in use, is a heat source. The dual-phase refrigerant-cooled circuit 200 further comprises a compressor 206, a condenser 208, at least one throttling valve 210, and a refrigerant path 212.

Reference numeral 300 in Figure 3 identifies a LED array according to the present invention. The LED array 300 comprises a plurality of LEDs 302a, 302b, 302c etc. The plurality of LEDs 302a-302z may be provided as a single LED module 304, or as a plurality of LED modules 304a, 304b, 304c, 304d as shown in Figure 3.

The LED array 300 comprises a refrigerant path 212 which is configured to transport a dual phase refrigerant. Any suitable dual-phase refrigerant may be used. A particularly suitable dual phase refrigerant may be R134a. Another particularly suitable dual-phase refrigerant may be R1234yf.

The refrigerant path 212 of LED array comprises a plurality of sections 306a, 306b, 306c, 306d. Each one of the plurality of sections 306a, 306b, 306c, 306d is configured to cool a portion of the LED array 300. In particular, cooling a portion of the LED array 300 means cooling one or more of the plurality of LEDs 302a-302z of the LED array 300.

One of the plurality of sections 306a of the LED array 300 further comprises a control valve 308a configured to control a flow rate of a refrigerant to said section 306a. Allowing individual control of a flow rate of a refrigerant to a specific one of the plurality of sections 306a, 306b, 306c, 306d allows for highly specific control of the cooling of those ones of the plurality of LEDs 302a- 302z of the LED array 300 which are in use and thus generating heat by the specific one of the plurality of sections 306a, 306b, 306c, 306d.

If the LEDs 302a-302z of the LED array 300 are provided as a single LED module 304, each one of the plurality of sections 306a, 306b, 306c, 306d is configured to cool a portion of the LED module 304.

If the LEDs 302a-302z of the LED array 300 are provided as a plurality of LED modules 304a, 304b, 304c, 304d, each one of the plurality of sections 306a, 306b, 306c, 306d may be configured to cool one of the plurality of LED modules 304a, 304b, 304c, 304d, as shown in Figure 3.

The LED array 300 of the present invention may be in the form of a UV head comprising a plurality of modules, each module comprising a plurality if LEDs. Alternatively, the LED array 300 of the present invention may be in the form of a LED module for a UV head, the LED module having a plurality of sub-sections. If the LED array 300 is a UV head having a plurality of LED modules, it may be width switched, i.e. the outermost LED modules may be switched off (e.g. to reduce the area of irradiation). Switching off the outermost LED modules reduces the width of the area being irradiated by the LEDs (i.e. “width switching”). On the other hand, the inner LED module(s) may be less commonly switched off while the UV head is powered. As such, it may be beneficial to provide additional granularity to the ability to control cooling of the outermost LED modules as compared to the inner LED module(s). To provide this additional granularity, the outermost LED modules may comprise a plurality of sections, each section having a control valve, whereas the inner LED module(s) may only comprise a single section having a control valve or fewer sections than the outermost LED modules.

In some embodiments, at least one of the plurality of sections 306a, 306b, 306c, 306d may be configured to cool more than one of the plurality of LED modules 304a, 304b, 304c, 304d.

In some embodiments, the fluid path 212 of the LED array 300 has a common inlet 307, and the LED array 300 comprises the control valve 308a configured to control a flow rate of a refrigerant to the section 306a and an additional control valve 308e in the common inlet 307 to control a flow rate of refrigerant to the sections 306a, 306b, 306c, and 306d, as shown in Figure 4. In some embodiments, the fluid path 212 of the LED array 300 has a common inlet 307, and each of the sections 306a, 306b, 306c, 306d comprises a control valve 308a, 308b, 308c, 308d configured to control a flow rate of a refrigerant to the corresponding section 306a, 306b, 306c, 306d and an additional control valve 308b in the common inlet 307 to control a flow rate of refrigerant to the section 306a, 306b, 306c, 306d, as shown in Figure 5.

In some embodiments, each of the sections 306a, 306b, 306c, 306d comprises a control valve 308a, 308b, 308c, 308d configured to control a flow rate of a refrigerant to the corresponding section 306a, 306b, 306c, 306d, as shown in Figure 6.

In some embodiments, at least one of the plurality of LED modules 304a, 304b, 304c, 304d is cooled by more than one of the plurality of sections 306a, 306b, 306c, 306d, 400, as shown in Figure 7, in which sections 306a and 400 of the refrigerant path 212 of LED array 300 are configured to cool the plurality of LEDs 302a-302z in LED module 304a.

In some embodiments, as shown in Figure 8, at least two sections 306a, 306b of the plurality of sections 306a, 306b, 306c, 306d of the refrigerant path 212 may be connected in series. In some embodiments, as shown in Figure 8, at least two sections 306c, 306d of the plurality of sections 306a, 306b, 306c, 306d of the refrigerant path 212 may be connected in parallel. Any appropriate combination of refrigerant sections being coupled in series and in parallel is envisaged.

As will now be appreciated, the various sections of the refrigerant path may be arranged in any suitable manner to enable the LED array to be cooled effectively and efficiently.

Preferred features of the invention are shown in Figure 9, which shows a LED array 300 according to the present invention. Additional ones of the plurality of sections 306a, 306b, 306c, 306d, 400 of the refrigerant path 212 of LED array 300 may comprise further control valves 600, 602 configured to control a flow rate of a refrigerant to said sections 306d, 400. Allowing individual control of a flow rate of a refrigerant to multiple specific ones of the plurality of sections 306a, 306b, 306c, 306d, 400 allows for highly specific control of the cooling of those ones of the plurality of LEDs 302a-302z of the LED array 300 which are in use and thus generating heat by the specific one of the plurality of sections 306a, 306b, 306c, 306d, 400.

In particular, controlling the flow rates of a refrigerant to a plurality of individual sections of the plurality of section 306a, 306b, 306c, 306d, 400 may enable more efficient cooling of LED array 300.

In particular, as module 304a is one of the outermost modules of LED array 300, it may be beneficial for each of sections 306a and 400 to comprise a control valve 308b, 600 to control the flow rate of refrigerant to the sections 306a and 400 to facilitate width switching of the LED array 300 by enabling more granular control of the cooling of the outermost module of LED array 300 than the cooling of the inner modules.

In some embodiments, LED array 300 may comprise a passive flow controller, such as flow restrictor 603 in section 306b. Flow restrictor 603 may be a narrowing of refrigerant path 212 in section 306b, such as an orifice plate. The flow restrictor 603 may be used to balance the flow of refrigerant to portions of the LED array. In particular, when it is known that a portion of the LED array will always be in use, a flow restrictor 603 may be used to control the flow rate of refrigerant to that portion.

LED array 300 may further comprise a controller 604, which is configured to control at least one of the control valves 308a, 600, 602. The controller 604 may be configured to control each of the control valves 308a, 600, 602. As will be appreciated, each of the plurality of sections of the refrigerant path can comprise a control valve, and each control valve can be controlled independently. However, it is also envisaged that the controller is configured to link the control of more than one control valve, such that the linked control valves are controlled simultaneously, and with a single control instruction.

The controller 604 may be configured to control at least one of the control valves 308a, 600, 602 responsive to an operating state of LED array 300. An operating state of LED array 300 may be a simple ON/OFF state of the whole LED array 300, or may be a power setting of the LED array 300, or the power settings of portions of the LED array 300.

The power setting may be the proportion of power relative to the maximum power (e.g. a duty cycle between 0%, i.e. off or no power, and 100 %, i.e. maximum power) of an individual one of the plurality of LEDs 302a...302z, of an individual one of the plurality of LED modules 304a, 304b, 304c, 304d; of a part of one or multiple ones of the plurality of LED modules 304a, 304b, 304c, 304d; or of part of or a whole of the LED array 300. As such, cooling of an individual one of the plurality of LEDs 302a...302z, of an individual one of the plurality of LED modules 304a, 304b, 304c, 304d; of a part of one or multiple ones of the plurality of LED modules 304a, 304b, 304c, 304d; or of part of or a whole of the LED array 300 may be controlled separately or together.

In some embodiments, the controller 604 may be configured to control at least one of the control valves 308a, 600, 602 responsive to, in addition to or as an alternative to an operating state or power setting, at least one of a pressure measurement and a temperature measurement of sensor 606.

Controller 604 may control at least one of the control valves 308a, 600, 602, over a wired connection. Alternatively or additionally, controller 604 may control at least one of the control valves 308a, 600, 602 wirelessly.

Sensor 606 may measure at least one of a pressure and a temperature of a refrigerant downstream of the plurality of LEDs 302a-302z, as shown in Figure 9. Alternatively, sensor 606 may measure at least one of a pressure and a temperature of a refrigerant upstream of the plurality of LEDs 302a-302z. Additionally or alternatively, sensor 606 may measure vapour quality, i.e. the ratio of liquid refrigerant to vapour refrigerant.

Multiple ones of the plurality of sections 306a, 306b, 306c, 306d, 400 may comprise at least one sensor 606. In some embodiments, at least one sensor 606 is provided for each section comprising a control valve 308a, 600, 602.

Although the control valves 308a, 308b, 308c, 308d, 308e, 600, 602; sensors 606; and flow restrictors 603 may be described as being upstream of LEDs 302a...302z or downstream of LEDs 302a...302z, any of the control valves 308a, 308b, 308c, 308d, 308e, 600, 602;sensors 606; or flow restrictors 603 may be provided upstream or downstream of LEDs 302a...302z.

In some embodiments, controller 604 is a pulse width modulation controller.

Controller 604 may receive signals from the, and may control the, sensors 606 over a wired connection, or wirelessly.

In some embodiments, and as described above, controller 604 is configured to control at least one of the control valves 308a, 600, 602 in a way which is linked to controlling another one of the control valves 308a, 600, 602 of the plurality of sections 306a, 306b, 306c, 306d, 400. For example, in an embodiment as shown in Figure 9, one of the plurality of sections 306a, 306b, 306c, 306d, 400 may comprise a sensor 606, whereas another one of the plurality of section 306a, 306b, 306c, 306d, 400 may not. As such, it may be beneficial to link control of control valve 600 to that of 308a.

LED array 300 may further comprise power circuitry 608 for controlling power to the LEDs, and/or the controller 604. In embodiments in which LED array 300 comprises circuitry 608, at least one of the plurality of section 306a, 306b, 306c, 306d, 400 is configured to enable cooling of the circuitry 608.

The LEDs 302a...302z and LED module(s) 304 shown in the embodiments of Figures 3 to 9 may represent only a portion of the LEDs and LED modules of LED array 300. In particular, if LED array 300 is a UV head, the LED array 300 may comprise a large number of LEDs in a large number of LED modules of which the LEDs 302a.. 302z and LED module(s) 304 of the LED array 300 shown in Figures 3 to 9 is representative. A plurality of the representated LED array 300 may be connected to a refrigerant system in parallel.

Figure 10 shows a perspective view of a module 700 of a LED array 300 as described herein. The module 700 comprises a housing 702 configured to house three sets of LEDs 704a, 704b, and 704c. Although the embodiment of Figure 10 houses three sets of LEDs 704a, 704b, and 704c, the module 700 may comprise more than three sets of LEDs, or less than three sets of LEDs. The sets of LEDs may be arranged along a longitudinal axis of module 700, or they may be arranged perpendicular to the longitudinal axis of module 700.

The housing may comprises a lens 706 mounted adjacent the sets of LEDs for focusing the light as required. The module 700 further comprises three control valves 708a, 708b, and 708c for controlling the flow of refrigerant into the housing and through the refrigerant path sections provided therein; these are described in further detail below with reference to Figure 11 . In this example, each control valve 708a, 708b, and 708c, is a MEMS device. The housing is also provided with an orifice 710, which may be an inlet or an outlet, for connecting to the refrigerant circuit, or to a further such module, as described above. The refrigerant path sections 712a, 712b, and 712c each comprise a plurality of fluid passages, which may be mirco-channels, configured to increase the surface area available for heat exchange between the LEDs (acting as heat sources when in use) and the refrigerant. In the example shown in Figure 10, the fluid passages are formed by a plurality of fins arranged in a direction parallel to the flow direction. Alternatively, for example, these fluid passages may comprise a sintered porous material to increase the surface area available for heat exchange.

As will be appreciated, the LED array 300 may comprise one or more modules 700.

As the refrigerant removes heat from the LEDs, the refrigerant changes from the liquid to the gaseous phase, and therefore expands. Therefore, the cross-sectional area of each of the refrigerant path sections 306a, 306b, 306c, 306d, 400, 712a, 712b, and 612c of Figures 3 to 10 may increase from an inlet to an outlet, i.e. from upstream of the LEDs to downstream of the LEDs. Otherwise, the pressure of the refrigerant downstream of the LEDs may be significantly higher than the pressure upstream of the LEDs, resulting in significant control issues.

Figure 11 shows a perspective view of a LED array 1100 having a common inlet 1102 for refrigerant. The common inlet 1102 terminates in an inlet manifold 1103. The inlet manifold comprises three control valves 1104a, 1104b, and 1104c. In this example, each control valve 1104a, 1104b, and 1104c is a MEMS device. Each MEMS device 1104a, 1104b, and 1104c controls a flow rate of the refrigerant to a corresponding fluid channel 1106a, 1106b, and 1106c.

Each of the corresponding fluid channels 1106a, 1106b, and 1106c terminates in one of the sections 1108a, 1108b, and 1108c of the refrigerant path. The MEMS devices 1104a, 1104b, 1104c are attached to, and controlled by, a control circuit 1109. Sections 1108a and 1108b are separated by a first refrigerant path separator 1111 ab, and sections 1108b and 1108c are separated by a second refrigerant path separator 1111 be. The sections 1108a, 1108b, and 1108c run adjacent a plurality of LEDs 1110 to remove heat from the plurality of LEDs 1110.

The cross-sectional area of the refrigerant path increases between the common inlet 1102 and a common outlet 1114 to account for the expansion of the refrigerant upon removing heat from the LEDs 1110 of LED array 1100. Heat may be removed from the LEDs 1110 via conduction through the separators 1111 ab, 1111 be and via a bottom surface 1113 of the flow path.

Before the refrigerant exits the LED array 1100 via common outlet 1114, refrigerant from the different sections 1108a, 1108b, and 1108 is recombined in an outlet manifold 1112.

Instead of the control valves 1104a, 1104b, 1104c being upstream of the sections 1108a, 1108b, and 1108c, the control valves 1104a, 1104b, 1104c may be provided downstream of the sections 1108a, 1108b, and 1108c.

Figure 12a shows a perspective view of a cross-section along the central section 1108b of LED array 1100 of Figure 11. The control circuit 1109 is not shown in Figure 12a to reveal the structure of the MEMS devices 1104b and 1104c.

MEMS device 1104b controls the flow rate of refrigerant into fluid channel 1106b and subsequently section 1108b of the flow path adjacent the LEDs 1110. MEMS device 1104b controls refrigerant flow from inlet manifold 1103 by controlling how much refrigerant enters the MEMS device 1104b via MEMS device inlet 1105b and exits the MEMS device 1104b via MEMS device outlet 1107b.

Figure 12b shows a side view of the cross-section of the LED array 1100 in Figure 12a. The flow path of refrigerant, depicted by the arrows proceeds from the common inlet 1102, to the inlet manifold 1103, into the MEMS device inlet 1105b, through the MEMS device 1104b, out of the MEMS device outlet 1107b, along fluid channel 1106b and fluid path section 1108b, into the outlet manifold 1112, and out of the common outlet 1114.

Figure 12b also clearly shows the increasing cross-sectional area of section 1108b which accounts for the expansion of the refrigerant upon removing heat from the LED array 1100. Similarly, the volume of the outlet manifold 1112 may be larger than the volume of the inlet manifold 1103; and the cross sectional area of the common outlet 1114 may be greater than the cross sectional area of the common inlet 1102.

Refrigerant path separators 1111 ab and 1111 be and/or bottom surface 1113 of the flow path may comprise projections or fins to increase the surface area available for heat exchange. The person skilled in the art will be aware of many types of conventional heat exchangers which may be used to increase the surface area available for heat exchange, and any such conventional heat exchanger may be used. Although the central fluid path section 1108b is shown to be wider than the outer fluid path sections 1108a and 1108c in Figure 11 , the width of each section 1108a, 1108b, and 1108c may be substantially identical, or the outer fluid path sections 1108a and 1108c may be wider than the central fluid path section 1108b. However, the embodiment of Figures 11 may be advantageous as it allows for more heat to be removed from the portions of the LED array 1100 which are likely to be the hottest.

The common inlet 1102 of LED array 1100 may be in the central portion of the LED array 1100, such that the refrigerant flows towards the two ends of the LED array 1100 from the middle rather than from one end of the LED array 1100 to the other, as shown in the embodiment of Figure 11. In such an embodiment, the LED array 1100 may require two common outlets 1114. Alternatively, the common outlet 1114 of LED array 1100 may be in the central portion of the LED array, in which case the LED array may have two common inlets 1102 on either end of the LED array. If the LED array 1100 has either two common inlets 1102 or two common outlets 1114, the valves or MEMS devices 1104a, 1104b, and 1104c to control the flow rate of refrigerant to the sections 1108a, 1108b, 1108c may advantageously be placed on the single common inlet 1102 or single common outlet 1114 so as not to double the required number of valves or MEMS devices 1104a, 1104b, and 1104c.

Figure 13a shows a perspective view of a cross-section along an outer section 1108c of a LED array 1300. Part of the control circuit 1109 which controls MEMS device 1104c is shown. MEMS device 1104c controls the flow rate of refrigerant from inlet manifold 1103 into fluid channel 1106c and subsequently section 1108c of the flow path adjacent the LEDs. Section 1108c comprises a plurality of fins 1302-1 ...1302-x which increase the surface area available for heat exchange.

Figure 13b shows a side view of the cross-section of the LED array 1300 in Figure 13a. The flow path of refrigerant, depicted by the arrows, is similar to that shown in Figure 12b and proceeds from the common inlet 1102 (not shown), to the inlet manifold 1103, into the MEMS device inlet 1105c, through the MEMS device 1104c, out of the MEMS device outlet 1107c, along fluid channel 1106c and fluid path section 1108c, into the outlet manifold 1112, and out of the common outlet 1114.

Figure 13b also clearly shows the increasing cross-sectional area of section 1108c which accounts for the expansion of the refrigerant upon removing heat from the LED array 1100. Similarly, the volume of the outlet manifold 1112 is larger than the volume of the inlet manifold 1103. Additionally, Figure 13b clearly shows the plurality of projections or fins 1302-1 ...1302-x which increase the surface area available for heat exchange. They are shown here as tubular projections, but may take any appropriate shape or form.

Figure 14a shows a perspective view of a cross-section along an outer section 1108c of a LED array 1400. Part of the control circuit 1109 which controls MEMS device 1104c is shown. In contrast to the embodiment shown in Figures 13a and 13b, the control circuit 1109 and MEMS device 1104 are positioned at the outlet of section 1108c. The MEMS device 1104c controls the flow rate of refrigerant out of the section 1108c into the subsequent outlet manifold 1112. Section 1108c comprises a plurality of fins 1402-1 ...1402-x which increase the surface area available for heat exchange.

Figure 14b shows a side view of the cross-section of the LED array 1400 in Figure 14a. The flow path of refrigerant, depicted by the arrows, is similar to that shown in Figures 12b and 13b, but proceeds from the common inlet 1102 (not shown), to the inlet manifold 1103, along fluid channel 1106c and fluid path section 1108c, into the MEMS device inlet 1105c, through the MEMS device 1104c, out of the MEMS device outlet 1107c, into the outlet manifold 1112, and out of the common outlet 1114 (not shown).

Figure 14b also clearly shows the increasing cross-sectional area of section 1108c which accounts for the expansion of the refrigerant upon removing heat from the LED array 1100. Additionally, Figure 14b clearly shows the plurality of projections or fins 1402-1 ...1402-x which increase the surface area available for heat exchange. They are shown here as tubular projections, but may take any appropriate shape or form. Figure 15 shows a flow diagram of the control method for a LED array refrigerant system as described above.

In step 1500, the controller 600 obtains at least one of a pressure measurement p from sensor 606, a temperature measurement T from sensor 606, or an operating state or power setting % of the LED array 300.

In step 1502, the controller controls one or more of control valve 308a, 600, 602 in response to the at least one of a pressure measurement p from sensor 606, a temperature measurement T from sensor 606, or an operating state or power setting % of the LED array 300.

The control method then returns to step 1500, such that the method provides a feedback control loop. If the temperature measurement T or the pressure measurement p are used, the control loop is a closed loop. The array input power or power setting % may be used in addition to the temperature measurement T or the pressure measurement p to act as moderation on the closed control loop, or instead of the temperature measurement T or the pressure measurement p in an open control loop.

For example, in step 1500 the controller 600 may obtain a temperature measurement T of the refrigerant in section 306a from sensor 606 which is in excess of a desired value. In such a case, the controller may be configured to control a control valve 308a of section 306a (or any other control valve such as control valves 600, 602) responsive to the temperature measurement T by increasing the flow rate of refrigerant to the portion of LED module 304 which is cooled by section 306a. The method then returns to step 1500, in which a further temperature measurement T is obtained, which may be lower than the first temperature measurement, and the controller is configured to control the control valve 308a to reduce the flow rate of refrigerant. These steps are repeated in a closed control loop.

Claims

CLAIMS:

1. A LED array configured to be cooled by a dual-phase cooling system, the LED array comprising: a plurality of LEDs; and a refrigerant path, adjacent the plurality of LEDs, comprising a plurality of sections, at least one section of the plurality of sections comprising a control valve configured to control a flow rate of a refrigerant to said section, wherein each one of the plurality of sections is configured to cool a portion of the LED array.

2. A LED array according to claim 1 , further comprising a plurality of modules, each module comprising a sub-set of the plurality of LEDs and at least one of the plurality of sections of the refrigerant path.

3. A LED array according to claim 2, wherein at least one of the plurality of modules comprises at least two of the plurality of sections of the refrigerant path, at least one of the at least two of the plurality of sections of the refrigerant path comprising a control valve.

4. A LED array according to Claim 2 or 3, wherein each module comprises an inlet manifold and an outlet manifold, said inlet manifold connected to a or each upstream end of said module’s at least one section of the refrigerant path, said outlet manifold connected to a or each downstream end of the said module’s at least one section of the refrigerant path.

5. A LED array according to any preceding claim, wherein at least two of the plurality of sections are arranged in series.

6. A LED array according to any preceding claim, wherein at least two of the plurality of sections are arranged in parallel.

7. A LED array according to any preceding claim, wherein at least two of the plurality of sections comprises a control valve.

8. A LED array according to claim 7, wherein each of the plurality of sections comprises a control valve.

9. A LED array according to any of claims 1 to 7, wherein at least one of the plurality of sections comprises a flow restrictor.

10. A LED array according to any preceding claims, wherein each of the plurality of sections of the refrigerant path is configured such that the cross-sectional area of said section increases from an upstream end to a downstream end.

11. A LED array according to any preceding claim, further comprising a controller configured to control the or each control valve.

12. A LED array according to claim 11 , wherein the controller is configured to control the or each control valve responsive to an operating state of the LED array.

13. A LED array according to claim 12, wherein the operating state is at least one of: a power setting; a duty cycle; and a proportion of the LED array in use.

14. A LED array according to any of claims 11 , 12 or 13, further comprising at least one of: a pressure sensor configured to measure the pressure within at least one of the plurality of sections of the refrigerant path; and a temperature sensor configured to measure the temperature within at least one of the plurality of sections of the refrigerant path, wherein the controller is configured to control the or each control valve responsive to at least one of: a pressure measurement of the pressure sensor; a temperature measurement of the temperature sensor; and an operating state of the LED array.

15. A LED array according to any of claims 11 to 14, wherein the controller is a pulse width modulation controller.

16. A LED array according to any of claims 11 to 15 when dependent upon claim 7 or 8, wherein the controller is further configured such that controlling at least one of the control valves of the plurality of sections is linked to controlling another one of the control valves of the plurality of sections.

17. A LED array according to any preceding claim, wherein at least one of the plurality of sections comprises a surface coating for promoting flow boiling of the refrigerant.

18. A LED array according to any preceding claim, further comprising at least one of control circuitry to control the LED array and drive circuitry to drive at least a portion of the LED array, wherein at least one of the plurality of sections is configured to enable cooling of at least one of the control circuitry and the drive circuitry.

19. A LED array according to any preceding claim, wherein the refrigerant path comprises a first portion which is closer to the centre of the LED array and a second portion which is further from the centre of the LED array.

20. A LED array according to claim 19, wherein the first portion of the refrigerant path is configured to be upstream of the second portion of the refrigerant path.

21 . A LED array according to any preceding claim, further comprising at least one quick- release coupling having a two-stage sealing process, configured to couple said refrigerant path to a cooling system.

22. A LED cooling system comprising at least one LED array according to any of claims 1 to 19, further comprising a compressor and a condenser in fluid communication with each other and the refrigerant path.

23. A LED cooling system according to claim 22, wherein at least one of the compressor and the condenser is water-cooled, preferable wherein the system further comprises at least one of a receiver vessel and a filter dryer.

24. A UV radiation source comprising: a LED array according to any of claims 1 to 21 ; or a LED cooling system according to any of claims 22 to 24.

25. A method of cooling a LED array according to any of claims 1 to 21 , the method comprising the steps of: obtaining at least one of: a pressure measurement of the refrigerant, a temperature measurement of the refrigerant, and an operating state of the LED array, and instructing the control valve of at least one of the plurality of sections to control a flow rate of said refrigerant to said at least one of the plurality of sections of the refrigerant path responsive to at least one of: the pressure measurement of the refrigerant, the temperature measurement of the refrigerant, and the operating state of the LED array.