Optical heater

Abstract

An optical heater 100 converts optical power into thermal energy and includes a housing 130, an associated optical cable 110, 112 and a fastener 133 to attach the optical heater to a chamber 310. In use, the chamber receives a substance to be heated. The optical cable is designed to receive light from an optical source, and the optical source may be a passive source such as a sun light collector, or an active source such as a lamp. The optical heater and associated chamber may be part of a heating system with a boiler 300 in which cold water is received at an inlet 320, heated by the optical heater and hot water is delivered via an outlet 330. The optical heater may include a heating target 120 and the target may function as a dispersive lens that allows the collected optical energy to be dispersed to the material to be heated, or the target may heat up and dissipate the heat by conduction and convection. The housing may be made of at least two parts, and a first part 131 may be made of a metal or a metal alloy material, such as brass, and a second portion 132 may be made of a transparent material such as glass or plastics.

Description

Technical Field The present disclosure relates to an optical heater. The disclosure also relates to a heating system comprising the optical heater coupled to a chamber for receiving a liquid or substance to be heated. Background An optical heater converts optical power into thermal energy. Such devices can be used in various heating systems. Several designs have been reported; for instance, patent document JPH03204567A describes an optothermal converter. However, current devices lack efficiency and practicality. Summary According to a first aspect of the disclosure, there is provided an optical heater comprising a housing adapted to receive an optical cable; and a fastening means configured to attach the optical heater to a chamber for receiving a liquid or substance to be heated. Optionally, the housing has an elongated shape. For instance the housing may have an elongated tubular shape. Optionally, the housing is sealed to prevent ingress of the liquid or substance into the housing. For instance, the housing may be waterproof. Optionally, the optical heater comprises a heating target provided within the housing and configured to receive optical power via the optical cable. Optionally, the housing comprises a first portion attached to a second portion. Optionally, the first portion has an elongated tubular shape, and the second portion forms a cap attached at the end of the first portion. Optionally, the second portion is made of a transparent material. For instance, the transparent material may comprise glass or plastic such as Polyfmethyl methacrylate) (PMMA), acrylic or poly carbonate . Optionally, the heating target is located within the second portion. Optionally, the heating target is transparent. For instance the heating target may be made of glass or plastic such as Poly(methyl methacrylate) (PMMA), acrylic or poly carbonate . Optionally, the heating target forms a dispersive lens. Optionally, the heating target is opaque or light absorbing. Optionally, the heating target is made of graphite. Optionally, the housing is made at least in part of a metal or a metal alloy material. For instance, the housing may be made of brass or of a stainless steel alloy such as Incoloy. Optionally, the fastening means comprises a flange. Optionally, the optical heater comprises a cable connector adapted to connect the optical cable to the housing. For instance, the cable connector may be a cable gland. Optionally, the optical heater comprises the optical cable. Optionally, the optical cable is optically coupled to the heating target. For instance, an end of the optical cable may be in direct contact with the heating target, or the end of the optical cable may be facing the heating target while leaving a gap between the end of the optical cable and the heating target. Optionally, the optical cable comprises a plurality of optical fibres. For instance the optical cable may be an umbilical cable. According to a second aspect of the disclosure, there is provided a system comprising an optical heater according to the first aspect coupled to a chamber for receiving a liquid or a substance to be heated. For instance, the system may be a heating system for a building and the chamber, the chamber of a boiler or water tank. Optionally, the chamber comprises a wall portion having an opening for receiving the optical heater, so that the housing of the optical heater fits within the chamber. Optionally, the system comprises a safety mechanism adapted to prevent an optical source coupled to the optical cable from producing or transmitting light upon detection that the optical heater is not correctly connected to the chamber. The optical source may be a passive source such as a sun light collector, or an active source such as a lamp. For instance, the flange may be part of a safety loop circuit such that if the flange is not engaged within the chamber opening, the safety loop circuit becomes broken. In turn another signal may be generated to prevent the optical source from producing or transmitting light or the breaking of the safety loop circuit itself may switch off the optical source. According to a third aspect of the disclosure, there is provided a method for heating a liquid or substance, the method comprising fitting an optical heater within a chamber for receiving the liquid or substance to be heated; wherein the optical heater comprises a housing adapted to receive an optical cable; and a fastening means configured to attach the optical heater to the chamber; and transmitting optical power to the optical heater via the optical cable to heat the liquid or substance. The options described with respect to the first aspect of the disclosure are also common to the second and third aspects of the disclosure. Description of the drawings The disclosure is described in further detail below by way of example and with reference to the accompanying drawings, in which: figure 1 is a diagram of an optical heater provided with a transparent heating target; figure 2 is a diagram of an optical heater provided with a non-transparent heating target- figure 3 is a diagram of a boiler fitted with an optical heater; figure 4 is a cross section of an exemplary umbilical cable; figure 5 is a schematic diagram of a heating system installed on a building; figure 6 is a flow chart of a method for heating a liquid or substance. Description Figure 1 is a diagram of an optical heater provided with a transparent heating target. The optical heater 100 includes an optical cable 110. The optical cable 110 may be an umbilical cable comprising a plurality of optical fibres. The umbilical cable 110 is designed to receive light from an optical source (not shown), such as a sun light collector or an active source such as a lamp. The optional heating target 120 is coupled to an end of the cable 110. The housing 130 encloses a portion of the cable and the heating target 120. The housing 130 has a cylindrical shape that extends between a first end and a second end. The housing 130 is also tubular, hence forming a cavity for receiving the cable 110, or the optical fibers 112 within it. In this example the housing has a first portion 131, a second portion 132, also referred to as end cap, and a flange 133 for securing the optical heater within an external chamber (not shown). The flange 133 may be replaced by other fastening means. For instance, the external chamber (usually a cylinder or buffer tank, vat or still) may be provided with an opening designed to receive the optical heater. This opening is commonly formed by way of a tank connector and threaded differently depending on country, application and tank size and normally comes pre-installed with the chamber or tank. For example, for UK domestic heating 2.1 / 4 BSP is the standard tank connector. The flange 133 may be designed to plug or screw into onto the opening so that the waterproof housing 130 is kept within the chamber and securely attached to the chamber wall. This flange 133 has several purposes. Firstly, it provides the means for a detachable yet waterproof seal between the optical cable and the liquid in the tank. It provides the possibility of an adapter between several thread types, thus allowing one model of optical element or tank to be sold to different markets and applications just by changing the flange. It provides a thermal insulator between the tank, element and outside world and can be further insulated with an insulating material coating surrounding. It could also act as a constituent of a safety mechanism whereby if the flange is not engaged within the chamber opening or / and housing within the flange, a safety circuit would be broken or incomplete or otherwise detect the lack of engagement, and this would prevent the optical source from producing light. A connector 140, also referred to as cable gland, may be used to connect the cable 110 to the housing 130. The cable 110 is preferably a continuous cable, as otherwise any joining of the cable would create optical losses, hence reducing efficiency. The cable gland 140 has several functions. The umbilical cable 110 may be provided with a protective sheath such as Kevlar or armored wire . In this case the umbilical cable 110 is wider than just the optical fibres within it. The cable gland 140 marks the point at which this protective sheath stops. The cable gland 140 may also be used to seal the optical fibers to the end of the protective sheath to prevent dislodgement. The content 112 of the umbilical (that is the optical fibers and any electric wire that may also be provided)continues within the housing 130 up to the region in which the heating target 120 is provided. This reduces the overall diameter of the housing that would be required to reduce cost and reduces manufacturing cost. It also provides a detachable holder for attaching or removing the aligned umbilical into the housing whilst securing it, whilst not having to drain down or remove water from the tank (which may be under pressure) for servicing or maintenance. This detachable aspect of the optical heater provides several advantages. When the flange 133 is screwed into the tank it can be done whilst allowing the cable to be inserted later without the rotational screwing motion breaking the fibres through twisting. The cable gland 140 may also contain an upper additional threaded sealing nut (not shown) that secures into the housing flange 133, for tightening down the umbilical post insertion. The sealing nut acts as a protecting seal against moisture and dust ingress that might otherwise fall into the housing cavity. It also acts as a light blocker and secondary thermal insulator, preventing light and heat loss towards the opening or umbilical or upwards into the umbilical itself. It also acts as a second aspect of a safety mechanism whereby should the gland 140 not be properly or fully engaged within the housing, a safety circuit would be broken or incomplete or otherwise detected, and this would prevent the optical source from producing light. The gland 140 (and sealing nut) may be pre-formed and shipped with the umbilical 110 and target assembly so it best fits tightly around the individual multiple optical fibre strands. The gland 140 may have a detachable locking and engagement mechanism to secure firmly to the housing 130, with minimal twisting and stress, so called "zero insertion force” connection. The first end of the housing may be provided with external and internal threads for receiving the flange 133, the cable gland 140 and the sealing nut. In this example the heating target 120 and the end cap 132 are transparent. For instance, they may be made of glass or plastic . The heating target 120 is located at the end of the housing 130 within the end cap 132, such that when engaged with the end cap 132 the optical heater can be placed deeper within the tank to allow the heat to best permeate into the middle region of the volume of liquid. The transparent target 120 then acts as a first dispersive lens, and the end cap 132 a second, allowing the optical energy to project into the liquid rather than being absorbed by elements of the optical heater. This prevents excessive heat generation within the optical heater itself and instead disperses the energy more evenly into the liquid away from the heater housing 130. The heating target 120 also provides a solid and more robust end to the fibres 112 of the umbilical cable 110, that may have to be pushed through a building during the installation, potentially protected with a cover at installation time. The open end of the umbilical cable is directed toward the transparent target 120 to allow the light emission, and thus the target 120 acts as a lens to emanate the light into the liquid. Similarly, the end cap 132 may also act or be designed as a lens. In order to have most effect and to minimize the chance of the cable not being completely inserted, the end of the umbilical and the heating target 120 may be designed with a mating profile. Several mating profiles could be envisaged, including a wedge profile. The target 120 and the end cap 132 may be positioned with a pre-determined distance between each other. When 120 and 132 act as lenses, the predetermined distance may be defined based on the focal lens of each lens so as to form a lens pair. The distance between the gland 140 and target 120 and internal distance with the element housing 131 to the target internal face maybe fixed as the target and cap act as a pair of optical lenses designed with certain focal length and can be made to touch or offset depending on the design. The end of the fibres 112 could be in contact with the target 120, but in some applications the fibers are only directionally aligned with and point towards the target 120 and the end cap 132. The transparent heating cap 132 is in contact with the first portion 131 of the housing. For instance, the end cap 132 may be bounded to the first portion 131 via a seal or with a layer of glue to make a water tight connection. The first portion 131 of the waterproof housing may be made of a metal or a metal alloy material. For instance, brass may be used due to its workable yet corrosive resistant properties. The second portion 132 may be made of a transparent material such as glass or plastic. This arrangement provides a detachable optical heater that can be connected to a liquid chamber for efficient optical to thermal energy conversion. As mentioned above the optical target is optional and the optical heater could be implemented without it. In this scenario light coming out of the optical fibres of the umbilical cable would be directly received by the end cap 132. Figure 2 is an alternative diagram of an optical heater provided with a non-transparent heating target. The optical heater 200, is similar to the optical heater of figure 1 and includes a cable or umbilical 110, a heating target 220 coupled to an end of the cable, and a waterproof housing 230 enclosing a portion of cable and a heat conductive tip 232. The heat conductive tip 232 may be a single piece continuation of the longitudinal first portion 231. In this case the heating target 220 is opaque, hence made of a light absorbing yet heat stable material. For instance, the heating target 220 may be made of strong yet low cost graphite, as used in high temperature welding tips. The end of the fibres 112 could be in contact with the target 220. In some application, especially when plastic optical fibres are used, it may be preferential to have a space between the fibres and the target 220 to prevent excessive heat buildup and melting of the umbilical fibres. Silica fibers tend to withstand much higher temperatures, and less or no spacer would be required. The housing 230 has a cylindrical shape that extends between a first end and a second end. In this example the housing has a longitudinal portion 231, and a flange 233, as described above with reference to figure 1. The longitudinal portion 231 may be made of a metal or a metal alloy material. For instance, the housing 230 may be made of brass or stainless steel Alloy such as Incoloy. Figure 3 is a diagram of a diagram of a boiler provided with an optical heater. The boiler 300 has a chamber 310 provided with an input 320 for receiving cold water, an output 330 for providing hot water, and an opening 340 for receiving an optical heater as described above with reference to figures 1 or 2. The boiler 300 is filled with water up to a desired level so that the optical heater is immersed in water. In use the boiler may be under pressure as the water is pumped and also expands on heating. For this reason, the optical heater connectors (for instance the flange) should be sufficiently robust to sustain pression forces. In operation the cable 110 carries optical power to the heating target 120 / 220 which heats up. The heat is then dissipated by conduction and convection from the heating target to the fluid, in this case water present inside the chamber 310. The optical heater can be designed to be compatible with existing heat storage system, so as to be easily retrofitted. It will be appreciated that depending on the application different types of liquids or substances may be used. Therefore, the optical heater may be used with a chamber filled with other liquids such as mash for whiskey distilling or ingredients for food manufacturing or plastic for molding or liquid ore for melting. Figure 4 is a cross section of an exemplary umbilical cable. The umbilical 400 contains a plurality of optical fibers also referred to as fiber cores. In this example the fibers are arranged in a hexagonal configuration. It will be appreciated that other layouts may be considered. The fibres include the optical fibres coming from each cell and carrying an optical beam / signal. The umbilical may also include electrical wires for carrying an electrical signal. When provided, the electrical wires can be used to implement some safety features. The number of optical fibres in the umbilical may vary. In this example the umbilical 400 includes 100 optical fibres labelled 410 and 10 electrical wires labelled 420. The umbilical 400 also includes an outer sheath or conduit430. The outer sheath may be armored or reinforced. This can be achieved using Kevlar. The umbilical may be provided with connectors at either end to allow easy connection between a light collector and the optical heater. Having many separate optical fibers (for instance a 100 or more) has the benefit of mechanical flexibility, as fibers can then slide over each other in the bundle when the umbilical is bent or twisted. This also increases robustness, provides a level of redundancy and increases pulling strength. Maximum fiber bend radius is an important parameter for fiber, as if bent too much light can escape, hence heavily impacting efficiency, or in extreme cases cause a safety hazard. The bend radius as defined by the American National Standards Institute [ANSI], will depend on various factors including the wavelength of light, pulling tension, tensile load, cladding material, type of fiber, cables outside diameter. The length of the umbilical will depend on the application. For installing the system on a house, the umbilical may have a length of at least 10 meters, for instance a length ranging between about 10m to about 50m. This would allow the umbilical fibre to extend from the roof of a building to a cylinder water tank on a ground floor. Alternatively, the umbilical maybe shorter, as desirable if the tank can be placed near the roof, or an external wall, when the panel can be wall mounted, this is the situation more likely when the system is used to heat a buffer tank for air source heat pumps or a pre-heater for warming water before it enters the main cylinder tank. Figure 5 is a diagram of a heating system installed on a building. The system 500 shows the boiler 300 of figure 3, in which the cable / umbilical 110 is connected to a light collector 510 which may be installed on the roof of a building. Light collected by the light collector 510 is transmitted to the optical heater 100 / 200 via the umbilical cable 110. The system 500 includes a safety mechanism to prevent the light collector 510 coupled to the optical cable 110 from producing or transmitting light when detecting that the optical heater 100 / 200 is not correctly connected to the chamber of the boiler 300. The fastening means such as the flange of optical heater may be part of a safety loop circuit designed such that if the flange is not engaged within the chamber opening, the safety loop circuit becomes broken (open circuit). When provided, the electrical wires of the umbilical can be used to form part of the safety loop circuit. In turn, a safety signal may be generated by a controller to prevent the light collector 510 from transmitting light. The controller may be configured to receive an electric signal traveling inside the umbilical. When the electric signal is not received, an open circuit is detected, and generates the safety signal. Alternatively, the breaking of the safety loop circuit itself may switch off the light collector or the light source. Figure 6 is a flow chart of a method for heating a liquid or substance. At step 610 an optical heater is fitted within a chamber for receiving the liquid or substance to be heated. The optical heater comprises a housing adapted to receive an optical cable; and a fastening means configured to attach the optical heater to the chamber. At step 620 optical power is transmitted to the optical heater via the optical cable to heat the liquid or substance within the chamber. A skilled person will appreciate that variations of the disclosed arrangements are possible without departing from the disclosure. Accordingly, the above description of the specific embodiments is made by way of example only and not for the purposes of limitation. It will be clear to the skilled person that minor modifications may be made without significant changes to the operation described.

Claims

1. An optical heater comprisinga housing adapted to receive an optical cable; anda fastening means configured to attach the optical heater to a chamber for receiving a liquid or substance to be heated.

2. The optical heater as claimed in claim 1, wherein the housing has an elongated shape.

3. The optical heater as claimed in claim 1 or 2, wherein the housing is sealed to prevent ingress of the liquid or substance into the housing.

4. The optical heater as claimed in any one of the preceding claims, comprising a heating target provided within the housing, and configured to receive optical power via the optical cable.

5. The optical heater as claimed in any of the preceding claims, wherein the housing comprises a first portion attached to a second portion.

6. The optical heater as claimed in claim 5, wherein the first portion has an elongated tubular shape, and wherein the second portion forms a cap attached at the end of the first portion.

7. The optical heater as claimed in claim 6, wherein the secondportion is made of a transparent material.

8. The optical heater as claimed in claim 7, when dependent on claim 4, wherein the heating target is located within the second portion.

9. The optical heater as claimed in claim 8, wherein the heating target is transparent.

10. The optical heater as claimed in claim 9, wherein the heating target forms a dispersive lens.

11. The optical heater as claimed in any one of the claims 1 to 6, when dependent on claim 4, wherein the heating target is opaque or light absorbing.

12. The optical heater as claimed in claim 11, wherein the heating target is made of graphite.

13. The optical heater as claimed in any one of the preceding claims, wherein the housing is made at least in part of a metal or a metal alloy material.

14. The optical heater as claimed in any one of the preceding claims, wherein the fastening means comprises a flange.

15. The optical heater as claimed in any one of the preceding claims, comprising a cable connector adapted to connect the optical cable to the housing.

16. The optical heater as claimed in any one of the preceding claims, comprising the optical cable.

17. The optical heater as claimed in claim 16, when dependent on claim 4, wherein the optical cable is optically coupled to the heating target.

18. The optical heater as claimed in any one of the preceding claims, wherein the optical cable comprises a plurality of optical fibres.

19. A system comprising an optical heater as claimed in any one of the preceding claims, coupled to a chamber for receiving a liquid or a substance to be heated.

20. The system as claimed in claim 19, wherein the chamber comprises a wall portion having an opening for receiving the optical heater, so that the housing of the optical heater fits within the chamber.

21. The system as claimed in claim 19 or 20, comprising a safety mechanism adapted to prevent an optical source coupled to the optical cable from producing or transmitting light upon detection that the optical heater is not correctly connected to the chamber.

22. A method for heating a liquid or substance, the method comprising fitting an optical heater within a chamber for receiving the liquid or substance to be heated;wherein the optical heater comprises a housing adapted to receive an optical cable; and a fastening means configured to attach the optical heater to the chamber; andtransmitting optical power to the optical heater via the optical cable to heat the liquid or substance.

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