Additive for a heat transfer fluid, and a heating and / or cooling system incorporating the same

Abstract

The present invention provides a composition provided for use as an additive to a heat transfer fluid. The composition comprises a silicone surfactant or polyether, or comprises a silsesquioxane compound. The invention also provides a heat transfer fluid for use in a heating and / or cooling system, wherein the heat transfer fluid includes water or a refrigerant and at least one additive in the form of the aforementioned composition. The invention also provides heating and cooling systems incorporating the heat transfer fluid.

Description

[0001]Additive for a heat transfer fluid, and a heating and / or cooling system incorporating the same The invention to which this application relates is an additive for a heat transfer fluid, and a heating and / or cooling system incorporating the same therein. Almost 40% of all the energy used in the U.K. is used to heat our homes and places of work. Nearly all this energy (85%) is used to heat water. This water is heated in boilers, by heat pumps or other means to temperatures up to 80oC and circulated through radiators or fan coils to heat individual spaces. The efficiency of boilers, heat pumps etc and radiator / fan coil design has been optimised to the extent that further improvements would not greatly improve fuel savings. Surfactants and their effect on energy improvement in a water environment have been known for some time. Most commonly, Alkyl Polyglucosides (APG’s) have been used to improve saltwater evaporation, and it has been demonstrated that less energy was used to evaporate water in a vat when the surfactant was added. It has been shown that APG’s are a thermally stable category of surfactant, which can improve energy efficiency under boiling conditions. However, it remained unknown for some time why radiators should become hotter in a central heating system with the added APG surfactant, as only a very small proportion of the circulating water in a heating circuit contacts hot metal in the boiler. The inventors of the present invention eventually surmised that the improvement in radiator temperature was associated with the reduced surface tension of the water in the system, caused by the presence of the surfactant. It was suggested by the inventors that the lower surface tension allowed water to access more of the radiator’s interior surface, thereby improving heat transfer through the radiator and into the room in which it is located. Treatments based on APG (mainly coco-glucoside) have been commercialised and these have delivered around 10%-15% energy savings. The main reason proposed for why they work is that they lower surface tension and allow the water to access more of the radiator or fan coil surface. Such examples are disclosed in granted British patent GB 2494073 and in published international patent application publication number WO 2016 / 128724 – both being disclosures developed by the inventor of the present application. Metal surfaces are not smooth and contain micro-indentations or micro-cracks, as well as much smaller indentations including nano-cracks. Water, which has high surface tension, ca 72 mN / m at 70oC to 80oC, will sit on top of most of these micro- indentations and thus have a lower surface contact. Agents that reduce the surface tension of water can result in better wetting and improved surface contact at the metal – liquid interface. The addition of 1,000 ppm of certain surfactants to water reduces its surface tension down to ca. 30 mN / m, improving the wettability of water and enhancing “liquid – metal” contact and therefore improving the transfer of heat. This mechanism has only recently been acknowledged in a peer reviewed journal (“Effect of surface tension on the thermal performance of a pulsating heat pipe – a review” Vaishnavi K. e t al. International Journal of Research in Engineering IT and Social Sciences ISSN 2250-0588; Volume 10, Issue 06; June2020 pps 29-34) stating that fluid physical properties play a large part in energy transfer and emphasising surface tension as being an important factor. The addition of a surfactant breaks the network of water structural bonding giving increased wettability and allowing more transport of water and the energy it contains on to the metal surface of for example a radiator or fan coil. Wettability hence depends on the interfacial tension between water and the metal surface. This is the adhesive force between the water and the metal, and the higher this force is, the wetter the surface will be. Surfactants have already been used in the UK, North America and in many other countries as energy saving products, and this capability has been heavily linked to the ability of these surface- active agents to lower the surface tension of water. However, while surfactants like alkyl polyglucosides (APG’s) reduce surface tension of water, they still do not allow water to access the complete surface. It is therefore an aim of the present invention to provide an improved additive for a heat transfer fluid of a heating and / or cooling system which overcomes the aforementioned problems associated with the prior art. It is a further aim of the present invention to provide an improved heat transfer fluid to maximise the thermal energy transfer from a heating / cooling system into a space in which it is located. It is yet a further aim of the present invention to provide improved heating and cooling systems which overcome the aforementioned problems associated with the prior art. According to a first aspect of the invention there is provided a composition provided for use as an additive to a heat transfer fluid, characterized in that said composition comprises a silicone surfactant or polyether, or comprises a silsesquioxane compound. Typically, said silicone surfactant or polyether is a soluble silicone surfactant or polyether. Typically, said silicone surfactant or polyether comprises a linear- or branched-chain siloxane. In one embodiment, said silicone surfactant comprises a branched-chain siloxane and has the general formula: wherein a = R = any one of the following functional groups: an alkyl group; a mono- or poly-unsaturated alkyl group; a fluorocarbon or hydrofluorocarbon; an aryl group; a heterocyclic group; ; - (CH2)2-COOH, a fluorocarbon or hydrofluorocarbon, or , R2 = -COOH, -NH2 , an alkyl group, or a fluorocarbon or hydrofluorocarbon. Typically, said branched-chain siloxane has the formula: wherein a = 0- and x = 1-5. Preferably, said branched-chain siloxane has the formula: wherein a = 0- = 3. Preferably, said branched-chain siloxane has the formula: wherein a = 0, In some embodiments, said branched-chain siloxane has the formula: wherein a = 8, In some embodiments, said branched-chain siloxane has the formula: wherein a = In one embodiment, said silicone surfactant comprises a linear- chain siloxane and has the general formula: wherein a = R = any one of the following functional groups: an alkyl group; a mono- or poly-unsaturated alkyl group; a fluorocarbon or hydrofluorocarbon; an aryl group; a heterocyclic group; ; wherein m = 1-25, n = 0-25, R1 = an alkyl group, an aryl group, - (CH2)2-COOH, a fluorocarbon or hydrofluorocarbon, or , R2= -COOH, -NH2, an alkyl group, or a fluorocarbon or hydrofluorocarbon. Typically, said linear-chain siloxane has the formula: = = = = = w = 1-5. In one embodiment, said silsesquioxane compound has the following general formula: wherein R = any groups: an alkyl group; a mono- or poly-unsaturated alkyl group; a fluorocarbon or hydrofluorocarbon; an aryl group; a heterocyclic group; ; - (CH2)2-COOH, a fluorocarbon or hydrofluorocarbon, or , R2= -COOH, -NH2, an alkyl group, or a fluorocarbon or hydrofluorocarbon. Typically, said silicone surfactant or silsesquioxane compound serves to reduce the surface tension of the heat transfer fluid to which it is added, in use. Typically, said silicone surfactant or silsesquioxane compound serves to reduce the contact angle of the heat transfer fluid, to which it is added, with an interior surface of a heating system, in use. Thus, the silicone surfactant or silsesquioxane compound increases the wettability of the heat transfer fluid to which it is added, thereby resulting in a greater amount of the heat transfer fluid contacting the said surface, in use. The increased contact between the heat transfer fluid and the surface increases the rate of transfer of thermal energy to the surface of the heating system, ensuring the heating system more efficiently transfers heat into the area in which it is located. Typically, the silicone surfactant or silsesquioxane compound is added to the heat transfer fluid in an amount such that it is present at a concentration of between 1.0ppm-5,000ppm, in use. Preferably, the silicone surfactant or silsesquioxane compound is added to the heat transfer fluid in an amount such that it is present at a concentration of between 50-1,000ppm, in use. More preferably, the silicone surfactant or silsesquioxane compound is added to the heat transfer fluid in an amount such that it is present at a concentration of between 50-200ppm, in use. In one embodiment, the composition comprises one or more further substances, provided in the form of carbon-based nanoparticles and / or metal oxide nanoparticles. Typically, said carbon-based nanoparticles may be any or any combination of graphene oxide nanoparticles, fullerene, nano diamond or single- or multi-walled carbon nanotubes. Typically, said carbon-based nanoparticles are added to the heat transfer fluid in an amount such that they are present at a concentration of about 0.01 v / v% to 10 v / v%, in use. Preferably, said carbon- based nanoparticles are added to the heat transfer fluid in an amount such that they are present at a concentration of about 0.01 v / v% to 1 v / v%, in use. Preferably, graphene oxide nanoparticles are provided. Typically, said graphene oxide nanoparticles are added to the heat transfer fluid in an amount such that they are present at a concentration of about 0.01 v / v% to 0.1 v / v%, in use. Preferably, said metal oxide nanoparticles may be selected from aluminium oxide, titanium oxide, iron oxide, magnetite, copper oxide, zinc oxide, silver oxide, magnesium oxide, zirconium oxide nanoparticles. In some embodiments, the metal oxide nanoparticles are added to the heat transfer fluid in an amount such that they are present at a concentration of about 1,000ppm (0.1 v / v%), in use. In one embodiment, the composition comprises one or more further substances, provided in the form of silicon oxide. The provision of one or more such substances, in addition to the silicone surfactant or silsesquioxane compound, serves to increase the thermal conductivity of the heat transfer fluid, when added thereto, in use. In another embodiment, the composition is provided in combination with one or more further compositions, provided in the form of carbon-based nanoparticles and / or metal oxide nanoparticles. Typically, said carbon-based nanoparticles may be any or any combination of graphene oxide nanoparticles, fullerene, nano diamond or single- or multi-walled carbon nanotubes. Typically, said carbon-based nanoparticles are provided at a concentration of about 0.01 v / v% to 10 v / v%, in use. Preferably, said carbon-based nanoparticles are provided at a concentration of about 0.01 v / v% to 1 v / v%. Preferably, graphene oxide nanoparticles are provided. Preferably, said metal oxide nanoparticles may be selected from aluminium oxide, titanium oxide, iron oxide, magnetite, copper oxide, zinc oxide, silver oxide, magnesium oxide, zirconium oxide nanoparticles. In some embodiments, the metal oxide nanoparticles provided at a concentration of about 1,000ppm (0.1 v / v%). In another embodiment, the composition is provided in combination with one or more further compositions, provided in the form of silicon oxide. In another embodiment, the composition is provided in combination with one or more further compositions, provided in the form of any or any combination of scale or corrosion inhibitors, biocides and / or anti-freeze agents. Typically, said scale or corrosion inhibitors may be selected from sodium nitrite, sodium molybdate, a combination of sodium nitrite and sodium molybdate, or a polyamine. Typically, said biocides may be selected from isothiazolone, bronopol, or tetrakis(Hydroxymethyl)-Phosphonium Sulfate (THPS). Typically, said anti-freeze agent may be selected from monoethylene glycol or monopropylene glycol. In some embodiments, the composition is provided in combination with at least a scale or corrosion inhibitor and a biocide. In another aspect of the present invention, there is provided a heat transfer fluid for use in a heating and / or cooling system, said heat transfer fluid including: water or a refrigerant; and at least one additive, characterized in that said additive comprises a silicone surfactant or polyether, or comprises a silsesquioxane compound. Typically, said silicone surfactant or polyether comprises a linear- or branched-chain siloxane. In one embodiment, said silicone surfactant comprises a branched-chain siloxane and has the general formula: wherein a = R = any one of the following functional groups: an alkyl group; a mono- or poly-unsaturated alkyl group; a fluorocarbon or hydrofluorocarbon; an aryl group; a heterocyclic group; ; - (CH2)2-COOH, a fluorocarbon or hydrofluorocarbon, or , R2 = -COOH, -NH2 , an alkyl group, or a fluorocarbon or hydrofluorocarbon. Typically, said branched-chain siloxane has the formula: wherein a = 0- and x = 1-5. Preferably, said branched-chain siloxane has the formula: wherein a = 0- = 3. Preferably, said branched-chain siloxane has the formula: wherein a = 0, In some embodiments, said branched-chain siloxane has the formula: wherein a = 8, In some embodiments, said branched-chain siloxane has the formula: wherein a = In one embodiment, said silicone surfactant comprises a linear- chain siloxane and has the general formula: wherein a = R = any one of the following functional groups: an alkyl group; a mono- or poly-unsaturated alkyl group; a fluorocarbon or hydrofluorocarbon; an aryl group; a heterocyclic group; ; wherein m = 1-25, n = 0-25, R1 = an alkyl group, an aryl group, - (CH2)2-COOH, a fluorocarbon or hydrofluorocarbon, or , R2= -COOH, -NH2, an alkyl group, or a fluorocarbon or hydrofluorocarbon. Typically, said linear-chain siloxane has the formula: = = = = = w = 1-5. In one embodiment, said silsesquioxane compound has the following general formula: wherein R = any groups: an alkyl group; a mono- or poly-unsaturated alkyl group; a fluorocarbon or hydrofluorocarbon; an aryl group; a heterocyclic group; ; - (CH2)2-COOH, a fluorocarbon or hydrofluorocarbon, or , R2= -COOH, -NH2, an alkyl group, or a fluorocarbon or hydrofluorocarbon. Typically, the silicone surfactant or silsesquioxane compound is present in the heat transfer fluid at a concentration of between 1.0ppm-5,000ppm, in use. Preferably, the silicone surfactant or silsesquioxane compound is present in the heat transfer fluid at a concentration of between 50-1,000ppm, in use. More preferably, the silicone surfactant or silsesquioxane compound is present in the heat transfer fluid at a concentration of between 50-200ppm, in use. In some embodiments, the heat transfer fluid includes one or more further additives, provided in the form of carbon-based nanoparticles and / or metal oxide nanoparticles. Typically, said carbon-based nanoparticles may be any or any combination of graphene oxide nanoparticles, fullerene, nano diamond or single- or multi-walled carbon nanotubes. Typically, said carbon-based nanoparticles are present in the heat transfer fluid at a concentration of about 0.01 v / v% to 10 v / v%, in use. Preferably, said carbon-based nanoparticles are present in the heat transfer fluid at a concentration of about 0.01 v / v% to 1 v / v%, in use. Preferably, graphene oxide nanoparticles are provided. Typically, said graphene oxide nanoparticles are provided in the heat transfer fluid at a concentration of 0.01 v / v% to 0.1 v / v%. Preferably, said metal oxide nanoparticles may be selected from aluminium oxide, titanium oxide, iron oxide, magnetite, copper oxide, zinc oxide, silver oxide, magnesium oxide, zirconium oxide nanoparticles. In some embodiments, the metal oxide nanoparticles are present in the heat transfer fluid at a concentration of about 1,000ppm (0.1 v / v%), in use. In one embodiment, the composition comprises one or more further substances, provided in the form of silicon oxide. In some embodiments, the heat transfer fluid includes one or more further additives, provided in the form of any or any combination of scale or corrosion inhibitors, biocides and / or anti-freeze agents. Typically, said scale or corrosion inhibitors may be selected from sodium nitrite, sodium molybdate, a combination of sodium nitrite and sodium molybdate, or a polyamine. Typically, said biocides may be selected from isothiazolone, bronopol, or tetrakis(Hydroxymethyl)-Phosphonium Sulfate (THPS). Typically, said anti-freeze agent may be selected from monoethylene glycol or monopropylene glycol. In some embodiments, the silicone surfactant or polyether, or silsesquioxane compound additive is provided in combination with at least a scale or corrosion inhibitor and a biocide. In another aspect of the present invention, there is provided a central heating system, said system including: a heat source; one or more radiators; a plurality of pipes interconnecting said heat source and one or more radiators; and a heat transfer fluid arranged to circulate through the heat source, one or more radiators, and pipes, in use; said heat transfer fluid comprising water and at least one additive, characterized in that said additive comprises a silicone surfactant or polyether, or comprises a silsesquioxane compound. Typically, the heat source is provided as a boiler, heat pump, or a heat exchanger. Typically, said silicone surfactant or polyether comprises a linear- or branched-chain siloxane. In one embodiment, said silicone surfactant comprises a branched-chain siloxane and has the general formula: wherein a = 0-20, b = 1-10, and x = 1-5; R = any one of the following functional groups: an alkyl group; a mono- or poly-unsaturated alkyl group; a fluorocarbon or hydrofluorocarbon; an aryl group; a heterocyclic group; ; - 2- a or or , R2 = -COOH, -NH2 , an alkyl group, or a fluorocarbon or hydrofluorocarbon. Typically, said branched-chain siloxane has the formula: wherein a = 0- and x = 1-5. Preferably, said branched-chain siloxane has the formula: wherein a = 0- = 3. Preferably, said branched-chain siloxane has the formula: wherein a = 0, In some embodiments, said branched-chain siloxane has the formula: wherein a = 8, In some embodiments, said branched-chain siloxane has the formula: wherein a = In one embodiment, said silicone surfactant comprises a linear- chain siloxane and has the general formula: wherein a = R = any one of the following functional groups: an alkyl group; a mono- or poly-unsaturated alkyl group; a fluorocarbon or hydrofluorocarbon; an aryl group; a heterocyclic group; ; - (CH2)2-COOH, a fluorocarbon or hydrofluorocarbon, or , R2 = -COOH, -NH2 , an alkyl group, or a fluorocarbon or hydrofluorocarbon. Typically, said linear-chain siloxane has the formula: wherein a = 1-10, b = 0-10, m = 1-25, n = 0-25, v = 1-5, and w = 1-5. In one embodiment, said silsesquioxane compound has the following general formula: wherein R = any groups: an alkyl group; a mono- or poly-unsaturated alkyl group; a fluorocarbon or hydrofluorocarbon; an aryl group; a heterocyclic group; ; - (CH2)2-COOH, a fluorocarbon or hydrofluorocarbon, or , further wherein R2 = -COOH, -NH2 , an alkyl or hydrofluorocarbon. Typically, the silicone surfactant or silsesquioxane compound is present in the heat transfer fluid at a concentration of between 1.0ppm-5,000ppm, in use. Preferably, the silicone surfactant or silsesquioxane compound is present in the heat transfer fluid at a concentration of between 50-1,000ppm, in use. More preferably, the silicone surfactant or silsesquioxane compound is present in the heat transfer fluid at a concentration of between 50-200ppm, in use. In some embodiments, the heat transfer fluid includes one or more further additives, provided in the form of carbon-based nanoparticles and / or metal oxide nanoparticles. Typically, said carbon-based nanoparticles may be any or any combination of graphene oxide nanoparticles, fullerene, nano diamond or single- or multi-walled carbon nanotubes. Typically, said carbon-based nanoparticles are present in the heat transfer fluid at a concentration of about 0.01 v / v% to 10 v / v%, in use. Preferably, said carbon-based nanoparticles are present in the heat transfer fluid at a concentration of about 0.01 v / v% to 1 v / v%, in use. Preferably, graphene oxide nanoparticles are provided. Typically, said graphene oxide nanoparticles are provided in the heat transfer fluid at a concentration of 0.01 v / v% to 0.1 v / v%. Preferably, said metal oxide nanoparticles may be selected from aluminium oxide, titanium oxide, iron oxide, magnetite, copper oxide, zinc oxide, silver oxide, magnesium oxide, zirconium oxide nanoparticles. In some embodiments, the metal oxide nanoparticles are present in the heat transfer fluid at a concentration of about 1,000ppm (0.1 v / v%), in use. In one embodiment, the composition comprises one or more further substances, provided in the form of silicon oxide. In some embodiments, the heat transfer fluid includes one or more further additives, provided in the form of any or any combination of scale or corrosion inhibitors, biocides and / or anti-freeze agents. Typically, said scale or corrosion inhibitors may be selected from sodium nitrite, sodium molybdate, a combination of sodium nitrite and sodium molybdate, or a polyamine. Typically, said biocides may be selected from isothiazolone, bronopol, or tetrakis(Hydroxymethyl)-Phosphonium Sulfate (THPS). Typically, said anti-freeze agent may be selected from monoethylene glycol or monopropylene glycol. In some embodiments, the silicone surfactant or polyether, or silsesquioxane compound additive is provided in combination with at least a scale or corrosion inhibitor and a biocide. In another aspect of the present invention, there is provided a chiller or cooling system, said system including: at least one condenser; at least one evaporator; a plurality of pipes interconnecting said condenser and evaporator; and a heat transfer fluid, arranged to circulate through the condenser, evaporator and plurality of pipes, in use; said heat transfer fluid comprising water or a refrigerant and at least one additive, characterized in that said additive comprises a silicone surfactant or polyether, or comprises a silsesquioxane compound. Typically, said silicone surfactant or polyether comprises a linear- or branched-chain siloxane. In one embodiment, said silicone surfactant comprises a branched-chain siloxane and has the general formula: wherein a = 0- R = any one of the following functional groups: an alkyl group; a mono- or poly-unsaturated alkyl group; a fluorocarbon or hydrofluorocarbon; an aryl group; a heterocyclic group; ; - 2- a or or , further wherein R2 = -COOH, -NH2 , an alkyl or hydrofluorocarbon. Typically, said branched-chain siloxane has the formula: wherein a = 0- and x = 1-5. Preferably, said branched-chain siloxane has the formula: wherein a = 0- = 3. Preferably, said branched-chain siloxane has the formula: wherein a = 0, In some embodiments, said branched-chain siloxane has the formula: wherein a = 8, In some embodiments, said branched-chain siloxane has the formula: wherein a = 20, In one embodiment, said silicone surfactant comprises a linear- chain siloxane and has the general formula: wherein a = R = any one of the following functional groups: an alkyl group; a mono- or poly-unsaturated alkyl group; a fluorocarbon or hydrofluorocarbon; an aryl group; a heterocyclic group; ; - (CH2)2-COOH, a fluorocarbon or hydrofluorocarbon, or , further wherein R2 = -COOH, -NH2 , an alkyl group, or a fluorocarbon or hydrofluorocarbon. Typically, said linear-chain siloxane has the formula: = = = = = w = 1-5. In one embodiment, said silsesquioxane compound has the following general formula: wherein R = any groups: an alkyl group; a mono- or poly-unsaturated alkyl group; a fluorocarbon or hydrofluorocarbon; an aryl group; a heterocyclic group; ; - (CH2)2-COOH, a fluorocarbon or hydrofluorocarbon, or , R2= -COOH, -NH2, an alkyl group, or a fluorocarbon or hydrofluorocarbon. Typically, the silicone surfactant or silsesquioxane compound is present in the heat transfer fluid at a concentration of between 1.0ppm-5,000ppm, in use. Preferably, the silicone surfactant or silsesquioxane compound is present in the heat transfer fluid at a concentration of between 50-1,000ppm, in use. More preferably, the silicone surfactant or silsesquioxane compound is present in the heat transfer fluid at a concentration of between 50-200ppm, in use. In some embodiments, the heat transfer fluid includes one or more further additives, provided in the form of carbon-based nanoparticles and / or metal oxide nanoparticles. Typically, said carbon-based nanoparticles may be any or any combination of graphene oxide nanoparticles, fullerene, nano diamond or single- or multi-walled carbon nanotubes. Typically, said carbon-based nanoparticles are present in the heat transfer fluid at a concentration of about 0.01 v / v% to 10 v / v%, in use. Preferably, said carbon-based nanoparticles are present in the heat transfer fluid at a concentration of about 0.01 v / v% to 1 v / v%, in use. Preferably, graphene oxide nanoparticles are provided. Typically, said graphene oxide nanoparticles are provided in the heat transfer fluid at a concentration of 0.01 v / v% to 0.1 v / v%. Preferably, said metal oxide nanoparticles may be selected from aluminium oxide, titanium oxide, iron oxide, magnetite, copper oxide, zinc oxide, silver oxide, magnesium oxide, zirconium oxide nanoparticles. In some embodiments, the metal oxide nanoparticles are present in the heat transfer fluid at a concentration of about 1,000ppm (0.1 v / v%), in use. In one embodiment, the composition comprises one or more further substances, provided in the form of silicon oxide. In some embodiments, the heat transfer fluid includes one or more further additives, provided in the form of any or any combination of scale or corrosion inhibitors, biocides and / or anti-freeze agents. Typically, said scale or corrosion inhibitors may be selected from sodium nitrite, sodium molybdate, a combination of sodium nitrite and sodium molybdate, or a polyamine. Typically, said biocides may be selected from isothiazolone, bronopol, or tetrakis(Hydroxymethyl)-Phosphonium Sulfate (THPS). Typically, said anti-freeze agent may be selected from monoethylene glycol or monopropylene glycol. In some embodiments, the silicone surfactant or polyether, or silsesquioxane compound additive is provided in combination with at least a scale or corrosion inhibitor and a biocide. In another aspect of the present invention, there is provided a method of treating a heat transfer fluid, said method including: adding to the heat transfer fluid an amount of an additive, characterized in that said additive comprises a silicone surfactant or polyether, or comprises a silsesquioxane compound. Typically, said silicone surfactant or polyether comprises a linear- or branched-chain siloxane. In one embodiment, said silicone surfactant comprises a branched-chain siloxane and has the general formula: wherein a = R = any one of the following functional groups: an alkyl group; a mono- or poly-unsaturated alkyl group; a fluorocarbon or hydrofluorocarbon; an aryl group; a heterocyclic group; ; - (CH2)2-COOH, a fluorocarbon or hydrofluorocarbon, or , R2= -COOH, -NH2, an alkyl group, or a fluorocarbon or hydrofluorocarbon. Typically, said branched-chain siloxane has the formula: wherein a = 0- and x = 1-5. Preferably, said branched-chain siloxane has the formula: wherein a = 0- = 3. Preferably, said branched-chain siloxane has the formula: wherein a = 0, In some embodiments, said branched-chain siloxane has the formula: wherein a = 8, In some embodiments, said branched-chain siloxane has the formula: wherein a = In one embodiment, said silicone surfactant comprises a linear- chain siloxane and has the general formula: wherein a = R = any one of the following functional groups: an alkyl group; a mono- or poly-unsaturated alkyl group; a fluorocarbon or hydrofluorocarbon; an aryl group; a heterocyclic group; ; - (CH2)2-COOH, a fluorocarbon or hydrofluorocarbon, or , R2= -COOH, -NH2, an alkyl group, or a fluorocarbon or hydrofluorocarbon. Typically, said linear-chain siloxane has the formula: w = 1-5. In one embodiment, said silsesquioxane compound has the following general formula: wherein R = any groups: an alkyl group; a mono- or poly-unsaturated alkyl group; a fluorocarbon or hydrofluorocarbon; an aryl group; a heterocyclic group; ; - 2- a or or , R2 = -COOH, -NH2 , an alkyl group, or a fluorocarbon or hydrofluorocarbon. Typically, the silicone surfactant or silsesquioxane compound is added to the heat transfer fluid such that it is present at a concentration of between 1.0ppm-5,000ppm. Preferably, the silicone surfactant or silsesquioxane compound is added to the heat transfer fluid such that it is present at a concentration of between 50-1,000ppm. More preferably, the silicone surfactant or silsesquioxane compound is added to the heat transfer fluid such that it is present at a concentration of between 50-200ppm. In some embodiments, the heat transfer fluid includes one or more further additives, provided in the form of carbon-based nanoparticles and / or metal oxide nanoparticles. Typically, said carbon-based nanoparticles may be any or any combination of graphene oxide nanoparticles, fullerene, nano diamond or single- or multi-walled carbon nanotubes. Typically, said carbon-based nanoparticles are present in the heat transfer fluid at a concentration of about 0.01 v / v% to 10 v / v%, in use. Preferably, said carbon-based nanoparticles are present in the heat transfer fluid at a concentration of about 0.01 v / v% to 1 v / v%, in use. Preferably, graphene oxide nanoparticles are provided. Typically, said graphene oxide nanoparticles are added to the heat transfer fluid such that they are present at a concentration of 0.01 v / v% to 0.1 v / v%. Preferably, said metal oxide nanoparticles may be selected from aluminium oxide, titanium oxide, iron oxide, magnetite, copper oxide, zinc oxide, silver oxide, magnesium oxide, zirconium oxide nanoparticles. In some embodiments, the metal oxide nanoparticles are added to the heat transfer fluid such that they are present at a concentration of about 1,000ppm (0.1 v / v%). In one embodiment, the composition comprises one or more further substances, provided in the form of silicon oxide. Embodiments of the present invention will now be described with reference to the following examples and figures, wherein: Figures 1a-b illustrate exterior and interior views of a thermal box and controller util ised to test the heat transfer efficiencies of various heat transfer fluids comprising various additives; Figure 2 illustrates the heat transfer capabilities of heat transfer fluids having differing additives therein, when tested with a thermal box illustrated in Figures 1a-b; Figure 3 illustrates the heat transfer capabilities of heat transfer fluids having differing concentrations of the same silicone additive incorporated therein, when tested with a thermal box illustrated in Figures 1a-b; Figure 4 illustrates the heat transfer capabilities of heat transfer fluids having differing nanoparticle additives therein, when tested with a thermal box illustrated in Figures 1a-b; Figure 5 i llustrates a comparison of the heat transfer capabilities of a heat transfer fluid having a sil icone additive incorporated therein, and a heat transfer fluid having a silicone additive and graphene oxide nanoparticles incorporated therein, when tested with a thermal box illustrated in Figures 1a-b; and Figure 6 i llustrates a comparison of the heat transfer capabilities of three heat transfer fluids each having a different silicone additive incorporated therein. The additive composition of the present invention comprises a silicone-based surfactant or silicone polyether, or silsesquioxane compound. Depending on the specific requirements of the system into which it is to be incorporated, the additive may be provided as a branched-chain or as a linear-chain silicone surfactant, or silsesquioxane compound, according to the following general formulae: wherein a R = any one of the following functional groups: an alkyl group; a mono- or poly-unsaturated alkyl group; a fluorocarbon or hydrofluorocarbon; an aryl group; a heterocyclic group; ; wherein m = 1-25, n = 0-25, R1 = an alkyl group, an aryl group, - (CH2)2-COOH, a fluorocarbon or hydrofluorocarbon, or , R2= -COOH, -NH2, an alkyl group, or a fluorocarbon or hydrofluorocarbon; Or: wherein a = R = any one of the following functional groups: an alkyl group; a mono- or poly-unsaturated alkyl group; a fluorocarbon or hydrofluorocarbon; an aryl group; a heterocyclic group; ; - 2- a or or , further wherein R2 = -COOH, -NH2 , an alkyl group, or a fluorocarbon or hydrofluorocarbon; Or: wherein R = any groups: an alkyl group; a mono- or poly-unsaturated alkyl group; a fluorocarbon or hydrofluorocarbon; an aryl group; a heterocyclic group; ; - 2- a or or , R2= -COOH, -NH2, an alkyl group, or a fluorocarbon or hydrofluorocarbon. Initial testing was carried out using a branched-chain siloxane having the general formula: wherein a = 0- = 3. A range of branched-chain siloxanes were tested and shown to be effective, specifically those having the following formulae: wherein a = 0, 1”); wherein a = 8, (“Surfactant 2”); and wherein a = (“Surfactant 3”). Generally, the silicone surfactant or silsesquioxane compound is added to the heat transfer fluid (generally water) of a heating or cooling system and can be done so at a concentration between 1.0ppm-5,000ppm. More preferable concentrations range from 100ppm-1,000ppm, and initial tests were carried out with the “Surfactant 1” surfactant at differing concentrations within this range. These were done so by creating a heavily insulated box, simulating a room, and placing a heating coil inside. A liquid was then circulated through the coil at a constant temperature of 66oC and circulated continuously through the coil. The temperature that the air space reached within the box was measured against the heating time and recorded by two thermal probes. The results were recorded by a data logger. Various liquids acting as heat transfer fluids were run through the coil, using water as a control, and subsequently water plus various additives were recorded. The first set of results are shown in the Figure 2. As can be seen, the addition of either alkyl polyglucoside (APG) at a concentration of 1,000ppm or graphene oxide nanoparticles at 1,000ppm (0.1 v / v%), had similar improvements in heat transfer from the coil to the surrounding space. Regarding APG, this is because its addition into water reduces its contact angle with the metal surface of the coil down to 40o. Water on its own has a contact angle of 80o. This reduces the surface tension somewhat and increases the amount of water contacting the metal surface of the coil. Regarding the graphene oxide nanoparticles, this additive does not reduce the contact angle of the water on the surface of the metal; rather, it increases the thermal conductivity of the water, resulting in a similar improvement as treating with APG. However, the silicone surfactant tested (noted in the legend simply as “Silicone”, but which is, in this case the “Surfactant 1” surfactant), demonstrates far greater performance than both APG and graphene oxide nanoparticles, even at the lower concentration of 100ppm. This results in the temperature in the box reaching a higher temperature at a much faster rate. The reasoning behind this is that the silicone surfactant additive with which the water is treated, has the effect of reducing the contact angle with the metal surface of the coil down to substantially 0o. This substantially reduces the surface tension of the fluid and increases its wettability, maximising contact between the liquid and metal and thus optimising the heat transfer process from the system and into the surrounding space. As is the case with the inclusion of APG, the silicone surfactant does not increase the thermal conductivity of the water in the way graphene oxide nanoparticles do; however, by enabling complete surface contact at the liquid / solid interface the thermal transfer capabil ities far outperform both APG and graphene oxide. Further testing was carried out utilizing the “Surfactant 1” surfactant, at concentrations of 200ppm, 500ppm and 1,000ppm, with the results shown in Figure 3 (again, noted in the legend as “Silicone”). As can be seen, the positive effect on the heat transfer capabilities of the fluid is maintained across the 100ppm- 1,000ppm range. In some embodiments of the invention, further additives may be included alongside or in combination with the silicone surfactant or polyether, or si lsesquioxane compound. For example, such additives may include carbon-based nanoparticles (such as graphene oxide discussed above, or fullerene, nano diamond or single- or multi-walled carbon nanotubes) and / or metal oxide nanoparticles, such as aluminium oxide, titanium oxide, iron oxide, magnetite, copper oxide, zinc oxide, silver oxide, magnesium oxide, zirconium oxide nanoparticles. In other embodiments, silicon oxide nanoparticles may be used as a further additive. These additives can be included to increase the thermal conductivity of the heat transfer fluid and thus further improve its heat transfer capabilities. Figure 4 illustrates the effect on heat transfer capabilities of a heat transfer fluid upon addition of a selection of carbon-based, metal oxide and silicon oxide nanoparticles, all at 1,000ppm (GO = graphene oxide nanoparticles). Figure 5 illustrates the comparison, against untreated water, of water plus the additive of Surfactant 1 at 100 ppm, and Surfactant 1 at 100 ppm plus graphene oxide nanoparticles at 1000 ppm (0.1 v / v%). As can be seen here, the combination of the silicone surfactant and the graphene oxide nanoparticles leads to a further improvement of the heat transfer capabilities, optimising both the contact angle reduction and the increased thermal conductivity. Finally, Figure 6 illustrates the comparison, against untreated water, of water plus Surfactant 1 at 100 ppm; water plus Surfactant 2 at 100 ppm; and water plus Surfactant 3 at 100 ppm (referenced in the legend as “Silicone 1”, “Sil icone 2”, and “Silicone 3” respectively). As can be seen, all three show clearly improved heat transfer capabilities than untreated water after just a 45 minute period. In addition, or alternatively to the above further additives, further compositions may also be used in conjunction with silicone-based surfactant or silicone polyether, or silsesquioxane compound, such as scale or corrosion inhibitors, biocides and / or anti-freeze agents. The composition of the invention may can be mixed with water with any one of or a combination of two or more of the above further additives to form a novel and effective heat transfer fluid. In some other embodiments, water may be substituted for a refrigerant, for example, when the fluid is to be used with chillers or cooling systems. The following tables provide examples of various compositions and concentrations which may be used in combination with the silicone-based surfactant or silicone polyether, or silsesquioxane compound, and while these are preferred examples, it will be understood that further examples are possible and intended. In each of the following examples, the concentration of the silicone- based surfactant or silicone polyether, or silsesquioxane compound in the system would be in the region of 0.2 to 2v / v %. Table 1: Scale / Corrosion Inhibitors Corrosion Inhibitor Concentration of Concentration in Table 2: Biocides Closed System Concentration of Concentration in Table 3: Antifreeze Products Product Concentration of Concentration in The addition of a relatively low concentration of surfactant will significantly reduce the surface tension of water and also reduce the contact angle. There is a group of silicone-based surfactants as defined by the present invention that can, at relatively low concentrations, reduce the surface tension of water to approximately 20 mN / m, and the contact angle between water and a solid (for example, steel in a radiator) to substantially 0o. A zero-contact angle means complete wettability. This type of surfactant is known as a super-spreader. It has been demonstrated that complete wettability caused by a zero-degree contact angle means that 3 times as much water, which is generally used as the heat transfer fluid in wet heating and cooling systems, is present on a surface than can be achieved by using a standard APG-based surfactant which is used in the prior art. Silicone surfactants or silicone polyethers, or a silsesquioxane compound as described in the present invention, contain both a water-insoluble silicone backbone and several water-soluble polyether pendant groups that can result in increased wettability. These surfactants not only greatly reduce the surface tension of water but increase the adhesive forces that bind water to the surface material. It has been shown that using a heat transfer fluid having an additive as defined in the present invention will heat a room much faster than water itself, and faster than a water containing other surfactants such as APG’s. Equally, water containing a silicone surfactant according to the present invention will heat a room faster than water containing purely metal oxide or graphene oxide nanoparticles. Nanoparticles make the water more thermally conductive; surfactants work because they make the surface wetter, that is to say, they reduce the surface tension of the heat transfer fluid (water) to which they are added. In some examples of the invention, combining the properties of both a silicone surfactant and metal oxide or graphene oxide nanoparticles together in a single composition, or as two additives alongside each other, can further optimise the heat transfer capabilities of a heat transfer fluid. In terms of energy transfer, super-spreaders such as the silicone surfactants or silicone polyethers, or a silsesquioxane compound, defined in the present invention are far superior to both the APG’s already commercialized in the marketplace, and also with respect to nanoparticle treatments that operate by increasing the thermal conductance of water. The present invention therefore provides an additive for a heat transfer fluid as part of a heating and / or cooling system, or a heat transfer fluid containing the additive, which has the effect of reducing the contact angle of the fluid with the interior surface of, for example, a radiator of a central heating system, to substantially zero degrees, thereby maximising the energy transfer between boiler output and heat transferred into a room.

Claims

CLAIMS 1. A composition provided for use as an additive to a heat transfer fluid, characterized in that said composition comprises a silicone surfactant or polyether, or comprises a silsesquioxane compound.

2. A composition according to claim 1, wherein said silicone surfactant or polyether comprises a linear- or branched-chain siloxane.

3. A composition according to claim 1, wherein said silicone surfactant comprises a branched-chain siloxane and has the general formula: wherein a =R = any one of the following functional groups: an alkyl group; a mono- or poly-unsaturated alkyl group; a fluorocarbon or hydrofluorocarbon; an aryl group; a heterocyclic group;;- (CH2)2-COOH, a fluorocarbon or hydrofluorocarbon, or ,R2= -COOH, -NH2, an alkyl group, or a fluorocarbon or hydrofluorocarbon.

4. A composition according to claim 3, wherein said branched- chain siloxane has the formula: wherein a = 0-and x = 1-5.

5. A composition according to claim 4, wherein a = 0-20, b = 1- 10, m = 8, n = 0, and x = 3.

6. A composition according to claim 4, wherein a = 0, b = 1, m = 8, n = 0, and x = 3.

7. A composition according to claim 4, wherein a = 8, b = 4, m = 8, n = 0, and x = 3.

8. A composition according to claim 4, wherein a = 20, b = 10, m = 8, n = 0, and x = 3.

9. A composition according to claim 1, wherein the sil icone surfactant or silsesquioxane compound is added to the heat transfer fluid in an amount such that it is present at a concentration of between 50-1,000ppm, in use.

10. A composition according to claim 1, wherein the composition is provided in combination with one or more further compositions, provided in the form of carbon-based nanoparticles and / or metal oxide nanoparticles.

11. A composition according to claim 10, wherein said carbon- based nanoparticles are provided as graphene oxide nanoparticles at a concentration of about 0.01 v / v% to 1 v / v%.

12. A composition according to claim 1, wherein the composition is provided in combination with one or more further compositions, provided in the form of any or any combination of scale or corrosion inhibitors, biocides and / or anti-freeze agents.

13. A composition according to claim 12, wherein said scale or corrosion inhibitors are selected from any or any combination of sodium nitrite, sodium molybdate, a combination of sodium nitrite and sodium molybdate, or a polyamine.

14. A composition according to claim 12, wherein said biocides are selected from any or any combination of isothiazolone, bronopol, or tetrakis(Hydroxymethyl)-Phosphonium Sulfate (THPS).

15. A composition according to claim 12, wherein said anti- freeze agent are selected from monoethylene glycol or monopropylene glycol.

16. A composition according to claim 12, wherein the composition is provided in combination with at least a scale or corrosion inhibitor and a biocide.

17. A heat transfer fluid for use in a heating and / or cooling system, said heat transfer fluid including: water or a refrigerant; and at least one additive, characterized in that said additive comprises a silicone surfactant or polyether, or comprises a silsesquioxane compound.

18. A heat transfer fluid according to claim 17, wherein said silicone surfactant or polyether comprises a linear- or branched-chain siloxane.

19. A heat transfer fluid according to claim 18, wherein said branched-chain siloxane has the formula: wherein a = 0-and x = 1-5.

20. A heat transfer fluid according to claim 19, wherein a = 0- 20, b = 1-10, m = 8, n = 0, and x = 3.

21. A heat transfer fluid according to claim 19, wherein a = 0, b = 1, m = 8, n = 0, and x = 3.

22. A heat transfer fluid according to claim 19, wherein a = 8, b = 4, m = 8, n = 0, and x = 3.

23. A heat transfer fluid according to claim 19, wherein a = 20, b = 10, m = 8, n = 0, and x = 3.

24. A heat transfer fluid according to claim 17, wherein the silicone surfactant or silsesquioxane compound is present in the heat transfer fluid at a concentration of between 50- 1,000ppm, in use.

25. A heat transfer fluid according to claim 17, wherein the composition is provided in combination with one or more further compositions, provided in the form of carbon-based nanoparticles and / or metal oxide nanoparticles.

26. A heat transfer fluid according to claim 17, wherein said carbon-based nanoparticles are provided as graphene oxide nanoparticles at a concentration of about 0.01 v / v% to 1 v / v%.

27. A heat transfer fluid according to claim 17, wherein the composition is provided in combination with one or more further compositions, provided in the form of any or any combination of scale or corrosion inhibitors, biocides and / or anti-freeze agents.

28. A central heating system, said system including: a heat source; one or more radiators; a plurality of pipes interconnecting said heat source and one or more radiators; and a heat transfer fluid arranged to circulate through the heat source, one or more radiators, and pipes, in use;said heat transfer fluid comprising water and at least one additive, characterized in that said additive comprises a silicone surfactant or polyether, or comprises a silsesquioxane compound.

29. A chiller or cooling system, said system including: at least one condenser; at least one evaporator; a plurality of pipes interconnecting said condenser and evaporator; and a heat transfer fluid, arranged to circulate through the condenser, evaporator and plurality of pipes, in use; said heat transfer fluid comprising water or a refrigerant and at least one additive, characterized in that said additive comprises a silicone surfactant or polyether, or comprises a silsesquioxane compound.

30. A method of treating a heat transfer fluid, said method including: adding to the heat transfer fluid an amount of an additive, characterized in that said additive comprises a silicone surfactant or polyether, or comprises a silsesquioxane compound.

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