Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F24—HEATING; RANGES; VENTILATING
  • F24H—FLUID HEATERS, e.g. WATER OR AIR HEATERS, HAVING HEAT-GENERATING MEANS, e.g. HEAT PUMPS, IN GENERAL
  • F24H3/00—Air heaters
  • F24H3/02—Air heaters with forced circulation
  • F24H3/04—Air heaters with forced circulation the air being in direct contact with the heating medium, e.g. electric heating element
  • F24H3/0405—Air heaters with forced circulation the air being in direct contact with the heating medium, e.g. electric heating element using electric energy supply, e.g. the heating medium being a resistive element; Heating by direct contact, i.e. with resistive elements, electrodes and fins being bonded together without additional element in-between
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F22—STEAM GENERATION
  • F22B—METHODS OF STEAM GENERATION; STEAM BOILERS
  • F22B1/00—Methods of steam generation characterised by form of heating method
  • F22B1/28—Methods of steam generation characterised by form of heating method in boilers heated electrically
  • F22B1/281—Methods of steam generation characterised by form of heating method in boilers heated electrically other than by electrical resistances or electrodes
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F24—HEATING; RANGES; VENTILATING
  • F24H—FLUID HEATERS, e.g. WATER OR AIR HEATERS, HAVING HEAT-GENERATING MEANS, e.g. HEAT PUMPS, IN GENERAL
  • F24H1/00—Water heaters, e.g. boilers, continuous-flow heaters or water-storage heaters
  • F24H1/22—Water heaters other than continuous-flow or water-storage heaters, e.g. water heaters for central heating
  • F24H1/225—Water heaters other than continuous-flow or water-storage heaters, e.g. water heaters for central heating electrical central heating boilers
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B6/00—Heating by electric, magnetic or electromagnetic fields
  • H05B6/64—Heating using microwaves
  • H05B6/80—Apparatus for specific applications
  • H05B6/802—Apparatus for specific applications for heating fluids

Definitions

• a microwave heating method and a relative microwave heating device are provided.
• the present invention relates to microwave heating, and to microwave heating devices. More particularly the invention relates to a method and to a relative device wherein use is made of microwave radiation, and of a microwave absorbing material capable of being heated and of transmitting heat in turn to a fluid with which it is in contact.
• a fluid heated in this manner can be used for space heating, or in the case of hot water, distributed for domestic and industrial consumption; in addition, high pressure steam generated by the method disclosed can be used to operate turbines or pistons.
• microwaves electromagnetic waves in the range of frequencies between 300 and 300,000 megahertz, commonly referred to as microwaves, are capable of inducing a rotational and to an extent vibrational effect in the molecules of materials possessing a high dielectric constant.
• microwave absorbing materials referred to also as dielectrics in the following specification, is that they excite when exposed to radiation and undergo a rise in temperature.
• microwaves are transparent to microwaves; these undergo no rise in temperature when exposed to radiation and are considered good insulators.
• materials which reflect microwave energy without heating and are considered good conductors.
• the different materials mentioned above can be used in conjunction with microwaves for different purposes: transparent materials for inert containers, such as crucibles; reflective materials for the external claddings of microwave systems; and dielectrics as heat sources by virtue of their capacity to excite when invested with microwave radiation.
• the frequencies that can be utilized for microwaves are 915 ⁇ 25, 2450 +13, 5800 ⁇ 75 and 22125 ⁇ 125 MHz. Of these the most widely used is 2450 MHz, enabling as it does a good penetration of materials combined with high surface intensity.
• the object of the present invention is to provide a method and a device such as will bring about heat exchange between a fluid and a source of heat consisting in a microwave absorbing material.
• a further object of the invention is to provide a method and a device whereby microwave energy can be used to produce hot air or hot water as a means of space heating or as a utility for domestic and/or industrial use.
• Yet another object of the invention is to provide a method and a device whereby microwave energy can be used to generate high pressure steam for operating turbines or pistons.
• -fig 2 is a further front perspective view showing a device according to the invention suitable for producing hot water
• -fig 3 is a further front perspective view showing a device according to the invention suitable for producing hot water or generating high pressure steam.
• Fig 1 illustrates a microwave device for producing hot air.
• the device comprises a microwave generator unit 1 consisting essentially in a magnetron 10 rated 700 W - 10 kW, operated off 220/380 V a.c. and producing frequencies of 2455 MHz and 915 MHz, a waveguide 11 and a waveguide resonator 12, which combine to direct a flow of microwaves, denoted by the arrows, onto a plurality of silicon carbide or boron carbide plates 20.
• the plates 20 in question are spaced apart one from another and mounted on a support 21 fashioned in a material capable of refracting microwaves, such as quartz, internally of a container 2 constructed in material capable of reflecting microwaves, such as steel.
• the container 2 of substantially parallelepiped embodiment, is associated both with the microwave generator unit 1 and with means by which to effect a forced induction of air, consisting for example in a fan unit 30 and a duct 31.
• the plates 20 undergo a rise in temperature and give off heat into the air to which they are directly exposed; the air is then expelled from the container 2 at a temperature of between 60 and 100 °C or higher, by way of suitable vents 22 fitted with grilles 23, in such a way as to warm the surrounding ambient.
• the device thus described can be embodied adopting compact dimensions, for example a few decimetres per side, which will be variable according to the quantity of hot air it is wished to produce.
• the plates 20 these would be fashioned from materials combining advantages of economy (i.e. low cost) with good heat dissipation; boron carbide is preferred by virtue of its greater resistance to oxidation at high temperature and its ability to heat at a faster rate.
• FIG. 1 shows a microwave device for producing hot water.
• microwaves emitted by a generator unit l 1 are directed at a dielectric, in this instance a coiled tube 24 fashioned from or faced externally with a microwave absorbing material.
• the coil 24 is housed internally of a container 2' of microwave reflecting material, and connected to a heating circuit or to a hot water distribution system. More exactly, the coil 24 is fashioned from tube of 10-15 mm diameter, some 20-30 cm in length, in a material selected from carbides of silicon, boron, titanium or tungsten, or borides of silicon, titanium or aluminium, etc., which might be pure or combined with nitrides of the same elements; the option also exists of using ferroelectric ceramics containing titanates of barium or lead or other metallic elements (zinc, manganese, copper, etc.). To advantage, the coil 24 is coated with a material transparent to microwaves such as will give greater mechanical strength and more readily dissipate excess temperature.
• Fig 3 illustrates a microwave device for producing hot water or generating steam at high temperature and high pressure.
• microwaves emitted by a generator unit 1" are directed onto a plurality of plates 25 fashioned from material able to absorb high frequency radiations and housed in a first container 26 embodied in material transparent to microwaves.
• Water directed through an inlet 28 into the first container 26 is heated rapidly on making contact with the plates 25 exposed to microwave radiation, and directed through an outlet 29 into the heating circuit or the hot water distribution system.
• This type of device is capable of discharging water or water vapour at temperatures between 60 and 80 °C, according to the quantity of water introduced and to the number of plates installed.
• the plates 25 might be between 10 and 25 in number, spaced apart 5...10 mm one from the next, and with typical dimensions of 30 x 15 x 1 cm.
• the plates 25 will be of boron nitride, exhibiting a honeycomb structure and immersed three quarters in deionized water.
• the first container 26 might be embodied in boron carbide or nitride reinforced with steel or other materials able to withstand high pressures.
• steam can be generated at pressures of 30 to 40 bar and temperatures of the order of 230 to 350 °C, in approximately one third of the time taken where use is made of materials unable to absorb high frequency radiations. Steam generated in this way can be used to advantage in driving turbines, for example, with at least a part of the heat being recovered by means of exchangers.
• the device of fig 3 is again compact, measuring substantially less than one metre on any side, the dimensions of the first container 26 being, by way of example, 30 x 15 x 40 cm.
• the magnetron 10 might be set at a certain distance from the container 2, and the microwaves directed into the container through a waveguide of suitable length.
• the microwave generator unit 1 or 1* or 1" is detached from the relative container 2 or 2' or 2", rather than attached as shown in the drawings.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• General Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Thermal Sciences (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Life Sciences & Earth Sciences (AREA)
• Sustainable Development (AREA)
• Sustainable Energy (AREA)
• Electromagnetism (AREA)
• Constitution Of High-Frequency Heating (AREA)
• Compositions Of Oxide Ceramics (AREA)

Applications Claiming Priority (3)

Publications (1)

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• 1991
  • 1991-06-21 IT IT91BO000224A patent/ITBO910224A1/it not_active Application Discontinuation
• 1992
  • 1992-06-19 JP JP5501417A patent/JPH06511547A/ja active Pending
  • 1992-06-19 EP EP92914891A patent/EP0593606A1/en not_active Withdrawn
  • 1992-06-19 AU AU22632/92A patent/AU2263292A/en not_active Abandoned
  • 1992-06-19 WO PCT/IT1992/000065 patent/WO1993000781A1/en not_active Application Discontinuation

Non-Patent Citations (1)

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