EP0125890A2 - Réchauffeur - Google Patents

Réchauffeur Download PDF

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Publication number
EP0125890A2
EP0125890A2 EP84303166A EP84303166A EP0125890A2 EP 0125890 A2 EP0125890 A2 EP 0125890A2 EP 84303166 A EP84303166 A EP 84303166A EP 84303166 A EP84303166 A EP 84303166A EP 0125890 A2 EP0125890 A2 EP 0125890A2
Authority
EP
European Patent Office
Prior art keywords
fluid
heat
heated
heating element
outlet
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP84303166A
Other languages
German (de)
English (en)
Other versions
EP0125890A3 (fr
Inventor
Brian Davy Collins
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
ENGINEERING DEVELOPMENTS (FARNBOROUGH) Ltd
Original Assignee
ENGINEERING DEVELOPMENTS (FARNBOROUGH) Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by ENGINEERING DEVELOPMENTS (FARNBOROUGH) Ltd filed Critical ENGINEERING DEVELOPMENTS (FARNBOROUGH) Ltd
Publication of EP0125890A2 publication Critical patent/EP0125890A2/fr
Publication of EP0125890A3 publication Critical patent/EP0125890A3/fr
Withdrawn legal-status Critical Current

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    • 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
    • F24—HEATING; RANGES; VENTILATING
    • F24H—FLUID HEATERS, e.g. WATER OR AIR HEATERS, HAVING HEAT-GENERATING MEANS, e.g. HEAT PUMPS, IN GENERAL
    • F24H7/00—Storage heaters, i.e. heaters in which the energy is stored as heat in masses for subsequent release
    • F24H7/02—Storage heaters, i.e. heaters in which the energy is stored as heat in masses for subsequent release the released heat being conveyed to a transfer fluid
    • F24H7/04—Storage heaters, i.e. heaters in which the energy is stored as heat in masses for subsequent release the released heat being conveyed to a transfer fluid with forced circulation of the transfer fluid
    • F24H7/0408—Storage heaters, i.e. heaters in which the energy is stored as heat in masses for subsequent release the released heat being conveyed to a transfer fluid with forced circulation of the transfer fluid using electrical energy supply
    • F24H7/0416—Storage heaters, i.e. heaters in which the energy is stored as heat in masses for subsequent release the released heat being conveyed to a transfer fluid with forced circulation of the transfer fluid using electrical energy supply the transfer fluid being air

Definitions

  • the present invention relates to a heater for generating a flow of hot fluid.
  • a standard hair drier has a fan which produces a flow of air which is expelled from the drier over an electrically heated coil or wire.
  • hot air blowers operating on a similar-principle to a hair drier, are used in a large number of situations e.g. for drying, softening of plastics materials or curing of adhesives. Similar arrangements are known for heating liquids.
  • the heating elements of such heaters have a relatively high thermal conductivity as this enables energy to be transferred quickly and efficiently to the gas (or liquid where appropriate).
  • Any heating, element will have a warm up time so that if the supply of energy at a high level is discontinued, the heating element will cool rapidly and there will then be a delay between the resumption of the energy supply and the heating element reaching the desired temperature. For this reason such heaters are normally operated continuously.
  • shrink wrapping For industrial processes in which a continuous supply of hot gas is required, such heaters are satisfactory. However, there are many industrial processes which require an intermittent hot gas supply. An example of this is in shrink wrapping.
  • shrink wrapping an item or items to be wrapped are enclosed in a loose sleeve or bag of thin film plastics material. The film is heated to a temperature at which the film shrinks to encase the item to be wrapped. Standard shrink wrapping plastics material films must be heated to a temperature between 80 0 C and 200°C in order to achieve the necessary shrinkage.
  • hot air guns in shrink wrapping which direct a jet or jets of hot air onto the plastics film.
  • These hot air guns operate on a similar principle to that previously described and have the same problem, namely that they must be operated continuously in order to maintain the heating element or elements at the desired temperature. It is usual to transport the articles to be wrapped past the hot air gun on a conveyor belt. It would be desirable for the hot air gun to produce a pulse of hot air only when an article to be wrapped is passing the gun, but this is not possible with the standard hot air guns because of the delays due to warm up time that would be imposed if the hot air gun was operated intermittently. Thus a large proportion of the energy output of the gun is wasted and the energy input to the gun must be maintained continuously at a high level.
  • shrink wrap articles In addition to the hot air gun, it is known to shrink wrap articles using a "shrink tunnel".
  • An article loosely wrapped in a plastics film is passed by a conveyor through an oven heated to approximately 150°C and 300 0 C.
  • the oven forms a heat mass which heats the air within it.
  • most shrink tunnels use fans within the oven to circulate the air in it.
  • the design of shrink tunnels inevitably results in very high energy losses, both due to radiation or convection from the oven itself and also due to the heating of the conveyor as well as the article.
  • the air within the oven is maintained at a continuously high temperature and so the effect of discontinuous energy output is not achieved. Also, such shrink tunnels are not portable.
  • the present invention seeks to overcome, or at least ameliorate, the problem of high energy loss when a hot air gun is operated intermittently, and provide a heater which produces pulses of heated fluid efficiently.
  • a heat element which is capable of storing heat energy and capable of transferring that heat energy to the fluid to be heated during a pulse of heated fluid.
  • a heating element capable of achieving these two results will be referred to hereinafter as a heat mass.
  • the heat mass stores heat energy so that it acts as a reservoir of heat energy whereby heat energy can be withdrawn from that reservoir during a fluid pulse and the reservoir be replenished by input of energy to the heat mass between the pulses.
  • the heat mass must have a heat capacity large enough to store a suitable amount of heat energy.
  • the material forming the heat mass to have a large specific heat capacity, such as a heat insulator, except that such materials generally have a low thermal conductivity and so would be inefficient in transferring heat energy to the fluid.
  • the thermal conductivity of at least the part of the heat mas adjacent the surface to be contacted by the fluid is sufficiently high, normally at least 30 Wm -1 K -1 , more preferably 50 Wm -1 K -1 . This limits the materials which may be used for the heat mass, and hence prevents maximisation of the specific heat capacity.
  • the desired heat capacity depends on a number of parameters:
  • the desired temperature of the gas must be about 80°C to 200°C and the permissible drop in temperature is less than 10% (usually about 2%).
  • a suitable temperature for the heat mass is about 500°C to 700°C and at least 100 kJ (preferably 800 kJ) of energy should be stored.
  • the heat capacity is desirably at least 200 JK -1 , preferably 1600 JK -1 .
  • the limitation on the thermal conductivity of the heat mass means that the material is desirably a metal.
  • a metal with high thermal conductivity such as aluminium may be used, although steel has been found suitable.
  • a mass of about 3.1 kg of steel is needed to achieve the heat capacity stated above.
  • the insulation of the heat mass must limit the energy lost. This may be calculated by noting the initial rate of temperature drop from the operating temperature with no energy supplied to the heat mass and no fluid being expelled from the heater.
  • the rate, with an operating temperature of about 500°C should preferably be less than 5 Ks -1 (preferably about 0.3 Ks -1 ).
  • the mean energy supplied to the mass may be made less than the mean energy transferred to the fluid during a fluid pulse.
  • the mean energy transferred to each pulse is more than ten times the mean energy supplied.
  • the present invention is applicable both to the heating of gases and to the heating of liquids.
  • the heating element and the means for generating pulses of gas or other fluid are preferably located in a housing which is movable to enable the hot gas output to be directed in any desired direction.
  • a heater according to the present invention in the form of a hot air gun may be located over a conveyor belt carrying articles to be shrink wrapped, the hot air output being produced only when an article is below the heater.
  • the input(s) for fluid and the output(s) of the heater are close together so that hot fluid may be recirculated past the heating element.
  • This may be achieved by providing inlets radially spaced by equal distances from a central outlet.
  • a linear array of inlets may be provided adjacent a corresponding array of outlets, or an elongate inlet and an elongate outlet may be provided side by side.
  • a heater in the form of a hot air gun 1 being a first embodiment of the present invention is positioned above a conveyor belt 2 on which are carried articles 3 to be enclosed within a plastics film 4 which is shrunk around the article 3 by heating the film 4.
  • the conveyor 2 carries the article 3 to a position directly below the outlet 5 of the gun 1 and the gun 1 is activated.
  • the conveyor may stop with the article directly below the outlet 5 or the article may be heated as it moves past the gun 1.
  • Hot air is directed from the output 5 onto the film 4. This heats the film and causes it to shrink.
  • the hot air is reflected by the film and the conveyor belt and is drawn back into the gun 1 through inlets 6.
  • the gun 1 has an outer casing 7 and contains a heating element having an outer heat mass 8 and an inner heat mass 9.
  • the heat mass is formed from a material having a thermal conductivity of at least 30 Wm -1 K -1 . Most metals satisfy this parameter, and aluminium has a particularly high specific heat capacity, so a small mass would be needed. However, aluminium also has a low density and hence the gun 1 would be bulky.
  • the preferred material is therefore stainless steel, because it has suitable thermal conductivity, specific heat capacity, density, emissivity and enthalpy and also is resistant to corrosion at high temperatures e.g. 500°C. With an operating temperature of 500°C and an air output temperature of about 100 0 C a mass of 3.1 kg of steel has been found to provide a suitable heat mass.
  • the mean energy transferred to each air pulse may then be more than 10 times the mean energy supplied.
  • the heat mass is a liquid encased in a metal shell, the metal transforming heat rapidly to the gas and the liquid acting as the main heat reservoir due to its high specific heat capacity.
  • metal it may be a bulk material, a spiral or spirals, or a tube, but is preferably formed by clamping plates of the metal to square section heating sources 13.
  • the heating sources may supply heat energy at the same rate, or at different rates, so that using either one or both gives three different heat inputs.
  • Inlet conduits 10 are formed between the outer and inner heat masses 8 and 9 extending from the inlets 6 to plenum chamber 11.
  • An outlet conduit 12 extends from the plenum chamber 11 to the outlet 5 through the centre of the inner heat mass 9.
  • the outlet conduit 12 is flared towards the outlet 5 to form a flared jet of hot air.
  • a plurality of inlet conduits 10 with corresponding inlets 6 may be provided spaced around a circle centred on a central outlet conduit 12.
  • the heating sources 13 extend through the outer and inner heat masses 8 and 9 and are thermostatically controlled to maintain the heat mass at a uniform temperature, e.g. 500°C to 700°C.
  • the air mover may be a venturi 14 powered by a supply of compressed air through a duct 15.
  • the compressed air passes into the inlet conduit 12 and the flow 16 of compressed air entrains air from the plenum chamber 11 thereby creating a jet of air in the outlet conduit 12.
  • the air mover may be a vaned pump as will be discussed later with reference to Fig. 5, or a fan. If a pump or fan is used, it is preferably made of stainless steel. Additional fans may be provided in the inlet conduits. The speed of such pumps and/or the speed of the venturi may be controlled to vary the volume and pressure of the hot air jet from the outlet 5.
  • the pressure of the air pulses is also effected by the angle of flare of the outlet conduit 12.
  • the pump or venturi 14 pumps hot air from the plenum chamber 11 through the outlet conduit 12 to the outlet 5.
  • air is drawn into the inlets 6 and through the inlet conduits 10 to the plenum chamber 11. Because both the inlet conduits 10 and the outlet conduit 12 are surrounded by the heat mass, the air passing through the blower is heated both in its passage from the inlets 6 to the plenum chamber and its passage from the plenum chamber to the outlet 5.
  • the casing 7 is formed by insulation 19 of a cast refractory material such as calcium silicate adjacent the outer portion 8 of the heat mass and outer skin 20 of e.g. polyester resin.
  • the insulation 19 enables the heat mass to be maintained continuously at a high temperature with only a small energy input.
  • the conductivity of the heat mass and the insulating properties of the insulation 19 determine the rate of cooling of the heat mass.
  • a high conductivity permits rapid transfer of heat to the air when the gun 1 is in operation but increases the heat loss, and hence the energy input necessary, when the gun 1 is not in use.
  • the temperature drop at the operating temperature (with no heat energy supplied and no air being expelled) needs to be less than 5°C per second (5 Rs- 1 ) if the energy input is to be kept low, and a suitable figure is 20°C per minute (0.3 Ks -1 ).
  • the insulation may be if approximately uniform thickness as shown in Fig. 2, but preferably is thicker in the part surrounding the plenum chamber 11 as shown in Fig. 3.
  • the casing 7, consisting of the insulation 19 and the outer skin 20 forms a horse-shoe shape with a central cavity 21 which houses the heat mass etc. which may be identical to that shown in fig. 2.
  • An aperture 22 is provided in the casing 7 for wires to connect the heating sources to an external power supply.
  • trunnions 23 may be provided on the casing 7.
  • an outer flange 24 at the bottom of the casing 7 which constrains the hot air reflected from an object into the vicinity of the inlet to the heater.
  • the transit time of the article 3 through the hot air jet or jets may be controlled by varying the speed of the conveyor, or the conveyor may be stopped below the blower for a suitable time.
  • a linear array of inlets and outlets may be used as shown in Figure 4.
  • Inlets 6 and outlets 5 extend in in two rows along the bottom of the blower 1 in a series of adjacent pairs. Each pair may communicate with a corresponding plenum chamber, or all the inlets and outlets may have a common plenum chamber.
  • the blower 1 When used for shrink wrapping, the blower 1 extends across the conveyor belt to form a hot air curtain through which the article must pass.
  • the array of inlets and outlets may be combined into two adjacent elongate slots, one of which is an inlet 6 and one an outlet 5. This arrangement is shown in Fig. 5. Again, a hot air curtain is formed.
  • a second embodiment of a hot air gun 1 has an inlet 6 and an outlet 5 as shown in Fig. 4.
  • An inlet conduit 10 from the inlet 6 and an outlet conduit 12 to the outlet 5 communicating with a common plenum chamber 11 are arrange on either side of a central heat mass 25.
  • Fins 26,27 may be provided in the inlet conduit 10 and the outlet conduit 12 respectively to improve heat transfer from the heat mass 25 to the air in those conduits.
  • a pump 28 is provided in the plenum chamber 11 to draw air from the inlet 6 to the outlet 5.
  • the pump comprises a vaned cylinder which entrains air and carries it from the inlet side of the plenum chamber 11 to the outlet side.
  • the pump 23 and the part 24 of the heat mass adjacent the pump it is possible to minimise the backflow of air so that most of the air entrained by the pump is expelled through the outlet conduit 12.
  • casing 7 formed by insulation 19 and an outer skin 20 is provided around the conduits 10,12 and the plenum chamber 11.
  • the present invention is particularly applicable to shrink wrapping processes, but may find application wherever an efficient source of hot air, gas or other fluid is required.
  • the dimensions of the article are preferably of the same order of magnitude as the width of the gun 1 and the distance between the gun 1 and the conveyor 2. If a much smaller article 3 is shrink- wrapped, the advantages of the present invention are also achieved but with reflection of hot air being primarily from the conveyor 2. When the dimensions of the article 3 are less than the width of the outlet 5, the hot air jet completely surrounds the article 3 improving the efficiency of the system.
  • the present invention is also applicable to the heating of liquids. This is particularly true of the embodiment of Fig. 6 where the pump 23 may pump liquids easily.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Thermal Sciences (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Heat-Pump Type And Storage Water Heaters (AREA)
  • Heating, Cooling, Or Curing Plastics Or The Like In General (AREA)
EP84303166A 1983-05-11 1984-05-10 Réchauffeur Withdrawn EP0125890A3 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB8312948 1983-05-11
GB838312948A GB8312948D0 (en) 1983-05-11 1983-05-11 Heater

Publications (2)

Publication Number Publication Date
EP0125890A2 true EP0125890A2 (fr) 1984-11-21
EP0125890A3 EP0125890A3 (fr) 1985-05-22

Family

ID=10542540

Family Applications (1)

Application Number Title Priority Date Filing Date
EP84303166A Withdrawn EP0125890A3 (fr) 1983-05-11 1984-05-10 Réchauffeur

Country Status (2)

Country Link
EP (1) EP0125890A3 (fr)
GB (1) GB8312948D0 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0233560A2 (fr) * 1986-02-07 1987-08-26 NATIONAL PATENT DENTAL PRODUCTS Inc. Appareil de chauffage
EP1397630A2 (fr) * 2000-11-28 2004-03-17 3SAE Technologies, Inc. Element chauffant et separateur a rendement eleve

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2016167A1 (fr) * 1968-08-22 1970-05-08 Linde Ag
FR2263471A1 (en) * 1974-03-04 1975-10-03 Stiebel Eltron Gmbh & Co Kg Electric storage heater flow controller - bimetal strip controls regulating flap in air mixing channel
FR2278962A1 (fr) * 1973-05-25 1976-02-13 Hurdequint Louis Soufflerie a air chaud destinee, en particulier, a la retraction de films d'emballage
DE3212479A1 (de) * 1981-10-15 1983-10-13 Licentia Patent-Verwaltungs-Gmbh, 6000 Frankfurt Vorrichtung zur durchfuehrung eines schweissverfahrens zur verbindung von kunststoffteilen

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2016167A1 (fr) * 1968-08-22 1970-05-08 Linde Ag
FR2278962A1 (fr) * 1973-05-25 1976-02-13 Hurdequint Louis Soufflerie a air chaud destinee, en particulier, a la retraction de films d'emballage
FR2263471A1 (en) * 1974-03-04 1975-10-03 Stiebel Eltron Gmbh & Co Kg Electric storage heater flow controller - bimetal strip controls regulating flap in air mixing channel
DE3212479A1 (de) * 1981-10-15 1983-10-13 Licentia Patent-Verwaltungs-Gmbh, 6000 Frankfurt Vorrichtung zur durchfuehrung eines schweissverfahrens zur verbindung von kunststoffteilen

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0233560A2 (fr) * 1986-02-07 1987-08-26 NATIONAL PATENT DENTAL PRODUCTS Inc. Appareil de chauffage
EP0233560A3 (fr) * 1986-02-07 1988-06-22 NATIONAL PATENT DENTAL PRODUCTS Inc. Appareil de chauffage
EP1397630A2 (fr) * 2000-11-28 2004-03-17 3SAE Technologies, Inc. Element chauffant et separateur a rendement eleve
EP1397630A4 (fr) * 2000-11-28 2004-12-15 3Sae Technologies Inc Element chauffant et separateur a rendement eleve

Also Published As

Publication number Publication date
GB8312948D0 (en) 1983-06-15
EP0125890A3 (fr) 1985-05-22

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Inventor name: COLLINS, BRIAN DAVY