US20040134480A1 - Convective system - Google Patents
Convective system Download PDFInfo
- Publication number
- US20040134480A1 US20040134480A1 US10/703,497 US70349703A US2004134480A1 US 20040134480 A1 US20040134480 A1 US 20040134480A1 US 70349703 A US70349703 A US 70349703A US 2004134480 A1 US2004134480 A1 US 2004134480A1
- Authority
- US
- United States
- Prior art keywords
- product
- coil
- volts
- coils
- cfm
- 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.)
- Abandoned
Links
Images
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
Definitions
- Heating can be carried out by conduction, radiation or convection.
- a wide variety of thermal processing applications are found throughout industry. Heat treating, joining, curing and drying operations are carried out in many different types of furnaces and ovens.
- the method of heating is normally a radiative technique with radiant electric heating elements placed along the walls of the furnace. Although such a method is efficient for temperatures above 1000° C. (1832° F.), the use of convection as the heat transfer mechanism is normally thought to be more efficient in the lower temperature ranges.
- One of the best devices for Air heating is an AirtorchTM.
- the following patents all pertain to best methods of heating air namely U.S. Pat. Nos. 5,766,458, 5,655,212, 5,963,709. Discussions on convective heating are available from (1) M.
- thermal processing ovens and furnaces are critical decisions in order to meet the needs almost all engineering products during their manufacture.
- Oven and furnace design must take into consideration heat transfer methods, the temperature uniformity, movement of the product, atmosphere, construction and the heat generation method.
- Heat processing equipment is usually classified as ovens operating to 1000° C. and as furnaces above this temperature.
- Batch and continuous designs are the common choices depending on the flexibility and productivity requirements.
- the source of heat is normally provided by oil, gas or electricity.
- the batch oven is the largest type of design used to manufacture the product.
- the continuous oven operates on a continuous or pusher basis. There are similarities between the batch and continuous, each having characteristics depending upon product design and processing conditions.
- Heat transfer to the work can be natural convection, forced convection or by radiation. Natural convection is slow and not very uniform. Forced convection on the other hand is easily controllable and can be directed for odd shapes. Radiant heat transfer at higher temperatures may be faster for some products but may contribute other problems to the products like non-uniformity and distortion, to mention a few. Forced convection offers advantages over radiant heating for a number of manufactured products. It is well known in the art that convective heating eliminates these problems
- Coil material commonly available metallic heating wire made of Nickel Chromium alloy or Fe—Al—Cr or Fe—Al, Ni—Cr alloy. Generally metallic wires can be heated in air to about 1200° C. Wire diameters from 0.1 mm to a 1.2 mm were tried for the experiments.
- Fe—Al—Cr alloy alloys made of Fe—Al—Cr—Nb or Fe—Al—Cr—Mo—Nb are expected to perform similarly as are other metallic & intermetallic systems
- thermocouple was located at about 3 mm from the exit nozzle plane. When located at the exit nozzle plane the thermocouple read even up to 980° C. It is expected that the upper range with metallic elements will be about 1000° C. for air temperature. Other gases depending on their thermal properties will have a different exit temperature. If the metallic elements are made of Mo, W or other such higher temperature metals the exit temperature could be much higher.
- wire sizes for the inner and outer coils could be different for different products.
- pitch can be different for each coil and different at different locations in the same coil.
- the pitch would be larger than at the main heating sections of the coils in order to keep the contacts cool. Spacers and other inserts between the coils are contemplated if required.
- Experiment 1 Outer coil provides rifling which increases heat transfer from the elements to air.
- a helical coil of 240 mm long ⁇ 13.2 mean dia, working out for 8.2 Ohms (18SWG A1 commercial wire) was used for testing.
- the coil was inserted in open-ended ceramic tube.
- the exit end of the coil was brought back to the inlet side through a ceramic insulating tube. (Refer FIG. 2).
- the coil was operated at 110 V, at a power rating of 1.47 kW.
- the airflow was maintained at 5 SCFM @ 0.4 Kgs/cm 2 working pressure.
- the exit temperature of the air stabilized at 560° C.
- Experiment 2 Inner coil over comes conda effect, and provides for annular area heating of air, which provides for the highest heat transfer to the air.
- the exit end of the coil was wound on its return on the ceramic insulating tube (Refer FIG. 2).
- the resulting coil resistance was 10.8 Ohms.
- the coil was operated with the same airflow, air pressure and operating voltage of 110 V.
- the coil now operated at 1.1 kW, and the exit temperature stabilized at 806° C.
- Experiment 3 Inner coil winding in the opposite direction of the outer coil gives opposite rifling with that of the outer coil. This causes a turbulence effect on the airflow, which increases heat transfer to the air. Furthering on experiment 2, the inner coil was wound in the opposite direction of the outer coil. All parameters were the same as Experiment 2. The exit temperature stabilized at 845° C.
- Molybdenum disilicide wires can be heated in air to 1900° C. but are more brittle than metallic wire.
- the coils were obtained from Micropyretics Heaters International Inc. who are the leading experts for molybdenum disilicide in the US.
- Wire diameter 3 mm, 4 mm or 5 mm may be used.
- Gap between coils tested was varied from 4 mm to 15 mm. Best results were obtained with the 5 mm wire.
- the coils are defined as those which can be electrically heated or heated by a combination of electric and other thermal methods.
- the coils can be metallic, molybdenum disilicide, silicon carbide, intermetallic, or ceramic.
Abstract
We have discovered a simple electrical assembly of heating coils which may be arranged to produce hot air or gas up to 1500° C. This assembly is the invention claimed in this patent.
Description
- Heating can be carried out by conduction, radiation or convection. A wide variety of thermal processing applications are found throughout industry. Heat treating, joining, curing and drying operations are carried out in many different types of furnaces and ovens. The method of heating is normally a radiative technique with radiant electric heating elements placed along the walls of the furnace. Although such a method is efficient for temperatures above 1000° C. (1832° F.), the use of convection as the heat transfer mechanism is normally thought to be more efficient in the lower temperature ranges. One of the best devices for Air heating is an Airtorch™. The following patents all pertain to best methods of heating air namely U.S. Pat. Nos. 5,766,458, 5,655,212, 5,963,709. Discussions on convective heating are available from (1) M. Fu, Kandy Staples and Vijay Sarvepalli. A High Capacity Melt Furnace for Reduced Energy Consumption and Enhanced Performance. Journal of Metals (JOM), May 1998, pg42 and (2) ADVANCE MATERIALS & PROCESSES magazine (pages 213 to 215, October, 1999).
- The proper selection of thermal processing ovens and furnaces is a critical decision in order to meet the needs almost all engineering products during their manufacture. Oven and furnace design must take into consideration heat transfer methods, the temperature uniformity, movement of the product, atmosphere, construction and the heat generation method. Heat processing equipment is usually classified as ovens operating to 1000° C. and as furnaces above this temperature. Batch and continuous designs are the common choices depending on the flexibility and productivity requirements. The source of heat is normally provided by oil, gas or electricity. The batch oven is the largest type of design used to manufacture the product. The continuous oven operates on a continuous or pusher basis. There are similarities between the batch and continuous, each having characteristics depending upon product design and processing conditions.
- Heat transfer to the work can be natural convection, forced convection or by radiation. Natural convection is slow and not very uniform. Forced convection on the other hand is easily controllable and can be directed for odd shapes. Radiant heat transfer at higher temperatures may be faster for some products but may contribute other problems to the products like non-uniformity and distortion, to mention a few. Forced convection offers advantages over radiant heating for a number of manufactured products. It is well known in the art that convective heating eliminates these problems
- We have discovered a new technique for very low cost convective heat generation. The basic method is to heat the air or gas through a concentric energized heating coil system as shown below in the diagram (FIG. 1). The concentric design is important as without it the air is not heated to the same temperature.
- The following tests were done with (1) metallic wire and (2) with molybdenum disilicide wire and the following results were obtained.
- 1. Metallic Wire
- Coil material commonly available metallic heating wire made of Nickel Chromium alloy or Fe—Al—Cr or Fe—Al, Ni—Cr alloy. Generally metallic wires can be heated in air to about 1200° C. Wire diameters from 0.1 mm to a 1.2 mm were tried for the experiments. We conducted the following experiments with the Fe—Al—Cr alloy (alloys made of Fe—Al—Cr—Nb or Fe—Al—Cr—Mo—Nb are expected to perform similarly as are other metallic & intermetallic systems):
- The best stable experiment to date where the air was heated to 850° C. at a 3.5 scfm flow rate had the following design features. Other experiments were also conducted where air was heated to close to 1000° C., however very long term tests at these higher experiments have not yet been carried out.
- Wire diameter 1.2 mm
- Outer wire separation (pitch) 0.285 mm
- Inner wire separation (pitch) 0.285 mm
- Winding: Opposite direction in inner and outer coil
- Gap between coils: 5.23 mm
- The thermocouple was located at about 3 mm from the exit nozzle plane. When located at the exit nozzle plane the thermocouple read even up to 980° C. It is expected that the upper range with metallic elements will be about 1000° C. for air temperature. Other gases depending on their thermal properties will have a different exit temperature. If the metallic elements are made of Mo, W or other such higher temperature metals the exit temperature could be much higher.
- Based on these results the device in FIG. 2 was constructed as a prototype.
- We contemplate that the wire sizes for the inner and outer coils could be different for different products. Similarly the pitch can be different for each coil and different at different locations in the same coil.
- Where the contacts are made to the incoming power supply line it is contemplated that the pitch would be larger than at the main heating sections of the coils in order to keep the contacts cool. Spacers and other inserts between the coils are contemplated if required.
- It is thought that the presence of the inner coil serves to overcome the “conda” effect and thus improves contact with the air.
- Some further experiments were conducted:
- Coil design was adjusted with the appropriate physics in mind.
- Experiment 1: Outer coil provides rifling which increases heat transfer from the elements to air.
- A helical coil of 240 mm long×13.2 mean dia, working out for 8.2 Ohms (18SWG A1 commercial wire) was used for testing. The coil was inserted in open-ended ceramic tube. The exit end of the coil was brought back to the inlet side through a ceramic insulating tube. (Refer FIG. 2). The coil was operated at 110 V, at a power rating of 1.47 kW. The airflow was maintained at 5 SCFM @ 0.4 Kgs/cm2 working pressure. The exit temperature of the air stabilized at 560° C.
- Experiment 2: Inner coil over comes conda effect, and provides for annular area heating of air, which provides for the highest heat transfer to the air.
- Furthering on experiment 1, the exit end of the coil, was wound on its return on the ceramic insulating tube (Refer FIG. 2). The resulting coil resistance was 10.8 Ohms. The coil was operated with the same airflow, air pressure and operating voltage of 110 V. The coil now operated at 1.1 kW, and the exit temperature stabilized at 806° C.
- Experiment 3: Inner coil winding in the opposite direction of the outer coil gives opposite rifling with that of the outer coil. This causes a turbulence effect on the airflow, which increases heat transfer to the air. Furthering on experiment 2, the inner coil was wound in the opposite direction of the outer coil. All parameters were the same as Experiment 2. The exit temperature stabilized at 845° C.
- Note that the opposite winding configuration gave a nearly 50° C. higher temperature. Table 1 below gives further experimental details and exit temperatures.
TABLE 1 Airflow cross Exit Experiment Coil section Air temperature Number resistance Voltage Current area Power Air Flow Pressure of air Experiment 1 8.2 110 13.4 25.1 mm2 1.47 kw 5 SCFM 7 Kg/cm2 560 Experiment 2 10.8 110 10 17.2 mm2 1.1 kw 5 SCFM 7 Kg/cm2 806 Experiment 3 10.8 110 10 17.2 mm2 1.1 kw 5 SCFM 7 Kg/cm2 845 Experiment 4 11.0 110 10 55.2 mm2 1.1 kw 3.5 SCFM 0.4 Kg/cm2 850 - 1. Molybdenum Disilicide Alloy Wire
- Molybdenum disilicide wires can be heated in air to 1900° C. but are more brittle than metallic wire. The coils were obtained from Micropyretics Heaters International Inc. who are the leading experts for molybdenum disilicide in the US.
- Wire diameter 3 mm, 4 mm or 5 mm may be used. An experiment was conducted with outer wire separation (pitch) 12.7 mm and inner wire separation (pitch) 12.7 mm.
- Gap between coils tested was varied from 4 mm to 15 mm. Best results were obtained with the 5 mm wire.
- Best results gave a temperature of 1165° C. to 1400° C. at different measurement positions with 1400° C. as set point on the controller and airflow set to 1 scfm. (Table 2). Note this configuration is trademarked Ultratorch™.
- Best results show a temperature of 1332° C. to 1500° C. at different measurement positions with 1500° C. as set point on the controller and airflow set to 1 scfm. (Table 3). Note this configuration is trademarked Ultratorch™.
- These hitherto-fore unavailable very high temperatures in gasses for transferring to parts has only been possible because of the new coil in coil design with the proper spacing and gaps provided that the two coils are electrically connected. It is also found that opposite winding in the inner and outer coils give rise to very high temperatures of the gas at the exit. (In the claim below cfm refers to cubic feet per minute)
- The typical uses of such a device is in low cost heating. Three different types of use classes are considered.
- 1. Heating of a chamber such as an oven or furnace which may or may not have other heating systems in it.
- 2. Heating of a fluid passing though the coils
- 3. Heat directed at a surface to cause heating of surface for applications such as coatings, hardening, debinding, glowing, etc.
- In the claims below the coils are defined as those which can be electrically heated or heated by a combination of electric and other thermal methods. The coils can be metallic, molybdenum disilicide, silicon carbide, intermetallic, or ceramic.
Claims (11)
1. A novel gas heater product, with a coil in coil heater assembly, and annular space for the gas where the inner and outer coils are connected electrically and the gas flow rate varies from 1 cfm to about 1000 cfm.
2. A novel gas heater product, with a coil in coil heater assembly, and annular space for the gas where the inner and outer coils are connected electrically and the wires in the inner and outer coil are wound in an opposing manner and the gas flow rate varies from 1 cfm to about 100 cfm.
3. The product of claim 1 or claim 2 where the gap between the coils is ranges from about 5 mm to about 14 mm.
4. The product of claim 1 or claim 2 wherein the ratio of the gap to the winding spacing ranges from about 4.5 mm to about 0.5 mm.
5. The product of claim 1 wherein the coils are wound in the same direction.
6. A product of claim 1 where the inner and outer diameter coil wires may be varied from about 0.1 mm to about 6 mm
7. A product of claim 2 where the inner and outer diameter coil wires may be varied from about 0.1 mm to about 6 mm
8. The product of claim 1 where the cross sectional area for air flow is about 15 to about 150 square mm
9. The product of claim 2 where the cross sectional area for air flow is about 15 to about 150 square mm.
10. The product of claim 1 where multiple coil and configurations are used in one housing.
11. The product of claim 2 where multiple coil and configurations are used in one housing.
Priority Applications (4)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US10/703,497 US20040134480A1 (en) | 2003-01-07 | 2003-11-10 | Convective system |
US11/682,107 US8119954B2 (en) | 2003-01-07 | 2007-03-05 | Convective heating system for industrial applications |
US12/514,516 US8435459B2 (en) | 2003-01-07 | 2007-11-14 | Heating and sterilizing apparatus and method of using same |
US13/767,923 US8652403B2 (en) | 2003-01-07 | 2013-02-15 | Heating and sterilizing apparatus and method for using same |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US43832103P | 2003-01-07 | 2003-01-07 | |
US10/703,497 US20040134480A1 (en) | 2003-01-07 | 2003-11-10 | Convective system |
Related Child Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US11/682,107 Continuation-In-Part US8119954B2 (en) | 2003-01-07 | 2007-03-05 | Convective heating system for industrial applications |
Publications (1)
Publication Number | Publication Date |
---|---|
US20040134480A1 true US20040134480A1 (en) | 2004-07-15 |
Family
ID=32717968
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US10/703,497 Abandoned US20040134480A1 (en) | 2003-01-07 | 2003-11-10 | Convective system |
Country Status (1)
Country | Link |
---|---|
US (1) | US20040134480A1 (en) |
Cited By (5)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20070145038A1 (en) * | 2003-01-07 | 2007-06-28 | Micropyretics Heaters International, Inc. | Convective heating system for industrial applications |
WO2008061139A2 (en) * | 2006-11-15 | 2008-05-22 | Micropyretics Heaters International, Inc. | Heating and sterilizing apparatus and method of using same |
AU2007215373B2 (en) * | 2006-02-09 | 2009-04-02 | P.H.E. Enterprises Pty Ltd | A heating assembly |
US20100129157A1 (en) * | 2003-01-07 | 2010-05-27 | Micropyretics Heaters International, Inc. | Heating and sterilizing apparatus and method of using same |
US20100150775A1 (en) * | 2006-11-15 | 2010-06-17 | Micropyretics Heaters International, Inc. | Apparatus and method for sterilizing items |
Citations (8)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3760315A (en) * | 1970-12-07 | 1973-09-18 | Bbc Brown Boveri & Cie | Electrical coil with spacing bands |
US3816706A (en) * | 1972-12-23 | 1974-06-11 | Eicherauer F | Heating member for a hair dryer |
US4149104A (en) * | 1976-12-15 | 1979-04-10 | Hitachi, Ltd. | Method of manufacturing a coil heater of an indirectly-heated type cathode electrode of electronic tubes |
US4350872A (en) * | 1978-11-14 | 1982-09-21 | Firma Fritz Eichenauer | Electrical heating element for fluid media and method for producing same |
US4794225A (en) * | 1987-10-09 | 1988-12-27 | Maese Hector L | Tube axial handheld blow dryer for hair |
US5426351A (en) * | 1991-06-25 | 1995-06-20 | Nec Corporation | Heater coil for electron tube |
US5841943A (en) * | 1997-04-25 | 1998-11-24 | Soundesign, Llc | Ducted flow hair dryer with multiple impellers |
US6013903A (en) * | 1996-09-24 | 2000-01-11 | Mifune; Hideo | Flame reaction material carrier and method of manufacturing flame reaction member |
-
2003
- 2003-11-10 US US10/703,497 patent/US20040134480A1/en not_active Abandoned
Patent Citations (8)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US3760315A (en) * | 1970-12-07 | 1973-09-18 | Bbc Brown Boveri & Cie | Electrical coil with spacing bands |
US3816706A (en) * | 1972-12-23 | 1974-06-11 | Eicherauer F | Heating member for a hair dryer |
US4149104A (en) * | 1976-12-15 | 1979-04-10 | Hitachi, Ltd. | Method of manufacturing a coil heater of an indirectly-heated type cathode electrode of electronic tubes |
US4350872A (en) * | 1978-11-14 | 1982-09-21 | Firma Fritz Eichenauer | Electrical heating element for fluid media and method for producing same |
US4794225A (en) * | 1987-10-09 | 1988-12-27 | Maese Hector L | Tube axial handheld blow dryer for hair |
US5426351A (en) * | 1991-06-25 | 1995-06-20 | Nec Corporation | Heater coil for electron tube |
US6013903A (en) * | 1996-09-24 | 2000-01-11 | Mifune; Hideo | Flame reaction material carrier and method of manufacturing flame reaction member |
US5841943A (en) * | 1997-04-25 | 1998-11-24 | Soundesign, Llc | Ducted flow hair dryer with multiple impellers |
Cited By (9)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20070145038A1 (en) * | 2003-01-07 | 2007-06-28 | Micropyretics Heaters International, Inc. | Convective heating system for industrial applications |
US20100129157A1 (en) * | 2003-01-07 | 2010-05-27 | Micropyretics Heaters International, Inc. | Heating and sterilizing apparatus and method of using same |
US8119954B2 (en) | 2003-01-07 | 2012-02-21 | Micropyretics Heaters International, Inc. | Convective heating system for industrial applications |
US8435459B2 (en) | 2003-01-07 | 2013-05-07 | Micropyretics Heaters International, Inc. | Heating and sterilizing apparatus and method of using same |
AU2007215373B2 (en) * | 2006-02-09 | 2009-04-02 | P.H.E. Enterprises Pty Ltd | A heating assembly |
WO2008061139A2 (en) * | 2006-11-15 | 2008-05-22 | Micropyretics Heaters International, Inc. | Heating and sterilizing apparatus and method of using same |
WO2008061139A3 (en) * | 2006-11-15 | 2008-09-25 | Micropyretics Heaters Int | Heating and sterilizing apparatus and method of using same |
US20100150775A1 (en) * | 2006-11-15 | 2010-06-17 | Micropyretics Heaters International, Inc. | Apparatus and method for sterilizing items |
US8940245B2 (en) * | 2006-11-15 | 2015-01-27 | Micropyretics Heaters International, Inc. | Apparatus and method for sterilizing items |
Similar Documents
Publication | Publication Date | Title |
---|---|---|
US8119954B2 (en) | Convective heating system for industrial applications | |
US5117482A (en) | Porous ceramic body electrical resistance fluid heater | |
US11956863B2 (en) | Multi-zone heater | |
US20110309068A1 (en) | Heating element for a hot air device | |
JP2003142037A (en) | Improved lamp | |
JPH0917849A (en) | Semiconductor wafer holding device, its manufacture and its use method | |
US20040134480A1 (en) | Convective system | |
US4179603A (en) | Radial blade heating device | |
KR100827469B1 (en) | Electic hot blast heater using high frequency induction heaing | |
JP4717932B2 (en) | Hot air heater | |
US4093816A (en) | Furnace heating apparatus | |
US3891828A (en) | Graphite-lined inert gas arc heater | |
AU2015206075B2 (en) | A wire tray for a microwave oven or a cooking appliance with microwave heating function | |
US6816671B1 (en) | Mid temperature plasma device | |
US4101724A (en) | Furnace conversion method and apparatus | |
WO2013019582A2 (en) | Method and manufacturing assembly for sintering fuel cell electrodes and impregnating porous electrodes with electrolyte powders by induction heating for mass production | |
EP1250554A1 (en) | Ceramic igniters and methods for using and producing same | |
JP2010113935A (en) | Heating unit | |
KR200441974Y1 (en) | Heater is composed of wire heating element and using heating-pipe for anealing furnac | |
US20060246807A1 (en) | Spark plug manufacturing apparatus and method of manufacturing spark plug | |
US20130175251A1 (en) | Compensating Heating Element Arrangement for a Vacuum Heat Treating Furnace | |
KR101394325B1 (en) | Heater and method for manufacturing the same | |
US5471032A (en) | Electrical resistance ignitor with spaced parallel filaments brazed in refractory block recesses | |
NL8004400A (en) | HEATING ELEMENT FOR AN ELECTRIC OVEN. | |
JP2003336971A (en) | Metal wire material induction-heating and melting device |
Legal Events
Date | Code | Title | Description |
---|---|---|---|
STCB | Information on status: application discontinuation |
Free format text: ABANDONED -- FAILURE TO RESPOND TO AN OFFICE ACTION |