GB2157821A - Radiant heaters - Google Patents
Radiant heaters Download PDFInfo
- Publication number
- GB2157821A GB2157821A GB08500382A GB8500382A GB2157821A GB 2157821 A GB2157821 A GB 2157821A GB 08500382 A GB08500382 A GB 08500382A GB 8500382 A GB8500382 A GB 8500382A GB 2157821 A GB2157821 A GB 2157821A
- Authority
- GB
- United Kingdom
- Prior art keywords
- tube
- steel
- radiant
- coating
- radiant heater
- 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- Withdrawn
Links
Classifications
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F24—HEATING; RANGES; VENTILATING
- F24C—DOMESTIC STOVES OR RANGES ; DETAILS OF DOMESTIC STOVES OR RANGES, OF GENERAL APPLICATION
- F24C15/00—Details
- F24C15/24—Radiant bodies or panels for radiation heaters
Abstract
A tube for a radiant heater has at least a part of its outer surface treated to make said surface duller and increase the surface area of said tube. The treatment, in the case of a stainless steel tube, is grit-blasting, whilst in the case of a mild steel tube the treatment is the application of a coating.
Description
SPECIFICATION
Radiant heaters
This invention relates to radiant heaters.
Existing radiant-tube heaters use standard mild-steel or stainless-steel tubing for the radiant emitter tube. Either helically welded or standard steel gas tubing is normal. The upper temperature limit for mild-steel tubing is usually taken as 450/500"C, and suitable grades (e.g.
304) of stainless-steel may be used at higher temperatures, say 700/800"C. Most radiant-tube heaters operate with the tube temperatures below about 700"C. The burner-tube in which combustion takes place is, therefore, sometimes made of stainless-steel for adequate service life, those tubes remaining cooler usually being of mild-steel. Apart from its temperature limitation, mild-steel also tends to deteriorate by corrosion due to condensation of water on the tube during the warmer periods when the heaters are not in use.
The emissivity (ability to radiate heat at a given temperature) of stainless steel is not very high because of its naturally shiny surface (the duller and darker a surface, the higher its emissivity, generally speaking), so that while the use of stainless-steel is advantageous in terms of resistance to deterioration at high temperature, the radiant output from it is not as high as that for mild-steel at a similar temperature. Typical quoted emissivities of the metals as formed are: stainless-steel, 0.4; mild steel, 0.6.
The invention therefore seeks to provide an improved form of radiant heater tube and hence an improved radiant heater.
According to one aspect of the present invention, there is provided a method of improving the emissivity and operational life of a tube of a radiant heater consisting of grit blasting at least a part of the surface of said tube so as to dull the said surface and increase the surface area of said tube. The tube will preferably be composed of stainless steel.
According to a second aspect of the present invention, there is provided a method of improving the emissivity and operational life of a tube of a radiant heater consisting of applying a coating to at least a part of the surface of said tube so as to dull the said surface and increase the surface area of said tube.
Preferably, said coating in the form of copper or 13% chromium steel, is applied by spraying.
In order to improve the emissivity and operating lifetime of radiant heater tubes, there will now be described two surface treatments, one for stainless-steel and the other for mild-steel: (i) for stainless-steel-a grit-blasted finish which makes the surface dull and increases the surface area;
(ii) for mild steel metal sprayed coating of higher quality material, for example copper, or 13% chromium steel ("stainless") which again makes the surface dull, increases the surface area and also improves the corrosion resistance and, therefore, life.
The effect of using these treatments on a radiant heater tube is to increase the radiant output by: (a) increasing the surface area for radiant heat transfer and (b) increasing the emissivity of the surface. In the case of the metal coating on mild-steel tubes, the surface is also more corrosion resistant.
This means that either the heater may be operated with an increase heat input to the tube for a greatly increased radiant output at the same operating temperature or at the same heat input for a similar heat output at a lower operating temperature, and therefore, a potentially longer service life.
The advantages of the surface treatments for radiant tubes are twofold-they increase the surface area and increase the emissivity, both important factors in the Stefan-Boltzmann relationship that determines radiant heat transfer.
Experimental Results
Measurements of radiant heat output from various surfaces at the same temperature (1 60 C) with various surface treatments yielded the following values for relative emissive power (normalised to plain mild-steel = 1.0-mild-steel being the commonest radiant heater tube material used in current commerical heaters): plain untreated shiny stainless steel 0.76 metal sprayed aluminium coating 0.79
metal sprayed Al/bronze coating 0.93
metal sprayed copper coating 0.94
grit-blasted stainless steel 1.47
metal sprayed 13% Chromium steel coating 1.76
Thus the emissive power is 1.9 times greater for the stainless-steel treatment (1.47/0.76) and 1.8 times greater for the mild-steel coated with 13% Chromium steel.
In service, it has been found that the "grit-blasted" surface of stainless steel after being heated a few times to service temperature (300 C-500 C), becomes oxidised to a matt black appearance due to a mixture of nicket, chromium and iron oxides which are black, green and brown respectively. This further enhances the emissivity of the radiant tube, increasing its relative radiant output even more so that it is similar to that of 13% chromium steel coated mild steel.
Claims (10)
1. A method of improving the emissivity and operational life of a tube of a radiant heater consisting of grit blasting at least a part of the surface of said tube so as to dull the said surface and increase the surface area of said tube.
2. A method according to Claim 1, wherein said tube is composed of stainless steel.
3. A method of improving the emissivity and operational life of a tube of a radiant heater consisting of applying a coating to at least a part of the surface of said tube so as to dull the said surface and increase the surface area of said tube.
4. A method according to Claim 3, wherein said coating is applied to said surface by spraying.
5. A method according to Claim 3 or Claim 4, wherein said coating is copper.
6. A method according to Claim 3 or Claim 4, wherein said coating is 13% chromium steel.
7. A radiant heater tube formed in accordance with Claim 1 or Claim 2 or any of Claims 3 to 6.
8. A radiant heater having a tube formed in accordance with Claim 1 or Claim 2 or any of
Claims 3 to 6.
9. A radiant heater having a tube at least a part of the outer surface of which has been treated to make it duller and increase its surface area.
10. Radiant heater tube substantially as herein described.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB848407055A GB8407055D0 (en) | 1984-03-19 | 1984-03-19 | Radianttube heaters |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB8500382D0 GB8500382D0 (en) | 1985-02-13 |
| GB2157821A true GB2157821A (en) | 1985-10-30 |
Family
ID=10558296
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB848407055A Pending GB8407055D0 (en) | 1984-03-19 | 1984-03-19 | Radianttube heaters |
| GB08500382A Withdrawn GB2157821A (en) | 1984-03-19 | 1985-01-08 | Radiant heaters |
Family Applications Before (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB848407055A Pending GB8407055D0 (en) | 1984-03-19 | 1984-03-19 | Radianttube heaters |
Country Status (1)
| Country | Link |
|---|---|
| GB (2) | GB8407055D0 (en) |
Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB523432A (en) * | 1939-01-06 | 1940-07-15 | Sanderson Brothers And Newboul | Improvements relating to burners and fittings for radiant tube furnaces and the like |
| GB565200A (en) * | 1943-06-29 | 1944-10-31 | John Martin Blair | Improvements in or relating to gas fires and radiants |
| GB893724A (en) * | 1957-10-18 | 1962-04-11 | Csf | Improvements in or relating to infra-red radiation heating elements |
| GB1395489A (en) * | 1970-11-30 | 1975-05-29 | Thermo Electron Corp | Heating apparatus |
-
1984
- 1984-03-19 GB GB848407055A patent/GB8407055D0/en active Pending
-
1985
- 1985-01-08 GB GB08500382A patent/GB2157821A/en not_active Withdrawn
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB523432A (en) * | 1939-01-06 | 1940-07-15 | Sanderson Brothers And Newboul | Improvements relating to burners and fittings for radiant tube furnaces and the like |
| GB565200A (en) * | 1943-06-29 | 1944-10-31 | John Martin Blair | Improvements in or relating to gas fires and radiants |
| GB893724A (en) * | 1957-10-18 | 1962-04-11 | Csf | Improvements in or relating to infra-red radiation heating elements |
| GB1395489A (en) * | 1970-11-30 | 1975-05-29 | Thermo Electron Corp | Heating apparatus |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8500382D0 (en) | 1985-02-13 |
| GB8407055D0 (en) | 1984-04-26 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |