EP0096021A1 - Construction de tubes a ailettes - Google Patents

Construction de tubes a ailettes

Info

Publication number
EP0096021A1
EP0096021A1 EP19810903215 EP81903215A EP0096021A1 EP 0096021 A1 EP0096021 A1 EP 0096021A1 EP 19810903215 EP19810903215 EP 19810903215 EP 81903215 A EP81903215 A EP 81903215A EP 0096021 A1 EP0096021 A1 EP 0096021A1
Authority
EP
European Patent Office
Prior art keywords
flange
heat
tube
temperature
tubes
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Withdrawn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
EP19810903215
Other languages
German (de)
English (en)
Inventor
Rune Andersson
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.)
Individual
Original Assignee
Individual
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 Individual filed Critical Individual
Publication of EP0096021A1 publication Critical patent/EP0096021A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F1/00—Tubular elements; Assemblies of tubular elements
    • F28F1/10—Tubular elements and assemblies thereof with means for increasing heat-transfer area, e.g. with fins, with projections, with recesses
    • F28F1/12—Tubular elements and assemblies thereof with means for increasing heat-transfer area, e.g. with fins, with projections, with recesses the means being only outside the tubular element

Definitions

  • This invention relates to an apparatus with tubes, provi ⁇ ded with gills and intended for a flowing medium, in par- - ticular flue gases from a combustion process, where the gills are designed to absorb an optimal amount of heat from the gases for transmission to a heat absorbing medium, e.g. water, in the tubes.
  • a heat absorbing medium e.g. water
  • the invention relates to gilled tubes for economisers in boilers.
  • the sections at the rear end of a boiler serve to absorb the final heat energy remained in the flue gases before they leave the unit through the stack. This heat recovery is normally accomplished by preheating the feed water and/ /or the air for the burners, and in general the heat ener- gy in the flue gases below 300°- 500°C is utilized. These sections are called economiser and air heater respective ⁇ ly, and the aim is of course to lower the flue gas tempe ⁇ rature in these sections as much as possible since this will result in an improvement of the heat economy. It can be shown that a decrease of the flue gas temperature of 10 -15 C will increase the efficiency by about 1 percent ⁇ age unit. The determination of the size of the heating surfaces of economisers and air heaters will thus be an economical evaluation where the improvement of the heat economy is balanced against the cost of the increased heating surface.
  • the lower limit for the cooling of the flue gases is de ⁇ termined by the temperature where there is a risk for condensation of especially sulphuric acid on the heating surfaces.
  • the sulphuric trioxide S0 3 that is formed when the fluel is burned reacts with the water vapour H 2 0 in the gases and forms sulphuric acid H 2 S0 ⁇ ,.
  • the temperature at which this is started is called the acid dew poinu, : and its value is dependant upon the type of fluel and its composition, especially the sulphur con ⁇ tent, the combustion method, excess iar and several other factors, and it is thus difficult to give an exact value of this temperature. Normally its value is in the region between 70°-170°C.
  • the heating surfaces are normally designed to resist the corrosive attacks from condensing sulphuric acid and simi- lar products.
  • the usual method is to make the heating sur ⁇ faces in this region with a cover from cast iron outside the steel tubes.
  • the purpose of the cast iron cover is to form the corrosion resistance while the steel tube consti ⁇ tutes the pressure resisting part.
  • the contact between the cast iron shell and the steel tube must of course be very good to give a good heat transfer through the material.
  • the primary function of the heating surfaces at the rear end of the boiler is to transfer heat from the flue gases on one side of the surfaces to the feed water or the co -
  • the flanges (gills) of a heat exchanger surface serve the purpose of improving the heat transfer on the side where the heat transfer co ⁇ efficient between the flowing medium and the surface is low.
  • This for example, is the case with gases as compared to fluids.
  • the low heat transfer coefficient is compensa ⁇ ted through the flange arrangement by the fact that the size of the heat absorbing surface is increased.
  • the dis ⁇ advantage with a flanged surface is that the surface temperature is different in different parts of the flange, and consequently the heat transfer at the tip of the flange will be lower than at the root since the tempe- rature difference between the surounding medium and the surface is lower at the tip than at the root. This is ex ⁇ pressed in the calculations by the so-called flange effi ⁇ ciency ⁇ , which is a measure of the relation between the average surface temperature of the flange and the tempera- ture at the root.
  • the embodiment of the invention is to give a solution with respect to the design of flanged heating elements, in par ⁇ ticular elements for economisers. Before this solution is presented a detailed technical summary will be given.
  • An economiser acts in principle as a heat exchanger with the purpose to transfer heat from a gas to a liquid.
  • ⁇ t mean temperature difference between hot and cold side, °C. At a given temperature difference the heat transferred is thus determined by the product of the heat, transfer co ⁇ efficient k and the surface size A.
  • the quantity k, which a flanged heater normally is related to the total size of the outer surface, can be divided into three components as follows: a) the heat transfer from the gas to the outer surface of the tube b) the heat transmission (conduction) through the tube material from the outer to the inner surface c) the heat transfer from the inner surface of the tube to the liquid in the tube.
  • ⁇ f heat transfer coefficient between the gas and the flanged outer surface
  • J/m 2 s C ⁇ . heat transfer coefficient between the inner surface of the tube and the liquid in the tube
  • A size of the tube surface between the flanges
  • m 2 A. inner surface size
  • A outer surface size of an unflanged tube
  • m 2 6 tube thickness
  • ⁇ heat conductivity of the tube material
  • J/m s C a form factor, which takes into account the curva ⁇ ture of the tube.
  • the flange efficiency ⁇ which thus is related to the heat transfer, is as mentioned before a measure of the relation between the average surface temperature of the flange and the temperature of the tube at the root of the flange, and it is an expression of the fact that the heat transmission capacity of the flange is smaller than that of the tube, measured per unit of surface area.
  • the size of the flange efficiency is depending upon the dimensions and the geometrical form of the flange, and the scope of the invention is to achieve the best efficiency by giving a formula for the geometrical form of the flange.
  • the op ⁇ timal solution can be expressed by the formula n n
  • x and y are coordinates in a right angled system
  • a and b are proportional to the outer dimensions of the flange in the x- and y-direction and n is a coefficient whose value is between
  • n should have a value between 2 and 5. Higher values than 5 gives a reduced flange efficiency and higher material consump ⁇ tion per unit area.
  • Enclosed drawing shows examples of various geometrical forms of flanges for finned and gilled tubes.

Landscapes

  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Geometry (AREA)
  • Thermal Sciences (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Physical Or Chemical Processes And Apparatus (AREA)
  • Heat-Exchange Devices With Radiators And Conduit Assemblies (AREA)

Abstract

Echangeurs thermiques se composant de tubes à ailettes utilisés notamment dans un dispositif de combustion. Selon l'invention, l'ailette possède une forme géométrique définie dans la formule$(10,)$où x et y représentent des coordonnées cartésiennes et a et b représentent la dimension extérieure selon les axes x et y respectivement et l'exposant de puissance n est supérieur à 2 mais inférieur à 5.
EP19810903215 1981-12-10 1981-12-10 Construction de tubes a ailettes Withdrawn EP0096021A1 (fr)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/SE1981/000367 WO1983002151A1 (fr) 1981-12-10 1981-12-10 Construction de tubes a ailettes

Publications (1)

Publication Number Publication Date
EP0096021A1 true EP0096021A1 (fr) 1983-12-21

Family

ID=20342949

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19810903215 Withdrawn EP0096021A1 (fr) 1981-12-10 1981-12-10 Construction de tubes a ailettes

Country Status (2)

Country Link
EP (1) EP0096021A1 (fr)
WO (1) WO1983002151A1 (fr)

Family Cites Families (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR789553A (fr) * 1935-05-03 1935-10-31 Delas Perfectionnements aux échangeurs de chaleur à tubes à ailettes
US2161898A (en) * 1935-10-07 1939-06-13 Elmer E Ledbetter Finned tube and method for forming the same
GB480152A (en) * 1936-07-02 1938-02-17 Economiseur Green L Improvements in tubular heat exchangers
US2557760A (en) * 1947-09-16 1951-06-19 C A Dunham Co Radiator
CH288848A (de) * 1949-09-12 1953-02-15 Kablitz Richard Röhrenwärmeaustauscher mit Rippenrohren und Stahlrohrseele.
CH488986A (de) * 1968-01-18 1970-04-15 Sulzer Ag Wärmeübertrager
DE2048235A1 (de) * 1970-10-01 1972-04-06 Schmoele Metall R & G Wärmetauscherrohr
SE342317B (fr) * 1970-12-30 1972-01-31 Gebelius Sven Runo Vilhelm
US3795125A (en) * 1972-01-27 1974-03-05 Universal Oil Prod Co High-fin integral finned tube of heat-resisting alloys, and multi-pass process for making the same

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO8302151A1 *

Also Published As

Publication number Publication date
WO1983002151A1 (fr) 1983-06-23

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Legal Events

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