FR2487956A1 - HEATING BODIES FOR DOMESTIC HOT WATER HEATER CENTRAL HEATING BOILERS - Google Patents

Abstract

THE INVENTION RELATES TO A HEAT EXCHANGER HEATER BODY FOR DOMESTIC BOILERS OF THE FORCED DRAFT TYPE. THE HEATING BODY 1 INCLUDES A BEAM OF LONGITUDINAL TUBES WITH EXTENDED SECTION 10, ARRANGED ACCORDING TO THE GENERATOR OF A CYLINDER SO AS TO FORM AN INTERNAL COMBUSTION CHAMBER. THE EXTENDED TUBES 10 ARE INCLINED AT AN ANGLE A WITH RESPECT TO THE RADIAL DIRECTION AB OF FLOW OF THE COMBUSTION GASES TO CREATE AN OBLIQUE ATTACK OF THESE GAS ON THE SAID TUBES. APPLICATION TO CONDENSING BOILERS.

Description

- 1 - The present invention relates particularly but not

  exclusively to domestic hot water central heating boilers with forced draft type gas. It relates to a new exchanger heating body that allows said boilers to operate with a partial or total recovery of the calories contained in the water vapor produced.

by the condensation of the gas.

  Indeed, it is known that during the combustion of a gas containing carbon and hydrogen which is the case of almost all combustible gases, hydrogen combines with the oxygen of the air

to produce water vapor.

  In boilers equipped with conventional heating bodies, this water vapor is evacuated by the chimney in a loss with the

  combustion products at a temperature generally

  be 110 and 2500C, this loss which is at least equal to the heat

  latent condensation or vaporization of water vapor

  about 10% of the calorific value of the gas. To recover

  these lost calories, it is necessary to be able to condense this vapor,

  this is what is done in the so-called condensing boilers.

  Unfortunately, in order to condense the water vapor contained in the products of combustion, it must be possible to cool them at

  contact of a heat exchange wall at a lower temperature than

  re at the so-called dew temperature which is generally around 551C. This means that this water vapor can never be condensed if the heating water circulating in the boiler is at a temperature above the dew point temperature of the products of combustion which in practice is around 550C, or if the exchange surfaces in contact with the products

  of combustion are themselves at a higher temperature than this.

  This is why in most known condensing boilers,

  the water of the circuit to be heated is put in direct contact with the

  combustion fuels using either a spray of water to

  through the products of combustion, ie the principle of the

  merge, the principle of the fluidized bed or the principle of

only water on trays.

  - 2 - But in all these boilers, there is no separation

  between the combustion products and the primary water circuit

  mayor. In addition, it is necessary to provide an interchange between

  the primary circuit and the secondary circuit, because of the aggression

  high water content of the primary circuit in direct contact with

  combustion products. Moreover, the direct contact

  combustion products have disadvantages. First of all-

  it limits the use of this type of generator for example to heating

  gade water pools or pools because the water outlet temperature is relatively low and during this contact,

  the water is acidified by dissolution of the carbon dioxide which gives rise to

  to carbonic acid which reduces the longevity of the apparatus.

  Moreover, we know condensation boilers in the-

  that there is a physical separation between water and water

  combustion products. Condensation appears as a result of the

  exceptional characteristics of the exchanger, as soon as the temperature

  return water from the boiler is less than 500C. This exchange

  may be of the volute type or constituted by layers of tubes

  in smooth copper or with fin extruded in the mass.

  But this type of exchanger is expensive and particularly

  voluminous since it involves a surface of inter-

  important mediator in highly conductive material to obtain condensation. There are also known condensing boiler heat exchangers made from a longitudinal tube bundle of elongated section disposed along the generatrix of a cylinder to form a cylindrical inner combustion chamber. These elongated section tubes are positioned so that the plane of

  symmetry of their section passes through the axis of revolution of the sample.

  cylinder arrangement, this arrangement being intended to promote the laminar flow of the combustion gases in the range of

  small thickness thus produced between each of the tubes.

  But from a thermal point of view, this provision creates a regime

  generally laminar gas flow which results in two consequences

  adverse effects: firstly the heat exchange coefficient - 3 -

  by convection at the gas interface, the wall of the tubes is relative-

  weakly, and on the other hand the heat exchange coefficient on the downstream face of the tubes is negligible vis-à-vis its value

on the upstream side.

  The present invention makes it possible to avoid these drawbacks and is intended to provide a heat exchanger heater body for particularly simple and economical condensation boilers while creating a turbulence regime in the flow of combustion gases between the longitudinal tubes in order to to obtain coefficients

  higher convective heat exchange rate.

  For this purpose, the subject of the invention is a heating body comprising

  a longitudinal tube bundle with elongated section

  along the generatrix of a cylinder to form a cylindrical interior combustion chamber characterized in that the

  the longitudinal median plane of each of the tubes is inclined by a

  angle relative to the radial flow direction of the combustion gases in the combustion chamber to create a

  oblique attack of these gases on said tubes.

  Other particular features and advantages of the invention

  will be apparent from the following description in which reference is made

  to the accompanying drawings which represent: FIG. 1 a diagrammatic cross-sectional view of the heating element according to the invention;

  - Figure 2 a half-view in cross section showing the inclination-

its minimum of tubes.

  There is shown in the figures a heat exchanger body 1

  consisting of longitudinal tubes with longitudinal elongated section

  formally distributed along the generatrix of a cylinder so as to form a cylindrical inner chamber 2 for the introduction

  a burner 3 also cylindrical.

  These tubes 10 in which circulates the fluid to be heated are on the one hand parallel to each other and on the other hand inclined at an angle α with respect to a radial direction AB of gas flow.

  in a cylindrical combustion chamber 2.

  - 4 - The angle of inclination of tubes is defined by the angle lying between the longitudinal median plane A1B1 of a tube and the radial plane AB passing through the intersection of the median plane A1B1 of the tube and the

  upstream face of this tube in the direction of gas flow.

  This angle of inclination has tubes 10 is for example close to

  300. However, an angle of inclination of

  at a limiting angle a0 shown in FIG. 2, and obtained

  when a radial plane AB! passing through the axis of the chamber of

  cylindrical bending 2 and between two tubes 10 longitudinal neighbors

is tangent to these two tubes.

  This arrangement has many advantages. First of all,

  on the one hand, it creates a turbulent regime in the

  flow of gases between the tubes 10 despite the low value of about 50 to 200 of the Reynolds number characterizing this flow of

  gas in order to obtain high convection coefficients and

  to increase the surface of the tubes exposed to radiation

  direct fire from the combustion chamber, so as to

  storing an "optically closed" heat exchange surface. The

  "optically closed surface" means that a light source

  having as its axis the axis of the combustion chamber and the burner

  cylindrical is not directly visible when looking

  of this exchanger, therefore on the exhaust side of the combustion gases.

  tion. We can not see in this case only traces

  indirect light coming out of the gaps between the tubes

  by internal reflections and the diffusion of the source

  Central light formed by the flames of the burner.

  In addition, this arrangement due to the oblique attack of gases

  of combustion on the tubes increases on the one hand the

  mique exchanged by convection by the turbulence created upstream of the tubes and consequently obtained between tubes and on the other hand the power

  heat exchanged by irradiation by exposing a greater sur-

  face of the tubes to the direct radiation of the flames of combustion of the gas.

  Of course, the use of elongated water tubes has been considered.

  but in the same way it will be possible to use oval tubes

  elliptical section or diamond section tubes, or elongated (oblong) section tubes with different contours on the face

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  5 upstream and the downstream face, for example so-called cross-section tubes.

  orange-shaped, or drop-shaped.

- 6 -

Claims (2)

R E V E N D I C A T IO N S   1 / Heating body for domestic hot water central heating boilers by tight-draft type gas   force comprising a bundle of longitudinal tubes with   elongated in which circulates the fluid to be heated, arranged along the generatrix of a cylinder to form a cylindrical internal combustion chamber characterized in that the longitudinal median plane A1B1 of each of the tubes (10) is inclined at an angle a relative to the radial direction AB flue gas flow for   create an oblique attack of these gases on said tubes.   2 / heating body according to claim 1 characterized in that the tubes (10) form an exchange surface optically closed thermal.   Heating element according to claim 1, characterized by   the fact that the angle of inclination a is of the order of 30-.   Heating body according to Claim 1, characterized in that the angle of inclination α is greater than a limiting angle a0 which is such that any radial plane AB 'passing through the axis of the cylindrical combustion chamber (2) and between   two adjacent tubes (10) are tangent to these two tubes.