US3312212A

US3312212A - Heat generating apparatus

Info

Publication number: US3312212A
Application number: US513734A
Authority: US
Inventors: Wilson Alfred
Original assignee: Colt Ventilation and Heating Ltd
Current assignee: Colt Ventilation and Heating Ltd
Priority date: 1964-12-14
Filing date: 1965-12-14
Publication date: 1967-04-04
Anticipated expiration: 1984-04-04
Also published as: NL6516134A; BE673747A; FR1458894A; SE319593B; GB1126662A

Description

April 1967 A. WILSON 3,312,212

HEAT GENERATING APPARATUS Filed Dec. 14, 1965 5 Sheets-Sheet 1 mF/a/i iNvsN-roR HLFR 51 Mum ATTQ April 4, 1967 A; WILSON HEAT GENERATING APPARATUS 3 Sheets-Sheet 2 Filed Dec. 14, 1965 El HG.

A ril 4, 1967 A. WILSO N 3, 1 2

' HEAT GENERATING APPARATUS Filed Dec. 14, 1965 5 Sheets-Sheet 5 HG. J.

INVENTOR ALFzEP Musau 1' United States Patent 3,312,212 HEAT GENERATING APPARATUS Alfred Wilson, Aldwick Bay, England, assignor to Colt Ventilation and Heating Limited, Surrey, Engiand, a British company Filed Dec. 14, 1965, Ser. No. 513,734 Claims priority, application Great Britain, Dec. 14, 1964, 50,902/64 2 Claims. (Cl. 126-116) This invention concerns improvements relating to heat generating apparatus of the kind comprising a heat-exchange chamber, a liquid or gaseous fuel burner directed into the chamber, and a jacket surrounding the chamber to define a passage for air to be heated, for example for space heating in factories, ofiices, warehouses or the like. In particular the invention is concerned with such apparatus wherein the gases within the heat-exchange chamber are subjected to a re-circulation effect.

Such apparatus, which is commonlyand preferably constructed of mild steel, has to be designed to operate between an upper limit (e.g. of 450 C. at which temperature mild steel begins to scale) and a lower limit representing the acid dew point at which low-temperature corrosion will occur. It is the upper limit which is here relevant. The hot combustion gases emerge from the burner mouth at a temperature in the vicinity of 1300- 1400 C. If the inner surface of the heat-exchange chamber were to be in direct contact with these gases temperatures in excess of said upper limit would be reached. To prevent such excessive heating, the hot gases emerge from the burner mouth as a jet along the central axis of the chamber with a sufi'iciently high velocity to entrain the gases surrounding said jet stream. The degree of entrainment is high in the region of the burner month where the velocity of the jet is at a maximum. The mass of the jet stream increases as these gases are entrained and since the total momentum remains unchanged the velocity falls oflf to compensate and the degree of entrainment diminishes correspondingly. By the time that the gases have traversed the length of the jet they have lost much of their forward velocity and are guided to turn round and flow back in the reverse direction annularly around the jet stream. To a considerable extent the reverted gases are in turn drawn into the jet stream. A large proportion of the gases is therefore recirculated around the chamber, possibly a number of times.

The reverse flow of gases around the jet stream is ensured by locating the exhaust porting from the chamber at the same end of the chamber as the burner month. By disposing the exhaust porting uniformly around the jet stream (e.g. equi-angularly spaced in a ring encircling the burner mouth) the jet stream and the reverse flow of gases assume a symmetrical form, for instance, substantially in the form of an annulus surrounding a central core constituted by said jet stream. The symmetrical disposition of the gases within the chamber provides more nearly uniform heat transfer from the heat-exchange chamber to the air passing over the chamber and within the surrounding heat-exchanger jacket and since the jet stream is enveloped by the cooler gases flowing in reverse hot spots are avoided.

The arrangement of ports referred to in the preceding paragraph prevents the very hot gases emerging from the burner mouth from impinging on the containing walls of the chamber. The emergent column of hot gas is kept to the central axis of the chamber and is surrounded by cooler gases. By the process of recirculation the column of hot gas is diluted by the cooler gases so that by the time the opposing Wall is reached its temperature has been very considerably reduced, mainly by the cooling effect referred to but in part also by radiation. In any event the consequences are two-fold: impingement of the jet stream on any surface of the chamber is avoided while at the same time the entire walls of the chamber are heated uniformly within the upper temperature limit specified above. Efficient heat transfer is thereby attained.

A common form of comparable apparatus has a cylindrical heat-exchange chamber with the jet stream from the burner directed along the axis of the cylinder, and to obtain uniform heat transfer the exhaust ports are equiangularly spaced around the burner, as described above, and the heat exchanger jacket has comprised a cylinder co-axially surrounding the chamber cylinder.

The present invention concerns heat generating apparatus comprising a heat-exchange chamber into which a jet of combustion products is directed from a burner at one end of the chamber towards the opposite end thereof and wherein a large proportion of the gases is recirculated around the chamber by entrainment of the gases surrounding the jet stream emerging from the burner, entrainment and recirculation of the gases being ensured by locating exhaust porting from the chamber at the same end of the chamber as the burner and the invention is characterised by a heat-exchange chamber which is substantially square in cross-section transverse to a longitudinal axis. Preferably the exhaust porting at the burner end of the chamber is located in corner regions of the square cross-section, and a heat exchanger jacket of substantially square cross-section co-axially surrounds the chamber to define a passage for air to be heated.

Preferably the exhaust ports are located in the burner end wall of the chamber one at each corner of the square cross-section to induce the reverse fiow of combustion gases along the natural channels at the corners of the chamber.

Advantageously exhaust ducting from the exhaust porting constitutes supporting leg means for the chamber assembly, and also provides heat transfer surfaces passed by the air to be heated.

The heat-exchange jacket may constitute an outer casing of the apparatus, being of a square cross-section most convenient for installation purposes and utilising space most effectively.

Advantageously, metal in sheet or other suitable form and having a high heat absorbtivity may be located in the air passage space between the chamber and the jacket to accept radiant heat from the chamber surface and deliver it to the air flowing over the metal by a convection process to increase the heat transfer effect, the mteal serving also to shield the jacket from such radiant heat.

The invention thus provides a heat generating apparatus which has improved combustion gas flow and heat exchange characteristics, and which for a given heat output can be made relatively smaller and cheaper than the known forms.

A practical application of this invention will now be described, by way of example only, with reference to the accompanying drawings whereof:

FIG. 1 is a front schematic view, partly in section, of an apparatus for space heating in a factory,

FIG. 2 is a schematic side view of the apparatus of FIG. 1, and

FIG. 3 is a schematic plan view, partly in section, of the apparatus of FIG. 1.

The apparatus comprises a vertically disposed combustion chamber 5 which is square in horizontal cross-section transverse to the vertical longitudinal axis x of the chambersee FIG. 3. A liquid (or gaseous) fuel burner 6 has its mouth 7 directed into the chamber from a lower end wall 3 of the chamber along said axis x towards an opposed upper closed end wall 9 of the chamber. Exhaust porting 10 is located at the burner end of the chamber in corner regions 11 of the square cross-section, in

a particular one exhaust port in the burner end wall 8 at each corner to induce the reverse flow of combustion gases (as indicated by the arrows y of FIG. 1) and along the natural channels at the corners of the chamber. The exhaust ports are axially behind and spaced radially outwardly of the burner mouth, as apparent from FIG. 1.

A heat exchanger jacket 12 of square cross-section coaxially surrounds the chamber so as to define a passage space 13 between the chamber and jacket of substantially uniform width for circulation air to be heated. The latter, for instance, is provided by a fan 14 driven by an electric motor 15, the air entering the jacket 12 through a grill or louvre 16 and passing upwardly through spaces 13 and over chamber 5 is delivered to a compartment 26 and thence discharged, at 17, to the space to be heated. The jacket (as shown in the drawings) preferably constitutes an outer casing of the apparatus, being of the square cross-section most convenient for installation purposes and utilising spacemost effectively. Also the air passages 13 in cross-section being in the form of the periphery of a square, provides a relatively greater heat exchange surface as compared with a casing of equivalent size and shape containing a cylindrical form of chamber and jacket. Or, for given heat output, the apparatus of the invention can be made relatively smaller and cheaper.

Exhaust ducting 18 extends downwardly from the exhaust ports and constitutes leg means for the chamber and burner assembly supporting the chamber from a floor 19 within casing 12. In the present particular arrangement there is an exhaust duct 18 from each port.10, each duct constituting a separate leg; pairs of the ducts 18 lead to an exhaust box 20 acting as bases for the assembly. Such ducts and boxes also provide heat trans fer surfaces passed by the air to be heated (see FIG. 1).

A row of tubes 21 extends from an exhaust box 26 to a header or collector 22 in compartment 26. The hot gases are discharged from header 22 to a flue or chimney (not shown). The air to be heated is upwardly directed by fan 14 to pass over chamber 5, boxes 20, support ducts 18, tubes 21 and header 22.

The provision of a square-section heat-exchange chamber has certain distinct advantages over, for instance, a cylindrical chamber. In particular a squaresection chamber provides a greater heat-exchange surface than a comparable cylindrical chamber. The square-section chamber 5 being accommodated within a square-section outer casing 12 provides an apparatus relatively smaller and cheaper than the known form referred to. The heat exchange characteristics of a square-section chamber are an improvement over the known form of apparatus re ferred to. Again the outer casing readily forms the jacket surrounding the chamber. A further and important advantage of a square-section chamber is that by selection of the size of the chamber in relation to the core size of the jet stream issuing from the burner it is possible to ensure that the recirculating gases shield the chamber walls from the jet stream while ensuring that the chamber walls are substantially uniformly heated and hot spots avoided. The natural channels at the corners of the chamber and the exhaust ports associated therewith provide relatively large gas-passage areas so that the gases pass therethrough at a relatively greater velocity with the result that the chamber walls defining the natural channels are adequately heated. The medial portion of each side wall between the corners is spaced from the jet stream to provide a relatively smaller reverse-flow gas-passage area than the natural channels. By selection of the size of the chamber in relation to the size of the core formed by the jet stream it may be arranged that the chamber walls are substantially uniformly heated. Similar considerations apply to chambers of other cross-sectional form as later mentioned.

Metal sheets 23 are located in heat exchanger spaces 13 each sheet lying parallel with tubes 20 and spaced between the respective side walls of the chamber 5 and jacket 12. Such sheeting readily accepts radiant heat from the chamber surface by absorbtion and delivers it to air flowing over both faces of the sheeting to increase the heat transfer effect. Air itself will not effectively take up radiant heat.. The sheets 23 serve also to shield the jacket from such radiant heat. Any other suitable form of the radiant-heat acceptor may be utilised instead of sheeting. Metal sheets 23 are described as being in an opposite pair of the spaces 13 which are next to the two rows of tubes. The sheets may additionally, or alternatively, be provided in the other pair of spaces 13. Because sheets of high heat absorbtivity may be readily used as described to increase the heat transfer effect and also to shield the outer casing of the apparatus the apparatus has improved heat-exchange characteristics.

The hot core of the jet stream travelling axially of the heat-exchange chamber is cooled by the diluent recirculation gases and the jet is enveloped by the cooler reverted gases with the consequence that the heat-exchange chamber is substantially uniformly heated i.e. hot spots are avoided. Because the chamber is substantially uniformly heated the rate of the throughput of the air directed over the chamber by the fan and between the chamber and the jacket is relatively low as compared, for instance, where excessively hot regions or hot spots exist requiring higher rates of circulation air flow adequately to carry away heat from said regions. The lower rate of air throughput provides for more effective heating of the circulating air. Furthermore the low circulation air fan pressures which may thus be used enable the noise level of the fan to be reducedthis is important when the apparatus is installed in offices and similar places where the level of background noise is low. Again such low velocity and fan pressures in turn enable frictional pressure losses in the external circulation air ducting of up to /2" water gauge to be imposed without significant fall off in heat output of the circulation air as normally occurs with high circulation air velocities.

While it is preferred that the heat-exchange chamber is of square cross-section this is not essential and the invention includes within its scope chambers of rectangular cross-section which approximate to the square-section form and which achieve the recirculation effect specified heretofore.

I claim:

1. A heat generating apparatus comprising an elongated closed structure of substantially square cross section forming a heat exchange chamber of substantially square cross section transverse to a longitudinal axis thereof; a jacket surrounding said structure forming the chamber; a burner located beneath the bottom of said chamber and delivering a jet combustion product from the bottom of the chamber towards the top thereof, said chamber being formed with exhaust ports located at the bottom of the chamber and at the corners of the square structure to provide for recirculation of the large proportion of the gases around the chamber by entrainment of the gases surrounding the jet stream emerging from the burner; one leg, each, located at the corners of said chamber and extending downwardly and supporting said structure within said jacket in raised position to provide space for said burner beneath the chamber, said legs being hollow and in communication with said exhaust ports to form exhaust ducting from the chamber; air inlet means formed in the bottom of said jacket; an air outlet means formed in the top of said jacket; said legs being located in the path of the air from said inlet to said outlet means and forming heat transfer surfaces passed by the air to be heated.

2. Apparatus according to claim 1 including a common exhaust collector box located in communication with the interior of a pair of adjacent legs, and a row of tubes extending from each collector box along the heat exchange chamber and within said jacket; a common header communicating with said row of tubes; said common col- 5 6 lector box, said tubes, and said common header being 2,346,876 4/1944 Torr 126-116 in the path of the air from said inlet to said outlet means. 2,424,765 7/ 1947 McCollum 15 8-1 X References Cited by the Examiner FOREIGN PATENTS UNITED STATES PATENTS 5 5981156 9/ 1959 2,1- ,83 1 1938 Sveikovsky 126-110 JAM-ES W. WESTHAVER, Primary Examiner.

Claims

1. A HEAT GENERATING APPARATUS COMPRISING AN ELONGATED CLOSED STRUCTURE OF SUBSTANTIALLY SQUARE CROSS SECTION FORMING A HEAT EXCHANGE CHAMBER OF SUBSTANTIALLY SQUARE CROSS SECTION TRANSVERSE TO A LONGITUDINAL AXIS THEREOF; A JACKET SURROUNDING SAID STRUCTURE FORMING THE CHAMBER; A BURNER LOCATED BENEATH THE BOTTOM OF SAID CHAMBER AND DELIVERING A JET COMBUSTION PRODUCT FROM THE BOTTOM OF THE CHAMBER TOWARDS THE TOP THEREOF, SAID CHAMBER BEING FORMED WITH EXHAUST PORTS LOCATED AT THE BOTTOM OF THE CHAMBER AND AT THE CORNERS OF THE SQUARE STRUCTURE TO PROVIDE FOR RECIRCULATION OF THE LARGE PROPORTION OF THE GASES AROUND THE CHAMBER BY ENTRAINMENT OF THE GASES SURROUNDING THE JET STREAM EMERGING FROM THE BURNER; ONE LEG, EACH, LOCATED AT THE CORNERS OF SAID CHAMBER AND EXTENDING DOWNWARDLY AND SUPPORTING SAID STRUCTURE WITHIN SAID JACKET IN RAISED POSITION TO PROVIDE SPACE FOR SAID BURNER BENEATH THE CHAMBER, SAID