US2069409A - Heat transfer apparatus - Google Patents

Description

Feb. 2, J, N.D, HEENAN 2,069,409

HEAT TRANSFER APPARATUS Filed April l2, 1935 5 Sheets-Sheei'. l

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Feb. 2, 1937.

J. N. D.- HEENAN 2,069,409

HEAT TRANSFER APPARATUS Filed April 12, 1935 :s sheets-sheet V2 Fell 2 1937 J. N.ID. HEENANl 2,069,409

HEAT TRANSFER APPARATUS Filed April l2, 1955 5 Sheets-Sheet 3 Patented Feb. 2, 1937 UNITEDV STATES PATENT oFFlcE HEAT TRANSFER APPARATUS John Nelson Dundas Heenan, Hemel Hempsted,

England Application April 12, 1935, Serial No. 16,068 In Great Britain September 14, 1934 I l1y Claims. (Cl. 257-240) This invention relates to heat transfer appa.-

' cording to the invention;

V as to constructional features and as to operation,

relatively inexpensive to manufacture and toV maintain in highly eilicient working condition.

A d iiiiculty hitherto attached to the employment of long tubes in economizers with a view to reducing the number of connecting bends and other ttings in a unit of any given heating surface has been one mainly of providing room in practice for withdrawal and replacement of faulty tubes when necessary and this has been sought to be overcome by arranging for the tubes to be withdrawn laterally from the supporting framework and associated casing parts, that is, in a direction at right angles to the axes of the tubes. I However, such alternative provision itself usually introduces the need, not present when an ordinary axial withdrawal of tubes is feasible, for .Y making detachable such vertical side bars and other parts of the actual supporting structure, framework or casing as comprise one or both sides of the economizer in order to permit of lateral withdrawal as indicated.

A further object of the invention is to obviate in heat exchangers generally, the choking of the gas passages due to\deposit from the heating gases, While maintaining high elciency of heat transfer and keeping the size of apparatus as small as possible for a given duty.

According to the invention I can provide for the easy withdrawal of tubes of economizers and tion also I am able, by attacking the root cause of sooting and like troubles, to avoid the latter substantially, and to provide apparatus comparatively easy -to keep in clean and eilicient condi- 50 tion.

ing description.

Referring tothe accompanying drawingsz- Figure 1 is a sectional elevation of one conlike apparatus in a limited space while at the Other objects of and advantages accruing from this invention will become apparent in the follow-,

struction of economizer or feed-water heater ac- Figure 2 is a cross sectional elevation of the device shown in Figure 1;

Figure 3 is a more or less diagrammatic plan 5 of a plurality of such devices in a convenient space relationship;

Figure 4 is a fragmental elevation, to a larger scale and partly in section in a longitudinal plane, `of tube units according to the invention; 10

Figure 5 is an end elevation of a header of a 'kind included in other views;

Figure 6 is a fragmental plan view, partly in f section, showing the end region of a tube unit;

Figure '7- is a cross sectional elevation of a lo gilled tube as embodied in other views;

Figures 8 and 9 are outline views drawn to equal scales illustrating the form andrsize of gas passages according to the presentivention and according to a known construction respectively. 20

In carrying the invention into effect in one convenientform, by way of example only, an economizer comprises, as show n in Figures 1, 2, and 3, a generally elongated rectangular framework comprising corner upright members a and up- 25 iight intermediate members a1, these various vertical members being braced together at suit- 'able intervals in height by longitudinal side members az extending from end to end 'to form a suitably rigid side .to'the structure. Transverse 3o transverse vmembers may be connected to the said 35 intermediate side uprights a1. The framework may generally comprise substantially I section ironwork as shown.

'I'he tubes in this construction are arranged in anumber -of superimposed sections each of which 40 alternating with the transverse members as above referred' to, and there may be any numberY of; such sections the tubes of which may be connecte'd up to vone another in any suitable way.v

Each section, as shown clearly in the larger scale ilgures and Figure 2, comprises a number of units b indicated generally by b in Figures .1 and 2, arranged in juxtaposition, the tubes which compose each unit lying one above the other and extending parallel to the sides c oi.' the support- 50 ing structure. Eachl unit in one construction comprises say four tubes di, dz, da, d4, Figure 4,v arranged vertically one aboveX the other in closel Y relationship and having their ends connected to headers e, f oi' generally rectangular or oblong l form. 'I'he preferred method of connecting tubes to headers will be described hereinafter.

Each section of the economizer is assembled, as shown in Figures l to 3, from a plurality of units b in such a way that the longer sides ei and fr of the corresponding headers e and f abut against one another at one end of the economizer while the shorter sides or top and bottom ends e2 and ,fz of the headers are arranged to t together and within the pairs of transverse supporting members a3 adjacent to the ends of the framework. Each section of the economizer shown comprises ten vertical rows of tubes, composed each of two superimposed units, all units of the lower two sections being four-tube units, while the extreme uppermost units of the top section are two-tube units. The end walls which define the heating gas conduit ofU the economizer are constituted by the assemblages of headers e and f at the opposite ends, these headers resting upon and forming a sufficient seal with the end transverse members as and with one another. IThe lowermost tubes of the lower units of each section may, for instance, receive support between the ends from one or more of the intermediate transverse members as shown in Figures 1 and 2. A section may of course comprise more or less vertical and horizontal rows of tubes, constituted by an appropriate number of units each of which comprises atleast two tubes one above the other and a header, of the kind described, at their opposite ends.

The framework is made of suicient width not only to accommodate the requisite number of units to form a section but also to provide, when the units are packed up sidewise into operative positions against one side wail of the structure, a suicient space g between-the last-entered unit and the opposite side wall to enable the said unit to be displaced or separated laterally from the next unit while remaining within the framework. By so providing it is possible to deflect such unit or slew it inside the transverse members of the frame so that the tubes of such unit may lie in a plane inclined to the other tubes and to the side of the economizer. It is found that, by so providing, the various units of tubes in a section can be withdrawn lengthwise, that is, along their own axes after they have been brought into the inclined position as mentioned above, and the withdrawal operation as will be understood is then effected through either of the end doors or the like at h, such as are commonly provided already on economizers for access to the connecting bends and the like. For removal of a unit, e. g. a defective unit (other than that occupying an outermost position, i.VV e. closest to the space g), all

such units in the Ysarne section as lie to the outside of the defective unit may be disconnected from the headers and/or other units and slewed into inclined positions; but only so many of these latter units need be actually withdrawn from the framework as may be necessary to provide sucient side room within the framework for' removal of the defective unit therefrom past any external obstruction.

A row of economizers constructed as above can be arranged for instance as in Figure 3 so that the ends of the several economizers are closer together than would admit of the removal of tubes by drawing straight out, i. e. in directions parallel to the side Walls of the economizer, and assuming the outer side walls of such economizers are to conform tn substantially one plane running along and parallel to the back of the several boilers forming with economizers an installation of quite a common type, there need be no diflculty in effecting the removal of economizer tubes notwithstanding the space limitations. In Figure 3 a unit b is shown in broken lines in the act of being withdrawn obliquely from the left hand economizer, and it will be seen that notwithstanding the closeness of the two economizers (considerably less than the overall length of an economizer) no fouling or obstruction occurs.

In view of the fact that the construction shown requires a clearance or dead space g between the outer units and the adjoining side wall of the framework for tube removal, provision has to be made for preventing such clearance acting to short circuit the passage of flue gases or other heating medium part the tubes unless it be desired to use such space for by-pass purposes.

If the said spaces or passages are to be used for acting as a gas by-pass when required, suitable. control can be provided by dampers, as indicated for instance at j in Figure 2. Alternatively, when no use of the space g is to be made for bypassing, suitable nlling pieces may be tted. If desired, such provision may comprise plate work on the transverse girder work a3 at regions such as 7c presenting one or more barriers against the passage of gases at the points mentioned.

It may in some cases be convenient or necessary to provide side baffle plates as k, detachably secured in any well known manner to the framework and close to the outermost tube units of each section, and arranged if necessary to co-operate with any horizontal or other baffle plates xedly secured as at k to the framework'when it is desired to close the space or spaces g to the stream of hot gases.

' Returning now to the construction of units, the headers for these are preferably, as in Figures 4 to 6, made by machining from solid mild steel blocks of a suitable rectangular or oblong shape. For those headers f which are to provide both the inlet to the unit and the outlet therefrom, the

block may be drilled through each end with a hole enough to accommodate tube ends m1, the number of such holes being conveniently four, giving two tube connections to each of the internal drilled out compartments Z; and the holes may be carried through the opposite wall Z4 to give suitable access as for instance for expanding the tubes. After the necessary drilling work has been done the end holes may be closed up permanently as by plugs Z5 and such side holes as le as are not required for connecting bends as n can be fitted with closures Z'z of a. more or less permanent kind.

For headers e which are to be connected to the opposite ends of tubes the blocks may be formed as'above but drilled right through from end to end, plugged at the ends and provided with transverse holes for attachment of the tubes at one side and provision of closure plugs or the like in all holes at the other side. For connecting one unit to another bends may as above be connected to the outermost of the transverse holes drilled into the double compartmented headers.

f Figures l and 4, one pair being connected to one the method in w are connected at the opposite end in alike manner to the second or single-compartmented tube header e already described. It will thus be seen that parallel flow can be provided from the doublecompartmented header along two .tubes to the opposite header and from these the flow may return in parallell through the second pair of tubes back to the other compartment of the first header to which an outlet connection is made.

The arrangement shown in Figures 1 and 2 embodies two-tube upper units each of which comprises single compartmented headers at each end. To one of such headers in each of the units a connection is made by a bend n1 from an inlet header or drum o. The ow of water is then downwards through the units immediately below, via the bends n, and finally via the bends n2 to the outlet header or drum p.

Other modes of forming the headers, e'. g. toA

provide different compartment arrangements, may enable any desired system of flow to be obtained, e. g. a series ow throughout or in. any desired sections or units of the economizer.

, It is preferred to provide the tubes of an economizer withgil1s for increasing the heating surface in a manner broadly quite well known. However, the use of gills of circular form in an arrangement such as the above where tubes are not staggered is unsuitable and it is therefore preferred to employ gills having their outlines conforming approximately to rectangles. By so providing one can arrange such gills so that those occurring on the adjacent tubes connected to a single pair of headers as a unit may be more or less continuous "with one another. Likewise the gill systems in one unit may in the assembled section be more or less continuous with those of vertically and laterally adjacent units.

A construction or form of gill suitable for employment herein is of a kind which has been genearlly described in British Patent Specification No. 337,236, the drawings of which clearly show ch`gills of adjacent tubes can be arranged to co-operate .to form rectilinear ducts at the bodies of the tubes and provide a heat exchanging surface which is wholly capable of being kept in clean condition. y

Referring again to the drawings', the specific construction of gilled tube' or, if desired, gillproviding casing or sleeve r, such as may be shrunk on a steel or other tube m, preferably comprises according to ,this invention parallel walls r1 arranged somewhat closer to one another than those shown in the prior specication above referred to; such walls may in some cases therefore not comprise tangents to the circular section of-the tube. In addition, if desired, the gills r2 may be carried inside. of the two wall n to provide more or less triangular webs ra running from the extremities of said walls into the cylindrical body n of the tube or sleeve r between saidwaus.

It will be understood that the overall width indicated by a: of the tubes with gills may be the same as the width of the headers indicated by latter 0.26.

1l or the former may be somewhat less than the apparatus.

When gilled sleeves or casings are used as in the drawings, these are preferably made in short sections, with a suitable form of spigot and socket Vjunction as indicated at s between pairs. The casings at the extremities of the tubes m are preferably provided with enlargements rs, recessed internally to provide sockets for the reception of spigot pieces t suitably attached to the inner sides of the headers e and f. In this way unequal expansion of a steel tube m and the assemblage of cast iron-sleeves r thereon can be accommodated, while the spigot pieces t protect the steel tubes against erosion Where they enter vthe headers.

It has been found that the tendency of gases to deposit dust, soot and the like in passages through which they flow is a function not only ofthe velocity of the gases, but also of what is known already in connection with water velocities as the hydraulic mean radius or the ratio of cross sectional area toperimeter of the passages. By calculation and experiment on the knowledge that the lower this factor the more deposition tends to occur, it is observed that a ratio eminently suitable for a high efficiency of heat transfer consistent with the substantial avoidance of deposition is about 0.3 or somewhat above, depending, however, upon other conditions such as moisture content.

In Figures l8 and 9 the diagrammatic views are to scale and show the gas passages a and 21 respectively according to the present construction and according to a known construction of staggered tube economizer; the hydraulic mean radius of the former being 0.39 and that of the The lines q and q1 represent the axes of adjacent tubes.

The effect of using a relatively high ratio is of course obtainable irrespective of whether an economizer or the like embodies any of the improvements already indicated. However, in a construction 0f heat exchanger wherein the gas ducts are such that the gases are not subject to tortuous movement, the draught losses are less for/a given speed of now, gas temperature remaining constant; and higher velocities together with concomitant high rate of heat transference and reduction of the size of the ,exchanger fora given duty are all practicable. The specific form of the present invention herein disclosed is improved in respect of all the aforesaid conditions by the adoption of rectilinear gas -ducts and the optimal practical hydraulic mean radius ,in combination.

The facility of cleaning `such tube arrangements, already indicated above, is well illustrated in the case when soot blowers are used.

. The actual jet of steam from a soot blower nozzle can come in contact with the whole of the heating surface which, of course is not the case with the staggered tube economizers; and in" the unfortunate event of the gaspassages becoming completely choked, with straight passages they ycan be brushed out, whereas with the staggered which follow, by the term hydraulic mean.

` radius is intended the ratio of cross-sectional area in square inches to perimeter in linear inches astypied by the gure' 0.3, which figure, of course, varies according to the scale of measurement which it' is convenient to employ. This ratio isdetermined in the construction specifically described by taking the area of a cross-section of the gas passages between the tubes in a plane parallel to the tube axes and dividing it by the perimeter of such area.

Modifications and additions may be introduced without departing from the scope of the invention as defined in the claims which follow.

I claim:

1. A tubular heat exchange apparatus comprising tube and header units the headers of which co-operate at opposite ends of the tubes, to form conduit-defining walls, all of said tube and header umts comprising vertically superimposed tubes and some of said units comprising one header having two compartments and tubes providing a plurality of parallel paths of flow from one of said compartments through some of said tubes to f the opposite header and parallel return paths through other tubes to the other compartment of said first header.

2. Apparatus as claimed in claim 1 including tube and header units in superposed relationship with two-compartment headers co-operating to form one of said walls, and detachable connections between vertically adjacent headers.

3. Tubular heat transfer apparatus comprisingAan open-ended framework, a section constituted by the lateral' juxtaposition inside said framework of tube units each consisting of -end headers connected by several tubes, which headers of different units co-operate to formwalls at the ends of the tubes, said framework being of a width greater than necessary to accommodate said tube section whereby to allow of lateral separation of said tube units into relatively inclined positions in preparation for withdrawall from said framework.`

4. An installation comprising a plurality of like elements each being an apparatus according to claim 3, said elements extending along a line running in the same general direction with their outer side walls, said elements being separated fromone another by a distance less than the length of the tube units but suiliciently great to enable tube units previously brought into said inclined positions in their respective frameworks to be withdrawn endwise therefrom. A

5. 4Apparatus as set forthin claim 3 in which the tubes are provided externally with gills for increasing the heating surface, said gills being of.

substantially rectangular construction and those of each tube co-operating with those of neighbouring tubes to subdivide the said conduit into substantially rectilinear passages.

6. A` tube unit for heat exchange apparatus consisting of an even number of tubes extending with their axes in parallelism in a single plane and connected at their opposite ends respectivelyto two oblong headers, one of said headers lhaving a single internal compartment receiving all' the adjacent tube ends, and the other header having internal partition means defining two separate compartments respectively receiving the opposite ends of one half of the tubes, and openings for the respective header compartments, the

tubes being provided externally with gills radiating outwardly to terminate substantially at planes 8. In a tubular heat exchange apparatus, 'a

plurality of tube units each comprising a row of tubes and a pair of headers connected respectively to opposite ends of said tubes whichheaders are adapted to be built together complementarily to co-operate in upright positions to form walls defining endwise a conduit traversed by said tubes, means extending-along the tubes in planes parallel to the axes of the latter, gills radiating at intervals from said means and so arranged as to co-operate therewith and with the corresponding parts of adjacent units of like construction to divide said conduit into a plurality of substantially rectilinear passages, which passages have a hydraulic mean radius of the order of 0.3 upwards.

9. In a tubular economizer, an assemblage of headers constituting two opposed walls of an upright gas conduit, tubes arranged in upright and horizontal rows and extending in parallelism across the said conduit from one of lsaid walls to the other, means extending along each tube in upright planes parallel to the tubes, and gills of rectangular form borne on opposite sides cf said means at intervals along the tubes, said means and gills of individual tubes coinciding respectively with the corresponding parts of vertically and of laterally adjacent tubes to subdivide said conduit into substantially rectilinear upright passages having a hydraulic mean radius of the order of 0.3 and upwards.

10. In a tubular economizer, tubes arranged in upright and horizontal rows and extending in Vparallelism across a gas conduit from one side thereof to the other, means extending along each tube in upright planes parallel to the tubes, and gills of rectangular form borne on opposite sides of said means at intervals along the tubes, said means and gills of individual tubes coinciding respectively with the corresponding parts of vertically and of laterally adjacent tubes to subdivide said conduit into substantially constant cross-section upright passages having a hydraulic mean radius of the order of 0.3 and upwards.

1l. A tubular economlzer having a gas conduit, tubes extending horizontally across said conduit in spaced rows, said tubes having means extending axially along their respective exteriors and gills radiating from said means at intervals along the tubes, the gills of the respective tubes approximating gills of adiacent tubes and said gills and means cooperating from tube to tube to sub-dividesaid. conduit into continuous upright JOHN NELSON DUDAS HEENAN.

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