US2215538A - Heat transfer device - Google Patents

Description

W. S. BLAUVELT HEAT TRANSFER DEVICE Sept. 24, 194-0.

Filed May 3, 1939 Warner: Bid

l provement in the transfer of heat from the heatbafiie is inserted, the areas of the constricted 55 preferably concentric therewith. Such baflie eleimmediately following the above restriction in-[ Patented Sept. 24, 1940 2,215,538

UNITED STATES PATENT OFFICE 7 2,215,538 HEAT TRANSFER DEVICE Warren S. Blauvelt, Troy, N. Y., assignor to Blauvelt Associates, Inc., Troy, N. Y., a corporation of New York Application May 3, 1939, Serial No. 271,485

4 Claims. (01. 138-38) My invention relates, in general, to an imment is preferably formed of cast iron or other provement in the transfer of heat through the good heat conducting material and which at the walls of a tube through which a first fluid flows same time has the characteristic of resisting and which is surrounded by a second fluid, heat corrosion and erosion' by the fluid flowing 5 being transferred through the walls of the tube through the tube. 6

either from the fluid within the tube to that The volume of gas is, of course, directly rewithout the tube or the reverse. lated to its absolute temperature, and its density,

The principal object of my invention is an under a given pressure, varies inversely'with its improvement in the transfer of heat through the absolute temperature. The pressure loss in pass- 10 walls of a tube from one fluid to another by the ing through a constricted opening Varies as the 10 use of a suitable baflle element disposed within square of its velocity and directly as its density, said tube through the walls of which heat is to and where the temperature of the gas to be be thus transferred. cooled varies over a wide range such as 2000,

A more specific object of my invention is an imin passing through a tube in which the multiple ed gases passing through a fire tube of a boiler openings through which the gas successively to the water surrounding the same although it is passes are successively reduced as the temperato be understood that my invention is not limited ture and volume thereof are reduced, or are sucs to this particular use. cessively enlarged if the passing gas is to be Other objects of my invention will appear in heated over a wide range and thereby greatly 20 the specification and the novel features thereof expanded. will be more particularly pointed out in the The baflle element l5 embodying my invention claims. is preferably disposed concentrically within the Y ihventien Will be be derstood by refertube In and in order to maintain the same in my ence to the accompanying drawing in which I such concentric position, the baffle is preferably 2 have illustrated a preferred embodiment therecast with a plurality of outwardlyextending arms of and in which or pins I8. In the embodiment of my invention 1 s a di a sect o al Vi w through illustrated, four such pins are extended out.- a fire tube of a boiler and Showing a ip e wardly near the lower portion of the baffle and heme e t. embodying y v i in front four other pins I81 extend outwardly near the 30 elevation, disposed in said tube and providing a upper end of the bafiie, the baffle conveniently series of constricted openings between the baflle being supported by a hook I!) and eye If. and the tube which, upwardly, are of successive- In the embodiment of my invention illustrated lypsmaller crosssectional area, and in Fig. 1, the successive enlargements 66 pro- Fig; 2 is a similar View through a baffle elegres'sively increase in diameter to form with the v35 ment in which the enlargements are all of the .tube lll constricted flow areas 20 which are sucsame size and the constrictions between said cessively reduced in the direction of flow of the enlargements and the associated tube would all gas in th tube, such areas being considerably have substantially the same areas. less than that of a tube section at that point 40 Like reference characters indicate like parts and producing an increase in the velocity of the 40 t 'u the dra-Wingas as compared with the velocity that would ob- Referring to the d w a fi st to F gtain if the baffle element were not present and I0 is & fi tube of boiler, the boiler being pother conditions remained the same. The edge resented by upper and lower tube sheets H and I2 of a given enlargement is defined by a line in a Provided With respective Openings and in plane generally perpendicular to the longitudinal v w h the respective ends of the fire tube are axis of the tube and to the general direction of welded or otherwise secured and sealed. A first th flow of gases through the tube and presents fluid which, i e Case O a boiler, is heated a sharp edge. Such constriction greatly reduces flows upwardly through the tube and the tube is the friction due to the flow of gas through each surrounded by a second fluid which, in the i1- restricted flow area resulting from the enlarge- ,60 lustrated embodiment of my invention, is water. ment of the baffle in that plane as compared with In accordance With y invention, a b fl e any restriction which continues for any apprement, indicated generally at I5, is disposed witbciable distance. The eddy currents which are in the fire tube in spaced relation thereto and promptly set up in the enlarged gas flow area crease the turbulence of flow and correspondingly increase the rate of heat transfer from the gases to the tube.

The effectiveness of heat transfer is still further increased by the passage of radiant heat either from the surface of the bafiie element to the surface of the tube and thence to the liquid surrounding it, or by radiation from the wall of the tube'to the surface of the baffle element. As the outer'surface of the bafiie element 15 is not in contact with the fluid surrounding the tube but is in contact with the fluid passing through said tube, the surface of said baflietends to assume the temperature of the fluid with which it is in contact, modified, however, by radiation from its surface to the surface of the tube if the fluid passing through the tube is at a higher temperature than the fluid surrounding the tube or by radiation to the surface of the baffie element from the surface of the tube if the fluid surrounding the tube is hotter than the fluid passing through said tube.

Where heat is to be transferred from a fluid surrounding tube It to a gas passing therethrough, the gases to which heat is to be transferred would be caused to flow downwardly through the tube Ill, the constricted flow areas between the enlargements of the baffle and the tube Ill being successively increased in the direction of the flow of gases.

The effectiveness of heat transfer of gases is further increased by the turbulence produced in the gases by the presence of the successive constrictions and enlargements of the ba flie. It is well known that when heated gases flow through a plain tube there is a film of gas molecules which may be considered substantially in contact with the inner surface of the tube and moving at a low velocity compared with the mean velocity of the gas passing through the tube, thus retarding, or interfering with, the heat transfer from the body of the gas to the tube. Whatever breaks up or reduces the thickness of such viscous film, or reduces the time of contact of the gas molecules in said film with the tube walls, tends to accelerate the heat transfer. The successive baffles, 16, which greatly constrict the flow area at their edges cause the advancing streams of gases which, flowing through the tube, are to be brought toward temperature equilibrium with the fluid surrounding the tube, to flow past said baffle edges at a suddenly increased velocity and to approach said constricted flow areas at a relatively abrupt angle with the wall of the tube, thereby greatly reducing the thickness of the viscous film of gas adjacent to the wall of the tube and increasing the turbulence of flow of said gases when approaching, when passing, and when receding from each of the said restricted flow areas between the outer edge of each baffle and the tube wall, thus facilitating the desired heat transfer. By making the portion 2i of the bafile element which defines the angle of recession in the flow of gas from each enlargement it more nearly parallel to the axis of the tube than portion 22 which defines the angle of approach, the pressure differential required to cause the gas to flow at any given velocity through a tube in which the baffle element is placed appears to be less than is required With other relationships be tween the angles of approach to and recession from the restricted flow areas at the outer edges of the successive bailles, with the wall of the tube.

The baffle element is preferably made hollow as indicated by dotted lines 23. The upper end ed through a wide temperature range. for fillets 26 which are preferablyformed at the of the battle may be provided with a plug 24 to which a hook l9 and eye I9| are attached and when removed, forms an opening through which the sand core may be removed.

While my invention is particularly adapted to facilitate heat transfer in a boiler, it is to be understood that it is equally well adapted to transfer heat in a recuperator, a condenser, or any other form of heat transfer. device" in which either a gas or a liquid'flows through a tube and in which the baffle element embodying my invention is placed. Furthermore, it may be used in the same way to transfer heat from a fluid, either liquid or gas which surrounds a tube to a fluid, either gas or a liquid which passes through the tube.

In the embodiment of my invention illustrated in Fig. 1 where there is a wide variation in the temperature of the gases in the tube, and where heat is to be transferred from said gases toa fluid surrounding the tube, the width of the zones located between the enlargements of the baffle are successively reduced in the direction of .the flow of the gas as the temperature and'consequently the volume thereof are reduced, the widest zone,

25, being located nearest the bottom of the bafile element where the gases are hottest, and the narrowest zone, 25a, being nearest the top of the baffle element where the .gases are coolest. On the other hand, where heat is to be trans- Within the tube, the width of the zones of the baffle should progressively increase in the direction of flow of gases if such gases are to be heatbottoms of the contractions, each zone is formed of two frustums, the larger base of each frustum being united to the larger baseof the next following frustum and the smallerbase of each frustum being joined to the smaller base of the next succeeding section. For example, the zone 25 comprises two frustums 25l and 252, the smaller base of the frustum 25| being joined to the smaller base of the following frustum 252 and the largerbase of the frustum 252 being joined to the larger base of the following frustum 253.

Where the range of temperature of a gas passing through a tube in which. the multiple baffle element embodying my invention is to be inserted is comparatively small, say or thereabouts,

there is little advantage in varying the cross sectional area of the constricted passages and in Fig. 2 I have illustrated, an embodiment of my invention which is suitable for use in such a situation and where the passages'b-etween the enlarged portions of the baffle and the surrounding tube are all of the same, or substantially the same, area. The baiile is, however, formed with alternate enlargements and constrictions in the same general way as that shown in Fig. 1 and will break up the viscous film which would nor- 'mally be located adjacent the inner "surface of the tube.

I have found in practice that the baflle element embodying my invention very greatly increases-- the heat transfer of gas passing through a fire tube to the water surrounding the same and experimental data indicates that with a suitable bafile embodying my invention installed in a boiler flue two feet long, the heat recovery in the flue as Except ferred from a fluid surrounding the tube to a gas ferred embodiment it is to be understood that the words which I have used are words of description rather than of limitation and that changes within the purview of the appended claims may be made without departing from the true scope and spirit of my invention in its broader aspects.

What I claim is:

1. In a heat transfer device, a tube, a single Y multiple bafile element disposed within and spaced from said tube to form a passage for the flow of a first fluid-and formed with a continuous outer surface, said bafile element having alternately circumferential crests and valleys for imparting turbulence to the first fluid in its flow through the said passage betweensaid bafile element and said tube, said tube being surrounded by an enclosure adapted to contain a second fluid.

2. In a heat transfer device, a tube, a single multiple bafile element disposed within and substantially concentric with said tube and spaced therefrom and forming therewith a passage through which a fluid may flow, the outer wall of said passage being substantially straight and uninterrupted in the direction of flow of said fluid, alternate portions of said baffle element having the general form of frustums of cones, the larger base of a given frustum being also the larger base of a following frustum, and the smaller base of a given frustum being united to the smaller base of the next following frustum, the angle of inclination of a given conical surface with respect to the axis of the frustum being greater with respect to the direction of flow of gases approaching the constrictions of the passage through the tube than the similar angle of inclination of the frustum leaving such construction.

3. In a heat transfer device, a tube, a single multiple bafile element disposed in said tube and. formed of frustums of cones, the larger base of a given frustum being also the larger base of the following frustum and the smaller base of a given frustum being united with the smaller base of the following frustum, said baflie being spaced from said tube to forma passage for the flow of a first fluid, two given frustums forming a zone and the width of the zones varying in the direction of the flow of said fluid, said tube being surrounded by an enclosure adapted to contain a second fluid.

4; In a heat transfer device, a tube the inner surface of which is substantially straight in the direction of its longitudinal axis, a single multiple bafile element disposed concentrically within and spaced from said tube to form a passage for the flow of a first fluid and formed with a continuous outer surface, said baiile element having alternately radially enlarged and radially reduced peripheral portions, the flow area between a given enlargement of said baffle and such tube being decreased at each such enlargement and increased following each such enlargement in the direction of flow of said fluid, and having the flow areas both at their enlargements and at their following reductions successively decreased and the distance between such reductions in flow area also successively decreased, said tube being surrounded by an enclosure adapted to contain a second fluid.

WARREN S. BLAUVELT.

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