US3458942A - Heat exchanger - Google Patents

Description

1969 I E. J. MARTIN ET AL I 3,458,942

HEAT EXCHANGER Filed April 20. 1967 2 Sheets-Sheet z INVENTORS non/D RHDC L IF'FE 701 M "iToRNEYs United States Patent ()ffice 3,458,942 HEAT EXCHANGER Edward J. Martin, London, and Bryan R. Radcliffe,

Epsom Downs, England, assignors to A.P.V.- Kestner Limited, Greenhithe, Kent, England Filed Apr. 20, 1967, Ser. No. 632,401 Claims priority, application Great Britain, Apr. 20, 1966, 17,330/ 66 Int. Cl. F26b 17/00 U.S. CI. 34-57 11 Claims ABSTRACT OF THE DISCLOSURE In a heat exchanger of the type in which particulate material to be heated or cooled is entrained in a fluid heat transfer medium, the passages of the exchanger are folded to reduce the overall height and the bottom bends are given a special cross-section to prevent deposition of entrained particles.

Background of the invention This invention relates to heat exchangers, particularly of the type in which particulate materials are entrained in a fluid medium which is hotter or colder than the temperature of the particulate material. A preferred heat transfer medium is air, which when hotter than the material is used to dry the material, and which when cooler than the material is used to cool it. By particulate throughout this specification is meant particles of solid or plastic material.

Known driers or coolers use a vertical tube at the base of which the material to be dried or cooled is entrained in a stream of air at the appropriate temperature, and at the upper end of which the warmed or cooled material is separated from the air stream. These driers or coolers have the disadvantage that in order to have the material in contact with the heat transfer medium for a suflicient length of time, the height of the tube has to be very long, frequently of the order of sixty feet.

Summary of the invention A heat exchanger comprising a plurality of parallel vertical passages interconnected at their ends by bends to form single folded passage, the inlet end of the passage being adapted to be supplied with particulate material to be treated and with a heat transfer medium at a chosen temperature, and the outlet end of the passage being fitted with means for separating the treated material from the heat transfer medium, in which the curvature of each bottom bend increases to a maximum and then decreases in passing from one sidewall of the passages interconnected by the bend, to the other sidewall.

One example of a drier of the present invention is illustrated in the accompanying drawing, in which:

FIGURE 1 is a diagrammatic sketch of one form of drier of the invention;

FIGURE -2 is a cross-section, to a larger scale, of one of the bottom bends of the drier shown in FIGURE 1, and

FIGURE 3 is a drawing illustrating the mathematical form of the bend of FIGURE 2.

The drier shown in the drawing includes a fan 2 for air, the output from the fan passing through a heater 4 before entering the inlet 6 of a Venturi tube 8. The throat 10 of the Venturi tube is of circular cross-section, and a feeder 12 is arranged to supply particulate material at a desired rate to the throat. The feeder 12 may be in the form of a chute, a screw feeder, or a pneumatic injector. The rate of feed of material, and the rate at which air is fed to the Venturi tube, are adjusted so that all of the 3,458,942 Patented Aug. 5, 1969 material fed to the throat 10 becomes entrained in the air stream and moves with it.

The outlet 14 of the Venturi tube is in the form of a divergent adapter of which the cross-section changes from being circular at the end next to the throat 10, to rectangular at its outlet end at which it is connected to the inlet of a folded tube assembly 16. This assembly comprises a plurality of vertical sections of tube connected by bends. The bends 18 at the top of the tubes are simple radiused bends, whereas the bends 20 at the bottom of the tube sections are shaped to prevent entrained particulate material being deposited at the bends.

It has been found that if the bends 20 are simple radiused bends, some of the material in the air stream is decelerated to such an extent that it cannot be supported by the air stream and becomes deposited in the bend. The effect of such deposited material is to make the air stream turbulent to such an extent that the rate of deposition of entrained material is accelerated until the bend is substantially completely blocked. It has been found by making the curvature of the bends 20 increase substantially uniformly before reaching a maximum after which it decreases smoothly until it merges into the substantially Zero curvature of the sidewalls of the upright tubes, the air stream plus entrained material is slowed uniformly while being turned through 180 and is then accelerated without any of the entrained material becoming deposited in the bend.

It has been found that a preferred form of cross-section of the bend is that of a conic section having its major axis vertical and displaced to one side of the centre wall of each bottom bend.

Each bend is made by inserting a moulded member 30 between two sidewalls 32, securing it to them by welds or other means. The distance of member 30 below the bottom of the centre wall 34 is determined accurately before the member 30 is secured in position.

The cross-sectional shape of bend 20 is preferably that of a parabola with its major axis parallel with the longitudinal axes of the ducts. However, it is envisaged that other forms of conic section, such as a part-ellipse or a hyperbola, would be effective. The invention would also work, but possibly with reduced efficiency, if the major axis were inclined to the vertical.

A preferred form of parabola would satisfy the equation l3y=x While this equation could be varied, the two limits for successful operation are 9y=x and 20y=x It is also important that the major axis of curve 20 be displaced laterally of the centre wall 34. This distance is shown as B in FIGURE 3. If W is the duct width, then B should be=0.3W.

The parameter C is also important, and should lie within the limits 0.5 8W and 0.91W.

For the given parabola l3y=x distance A, i.e. the nearest point of the curve 20 to the centre wall, is 0.45W, and C is 0.68W.

In FIGURE 3, the curve 20 intersects the left-hand wall 30 at x=l.3W, the right-hand wall at x=0.7W, regard being given to signs.

Reverting to FIGURE 1, at the top of the last vertical tube section 22, the air and entrained material pass to a cyclone separator 24, from which the carrier air is extracted by a fan 26, and the dried material emerges from the outlet 28 of the separator.

It will be appreciated that if it is desired to increase the time luring which the particulate material is in contact with the heat exchanger medium, it is possible to arrange for this, without increasing the overall height of the exchanger, by adding another U-shaped portion of tubing and interconnecting it by means of bends 18 and 20.

Although the heat exchanger of the embodiment illustrated is shown as having all the vertical tube sections lying in the same plane, it is within the scope of the present invention for each vertical portion 22 of the tubing to be displaced by 90 from the vertical plane containing the centre line of the two preceding vertical tube sections 22. This can be repeated more than once in a heat exchanger so that, if desired, the outlet 28 of the separator can be adjacent to the feeder 12. With this arrangement, it is preferred that the cross-sectional shape of the tubes 22 be square. With both this modification and with the original embodiment the time of contact of the materials with the medium can be prolonged at the expense of additional fioor space without an increase in the overall height of the exchanger. The constants given apply when the dimensions are measured in centimetres. For other scales of measurement other constants would be used.

We claim:

1. A heat exchanger comprising a plurality of parallel vertical tubular sections, a plurality of 180 bends connecting the ends of said tubular sections together in series to form a single folded passageway having bottom bends, inlet means for supplying a particulate material to be treated and a fluid heat exchange medium to one end of said passageway, and outlet means connected to the other of said passageway for recovering the treated particulate material, wherein the cross section of the bottom wall of each bottom bend taken vertically is a conic section asymmetrically disposed relative to the two tubular sections joined by said bend, the major axis of the conic section being displaced downstream of the junction of the joined tubular sections thereby to provide an acceleration of the flow stream thereat.

2. A heat exchanger according to claim 1, in which each of said bottom walls is parabolic.

3. A heat exchanger according to claim 2, in which the equation of the parabola lies within the limits 9y=x and 20y=x 4. A heat exchanger according to claim 2, in which the adjacent vertical tubular sections have a common dividing wall.

5. A heat exchanger according to claim 4, in which the major axis of the curve of each bottom wall is displaced downstream to one side of said common dividing wall a distance equal to 03W, where W is the width of said tubular sections.

6. A heat exchanger according to claim 4, wherein the longitudinal displacent of the lower end of said common dividing wall from the origin of the parabola lies within the limits 0.58W and 0.9lW, where W is the width of each tubular section.

7. A heat exchanger according to claim 4, wherein the minimum spacing of the curve of each bottom wall from the common dividing wall is 0.45W, where W is the width of each tubular section.

8. A heat exchanger according to claim 1, in which the cross-section of each tubular section is rectangular.

9. A heat exchanger according to claim 1, in which the top bends are simple radiused bends.

10. A heat exchanger according to claim 1, in which the axes of all the vertical tubular sections lie in the same plane.

11. A heat exchanger according to claim 1, in which the axes of the vertical tubular sections lie in at least two planes which intersect along a vertical line.

References Cited UNITED STATES PATENTS 1,866,768 7/ 1932 Haris. 2,419,245 4/1947 Arveson. 2,819,890 1/1958 Rosa et al. 3,048,930 l/l962 Holzrichter et al.

FOREIGN PATENTS 898,831 6/1962 Great Britain. 248,062 4/ 1947 Switzerland.

FREDERICK L. MATTESON, JR., Primary Examiner HARRY B. RAMEY, Assistant Examiner

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