Heat Exchanger

Abstract

A heat exchanger has wall means defining an enclosed space, at least one extending surface heat transfer member defining in cooperation with the wall means at least two flow channels in the enclosed space separated by the heat transfer member and contiguous particles packed in at least one of the channels to rigidly support the walls of the channel while permitting fluid flow through said channel.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention:

The present invention generally appertains to new and novel improvements in heat exchangers and more particularly relates to new and novel improvements in the heat transfer surface construction of heat exchangers.

2. Description of the Prior Art:

Conventional heat exchangers are constructed from shells and tubes or pipes and such shell and tube exchangers have a long history of successful operation. They have many advantages, such as ease of cleaning and repairing, and are in widespread use. However, in spite of the many advantages and wide acceptance of such shell and tube exchangers, there are a number of problems associated with their design, manufacture and use. Some of the most serious of these problems are:

1. The joints in such exchangers are expensive to make and are not entirely dependable, since they have a tendency to leak. The integrity of the joints depends upon the physical properties of the tube material and upon the skill of the assembler with the range of useful tube materials being limited and assembly and repairs being expensive.

2. The tube walls must be at least thick enough to withstand the pressure, resist corrosion and establish a good tube/sheet joint which, therefore, sets a minimum wall thickness for various materials. This adds to the cost of fabrication and repair.

3. The tubular exchanger is basically a cross-flow unit with baffles being required to redirect the shell-side fluid back and forth across the bundle in order to achieve counter-flow between the fluids. As a consequence, there are many mechanical joints between the tubes and the baffles and such encounter vibration damage.

4. The range of velocities which can be accommodated is limited, with many times multi-pass arrangements being necessary to obtain the desired fluid velocities.

SUMMARY OF THE INVENTION

The present invention envisions the design and construction of heat exchangers and heat transfer devices from sheet material which is far less expensive than tubes, pipes and shells. The sheet material forms the boundaries for flow channels with at least one of the channels being packed tightly with packing material comprising particles of generally uniform and preferably spherical size and shape. The fluid pressure inside such packed but fluid-traversable channel will be less than the fluid pressure in the adjacent unpacked and unobstructed channel with the packing supporting the walls of the flow channel against the external pressure. The supported sheet material constitutes a heat transfer member that can be fashioned into a variety of flow channel shapes and forms.

Of course, the flow path through the packed channel will be tortuous and the fluid velocities must be kept low to avoid excessive pressure drop. Therefore, the supported surface exchanger is particularly useful where the heat transferred from a unit volume of fluid in the packed channel is high as compared to the heat transferred to a unit volume of fluid in the unobstructed channel. Such situations regularly exist where a phase change is occurring in the packed channel as in condensing or boiling, and where heat is exchanged between a gas in the unobstructed channel and a liquid in the packed channel. Condensers, evaporators and liquid-air type exchangers are typical general applications.

Several applications which have been recognized as being particularly attractive are multi-stage flash evaporator for seawater desalting, vertical packed channel evaporator for seawater desalting, water/air exchangers for ` dry ` cooling towers and water coolers, corrosive fluid exchangers and fluid concentrators.

As mentioned above, there is a significant material cost advantage presented by the sheet material concept of the supported heat transfer surface, according to this invention. In addition, the sheet material of the supported heat transfer surface is not a pressure carrying member but simply transfers pressure to the supporting and packing particles. In contradistinction, the tube wall in a tubular exchanger must be sufficiently thick to withstand the pressure differential, withstand corrosion and have sufficient material to provide a good joint with the tube sheet. With the sheet material, there will be no tube sheet joints. While the sheet material must withstand corrosion, the thickness of the sheet material can in most cases be much less than the tube wall thickness of corresponding tubular exchangers. In such tubular exchangers the tubing material must have sufficient ductility so as not to crack or split when the tube is rolled into the tube sheet. It must have a yield strength which can facilitate the rolling-in process. On the other hand, the supported heat transfer surface sheet material does not have to meet stringent yield, ductility and high-strength requirements and a variety of materials which are not suitable for tubular exchangers can be used as the materials for the present invention. In fact, plastics or other materials, which have special qualities such as corrosion resistance or very low cost, can be used because of their cost and process advantages.

Tube sheet joints are expensive to make and tube sheets, baffles and tube supports are also expensive. Consequently, the cost per square foot of a completed tube bundle is almost twice the cost of the initial tube. With the present invention, the supported heat transfer surface requires only a minimum of welds, bends and forming and its fabrication costs are well below that of tube bundles, which require skilled labor in their layout. With the supported heat transfer surface simple machinery can be used in the fabrication, such as sheet metal breaks and automatic welders and less skilled labor can produce the units in less time than required in the fabrication of the usual tubular exchangers.

While the particles are primarily intended to serve a structural function with external pressure being transmitted to the packing constituted by such particles, it is envisioned that such particles can contribute to the transfer of heat, and depending upon conditions, such contribution may be substantial and important. Generally, however, the material of the particles depends upon availability. Such materials as coarse sand, smooth gravel or spherical pellets of concrete, plastic or ceramic may be used, providing they are unaffected by the heat transfer fluids and are strong enough to resist crushing and erosion.

Selection of the composition of the heat transfer sheet material will be based upon the service and operating conditions. Sheet material thickness should generally be based on pressure differential, cost, strength, handling ease and corrosion and erosion requirements. Typical thicknesses of the heat transfer sheet material may be in the range from about 10 to about 30 mils. Since strength of the sheet material is less important than is tube wall strength in conventional tubular exchangers, it may be economical to use a thinner but more noble material. For example, it may be desirable to use thin titanium sheets to construct desalting equipment. In exchangers operating at less severe temperature and pressure conditions plastic sheet material may be employed and, for highly corrosive services, materials such as Teflon sheet may be advisable.

Thus, the primary object of the present invention is to provide a heat exchanger or heat transfer device wherein the channels for the flow of fluids therethrough are formed from sheet material with certain of the channels being packed with particles that permit flow of fluid therethrough while rigidly supporting the walls of the channels against external pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of a fluid-fluid counterflow heat exchanger constructed in accordance with the principles of this invention;

FIG. 2 is a side elevational view of the exchanger of FIG. 1;

FIG. 3 is a transverse vertical sectional view taken on line 3--3 of FIG. 1;

FIG. 4 is an end elevational view of the exchanger of FIG. 1;

FIG. 5 is a transverse vertical sectional view taken on line 5--5 of FIG. 4;

FIG. 6 is a horizontal, cross-sectional view taken on line 6--6 of FIG. 2;

FIG. 7 is an enlarged perspective showing of the interior sealing and closure structure of the exchanger shown in FIG. 1;

FIG. 8 is a fragmentary enlarged side view of a portion of the packed channel showing the packing particles in elevation;

FIG. 9 is a detailed elevational view of the packing particles arranged in a square pitched pack;

FIG. 10 is a sectional view taken on line 10--10 of FIG. 9;

FIG. 11 is a detailed elevational view of the packing particles arranged in a triangular pitched pack;

FIG. 12 is a sectional view taken on line 12--12 of FIG. 11;

FIG. 13 is an enlarged detailed perspective view of a fragmentary portion of the channel structure of the exchanger, showing the packed and unpacked channels with the latter lying between the illustrated packed channels;

FIG. 14 is a side elevational view of a condenser formed in accordance with this invention and embodying the concept of the packed channels thereof;

FIG. 15 is a transverse vertical sectional view taken on line 15--15 of FIG. 14;

FIG. 16 is a side elevational view of a counterflow heat exchanger constructed in accordance with the principles of the present invention and embodying the concept thereof; and

FIG. 17 is a transverse vertical sectional view taken on line 17--17 of FIG. 16.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now more particularly to the accompanying drawings and initially to FIGS. 1 to 7, the reference numeral 10 generally designates a fluid-fluid counterflow heat exchanger embodying the principles of the present invention. The exchanger 10, as shown especially in FIG. 3, is formed from sheet material and includes a bottom wall sheet member 12, a U-shaped cover or container wall member 14 and a corrugated sheet member 16 which is the heat transfer member. The bottom plate or wall 12 serves as the bottom of the exchanger and is provided at opposite ends with transversely extending trench-like headers 18 and 20 that constitute the inlet and outlet headers and to which connections 22 of a suitable type are attached.

The bottom plate 12 has side edge flanges 24 that complement the laterally outstanding side edge flanges 26 provided on the side walls 28 of the cover member 14 with such flanges being secured together by bolt assemblies 30. The intermediate corrugated sheet member 16 also has outermost side walls 32 and 34 provided with lateral edge flanges 36 which are positioned between the flanges 24 and 26 and clamped therebetween by the bolt assemblies 30 so as to mount the sheet member in place.

The sheet member 16 is a thin wall extended surface sheet that is formed in serpentine fashion with a number of parallel loops or bends 38 each defined by parallel spaced apart walls 40 and 42 closed at their lower ends 44 by closed integral bight portions or arcuately closed ends 46 and being open at their upwardly facing open upper ends 48 which are spacedly confronted by the overlying top wall 50 of the cover sheet 14. The zig-zag arranged and formed loops or bends 38 extend spacedly from the top wall 50 of the cover sheet to the bottom plate 12 and define channels 52 with the cover member and channels 54 with the bottom plate, as can be appreciated from FIG. 3. The channels 52 are open to the cover member and closed to the bottom plate while the channels 54 are open to the bottom plate and closed to the cover member or sheet 14.

The adjoining front and rear edges of the side by side spaced apart walls of adjoining bends or loops 38 are seam jointed or welded together, as at 56 in FIG. 6, so that they cooperate to form the closed ends of the channels 54 which are only open to the headers for the flow of for example a condensible gas or condensed liquid therethrough with warm gas or liquid entering the inlet header 18 and cool liquid leaving the outlet header 20. The condensible liquid is cooled in its passage between the headers by air flowing through the channels 52 in a path longitudinally of the exchanger 10. Screens or the like 19 are positioned at the top of the inlet header 18 and the outlet header 20 to restrict the particles to the packed channels 54 while permitting fluid to pass freely from the inlet header 18 to the packed channels 54 and hence to the outlet header 20.

The condenser channels 54 are packed with particles 58 that support the sheet 16 on its inside or on the low pressure side thereof with the packing particles supporting the walls of the flow channels 54 against the external pressure of the air flowing in the channels 52. The fluid pressure in the air flow channels 52 is greater than the fluid pressure in the adjacent condenser channels 54.

Two supported and adjoining channels 54 are shown in FIG. 13 in relation with an intermediate unobstructed flow channel 52 with the particles 58 being packed into the channels 54 so as to support the thin wall sheet 16 and maintain the rigid formation of the low pressure channels 54. The particles, as will be more particularly described, are spherical in shape and may be packed in a particular formation so as to present a uniform flow path through the channels 54. As shown in FIG. 13, the fluid pressure within the packed channels 54 of width S is less than the fluid pressure within the unobstructed channel 52 of width W. Since the packing is tightly packed within the flow channels 54 of width S, the differential pressure actually presses the packed channels into very rigid form. Furthermore, the pressure differential can be substantially greater than could be supported by a tube of diameter S and tube-wall thickness T.

The packing material can be of many forms. As illustrated, the particles 58 are solid ball elements formed from ceramic or concrete. The particles are preferably generally spherical and of uniform size. Non-uniform size particles will tend to pack more solidly and reduce the porosity or flow characteristic of the channels 54. Glass or plastic beads may be used as well as screened coarse sand particles and pebbles. The size of the particles is not critical but, in general, particles of one-tenth to one-half inch in diameter are preferred.

Various packing arrangements of the spherical packing particles or elements 58 may be utilized. For example, as shown in FIGS. 9 and 10, the particles or spherical elements 58 are packed in the square pitched pack 60. In FIGS. 11 and 12, the particles or spherical elements 58 are arranged tightly in a triangular pitched pack 62. In either of such arrangements or in any other packed arrangement, the particles are held tightly against accidental shifting and rigidly support the thin walled extended surface sheet 16. The particles primarily serve the function of supporting the extended surface sheet 16 but may also contribute to the transfer of heat as a secondary function.

The dimensions of S and W can be varied and adjusted to achieve a number of desirable characteristics, i.e. different channel flow areas and hence different velocities, heat transfer coefficients and pressure drops. Thus, S or W can be varied from point to point where a wider channel is formed to distribute the fluid more evenly into the lower flow channels 54. It should also be noted that various designs, such as fluted surfaces, can be embossed or formed on the sheet member 16 to enhance the heat transfer properties of the supported surface sheet 16. The folded sheet member 16 can be fashioned into a variety of flow channel shapes and many kinds of heat exchangers can be formed from these shapes.

The dimensions S and W can be varied at any point in the exchanger provided that their sum is maintained constant. However, if the outside dimensions of the exchanger are varied appropriately, the sum of W and S need not be kept constant. Thus, the flow paths or channels for the two fluids can be varied to suit conditions.

The width of the flow space W, as shown in FIG. 13, between the packed channels S typically could be about one-half inch although it may be several times larger or smaller than this value. The hydraulic radius and hence the heat transfer and hydraulic characteristics of the flow channel are similar to those of a tube or pipe with a diameter of twice W.

The width S of the packed spaces, as shown in FIG. 13, between the sheet material of the heat exchanger should be such that fluid velocities within these spaces are reasonable. The porosity or fluid traversability of such spaces will vary between 10 and 40 percent depending upon the nature of the packing and its approach to perfect spherical shape. Typically, the width of the space S could also be about one-half inch.

The packing particles should be of uniform size and generally spherical. Non-uniform size particles will tend to pack more solidly and reduce the flowability characteristic or porosity of the packed spaces since the smaller particles, in such case, would tend to fill the voids between larger particles. Thus would not be desired in most cases. As shown in FIGS. 9 and 11, the uniform spheres can be packed in packing arrangements of square pitch pack and triangular pitch pack, such being illustrative of types of packing arrangements. Usually three to six layers of particles would be typical. Thus, for example, when W is one-half inch in width, the particles would range from about one-fifth inch diameter (three layers) to one-tenth inch diameter (six layers).

In FIGS. 14 and 15, an alternate arrangement is shown wherein the condenser 64 has a vapor inlet 66 and a liquid outlet 68 with the vapor/liquid flowing in the unobstructed tortuous channel 70, the air flow channels 72 being filled with tightly packed particles that support the channel defined by a pair of spaced extended surface sheets. The packed particles are maintained in the desired location by screen or the like end walls 80 which while maintaining the particles within the device do not materially restrict the flow fluid therethrough. In FIGS. 16 and 17, a counterflow heat exchanger 74 is shown with the same having unobstructed fluid flow channels 76 and particle air channels 78 defined by the supported extended surface sheet member 79.

Claims

I claim:

1. A heat exchanger comprising wall means defining an enclosed space, at least one thin wall non-pressure carrying extended surface heat transfer sheet member defining in cooperation with said wall means at least two flow channels, one of said flow channels comprising a condenser channel normally operating at a lower pressure than the pressure in said enclosed space, means supporting the thin wall sheet member and maintaining the flow channels including the low pressure condenser channel in rigid formation, said supporting means comprising contiguous particles packed in at least the low pressure condenser channel while permitting fluid flow through the channels.

2. A heat exchanger comprising wall means defining an enclosed space, at least one thin wall non-pressure carrying extended surface heat transfer sheet member defining in cooperation with said wall means at least two flow channels, one of said flow channels normally operating at a lower pressure than the pressure in said enclosed space, means supporting the thin wall sheet member and maintaining the flow channels in rigid formation, said supporting means comprising contiguous particles packed in at least the low pressure channel while permitting fluid flow through the channels.

3. A heat exchanger comprising wall means defining an enclosed space, at least one thin wall non-pressure carrying extended surface heat transfer sheet member defining in cooperation with said wall means at least two flow channels, one of said flow channels comprising a condenser channel normally operating at a lower pressure than the pressure in said enclosed space, means supporting the thin wall sheet member and maintaining the flow channels including the low pressure condenser channel in rigid formation, said supporting means comprising contiguous particles packed in said channels and said enclosed space while permitting fluid flow through the channels.

4. A heat exchanger as defined in claim 2 comprising a pair of folded thin wall extended surface heat transfer sheet members in spaced relation and defining in cooperation with said wall means two or more flow channels in said space.

5. A heat exchanger as defined in claim 2 wherein more than one flow channels are operating at the lower pressure than are other flow channels and each of the flow channels operating under the lower pressure are packed with the contiguous particles.

6. A heat exchanger as defined in claim 2 wherein the contiguous particles are generally spheroidal and of uniform size.

7. A heat exchanger as defined in claim 6 wherein the contiguous particles are generally in a square pitch pack.

8. A heat exchanger as defined in claim 6 wherein the contiguous particles are generally in a triangular pitch pack.