Heat Exchanger

Abstract

A heat exchanger having an externally finned pipe in which a first heat exchanger fluid flows, with the fins lying in a plane essentially perpendicular to the axis of the pipe, a length of said finned pipe being enclosed within a casing so that the walls of the casing are essentially adjacent to the fins at least at two opposed generating lines, and the inner space of said casing serving for the flow of a second heat exchange fluid, whereby the latter is compelled to flow substantially at a right angle to the axis of said pipe.

Description

BACKGROUND OF THE INVENTION

In heat exchangers between two different fluids A and B separated by a wall, if the heat exchange through convection between fluid A and the wall is more difficult than that between the wall and the fluid B, for example because of the greater viscosity of the fluid A, the solution is well-known of resorting to a separation wall that has a more extensive surface in contact with fluid A than that in contact with fluid B. This is achieved for example by equipping the surface in contact with fluid A with fins; particularly providing a pipe through which fluid B flows with external fins lapped by fluid A. But the efficiency of a heat exchanger using a pipe of this type is rather low if fluid A, through increased viscosity due to cooling, ceases to flow within the spaces between the adjacent fins and the subsequent fluid passes over this non-moving stratum without coming into contact with the finned surface and without appreciably being cooled.

OBJECT AND SUMMARY OF THE INVENTION

The object of this patent application is to achieve a heat exchanger using a pipe finned externally, with the direction of the fins being essentially perpendicular to the axis of the curve generated by the pipe, through which condition the velocity of the fluid A is activated in the above-mentioned spaces, and thus the thermal exchange is substantially improved as a result of this activation of the velocity. It is obvious that an external energy is required for this activation to offset the load losses of either viscous or turbulent type, energy furnished to liquid A by a circulating pump; but the proportioning of the proposed exchanger can be made optimal in the individual case so as not to require an excessive head which can therefore be taken care of with a normal circulation pump. The advantages of the exchanger according to this invention, in relation to a conventional exchanger, consist first of all in a decisive reduction in the exchange surface required and therefore in the weight, dimensions and cost; but also in a greater quickness of response since the thermal inertia of the exchanger according to the invention is rather low; further, in this exchanger the danger of leaks of one of the fluids into the other through the separating wall is avoided; a further characteristic of the present exchanger is, in fact, that of using a finned pipe through which fluid B flows located within a casing, while fluid A within said casing flows on the outside of the finned pipe; the finned pipe being constructed in accordance with current technology in a single piece and without welding, internal leaks are impossible; the only possibility for leakage of fluid A would be toward the exterior at the point where the two ends of the abovementioned pipe pass from the interior of the casing to the exterior; a possibility which, for that matter, can be easily excluded by using, for example, rubber or synthetic seals.

The casing which contains the finned pipe is, according to the invention, constructed with two opposing walls which adhere to the crest or form of the finned pipe, so as to obtain a reduction in the section concerned with the flow of fluid A, without causing the load losses to rise to the point of requiring an excessive increase in the power absorbed by the circulating pump.

The proposed solution produces an improvement in the thermal exchange between the fluids not only because the increase in velocity of fluid A prevents the danger of non-flow, but also because, fluid A being obliged to pass predominantly within the spaces between the fins, the reduction of thickness of the fluid current which laps the finned surface assures an efficient cooling of the entire contents. In fact, in laminar flow the cooling of the various borders or fillets by fluid A occurs through conduction and the fluid borders which cool by contact with the finned surface cool those of the over-lying strata all the more rapidly the smaller the thickness of the fluid mass. From that comes the possibility of reducing the distance of flow of fluid A and therefore the dimensions of the exchanger inasmuch as the dwell time is diminished, that is, the time necessary for the parts of the fluid borders cooled by the finned wall to cool through contact with the over-lying ones.

With a finned pipe having a rectilinear course within the casing and with a casing having a substantially parallelepiped form, the two opposing walls of the casing which adhere to the crest of the fins can be flat and essentially parallel; but, in order for fluid A to be guided between the spaces of the fins for a greater distance, it is well for the two opposing walls of the casing to adhere to the crest of the finning of the pipe for a discrete distance along the circumferential line of the crest of the finning; in this case, in the zone of contact with the crest of the finning, the surface of the casing assumes an essentially cylindrical form coaxial with the axis of the finned pipe.

The same result is obtained if, in the spaces between the flat walls of the casing and the crests of the fins of the pipe (where the crests are not near the walls) there are placed elements shaped essentially triangularly (with the sides of the triangle possibly curved) with an axis having a course parallel to the axis of the finned pipe.

In reference to the extent of the capacity and thermal exchange desired, a modification foreseen for the exchangers above-described can be advantageous; within the casing which contains at least one finned pipe, there can be arranged suitable deviating baffles perpendicular to the axis of the pipe itself (possibly obtained by modifying only the form of the casing), placed above and below the pipe in the direction of flow of fluid A and conveniently staggered, so that fluid A is compelled to lap successively various zones axially adjacent to the finned pipe following an essential sinusoidal or better a zig-zag course.

Due to its characteristics, the exchanger according to the invention has proved to be suitable in many installations, but particularly in motor-vehicles, in which it is necessary to effect a heat exchange between the lubricating oil and the cooling water of the motor, and where it can happen that spaces of particular form or dimensions are available in which it would be impossible to install a conventional exchanger which is too big and too heavy.

The exchanger according to the invention is composed of a pipe in which the first of said liquids flows and which is equipped with external finning lying in a plane essentially perpendicular to its axis, said piping having one of its sections contained within a casing whose wall is essentially adjacent to said finning at least at the point of two opposite generated lines of said piping, the space enclosed within said casing constituting the passage for the second of said liquids which moves within said casing principally in a direction at a right angle to said piping.

The advantages and characteristics of the exchanger according to the invention will be better understood from the possible embodiments of the invention illustrated in the attached drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view taken along line I--I of FIG. 2;

FIG. 2 is a view taken along line II--II of FIG. 1;

FIG. 3 shows a modified exchanger along line III--III of FIG. 4 in section along line III--III of FIG. 4;

FIG. 4 is a view taken along line IV--IV of FIG. 3;

FIG. 5 is a view in section along line V--V of FIG. 3;

FIG. 6 shows an axial cross-section of an exchanger constructed with a finned pipe having it axis wound in spiral form;

FIG. 7 is a partial view along line VII--VII of FIG. 6;

FIG. 8 is a part of an axial section of a variation of the exchanger of FIG. 6; and

FIG. 9 is a part of an axial section of the exchanger of FIG. 6 further modified.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In FIGS. 1 and 2 are indicated a finned pipe 10, with the direction of the fins being perpendicular to the axis of the pipe constructed in a single piece and, in this particular instance, shaped in the form of a U, a casing 11 contains the finned pipe, and 12 and 13 denote the smooth terminal parts of the pipe, outside the casing, to which are attached with seals the inlet and discharge pipes respectively of the cooling fluid B, and the pipes are not shown in the figures. Indicated 14 and 15 are the two finned branches with a rectilinear axis inside the casing and 16 the connecting elbow between the two branches outside bottom wall 17 of the casing, and the elbow is also preferable smooth. Casing 11 has one wall, indicated 18, which is movable, suitable for facilitating the cleaning operations, consisting of a flange joined in a conventional manner (not shown) to the corresponding counter-flange of the body of the casing using an in-between gasket 38. The two branches 14 and 15 are welded to the wall 17 of the casing and connected with a gasket seal to flange 18 by means of rings 20 and 23 at the point of passage from the inside of the casing to the outside.

In wall 22 is machined a hole in which inlet pipe 21 is welded for the cooling of fluid A, and in wall 19 a hole in which is welded the outlet pipe for fluid A.

Arrows 25 and 26 indicate the direction of the flow of fluid B within the finned pipe 10, arrows 27 and 28 indicate the direction of movement of the fluid A within the casing 11 where it is effectively cooled since walls 29 and 30 of the casing adhere to the crests of the finned pipe, and the fluid is forced to pass predominantly within the spaces between the fins.

In fact, walls 29 and 30 of the casing 11 are formed in the zone of contact with the crests of the fins of the pipe 10 so as to assume an essentially cylindrical form coaxial with the axis of each of the two branches 14 and 15 with the advantage that, fluid A being guided between the spaces within the fins for a more extensive distance, a good heat exchange between fluid A and fluid B is achieved.

The exchanger shown in FIG. 3 is constructed with a pipe 32 consisting of a single finned section 37 inserted within a casing 39; finned pipe 32 has its end parts 33 and 34 smooth extending outside of walls 35 and 36 respectively of casing 39; seal rings 45 and 46 are located at the point of passage from the inside of the casing to the outside. The inlet and discharge pipes of fluid B joined to ends 34 and 33 of the finned pipe are not shown, but arrows 41 and 40 indicate the direction of flow of fluid B within the finned pipe 32.

The walls of casing 39 are shaped in the zone of contact with the crests of the fins of the section 37, so as to assume an essentially cylindrical form coaxial with the axis of the finned section, and contain recesses 42 through which they adhere to the crests of the fins blending with the waved zones, but predominantly remain away from the crests of the fins so as to form the cavities indicated with 53.

FIGS. 4 and 5, which show two views of the exchanger, sectioned respectively along lines IV--IV and V--V of FIG.3, clarify the detailed form of the casing.

To the walls of the casing are welded pipes 43 and 44 for the inlet and outlet of fluid A, with arrows 47 and 48 indicating respectively the direction of movement of fluid A at the inlet of the casing and at the outlet of same.

The alternating of cavities and recesses in the walls of the casing, located in the axial direction and suitably baffled, obliges fluid A to wash against the finned surface of pipe 32 following a sinusoidal or better a zig-zag course, as indicated by arrows 49 and 50, that is, after fluid A has washed against the finned surface of a first section of pipe, flowing within the spaces between the fins as indicated by arrows 51 and 52 of FIG. 4, it is conveyed from the cavity 53 toward the subsequent section of the pipe and obliged to flow again within the spaces of the fins.

This exchanger was achieved as a pipe having a single finned section, but naturally one could use, as in the previous constructions, a U-shaped pipe with deviating or diverging branches installed within the casing suitably baffled which could oblige the fluid to flow onto the finned surfaces of the pipes in a zig-zag course. Exchangers based on the same structural concepts can be achieved with several finned branches installed within the casing using either one pipe in the form of a coil or several pipes equipped with an inlet manifold and an outlet manifold for fluid B.

In FIG. 6, 54 indicates the finned pipe with the fins extending perpendicularly to the axis generated by the pipe itself, as is clearly shown in FIG. 7; 59 and 60 indicate its ends which are smooth, and in this construction the pipe in its finned portion has its axis wound in a spiral in closed-coil fashion; 55 indicates a casing which contains a finned pipe, 56 the external cylindrical wall, 57 an internal cylindrical wall, and 58 a circular wall having a whole 65 and which is integral with the cylindrical wall 57.

61 and 62 indicate two end covers in which are machined holes 77 and 78 (with the respective recess for seal rings 87 and 88) for the passage of the smooth ends 59 and 60 of the finned pipe 54 from the inside of the casing 55 to the outside, and 79 and 80 indicate threaded holes in which are screwed, with previous placement of seal washers 83 and 84, inlet and outlet fittings 81 and 82 for the fluid A to be cooled. Fluid B flows within finned pipe 54 in the direction indicated by arrows 86 and 85.

In covers 61 and 62 are further machined coaxial holes 63 and 64; 66 indicates a tie-rod, threaded at both ends 67 and 68, inserted in holes 63 and 64 of the covers and in hole 65 of circular wall 58 with the interposing of two spacers 69 and 70, which tie-rod serves to secure the various components of the exchanger. A nut 71 is screwed on threaded end 67 and nut 72 on threaded end 68 there having been inserted previously between the nuts and the covers, washers 73 and 74 which assure a good seal at the points of the holes 63 and 64. For the purpose of avoiding leakages of the fluid A toward the outside, two rings of elastic material 75 and 76 are installed between the wall 56 and the covers 61 and 62.

Arrows 89 and 90 indicate the direction of flow of fluid A at the inlet and outlet of casing 55.

Fluid A which flows within the casing in the space contained between the two walls 56 and 57 in a direction parallel to the lines generated by the cylindrical walls is obliged to pass predominantly within the spaces between the fins and therefore to wash against the finned surfaces of the pipe becoming substantially cooled within a limited space.

In the further variants of the exchanger, shown in FIGS. 8 and 9, the same numbers indicate the parts that are analogous to those of the exchanger of FIGS. 6 and 7; in the first embodiment, two elements 91 and 92 are visible shaped with a triangular cross-section with the sides of the triangle curved arranged with the axis wound in the form of a coil parallel to the axis of the finned pipe. The abovementioned elements, inserted in the spaces between the walls 56 and 57 of the casing and the crests of the fins of pipe 54, oblige fluid A to flow within the spaces of the fins, guiding it through a larger area, with a further improvement of the heat exchange, an advantage which is obtained also in the case of the exchanger shown in FIG. 9, in which 93 and 94 indicate the external and internal walls of the casing of finned pipe 54, which are cylindrical surfaces in the form of waves, with the course of the waves being spiral and parallel to the course of the axis of the coiled finned pipe.

Claims

What I claim is:

1. A heat exchanger for heat exchange between two liquids, one of which liquids is viscous, including a cylindrical casing having an inner surface, an inner cylindrical member of lesser diameter than the casing within the casing and having an outer surface, said casing being provided with an inlet and an outlet for the viscous liquid, a finned tubing within the casing, said tubing having inlet and outlet ends, the tubing having outer fins lying in a plane perpendicular to the axis of the tubing, said tubing being helically wound with closely adjacent turns to provide a cylindrical assembly, the other liquid flowing inside the tubing from the inlet to the outlet, and the turns of the tubing being at least partially but not completely enclosed between the inner surface of the casing and the outer surface of the cylindrical member so that the outer contours of the fins are adjacent said surfaces thereby compelling the viscous liquid to flow through the passages defined between the fins of the tubing, thus preventing stagnation zones from being formed and maintaining the heat exchange at the optimum level.

2. The heat exchanger as claimed in claim 1 in which between the inner surface of the casing and the outer surface of the cylindrical member and the crests of the fins are located elements triangular in cross section, with the sides of the cross section following a helical path parallel to the axis of the wound tubing.

3. The heat exchanger as claimed in claim 1 in which the inner surface of the casing and the outer surface of the cylindrical member are shaped to provide a helical path parallel to the course of the axis of the wound tubing.