US2997280A - Heat exchangers and matrices therefor - Google Patents

Description

Aug. 22, 1961 F. H. KEAST HEAT EXCHANGERS AND MATRICES THEREFOR 2 Sheets-Sheet 1 Filed May 4, 1959 FIG.

0 A m M N. w w ME 8 Aug. 22, 1961 KEAsT 2,997,280

HEAT EXCHANGERS AND MATRICES THEREFOR Filed May 4, 1.959 2 Sheets-Sheet 2 nwewroR 7/? H. KEAST States This invention relates to heat exchangers and matrices therefor.

The purpose of a heat exchanger is to transfer heat from one working fluid to another and it is normally desirable to design heat exchangers to maintain fluid pressure losses as low as possible. In the majority of heat exchangers, leakage of one working fluid into the other is not permissible and it is therefore necessary for the transfer of heat to take place through dividing walls. The most efficient dividing wall from the point of view of low pressure losses is a flat plate arranged so that one working fluid flows across one surface of the plate and the other working fluid flows across the other surface of the plate. Such an arrangement has low heat transfer efficiency and one way in which this efficiency can be improved is by the introduction of turbulence or eddies in one or more of the working fluids. Another problem in the design of heat exchangers is that often the two working fluids are at different pressures so that there is a pressure difference across the heat transfer plates or dividing walls which therefore have to be made sufficiently strong to withstand the pressure difierence.

It is an object of this invention to provide a heat exchanger matrix having high heat transfer efficiency with low pressure loss characteristics and also having a high resistance to damage due to pressure differences between the working fluids.

It is a further object of the invention to provide a heat exchanger which is structurally strong, has high heat transfer efliciency and low pressure loss characteristics.

It is well known that, if a fluid is caused to pass through a straight tube, a boundary layer of slow moving fluid forms on the interior walls of the tube whereas the central portion of the fluid moves with greater velocity than the boundary layer. If the situation isnow considered in which the fluid is caused to pass through a curved tube then secondary flow or eddies will appear in the fluid as follows. The relatively fast flowing central core of the fluid will tend to move to the outside of the curve and this movement produces a region of high pressure within the tube at the outer radius of the curveand also a low pressure region at the inside surface of the curve. The resulting difference in pressure will cause the boundary layer to begin to move from the zone of high pressure to the zone of low pressure and thus eddy currents are set up in the working fluid which may be used to assist in heat transfer without incurring substantial pressure losses.

However, it is not altogether practical to put together a stack of such curved tubes to form a heat exchanger. Ditflculty is encountered with the manifolding required to lead the working fluids into and out of the stack since if the benefit of the curve is to be taken by both working fluids then the working fluids have to be fed in parallel directions through the ends of the tubes and alternate passages have to be supplied with one working fluid while the other passages have to be supplied with the other working fluid. It will be appreciated that this requires complicated manifolding. If one working fluid was passed through the stack at right angles to the other working fluid then one working fluid would not get the benefit of the curve and there would be no turbulence in the one working fluid although there would be turbulence atent 7Q 2,997,286 Patented Aug. 22, i

vin the other working fluid which might assist in the heat transfer.

By means of the present invention turbulence is given to both streams of working fluid and also the heat exchanger or matrix is made so that it will resist pressure differences between the working fluids in either direction, that is to say either working fluid may be at a higher pressure than the other, up to the designed limit of the apparatus, without rupturing the matrix or the heat exchanger.

The invention will now be described by way of example with reference to the accompanying drawings, in which like reference numerals indicate similar parts throughout the several views, and in which:

FIGURE 1 is a perspective view, partly broken away, of one embodiment of the invention,

FIGURE 2 is a diagram indicating the shape of the plates used in the heat exchanger matrix of the invention,

FIGURE 3 is a diagram showing the eddy currents induced in passages in the matrix, and

FIGURE 4 is a perspective view, partly broken away, of a second embodiment of the invention.

Referring now to FIGURES l and 2, the heat exchanger matrix is indicated generally at 10 and comprises a plurality of superposed plates, the upper four of which are indicated at 11, 12, 13 and 14. Each of the plates of the stack is similar and is of generally rectangular outline when viewed in plan with two pairs of opposed edges, the plates in the stack being arranged so that their corresponding-edges are in alignment. Secured to a set of aligned edges of one pair of opposed edges of the plates is a duct 15 of rectangular cross section and secured to the other set of aligned edges of the pair is a duct 16 of rectangular cross section. A duct 17 is secured to one set of aligned edges of the other opposed pair of edges of the plates and a duct 18- is secured to the other set of aligned edges of the other opposed pair.

Each plate 11, .12, 13, 14 etc. is formed to provide similar opposed surfaces consisting of parts of surfaces of revolution of a planar curve about an axis outside the curve but in a plane thereof. Referring to FIGURE 2, one of the plates, for example the plate .11 is shown and the opposed surfaces 19 and 19a of the plate define curved surfaces such as would be generated by rotating the curves 20 and 21 respectively about an axis 22. The curve 20 is convex towards the axis 22 and diverges from an inner portion or crest 23 nearest the axis. Similarly, the curve 21 is convex towards the axis and has an inner portion or crest 24 nearest the axis. The curves 20 and 21 are identical but spaced and parallel and each diverges from its crest away from the axis. The curves lie in the plane of the paper, as does the axis 22, and rotation of the curves about the axis will sweep out the surfaces 19 and 19a. It will be seen that, as a result, each plate has a curvature in two directions at right angles to each other, the curvature in one direction being of opposite sense to the curvature in the other direction. Each of the surfaces 19 and 19a might also be described as being an inner peripheral portion of a torus, or in other words, saddle-shaped. As mentioned above, each of the plates is similar and they are placed in the stack so that they are spaced apart and orientated in a similar manner, i.e. if they were allowed to rest one on top of the other they would nest with adjacent surfaces in contact. The passages between adjacent plates will there fore be parallel sided; the passage between the plates 11 and 12 is indicated at 25 and the passage between the plates 12 and '13 is indicated at 26.

The plates of each adjacent pair are held' in spaced apart relation by generally flat walls along opposed edges, thus the plates 11 and 12 are held in spaced apart relation by a wall 27 which extends between aligned edges of the plates and by a similar wall at the opposed edges of the plates (not shown). The other edges of the plates 11 and 12, indicated at 28, 29 respectively are not provided with a wall and define an entry into the passage 25. In a similar manner the plates 12 and 13 are held in spaced apart relation by a wall 30 which extends between aligned edges of the plates and by a wall (not shown) similar to the wall 30 at the opposed edges of the plates. However, the other opposed edges 31, 32 of the plates 12, 13 are left open to provide an entrance to the passage 26. The plates 13 and 14 are held in spaced apart relation by walls, one of which is shown at 33, similar to the wall 27, and the remaining plates of the stack are held in spaced apart relation by walls similar to the walls 27, 3t and 33.

The passage between the plates 13 and 14 is indicated generally at 34-. 'It will be seen that alternate passages, e.g. passage 25 and 34, extend between the ducts 15 and 16 whereas the other passages interposed between the alternate passages, e.g. the passage 26, extend between the ducts 17 and 18. The alternate passages, e.g. 25 and 34, are sealed from the duct 17 by the walls 27, 32, etc. and from the duct 18 by similar walls (not shown). The passages interposed between the alternate passages, e.g. the passage 26, are sealed off from the ducts 15 and 16 by walls similar to the wall 30. It will be appreciated that one working fluid may be passed into the duct 17, between the plates, and out through the duct 18. Similarly another working fluid may be passed into the duct 15, between the plates and out through the duct 16. The fluid passing through the ducts 15 and 16 will pass through the alternate passages 25, 34, etc. and the fluid passing through the ducts 17 and 18 will pass through passages interposed between the alternate passages, e.g. through the passage 26.

Ribs 35 are interposed between the plates 11 and 12 and extend from the aligned edges of the plates exposed to the duct 15. It will be seen from FIGURE 1 that the ribs extend only part way along the passage 25. In a similar manner, ribs 36 extend between the plates 12 and 13 in the passage 26 but only extend part way along the passage. The purpose of these ribs is to induce the eddy currents as will now be described.

Referring now to FIGURE 3, plates 11, 12 and 13 have been shown by way of example although the mechanism setting up the eddy currents is similar between all the plates.

Taking for example the portion of passage 25 between the end wall 27 and the next adjacent rib 35, fluid flowing through this part of the passage will flow around a curved path due to the curvature of the plates '11 and 12 and as a result of this curvature a zone of high pressure will be developed as indicated by the small arrows 37 and, as explained above, the boundary layer will move in the directions of the arrows 38 and turbulence will be set up resulting in greater efiiciency of heat exchange.

The ribs 35 need only extend part way along the passage 25 because once the eddy currents have been set up they will last for some time and the length of the ribs is adjusted so that the eddy currents will last substantially until the fluid passes out from the passage into the duct 16.

Referring now to the part of the passage 26 between the wall 30 and the next adjacent rib 36, the fluid flowing through this part of the passage will produce a zone of high pressure indicated by arrows 39 and will cause movement of the boundary layer in the direction shown by the arrows 40. The resulting movement will cause turbulence and will therefore assist in heat exchange.

It will therefore be seen that, by virtue of the double curvature of the plates, turbulence will be induced in each working fluid whereby heat exchange through the plates is increased.

The heat exchanger according to the invention has a further important advantage as follows. Curved sheet metal structures have a high resistance to bursting forces but a much lower resistance to collapsing forces. Due to the double curvature of the plates of the heat exchanger of the invention they can resist a pressure difference in either direction as a bursting force. Thus, for example, if the pressure in the passage 25 is greater than pressure in the passage 26, the plate 12 resists the pressure difference as a bursting force due to its curvature about an axis parallel to the axis XX in FIGURE i. On the other hand, if the pressure in the passage 26 is greater than the pressure in the passage 25, then the plate 12 withstands the pressure difference as a bursting force due to its curvature about an axis parallel to the axis YY in FIGURE 1. Similar considerations hold for all the heat transfer plates in the matrix so that a heat exchanger made according to the invention i capable of withstanding pressure diflerences in either direction as bursting forces and therefore, for given structural strength, will withstand a greater pressure difference than if it had to withstand the pressure diiference acting as a collapsing force.

Furthermore, it will be seen from FIGURE 1 that the manifolding problems are easily solved by the construction shown. If the plates are made generally rectangular in plan then a very simple manifolding system is possible requiring only one inlet duct and one outlet duct for each working fluid and the ducts for one working fluid do not interfere with the ducts of the other working fluid.

Referring now in FIGURE 4, there is shown a second embodiment of the invention in which the plates forming the matrix are caused to have a greater surface area than in the embodiment shown in FIGURE 1. The opposed surfaces of the plates in FIGURE 4 are again formed by rotating a planar curve about an axis in a plane but in the case of FIGURE 4 the angle through which the curve is rotated is approximately 300 whereby an incomplete ring structure is provided. The matrix is indicated generally at 41, an inlet duct for one working fluid at 42, and an outlet duct for the same working fluid at 43. An inlet duct for the other working fluid is indicated at 44 and an outlet duct for the other working fluid is provided at 45. The operation of the matrix is similar to that described with reference to FIGURES 1, 2 and 3 and it is thought that further explanation need not be made.

The configuration of FIGURE 4 is useful for applying to cylindrical structures, for example gas turbine engines. Even with this rather more complex configuration the manifolding problems are easily solved since the working fluids pass through the matrix in directions generally perpendicular to one another and the manifolds are associated with opposed edges of the matrix.

It will be seen that the invention provides a simple heat exchanger matrix in which eflicient heat exchange takes place with but little pressure loss. Moreover, the matrix of the invention is capable of withstanding pressure differences between the working fluids and these pressure differences may act in either direction or may fluctuate in direction during operation without affecting the matrix. Furthermore, the manifolding required to feed the Working fluids into the exchanger is extremely simple.

It will be understood that the form of the invention herewith shown and described is a preferred example and various modifications can be carried out without departing from the spirit of the invention or the scope of the appended claims.

What I claim as my invention is:

1. A heat exchanger matrix comprising a plurality of heat transfer plates, each plate being formed to provide similar opposed surfaces consisting of parts of surfaces of revolution of a planar curve about an axis outside the curve but in the plane thereof, the curve being convex towards the axis and diverging from a crest which is nearest the axis, and means holding the plates together in similar orientations and in spaced apart relation to form a stack and to define fluid flow passages between adjacent plates.

2. A heat exchanger matrix comprising a plurality of similar heat transfer plates, each plate being formed to provide similar opposed surfaces consisting of parts of surfaces of revolution of a planar curve about an axis outside the curve but in the plane thereof, the curve being convex towards the axis and diverging from a crest which is nearest the axis, and means holding the plates together in similar orientations and in spaced apart relation to form a stack and to define fluid flow passages between adjacent plates, the plates in the stack being arranged so the axes of revolution of the opposed surfaces of all the plates are parallel.

3. A heat exchanger matrix comprising a plurality of similar heat transfer plates, each plate being formed to provide similar opposed surfaces consisting of parts of surfaces of revolution of a planar curve about an axis outside the curve but in the plane thereof, the curve being convex towards the axis and diverging from a crest which is nearest the axis, each plate having two pairs of opposed edges, means holding the plates together in similar orientations and in spaced apart relation to form a stack and to define fluid flow passages between adjacent plates, corresponding edges of the plates of the stack being in alignment, and ribs extending between adjacent plates from aligned edges of the plates.

4 A heat exchanger matrix comprising a plurality of similar heat transfer plates, each plate being formed to provide similar opposed surfaces consisting of parts of surfaces of revolution of a planar curve about an axis outside the curve but in the plane thereof, the curve being convex towards the axis and diverging from a crest which is nearest the axis, each plate having two pairs of opposed edges, means holding the plates together in slmilar orientations and in spaced apart relation to form a stack and to define fluid flow passages between adjacent plates, corresponding edges of the plates of the stack being in alignment, ribs extending between adjacent plates defining alternate passages in the stack, the ribs extending from aligned edges of one of said opposed pair of edges, and further ribs extending between adjacent plates defining the passages in the stack interposed between said alternate passages, said further ribs exteinding from aligned edges of the other pair of opposed e ges.

5. A heat exchanger matrix comprising a plurality of similar heat transfer plates, each plate being substantially rectangular when viewed in plan and having two pairs of opposed edges, each plate being formed to provide similar opposed surfaces consisting of parts of surfaces of revolution of a planar curve about an axis outside the curve but in the plane thereof, the curve being convex towards the axis and diverging from a crest which is nearest the axis, and means holding the plates together in similar orientations and in spaced apart relation to form a stack and to define fluid flow passages between adjacent plates, the corresponding opposed edges of the plates of the stack being in alignment.

6. A heat exchanger matrix comprising a plurality of similar heat transfer plates, each plate being substantially rectangular when viewed in plan and having two pairs of opposed edges, each plate being formed to provide similar opposed surfaces consisting of parts of surfaces of revolution of a planar curve about an axis outside the curve but in the plane thereof, the curve being convex towards the axis and diverging from a crest which is nearest the axis, means holding the plates together in similar orientations and in spaced apart relation to form a stack and to define fluid flow passages between adjacent plates, the corresponding opposed edges of the plates of the stack being in alignment, ribs between adjacent plates defining alternate passages in the stack, the ribs extending from aligned edges of one of the opposed pair of edges and extending only part way along the passages, and further ribs, extending between adjacent plates 6 defining passages interposed between said alternate passages, said further ribs extending from aligned edges of the other pair of opposed edges and extending only part way along the passages.

7. A heat exchanger comprising a plurality of heat transfer plates, each plate being formed to provide similar opposed surfaces consisting of parts of surfaces of revolution of a planar curve about an axis outside the curve but in the plane thereof, the curve being convex towards the axis and diverging from a crest which is nearest the axis, means holding the plates together in similar orientations and in spaced apart relation to form a stack and to define fluid flow passages between adjacent plates, and means associated with edges of the plates for passing one working fluid through alternate passages of the stack and for passing another working fluid through the passages in the stack interposed between said alternate passages, whereby heat exchange takes place between the working fluids through the transfer plates.

8. A heat exchanger comprising a plurality of similar heat transfer plates, each plate having two pairs of opposed edges and being formed to provide similar opposed surfaces consisting of parts of surfaces of revolution of a planar curve about an axis outside the curve but in the plane thereof, the curve being convex towards the axis and diverging from a crest which is nearest the axis, means holding the plates together in similar orientations and in spaced apart relation to form a stack and to define fluid flow passages between adjacent plates, the plates in the stack being arranged so that said axes of revolution of the opposed surfaces of all the plates are parallel, means associated with one pair of opposed edges of each plate for passing one working fluid through alternate passages of the stack, and means associated with the other pair of opposed edges of each plates for passing another working fluid through the other passages in the stack interposed between said alternate passages, whereby heat exchange takes place between the Working fluids through the plates.

9. A heat exchanger comprising a plurality of similar heat transfer plates, each plate having two pairs of opposed edges, the edges of one pair being perpendicular to the edges of the other pair, each plate also being formed to provide similar opposed surfaces consisting of parts of surfaces of revolution of a planar curve about an axis outside the curve but in the plane thereof, the curve being convex towards the axis and diverging from a crest which is nearest the axis, means holding the plates together in similar orientations and in spaced apart relation to form a stack and to define fluid flow passages between adjacent plates, the plates in the stack being arranged so that said axes of revolution of the opposed surfaces of all the plates are parallel and so that their corresponding edges are aligned, means associated with one pair of opposed edges of each plate for passing one working fluid through alternate passages of the stack, and means associated with the other pair of opposed edges of each plate for passing another working fluid through the other passages in the stack interposed between said alternate passages, the working fluids being directed to flow in directions generally perpendicular to one another whereby heat exchange takes place between the working fluids through the plates.

10. A heat exchanger comprising a plurality of similar heat transfer plates, each plate having two pairs of opposed edges with the edges of one pair being perpendicular to the edges of the other pair, each plate also being formed to provide similar opposed surfaces consisting of parts of surfaces of revolution of a planar curve about an axis outsidethe curve but within the plane thereof, the curve being convex towards the axis and diverging from a crest which is nearest the axis, means holding the plates together in similar orientations and in spaced apart relation to form a stack and to define fluid flow passages between adjacent plates, the plates in the stack being arranged so that said axes of revolution of the opposed surfaces of all the plates are parallel and so that corresponding edges of the plates are aligned, means associated with one pair of opposed edges of each plate for passing one working fluid through alternate passages of the stack, means associated with the other pair of opposed edges of each plate for passing another working fluid through the other passages of the stack interposed between said alternate passages, ribs extending between adjacent plates which define said alternate passages and extending from aligned edges of said one pair of opposed edges part way along the passages, and further ribs extending between the plates which define said other passages, said further ribs extending from aligned References Cited in the file of this patent UNITED STATES PATENTS 1,720,536 Young July 9, 1929 1,883,769 Derry Oct. 18, 1932 2,768,814 Frey et a1. Oct. 30, 1956 2,834,582 Kablitz May 13, 1958

Images