The present invention relates to heat exchangers of the regenerative type.

One well known form of regenerative heat exchanger is the jungstrom type, in which a rotary member is stacked with several packs of substantially parallel, spaced heat transfer plates and two substantially semi-circular regions of this rotary member are separated by so-called "sector plates" and the gas to be heated is fed usually in one axial direction through one of these semi-circular regions and the gas to be cooled is fed in the opposite axial direction, through the other semi-circular region, while the member is rotated about its axis.

Various forms of plates have been suggested for stacking in the heat exchanger.

British Patent 1335205 discloses a particularly efficient form of plates in which a pack of the plates includes superimposed profiled plates which form channels for heat exchanging fluids. Each plate includes integral and parallel ridges disposed on each side of the plate these being separated by flat portions of a width greater than the height of the ridges, considered from the median plane of the plate. Each ridge on one side of the plate is formed adjacent a ridge on the other side of a plate so that the ridge is disposed on each side of the plate forming substantially open S-shaped portions when viewed in cross-section. The plates of the pack are so disposed that the ridges of one plate lie transversely to the ridges of an adjacent plate or plates, so that adjacent plates are in contact with each other solely at points spaced along the crests of the ridges. In this way channels are defined which include regions which extend into the open S-shaped portions of the ridges.

It is found that a very good heat exchange can be achieved with such a construction and the plates themselves

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can be manufactured reasonably economically.

However, in use of this type of heat exchanger there can be a relatively high pressure drop of the gases flowing therethrough. The gases are usually caused to flow by fans and if the resistance to flow through the packs of heat exchange plates is high, then the amount of energy required to drive the fans is increased. It could be advantageous significantly to increase the overall efficiency of the system. It is now proposed, according to the present invention, to provide a heat exchanger comprising a rotary member and means to selectively feed hot and cold gases through the heat exchanger, to provide a hot end and a cold end to the heat exchanger, there being a plurality of bundles of heat exchange elements mounted in the heat exchanger, each of the bundles including superimposed profiled plates forming channels for the heat exchanging fluids, each plate including integral and parallel ridges disposed on each side of the plate and separated by flat plate portions of a width greater than the height of the ridges, considered from the median plane of the plate, each ridge on one side of a plate being formed adjacent a ridge on the other side of the plate, whereby the ridges disposed on each side of the plate form substantially open S-shaped portions, when viewed in cross section, the plates of the pack being so disposed that the ridges of one plate lie transversely to the ridges of at least one adjacent plate, so that adjacent plates are in contact with each other solely at points spaced along the crests of the ridges, thereby defining said channels which include regions which extend into the open S-shape portions of the ridges, the resistance to flow of the fluid through said channels being •significantly less at the cold end of the heat exchanger than at the hot end. With such a construction, because the resistance

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to flow of the fluid through the channels is significantly less at. the cold end of the heat exchanger than at the hot end, the overall efficiency can be significantly improved. It is advantageous to have the cross-sectional dimensions of the channels formed between the plates relatively small at the hot end thereby causing a significant amount of turbulent flow this giving rise to good heat exchange at the hot and medium temperature parts of the heat exchanger. However, it has been found that at the cold end of the heat exchanger the heat exchange requirement is not so great and so the turbulence of flow need not be so high. It is thus, unexpectedly, found that the overall efficiency can be increased by reducing the resistance to flow at the cold end of the heat exchanger and thereby reducing the necessary power input to the fans driving both the hot and cold gases.

The resistance to flow of the fluid through the channels can be decreased at the cold end by arranging that the height of the ridges, and thus the spacing between the plates, at the cold end of the heat exchanger to be significantly greater than that at the hot end of the heat exchanger. In particular it has been found that if the height of the ridges at the cold end is between 1.25 and 2 times the height of ridges at the hot end of heat exchanger beneficial results can be achieved.

It is also possible to increase the cross-section of the channels by increasing the pitch between the ridges of the cold end as compared with the pitch between the ridges at the hot end of the heat exchanger. In a particularly preferred arrangement, the ratio of pitch of the ridges to the height of the ridges of the plates of the cold end is between 3.5 and 5.25.

Further advantages can be achieved by changing the angle of the ridges of the plates so that a more direct through flow for the gases can be achieved. For example it

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has been found when the plates are substantially rectangular in shape, the axes of the ridges at the cold end are preferably angled to two opposite longitudinal edges of the plate at an angle of between 15 and 20 degrees, whereas those at the hot end are at a rather greater angle, usually at least 20 degrees. This can produce the same effect or enhance the effect of having the cross-section of the channel increased at the cold end. According to a further aspect of the present invention there is provided a pack of heat transfer plates for the cold end of a regenerative heat exchanger each including superimposed profiled plates forming channels for heat exchange fluids, each plate including integral and parallel ridges disposed on each side of the plate and separated by flat plate portions of a width greater than the height of the ridges, considered from the median plane of the plate, each ridge on one side of the plate being formed adjacent a ridge on the other side of the plate, whereby the ridges disposed on each side of the plate form substantially open S-shaped portions, when viewed in cross section., the plates of the pack being so disposed that the ridges of one plate lie transversely to the ridges of the at least one adjacent plate, so that adjacent plates are in contact with each other solely at points spaced along the crests of the ridges, thereby defining said channels, which include regions which extend into the open S-shaped portions of the ridges, the ratio of the pitch between the ridges to the height of the ridges being between 3.5 and 5.25. The invention further provides a pack of heat transfer plates for the cold end of a regenerative heat exchanger comprising superimposed generally rectangular profiled plates forming channels for the heat exchange fluids, each plate including integral and parallel ridges disposed on each side of the plate and separated by flat

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plate portions of a width greater than the height of the ridges, considered from the median plane of the plates, each ridge on one side of a plate being formed adjacent a ridge on the other side of the plate, whereby the ridges disposed on each side of the plate form substantially open S-shaped portions, when viewed in cross section, the plates of the pack being so disposed that the ridges of one plate lie transversely to the ridges of at least one adjacent plate, so that adjacent plates are in contact with each other solely at points spaced along the crests of the ridges, thereby defining said channels which include regions into the open S-shaped portions of the ridges, the axes of the ridges being angled to two opposite longitudinal edges of the plates at an angle of between 15 and 20 degrees.

In order that the present invention may more readily be understood, the following description is given, merely by way of example, reference being made to the accompanying drawings in which:- Figure 1 is a plan view of a heat transfer plate for a pack according to the invention, and for use at the hot end of a heat exchanger according to the invention;

Figure 2 is an end view of the plate viewed in the direction of the line II-II in Figure 1; Figure 3 is a perspective view of two superimposed heat exchange plates of Figures 1 and 2, illustrating the channel system of a plate pack formed from such plates;

Figure 4 is a view similar to Figure 1 of a plate for a plate pack according to the invention for use at the cold end of the heat exchanger; and

Figure 5 is a view similar to Figure 2 of the plate of Figure 4.

The plate 10 illustrated in Figure 1 is formed of sheet metal of approximately 0.5 millimetres thickness, the

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plate being generally rectangular and having one of its longitudinal edges indicated at 11. The plate includes flat portions 12 and parallel folded integral ridges 14 which extend at an angle -*- to the longitudinal edge 11, this angle, for the hot end of the heat exchanger, being preferably at least 20°.

Figure 2 shows in detail the cross-section of the plate as taken along the section line 2-2 of Figure 1. Thus the ridges 14 can be seen as comprising ridges 15 disposed one each side of the plate to form substantially S-shaped portions, when viewed in cross-section, the double ridges being interconnected by an angled cross-over portion 16.

As can be seen in Figure 3, when two identical plates are stacked relative to one another, but in the reverse sense, the plate of the pack are so disposed that the ridges of one plate lie transversely to the ridges of the adjacent plate or plates, and the adjacent plates are in contact with each other solely at points spaced along the crests of the ridges.

In Figure 2 the pitch between the ridges is indicated by the reference P and the height of the ridges from the median plane of the plate is indicated as N. In the plates of Figures 1, 2 and 3, the pitch P is 35 millimetres and the height N is 5 millimetres while the angle & is 20°.

In the modified construction shown in Figures 4 and 5, the plates to be used at the cold end of the pack, the pitch P is again 35 millimetres, but the ridge height is 8.9 millimetres and the angle oi is between 15 and 20°. This arrangement ensures that the cross-section of the channels is nearly 80% greater and this, in addition, to the angle &. being smaller, gives rise to a much smaller resistance to flow of gas in the channels. In the particular construction shown, in Figures 1, 2 and 3 the

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ratio P/N is 7 whereas in the structure of Figures 4 and 5 the ratio P/N is 3.93. An alternative profile has the pitch P between 25 and 35 millimetres and the height N 6.8 millimetres in which case the ratio P/N is between 3.68 and 5.15. It is believed that advantageous results arise if the ratio P/N is between 3.5 and 5.25.

The plates at the cold end are preferably of a thicker material, for example 0.8 millimetre rather than 0.5 millimetre to enable these plates to withstand the greater stresses and the liability to corrosion at the cold end. For example, at the cold end there is a greater likelihood of condensation and the formation of acidity which gives rise to a greater degree of corrosion of the plates at the cold end and it is therefore advantageous for these plates to be made thicker. Also at the cold end there is a greater likelihood of sooting up and it has been found that having a larger ccoss-section of the channels and the smaller angle of inclination e*^ , the operation of a soot-blower is greatly facilitated.

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