The plate-fin type heat exchanger has a large heat transmission area per unit volume, and has been widely used as a heat exchanger in a small size and having a high operating efficiency.
When the cross-sectional shape of the plate-fin type heat exchanger is illustrated in a square as shown in FIGS. 1(A), 1(B), and 1(C) of the accompanying drawing, a primary fluid to be heat-exchanged is denoted by an arrow marked in a solid line, a secondary fluid is denoted by an arrow marked in broken lines (as a matter of course, the primary fluid and the secondary fluid are separated by a partition plate). The heat exchanger is classified by the flow of these two fluids and can be broadly classified into a parallel flow type heat exchanger 22, in which the two fluids flow in mutually intersecting directions, this being an intermediate type between the parallel flow type and the counter-flow type heat exchangers. When the heat exchanging efficiency of these plate-fin type heat exchangers 20, 21 and 22 is expressed by .eta., and temperatures at both inlet and outlet ports for the primary fluid and the secondary fluid are respectively denoted as T.sub.1, t.sub.1, T.sub.2 and t.sub.2 as shown in FIGS. 1(A), 1(B) and 1(C), the heat exchanging efficiency .eta. can be represented as follows. ##EQU1## Here, the temperatures T.sub.2 and t.sub.2 at the outlet ports of the heat exchanger vary depending on the flow rates of both fluids; however, the temperatures of both fluids which are in mutual contact through a plate become substantially coincident, if and when both fluids are caused to flow at a very low speed. As a result of this, the temperatures T.sub.2 and t.sub.2 are substantially equal (T.sub.2 .apprxeq.t.sub.2) in the parallel flow type heat exchanger, and, from the above equation, T.sub.2 .apprxeq.(T.sub.1 +t.sub.1)/2, hence .eta..apprxeq.50%. In other words, the maximum heat exchanging efficiency of the parallel flow type heat exchanger becomes 50%. Also, the temperatures T.sub.1, t.sub.1, T.sub.2 and t.sub.2 are in a relationship of T.sub.2 .apprxeq.t.sub.1, t.sub.2 .apprxeq.T.sub.1 in the counter-flow type heat exchanger 21, and, from the above equation (1), .eta..apprxeq.100%. That is to say, if it is possible to effect the heat exchanging operation under the ideal conditions with a perfectly heat-insulated system, the counter-flow type heat exchanger exhibits its maximum heat exchanging efficiency of 100%. On the other hand, the orthogonally intersecting flow type (or slantly intersecting flow type) heat exchanger 22 is classified in between the parallel flow type heat exchanger 20 and the counter-flow type heat exchanger 21, so that the maximum heat exchanging efficiency thereof ranges from 50% to 100% depending on an angle, at which the two fluids intersect. From the above, it may be understood that the counter-flow type heat exchanger 21 is ideal, in its actual use, the two fluids cannot be separated perfectly, because the inlet and outlet ports of these two fluids to be heat-exchanged are in one and the same end face, hence such ideal counter-flow type heat exchanger 21 is non-existent. In the following discussion, actual circumstances in the heat exchanging operations will be explained by reference to an air-to-air heat exchanger used in the field of air conditioning.
Recently, the importance of ventilation in a living space to increase its air conditioning (cooling and warming) effect has again been brought to attention of all concerned, as the heat insulation and the air tightness characteristics of the living space from an external atmosphere has been improved. As an effective method of ventilation of the living space without affecting the cooling and warming effect, there has been suggested one that carries out the heat exchanging operation between exhaustion of contaminated air in the room and intake of fresh external air. In this case, a remarkable effect has results where the exchange of humidity (latent heat) can be done simultaneously with exchange of temperature (sensible heat). As an example of a method for attaining such purpose, there has been put into practice an orthogonally intersecting flow type (or a slant intersecting flow type) heat exchanger as shown in FIG. 2 which has been known by Japanese Patent Publication No. 19990/1972. In the drawing, numeral 1 refers to partitioning plates to separate the intake air and the exhaust air, and numeral 2 refers to fins which form a plurality of parallel flow paths for guiding the intake air or the exhaust air.
For the size-reduction or the high performance of the heat exchanger, the above-mentioned counter-flow type is preferable. While it is considered impossible to realize the plate-fin type heat exchanger which is of the perfect counter-flow type and which is capable of industrialized mass-production, there are several laid-open applications which have realized, in part, such counter-flow system. Of these, Japanese Utility Model Publication No. 56531/1977 appears to be the one with the highest practicability, and the following explanation is given as to the heat-exchanger disclosed in this utility model publication as an example of known art. The heat exchanger as taught in this published specification is of such a construction that corrugated heat exchanging elements 3 in a square or a rectangular shape are piled up in a staggered form, as shown in FIG. 3(A), each end part 4 of which is fitted into an opening 6 formed in a closure plate 5 shown in FIG. 3(B) to tightly close the adjacent heat exchanging element 3, 3. In addition, reference letter (M) in the drawing designates a flow of the primary air current, and reference letter (N) denotes a flow of the secondary air current. In this heat exchanger, each air current, after it has passed through the heat exchanging elements 3, impinges on the closure plate 5 through an empty space (S) formed between the adjacent heat exchanging elements 3, 3 to thereby perpendicularly divert its flow direction.
The published specification does not contain a description as to the performance of the heat exchanger, except for simply stating convenience in its use. As a potential structural defect, however, it may be presumed that automated manufacturing of this heat exchanger is difficult to be implemented because the end parts 4 of the heat exchanging elements 3, 3 in corrugated form have to be fitted into the openings 6 of the closure plate 5 to manufacture the heat exchanger, hence the apparatus is lacking in an industrialized mass-productivity capability.