For the strongest possible heat exchanging contact between a medium and a heat-conducting plate, which for instance forms part of a heat exchanger, it is desirable that the medium flowing along the plate, for instance a gas or a liquid, displays a turbulent flow pattern on the surface. The thermal boundary layer is hereby effectively broken up and the coefficient of heat transfer can be increased considerably without this being accompanied by substantially increased pressure losses. With a view to the above the invention provides a device for enhancing heat transfer between a heat-con¬ ducting plate, for instance forming part of a heat ex¬ changer, and a medium flowing therealong, for instance a gas or a liquid, which device comprises: a plate for placing in the medium flow such that the flow direction is parallel to the principal plane of the plate, which plate bears lips which each have a substan¬ tially prismatic form, the principal direction of which substantially coincides with the flow direction, which plate is placed relative to the heat-conduct¬ ing plate such that the lips extend at a short distance therefrom or are in contact therewith.

Surprisingly, it has been found that the described form of the lips can cause a very strong turbulent flow accompanied by a correspondingly low thermal resistance.

The device is preferably embodied such that the lips are placed in staggered manner.

A preferred embodiment has the special feature that the lips incline upward with a smooth transition out of the principal plane and have a bent back free end zone.

A simple and effective embodiment has the special feature that the lips have a rectangular form and are connected on a short side to the plate.

A surprisingly solid effectiveness is obtained with an embodiment in which the said short side connects onto two continuous holes in the plate, between which holes extends a corrugated lip portion. This structure ensures that the lips can be very easily pressed elastically. Simple in terms of production technique is the embodiment in which the lips are pressed out of the principal plane of the plate. Use can be made for this purpose of a punching device which, while retaining one connecting edge, separates the lips from the rest of the plate and presses them out of the principal plane of the plate.

An increase in the turbulent character of the medium flow is obtained with an embodiment in which the projec¬ tions of the lips mutually intersect in the flow direc¬ tion. The plate according to the invention preferably has the special feature that the plate is adapted for posi¬ tioning in adjoining relation to a plate which is in heat exchanging co-action with the medium. For instance for use in a heat exchanger with a plurality of heat exchang- ing fins or flat hollow panels located at mutual dis¬ tance, the plates according to the invention can be placed between these layers. It will be apparent that for the greatest possible effectiveness the plate according to the invention must be active over the greatest possi- ble part of the heat exchanging surface.

Attention is drawn to the fact that, for instance in the context of use in a heat exchanger of the described type, the lips can protrude from the plate on either side thereof. A specific embodiment is that in which the plate consists substantially of steel, for instance stainless steel or spring steel.

For the sake of completeness attention is drawn to the fact that the lips can also be separate elements which are connected to a plate in suitable manner, for instance by glueing, soldering, (resistance) welding, with rivets etc.

The invention will now be elucidated with reference to the annexed drawing. Herein: figure 1 shows a partly broken away perspective view of a heat exchanger with a device according to the inven- tion; figure 2 is a view corresponding with figure 1 of another heat exchanger; figure 3 shows partially in front view, partially in cross section a heat exchanger in another embodiment; figure 4 shows a partly broken away perspective view in the form of an exploded view of yet another heat exchanger with a device according to the invention; figure 5 shows a cross section through a detail of a heat exchanger with devices according to the invention; figure 6 is a perspective view on enlarged scale of a part of a device according to the invention; and figure 7 is a perspective view corresponding with figure 6 of a preferred embodiment.

Figure 1 shows a heat exchanger 1 with four plates 2-5 through which medium can flow and which are connected to an inlet manifold 6 and an outlet manifold 7. The plates 2-5 are arranged in a housing 8 which via connec¬ tions (not shown) is also incorporated in a second medium flow for heat exchanging contact with medium flowing through plates 2-5.

Between plates 2-5 are placed three plates 9,10,11 according to the invention. These are all embodied iden¬ tically. They bear on either side of the plate lips 12,13 which protrude out of the principal plane of the plate and which each have a substantially prismatic form, the principal direction of which at least more or less coin¬ cides with the direction of flow of the medium flowing past. Each lip 12,13 inclines upward with a smooth tran-

sition out of the principal plane of the relevant plate and has a bent back free end zone. Each lip has a rectan¬ gular form and is connected to the associated plate with a short side. The lips are formed by punching and a working wherein the lip is pressed out of the principal plane of the plate.

For the sake of clarity the respective plates in figure 1 (and also in figure 2) are drawn at some mutual distance. For the purpose of a good heat transfer it is recommended however that each lip extends in the immedi¬ ate vicinity of an adjoining heat-conducting plate or is in contact therewith.

Figure 2 shows a heat exchanger 14 wherein, at variance with the embodiment of figure 1, use is made of a zigzag-folded hollow panel 15, between the layers of which extend the plates 9,10,11 according to the inven¬ tion.

Figure 3 shows a heat exchanger 16 wherein the housing 17, at variance with the housings according to figures 1 and 2, has a cylindrical form. This heat ex¬ changer 16 also has a zigzag-formed hollow panel 18 through which medium can flow, between the layers of which extend plates according to the invention, which are designated respectively 19,20,21,22,23,24,25. This figure clearly shows that the respective lips press against the adjoining surfaces of the panel 18. Attention is drawn to the fact that it can be seen more clearly in this figure 3 than in the preceding figures that the projections of the lips mutually intersect in the flow direction. Figure 4 shows a heat exchanger 26. This comprises one spirally wound hollow plate 28 through which medium can flow via manifolds 26,27 and to which is connected a wound plate 29 according to the invention. For the sake of clarity in the drawing the plates 28 and 29 are drawn in exploded view.

Figure 5 shows a part of a heat exchanger 30. This comprises a plurality of hollow panels 31 placed one above another through which medium can flow, plates 32