HEAT EXCHANGER

Abstract: A heat exchanger for heat transfer between two mediums comprises a tubular shell (10) and a finned tube (11) provided in the shell. One medium flows in the shell, and the other medium flows in the finned tube. The shell is divided into two chambers (13, 14), provided on either side of the finned tube, so that the medium flowing through the shell enters into the first chamber (13) which is positioned above the second chamber (14) and then flows downwards between the fins (12) into the second chamber (14). The shell has an elongate cross section, the fins of the tube abutting two opposite walls of the shell. The position of the tube within the shell can change along the length of the shell. The heat exchanger is intended for condensation of vapour, e.g. in connection with heat pumps. Vapour is then fed into the shell, and a cooling medium is fed into the tube. The flowing vapour promotes the discharge of the condensate from the fins. In one embodiment, the shell is wound to an upright coil in which the condensate is collected at the lower end of the coil.

Description: Heat exchanger. Technical Field The present invention is related τo a heat exchanger providing heat transfer between two mediums. The heat ex¬ changer comprises a tubular shell and a finned tube provi- ded in the shell, the fins of the fube being substantially perpendicular to the direction of the tube. One medium is flowing in the shell outside the finned tube and the other medium is flowing in -he finned tube. The heat exchanger is particularly intended for use in vapour condensers, e. g. in connection with heat pumps and similar devices in which the vapour is routed through the shell outside the finned tube and a cooling medium is routed through the finned tube. Background Art It has been proposed to use finned tubes in heat ex- changers for providing heat transfer between two flowing mediums. An example of such a prior art device is described in FR 2 083 547. The finned tubes are advantageous due to their large heat transfer surfaces. VThile these prior art heat exchangers can be used for condensing vapour, they ha- ve in this use the disadvantage that the condensate has a tendency to remain on the fin surfaces, τhus reducing the capacity of the heat exchanger and causing a slow down of the condensation process. Disclosure of Invention The main object of the invention is to provide a heat exchanger utilizing the advantage of the large heat trans¬ fer surfaces of the finned tubes but eliminating or at least reducing the tendency of the condensate ' to remain on the heat transfer surfaces. According to the invention, this object is obtained by a heat exchanger having the features set forth in the claims. Due to the fact that the shell is divided into two chambers provided on either side of the finned tube, .one medium. can flow between -he fins of the finned tube in good contact with the fins, thus providing a good heat transfer between the medium flowing in the shell outside the finned tube and the medium flowing in the finned tube. Due to the fact that the tube fins abut two opposite walls of the shell, a good heat transfer is provided between the finned tube and the shell, so that also the shell will form a heat transfer surface for further improving the heat exchange between .the two mediums passing through the heat exchanger. By position¬ ing the finned tube diagonally in the shell , so that at the inlet end of the shell the first chamber occupies the larger portion of the space available outside the finned tube and at the outlet end of the shell the other chamber occupies the larger portion of the space available outside the finned tube, a comparatively large inlet and outlet can be provided, although the shell has a small cross section area. Thus, comparatively large amounts of the first medium can be fed into the shell, enabling the transfer of large amounts of heat between the two mediums. When the heat ex¬ changer is used for condensing .vapour, the vapour being fed into the shell and a cold .medium, e.g. a cold liquid, being fed into the finned tube, the vapour flowing between the fins will remove the condensate from the fin surfaces, so that the condensate does not remain on the fins and pre¬ vent further condensation. This effect is particularly evi- dent, when the first: chamber, i.e. the inlet chamber, in the shell is positioned above the second chamber, i.e. the outlet chamber. 3y designing the shell as an upright coil having a steep pitch, the condensate can be collected in the lower portion of the coil, where it will surround the finned tube, thus supercooling the condensate. Two embodiments of the heat exchanger according to the invention will now be described more in detail below with reference tc the accompanying drawings. Brief Description of Drawings Figure 1 is a side view of a finned tube having a surrounding straight shell. Figure 2 is a cross section through the shell along the line II-II in Figure 1. Figure 3 is an embodiment according to Figures 1 and 2 in which the shell has been wound to a coil. Best Mode for Carrying Out the Invention The embodiment of the invention shown in Figure 1 comprises a tubular outer shell 10 having a substantially oval cross section, as shown in Figure 2. A finned tube 11 is inserted in the shell 10. The fins 12 of the tube consist of annular.discs provided substantially perpendicularly to the longitudinal direction of the tube. The fins of the tu¬ bes of this type are normally made by rolling and turning tubes'having thick walls, so that the fins form an integral part of the tube. Alternatively, the fins can form -a. helix surrounding the tube along its length. The fins 12 of the finned tube 11 abut two opposite walls of the shell 10, as shown in Figure " 2. This abutment will provide a good heat transfer between the finned tube 11 and the shell 10, so that also the inner surface of the shell will provide a heat transfer surface for heat transfer between the two e- diums flowing through the shell and the finned tube. The shell, having a larger cross section area than the finned tube, is divided into two chambers 13,14 by the finned tu¬ be 11, the chambers running from one end of the shell to the other and. being provided on either side of the finned tube, so that the medium entering the first chamber 13 has to flow between the fins 12 of the tube to enter the second chamber 14. In the embodiment shown in Figures 1 and 2, the shell 10 is a straight tube into which a straight fin¬ ned tube 11 has been inserted diagonally, so that at the inlet end of the shell the first chamber 13 occupies the larger portion of the space available outside the finned tube and at the outlet end the second chamber 14 occupies the larger portion of the space available outside the fin¬ ned tube. This will facilitate the attachment of an inlet pipe 15 and an ou let pipe 15-, respectively. The pipes 15,15 can be comparatively thick, although the shell has a small cross section. The finned tube 11 is also provided with an inlet pipe 17 and an outlet pipe 18 for the medium flowing through the finned tube, the inlet and outlet pipes, how¬ ever, being reversed as compared with the corresponding pipes of the shell, so that the two mediums will flow in opposite directions through rhe heat exchanger. The flow directions of the mediums have been indicated by arrows in Figure 1. The heat exchanger according to the invention can be used for condensing vapour. If so, the shell of the heat exchanger is preferably designed as an upright coil having a steep pitch. An embodiment of this xype has been shown in Figure 3, where the same ref rence numerals as in Figure 1 have been used for the corresponding elements. The finned tube 11 has been positioned diagonally in the shell 10 also in this embodiment, so that the connection pipe 17 of the finned tube at the outlet end of the shell is situated in the upper portion of the shell and the connection pipe 18 at the inlet end of the shell is situated in the lower por¬ tion of the s-hell. Thus, the first chamber 13 of the shell is positioned above the second chamber 14. This is particu¬ larly convenient for the condensation process, because the vapour flowing Throug the shell efficiently contributes to the removal of the condensate from the fin surfaces , as the vapour will be flowing substantially in the same directions as the condensate, viz. downwards. Because the shell 10 has been wound tc an upright ceil having a steep pitch, the condensate can be collected at the lower portion ' of the coil. Under these circumstances, a comparatively small volume of condensate will be sufficient for surround¬ ing the finned tube. This will cause a supercooling of the condensate, i.e. the temperature of h condensate will be lowered below the condensatir.g temperature, because further cooling is provided by the medium in τ e finned tube. An outlet 19 has been provided - the lowe portion of the coil for draining the condensate. While only two embodiments of -he heat exchanger ac¬ cording to the invenτion have been shown and- described, it is evident that many different embodiments and modifications are possible within the scope of the invention. E.g., it is not necessary that the shell has an oval or elongate cross section. The shell can also have a circular cross section, but in that case sealing elements have to be provided bet¬ ween the finned tube and the walls of the shell, so that two separate chambers are formed in the shell, τhe chambers being connected to each other only through the spaces bet¬ ween the fins of the tube. Such sealing elements may be used also when the shell has an oval or elongate cross section. The finned tube must not necessarily run diagonally through the shell but can alternatively run along the central axis of the shell. However, in that case the shell must be sea¬ led at its ends by special walls. In the embodiment shown on the drawings, the closure of the shell at the ends may be provided by deformation of the shell to contact with the in¬ let and outlet pipes, the complete sealing then being pro¬ vided by e.g. soldering. When the shell is wound to a coil, the elongate cross section of the shell preferably can have its longer axis in parallel with the axis of the coil, as this will make it easier to wind the coil with a small dia¬ meter. However, it is important that the lower wall of the shell has a shape that at least slightly differs from the shape of the fins , so that the condensate can flow in the shell along the full length of the shall. The heat exchanger can also advantageously be used for evaporation, if a hot medium is forced through the finned tube.

Claims: Claims . 1. Heat exchanger providing heat transfer between two me¬ diums for vapour condensation, comprising a tubular shell (10) and a finned tube (11) provided in the shell, the fins (12) of the tube being substantially perpendicular to the direction of the tube, wherein the internal cross section area of the shell is larger than the area enclosed by the outer periphery of the fins (12), the first medium, which is a vapour, passing through the shell outside the finned tube and the second medium, which is a cooling medium, passing through the finned tube, characterized in that the shell (10) is divided into two chambers (13,14) which are provided on either side of the finned tube (11) , the first chamber (13) being provided above the second chamber (14), so that the vapour passing through the shell (10) outside the finned tube (11) enters the first chamber (13) and passes downwards between the fins (12) of the tube (11) to the second chamber (14). 2. Heat exchanger according to claim 1, characterized in that the shell (10) has an elongate cross section area and that the fins (12) of the tube (11) abut two opposite walls of the shell. 3. Heat exchanger according to claim 1 or 2, characterized in that the shell (10) has an inlet (15) at one end and an outlet (16) at the other end for the first medium, the fin- ' ned tube (11) being provided ax the inlet end of the shell (10) in the lower portion of the shell and at the outlet end of the shell in the upper porxion of the shell, so that at the inlet end of the shell the first chamber (13) occupies the larger porxion of the space available outside the fin- ned tube and at the outlet end cf the shell the second chamber (14) occupies the larger portion of the space avail¬ able outside the fi ned tube. 4. Heat exchanger according to claim 3, characterized in that the shell (1G) is wound xo an upright coil having a steep pitch. 5. Heat exchanger according to claim 4, characterized in that the major axis of the cross section area of the shell (10) is parallel with the axis of the cylindrical coil. 6. Heat exchanger according to claim 4 or 5, characterized in that the inlet (15) for the first medium is provided in the upper portion of the coil and that an inlet (17) for feeding a cold liquid into the finned tube (11) is provi¬ ded in the lower portion of the coil, in which means (19) are provided for draining the condensate. 7. Heat exchanger according to claim 6, characterized in that the lower wall of the shell (10) has a shape which at least to some extent diverges from the shape of the fins (12), so that the condensate can flow in the shell along its full length. 8. Heat exchanger according to claim 1, characterized in that each chamber (13,14) extends from one end of the shell (10) to the other end of the shell.

Inventors: AKERMAN GERT AKE ELOF
Applicants: AKERMAN GERT AKE ELOF, WIRSBO BRUKS AB
Application year: 1982
Main classification: F28D7
IPC codes: F28D7