GB2349455A

GB2349455A - Heat exchange assembly

Info

Publication number: GB2349455A
Application number: GB9909035A
Authority: GB
Inventors: Sen-Fuh Chang; Ku-Hsu Shen; Peng-Chu Chiu
Original assignee: NUTEC ELECTRICAL ENG CO Ltd
Current assignee: NUTEC ELECTRICAL ENG CO Ltd
Priority date: 1999-04-20
Filing date: 1999-04-20
Publication date: 2000-11-01
Also published as: GB9909035D0

Abstract

A heat exchange assembly 10 includes a substantially flat pipe 12 for a working medium to flow through and a hygroscopic 14 enveloping the pipe. The hygroscopic sheet 14 contains water which receives heat from the working medium to evaporate as vapor which in turn is carried away by air flow over the assembly. Multiple heat exchange assemblies 10 and multiple evaporative heat exchange assemblies 40, each comprising an undulating frame 42 and a hydroscopic sheet 44 enveloping over the frame 42 can be stacked alternatively to form a heat transfer unit. The flat pipe 12 may have an undulate board disposed within the passage of the pipe. The flat pipe 12 may be serpentine within the hygroscopic sheet 14. The heat Exchange Assembly may be condenser.

Description

HEAT TRANSFER PIPE ASSEMBLY The present invention relates to heat transfer pipes and more particularly to heat transfer pipes for condensers which achieve heat exchanging through evaporation of water kept in contact with the pipes and flow of air over the pipes.

The coefficient of performance (COP) for contemporary refrigeration systems ranges from about 3 to 6 and cannot be higher due to the difficulty in raising the heat transfer efficiency of heat exchangers.

Similarly, the energy efficiency ratio (EER) for air conditioning systemsthe most widely application of refrigeration principles-is about 2.7 at best in the case of air-cooled type and about 3.5 at best in the case of water-cooled type due to the bottleneck concerning the heat transfer efficiency of existing heat exchangers.

Conventional evaporative condensers in their initial development were equipped with fins on their pipes in order to increase heat exchange area. However, in the case where hard water is used, accumulation of particles on their surfaces not only is difficult to clean but also lowers heat transfer efficiency. In addition, the fins are adverse to good air flow so a larger power fan is required. In later types of condenser pipes without fins, the spraying pressure and density of water and the flow speed of air were found to be difficult to efficiently control.

The present invention aims to provide a high efficiency heat exchanger which finds particular application to, but not limited to, condensers.

One object of the present invention is to provide a heat transfer pipe assembly which effectuates heat removal of a working medium flowing therethrough by ambient air flowing thereover, comprising a substantially flat pipe and a hygroscopic sheet enveloping or covering over substantially flat pipe. Removal of the heat of the working medium is achieved by evaporation of the water contained in the hygroscopic sheet.

Another object of the present invention is to provide a heat transfer unit comprising : a plurality of the above-said heat transfer pipe assemblies and a plurality of evaporative heat exchange assemblies each comprising an undulate frame and a hygroscopic sheet enveloping over the undulate frame. The plurality of heat transfer pipe assemblies and the plurality of evaporative heat exchange assemblies are alternately stacked and the frame of each evaporative heat exchange assembly are undulated along a direction which is substantially parallel to the flow direction of working medium. With this construction, an excellent heat exchange can be achieved between the working medium flowing within the pipe and the air flowing through the undulate frame of each evaporative heat exchange assembly.

Other objects, advantages and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

IN THE DRAWING: Fig. 1 is a perspective view of a heat transfer unit constructed in accordance with the present invention; Fig. 2 is a plan view of a heat transfer pipe assembly constituting part of the heat transfer unit of Fig. 1; Fig. 3 is a cross-section along line 3-3 of Fig. 2; Fig. 4 is a perspective view of an evaporative heat exchange assembly constituting part of the heat transfer unit of Fig. 1; Fig. 5 is a detailed view showing a portion of the evaporative heat exchange assembly of Fig. 4; Fig. 6 is a perspective view of a modified heat transfer pipe assembly; and Fig. 7 is a cross-section along line 7-7 of Fig. 6.

Referring to the drawings and initially to Figs. 1,2 and 4, a heat transfer unit in accordance with the present invention is shown. In the figures, the heat transfer unit is constructed as a condenser which can be used, for example, in a refrigeration system or an air conditioning system, as is known in this art. The heat transfer unit essentially comprises a plurality of heat transfer pipe assemblies 10 and a plurality of evaporative heat exchange assemblies 40. Each heat transfer pipe assembly 10 comprises a pipe 12 and a hygroscopic sheet 14 enveloping or enclosing over the pipe 12. Fig. 6 shows a modified heat transfer pipe assembly 100 which comprises a pipe 110 and a hygroscopic sheet 140 enveloping over the pipe 110. As shown in Fig. 5, each evaporative heat exchange assembly 40 comprises an undulate frame 42 generally made of metals and a hygroscopic sheet 44 enveloping over the undulate frame 42. The sheet 14 or 44 is made of a hygroscopic material having good liquid-containing capability in order to keep it in a state that is full of liquid adequately supplie. The plurality of heat transfer pipe assemblies 10 and the plurality of evaporative heat exchange assemblies 40 are alternately stacked with the aid of suitable end and side supports 202 and 204 as shown in Fig. 1.

The heat transfer pipe assembly 10 is substantially flat as depicted in Fig. 1. The term"substantially flat"as herein used means that the height of the pipe assembly is relatively small as compared to its length and width so as to define a first flat wall 16 and a second opposite flat wall 18 (cf. Fig. 3), irrespective of the shape or configuration of the pipe 12.

In this regard, although the pipe 12 of Fig. 3 is serpentine within the hygroscopic sheet 14, the first flat wall 16 and the second flat wall 18 still can be clearly identified. Similarly, a first flat wall 146 and a second flat wall 148 are seen in the pipe 110 of Fig. 6. Referring to Fig. 2, the serpentine pipe 12 comprises a number of substantially straight segments 122 (three in this embodiment) spaced apart from each other and a corresponding number of blocks 36 of hygroscopic material are disposed in the space between adjacent segments 122. It is noted that hygroscopic blocks 37 may also be provided at a turning segment 124 of the pipe 12, in addition to the hygroscopic blocks 36. Moreover, it is not necessary for the hygroscopic sheet 14 to be endless and to envelop the whole outer wall of the heat transfer pipe assembly 10, it being sufficient that only the first and second flat wall 16 and 18 are enveloped by the hygroscopic sheet 14.

Between the first and second flat walls 16 and 18, a passage 19 is defined for a working medium to flow through, as shown in Fig. 3. For this purpose, an inlet 22 and an outlet 24 are provided in the pipe 12, as shown in Fig. 2. In practical application, again referring to Fig. 1, individual connecting conduits 26 and 28 are connecte to the inlet 22 and the outlet 24 and inlet and outlet conduits 32 and 34 common to the connecting conduits 26 and 28 of alternately arranged pipe assembly 10 are provided to afford a single inlet and a single outlet. As shown in Fig.

3, to increase the heat transfer area, a plurality of undulate boards 60 are each disposed within one of the plurality of substantially straight segments 122 of the pipe 12 and undulated along a direction which is perpendicular to a flow direction of the working medium within the pipe 12. The undulate board 60 forms a number of consecutive top and bottom ridges 62 and 64 which are secured to and make contact with the inside surfaces of the first and second flat walls 16 and 18, respectively. As can be understood, both the pipe 12 and the board 60 are generally made of metals, such as copper or aluminum. Moreover, the frame 42 of the evaporative heat exchange assembly 40 is undulated along a direction substantially perpendicular to the flow direction of working medium within the pipe 12.

In use, the working medium flowing through the pipe 12 contacts and transfers heat to the inside surface of the pipe 12 and the undulate board 60 (if present), which in turn transfer heat to the hygroscopic sheet 14 and the hygroscopic blocks 36. Since the hygroscopic sheet 14 and the hygroscopic blocks 36 contain water which receives heat, the water will go through a phase change to evaporate as vapor. Due to the alternately stacked arrangement of the heat transfer pipe assemblies 10 and the evaporative heat exchange assemblies 40 and the undulating direction of the heat exchange assemblies 40, upon an air flow in the direction indicated by arrow F shown in Fig. 1, the vapor will be carried away by the air flow. In addition to this heat exchange, the evaporative heat exchange assembly 40 has additional contribution by the fact that the frame 42 which conducts heat efficiently between its uppermost part and lowermost part and by the sheet 44 which evaporates the contained water in the same manner as the sheet 14.

Figures 6 and 7 show a modified heat transfer pipe assembly 100 which, unlike the serpentine heat transfer pipe assembly 10, is basically of a linear pipe construction. In this modified assembly 100, the pipe 110, the sheet 140 and the board 160 are essentially the same as the abovementioned pipe assembly 10 and their function and operation are the same as well so that a further description is believed not necessary.

It is to be understood, however, that even though numerous characteristics and avantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.

Claims

CLAIMS 1. A heat transfer pipe assembly which effectuates heat removal of working medium flowing therethrough by ambient air flowing thereover, comprising: a substantially flat pipe having a first and a second opposite flat walls and a passage between the first and second flat walls for a working medium to flow through; and a hygroscopic sheet enveloping over at least the first and second flat walls.
2. The assembly as claimed in claim 1, further comprising an undulate board disposed within the passage of the pipe.
3. The assembly as claimed in claim 1, wherein the substantially flat pipe is serpentine within the hygroscopic sheet.
4. The assembly as claimed in claim 3, further comprising a plurality of hygroscopic blocks, and wherein the substantially flat pipe comprises a plurality of substantially straight segments spaced apart from each other with each of the plurality of hygroscopic blocks being disposed in the space between adjacent straight segments of the pipe.
5. The assembly as claimed in claim 4, further comprising a plurality of undulate boards each being disposed within one of the plurality of substantially straight segments of the pipe and being undulated along a direction which is perpendicular to the first direction.
6. A heat transfer unit comprising: a plurality of heat transfer pipe assemblies each comprising a substantially flat pipe and a first hygroscopic sheet enveloping over the substantially flat pipe, the pipe having a first and a second opposite flat walls and a passage between the first and second flat walls for working medium to flow through in a first direction; and a plurality of evaporative heat exchange assemblies each comprising an undulate frame and a second hygroscopic sheet enveloping over the undulateframe; the plurality of heat transfer pipe assemblies and the plurality of evaporative heat exchange assemblies being alternately stacked and the frame of each evaporative heat exchange assembly being undulated along a second direction which is substantially parallel to the first direction.
7. The unit as claimed in claim 6, further comprising a plurality of hygroscopic blocks, and wherein the substantially flat pipe comprises a plurality of substantially straight segments substantially parallel to and spaced apart from each other with each of the plurality of hygroscopic blocks being disposed in the space between adjacent straight segments of the pipe.
8. The assembly as claimed in claim 7, further comprising a plurality of undulate boards each positioned within one of the plurality of substantially straight segments of the pipe and being undulated along a direction which is perpendicular to the first direction.