GB2217828A

GB2217828A - Heat exchangers

Info

Publication number: GB2217828A
Application number: GB8908741A
Authority: GB
Inventors: Roland Lederer
Original assignee: MTU Motoren und Turbinen Union Muenchen GmbH
Current assignee: MTU Aero Engines GmbH
Priority date: 1988-04-20
Filing date: 1989-04-18
Publication date: 1989-11-01
Also published as: JPH01315623A; DE3813202A1; FR2630534A1; GB8908741D0

Description

-1 HEAT EXCHANGER 2217828 The invention relates to a heat exchanger for

two spatially separated flowing media.

DE-PS 31 46 089 shows a heat exchanger having two collecting pipes which are of straight construction and are arranged in parallel. The arrangement, with cross-counter-current flow through it, makes possible a good degree of heat exchange and low-stress compensation of thermal expansion. A disadvantage with the embodiment shown is that the gas stream flowing on the outside has to flow through an approximately rectangular flow duct, which therefore sets structural limitations with respect to installation conditions.

Embodiments of the invention may provide a heat exchanger which makes possible a rotationally symmetrical arrangement and flow.

According to one aspect of the invention there is provided a heat exchanger for two spatially separated flow media of different temperatures, having two collecting pipes joined together by means of several profiled pipes, wherein the collecting pipes are annular and are arranged coaxially, and the profiled pipes extend radially inwardly or outwardly of each collecting pipe and are similarly curved as viewed in the coaxial direction of the collecting pipes, the profiled pipes being evenly distributed around each collecting pipe and evenly spaced from each other over a substantial portion of the length of each profiled pipe. Advantageously, the curve of each profiled pipe is such that over the said portion of its length the perpendicular spacing between it and adjacent pipes is not significantly different at different radii.

According to another aspect of the invention there is provided a heat exchanger for two spatially separated flow media of different temperatures, having 1 is 1 two collecting pipes interconnected by several profiled pipes for conducting one of the'flow media, wherein the collecting pipes are annular and are arranged coaxially, and the profiled pipes extend radially inwardly or outwardly of each collecting pipe into an gpnular flow passage for the other flow medium defined by the annular collecting pipe, the profiled pipes being shaped so that the flow cross-section of the annular passage between any two profiled pipes is approximately uniform over the radial extent of the passage. In this way the flow cross- sectional area for any given radial increment should be approximately constant.

This arrangement makes it possible, while retaining the advantages of known heat exchangers such as cross-counter-current operation and good heat expansion characteristics, to achieve a uniform flow and hence high efficiency with an annular flow duct. The use of the heat exchanger in rotationally symmetrical units, such as aeroplane gas turbines, is therefore possible.

The construction of the profiled pipes gives a uniform flow duct,and hence an axial flow with a high degree of efficiency can be achieved. In particular secondary flows, for example in the radial direction, are avoided.

A particularly preferred application consists in using the heat exchanger of the invention as an air pre-cooler in the intake duct of an aeroplane gas turbine. In supersonic applications an air pre-cooler is advisable for obtaining a high flight Mach number because of the high ram temperatures occurring, for which the installation of the heat exchanger of the invention is suitable. Of particular advantage is the free capacity for thermal expansion of the profiled 1 i 1 i i i 7 r 7 1 1 1 i i 1 pipes which results in a good heat shock sensitivity.

The installation dimensions of the heat exchanger can vary according to requirements; in particular a radially inner cylindrical core chamber can be constructed as a bypass duct. The geometry of the heat exchanger can be adapted to that of flow ducts or outer dimensions of gas turbines.

In one embodiment of the invention the collecting pipes are axially offset and the yoke-shaped profiled pipes extend radially outside them and are' joined to them approximately perpendicularly to their circumferential axes, i.e. the ring-shaped axes of the pipes. Thus a simple joining of the profiled pipes to the collecting pipes can be achieved since the bores to be formed in the collecting pipes can be made perpendicularly.

According to another embodiment of the invention the yoke-shaped profiled pipes extend radially inside the annular collecting pipes and are joined to them at an acute angle to their circumferential axes. This allows a favourable supply and discharge of the media to be conveyed through the collecting pipes from outside. In addition the collecting pipes can be made with a small flow cross section.

The profiled pipes are preferably provided with spacers between them. Thus the predetermined spacing of the profiled pipes can be maintained, and flow-induced oscillations and shock loads can be avoided or do not strain the seams of the profiled pipes.

In an advantageous development of the invention there is provided a core chamber through which media can flowifreely in the axial direction, and the diameter of this chamber may be approximately 0.7 is i times that of the outer diameter of the heatexchanger. This means that the core chamber has approximately the same flow cross-section as the heat exchanger and hence, by means of auxiliary flaps, the in-flowing gas stream can be made to flow alternatively through the heat exchanger or the core chamber used as a bypass.

When a core chamber is present, guide flaps are preferably provided which convey the flowing air stream through the heat exchanger or, alternatively, the core chamber. This allows the air stream to be supplied directly to the gas turbine in the case of low flight Mach numbers and the flow losses occuring in the heat exchanger are avoided. At high Mach numbers the heat exchanger is connected by turning the guide flaps, and the high ram temperatures thus occurring are reduced.

In yet another embodiment the collecting pipes are arranged concentrically and the profiled tubes extend approximately perpendicularly to the inner collecting pipe. This makes possible a heat exchanger of small axial length-through which media can flow axially.

In an advantageous development of the nvention the heat exchanger is arranged in an intake duct of a turbo drive unit. This allows pre-cooling of the air supplied to the drive unit, and in high flight Mach numbers this makes itself apparent in the form of increased efficiency.

For a better understanding of the invention embodiments will be described in detail below, with reference to the accompanying drawings, in which:

Fig. 1 shows an axial section through a heat exchanger in accordance with the invention; Fig. 2 shows a schematic cross-sectional view -V of the heat exchanger of Fig.1; Fig. 3 shows an axial section of a second embodiment; Fig. 4 shows a schematic cross-sectional view of the heat exchanger of Fig.3; Fig. 5 shows a further embodiment of the invention in cross-section; Fig. 6 shows an axial section of a turbo drive unit flow duct; Fig. 7 shows an axial section through a turbo drive unit; Fig. 8 shows an axial section through another embodiment of a turbo drive unit.

In the heat exchanger shown in Fig. 1 two axial, annular collecting pipes 2, 3 are shown, arranged one behind the other with regard to their common annular axis. Over the outer circumference several yoke-shaped pipes 4 are fitted on both collecting pipes 2, 3, by means of which the collecting pipes 2, 3 are in flow connection with each other. As shown in Fig. 2 with reference to the collecting pipe 2, the profiled pipes 4 are curved in the circumferential direction so that the perpendicular distances 9 between adjacent profiled pipes 4 are substantially the same over their entire extent. This means that there is a substantially uniform flow crosssection per unit area over the radial extent of the heat exchanger.

In the embodiment of the invention shown in Fig. 3 the collecting pipes 2, 3 are provided on their inner circumference with yoke-shaped profiled pipes 4.

As can be seen from Fig. 4 the profiled pipes 4 are also curved in the circumferential direction in order to obtain a uniform spacing 9., For this purpose the 35, profiled pipes 4 are provided with fitted spacers 10 which guarantee the maintainance of the spacings 9. These spacers 10 can be constructed as rings running concentrically to the collecting pipes 2, 3, as rings individually surrounding the profiled pipes or as other known embodiments.

The embodiment of the invention shown in Fig. has two concentrically arranged collecting pipes 2, 3 which are joined for flow by profiled pipes 4 arranged in the annular space between them. The profiled pipes 4 are curved in the circumferential direction and the connection to the inner collecting pipe 3 is preferably approximately perpendicular to the collecting pipe at that point. In this embodiment also the perpendicular spacing 9 between the individual profiled pipes 4 is substantially constant over the entire radial extent. Spacers 10 can also be provided.

Fig. 6 discloses the use of the heat exchanger of the invention in the intake duct 5 of a turbo drive unit 6. The heat exchanger 1 is so constructed that its inner core chamber 8 (see Fig.5) has approximately the same flow cross-section as the chamber 11 in which the profiled pipes 4 are located. By switching the guide flaps 7 the in-flowing air stream 12 can flow through the chamber 11 or the core chamber 8 as desired. At low flight Mach numbers the core chamber 8 will receive the flow and the heat exchanger is advantageously protected from damage by foreign bodies which are sucked in, for example birds. In addition flow losses due to the heat exchanger are avoided. At higher flight Mach numbers the guide flaps 7 are laid in the position shown and the air stream 12 is conveyed into the chamber 11 and hence into the effective area of the heat exchanger.

In the fan drive unit 13 schematically shown in Fig. 7 there are provided fan blades 15 fitted over i i i -t C the circumference of a rotor 14. The fan blades 15 are surrounded by a cylindrical casing 16. Part of the air stream conveyed by the fan blades 15 reaches the annular intake duct 17 of a gas turbine 18. This consists substantially of a compressor 19, a combustion chamber 20 and a turbine 21 connected one behind the other. Behind the compressor 19 part of the compressed air is branched off into the pipe line 22 and conveyed to the collecting pipe 2 of the heat exchanger 1. The compressed air flows to the collecting pipe 3 through the yoke-shape profiled Pipes 4 fitted over the circumference of the collecting pipe 2, and it is cooled by the air in the annular bypass duct 24 of the fan drive unit 13 in the crosscounter stream. By means of the pipe line 23 the cooled air is conveyed into the inside of the rotor and to the blades of the high pressure turbine stage for cooling. Alternatively to the cooling by the by-pass air stream, the compressed air can also be cooled by hydrogen.

The embodiment shown in Fig. 8 is a turbofan ramjet engine 26 which substantially comprises a displacement tip 27, an intake 31, a gas turbine drive unit 28 with a bypass duct 29 and a thrust nozzle 30. The heat exchanger 1 of the invention shown only schematically is arranged here only in the int ake duct of the gas turbine unit 28, whilst the bypass duct 29 remains unaffected.

1 4

Claims

CLAIMS:

Heat exchanger for two spatially separated flow media of different temperatures, having two collecting pipes joined together by means of several profiled pipes, wherein the collecting pipes are annular and are arranged coaxially, and the profiled pipes extend radially inwardly or outwardly of each collecting pipe and are similarly curved as viewed in the coaxial direction of the collecting pipes, the profiled pipes being evenly distributed around each collecting pipe and evenly spaced from each other over a substantial portion of the length of each profiled pipe.
2. Heat exchanger according to claim 1, wherein the curve of each profiled pipe is such that over the said portion of its length the perpendicular spacing between it and adjuacent pipes is not significantly different at different radii.
3. Heat exchanger for two spatially separated flow media of different temperatures, having two collecting pipes interconnected by several profiled pipes for conducting one of the flow media, wherein the collecting pipes are annular and are arranged coaxially, and the profiled pipes extend radially inwardly or outwardly of each collecting pipe into an annular flow passage for the other flow medium defined by the annular collecting pipes, the profiled pipes being shaped so that the flow cross-section of the annular passage between any two profiled pipes is approximately uniform over the radial extent of the passage.
4. Heat exchanger according to any preceding claim, wherein the collecting pipes are of approximately the same diameter and are arranged axially one beyond the other and the profiled pipes are 1 1 1 1 c.

1 1 16 approximately yoke-shaped.
5. Heat exchanger according to claim 4, wherein the yoke-shaped profiled pipes extend radially outwardly of the annular collecting pipes and are joined to them approximately perpendicularly to the pipe axes.
6. Heat exchanger according to claim 4, wherein the yoke-shaped profiled pipes extend radially inwardly of the annular collecting pipes and are joined to them at an acute angle to the collecting pipe axes.
7. Heat exchanger according to any preceding claim, wherein the profiled pipes are provided with spacers.
8. Heat exchanger according to any preceding claim and having a core chamber through which media can flow freely in the axial direction, the diameter of this chamber being approximately 0.7 times that of the outer diameter of the heat exchanger.
9. Heat exchanger according to claim 8, further comprising guide flaps which can be set so as to convey the in-flowing air stream either through the heat exchanger or through the core chamber.
10. Heat exchanger according to any of claims 1 to 3, wherein the collecting pipes are arranged concentrically to each other.
11. Heat exchanger according to claim 10, wherein the profiled pipes are joined to the inner collecting pipe approximately perpendicularly to its pipe axis.
12. Heat exchanger according to any preceding claim and arranged in an intake duct of a turbo drive unit.
13. Heat exchanger substantially as described herein with reference to any of the embodiments shown in the accompanying drawings.

PubUsbed 19B9 at The Patent OMoe. State House, 66,171 High RolborI3, L0ndonWC1R4Tp. Furthereopies maybe obtainedfromTh.

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Sales Brancb, St Mary Cr ton, Wen BR5 3RD. P"'nted by M't"ttPlaz tOchlIlQues W, St Mary Cray, Kent, C;on. - 1/87