GB2218790A

GB2218790A - Regenerators for cooling apparatus

Info

Publication number: GB2218790A
Application number: GB8908944A
Authority: GB
Inventors: Derrick John Haines
Original assignee: British Aerospace PLC
Current assignee: BAE Systems PLC
Priority date: 1988-04-25
Filing date: 1989-04-20
Publication date: 1989-11-22
Anticipated expiration: 2009-04-20
Also published as: FR2630531A1; GB8809707D0; JPH0244158A; GB2218790B; FR2630531B1; DE3913050A1; GB8908944D0

Description

1 I,- 11 1 - COOLING APPARATUS This invention relates to cooling

apparatus, more particularly but not exclusively to a so-called thermo-acoustic cooler, of which the operation is based on a thermodynamic phenomena described, for example, in "Natural Engines", Physics Today, August 1985; "Understanding Some Simple Phenomena In Thermo-Acoustics With Applications To Acoustical Heat Engines", Am. J. Phys, 53(2) February 1985; "Theory and Calculations for an Intrinsically Irreversible Acoustic Prime Mover Using Liquid Sodium As Primary Working FluiO, J. Acoust. Soc. Am. 78(2), August 1985; and "Heat Transfer", Volume 1, page 297, Max Jacob, John Wiley and Sons, 1955 Edition.

Briefly, such coolers operate through the movement, compression and expansion of a working fluid, e. g. a gas or vapour, in an enclosure in a manner similar to the behaviour of air in an organ pipe - the behaviour of the working fluid in fact obeying the same laws of physics which pertain to air in an organ pipe apart from slight modification due to the presence of a structure known as a regenerator which is sometimes placed inside the enclosure or 'pipe' of the thermo- acoustic cooler. The regenerator is a kind of heatexchanger through or past which the working fluid flows and which has the function of receiving heat energy from the working fluid, temporarily storing it, and giving it up again in such a way that given the movement, compression and expansion of the working fluid, heat is transferred from one part, called the 'cold end' of the cooler to a part at the other side of the regenerator. Regenerators are also used, for a similar purpose, in cooling devices operating on the Stirling Cycle.

2r21B790 2 The performance of a thermo-acoustic cooler relies on the existence of a time phase lag between the working fluid pressure cycle and the temporary storage of enerLry by the regenerator, and also upon the efficiency with which thermal energy can be transferred to and from the regenerator.

According to the present invention there is provided a cooling device of the kind comprising a regenerator and a working fluid which is in contact with the regenerator and which is also subjected to movement, compression and expansion so as to produce a cooling effect, said regenerator defining at least one surface alongside which said working fluid passes and which has a plurality of portions projecting out into the working fluid so as to create local discontinuities in the laminar boundary layer flow of the working fluid and hence improve heat transfer between the regenerator and working fluid and further so as to create localised heat source/heat sink sites for increasing the thermal phase lag between said surface and the bulk of the member defining that surface.

For a better understanding of the invention, reference will now be made, by way of example, to the accompanying drawings, in which: - Figure 1 is a sectional view of part of a thermo-acoustic cooler; and, Figure 2 is a sectional view of part of a regenerator used in the Figure 1 cooler.

The cooler of Figure 1 comprises an elongate enclosure or organ pipe 1 containing a working fluid and a regenerator in the form of a plurality of thin, flat plates 2 extending parallel to one another and 1 V the axis of the pipe. The working fluid flows through the regenerator, i. e. past the surfaces of plates 2, and is also subjected to expansion and compression such that a cooling effect is generated at one end (not shown) of the pipe. The means for producing the flow, expansion and compression of the fluid is also not shown.

As shown in Figure 2, each plate 2 has, on each of its two faces, a plurality of pads 3 which project from the face of the plate into the laminar boundary layer 4 of the working fluid and which hence break up that layer so giving better heat transfer. They also form a series of local heat sink/heat source sites on the plate which permit the thermal phase lag between the surface of each plate and its bulk to be maximised, (the theoretical optimum for a thick regenerator plate being 45 0 - see the fourth of the prior art references mentioned earlier).

Instead of the pads 3, there may be provided a series of strips (not shown) extending transverse to the directions of flow of the working fluid, i.e. so that in crosssection, they appear just like the pads in Figure 2.

By way of example, the regenerator plates 2 may be made of quartz, silicon or ceramic and they may be 0.5mm thick. Meanwhile, the pads or strips may be of aluminium deposited in any appropriate manner onto the plates 2 and they may have a thickness of 0.5 microns, may be 0.125mm across and may be at 0.175mm centres. The working fluid may be Nitrogen at a pressure of ten atmospheres and the local bulk movement of the Nitrogen, i.e. the movement indicated by the arrow 5 in each of Figures 1 and 2, may be 0. 5mm or greater.

4 Instead of flat plates, the regenerator may comprise a plurality of nested coaxial tubular plates (not shown) again with pads or strips on the surfaces.

As will be appreciated by those skilled in the art, for best acoustic efficiency, the regenerator plates may have tapered ends and/or may have different lengths so as to reduce acoustic refelections (which may lead to generation of harmonics). In addition, of course, it is desirable that the cross-sectional area available for gas flow should be as nearly constant as is physically practical throughout the length of the organ pipe so that, in the region of the regenerator, the transverse dimensions of the pipe may be made greater than elsewhere to allow for the presence of the plates.

S, - 5

Claims

1 A cooling device of the kind comprising a regenerator and a working fluid which is in contact with the regenerator and which is also subjected to movement, compression and expansion so as to produce a cooling effect, said regenerator defining at least one surface alongside which said working fluid passes and which has a plurality of portions projecting out into the working fluid so as to create local discontinuities in the laminar boundary layer flow of the working fluid and hence improve heat transfer between the regenerator and working fluid and further so as to create localised heat source/heat sink sites for increasing the thermal phase lag between said surface and the bulk of the member defining that surface.

2. A cooling device according to claim 1, wherein said cooling device comprises an elongate enclosure.

3 A cooling device according to claim I or claim 2, wherein said regenerator comprises a plurality of thin flat plates extending parallel to one another and the axis of the elongate enclosure.

4 A cooling device according to claim 1 or claim 2 wherein said regenerator comprises a plurality of nested coaxial tubular plates.

A cooling device according to anyone of the preceding claims wherein said portions projecting into the working fluid comprises a plurality of pads.

6 A cooling device according to anyone of the proceeding claims, wherein the cooling fluid is Nitrogen.

7 A cooling device substantially as hereinbefore described with reference to, and as illustrated in the accompanying drawings.

Published 1989 at The Patent Office, State House, 6671 High Holborn. London WClR 4TP Further copies maybe obtained from The Patent Office. Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD. Printed by Multiplex techniques ltd, St Mary Cray, Kent, Con. 1/87