EXCHANGE GAS HEAT EXCHANGER

Abstract

A heat-exchanger (1) consists of a series of closely-spaced, essentially planar, pressure elements (11). Each pressure-element comprises a laminated plate-pair having surfaces formed to provide a plurality of ribbon like cavities between the plates, through which a working fluid can flow. Each plate-pair is joined around the common perimeter to produce a pressure-tight envelope having fluid-inlet and outlet ports at suitable locations. Between adjoining pressure-elements, heat-conductor plates (20) of corrugated profile are located; providing a series of narrow, approximately triangular-sectioned channels, distributed across each pressure-element, through which hot exhaust-gases can form a counter-flow with that of the pressure-element working fluid. The heat-conductor plates are engineered to react pressure-loading from the pressure-elements. The complete assembly of pressure-elements and heat-conducting plates is contained, in the direction of the major axis of the enclosure (23), between end-plates (25) retained by the body of the enclosure; by tie-rods, bars, or similar means.

Description

FIELD

This invention relates to improvements in the art of heat-exchanger design and in particular to a heat-exchanger suitable for use in conjunction with an internal-combustion engine.

BACKGROUND

Heat-to-work energy transformations cannot be performed with 100% efficiency due to physical phenomena characterised by the thermodynamic laws. In the case of the internal-combustion engine, the work output is often approximately 30% of the energy released as heat by the combustion of the fuel. Typically, a similar amount of energy is lost as heat in the exhaust-gases expelled from an engine. The balance of the combustion-heat energy is lost to cooling water and to mechanical losses etc.

It is desirable to recover exhaust-gas heat-energy for the purpose of doing work, so that the overall efficiency of the prime-mover in question is increased. One method that can be used is to pass the hot exhaust-gases through a heat-exchanger through which a working-fluid, typically water, is pumped. In a suitable heat-exchanger, the water can be evaporated into steam at a pressure sufficient to do mechanical work in an expansion engine. The, nett, work done by the steam is then additional to the work output of the prime-mover so that an overall increase in efficiency is effected.

Heat-exchanger embodiments can be realised as various arrangements of tube and/or plate elements in differing proportion; the working elements of some heat-exchangers being derived entirely from tube, others being derived entirely from plate. Normally heat-exchanger design choices are dominated by the type of thermo-fluids involved, their temperature, state and working pressures. It is usual to choose circular-sectioned tubing for high-pressure applications because of its ready suitability to pressure containment. Plate-type heat-exchangers are considered amongst the most efficient of the heat-exchanger types. This is because of two design features; firstly the large surface area that the type can realise for heat-transfer and secondly, because the mass of the working thermo-fluids can be disposed at very small distances from the heat-exchanging surfaces. This second feature is particularly relevant to effective heat-transfer by conduction. Plate-type heat-exchangers are normally considered to be suitable for low-pressure operation.

Many internal-combustion engine applications require operation at a wide range of engine speeds and throttle openings. An ideally matched exhaust heat-recovery system would demonstrate a high efficiency over the same, wide, operating-range so that the cost-effectiveness of the system was not compromised by partial inefficiencies. The degree of convective heat-transfer, with a heat-exchanger, is dependant on the strength of the circulation of the thermo-fluids involved and therefore heat-exchangers which are strongly dependant, by design, on convective heat-transfer are subject to degraded performance at reduced thermo-fluid-velocities. Since a prime-mover operating at reduced speed and/or partial throttle opening will provide reduced exhaust-gas volume-flow, the internal fluid-velocities of an associated heat-exchanger will fall proportionally and provide lower heat-transfer efficiencies as a result. Conductive heat-transfer is a desirable feature of a heat-exchanger required to operate over a range of exhaust-gas, volume-flows (because fluid velocity is then not a performance factor) and therefore the efficiency of a heat-exchanger with this feature will not be reduced by fluid-dynamic effects at low engine speeds.

It is the object of the present invention to provide a plate-type heat exchanger which can operate at moderately high operating pressures and at high efficiency over a wide range of working-fluid mass-flows.

DESCRIPTION

A heat-exchanger consists of a series of closely-spaced, essentially planar, pressure-elements arranged normally to the major axis of an enclosure. Each pressure-element comprises a laminated plate-pair, at least one of which plates has a surface formed so as to provide a plurality of narrow, ribbon-like cavities, between the plate-pairs, through each of which cavities a working fluid can flow in the manner of a thin film. Each laminated plate-pair is joined around the common perimeter by welding, brazing or other suitable method, to produce a pressure-tight envelope having fluid inlet and outlet ports formed at suitable locations on the perimeter. In the spaces between adjoining pressure-elements, heat-conductor plates, of corrugated, deeply serrate, profile, are located, to provide a series of narrow, approximately triangular-sectioned channels, distributed across each pressure-element, through which hot exhaust-gases can be directed, to form a counter-flow with that of the pressure-element internal working fluid. The peaks of successive corrugations engage with linear recess-features present in one or both of the pressure-element plates that bound the space between successive pressure-elements, such linear-recess features being associated with the multiple narrow channels provided within each pressure-element envelope. The material of each corrugated conductor-plate is disposed predominantly in the direction of the major axis of the heat-exchanger enclosure, to provide a series of compressive load-paths between adjacent pressure-elements, distributed evenly across the plane of each pressure-element. The conductor-plate material is given a thickness sufficient to realise a safe working stress, for the material operating conditions, and to prevent compressive buckling of the corrugated surfaces extending between adjacent pressure-elements, so as to enable the corrugated plates to react loading applied normally to the plane of each pressure-element by the internal working-pressure. The complete assembly of pressure-elements and heat-conducting plates is contained, in the direction of the major axis of the enclosure, within end-plates retained by the body of the heat-exchanger-enclosure acting structurally, as a tension member, in reaction to the internal working pressure of the pressure elements. Alternatively, the end plates can be restrained by attached tie rods, bars or similar means, so that the complete pressure-element assembly is structurally independent of the heat-exchanger enclosure.

A specific embodiment of the invention is further described by way of example and with the assistance of the accompanying drawings in which;

FIG. 1 shows four aspects of the outside of a heat-exchanger and indicates the locations of horizontal section A-A and transverse section B-B.

FIG. 2 shows horizontal section A-A

FIG. 3 shows transverse section B-B, taken through the plane of a single pressure-element revealing a view of the inside surface.

FIGS. 4(a) and 4(b) show, part, sectional views of pressure-element embodiments.

FIG. 5 shows a transverse section through a heat-exchanger system of two serially connected heat-exchangers and an intervening exhaust-gas catalyst.

With reference to FIGS. 1, 2, 3, 4(a) and 4(b):

A heat-exchanger 1 has a plurality of pressure-elements 11, each pressure-element consisting of two plates 12 laminated by joining around their common perimeter 13. Pressure-elements 11 have cavities 14 provided within by the surface features 15 in plates 12. Inlet ports 16 and outlet ports 17 are situated at suitable locations on perimeter 13. Inlet passage 18 and outlet passage 19 are provided for the transport of working fluid into and out of the pressure-element 11 series. Corrugated plates 20, of serrate profile, are located between subsequent pressure-elements 11 so that the peaks 21 of corrugated plates 20 engage with surface features 15. Ports 22 are arranged to admit exhaust gases into enclosure 23. Port 24 is arranged to conduct exhaust gases from enclosure 23. Ceramic insulators 25 intervene between the assembly of pressure-elements 11 and corrugated plates 20 and retaining end-plates 26. Thermal insulation 27 externally encloses heat-exchanger enclosure 23.

Referring to FIG. 4(a), there is disclosed at large scale, a part, sectional, detail of two successive pressure-elements 11 in a series, in which both laminated plates 12, of each pressure-element, possess surface feature 15, for the engagement of peaks 21 of each corrugated plate 20. FIG. 4(b) discloses at large scale, a part, sectional, detail of three successive pressure-elements 11 in a series, in which one only of the laminated plates 12, of each pressure-element, possess surface feature 15. Either arrangement shown is structurally feasible, but the embodiment of FIG. 4(a) is preferred because of the better integration of parts, for superior structural integrity and for superior thermal conductivity.

Referring to FIG. 5, there is shown a heat-exchanger system 2, comprising two heat-exchangers 1, combined within a common enclosure 23, with serial, working-fluid, connection 28. Exhaust-gas catalyst 29 is located between heat-exchangers 1, so that exhaust-gases passing through enclosure 23, via ports 22, are directed through the first encountered heat-exchanger 1, then through the exhaust-gas catalyst 29, subsequently passing through the second encountered heat-exchanger 1, finally, to be conducted from enclosure 23 via port 24.

Claims

1) An exhaust gas heat-exchanger, comprising;

A series of substantially planar, heat-transfer pressure-elements, each said pressure-element having planar alignment normal to the major axis of an enclosure and consisting of laminated plate-pairs, joined around a common perimeter; at least one said laminated plate having ribbed surface-features to provide a parallel series of narrow cavities, within each pressure-element, in internal communication with inlet and outlet ports, suitably located on the said perimeter, for the passage of a working fluid;

a series of corrugated plates, of deeply-serrate profile, forming compression-reacting elements, located between successive pressure-elements and engaging with the said ribbed surface-features to provide channels for the passage of exhaust-gas between adjacent pressure-element surfaces;

an enclosure having inlet and outlet ports for the passage of exhaust gas and having structural means to contain the, mutually opposed, working forces from the pressure-vessel series, acting outward in parallel alignment with the said major axis of the enclosure;

means to convey working-fluid from a connection external to the said heat-exchanger enclosure, to the said pressure-vessel inlet ports and means, to convey the heated or evaporated fluid from the said pressure-vessel outlet-ports to a connection external to the heat-exchanger enclosure.

2) A heat-exchanger as in claim 1, in which the working forces from the pressure-vessel series are contained between end-plates mutually restrained by tie-rod or similar means in which the structural system is independent of the heat-exchanger enclosure.

3) A heat-exchanger system, consisting of two heat-exchangers, as in claims 1 or 2, in which the said heat-exchangers are combined in the form of a conjoined or common, enclosure, arranged for the passage of heated exhaust-gas, in which the said heat-exchangers are serially connected with respect to the passage of the working-fluid and said heat-exchangers being ordered within the exhaust gas stream so that there is a first, high-temperature, heat-exchanger and a second, lower-temperature, heat-exchanger;

an exhaust-gas catalyst located within the said heat-exchanger system enclosure, between said first heat-exchanger and said second heat-exchanger within the exhaust-gas passage, for the purpose of exhaust-gas purification treatment.