US2904242A - Pressure exchangers - Google Patents

Description

Sept. 15, 1959 R. D. PEARSON PRESSURE EXCHANGERS Filed June 28, 1956 United States Patent 2,904,242 PRESSURE EXCHANGERS Ronald D. Pearson, Chester-field, England Application June 1956, SerialNo. 594,461

9 Claims. (Cl. 230-69) ,Thisinvention relates to machines, hereinafter referred to'as pressure exchangers, in which each of a plurality of cells serves cyclically to receive. gas from a source of lower pressure and discharge it to a pressure-increasing means, and to receive gas from. said pressure-increasing means and discharge it to a region of lower pressure. The cells are arranged around the periphery of a rotor mounted to pass over appropriate permanently-open ports in a stator. (Of course, the terms rotor and stator are used relatively, the one to the other, so that it might be that the rotor is stationary in space and that the stator? rotates about the rotor.) The admission and discharge of the gas to and from the cell in the lower and in the higher pressure stages is hereinafter referred to as scavenging; being defined as a condition in which both ports of the cell being open togetherfor a suflicient duration of time, there occurs a displacement of a substantial part'of the former contents from the cell, and their replacement by fresh gas.

The pressure-increasing means is conveniently a combustion chamber wherein the received gas is made to burn with a fuel to increase both its volume and temperature.

Conveniently, too, but not necessarily, the motion of the gas into and out of the cell in both of the scavenging stages is unidirectional, so that it is possible to speak of an inlet to and an outlet from the cell, the inlet beingon one flank of the rotor and the outlet on the other flank.

When the machine is arranged as an engine, it serves to convert some of the pressure energy from said pressure increasing means into kinetic energy.

One of the objects of the present invention is to provide that a scavenging stage is immediately preceded by what is 'hereinafter'referredto as prescavenging, when the gas within the cell is accelerated towards that port from which it is aboutto'be discharged the scavenging stage.

The following description relates to the accompanying drawings which show, by way of example only, one embodiment of the invention. In the drawings:

Figure 1 isr a developed view of a pressure. exchanger in accordance with this invention; and I Figure 2 is a diagram showing. the mode of wave representation in Figure 1.

In Figure 1 is showna development of the rotor and stator'system of a pressure exchanger embodying the present invention, with a rotor R moving from right to left as indicated by the arrow between the two flanking parts of a statorfS. The rotor has an array of cells in its'p eriphery; and the stator has a number of ducts whose months at fixed positions around the inner periphery of the stator open towards the path of movement of ports leading into and out of the cells.

The rotor cells' Each of the similar cells C in the rotor R has an inlet port Ci and'an outlet port Co, the latter having its adjacent'cell walls bent backwards.

2,904,242 Patented Sept. 15, 1959 The stator ducts ceiving duct Ho, and the low pressure pre-scavenging receiving duct PLo.

The pressure-exchange cycle Thus the cycle through which such a cell C passes consists of five stages, of low and high pressure scavenging and pre-scavenging and of compression. More particularly, this cycle is as follows:

(1) Low pressure scavenging: When the cell is at the righthand side of the drawing, its inlet and outlet ports Ci and C0 are both open to the respective low pressure scavenging delivery and receiving ducts Li and L0. This is the low pressure scavenging stage; the outlet Lo discharges to the atmosphere and the inlet Li receives air from the atmosphere either directly or via a fan.

(2) Compression: From the low-pressure scavenging stage L the cell passes to the compression stage where the cell inlet Ci is closed while the outlet Co isopen to the delivery duct CH1.

(3) High pressure pre-scavenging: In the high-pressure pro-scavenging stage PH, the cell inlet Ci is open to the high pressure delivery duct Hi and the cell outlet C0 is open to the receiving duct PHo.

(4) High pressure scavenging: High pressure scavenging exists when both cell inlet and outlet are connected to the respective high pressure ducts Hi and H0. The receiving duct Ho leads to a combustion chamber (not shown) and the delivery duct Hi takes from the combustion chamber.

(5 Low pressure pre-scavenging: Beyond the high pressure scavenging stage is the low pressure pro-scavenging stage PL. Here the cell inlet Ci is at first closed and is then opened to the inlet Pli. The outlet is open firstly to the pre-scavenging outlet PLo, and then to the lowoutlet L0.

pressure scavenging Wave propagation the reflecting end.

The path of a compression wave in space, i.e. relative to the stator, is shown by a pair of continuous lines and that of a rarefaction Wave by a pair of broken lines; first line of each pair marks the foot of the wave and the second line marks the head. As is known, compression Waves tend to grow steeper as they progress, and rarefaction Waves to grow shallower, so that the two full lines of a pair converge, while broken lines diverge. A

compression wave is transformed into a shock wave when.

a pair of full lines meet.

The method of wave representation is shown more clearly in Figure 2, showing the progress of a compression wave 110, 111, from cell inlet to outlet. The line marks the foot of the wave and the line 111 the head, in relation to the forward wall of the cell, (It has is set up in the cell from that port, and.

the

always to be remembered that the cell has a finite width circumferentially of the rotor and that the waves extend over the full cell width.) The cross hatched areas 112 indicate the sloping wave front in which the pressure and particle velocities increase steadily from wave foot totwave head; the particle velocity being'in' the. direction of wavetravel though at. much lower. speed. The areas. 1113'. following. the sloping wave. front represent azone inzwhichpressure and particlevelocitiesare steady and must remain so until affected. by passage of some other wave front such as rarefaction wave 114115;

A- pair of waves of opposite sense following one an other within a cell-length constitute a pulse; a compression pulse or a rarefaction pulse according as the-leading wave-isone of compression or of rarefaction. Thus the pair. of waves 110, 111; 114, 115, together constitute a compression pulse.

The occurrence of a wave may be advantageous or deleterious; and the present invention is concerned with the; generation and utilisation of waves that are advantageous. In general, waves are to be generated in the prescavenging stages and utilised there to accelerate the gas in the. cell towards that port cell from which they are to' be discharged in. the succeeding scavenging stage.

A certain wave pattern will exist for one set of condi: tions' only, the condition exerting the most influence on the wave pattern being the rotor speed. In Figure 1, therefore, the wave pattern shown is that obtaining when conditions approximate to design values; however, it is so arranged and it is one of the objects of this invention that the change in pattern caused by variation in' operating conditions has only a minor effect upon the performance of the machine.

The wave cycle Thefollowing are the waves that are developed in the cell in its cyclic movement from low pressure scavenging through compression, high pressure prescavenging and scavenging and low pressure prescavenging back to low pressure scavenging.

In Figure l, as a cell C moving from right to left approaches the end of the low pressure scavenging stage L the flow of gas through the cell is retarded by waves of compression 3 and 4 travelling from the celloutlet Co towards the cell inlet Ci and generated by the gradual closing of the cell outlet C to the low pressure scavenging discharge duct Lo, i.e. the wave 3 by a partial and the wave 4 by the complete closure. The reception of Wave 3' at the inlet end Ci causes substantial cut-off of :the flow into the cell from the stator inlet duct Li, but without that reversal of flow into duct Li which would occur if no partial closure of L0 preceded the complete closure, so that waves 3 and 4 coincided and'their combined amplitude therefore were greater.

The waves 3 and 4 are desirable waves, since by them the energy remaining in the cells after scavening is substantially used to produce a supercharging eifect; but the reflected waves 6 and 7 form a rarefaction pulse which if further reflected would be undesirable. They are substantially neutralised on reception at the pre-compression nozzles CHi feeding the outlet ends of each cell.

Precompression is effected by introducing gas from duct CHi at. an elevated pressure so that compression wave is produced. This wave is reflected from the closed inlet Ci aswave 8 producing, further. compression; Although wavesS and 8 are desirable, the further refiectionof wave 8 from the outlet end wouldbe undesirable. By suitable design of the nozzles in precompression duct CHi to give sufficient pressure dropthe'desired neutralisation of wave 8 is eflected.

After transit of wave 8 the cellicontains stagnant gas at an elevated pressure substantially equalv to that in prescavenge-receiving duct PHo, so that the cell contents are. not; influenced when the cell is opened to. this. duct on furthermovement of the rotor.

Prescavenging is produced by opening the cell inlet Ct to the high pressure scavenging delivery duct Hi, when a compression wave 9 completes the compression process and accelerates the cell contents to scavenging speed. The pre-scavenging receiving duct PHo is so positioned as to receive wave 9 and on arrival this wave causes discharge from the cell to commence.

By restriction of the cell outlets preferably by using bent back trailing edges as at. C0. the reflection of wave 9 as a rarefaction wave can be at least reduced.

On passing the wall beyond PHo,. the cell. enters the high pressure scavenging stage H and to prevent the formation of'a pressure pulse by temporary flow stoppage the width of the wall ismade less tharrthe cell width or less than the width of subsidiary channels if fitted in the outlet end.

Hot gas enters the cell at its inlet end from duct Hi and cold. gas is, withdrawn from thev outlet end H0; the progressof theinterface. between, the. two gasesis indicated by. line2.

At the. endv offthe, high pressure scavenging stage. the scavengingflow is. arrested in two stages by rarefaction waves. 10 and. The first wave 10. isproduced by par.- tial restriction of the cell inletcausedby the change to :1 highangle inlet nozzle of.-the delivery. duct Hi. Wave 1 2-isproduced by complete cut oif'from-delivery duct Hi; Termination of scavengingin two stages as described. is desirable inorder to improve thetflow conditions at the receiving duct.Ho, especially at lower speeds ofopera tion. Also, thehigh: anglenozzle serves to neutralisezany unwanted residual waves. received. by it.

An imporant rarefaction; wave 11' is. produced upon opening the cell outlet Cotoduct- PLo at a lower pressure and is supplemented by reflection of wave 10-fi'om the wall between Ho andPLo. In the same way the final rarefaction wave 15 produced by opening. thecell to the low pressurescavenging discharge duct L0 is reinforced' bythe reflection of. wavelZ.

Wave 11refiects. from the closed. inlet end aswave13 and is followed closely by compression wave.14' produced by. opening the. cell inlet tothe lowpressure prescavenging delivery duct PM. An undesirable retarding pulse 13,. 14- is. thereby produced. which will be continually. reflected from the. cell endsduring scavenging as indicated for the first such reflection by. pulse 16, 17, and which. increases in width asethe. speed reduced. Substantial neutralisation otwave-15zbyimpingement on the nozzles PM is ensuredby'correctdesignof.thenozzles PLi; gas for. PLi-is.fedQfromteXpansiOn; duct BLo:

The dividingvwall between PM and. Li isv of; narrowerwidth thant thecellin, order to prevent. production. of an undesirable rarefaction; pulse. I

The interface. between incon ring fresh; gas from inlet Li and spent. gas is. shown progressing along. a. cellby line 1.

The apparatus. and. its operations. having. thus been described, it remains to pointtout how that apparatus embodies the featuresof the presentinvention.

Thusit will be seen thatapre-scavenging. acceleration of gas in a cell approaching the high. pressure scavenging stage. H or. the low. pressure. scavenging, stage L. is eflfected: by changing thev conditionof a. celL port, that is to say opening it or. closing. it, so astocausel an appropriatev wave to be. transmitted. through. the, cell. By an appropriate wave is.meant: acompression. wave such as wave. 9 travelling towards the. port such as the cell. outlet Co. from. which the scavenging dischargev is.to. occur; or a rarefaction. wave such. as wave. 11- travelling. away from that port. 4

The high pressure scavenging stage H is preceded by pre-scavenging in which. one cell port namely the cell inlet- Ci is open to the scavenging inlet duct Hi and another cell port. namely the cell outlet Co. is'ope t0 the qqq y i g duct PI-Io receivingggas, iron; theJcelland returning it at least in part to some other point in the cycle namely at the earlier point CI-Ii.

Again, between the low and high pressure scavenging stages L and H a cell port such as Co is open to a delivery duct such as CHi receiving gas from a duct such as PHo into which the cell is discharging through one cell port such as C0 when another cell port such as Ci is open to the high pressure delivery duct Hi.

Between the low pressure scavenging stage L and the high pressure scavenging stage H, there occurs a compression in which one cell port namely the cell inlet Ci is closed by the wall between delivery ducts Li and Hi and another cell port namely the cell outlet C0 is open to the delivery duct CI-li which receives gas from the outlet duct PI-Io to which outlet duct PHo the cell outlet C0 is open when the cell inlet Ci is open to the high pressure delivery duct Hi.

Between the high pressure scavenging stage H and the low pressure scavenging stage L, one cell port namely the cell inlet Ci is closed by the wall between delivery ducts Hi and PLi and another cell port namely the cell outlet C0 is open to the receiving duct PLo supplying gas to the inlet duct PLi to which the cell inlet Ci is open when the cell outlet C0 is open to the low pressure receiving duct Lo.

In a cell approaching the high pressure scavenging stage there occurs a prescavenging acceleration of the gas: this is effected by opening one cell port namely the cell inlet Ci to the high pressure delivery duct Hi and another cell port namely the cell outlet C0 to the receiving duct PHo connecting with the delivery duct CHi to which the cell is open after leaving the low pressure scavenging stage L but before reaching said receiving duct M10.

The opening of one cell port namely the cell inlet Ci to the prescavenging delivery duct PLi occurs only when the pressure within said port Ci is reduced below that in the duct PLi by the arrival of a rarefaction wave 11 originating at another cell port namely the cell outlet Co with the opening of the cell outlet C0 to a duct at lower pressure namely the prescavenging exhaust duct PLO.

It will of course he understood that the invention may take many other 'forms than that shown in the accompanying drawing. In one modification, the shaping of the wall between nozzles Hi and PLi is such that the duct Hi is not closed off completely until the moment before the cell inlet Ci is opened to the duct PLi; in other words the taper is longer and shallower. Other machines within the invention may have unshrouded cells, that is to say, the cell cavities are open to the rotor periphery, where they sweep a stator surface that may or may not have ducts opening through it.

What I claim is:

l. A pressure exchanger comprising a rotor having a plurality of radially extending partitions about the periphery thereof to form a plurality of cells which are open at opposite sides of the rotor, a stator having a wall adjacent each side of the rotor, each wall having ducts therein communicating with the openings in the cells, the ducts in a first wall defining delivery ducts and those in the second wall defining receiving ducts and being in operative alignment with each other, means for supplying scavenging gas at a low pressure to a first delivery duct, means for supplying scavenging gas at a high pressure to a second delivery duct, a low pressure pre-scavenging receiving duct in the second wall between the high and low pressure scavenging receiving ducts and substantially opposite a wall portion between the high and low pressure scavenging delivery ducts.

2. A pressure exchanger comprising a rotor having a plurality of radially extending partitions about the periphery thereof to form a plurality of cells which are open at opposite sides of the rotor, a stator having a wall adjacent each side of the rotor, each wall having ducts therein communicating with the openings in the cells, the ducts in a first wall defining delivery ducts and those in the second wall defining receiving ducts and being in operative alignment with each other, means for supplying scavenging gas at a low pressure to a first delivery duct, means for supplying scavenging gas at a high pressure to a second delivery duct, a low pressure pre-scavenging duct in the first wall between the high and low pressure scavenging delivery ducts, said pre-scavenging duct being smaller than and in alignment with a portion of the low pressure scavenging receiving duct and in communication with the cells.

3. A pressure exchanger as in claim 2 in combination with a low pressure pre-scavenging receiving d-uct in the second wall between the high and low pressure scavenging receiving ducts and substantially opposite a wall portion between the high and low pressure scavenging delivery ducts.

4. A pressure exchanger comprising a rotor having a plurality of radially extending partitions about the periphery thereof to form a plurality of cells which are open at opposite sides of the rotor, a stator having a wall adjacent each side of the rotor, each wall having ducts therein comrnunicating with the openings in the cells, the ducts in a first wall defining delivery ducts and those in the second wall defining receiving ducts, means for supplying scavenging gas at a low pressure to a first delivery duct, means for supplying scavenging gas at a high pressure to a second delivery duct, a further duct in the second wall between the low and high pressure scavenging receiving ducts for delivering gas at high pressure to the cells, and a high pressure pre-scavenging receiving duct in the second wall in communication with the cells, positioned between the further duct and the high pressure scavenging receiving duct and in communication with the :further duct.

5. A pressure exchanger as in claim 4 in which the pre-scavenging duct overlaps a portion of the outlet of the high pressure scavenging delivery duct.

6. A pressure exchanger comprising a rotor having a plurality of radially extending partitions about the periphery thereof to form a plurality of cells which are open at opposite sides of the rotor, a stator having a wall adjacent each side of the rotor, each wall having ducts therein communicating with the openings in the cells, the ducts in a first wall defining delivery ducts and those in the second wall defining receiving ducts, means for supplying scavenging gas at a low pressure to a first delivery duct, means for supplying scavenging gas at a high pressure to a second delivery duct, a further duct in the second wall between the low and high pressure scavenging receiving ducts for delivering gas at high pressure to the cells and a low pressure pre-scavenging receiving duct opening through the second wall in communication with the cell opening and positioned between the high pressure receiving duct and the low pressure scavenging receiving duct, said pre-scavenging receiving duct being substantially opposite a wall portion between the high and low pressure scavenging delivery ducts.

7. A pressure exchanger as in claim 6 in which the high pressure pre-scavenging receiving duct overlaps a portion of the outlet of the high pressure scavenging delivery duct.

8. A pressure exchanger comprising a rotor having a plurality of radially extending partitions about the periphery thereof to form a plurality of cells which are open at opposite sides of the rotor, a stator having a wall adjacent each side of the rotor, each wall having ducts therein communicating with the openings in the cells, the ducts in a first wall defining delivery ducts and those in the second wall defining receiving ducts, means for supplying scavenging gas at a low pressure to a first delivery duct, means for supplying scavenging gas at a high pressure to a second delivery duct, a further duct in the second wall between the low and high pressure scavenging receiving ducts for delivery gas at high pressure to the cells and a prescavenging low pressure delivery duct in the References Cited in the file of this patent UNITED STATES PATENTS Lebre' June 23, 1936 Seippel Apr. 30; 1946' FOREIGN PATENTS Belgium May 31, 1952'

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