US3252505A

US3252505A - Rotary heat exchanger

Info

Publication number: US3252505A
Application number: US204462A
Authority: US
Inventors: Jr George J Huebner
Original assignee: Chrysler Corp
Current assignee: Old Carco LLC
Priority date: 1962-06-22
Filing date: 1962-06-22
Publication date: 1966-05-24
Anticipated expiration: 1983-05-24
Also published as: GB1040285A

Description

y 4, 1966 G. J. HUEBNER, JR 3,252,505

ROTARY HEAT EXCHANGER Filed June 22, 1962 5 Sheets-Sheet 1 INVENTUR. Geo rye flzze'zrzef, Jr!

irranvvz' si 1965 G. J. HUEBNER, JR 3,252,505

ROTARY HEAT EXGHANGEH Filed June 22, 1962 5 Sheets-Sheet 2 INVEN TOR. Geo rye J' b zzeirzer; J7?

BY ALA/1m wh m May 24, 1966 G. .1. HUEBNER, JR

ROTARY HEAT EXCHANGER 5 Sheets-Sheet 3 Filed June 22, 1962 "4 4 a 1 a. V z 7 2 d g Q w 2 y M 4 z 4 7 4 x IN VEN TOR. fieo rye flael/ver; BY

May 24, 1966 G- J. HUEBNER, JR

ROTARY HEAT EXGHANGER 5 Sheets-Sheet 5 Filed June 22, 1962 Nudneiz (Vz/r ref: Far 717M227; 407117740" 770w United States Patent This application is a continuation-in-part of copending application Serial No. 379,673, filed September 11, 1953, now abandoned.

This invention is concerned with improvements in a I regenerator of the counterflow type for an automotive gas turbine engine wherein the difficult problems of reducingweight and size are of paramount importance and must be considered concurrently with the problems of minimizing resistance to gas flow through the regenerator matrix while at the same time achieving rapid and efiicient heat transfer from the hot exhaust gases to the cooler high pressure inlet air from the compressor.

According to one embodiment of the invention as set forth in the following specification, a rotary heat exchanger having a generally cylindrical form is provided with a hub upon which is formed a glass matrix struc ture having smooth straight axially extending passages therethrough. A peripheral rim member is mounted upon the glass structure in concentric relationship with respect to the hub. The assembly is mounted transversely with respect to the air discharged from an intake compressor unit and with respect to the exhaust passageways of a gas turbine powerplant. The axial passages through the glass matrix structure are adapted to'conduct the compressed intake air and exhaust gases there/through at angularly spaced positions. The exhaust gases are effective to heat the proximate glass structure to a temperature which approaches in magnitude the temperature of the powerplant exhaust gases. Upon rotation of the regenerator about its axis, the heated portion of the regenerator glass matrix is brought into contact with the cooler compressed intake air as the same passes through the heated air passages, thereby heating the compressed gas turbine intake air which is then conducted to the burner.

One of the several objects of the present invention is to provide a rotary regenerator unit which will be capable of establishing a temperature gradient across the length of the gas passages therein. The temperature gradient is highly desirable because it makes possible a greater increase in the temperature of the intake air.

Another object of the present invention is to provide a rotary regenerator unit for use with a gas turbine powerplant or the like which is resistant to corrosion during high temperature operating conditons.

Another object of the present invention is to provide a rotary regenerator unit for use with a gas turbine powerplant or the like which is adapted to retain uniform dimensions and to resist the tendency to warp while it is being heated by the turbine exhaust gases. This antiwarping feature is of considerable importance in that the intake air must be effectively sealed from the exhaust gases in order' to maintain operating efliciency at a relatively high value. Working of the regenerator greatly impairs the effectiveness of the sealing structure.

Another object of the present invention is to provide a rotary regenerator unit for use with a gas turbine powerplant or the like which is relatively light in weight and inexpensive to manufacture and which achieves optimum heat transfer efficiency with minimum size and weight.

Although the counterflow type regenerator itself is not new, such as a regenerator wherein comparatively cool inlet air flows in one direction through parallel gas passages of the matrix, followed by flow of the hot exhaust gases in the opposite direction through the same passages, gives rise to particular problems in the attainment of efiicient operation which are not encountered in other types of heat exchangers. An important aspect of the present invention has been the discovery that a particular relationship between the thickness of the walls of the individual gas passages and the shape and hydraulic diameter of these passages results in a regenerator of optimum heat transfer efiiciency with minimum size and weight. In particular, it has been discovered that the reduction in thickness of the individual gas passage walls goes hand-in-hand with an appreciable elongated cross sectional shape in order to obtain optimum heat transfer.

'In order to concisely set forth the structural characteristics and mode of operation of the present invention, reference will be made to the accompanying drawings in which:

FIGURE 1 is a schematic representation of an automobile gas turbine powerplant showing the relative position of the various components thereof including the rotary regenerator of the present invention;

FIGURE 2 is an end view of the assembly of FIG- URE 3;

FIGURE 3 is a complete assembly view of an actual operative gas turbine powerplant showing the rotary heat exchanger of the present invention incorporated therein;

FIGURE 4 is a View taken along section line 4-4 of FIGURE 3 showing the segmental inlet and outlet portions for conducting air through the regenerator in either axial direction;

FIGURE 5 is a perspective view partly in section showing the rotary regenerator unit of the present invention isolated from the assembly of FIGURE 3;

FIGURE 6 is a detail enlarged view showing the structure of the glass matrix of FIGURE 5;

FIGURE 7 is an enlarged schematic cross sectional view showing the heat flow associated with a single gas fiow passage;

FIGURE 8 illustrates the relationship between Nusselts number N and a function =K T/K D for various regenerator flow passages of the type illustrated in FIGURE 7; and

FIGURE 9 illustrates the relationship between Nusselts number and the wall thickness of various ceramic regenerator flow passages of the type illustrated in FIG- URE 7.

For a more complete description, reference will be made first to the schematic representation of a gas turbine powerplant in FIGURE 1 wherein numeral 10 is used to designate the gas turbine compressor with an inlet at 11 and a'high pressure discharge passage at 12. The passage 12 conducts intake air to the rotary regenerator 13 which in turn allows the intake air to pass axially therethrough into passage 14 and the burner 15. Upon reaching the burner, the intake air is mixed with fuel and then burned. The burned gases pass through passage 17 to the turbine 18 which in turn drives the compressor shaft 19 and the power output shaft 20. The hot turbine exhaust gases are then conducted through passage 21 and the regenerator 13 to the exhaust port 22. The exhaust gases cause a portion of the regenerator to become heated while passing therethrough. A suitable driving means 23 is provided to rotate the regenerator about its own axis which causes the portion of the regenerator unit which is heated by the exhaust gases to come in contact with the intake air passing from passages 12 to 14 thus heating the same to a temperature which approaches in value the temperature of the exhaust gases.

Having thus described the general arrangement of the component elements of the powerplant, reference will now be made to the operative powerplant assembly as shown in FIGURE 3 which incorporates the regenerator unit of the present invention. The compressor unit, shown generally at 10, comprises a converging inlet 11 which is open to the surrounding atmosphere throughout its entire periphery. A rotor member 24 of the compressor is effective to force the intake air from the inlet portion 11 into an annular diffuser member 29 where a suitable intake air pressure head is created. The rotor member 24 comprises suitable vanes 25 disposed about the hub 28 of the rotor for forcibly feeding the intake air to the diffuser 29 and also a radially extending portion 26 having a peripheral discharge opening 30 for creating a centrifugal head. The diffuser 29 blends into a wide mouthed port-ion, shown at 31, as it progresses circumferentially about the axis of the powerplant. The portion 31 covers a segmental portion of the regenerator unit shown at 13. This segmental portion is shown at X in FIGURE 4. A graphite sector plate or seal 32 is provided for sealing the inlet portion 31. Smooth contact surfaces 32' and 32 are provided on seal 32 for engaging the rotating surface of the regenerator unit 13 and the diffuser portion 31 respectively. An additional sealing means may be provided at 33 to insure a sealing contact between portions 31 and the stationary graphite seal 32. Another graphite sector plate or seal 35 is provided on the opposite side of the regenerator unit and is shaped similar to seal 32. Both of the seals 32 ad 35 have segmental openings to allow the portion X of the regenerator unit to be exposed.

The passage 14, which was referred to previously in connection with the schematic drawing of FIGURE 1, is shown in FIGURE 3 in close proximity to the regenerator unit 13 and is adapted to conduct the intake air passing through the regenerator from diffuser portion 31 to the burner 15. After the fuel is mixed with the intake air and burned, the burned gases pass into the passage 36 and then into the exhaust chamber 42. While passing from passage 36 to chamber 42 the burned gases pass through an annular channel 37 in which are disposed annular cascades of turbine blades 38 and 39 and associated stator blades 40 and 41. The burner 15 is illustrated by means of an outer elevation view in FIGURE 2. The actual path followed by the intake air and combustion gases through the burner will not be described in detail since the burner does not form a part of this invention.

The blades 38 are mounted upon a primary turbine member 43 which is mounted upon an axially extending shaft assembly 44 which in turn is drivably secured to the compressor rotor hub 28. The blades 39 are mounted upon a secondary turbine member 45 which is mounted upon an axially extending shaft 46. The shaft 46 is drivably connected to the input pinion gear of a reduction gear transmission assembly which is designated generally by numeral 47. A power absorbing means may be connected to the transmission power output tails'haft 48.

The exhaust chamber 42 is formed to cover a large segmental portion of the regenerator unit 13 which is shown at Y in FIGURE 4. The graphite seals 32 and 35 are also provided with mating segmental openings to cause the portion Y of the regenerator to be exposed to the exhaust gases. A suitable housing 50 is adapted to form a passageway 51 to conduct the exhaust gases passing through the segmental portion Y of the regenerator to an exhaust port.

It should be noted from FIGURE 3 that the seals 32 and 35 are effective to seal the exhaust gases passing from chamber 42 to passageway 51 as well as to seal the intake air passing from portion 31 to passageway 14 so that the exhaust gas and intake air are not intermixed.

The total area provided at Y for the passage of the exhaust gases through the regenerator unit is larger than the area at X for the intake air because the volume occupied by the heated exhaust gas is necessarily larger. It

has been found that a ratio of approximately two to one between the exhaust and intake areas is adequate for the usual operating temperatures encountered.

The regenerator unit 13, which comprises the subject matter of the present invention, is shown more in detail in FIGURES 5 and 6. The unit itself comprises a hub 52 and a rim portion 53 which may be made of any suitable material, such as steel. The hub may be provided with a suitable bearing means, as shown in FIGURE 3 at 54, for rotatably mounting the regenerator unit upon a shaft 55 which in turn is suitably mounted in the outer housing. The rim portion is provided with a peripheral ring gear 56 which serves as a means for driving the regenerator unit about its own axis on bearing means 54. Any suitable power source may be used to drivably engage the ring gear 56.

The body of the regenerator unit 13 comprises a glass matrix structure which is formed upon the hub 52 and secured thereon by means of the concentric rim portion 53. The term glass herein includes any smooth surfaced glass-like or ceramic material capable of withstanding the cyclic temperature extremes to which the regenerator is subject during operation and having a high coefficient of specific heat and low coefficients of thermal conductivity and expansion. The glass matrix structure, as seen in FIGURES 5 and 6, comprises a thin glass strip or ribbon 60 having a thickness of approximately .004 inch, but which may vary as described below in accordance with FIGURE 8, depending on the thermal and strength properties of the specific material. A series of transverse ribs 61 are formed on the glass strip at spaced intervals of approximately .150 inch. It is desirable to form the ribs with a height of approximately .012 inch. The strip 60 is wound about the hub 52 so that the ribs are effective to maintain a clearance between the layers as shown in FIGURE 6. The layers of glass strips may be fused together during the winding operation or they may be fused together as a unit after the winding has been completed.

The axial thickness of the glass matrix may be varied according to the design requirements. It has been found, however, that a thickness of approximately three inches is adequate when the unit is used with a gas turbine power plant having a rated power of about horsepower. The other dimensions may also be varied as described in more detail below in order to adapt such a regenerator unit to a particular application.

For the purpose of particularly pointing out the mode of operation and the effectiveness of the present invention, the path of gas flow through the gas turbine power plant will be followed together with a reference to some typical operating temperatures for a 150 horsepower power plant. An attempt has been made to illustrate the path of gas flow by means .of arrows in FIGURE 3.

It will be assumed that standard atmospheric conditions exist at the intake portion of the compressor 10. When the intake air reaches the rotor 24 of the compressor, the temperature is still about the same as the temperature of the surrounding atmosphere. When the air passes through the rotor and is compressed, the temperature increases to approximately 400 F. The temperature of the intake air is therefore approximately 400 F. at the time it enters the inlet segmental portion X of the regenerator unit 13. While passing through the regenerator from chamber 31 to passage 14, the intake air temperature is increased to about 900 F. The passageway 14 conducts the heated intake air to the burner 15 where the combustion process causes the temperature to increase to about 1500 F. The products of combustion are conducted through passage 36 to the turbine members. The work performed on the turbine member is accompanied by a temperature drop to approximately 1000 F. The heated exhaust gases then pass from chamber 42 through the segmental portion Y of the heat exchanger unit and heat up the glass matrix. This is accompanied by a temperature drop in the exhaust gases to approximately 500 F. The passageway 51 then conducts the cooled exhaust gas out a suitable exhaust port.

It should be observed that the hot exhaust gases pass from one side of the heat exchanger to the other in an axial direction. Accordingly, because of the low thermal conductivity of the matrix, a temperature gradient will become established across the axial thickness of the unit with the higher temperature existing at the gas inlet side which is closest to chamber 42 and the lower temperature existing at the gas outlet side. The regenerator unit is constantly rotated during the operation of the power plant. Accordingly, the hotter part of the matrix will be in contact'with the intake air outlet side when rotated so as to intersect the intake air stream. The cooler part of the matrix will, of course, come into contact with the intake air inlet side. Because of the temperature gradient, it is possible to heat the intake air to a higher value than that which would result if such a gradient did not exist, since the intake air comes in contact with portions of the matrix which are heated to a temperature considerably greater than the mean temperature. Since the overall thermal efficiency of the engine is directly dependent upon the temperature of the intake air, it is possible to obtain a higher overall efiiciency for the entire unit by making use of the regenerator unit of the present invention.

Prior to the present invention, little was known to the art regarding the heat transfer properties of a multitude of small parallel gas passages having thin walls of the character and dimensions disclosed herein. In order to facilitate understanding of some of the problems involved, an enlarged cross sectional view of a single gas passage 62 is illustrated in FIGURE 7 wherein two of the heat flow components are indicated by arrows A and B.

Hot exhaust gas flowing through passage 62 in a direction perpendicular to the plane of the paper will transfer heat to the inner side walls as indicated by the arrows A. It has long been recognized that the thinner the

walls

60 and 61, the greater will be the surface area for any given weight of material and, as far as this factor is concerned, the greater will be the total heat transfer from the gas to the passage walls in a given time limit.

In order to take advantage of the thin-walled effect, the obvious step was to employ a fibrous matrix, as for example glass or metal fibers for the heat exchange medium. Such constructions have been unsuitable for use with automotive gas turbine engines wherein the gas flow is at comparatively high velocity and pressure. Not only do particles of the fibrous material break off when subject to the high pressure and cyclic temperature changes and damage the extremely high speed turbine blades, but the resistance to gas flow is prohibitive in a regenerator having random gas flow passages.

Accordingly, the present invention utilizes a multitude of preformed flow passages having thin smooth walls extending directly through the regenerator in axial side-byside relationship and sealed along their axial length to prevent circumferential flow of gases from one gas passage to another within the regenerator matrix. The use of the smooth axial flow passages enables an increase in the total surface area to an optimum value for any given weight of regenerator without unduly increasing the flow resistance. It will also be assumed herein that the regenerator matrix is designed for laminar allow of the gases therethrough, as distinguished from turbulent flow, for the sake of minimizing the resistance to the gas flow. In addition as described more fully below, the dimensions specified achieve optimum thermal efficiency by providing answers to problems that were not known to exist heretofore.

Referring to FIGURE 7, it has been found that the transfer of heat from the gas to the passage walls of elongated cross sectional area is substantially less adjacent the small edges a than at the mid-region of the long dimension [2 of the passage. Thus each flow passage 62 adjacent its small edges a will be relatively cooler than said mid-regions. In consequence, the portions of each gas passage 62 adjacent its opposite small edges a will be relatively ineffective as a heat transfer medium unless the heat flow indicated by the arrows B within the material of the walls can be used to conduct heat within the passsage side walls toward -the small edges a.

It is therefore to be realized that a definite but heretofore unexpected relationship exists between cross sectional elongation and Wall thickness. The less elongation and the greater number of total gas passages, the greater will be the total effect of the small edges a in reducing the heat transfer efficiency of the regenerator. Where the walls are reduced to a film-like thickness, as in the present invention, the cross sectional elongation must be increased substantially, otherwise the loss in heat transfer efiiciency resulting from reduced heat transfer toward the small edges of each passage becomes a significant consideration.

On the other hand, the thinner the passage walls, the greater will be the resistance to heat flow therein toward the small edges a and the greater will be the loss in heat transfer efficiency. This latter concept is directly opposed to the practice heretofore of attempting to increase the total surface area and heat transfer efficiency by decreasing the wall thickness of the individual gas passages. As

explained below, the gas passage walls cannot be reduced in thickness below a predetermined minimum without sacrificing optimum heat transfer efficiency.

As the heat flow in the direction of the arrows B increases, FIGURE 7, the effective utilization of the small end regions of the elongated gas flow passages and correspondingly the heat transfer efiiciency of the regenerator will be increased. Likewise, as the elongation of the cross sectional area of each gas passage is increased, the total effect of the small edge portions a of all the passages tending to reduce the regenerator heat transfer efficiency will be decreased.

If we assume side walls 60 of infinite thickness so as to minimize resistance to heat flow in consequence of the wall thickness factor, a modulus of heat transfer effectiveness well known as Nusselts number can be correlated directly with the heat flow within the walls of the gas passages in the directions of the arrows B. For a gas flow passage of square cross section, Nusselts number equals 3.6.

For an elongated gas passage having side Walls in the ratio 'to 12 as specified by applicant, Nusselts number increases to slightly less than 7. Thereafter as the elongation increases to infinity (parallel side wallswith no small end walls) Nusselts number increases to approximately 8.2. The ratio of the dimensions b/a=G is hereinafter referred to as the aspect ratio. Thus as the elongation or aspect ratio G increases from a square or 1:1 ratio to 150:12 ratio, Nusselts number rapidly doubles in value. As the elongation is increased infinitely, Nusselts number asymptotically approaches 8.2. The ratio 150112 is accordingly within a critical range in that it is at the region of optimum Nusselts number for any practical obtainable increase in the elongation or aspect ratio G. Below the optimum aspect ratio, Nusselts number decreases rapidly. Above the optimum aspect ratio, any advantage obtained from an increase in Nusselts number is negligible whereas the feasibility of increasing the aspect ratio rapidly decreases because of the lack of rigidity of the thin walls which cannot be maintained in parallel spaced relationship over extended distance without intermediate support.

Refering to FIGURE 8, Nusselts number N =HD/K is plotted against a dimensionless parameter =K T/K D. In the above expressions:

H is the coefficient of thermal conductance between the walls of the gas passage 62 and the gas flowing therein and measures the quantity of heat flow between the gas and a unit area of the sidewalls per unit time and temperature diflerential.

D is the hydraulic diameter of the'elongated passage 62 and equals four times the flow area divided by the perimeter, which for a rectangle is 2ab/(a-t-b).

T is the thickness of the sidewalls b, the thickness of the walls a being unimportant when the aspect ratio G=b/a is large. Both T and D are linear measurements, expressed for example in feet (ft).

K and K are the coeflicients of thermal conductivity of the sidewalls and gaseous fluid medium respectively and measure the quantity of heat flow per unit time and temperature differential along a unit distance within the sidewalls and gaseous medium respectively. Inasmuch as the combusition products of an automotive gas turbine engine comprise a comparatively small portion of the total mass of the inlet air, the difference in the value of K: for the inlet air and exhaust gas is negligible. Hence the value of K for air is feasibly employed herein.

It is apparent that Nusselts number N is also dimensionless because, employing conventional units, H /K: can be expressed as is therefore dimensionless. The family of curves in FIG- URE 8 accordingly represent the relationships between two dimensionless parmeters at various aspect ratios and are entirely independent of the material employed for the walls of the gas passage 62 and the fluid flowing therethrough. Regardless of the composition of the fluid medium or the material of the regenerator matrix, there is a definite value of N for each value of and G.

For a regenerator of any given size, the total heat transfer area of the matrix will be increased by increasing the number of gas passages 62. Thus the hydraulic diameter D of each passage 62 will be as small as practicable in order to obtain the maximum number of gas passages 62, the smallness of the hydraulic diameter being limited by the total axial pressure drop across the regenerator that can be tolerated and the volume of gas that can be accommodated by laminar flow. Inasmuch as as N increases in value, the conductance H and correspondingly the efficiency of the regenerator increases. Similarly, g5 and correspondingly the weight of the regenerator will increase in value with increasing wall thickness T by reason of the expression =K T/K D.

It is apparent from FIGURE 8 that Nusselts number N increases rapidly as the aspect ratio G increases to the

practicable limits

10 or 12, as explained above, but decreases rapidly with decreasing 5 at values smaller than approximately 10, which latter value defines the knee or approximate mid-point of the sharp bend of each curve. For larger values of gb, the thickness T of the passage sidewalls can be increased infinitely without appreciably enhancing the value of Nusselts number N.

On the other hand, as indicated by the two vertical 10% measurements associated with 6:10 and G=12 respectively in FIGURE 8, 90% of the theoretical maximum value of Nusselts number N is obtained on the 6:10 curve if 5 is approximately 4, and is obtained on the G=12 curve if is approximately 5. The optimum value of q for minimum regenerator mass and maximum heat transfer effectiveness as measured by Nusselts number N is therefore approximately 10, (log =1) but values of 5 as low as 4 (log =.6) will achieve more than 90% of the value of Nusselts number if the aspect ratio G is greater than 10; and similar values of N are obtained when log p is 1.4 and G is 6. The two vertical 10% measurements indicate the range of within the upper 10% of the maximum theoretical values of N associated with the curves G=10 and 6:12 respectively. N decreases very rapidly as G decreases toward 4. The lower practical limit for G from a thermo-dynamic standpoint is thus somewhere between 4 and 6 and may be stated as being on the order of about 5.

Specific values of gas passage wall thickness for glass or ceramic where G=10 and Kf/Kw'- .026 are illustrated for various hydraulic diameters in FIGURE 9 to emphasize the sharp drop in heat transfer effectiveness when the wall thickness is decreased below the critical value. The uppermost curve D=.025" corresponds approximately to the hydraulic diameter of the gas passage 62 in FIG- URE 7, wherein the wall thickness of the ceramic gas passages ranges between approximately .0025" and .006 for values of 5 between approximately 4 and 10. The optimum wall thickness for other suitable matrix materials having the desired high specific heat and low coefficients of thermal conductivity and expansion will similarly be determined by the value of in the critical range log 6:11.4. The maximum hydraulic diameter D equal to .06" may be calculated by substituting the minimum value of equal to 4, the maximum wall thickness T equal to .006", and the value of [(j/Kw equal to .026 in the expression: equals K T/K D.

I claim:

1. A counterflow type regenerator matrix for an automotive gas turbine engine wherein high temperature exhaust gases and cooler inlet gases are alternately directed through portions of said matrix in opposite directions by substantially laminar flow, said matrix comprising a comparatively rigid ceramic body having a multitude of substantially parallel gas passages of elongated cross sectional area, the walls of longer cross section of each gas passage being substantially parallel to each other and sufliciently smooth and impervious to said gases to effect said laminar flow and being at least several times longer than the smaller cross sectional dimension of said passage, the hydraulic diameter of each gas passage being not greater than a value on the order of about .06", and log K T/ KfD being between values on the order of about .6 and 1.4, wherein K, is the coefficient of thermal conductivity of. the gas flowing through said gas passages, K is the coeflicient of thermal conductivity and T is the thickness of said walls of longer cross section, and D is the hydraulic diameter of said passages.

2. The generator matrix as in claim 1 wherein the spacing between said walls of longer cross section is on the order of about .01".

3. The regenerator matrix as in claim 2, wherein the ratio of the long dimension to the short dimension of the cross section of each gas passage is not less than a value on the order of about 5.

4. The regenerator matrix as in claim 1, wherein the ratio of the long dimension to the short dimension of the cross section of each gas passage is not less than a value ranging on the order of from about 10 to 6 while log K T/K D ranges correspondingly on the order of from about .6 to 1.4.

5. The regenerator matrix as in claim 4 wherein the spacing between said walls of longer cross section is on the order of about .01".

6. A counterflow type regenerator matrix for an automotive gas turbine engine wherein high temperature exhaust gases and relatively cooler inlet gases are alternately directed through portions of said matrix in opposite directions by substantially laminar flow, said matrix comprising a comparatively rigid body of ceramic material having a comparatively high coefiicient of specific heat and a comparatively low coefiicient of thermal conductivity and being formed with a multitude of substantially parallel gas passages of elongated cross sectional area, the walls of longer cross section of each gas passage being substantially parallel to each other and suflieiently smooth and impervious to said gases to effect said laminar fiow and being at least several times longer than the smaller cross sectional dimension of said passage, and log KWT/KID being on the order of about 1, the hydraulic diameter of each gas passage being not greater than a value on the order of about .06, wherein K is the coefficient of thermal conductivity of the gas flowing through said gas passages, K is the coeflicient of thermal conductivity and T is the thickness of said walls of longer cross section, and D is the hydraulic diameter of said passages.

7. The counterflow type regenerator matrix as in claim 6, said coefficients of specific heat and thermal conductivity being comparable to the corresponding coefiicients of high temperature resistant glass.

8. The counterflow type regenerator matrix as in claim 7, the spacing between the walls of longer cross sectional dimension being on the order of about .01.

9. The counterflow type regenerator matrix as in claim 8, the ratio of the longer cross sectional dimension to the shorter cross sectional dimension of each gas passage being not less than a value on the order of about 5.

10. The counterflow type regenerator matrix as in claim 6, the hydraulic diameter of each gas 'passage being on the order of about .02".

11. The counterflow type regenerator matrix as in claim 10, the ratio of the longer cross sectional dimensiOn to the shorter cross sectional dimension of each gas passage being not less than a value on the order of about 5.

12. In combination, a counterflow type regenerator of an automotive gas turbine engine for transferring thermal energy from a stream of heated exhaust gases to a generally oppositely directed stream of relatively cooler inlet gases, said regenerator comprising a comparatively rigid ceramic matrix having a multitude of substantially parallel gas passages of elongated cross section adapted for substantially laminar flow of said gases therethrough, the Walls of longer cross section for each gas pas-sage being substantially parallel to each other, and sufficiently smooth and impervious to said gases to effect said laminar flow, the ratio of the long dimension to the short dimension of the cross section of each gas passage being not less than a value on the order of about 5, the hydraulic diameter of each, gas passage being not greater than a value on the order of about .06, means for conducting the two oppositely directed streams of gases alternately to a portion of said matrix for said laminar flow thereth-rough, and log K T/K D being between values on the order of about .6 and 1.4 wherein K and K are the coefiicients of thermal conductivity of said walls of longer cross section and the gas flowing through said passages respectively, T is the thickness of said walls of longer cross section, and D is the hydraulic diameter of each gas passage.

References Cited by the Examiner UNITED STATES PATENTS 2,023,965 12/1935 Lysholm 165-1 2,552,937 5/1951 Cohen 1651O 2,596,642 5/1952 Boestad 165-166 2,706,109 4/1955 Od-rnan 165l0 ROBERT A. OLEARY, Primary Examiner. CHARLES SUKALO, Examiner.

R. E. BACKUS, Assistant Examiner,

Claims

1. A COUNTERFLOW TYPE REGENERATOR MATRIX FOR AN AUTOMOTIVE GAS TURBINE ENGINE WHEREIN HIGH TEMPERATURE EXHAUST GASES AND COOLER INLET GASES ARE ALTERNATELY DIRECTED THROUGH PORTIONS OF SAID MATRIX IN OPPOSITE DIRECTIONS BY SUBSTANTIALLY LAMINAR FLOW, SAID MATRIX COMPRISING A COMPARATIVELY RIGID CERAMIC BODY HAVING A MULTITUDE OF SUBSTANTIALLY PARALLEL GAS PASSAGES OF ELONGATED CROSS SECTIONAL AREA, THE WALLS OF LONGER CROSS SECTION OF EACH GAS PASSAGE BEING SUBSTANTIALLY PARALLEL TO EACH OTHER AND SUFFICIENTLY SMOOTH AND IMPERVIOUS TO SAID GASES TO EFECT SAID LAMINAR FLOW AND BEING AT LEAST SEVERAL TIMES LONGER THAN THE SIMILAR CROSS SECTIONAL DIMENSION OF SAID PASSAGE, THE HYDRAULIC DIAMETER OF EACH GAS PASSAGE BEING NOT GREATER THAN A VALUE ON THE ORDER OF ABOUT .06", AND LOG10 KWT/ KFD BEING BETWEEN VALUES ON THE ORDER OF ABOUT .6 AND 1.4, WHEREIN KF IS THE COEFFICIENT OF THERMAL CONDUCTIVITY OF THE GAS FLOWING THROUGH SAID GAS PASSAGES, KW IS THE COEFFICENT OF THERMAL CONDUCTIVITY AND T IS THE THICKNESS OF SAID WALLS OF LONGER CROSS SECTION, AND D IS THE HYDRAULIC DIAMETER OF SAID PASSAGES.