US3416011A - Thermionic converter heat exchangers - Google Patents

Description

Dec. 10, 1968 F. J. LYCZKO 3,416,011

THERMIONIC CONVERTER HEAT EXCHANGERS Filed March 29, 1965 5 Sheets-Sheet 2 FIG. 2

INVENTOR FELIX J. (YCZ/(O W W W ATTORNEY Dec. 10, 1968 F. J. LYCZKO THERMIONIC CONVERTER HEAT EXCHANGERS 5 Sheets-Sheet 3 Filed March 29. 1965 INVENTOR FEA /X J? LYCZA'O BY M, M 1- 2111444174.

ATTO R N EY United States Patent Office 3,416,011 Patented Dec. 10, 1968 3,416,011 THERMIONIC CONVERTER HEAT EXCHANGERS Felix J. Lyczko, Boxford, Mass., assignor to Thermo Electron Corporation, a corporation of Delaware Filed Mar. 29, 1965, Ser. No. 446,476 12 Claims. (Cl. 310-4) ABSTRACT OF THE DISCLOSURE A system for transferring heat between a fluid and a heat exchanging wall or between two fluids through a separating heat exchanging wall or walls against which at least one of the fluids is directed substantially perpendicularly at a velocity suflicient to disrupt stagnant boundary layers formed adjacent the wall. The fluid or fluids are caused to traverse a passage which is intersected by baffles forming a group of plenum chambers. Apertures are formed in the plenum chambers to cause multiple jetting actions of the fluid substantially perpendicularly upon the heat exchanging wall. The design of the system is such that the various chambers are formed from a plurality of substantially identical members and may be used to preheat the air employed to support combustion of fuel by heat exchange with the combustion gases which may directly heat high-temperature operating devices such as thermionic converters.

It is a principal object of the present invention to provide heat exchangers in which the exchange of heat between the different fluid media, at least one of which is gaseous, on the opposite sides of the heat exchange surface takes place with greater efiiciency than in heretofore known heat exchangers.

Another object of this invention is to provide heat exchangers of novel design which can readily be made by stacking like sections, composed of baffles which for low temperature operations can be relatively low cost, stamped sheet metal parts, in predetermined relation requiring a minimum of welded or brazed joints.

Still another object of this invention is to provide such heat exchangers, formed from bafiles operable at relatively high temperature levels, i.e., above about 600 R, which can readily and economically be made from refractory materials such as ceramic materials or silicon carbide, resistant to oxidation at such high temperature levels.

Still another object of this invention is to provide fuel fired thermionic converters in which the electron emitters are heated by combustion gases, with such heat exchangers for preheating the air employed to support combustion of the fuel by heat exchange with the combustion gases.

Fuel fired thermionic converters are relatively small and compact. For eflicient operation the electron emitters must be heated to relatively high temperatures, for example, about 2800 F. in the case of cesium diodes. In order to obtain such high temperatures, it is essential that the air supporting combustion of the fuel be preheated to a high temperature. Heat exchangers available prior to the present invention, as a practical matter, could not be used in fuel fired thermionic converters, among other reasons, because they did not operate at the necessary heat exchange eificiencies to preheat the air to the desired temperatures, or their surface area requirements for efiicient operation were so large as to render them unsatisfactory for use in thermionic converters. The present invention provides an unusually compact design of fuel fired thermionic converter having a heat exchanger which gives efficient heat exchange between the flowing stream of air supporting combustion of the fuel and the flowing stream of resultant combustion gases efiecting efiicient preheating of the air stream and resulting in the generation of combustion gases at the desired temperatures.

Other objects and advantages of this invention will be apparent from the following detailed description taken in connection with the accompanying drawings, in which are shown, for purposes of exemplification, preferred embodiments of this invention, to which, however, this invention is not confined.

In the drawings:

FIGURE 1 is a vertical section through a heat exchanger embodying this invention; the heat exchanger of this embodiment is employed with a combustion chamber for generating combustion gases for heating the emitters of an assembly of thermionic converters;

FIGURE 2 is a fragmentary view partly in perspective and partly in section, showing a modified form of heat exchanger embodying this invention;

FIGURE 3 is a perspective view on a reduced scale, as compared with the scale of FIGURE 2, of one of the members which when stacked and the large imperforate diameter abutting outer side wall portions of adjacent members suitably joined as by brazing, forms the main portion of the heat exchanger of FIGURE 2; and

FIGURE 4 is a fragmentary perspective view, partly in section, of still another modification of a heat exchanger embodying this invention.

The heat exchangers of this invention are particularly designed for use in effecting exchange of heat from one fluid to another, at least one of the fluids being in the gaseous phase, for effecting heat exchange at high temperature levels, e.g., at temperatures above about 600 F. or for effecting heat exchange between a corrosive gas and another fluid. At such high temperature levels and/or when corrosive gases are involved, conventional materials of construction cannot, as a practical matter, be used because excessive oxidation or corrosion takes place. With heat exchangers heretofore used at such high temperature levels, or handling corrosive gas or gases, requiring refractory or other construction materials capable of resisting oxidation at such high temperature levels or corrosion, respectively, it was difiicult to fabricate such materials in the shapes required for the different flow passes of the heat exchanger. This factor materially adds to the expense of producing such heat exchangers. The present invention, involving as it does the special shapes hereinafter disclosed, which can readily be cast or otherwise shaped from refractory and other construction materials, capable of withstanding oxidation at high temperature levels, including ceramic materials, silicon carbide and other high temperature resistant materials, lends itself eminently satisfactorily to the production of heat exchangers employed at high temperature levels. The invention, however, can be embodied in heat exchangers operated at relatively low temperature levels, in fact, at any desired temperature level, with economies in the construction and operation of the heat exchanger because the novel design features embodied in the heat exchangers of this invention lend themselves to the economical fabrication of (a) heat exchangers employing conventional construction materials such as steel and other metals which can be used in heat exchangers operating at temperatures below about 600 F. as well as in (b) heat exchangers employing refractory and other materials resistant to oxidation and corrosion at high temperature levels.

In addition to the fuel fired thermionic converter field, in which the heat exchangers of this invention as noted give eflicient heat exchange between the air for supporting combustion of the fuel and the exiting combustion gases, the heat exchangers of this invention find particular application in fields of use such as boilers and other equipment where fuel is burned employing preheated air or other free oxygen-containing gas to support combustion; in kilns including metallurgical kilns where ores and other materials are roasted at high temperatures in an oxidizing atmosphere; for carrying out calcinations and in the chemical industries generally involving the How of corrosive gases or liquids passing in heat exchange relation and where, to minimize corrosion, refractory-pr other corrosion-resistant materials must be used, difficult to fabricate in intricate shapes or to form gas-tight joints required to delineate the passageways through which a hot gas or liquid flows in indirect heat exchange relation with a liquid or gas to be heated, at least one of the flowing streams being in the gaseous phase.

In this specification, in the interests of brevity, the expression air will be used to refer to a free-oxygen containing gas. It will be understood that instead of air, oxygen or oxygen enriched air can be used; and the reference to air is not intended to limit the invention to air alone where reference to air occurs. Air, of course, is representative of one of many difierent fluids which can be heated or cooled in the heat exchangers of this invention.

In describing the heat exchangers shown in the drawings, all references to inner and outer are relative to the longitudinal axis of the exchanger; thus the side of a wall closer to this axis is the inner side, the opposite side, the outer side.

FIGURE 1 shows a preferred adaptation of the heat exchanger embodying this invention, namely for preheating air employing the products of combustion used to heat the emitters of thermionic converters. In FIGURE 1, is an annular combustion chamber; 11 the emitter shell of one of a plurality of thermionic converters arranged radially about end 12 of combustion chamber 10; 13 is a cylindrical exhaust passageway for the combustion gases exiting from the combustion chamber 10; 14, one of a number of fuel injectors for the combustion chamber 10, which fuel injectors receive fiuid fuel from the main or manifold 15; and 16 the heat exchanger through which flows in indirect heat exchange relation in generally sinusoidal paths of flow, as explained more fully hereinafter, the air to support combustion of the fuel supplied by injectors 14 and the combustion gases. While the heat exchangers shown in the drawing are cylindrical, it will be appreciated that the invention is not limited thereto and can be tubular with planar walls rather than circular in section.

End 12 of combustion chamber 10 is formed with a plurality of closely spaced circularly positioned orifice openings 18, to jet combustion products exiting from the combustion chamber 10 onto the emitter shells 11. From the emitter shells the combustion products flow into a plenum chamber 19 which is in open communication with one end 21 of exhaust passageway 13. The construction shown here is provided with a thick layer 17 of a good heat insulation enveloping the parts at elevated temperatures to minimize heat losses; those parts exposed to the highest temperatures such as the plenum chamber 19 are preferably provided with a layer of insulation 17 resistant to high temperatures, positioned between insulation 17 and the high temperature surfaces as shown in FIG- URE 1.

Combustion chamber 10 has therein bafile members or swirlers 22 through which preheated air entering through ports 23 flow. These swirlers 22 produce a turbulent flow of the preheated air with consequent production of a turbulent mixture of preheated air and fluid fuel which once ignited burns efficiently to produce hot combustion gases flowing through the combustion chamber 10.

In FIGURE 1 the diode or thermionic engine 24 can be of any known type including the type of diodes disclosed and claimed in US. Patent 3,054,914. A plurality of these diodes are arranged in a generally circular configuration about end 12 of combustion chamber 10, supported by brackets 25' extending from the side walls 26 .4 of housing 27. These brackets 25 are secured to lugs 28 on the sides of the radiator assembly 29 which communicates with the collector in the interior of the emiter shell 11 to maintain the desired thermal balance between the collector and the emitter. 30 is a cesium reservoir for supplying cesium to the electrode space between the emitter and the collector and thus reduce space charge as known for cesium diodes or thermionic engines. As the construction of such cesium diodes is known and the diodes per se represent one of many different types of equipment with which the heat exchanger of this invention can be used, further description of such diodes is believed unnecessary.

The heat exchanger embodying this invention, shown in FIGURE 1, is produced by stacking a plurality of like members M, as hereinafter described. Each member comprises an imperforate outer substantially cylindrical side wall portion 31 formed with a terminal end 32 of reduced thickness and an opposite end 33 also of reduced thickness for placement in abutting relation with the reduced thickness end 32 of an adjacent member of the stack as clearly shown in FIGURE 1. The joint between reduced thickness portion 33 and 32 of adjacent members of the stack can be formed by brazing. When the units are thus stacked the outer wall 34 of the heat exchanger results.

Contiguous and integral with the outer side wall portion 31 is the first orifice plate portion 35 consisting of the inwardly or generally laterally extending portion 36 which forms a continuation of the reduced end portion 33, a substantially cylindrical orifice plate portion 37 and a terminal inwardly or laterally extending portion 38 which extends in a direction away from the outer wall 34. Orifice plate portion 37 is formed with a plurality of small orifice openings 39 arranged in a circle therein. Contiguous and integral with portion 38 is an inner imperforate substantially cylindrical side wall portion 41. End 42 of inner wall portion 41 is for-med with an inclined inner ground joint area 43 and the opposite end of inner wall portion 41 is formed with similarly inclined outer ground joint area 44. The inclined inner ground joint area 43 of one member, when the members are stacked as shown in FIGURE 1, seats on the inclined outer ground joint area 44 of the immediately adjacent member forming a gas-tight joint 45.

A second orifice plate portion 47 (FIGURE 3), substantially cylindrical in shape, has therein a plurality of closely spaced orifice openings 48 and is connected by inwardly or generally laterally extending portion 49 with one end of inner side wall portion 41. An imperforate closure plate 51 extends completely across the terminal ends of the second orifice plate portion 47.

In the structure shown in FIGURE 1, a terminal member M is shaped, by elimination of the imperforate closure plate 51 to provide an exit port 53 for the combustion gases. Port 53 can communicate with a waste heat boiler, or the atmosphere. An annular air supply chamber 54 is positioned adjacent and surrounding the inner imperforate side wall portion 41 of terminal member M. Air is supplied to chamber 54 through a pipe 55. Chamber 54 has therein the orifice plate portion 35 having the orifice openings 39 of a truncated terminal member M, shaped as shown in FIGURE 1, which cooperates with member M to form portions of the flow passages on the opposite sides of the heat transfer wall S hereinafter more fully described.

The central cylindrical exhaust passageway 13 is formed with a generally cylindrical cap 56, the side walls 57 of which are provided with a plurality of circularly arranged closely spaced orifice openings 58 for forming closely spaced jets of combustion gases impinging on the portion of the heat transfer wall S opposite these orifice openings. The portion of the heat exchanger immediately adjacent cap 56, is for-med by a cylindrical collar 59 which is suitably brazed to end 60 of member M', shaped as shown in FIGURE 1. Member M comprises a closure plate portion 51, an orifice plate portion 47 having a plurality of circularly arranged orifice openings 48 therein and an inner imperforate side wall portion 6 2, one end of which is suitably joined to one end of collar 59, as by brazing. The opposite end of collar 59 abuts the lateral walls 63 containing the ports 23 of the combustion chamber 10.

The respective (1) outer imper-for-ate substantially cylindrical side wall portions 31; (2) first orifice plate portion 37; (3) imperforate substantially cylindrical inner side wall portion 41; and (4) second orifice plate portion 47 are of gradually decreasing diameter as shown in FIGURES 1, 2 and 3. This the outer contour of each member is of stepped configuration. When the units are assembled in stacked relation the successive joints 45, along the length of the heat exchanger and the inner imperforate cylindrical wall portions 41 form the heat transfer wall S of the heat exchanger. Walls 34 and S define an annular outer flow passage F1 in heat exchange relation with an inner flow passage F2 separated from each other by the heat exchange wall S. One of the fluids flows in a generally sinusoidal path through flow path P1 with alternate components passing towards the wall S and through the orifice openings 39 forming closely spaced jets of fluid impinging on heat transfer wall S and away from Wall S, as indicated by the arrows in flow passage F1 on FIGURE 1. The other fluid flows through the inner flow passage F2 in a generally sinusoidal path alternately extending through the orifice openings 48 forming jets impinging on wall S and away from wall S through the flow paths identified by the arrows in flow passage F2 on FIGURE 1.

The orifice openings 39, 48 and 58 are suitably dimensioned to form closely spaced jets which impinge on the heat transfer surface S. These orifice openings can be of any desired shape, including circular, elliptical or other desired configuration. The cross-sectional area of these jets are controlled by the cross-sectional area of the orifice openings 39, 48 and 58. The smaller the crosssectional area of these openings the better, provided they are not so small that they will become clogged during operation by finely divided particles in the combustion products. For the orifice plate portion 37 having a diameter of about 3.15 inches eight openings evenly spaced, each having a diameter of about /2 inch, have been found effective. For the orifice plate portion 47 having a diameter of about 1.7 inches, eight openings each having a diameter of 0.5 inch can be used. This data is, of course, given for exemplary purposes. It Will be understood that the orifice plate portions can have any desired number of orifice openings which result in the formation of a multiplicity of closely spaced, small cross-sectional area jets impinging on the heat transfer wall so that substan tially the entire area of this wall has these fine jets playing on the opposite sides thereof, thus minimizing, if not completely preventing, retention of stagnant gas or a laminar boundary layer of gas on either side of wall S and insuring optimum heat transfer therethrough.

It will be noted that the shape of the individual members M is such that they can readily be cast from refractory material or stamped from sheet metal parts. By stacking members M, as shown in FIGURE 1, the two annular flow passages F1 and F2, separated by the heat transfer wall S, are produced. The ground joint areas 43 and 44 require no brazing or welding to form gas-tight joints when the heat exchangers are operated at moderate superatmospheric pressures or under atmospheric or sub-atmospheric pressure conditions. The heat exchanger and communicating combustion chamber can be operated under induced draft or forced draft with the air supplied under positive pressure to pipe 55. When relatively high pressures are used, say about 3 p.s.i.g., instead of the joints 45, formed by the contacting ground areas 43 and 44, brazed joints may be used where the inner imperfo- 6 rate substantially cylindrical portions bers M abut.

Terminal members M, M" and M'" in FIGURE 1 can be produced from members M by removing so much of a member M as is needed to produce members M, M" and M, respectively. Hence with one basic shape, represented by the shape of member M, the heat exchanger can be fabricated requiring the brazing of the outer overlapping portions to form the outer wall 34, for utilization of the heat exchanger under moderate elevated pressures, under atmospheric pressure conditions or under subatrnospherrc pressure conditions. Such pressure conditions represent the commonly encountered pressure conditions under which heat exchangers are operated. Where relatively high superatmospheric pressure conditions are encountered the joints 45 formed by the contacting ground areas 43 and 44 cannot be used but in lieu thereof brazed joints at the contacting areas of the portions of the member M forming the heat transfer wall S should be used.

While the preferred construction involves the stacking as members M, as shovm in 41 of adjacent memof individual members such FIGURES 1 and 2, the invention is not limited thereto. The heat exchangers of this invention can be fabricated with cylindrical or other shaped Walls 34 and S of one or multiple piece construction to define the flow passages F1 and F2 and baflle members having orifice plate portrons provided with orifice openings therein positioned in spaced relationship in these flow passages to provide the generally sinusoidal flow paths alternately toward and away from the heat transfer surface separating the flow passages F1 and F2 with the jetting of the different fluid media on the opposite sides of the heat transfer surface in a multiplicity of small closely spaced jets substantially completely covering the entire area of the heat transfer surface and thus insuring optimum heat transfer.

'In operation, of the structure shown in FIGURE 1, a r introduced at about 70 F. flows in a generally sinusoidal path with the jetting of the air in a multiplicity of closely spaced jets onto the heat transfer Wall S at a plurallty of spaced points along the length of this wall and throughout substantially the entire periphery of the wall. Employing seven stages, as shown, each stage constituting the zone of the heat exchanger in which an orifice plate havmg orifice openings is positioned for passage of air through the orifice openings to form jets impinging on the heat transfer wall S, the air is heated to a temperature of about 2250 F. at the point where it leaves the seventh or last stage. At this temperature the hot air enters the combustion chamber mixing with the fluid fuel introduced therein through the fuel jets 14.

The resulting combustion gases, at a temperature of about 2800 F. impinge on the emitter shell 11 and exit through the exhaust flue 13 entering the first of the seven stages of the heat exchanger at a temperature of about 2600 F. A temperature drop of about 300 F. takes place in each of the seven stages. The combustion gases exit from the last stage at a temperature of about 500 F. at which temperature it is discharged through the exhaust duct 53.

The heat exchanger of FIGURE 2, in general, is similar to that of FIGURE 1. Like parts in the heat exchanger of FIGURE 2 are identified by the same reference characters as in FIGURE 1. In FIGURE 2 the fluid to be heated is supplied through pipe 71 which leads into an annular chamber '72. The inner Wall of chamber 72 is defined by an orifice plate portion 35 provided with closely spaced orifice openings 39 through which the fluid is jetted onto the heat transfer wall S. The fluid, which can be any gas or liquid to be heated, flows in a generally sinusoidal flow path through passage F1 in heat exchange relation with a hot fluid flowing through passage F2; at least one of the fluids flowing through the passages F1 and F2 should be in the gaseous phase.

The hot fluid is supplied to the heat exchanger through the centrally positioned inlet pipe 76 which communicates with the orifice openings 48 positioned to jet the hot fluid onto the lower portion (viewing FIGURE 2) of the heat transfer wall S. This fluid exits through the port 78 in the housing 79'. The fluid exits from flow passage F1 through the ports 81 which lead into a chamber 82. When air is preheated by flow through passage F1, the hot air from chamber 82 can be fed to a combustion chamber, which supplies the resultant combustion gases, after utilization, if desired, to impart heat to any desired surface or material, to inlet pipe 76 of the heat exchanger.

In the structure of FIGURE 2 the insulation 17 desirably is maintained under compression by means of one or more springs 83 disposed between the walls 84 and 85. The portion of the heat exchanger above wall 85 containing the inlet pipe 71 supplying the fluid to be heated, as a general rule, need not be insulated because the fluid to be heated is supplied under ambient temperature conditions and hence does not require insulation to minimize heat losses.

The heat exchanger of FIGURE 4 involves multiple annular paths of flow for the fluid media. Flow passages F4, F6, F8 and F10 are for the fluid to be heated which enters at the lower portion of the heat exchanger, as hereinafter described, at a relatively low temperature, usually atmospheric temperature, and exits at the upper portion of the heat exchanger at an elevated temperature. Flow passages F5, F7, F9 and F11 are the passages for the flow of the heating fluid which enters at the upper portion of the heat exchanger and exits into the manifold or chamber 87 at the lower portion of the heat exchanger. While four flow passages for each of the two fluid media are shown in FIGURE 4, it will be appreciated any desired number of such passages can be employed.

The passages F4 and F6, through which the fluid to be heated flows upwardly, have therebetween the flow passage F through which the hot medium flows downwardly. Similarly, flow passages F6 and F8 .are positioned on the opposite sides in indirect heat exchange relation with flow passage F7; flow passages F8 and F are positioned on the opposite sides of flow passage F9; and flow passage F11 is the innermost flow passage. These flow passages are formed by cylindrical walls 88 and S (the walls between adjacent flow passages through which heat transfer takes place are indicated by the ref erence letter S) concentrically positioned and spaced, as shown in FIGURE 4, to delineate the lateral extent of the respective flow passages. Positioned in each annular passageway thus produced are baflle members 89 arranged in a row extending substantially the full length or height of the respective passageways. These baflle members consist of a cylindrical vertically extending wall member 91 having therein a plurality of closely spaced orifice openings 92. Flange members 93 and 94 extend laterally in opposite directions from the top and bottom of each cylindrical member 91. These flange members are dimensioned so that the opposite edges of the respective flanges 93 and 94 are in frictional contact with the side walls 88 and S of the passageways in which they are positioned. Spacer members 95, desirably in the form of blocks, as shown in FIGURE 4, are positioned between the baflle members of each row to thus space each upper baffle member relative to the battle member immediately therebelow and provide for the generally sinusoidal path of flow in each of the flow passages F4 to F11, inclusive.

A manifold 96 is positioned near the low portion of the heat exchanger. This manifold is defined by an outer cylindrical wall 97, an inner wall 98, bottom wall 99 and top wall 101. The outer wall 97 is provided with a series of peripheral openings 102 for supplying fluid to be heated to the manifold 96. Manifold 96 has passing therethrough in a vertical direction circularly arranged rows of pipe-like passes 103. One such circular row of passes 103 is present for each of the flow passages F5, F7, F9

and F11. These flow passes place the flow passages F5, F7, F9 and F11 in communication with the exit mani fold 87. The top .101 of the manifold 96 has circularly arranged rows of openings 104 which place the manifold in communication with the lower portions of each of the flow passes F4, F6, F8 and F10. As clearly shown in FIGURE 4, where portions of the flow passes 103 have been broken away, the manifold 96 provides for flow of the fluid medium introduced thereinto across the full extent of this chamber extending from the outer wall of the heat exchanger to the inner wall of the flow passage F10 so as to supply each of the annular flow passages F4, F6, F8 and F10 with fluid which flows upwardly in a generally sinusoidal path through these flow passages.

The structure of the upper portion of the heat exchanger is generally similar to that described in connection with the manifold 96. At the upper portion of the exchanger a manifold 110 has inlet openings 111 for supply of the hot fluid to the upper portion of each of the passages F11, F9, F7 and F5. Top wall .112 of this manifold has circular rows of exit openings 113 which communicate with the upper portions of the flow passages F4, F6, F8 and F10 for flow of the fluid which has been heated into the manifold chamber 114.

It will be noted that the parts of the heat exchanger of FIGURE 4 are of comparatively simple shape and hence can readily be fabricated from refractory construction materials including ceramics and silicon carbide. In forming the heat exchanger it is only necessary to assemble the respective manifolds or headers with the cylindrical walls defining the flow passages and place in these passages the baffle members 91 and the spacers 95. Brazing or otherwise joining the baffle members and/ or spacers is not necessary.

In operation of the heat exchanger of FIGURE 4, in each pair of adjacent passages, for example, F4 and F5, fluid to be heated flows upwardly in passage F4 in a generally sinusoidal path passing through the orifice openings 92 and impinging on the heat transfer wall S which separates these two flow passages. In the adjacent passage F5 hot fluid flows in a counter-current direction impinging on the heat transfer wall separating these two flow passages. Thus the opposite sides of the heat transfer walls separating the flow passages F4 and F5; F6 and F7; F8 and F9; and F10 and F11 has jetted thereon in a multiplicity of closely spaced jets the respective fluids flowing on opposite sides of the separating heat transfer wall with consequent optimum heat transfer from the fluid at elevated temperature to the fluid at the lower temperature.

The preferred materials of construction for the heat exchangers of this invention depends chiefly on the service conditions under which the heat exchangers are used. For thermionic engine application Where high heat exchange surface temperatures are encountered (2000 F. or higher), at low to moderate internal pressures from 1" of water to 3 p.s.i.g., silicon carbide is the preferred material of construction. The heat exchange wall surface S of FIGURES 1 and 2 and the walls S of FIGURE 4 should be as thin as possible, consistent with strength requirements under the conditions of use, in order to obtain optimum heat transfer.

Where the heat exchangers are used under moderate temperature conditions and relatively low pressures, from 1" of water to 3 p.s.i.g., low carbon steel, aluminum, brass and nickel alloys can be used as the construction material. Where high pressures are encountered, under moderate temperatures from 500 F. to 2000" F. nickel alloys, chromium, tungsten, cobalt, molybdenum and steel can be used as the construction material. In all cases the heat transfer surface S and S is made as thin as possible, consistent with safety factors, strength of the construction material and the stresses encountered in use.

It will be noted the present invention provides heat exchangers which are highly eflicient with particular reference to the transfer of heat from one fluid medium to another flowing through the heat exchanger. The heat exchangers of this invention are of novel design, can readily be made by stacking like sections in predetermined relation requiring a minimum of welded or brazed joints in forming the heat exchanger and the parts are so designed that they can readily and economically be made from refractory materials such as the ceramic materials and silicon carbide resistant to oxidation at high temperature levels.

The heat exchanger of this invention enables a marked saving in installation, operation and maintenance expense to be effected for the same temperature differential between the inlet and exit temperatures of the fluid which is cooled therein or the same heat input into the fluid which is heated therein. Due chiefly to the higher efliciency obtained by the jetting of the fluids on the opposite sides of the heat transfer surface, a marked saving in the size and hence initial cost of the exchanger can be effected for any installation operated to yield the same aforesaid temperature differential or same heat input. Heat exchangers of this invention, designed to give predetermined temperature differential or heat input, require lower fluid pumping and maintenance costs as compared with heretofore available heat exchangers. Moreover the novel design of members M, which can be produced economically by stamping from sheet metal, when metal is the construction material, for relatively low temperature operations, or cast from refractory mate rials, when such materials are the construction materials for high temperature operation or for handling corrosive fluids, and which members M can be stacked to produce the exchanger, results in a material saving in initial cost of the exchanger.

For the above and other reasons, the heat exchangers of this invention find particular application in fuel fired thermionic converters. In fact, the heat exchanger of this invention is chiefly responsible for the successful design and operation of fuel fired thermionic converters.

This invention is not restricted to the present disclosure, including the embodiments shown in the drawings, otherwise than as defined by the appended claims.

What is claimed is:

1. In a fuel fired thermionic converter having, an electron emitter, a combustion chamber, means for supplying fuel to said combustion chamber and means for jetting combustion gases generated in the combustion chamber onto the electron emitter to heat the emitter, the combination therewith of a first longitudinally elongated passageway defined by inner and outer walls communicating with the combustion chamber for the flow of an oxygen containing gas into the combustion chamber, a second longitudinally elongated passageway defined by inner and outer walls communicating with the combustion chamber for flow of the combustion gases from the combustion chamber therethrough, at least one of said Walls being common to both passageways and constituting a heat transfer surface, means including orifice openings in said first passageway for effecting flow of the oxygen containing gas stream passing therethrough in a generally sinusoidal path of flow alternately outwardly, toward and away from said heat transfer surface with alternate components of said sinusoidal path passing toward said heat transfer surface through said orifice openings to form a plurality of closely spaced jets impinging onto one side of said heat transfer surface, and means including orifice openings in said second passageway for effecting flow of the combustion gases passing therethrough in a generally sinusoidal path of flow alternately outwardly, toward and away from said heat transfer surface with alternate components of said sinusoidal path passing toward said heat transfer surface through said orifice openings positioned in said second passageway to form a plurality-of closely spaced jets of combustion gases impinging onto the other side of said heat transfer surface.

2. In a fuel fired thermionic converter having, an electron emitter, a combustion chamber, means for supplying fuel to said combustion chamber and means for jetting combustion gases generated in the combustion chamber onto the electron emitter to heat the emitter, the combination therewith of two annular passageways positioned side-by-side with the longitudinal axes of both of said passageways substantially coincident, said passageways being separated from each other by a heat transfer wall and communicating with said combustion chamber, one for supplying an oxygen containing gas to support combustion of the fuel in said combustion chamber and the other for receiving the combustion gases from the combustion chamber, said annular passageways being formed by stacking a plurality of like members each comprising a substantially cylindrical imperforate outer side wall, a first cylindrical orifice plate portion of smaller diameter than the diameter of the outer side wall portion, said orifice plate portion having a circular row of closely spaced orifice openings therein, a substantially cylindrical imperforate inner side wall portion of smaller diameter than the diameter of said first orifice plate portion, a second substantially cylindrical orifice plate portion havtion having a circular row of closely spaced orifice openings therein and having a diameter less than the diameter of said inner cylindrical sidewall portion and a substantially circular closure plate member.

3. In apparatus for transferring heat between a fluid and a longitudinally extending heat exchanging wall, a fluid confining means including a passage for directing a flow of fluid through said apparatus in a direction generally parallel to said heat exchanging wall, a plurality of baffle means interposed at intervals along said passage to form plenum chambers between adjacent baffle means, said baffie means each including one or more jet forming apertures, each said aperture directing said fluid as a jet of relatively high velocity from a plenum chamber impinging against said wall in a direction substantially perpendicular to said wall, the said jet forming apertures and each said plenum chamber constituting the sole means for the flow of said fluid through said passage.

4. In heat exchanging apparatus as defined in claim 3, the combination for transferring heat from said fluid to a second fluid which includes two fluid confining means, one for each said fluid, said fluid confining means being located on opposite sides of said heat exchanging wall.

5. In heat exchanging apparatus as defined in claim 4, the combination in which the jets formed by the jet forming apertures in the bafiie means in one said fluid confining means impinge against the said heat exchanging wall at a location substantially opposed to the location at which the jets formed by the jet forming apertures in the bafiie means in the other said fluid confining means impinge against the opposite side of said heat exchanging wall.

6. In heat exchanging apparatus as defined in claim 4, the combination in which a plurality of said heat exchanging walls are provided, each said wall having associated therewith a pair of fluid confining means.

7. In heat exchanging apparatus as defined in claim 3, the combination in which the velocity of each said jet of said fluid when impinging against said wall is in excess of feet per second and wherein the velocity of said fluid in each said plenum chamber is less than about 30 feet per second.

8. In heat exchanging apparatus as defined in claim 7, the combination in which the velocity of each said jet is between 200 and 300 feet per second.

9. In heat exchanging apparatus as defined in claim 3, the combination in which said heat exchanging wall is a tube and said fluid confining means comprises a tube of larger diameter arranged concentrically of said first recited tube.

10. In heat exchanging apparatus as defined in claim 3, the combination in which each said heat exchanging wall and each said fluid confining means is generally tubular in shape.

11. A heat exchanger for transferring heat from a first fluid to a heat-exchanging Wall comprising a plurality of similar members stacked to form an array, each of said members having apertures formed therein facing said Wall, means for introducing said first fluid into one of said members to be jetted therefrom through said apertures substantially perpendicularly upon said wall, means forming passages for transferring said first fluid from adjacent said wall to the interior of each successive member of said array to be repeatedly jetted substantially perpendicularly upon said wall whereby heat is transferred between said first fluid and said Wall.

12. A heat exchanger as defined in claim 11 wherein said members comprise a plurality of substantially identical cylinders having stepped sections nested to form a stacked array, certain of said stepped sections joining to form said heat-exchanging wall as a continuous unbroken tube, a first group of said apertures being formed in stepped sections facing the inner surface of said heatexchanging wall, a second group of said apertures being formed in stepped sections facing the outer surface of said heat-exchanging wall, the outermost of said stepped sections forming a tubular boundary wall, and means for introducing a second fluid within said tubular boundary wall, said first fluid being jetted substantially perpendicularly through said first group of apertures against the inner surface of said heat-exchanging wall and said second fluid being jetted substantially perpendicularly against the outer surface of said heat-exchanging wall whereby heat is transferred between said first fluid and said second fluid.

References Cited UNITED STATES PATENTS 1,275,366 8/1918 Bell 122392 2,688,986 9/1954 OBrien 138-38 2,949,679 8/ 1960 MacCracken et al. 34133 3,034,769 5/ 1962 Bertin et a1 -109 J. D. MILLER, Primary Examiner.

D. F. DUGGAN, Assistant Examiner.

US. Cl. X.R. 165-154, 109

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