US3839094A - Fluidic thermoelectric generator - Google Patents

Abstract

A thermoelectric generator that utilizes the high temperature generated by fluid compression waves within a resonant tube that is subject to a supersonic air stream. The resonant tube, which may take any one of a number of forms, is located in a nose cone of the projectile that has a nozzle formed at the ogive for directing the fluid flow created while the projectile is in flight onto the open end of the resonant tube. This fluid flow sets up complex cyclical compression waves within the resonant tube which subsequently causes heating of the fluid therein due primarily to the friction within the tube and to the nonisentropic compression of the fluid interacting with the shock waves therein. The heating of the fluid and the high amplitude fluctuations cause a thermoelectric crystal placed near the closed end of the resonant tube to emit an electrical output. The electrical output may be utilized as a power source for any of a number of electrical devices within the projectile.

Description

0 limited States Patent 11 1 1111 3,839,094 Campagnuolo 1 Oct. 1, 19 74 FLUIDIC THERMOELECTRIC GENERATOR 3,630,150 12/1971 Rakowsky.... 89/1 B x 3,641,346 2/1972 L h b 136213 UX [751 Inventor: Carl Campagnmloh Potomac 3,691,408 9 1972 310 4 3,719,532 3/1973 Falkenberg et a1. 310/4 Assignee: The United States of America as 3,733,499 5/1973 D618 (it al. l36/2l3 UX represented y the secretary of the 3,736,447 5/1973 Zauderer 310/4 Army Washington Primary Examiner-T. H. Tubbesing [22] Filed: June 30, 1972 Assistant Examiner-G. E. Montone [211 Appl' No; 267,739 Attorney, Agent, or FirmEdward J. Kelly; Saul Elbaum [52] US. Cl 136/213, l36/2O5,33ll()/l41, 57 TR C [51] Int Cl H02 1 A thermoelectric generator that utilizes the high tem- [58] Field of Search 310/4, 15, 11; 102/924, Perame generatedhby 1 cFmpressm waves 1 [02/49] 89/1 116/137 R, 259/4 a resonant tube t at is sub ect to a supersonic air 136/205 3 21 stream. The resonant tube, which may take any one of a number of forms, is located in a nose cone of the projectile that has a nozzle formed at the ogive for di- [56] References cued recting the fluid flow created while the projectile is in UNITED STATES PATENTS flight onto the open end of the resonant tube. This 783,208 2/1905 K hl 1 15/137 R fluid flow sets up complex cyclical compression waves 2,666,039 W 1 et a1 l36/213 X within the resonant tube which subsequently causes 3,123,739 6/ :964 O Connor 310/4 heating of the fluid therein due primarily to the i 5 3;; 32 7, tion within the tube and to the non-isentropic com- 340805O 10/1968 zg 25924 pression of the fluid interacting with the shock waves 3711:1125 1111968 Marks.IIIIIIIIIIIIIIIIIIII 11111310711 theheih- The heethe ef the hhhd ehd the high emph- 3:415 93 2 19 campagnualo et H 102 92 4 tude fluctuations cause a thermoelectric crystal placed 3,467,840 9/1969 Weiner 310/4 near the closed end of the resonant tube to emit an 3,484,61 1 12/1969 Futaki 136/213 UX electrical output. The electrical output may be utilized 3,549,914 12/1970 Jones, Jr. ct a1 310/11 as a power source for any of a number of electrical deg/lllafl'oel et a1 vices within the projectile. vans 3,621,310 11/1971 Takeuchi et a1. 310/11 8 Clalms, 4 Drawmg Figures FLUIDIC THERMOELECTRIC GENERATOR RIGHTS OF GOVERNMENT The invention described herein may be manufactured, used, and licensed by or for the U.S. Government for governmental purposes without the payment to me of any royalty thereon.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to flueric generators, and, more particularly, to a flueric generator that utilizes a resonant tube in combination with a thermoelectric crystal as a power source.

2. Description of the Prior Art In missile and projectile fuzes, it is important that an electrical source be provided which will operate reliably for short periods of time. This is normally accomplished by actuating a battery a short time after the missile or projectile has become airborne. Or, perhaps a fluidic-electrical generator is utilized such as disclosed in U.S. Pat. No. 3,555,314. The latter device requires a multitude of moving parts, such as diaphragms, rods, and springs. Such mechanical or electromechanical devices are relatively complicated and often unreliable in their operation due to inherent tendencies to either wear out or break down.

It is therefore a primary object of the present invention to provide a fluidic means for generating electricity in a missile or projectile that is devoid of any moving parts.

Another object of the present invention is to provide a thermoelectric generator that relies-on the dynamic flow properties of fluid for its actuation, operation and maintenance.

Another object of the present invention is to provide a thermoelectric generator to use in a missile or a projectile that will generate electricity upon the entrance of ram air into the ogive of the projectile only after the projectile is a safe distance from the launching pad.

A further object of the present invention is to provide a thermoelectric generator for use in a missile or projectile that avoids the dependence upon any externally generated electrical initiation signal by relying solely upon the environmental supersonic fluid flow created as the projectile flies through the air.

SUMMARY OF THE INVENTION A resonant tube closed at one end is adapted to receive the supersonic flow coming through the ogive of a missile or projectile. The supersonic flow causes the tube to resonate and heats up its closed end at which is located a thermoelectric crystal. The crystal, which may be, for example, bismuth telluride, lead telluride, or barium titanate, emits an electrical output which can be used to power a fuze or trigger a squib. This power can only be available when the projectile is in flight, thereby providing an important safety feature to the system.

BRIEF DESCRIPTION OF THE DRAWING The specific nature of the invention as well as other objects, aspects, uses, and advantages thereof will clearly appear from the following descriptions and from the accompanying drawings, in which:

FIG. 1 illustrates the combination of a resonant tube and a thermoelectric crystal in accordance with the present invention;

FIG. 2 represents another embodiment of a resonant tube and a crystal in accordance with the present invention;

FIG. 3 represents another preferred embodiment of a resonant tube in combination with a thermoelectric crystal in accordance with the teaching of the present invention; and

FIG. 4 represents still another embodiment of a resonant tube in combination with the crystal of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The embodiment depicted in FIG. 1 illustrates a resonant tube 14 with an open end 16 and a closed end 18 located adjacent a thermoelectric crystal 10 that has electrical leads at 12 extending therefrom. The entire resonant tube apparatus of FIG. 1 can be located within the ogive of a projectile (not shown) such that the ram air received while the missile or projectile is in flight is directed onto the open end 16 of resonant tube 14 so as to produce internal resonant oscillations. The crystal 10 is of the thermoelectric type such as barium titanate, bismuth telluride, or lead telluride, and generates an electrical output as a result of the application of heat and/or oscillating high amplitude fluctuations in the resonant tube.

In 1954, Dr. Sprenger in MITTEILUNGEN AUS DEN INSTITUT FUR AERODYNAMIK Vol. 21, pages 18 through 34, (AERE LIBRARY TRANSLA- TION 687), taught that a resonant cavity, closed at one I end, will become heated at the closed end when it is stimulated into oscillation by means of a free fluid flow. The resonant cavity becomes heated at its closed end because the fluid at the base is compressed with each cycle of oscillation. Shadow graph studies of resonant tubes indicate that shock waves exist within the tube which are generated by a normal shock in a state of instability oscillating between the mouth of the tube and the nozzle exit. When the normal shock is close to the nozzle exit, a compression wave travels down the tube which becomes steeper due to friction within the walls of the tube. The shock impinges at the closed end and is reflected. Upon exiting from the tube, it causes a lower pressure at the entrance. At this time, the normal shock moves across the region of instability and causes an expansion wave to be drawn into the tube. After reflection, the expansion wave arrives at the mouth of the tube and causes the normal shock to move back toward the nozzle. Thus, a new compression wave is generated and the cycle repeats.

The heating of the fluid is attributed to the friction within the tube and a non-isentropic compression of the fluid across the shock wave. While a theoretical determination of the temperature in the tube is greatly complicated by the complex wave distribution, it suffices to say that extremely small tubes in the order of the 0.2 inches in diameter can be used to produce extremely high temperatures in the range of 600 to 1,000F., and these temperatures are sufficient to initiate the operation of crystal 10 in the device of FIG. 1. It should also be noted that the temperatures mentioned are generated in fractions of seconds from the time the fluid jet impinges upon the resonant tube.

During the operation of the device in FIG. 1, ram air will be directed onto the opening 16 of resonant tube 14, setting the tube 14 into resonance, thus heating the tube at its closed end 18 due to the compression waves discussed above. The tube is insulated and the temperature within rises rapidly. Within approximately half a second, crystal will be stimulated into oscillation to produce electricity along output wires 12. The operation of the thermoelectric crystal 10 of FIG. 1 can best be understood by referring to specialized reference texts on the subject, such as Walshs Energy Conversion, Ronald Press, 1967, Ch. 5.

The resonant tube 24 shown in FIG. 2 has been found to produce even better results than the resonant tube 14 used in the embodiment of FIG. 1. Tube 24 consists of an open end 28 leading to a tube of diameter D. Tube 24 is modified by placing a restrictor 26 of internal diameter d within the resonant cavity. The function of the restrictor 26 is to trap some of the hot gas which would have been carried away from the closed end by the expansion wave discussed above. The position of restrictor 26 within the tube 24 is very important and proper placement of the restrictor 26 will maximize the temperature which can be obtained at the closed end of tube 24 adjacent to crystal 20. Experiments were conducted to demonstrate the temperature at the closed end of the tube 24 for various values of L/x, wherein L is the length of the whole resonant cavity and x is the distance between restrictor 26 and the closed end of the tube 24. It was discovered that the maximum temperature was produced at the closed end adjacent to crystal 20 when L/x was approximately equal to 8. After approximately 4 seconds, the temperature would be in excess of 600F. The use of this tube in the embodiment shown would insure sufficient temperature to initiate the operation of thermoelectric crystal 20.

The resonant tube depicted in FIG. 3 is more thoroughly described in my copending application Ser. No. 238,1 38, filed Mar. 27, 1972, now US. Pat. No. 3,798,475. Resonant tube 34 is seen to consist of a member 36 disposed across the center of the open end 39 of cavity 34 in front of the entrance to the remainder of the tube. Tube 38 represents an external nozzle that provides a supersonic flow of air to the resonant tube 34 and its associated apparatus. As fluid flows out of tube 38, it encounters member 36 and is separated into two halves. Because of the location of the entrance to cavity 34 with respect to member 36, part of the separated fluid encounters the edges of cavity 34 and thereby flows into the cavity. The fluid entering the cavity fills the cavity until the pressure within the cavity becomes greater than atmospheric pressure, when fluid leaves the cavity thus lowering the pressure. When the pressure in the cavity becomes lower than atmosphere, the fluid returns to the cavity and a new cycle initiates. The member 36 which creates a fluid instability condition at the open end 39 of cavity 34 contributes to the triggering mode of the oscillator. The heat and oscillations thereby generated at the closed end of cavity 34 initiates the operation of thermoelectric crystal 30, thus causing an electrical output to be fed along wires 32 for the purposes as stated hereinabove.

Another type of resonant tube/oscillator which may be used in the device of the present invention is depicted in FIG. 4, which shows a sting oscillator 48 located within a resonant tube 44 adapted to receive ram air from nozzle 38. The operation of the sting oscillator 48 can be best understood with reference to US. Application Ser. No. 47,505 filed June 18, 1970. Basically, sting 48, held in place by ribs 50 onto the walls of a resonant cavity 44, is placed axially or centrally in the path of the fluid flow from nozzle 38. As fluid strikes sting 48, high spin fluid vortices are shed by the sting and progress into the cavity expanding and decreasing their rate of spin, thus converting their rotational kinetic energy into pressure. The pressure builds up with translation of the vortices, thus producing a steepening pressure wave. The pressure wave will reflect off the rear wall of cavity 44 and be expelled from the opening 46. Thus it is seen that sting 48, by causing instabilities in the fluid flow, will change the steady state fluid flowing from nozzle 38 into one of periodic pressure pulsation, i.e., the pressure alternately increases and decreases within cavity 44 with periodic response as long as an input flow is present at opening 46. As explained above, the heating of the resonant tube at its base end near crystal 40 will activate the crystal to emit electrical energy along wires 42.

It is seen that I have provided a thermoelectric generator that has potential wide application as an electrical energy source in both missiles and armed projectiles. The device relies only upon the dynamic supersonic flow properties of fluids and has no moving parts, thus contributing to its simplicity, low cost, ruggedness, and long shelf life. It is evident that the heat generated at the base of the resonant tubes described hereinabove could also be transferred at one junction of a thermopile and the same results obtained as described above. While the thermoelectric generator of my invention has been described in the context of this application in ordnance projectiles and missiles, it will be apparent to those skilled in the art that a wide variety of other uses are possible. It will be further apparent that the embodiments shown are only exemplary and that various modifications can be made in construction and arrangement within the scope of the invention as defined in the appended claims.

I claim as my invention:

1. Apparatus for generating electricity in response to a fluid flow, comprising:

a. a resonant tube having an open end and a closed end;

b. means for directing said fluid flow onto said open end of said resonant tube to produce fluid compression waves therein;

c. a thermoelectric crystal that generates electrical energy in response to heat produced at said closed end of said resonant tube by said fluid compression waves. 7

2. The invention according to claim 1 wherein said resonant tube includes a restrictor located on the inner wall of said resonant tube for retaining within said resonant tube a portion of the heat produced at said closed end, said restrictor having an inner diameter that is smaller than the inner diameter of said resonant tube.

3. The invention according to claim 1 wherein said resonant tube includes a rigid rod attached concentrically within said resonant tube and having a tapered end directed outwardly from said open end of said resonant cavity for causing perturbations in said fluid flow.

4. The invention according to claim 1 wherein said resonant tube includes a member that extends across said open end of said resonant cavity for separating incoming fluid and for converging said fluid at downsaid fluid flows.

7. The invention according to claim 1 wherein said thermoelectric crystal is selected from the group consisting of bismuth telluridc, lead telluridc. and barium titanate.

8. The invention of claim 2 wherein said restrictor is located within a resonant tube of length L at a distance X from said crystal and wherein the ratio of L/X is 8.

Claims (8)

1. APPARATUS FOR GENERATING ELECTRICITY IN RESPONSE TO A FLUID FLOW, COOPRISING: A. A RESONANT TUBE HAVING AN OPEN END AND A CLOSED END; B. MEANS FOR DIRECTING SAID FLUID FLOW ONTO SAID OPEN END OF SAID RESONANT TUBE TO PRRODUCE FLUID COMPRESSION WAVES THEREIN; C. A THERMOSELETRIC CRYSTAL THAT GENERATES ELECTRICAL ENERGY IN RESPONSE TO HEAT PRODUCED AT SAID CLOSED END OF SAID RESONANT TUBE BY SAID FLUID COMPRESSION WAVES.

2. The invention according to claim 1 wherein said resonant tube includes a restrictor located on the inner wall of said resonant tube for retaining within said resonant tube a portion of the heat produced at said closed end, said restrictor having an inner diameter that is smaller than the inner diameter of said resonant tube.

3. The invention according to claim 1 wherein said resonant tube includes a rigid rod attached concentrically within said resonant tube and having a tapered end directed outwardly from said open end of said resonant cavity for causing perturbations in said fluid flow.

4. The invention according to claim 1 wherein said resonant tube includes a member that extends across said open end of said resonant cavity for separating incoming fluid and for converging said fluid at downstream area, whereby periodic alterations of flow are induced in said resonant cavity.

5. The invention according to claim 4 further including a circular orifice mounted upstream of said open end of said cavity.

6. The invention according to claim 1 wherein said resonant tube comprises a substantIally conically-shaped body, the tapered end of said body being the closed end of said cavity, the open end of said cavity being the base of said conically-shaped body into which said fluid flows.

7. The invention according to claim 1 wherein said thermoelectric crystal is selected from the group consisting of bismuth telluride, lead telluride, and barium titanate.

8. The invention of claim 2 wherein said restrictor is located within a resonant tube of length L at a distance X from said crystal and wherein the ratio of L/X is 8.

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