U.S. patent number 3,830,060 [Application Number 05/336,319] was granted by the patent office on 1974-08-20 for solid medium thermal engine.
This patent grant is currently assigned to The United States of America as represented by the Administrator of the. Invention is credited to Richard M. Beam, Le Roy R. Guist, James R. Jedlicka.
United States Patent |
3,830,060 |
Jedlicka , et al. |
August 20, 1974 |
SOLID MEDIUM THERMAL ENGINE
Abstract
A thermal engine apparatus including an elongated cylindrical
tube of metal providing a single phase working substance supported
to rotate freely about its longitudinal axis while being subjected
to continuous bending moment producing stress loads applied
intermediate its ends wherein the bending moment causes portions of
the tube to alternately pass through states of compression and
tension as the tube rotates about its axis. The apparatus further
includes structure for positioning the cylindrical tube relative to
a source of radiant energy such that the radiant energy strikes
that portion of the tube surface which is under compression,
transfers thermal energy thereto, and the consequent expansion
creates an unbalance of internal forces which causes the body to
rotate about its axis.
Inventors: |
Jedlicka; James R. (Saratoga,
CA), Guist; Le Roy R. (Campbell, CA), Beam; Richard
M. (Santa Clara, CA) |
Assignee: |
The United States of America as
represented by the Administrator of the (Washington,
DC)
|
Family
ID: |
23315557 |
Appl.
No.: |
05/336,319 |
Filed: |
February 27, 1973 |
Current U.S.
Class: |
60/527 |
Current CPC
Class: |
F03G
7/06 (20130101) |
Current International
Class: |
F03G
7/06 (20060101); F03g 007/06 () |
Field of
Search: |
;60/23,26 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Geoghegan; Edgar W.
Assistant Examiner: Burks, Sr.; H.
Attorney, Agent or Firm: Brekke; Darrell G. Morin, Sr.;
Armand G. Manning; John R.
Claims
We claim:
1. Thermal engine apparatus, comprising:
a generally tubular body having a circular transverse cross section
mounted for rotation about its axis of symmetry, said body having
axially directed compressive forces developed therein on one side
of said axis and axially directed tensile forces developed therein
on the opposite side of said axis; and
means for heating the compression loaded side of said body whereby
the resultant expansion causes internal forces to be developed
within said body tending to impart rotational motion of said body
about said axis.
2. Thermal engine apparatus as recited in claim 1 wherein said body
includes an elongated tubular member journaled at one end to means
for applying a clockwise bending moment to said body and journaled
at the opposite end to means for applying a counter-clockwise
bending moment to said body, said bending moments being operative
to develop additional compressive and tensile forces in said
body.
3. Thermal engine apparatus as recited in claim 1 wherein said body
includes an elongated tubular member bowed end-to-end to form a
torus having said compressive forces developed within its inner
annular portion and said tensile forces developed within its outer
annular portion.
4. Thermal engine apparatus for converting radiant energy to
rotational kinetic energy comprising:
a hollow, elongated, generally cylindrical body disposed to have
its longitudinal axis lying along the intersection of an imaginary
horizontal plane and an imaginary vertical plane, said body being
divided by said planes into four imaginary longitudinal
quadrants;
stressing means for applying forces to said body for causing the
quadrants disposed on one side of said planes to be subjected to
compression and the quadrants disposed on the opposite side of said
one plane to be subjected to tension; and
means for positioning said body relative to a source of radiant
energy so that said radiant energy strikes one of said quadrants
subjected to compression and transfers thermal energy thereto, said
positioning means including means for rotably supporting said body
about said axis, said thermal energy causing expansion, increased
stress, and rotary motion in said body, said rotary motion being
about said longitudinal axis.
5. Thermal engine apparatus as recited in claim 4 wherein said
stressing means includes means for applying a clockwise moment
lying in said vertical plane to one end of said body and for
applying a counter-clockwise moment lying in said vertical plane to
the other end of said body.
6. Thermal engine apparatus as recited in claim 4 wherein said body
includes a metallic tubular member having an exterior surface
coated with a layer of optically black material having better heat
absorptivity and emissivity characteristics than said member.
7. Thermal engine apparatus as recited in claim 4 and further
comprising means for directing radiant energy onto said body, and
wherein said means for positioning said body includes a sun locator
and servo means for orienting said body so that the radiant energy
from the sun impinges on one of said body quadrants subjected to
compression.
8. Thermal engine apparatus as recited in claim 4 wherein said
stressing means includes a collar-like weight member disposed about
said body.
9. Thermal engine apparatus as recited in claim 4 wherein said
means for positioning said body includes a first end support and a
second end support respectively engaging opposite ends of said
body, and wherein said stressing means includes force applying
means located adjacent each of said end supports and operative to
apply forces which tend to bend said body in an arc.
10. Thermal engine apparatus as recited in claim 9 wherein said
force applying means includes a first collar-like weight member
disposed about said body proximate one end of said body, and a
second collar-like weight member disposed about said body proximate
the opposite end of said body.
11. Thermal engine apparatus as recited in claim 9 wherein said
force applying means includes means journaled to said body and
affixed to said end support means for applying transverse loading
to said body.
12. Thermal engine apparatus, comprising:
an elongated tubular member closed upon itself to form an annular
body having an inner annular portion subjected to compressive
stress and an outer annular portion subjected to tensile stress;
and
means for applying heat to said inner annular portion whereby
resultant expansion of that portion creates forces within said body
which tend to cause the portion of said body presently forming said
inner annular portion to rotate into the position of the portion of
said body forming said outer annular portion and vice versa.
Description
The invention described herein was made by employees of the United
States Government and may be manufactured and used by or for the
government for government purposes without the payment of any
royalties thereon or therefor.
BACKGROUND OF THE INVENTION
The invention generally relates to thermal engine apparatus and
more particularly to thermal engines using a single phase metallic
working substance to convert thermal energy directly into
mechanical energy.
DESCRIPTION OF THE PRIOR ART
Thermal engines operating pursuant to the principles of thermal
expansion of metals have been proposed in the past. For example,
structures such as that shown in the U.S. Pat. to Taylor No.
3,316,415 rely on the use of bi-metallic strips moving on rollers
to convert heat induced metallic expansion into a resultant body
motion. Other structures such as that disclosed in the U.S. Pat. to
Donatelli, et al., No. 3,495,406 rely on laser beam energy or the
like to exert direct physical force upon a rotary member to cause
the member to rotate. A still further structure described in the
U.S. Pat. to Adams, No. 3,430,441, provides an engine for
converting heat energy to mechanical energy by thermal expansion
and contraction of bi-metallic elements which are passed through
heating and cooling zones established within an engine housing.
The direct conversion of heat energy into mechanical energy through
the thermal expansion properties of solids has been utilized for
control and measurement functions as illustrated by the U.S. Pat.
Nos. to Lord, 3,213,284, and McCusker, 3,213,285 relating to
heliotropic orientation mechanisms. The U.S. Pat. to Schalkowsky,
No. 3,348,374, refers to a sun referenced orientation device in
which solar energy is directly converted to mechanical forces for
orientating space vehicles relative to the position of the sun.
Although these and numerous other approaches have been proposed and
utilized to provide thermally driven motive power sources, most
prior art devices have been so mechanically complicated or grossly
inefficient as to be impracticable.
SUMMARY OF THE PRESENT INVENTION
It is therefore a principal object of the present invention to
provide a thermal engine which is mechanically simple and
operationally feasible for certain applications.
Briefly, a preferred embodiment of the present invention includes a
single phase working substance in the form of a generally
cylindrical metallic tube supported such that it is free to rotate
about its axis while being subjected to continuous bending moment
stressing the body along its longitudinal axis of rotation. The
stressing causes certain portions of the tube to be subjected to
compression while other portions are under tension as the tube is
caused to rotate about its axis. Means are provided for positioning
the tube such that radiant energy from a remote source is
concentrated on that portion of the cylindrical tube which is under
maximum compression with the result being that heat absorbed by
this portion causes an imbalance of internal forces which tend to
impart a rotational moment to the tube so that it rotates about its
axis.
Among the primary advantages of the present invention are its
simplicity of operative mechanical structure and its ability to
function in a gravity free environment.
These and other objects and advantages will no doubt become
apparent to those of ordinary skill in the art after having read
the following detailed description of the preferred embodiments
illustrated in the several figures in the drawings.
IN THE DRAWINGS
FIG. 1 is a perspective view schematically illustrating a thermal
engine apparatus in accordance with the present invention;
FIGS. 2-5 are schematic diagrams to aid in describing the operation
of the present invention;
FIG. 6 is a diagram illustrating measured operational
characteristics of one embodiment of the present invention;
FIG. 7 is a perspective diagram schematically illustrating an
alternative embodiment of the present invention for use in a
gravity-free environment;
FIG. 8 is a diagram schematically illustrating still another
alternative embodiment of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring now to the drawings, a simplified embodiment of a thermal
engine 10 is shown in FIG. 1 which operates to convert thermal
energy directly into rotational kinetic or mechanical energy in
accordance with the present invention. Engine 10 includes a thin
walled cylindrical tube 12 formed of a suitable metal to provide a
single phase solid working body. The exterior surface of tube 12 is
coated with a thin layer of flat black paint or the like to
increase the absorptivity and emissivity of the body. Cylindrical
extension shafts 14 and 16 are fixed to opposite ends of tube 12
and mate with a pair of support columns 18 and 20. Shafts 14 and 16
are disposed coaxial with tube 12 and are journaled to columns 18
and 20 by means of support bearings 22 and 24 respectively.
External loading masses in the form of annular weights 26 and 28
are coaxially mounted upon the shafts 14 and 16 respectively, at
selectable distances from the columns 18 and 20. The weights 26 and
28 establish uniform longitudinal bending moments which
continuously stress tube 12 so that its uppermost longitudinal
portion is subjected to compression and its lower most longitudinal
portion is subjected to tension. Bearings 22 and 24 permit the
balanced mass comprised of tube 12, shafts 14 and 16 and weights 26
and 28 to rotate freely about the common axis 13. Since the
stressing forces applied by weights 26 and 28 are fixed in
direction due to gravitational forces, the bending stresses within
tube 12 remain positionally fixed independent of the bodies
rotation. Thus, with tube 12 stationary or in rotation, the topside
longitudinal portion (illustrated as the upper quarter sections I
and II in FIG. 4) is always under compression relative to the
bottomside longitudinal portion (illustrated as the lower quarter
sections III and IV in FIG. 4) and the bottomside portion is always
under tension relative to the topside portion.
As suggested by the drawing, tube 12 is positioned in alignment
with a source of heat radiation illustrated in the form of a bank
of lamps 30 disposed such that the heat rays generated thereby are
focused upon at least part of that portion of tube 12 which is
under compression. The thermal flux intensity may be controlled by
changing the distance between the bank of lamps 30 and tube 12. The
lamps are positioned slightly off the vertical plane (by about
5.degree.) so that the engine will be self-starting. No heat is
applied to the bottomside of tube 12 and preferably, conditions are
such that heat is readily removed therefrom by radiation or
convection.
As the temperature of the upper portion of tube 12 is increased due
to the incident radiation, the metal in that portion will tend to
expand and disrupt the balanced equilibrium conditions with the
result being that a torque is developed within tube 12 which causes
the tube to revolve about its axis 13.
Referring now to FIGS. 2-6 a more detailed analysis will be given
to explain the operating mechanisms of the present invention.
If an element 40 of a solid such as illustrated in FIG. 2 is first
loaded externally to produce a stress distribution .sigma..sub.x on
its opposite surfaces and then heated to produce a temperature
increase .DELTA..UPSILON., the work .DELTA..omega. done on the
external loading due to the temperature increase is
.DELTA.W = .sigma..sub.x A .alpha. .DELTA. T .DELTA. x (1)
where A is the cross-sectional area of the element, .DELTA.x the
length of the element, and .omega. the coefficient of thermal
expansion of the solid. Equation (1) is based on the uncoupled
theory of thermoelasticity which assumes that temperature is
independent of strain. The work rate or power (P.sub.o ) is
then
P.sub.o = .DELTA.W/.DELTA.t = .sigma..sub.x Ax (.DELTA.T/.DELTA.t)
.DELTA.x (2)
The rate of change of temperature with respect to time t is related
to the thermal power P.sub.i into the element so that
P.sub.i = .rho.cA .DELTA.x (.DELTA.T/.DELTA.t) (3)
where .rho. and c are the density and specific heat of the solid.
If the thermal efficiency of the process is denoted by e.sub.T,
then from equations (2) and (3)
e.sub.T = P.sub.o /P.sub.i = .sigma..sub.x .alpha./.rho.c
(unidirectional stress) (4)
If the applied stresses .sigma..sub.x are reversed in direction
during the cooling portion of a cycle, the thermal efficiency for
the complete heating and cooling cycle is
e.sub.T = P.sub.o /P.sub.i = 2.sigma..sub.x .alpha./.rho.c
(bidirectional stress) (5)
If the element is placed under triaxial stress instead of uniaxial
stress, the thermal efficiency is increased threefold to
e.sub.T = 6.sigma..sub.x .alpha./.rho.c (triaxial, bidirectional
stress) (6)
For a system utilizing the solid phase cycle and nonregenerative
heating, equations (4), (5), and (6) represent the maximum thermal
efficiencies that can be attained.
As described above a simple design of a solid phase engine which
utilizes uniaxially stressed material consists of a tube, such as
that shown in at 12 in FIG. 1 and schematically illustrated at 50
in FIG. 3, that is free to rotate but has an applied moment fixed
in the inertial reference frame. The inertial coordinate system is
defined as xyz. The tube 50 is free to rotate about the x-axis and
no moment can be carried by the end supports 52 and 54 (pinned
ends). The applied moment vector, M.sub.z (x) identified in FIG. 4,
is assumed to remain parallel to the z axis. The moment may be due
to the weight of the cylinder or applied loading. The thermal
loading is provided by a planar flux field of radiant energy with
magnitude Q.sub.o which acts normal to the x-axis and at an angle
.PSI. with the y-axis (FIGS. 3 and 5).
If .theta. is the circumferential coordinate measured from a
reference point fixed to the tube 50 (FIG. 5) and R and h are the
radius and wall thickness of the tube 50, the differential power
produced by an element of the tube is from equation (2),
dP.sub.o = .sigma..sub.x (x,.theta. ,t)hR
d.theta.a(.delta.T(.theta. ,t)/.delta.t)dx (7)
and the total power produced by the engine is obtained by
integrating expression (7) over the whole tube 50: ##SPC1##
If the tube is rotating at constant angular velocity .omega., the
stress is related to the moment from simple beam theory where for
R>>h:
.sigma..sub.x (x,.theta. ,t) = [M.sub.z (x)cos(.theta. +
.omega.t)]/.pi.R.sup.2 h (9)
To complete the computation of the power output from equation (8),
it is necessary to evaluate the temperature distribution in the
tube 50. The heat balance equation for a ring element of the tube
of unit length in the x direction is
kh.delta..sup.2 T(.theta. ,t)/R.sup.2 .delta..theta..sup.2 -
.rho.ch.delta.T(.theta. ,t)/.delta.t = .xi..epsilon.T.sup.4
(.theta. ,t) - .gamma.(.theta. ,t) (10)
where k is the material thermal conductivity, .xi. the
Stephan-Boltzmann constant, and .epsilon. the thermal emissivity of
the tube surface. The following basic assumptions have been made to
obtain equation (10):
a. The heat loss from the tube is by radiation;
b. There is no thermal conduction in the longitudinal (x) direction
and T(.theta. ,t) is the average temperature through the thickness;
and
c. .gamma. is the total flux distribution into the tube.
For a large class of engines and operating conditions the variation
in temperature (denoted T(.theta. ,t) around the circumference will
be small compared to the average temperature (T.sub.A) of the tube,
that is,
T(.theta. ,t) = T.sub.A + T(.theta. ,t) .vertline.T(.theta.
,t).vertline. << T.sub.A (11)
if condition (11) is introduced into the heat balance equation (10)
and only first-order terms retained, one obtains
kh.delta..sup.2 T(.theta. ,t)/R.sup.2 .delta..theta..sup.2 -
.rho.ch.delta. T(.theta. ,t )/.delta.t -
4.xi..epsilon.T.sub.A.sup.3 T(.theta. ,t) =
.xi..epsilon.T.sub.A.sup.4 - .gamma.(.theta. ,t) (12)
If the thermal absorptivity of the tube's surface is .alpha..sub.T
and the tube is rotating with constant angular velocity .omega.,
the function .gamma.(.theta. ,t) becomes
.gamma.(.theta. ,t) = .alpha..sub.T Q.sub.o g(.theta. + .omega.t -
.psi.) (13)
where g is a functional relationship. Expressed as a Fourier series
representation, ##SPC2##
The "steady state" or particular solution for equation (12) with
.gamma. defined by equation (14) can be written ##SPC3##
where T.sub.n (.theta. ,t) is the solution to the equation
kh.delta..sup.2 T.sub.n (.theta. ,t)/R.sup.2 .delta..theta..sup.2 -
.rho.ch.delta.T.sub.n (.theta. ,t)/.delta.t -
4.xi..epsilon.T.sub.A.sup.3 T.sub.n (.theta. ,t) = - .alpha..sub.T
Q.sub.o a.sub.n cos n(.theta. + .omega.t - .psi.) (16)
For all n<0;
a.sub.o = .xi..epsilon.T.sub.A.sup.4 /.alpha..sub.T Q.sub.o
since T.sub.A has been assumed time independent. A particular
solution to equation (16) can be easily obtained in the form
T.sub.n (.theta. ,t) = T.sub.n (.theta. + .omega.t - .psi.) =
T.sub.n (.eta.) (17)
Equation (16) becomes
khT.sub.n "(.eta.)/R.sup.2 - .rho.ch.omega.T.sub.n '(.eta.) -
4.xi..epsilon.T.sub.A.sup.3 T.sub.n (.eta.) = -.alpha..sub.T
Q.sub.o a.sub.n cos n.eta. (18)
where a prime is used to denot differentiation with respect to
.eta..
A particular solution to equation (18) is
T.sub.n (.eta.) = -{R.sup.2 .alpha..sub.T Q.sub.o a.sub.n
cos[n.eta. - arctan pn/(q - n.sup.2)]}/khpn[ 1 + (q - n).sup.2
/(pn).sup.2 ].sup.1/2 (19)
where p is the negative reciprocal of the Fourier modulus
p = -.rho. c.omega. R.sup.2 /k (20)
and
q = -4.xi..epsilon.T.sub.A.sup.3 R.sup.2 /kh (21)
With the notation
A.sub.n = R.sup.2 .alpha..sub.T Q.sub.o a.sub.n /khpn[1 + (q -
n.sup.2)/( pn).sup.2 ].sup.1/2 (22)
.PHI..sub.n = arctan pn/(q - n.sup.2) , - (.pi./2) < .PHI.
.ltoreq.(.pi./2) (23)
the solution to the heat balance equation (12) with thermal input
.gamma. defined by equation (14) can be written ##SPC4##
and ##SPC5##
The output power of the engine [equation (8) ] may now be computed
with expressions (9) and (25) as ##SPC6##
However, this can be reduced to ##SPC7##
Introduction of A.sub.1 from equation (22) into the power equation
produces ##SPC8##
If the radiant heat absorbed by an element is assumed to be
proportional to the cosine of the angle between the normal to the
surface and the thermal radiation direction (Lambert's law), then
the function g, required in equation (13), becomes
g(.theta.+.omega.t-.psi.) = 0
-.pi..ltoreq.(.theta.+.omega.t-.psi.).ltoreq.-.pi./2 3 =
cos(.theta.+.omega.t-.psi.)
-.pi./2.ltoreq.(.theta.-.omega.t+.psi.).ltoreq..pi./ 2 = 0
.pi./2.ltoreq.(.theta.-.omega.t+.psi.).ltoreq..pi. (29)
and a.sub.1, required in equation (28), becomes ##SPC9##
The power output equation becomes ##SPC10##
Given the material thermal and geometric properties, the operating
speed, the flux intensity and location, and the applied moment
distribution, one can compute the power output for the engine.
Special Case .vertline. q.vertline. <<1,p<<1. For many
engines and operating conditions the approximations
.vertline.q.vertline. = 4.xi..epsilon.T.sub.A.sup.3 R.sup.2 /kh
<< 1 (32)
and
.vertline.p.vertline. = .rho. c.omega..sup.2 R.sup.2 /k >> 1
(33)
are valid. If these conditions are introduced into the power
equation (31) and the phase angle equation (23) one obtains
##SPC11##
Thus the power is maximum if the thermal radiation is on "top"
(.PSI. = 0) of the tube and zero if the thermal radiation is to the
side (.PSI. = .+-..pi./2) of the tube. Note also that the power
output is negative if .vertline..PSI..vertline. < .pi./2 (but
less than .pi.).
If the applied moment distribution is uniform along the length of
the tube (M.sub.z (x) = M.sub.zo) then
P.sub.o = (M.sub.zo .alpha..alpha..sub.T Q.sub.o
l/2h.rho.cR)sin[.psi. + (.pi./2)] (35)
The thermal power input to the engine is
P.sub.i = 2.alpha..sub.T Q.sub.o Rl (36)
therefore, the thermal efficiency is
e.sub.T = (M.sub.zo .alpha. /4h.rho.cR.sup.2)sin[.psi. + (.pi./2)]
(37)
The maximum stress in the tube is related to the moment by
.sigma..sub.max = M.sub.zo /.pi.R.sup.2 h (38)
therefore, the thermal efficiency can be written
e.sub.T = (.pi..sigma..sub.max .alpha./4.rho.c)sin[.psi. +
(.pi./2)] (39)
or with thermal radiation on "top" of the tube (.PSI. = 0):
e.sub.T = .pi..sigma..sub.max .alpha./4.rho.c (40)
In an experimental engine built along the lines illustrated in FIG.
1 the working substance was stainless steel (type 304 annealed)
which has been welded into a thin walled cylindrical configuration
to form tube 12. The surface of tube 12 was sprayed with a thin
coat of flat black paint to increase absorptivity and emissivity.
An almost uniform bending moment was applied to tube 12 by annular
weights 26 and 28 mounted on shafts 14 and 16 between the ends of
tube 12 and the support bearings 22 and 24. The stress applied to
tube 12 was easily varied by translating the weights along the
shafts.
Radiant energy was provided in the laboratory by a string of
photographers photo-spot lamps, and the thermal flux intensity on
the tube 12 was controlled over a range of one to a maximum of
about five solar constants by changing the distance between the
lamps and the tube. The lamps were positioned slightly off the
vertical plane by about 5.degree. so that the engine would be self
starting. The performance data for the experimental engine is shown
graphically in FIG. 6.
Net torque was measured by a Prony break, and the net power output
was computed. Frictional aerodynamic and visco-elastic power losses
were established from the lamps-off (at operating temperature)
decay rates of the engine speed. The total power output curve is
the sum of the power loss in the new power.
The thermal energy passing through the working substance was
determined with the aid of a transient calorimeter constructed with
the curvature of the tube 12 and sprayed with a thin coat of flat
black paint. The theoretical power output shown in FIG. 6 was
obtained by multiplying the theoretical thermal efficiency factor
(equation 40) by the experimentally determined thermal energy
input. The discrepancy between theory and experiment could be
attributed to many factors, however, the most probable sources of
error were (a) accuracy of material properties used in calculating
theoretical efficiency, (b) accuracy of the loss measurements since
these data were taken for lamps-off condition (although near
operating temperature), and (c) accuracy of the experimental
determination of the thermal input to the tube.
In the analysis for thermal efficiency, the dominant mechanism for
heat rejection from the tube was assumed to be radiation (equation
10). If convective heat transfers are calculated and compared to
the radiative heat transfer at the conditions of the test, the two
will be comparable in magnitude. Additional analysis not included
here demonstrates that the thermal efficiency is governed by the
circumferential variation in the heat transfer rather than by its
magnitude. If all heat were rejected at the tube bottom rather than
uniformly around the tube for example, the thermal efficiency would
increase by a factor of 2. Forced convection caused by the angular
velocity of the tube should give rise to heat rejection uniform
with respect to circumference and therefor will predict the same
thermal efficiency as for radiation. If natural convection
dominates however, heat rejection will be largest at the bottom of
the tube and the thermal efficiency would be increased.
Two types of instabilities were encountered in the operation of the
experimental engine, one at low speeds and one at high speeds. Both
instabilities were apparently due to the coupling of the thermal
input and the tube deformations. The low speed instability range is
indicated in FIG. 6. At these speeds a thermally induced bow forms
in the tube which produces an unbalance of the rotating weights.
Because of the unbalance the bowed region moves at lower angular
velocities when passing the heat input plane thereby causing an
increase in the amount of thermal bow.
The amplitude of the bow increases until the unbalance is so large
that the engine rotation ceases. However, rotation can be restored
by reducing the torque loading to a value that permits the engine
running speed to exceed the minimum instability speed.
The second instability occurred when the engine was operated at
speeds near one-half the first critical speed, defined as the speed
corresponding to the first mode bending frequency of the tube. When
this speed was approached, a thermally coupled operational
instability occurred which rapidly built up without apparent limit
cycle.
The relatively high losses of the experimental engine reflected in
FIG. 6 have been determined to result from joint slippage in the
connection between the shafts and the tube and in a later
modification in which the joint was welded the losses were
significantly reduced.
Referring now to FIG. 7 of the drawing, an embodiment similar to
that of the FIG. 1 embodiment, but modified for use in a
gravity-free environment such as outer space, is shown at 110. As
in the previous embodiment the structure includes a cylindrical
tube 112 forming a working body having shafts 114 and 116 affixed
to each end. The shafts are journaled to a pair of supports 118 and
120 by bearings 122 and 124. The primary difference between this
embodiment and that previously described is that since there are no
gravity forces to act upon annular stressing weights, means must be
provided for simulating the gravity function. In this case, such
stressing forces are applied by means of spring loaded bearing
structures 126 and 128 which apply biasing forces downwardly toward
the support base 119. A suitable radiation focusing means 130 is
positioned to focus rays of sunlight or other radiation onto a
particular longitudinal portion of tube 112.
Since the apparatus 110 must always be oriented so that the
focusing means 130 can focus sun rays onto a particular portion of
tube 112, means such as the inertially stabilized platform
schematically illustrated at 160 must be provided along with a
suitable sun position locating means 162 and an engine position
control mechanism 164. Locator 162 detects the relative position of
the sun and develops an output signal for energizing position
control means 164 causing it to maintain engine 110 oriented in the
proper direction relative to the sun.
Still another alternative embodiment of the present invention can
be constructed without weights for use in a non-gravitational
environment by closing the tube upon itself to form a torus 212 as
illustrated in FIG. 8 of the drawing. The tube must undergo only
elastic bending when it is formed into a torus. Torus 212 is
likewise coated with a layer of black paint or the like to increase
its absorptivity and emissivity, and is suspended within a housing
214 by any suitable means. For example, ring magnets 216 may be
positioned within housing 214 for creating a magnetic field to
magnetically suspend the torus within housing 214. Positioned at
the bottom of housing 214 and aligned with the central aperture of
torus 212 is a parabolic reflector 218 which is designed to reflect
radiation from the sun onto a particular portion of the facing
surfaces of the torus.
Housing 214 is provided with a circular opening 220 for allowing
the sun rays to reach reflector 218 while at the same time masking
rays which would otherwise impinge directly upon the surface of
torus 212. Where this embodiment is to be used in an outer space
embodiment a suitable guidance reference such as the suggested
inertially stabilized platform 260 may be provided for carrying a
sun locator 262 and a position control means 264 as in the previous
embodiment. Sun detector 262 will detect the relative location of
the sun and generate an electrical signal for energizing control
means 264 which will in turn orient engine 210 in the proper
direction to receive the rays of sunlight.
In operation, as the solar rays are received and reflected by
reflector 218 onto a particular quarter section of torus 212, the
metallic fibers in the irradiated region will tend to expand due to
the increase in temperature and as in the previous embodiment
create internal forces within torus 212 which tend to impart rotary
motion to the structure causing it to roll about its own axis. In
order to provide a power take-off, any suitable means of coupling
may be provided which is consistent with the particular suspension
mechanism utilized. It will be appreciated that in this embodiment
heat applied to the inner annular surfaces of the torus will enable
the device to deliver power without the use of either weights or
externally loaded bearings to stress the cylindrical body.
Whereas the above description has been limited to three simplified
embodiments it is to be understood that these embodiments are
greatly simplified and offered for purposes of illustration only.
It is contemplated that after having read the above disclosure, one
of ordinary skill in the art will envision many other alterations,
modifications and further embodiments of the invention. It is
therefore to be understood that the above disclosure is not to be
taken as limiting and that the appended claims are to be
interpreted as covering all such alterations and modifications as
fall within the true spirit and scope of the invention.
* * * * *