Ends of metal tube are fastened to axles which are supported on bearings so tube can rotate about its long axis while subjected to invariant bending moment that stresses it along longitudinal axis of rotation. Heat absorbed leads to expansion of metal, which unbalances internal forces and generates rotational moment in tube

Beam, R. M.

Guist, L. R.

Jedlicka, J. R.

English

NASA Technical Reports Server

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December 1973	 B73-10493 
NASA TECH BRIEF 
Ames Research Center 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Metal Tube Used as Solar Engine 
A thin-walled metal tube is the working medium 
for a thermal engine which is structurally simple 
when compared with other engines that are based on 
the expansion of gases, fluids, or metals.
- 
The diagram is a simplified sketch of the basic 
elements of the solar engine. The ends of the metal 
tube are fastened to axles which are supported on 
bearings so that the tube can rotate about its long 
axis while subjected to an invariant bending moment 
that stresses it along the longitudinal axis of rotation. 
The stressing causes the top of the tube to be sub-
jected to compression while the bottom is under ten-
sion. The tube is positioned so that radiant energy 
from a source is concentrated largely on the top; heat 
absorbed leads to an expansion of the metal, which 
unbalances internal forces and generates a rotational 
moment in the tube. 
The thin-walled cylindrical tube is formed of metal 
to provide a single-phase-solid working body and is 
coated with a thin layer of flat-black paint to increase
the absorptivity and emissivity of radiant energy. 
External masses in the form of annular weights are 
coaxially mounted on the shafts at the greatest dis-
tances from the support bearings; the weights estab-
lish uniform longitudinal bending moments which 
continuously stress the tube so that its uppermost 
longitudinal portion is compressed and its lower por-
tion is under tension. Since the stressing forces ap-
plied by the weights are fixed in direction because of 
gravity, the bending stresses within the tube are in-
dependent of rotation. 
As suggested in the diagram, the tube is positioned 
so that heat rays from a source of radiation fall upon 
the portion of the tube which is under compression. 
The source is positioned slightly off the vertical plane 
(by about 5°) so that the engine will be self-starting. 
No heat is applied to the bottom of the tube and, 
preferably, conditions are arranged so that heat is 
readily removed therefrom by radiation or convection. 
A solar engine using a solid as a working medium 
has a low thermal efficiency when compared with 
engines using gases or liquids, but it is especially use-
ful for the direct conversion of solar energy into 
mechanical motion when design simplicity is of pri-
mary importance. 
References: 
1. Beam, R., and Jedlicka, J.: A Solar Engine Using 
the Thermal Expansion of Metals. Solar Energy, 
vol. 15, p. 188, 1978. 
2. Jedlicka, J.: Solid State Solar Engine. The Physics 
Teacher, vol. 10, p. 475, 1972. 
(continued overleaf) 
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Aeronautics and Space Administration. Neither the United States 	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States	 will be free from privately owned rights.
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Note: 
No additional documentation is available. Specific 
questions, however, may be directed to: 
Technology Utilization Officer 
Ames Research Center 
Moffett Field, California 94035 
Reference: B73-10493
Patent status: 
Inquiries concerning rights for the commercial use 
of this invention should be addressed to: 
NASA Patent Counsel 
Mail Code 200-1A 
Ames Research Center 
Moffett Field, California 94035 
Source: James R. Jedlicka, LeRoy R. Guist,

and Richard M. Beam

Ames Research Center

(ARC-10461) 
B73-10493	 Category 03
	 •


Metal tube used as solar engine

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