Tubular solar collector system

A tubular solar collector system is provided in which a heat absorbing fluid is contained within tubular solar collectors completely separate and independent from a fluid circulated through the manifold to which the tubular collectors are operably attached. The collectors extend downwardly from the generally horizontal manifold so that when the fluid within the tubular collector is heated by incident solar radiation it is circulated to a heat exchanger in the manifold by thermosyphoning action.

FIELD OF THE INVENTION 
The present invention relates to solar collectors. More particularly, the 
present invention relates to solar collectors of the type employing a 
plurality of vacuum jacketed glass tubular collector members. 
BACKGROUND OF THE INVENTION 
In tubular types of solar energy collector systems, a plurality of vacuum 
jacketed glass tubular collector elements are operably connected into a 
manifold which serves to distribute and collect working fluid circulated, 
for example, by means of a pump through the tubular solar collector 
members for heating therein. Such systems are exemplified by the following 
U.S. Pat. Nos. 980,505; 3,952,724; 4,018,215. Among the disadvantages of 
the foregoing types of systems is the fact that a break in any one of the 
tubular solar collectors will result in a loss of fluid from the system, 
thereby making the entire system inoperable. Additionally, if vacuum is 
lost in one or more of the vacuum jackets of the tubular collector, the 
entire system may have to be shut down in order to repair or replace such 
tubular member. 
SUMMARY OF THE INVENTION 
The present invention provides a tubular type solar energy collector system 
which is designed so that a break in any one of the tubular collector 
members does not render the system inoperable and indeed permits a simple 
and rapid replacement of damaged tube or tubes without shutting down the 
entire system. 
Broadly stated, the tubular solar collector system of the present invention 
includes a manifold having a plurality of generally downwardly extending 
vacuum jacketed tubular solar collector members operably and detachably 
connected to the manifold via heat exchange members within the manifold. 
Each tubular solar collector member is sealed or closed at its ends and 
contains a first fluid therein which during operation is circulated by 
thermosyphoning flow in heat exchange relationship with a heat exchange 
member of the manifold for heating a second separate fluid circulated 
through the manifold. Since the fluid circulated through the manifold (and 
ultimately transferred to a point of use) is separate from the fluid 
circulating in the tubular solar collector, any break in a collector tube 
merely renders that one tube ineffective but permits the system to 
continue to operate. Additionally, the damaged tube can be readily 
replaced without shutting down the entire system. 
These and other embodiments of the present invention will be appreciated 
upon a reading of the specification in conjunction with the accompanying 
drawings.

DETAILED DESCRIPTION OF THE INVENTION 
Referring now to the Drawings, it should be noted that like reference 
characters designate corresponding parts throughout the several drawings 
and views. 
FIG. 1 shows an embodiment of the invention and the operation of a solar 
collector system in accordance therewith. Specifically, the solar 
collector is composed of a manifold 10 having a fluid inlet port 11 and a 
fluid outlet port 12. Located within the manifold are a plurality of heat 
exchanger means 14. As can be seen, the heat exchanger means 14 are 
provided with expanded heat exchange surfaces or fins 15. 
Attached to the manifold 10 are a plurality of vacuum jacketed tubular 
solar collectors 16. As is shown in FIGS. 1 and 2, the vacuum jacketed 
tubular solar collectors 16 are positioned such that in use they extend 
downwardly from manifold 10 and they are, of course, in operable 
communication with heat exchanger means 14. The tubular collectors 16 have 
been shown partially broken away and in cross-section in order to more 
clearly illustrate the structure of the tubular collectors 16 and their 
connection to the manifold 10. 
As can be seen throughout the several drawings and views, the vacuum 
jacketed tubular collectors 16 have an outer light transparent tube 17 of 
a convenient length, say from 4 to 7 feet, and preferably of standard 
diameter similar to fluorescent light tube, for example 2" O.D. Within the 
exterior tube 17 and extending at a first end therebeyond is an inner tube 
18 obviously of lesser diameter than the outer tube 17. The inner tube 18 
is secured within the outer tube 17 such that the space therebetween can 
be and is evacuated. Thus, outer tube 17 provides a vacuum jacket for 
inner tube 18. 
In the embodiments shown in FIGS. 1, 3, 4 and 5, a fluid distribution tube 
21 is located centrally within the inner tube 18 by means of spacers 22. 
The tubes 17 must be light transparent, and, consequently, for all 
practical purposes will be made from glass. The tubes 18 and 21 and 
spacers 22 may be made of glass or any other material that will withstand 
operating temperatures generally in the range of about 50.degree. C. to 
about 200.degree. C. Preferably, tubes 17, 18 and 21 and spacers 22 are 
fabricated from known or standard glass materials, such as lime glass 
compositions or borosilicate compositions. Both of these glasses are 
eminently suitable since they are relatively inexpensive. 
In the present invention, the inner tube 18 is coated on either its outer 
or inner wall, and preferably on its outer wall, with an energy absorbing 
coating having a very high absorptivity and low emissivity such as black 
chrome, nickel, lead, black carbon and certain copper oxides. The coating, 
of course, can be applied by painting the exterior surface thereof or by 
other well known techniques. 
As can be seen, particularly with reference to FIG. 1, the manifold 
receptacle for the solar collector tubes 16 is comprised of a 
substantially cylindrical (in cross-section) heat exchange member 14 which 
extends into the interior of manifold 10. As noted hereinabove, the heat 
exchange members 14 are provided with a plurality of heat exchange 
surfaces or fins 15. The first end of the inner tube 18 of the tubular 
collector 16 is designed to fit in close contact with the heat exchanger 
14. As is shown in FIG. 1, the tubular collector 16 is held fast in the 
manifold by means of a gasket or O-ring 24. The gasket or O-ring may be 
made of rubber or suitable plastic material. Optionally, as is shown in 
FIG. 4, the heat exchange member 14 may have an internal thread 25 and the 
tubular collector 16 may also be provided at one end with a mating thread 
portion 26. This threaded portion 26 is a metal threaded portion that is 
joined to the glass by suitable glass to metal seal. Other suitable 
techniques may be employed for holding the tubular collector 16 in 
contact, at its first end, with the heat exchanger 14. 
It should be noted that the inner tube 18 of tubular collector 16 is closed 
at bottom end of tube 18. Also, inner tube 18 contains a charge of a heat 
absorbing working fluid, such as water, a silicone or a heat transfer oil. 
Depending upon the vapor pressure of the working fluid, it may be 
necessary to make some accommodation for the pressure increase that may 
result from heating the working fluid during use of the collector. Thus, 
the working fluid may be sealed within inner tube 18 under reduced 
pressure as a simple and effective technique for adjusting for potential 
increased pressure within the tube. Other techniques also may be employed. 
For example, top 27 of threaded portion 26 may be designed as a flexible 
diaphragm. 
As will be readily appreciated, the collector system is installed 
preferably in an oblique position and always with the manifold in a 
generally horizontal position with respect to the ground and with the 
manifold being above the tubular collectors 16. 
In operation, as solar radiation impinges on the tubular solar collector, 
the solar energy, primarily in the form of light, is absorbed by the 
absorbing surface and the heat generated is transferred to the working 
fluid within the tubular collector. The heated fluid then expands, becomes 
less dense, and begins to rise. As a consequence, the heated fluid begins 
to flow toward the heat exchanger member 14 where it transfers its heat to 
the heat exchanger member. As the liquid cools by such heat transfer, it 
becomes more dense and begins to flow downward. Thus, the fluid is 
circulated by thermosyphoning action and flows, as is shown by the arrows 
in FIG. 1. A second fluid is separately circulated, for example by means 
of a pump (not shown), through the inlet port 11 of manifold 10 in heat 
exchange relationship with the heat exchange members 14. Thus, the heat of 
the first fluid is exchanged or given up to the second fluid via the heat 
exchanger members and the first fluid is returned back downwardly toward 
the distal end of the solar collector where it is again heated. The second 
fluid in the manifold is removed via the outlet port 12 to a point of use. 
One of the significant advantages of the tubular solar collector system of 
this invention is that should any one of the tubular collectors be damaged 
or malfunction, the entire system need not be shut down. Indeed, the 
entire system can operate with one or two defective tubes. Additionally, 
the defective unit may be removed and a replacement unit inserted also 
without shutting down the entire system. 
As will be appreciated, the tubular collector system of this invention may 
be fabricated in modular sections and subsequently a plurality of modules 
may be interconnected in series as is shown in FIG. 2. Additionally, 
parabolic and/or focusing reflectors can be placed behind the tubular 
solar collectors for concentrating solar radiation incident upon the 
collector. These and other modifications and alternatives may be resorted 
to without departing from the spirit and scope of the appended claims.