Data processing: generic control systems or specific application – Specific application – apparatus or process – Electrical power generation or distribution system
Reexamination Certificate
1997-06-30
2001-07-10
Cuchlinski, Jr., William A. (Department: 3661)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Electrical power generation or distribution system
C700S195000, C428S570000, C428S402000, C428S627000, C428S634000, C423S439000, C429S047000, C429S047000
Reexamination Certificate
active
06259971
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
The present application relates to low-power portable fuel cells.
Background: Fuel Cells
A fuel cell is an electrochemical power source which is very attractive for many applications. A fuel cell may be regarded as a type of battery, but is significantly different from most common battery chemistries.
All batteries derive energy from a chemical reaction of some sort. In a fuel cell, the chemical reaction is the oxidation of a gaseous or liquid fuel (typically hydrogen), which may be supplied from an external supply. Thus, fuel cells can avoid the lifetime constraints of primary (non-rechargeable) batteries while also avoiding the degradation due to recharging and discharging which affects most rechargeable battery chemistries. The chemical reactions used in fuel cells are relatively energetic, and thus the amount of energy per unit weight is relatively high.
Much of the work on fuel cells has been directed towards larger fuel cells, in the range of a kilowatt to tens of kilowatts or more. However, the high energy density of fuel cell chemistries also makes them attractive for many portable applications, in which the energy requirements are far smaller. In particular, the development of gel-stabilized fuel cell technologies has made fuel cells much more attractive for portable applications. In such applications, the requirements of user convenience and comfort are crucial.
The oxidation of hydrogen produces water. Methanol and other hydrocarbon fuels have been proposed for fuel cells, but oxidation of any hydrocarbon fuel will produce water (as well as carbon dioxide, which is gaseous and not a problem). A fuel cell will also produce some heat, and some of the water produced will be water vapor rather than liquid water. However, some of the water vapor will condense as liquid water (either in the fuel cell plumbing, or shortly afterwards as the exhaust vapor cools). Thus liquid water will be generated.
The generation of liquid water is a significant problem: users do not want a computer which drips on their paperwork. The total flow of water is very small—on the order of one drop per minute, for 50 W of power—but this is enough to be a serious nuisance in some applications.
FIG. 1
shows a typical small fuel cell for portable applications. This cell is supplied with air and hydrogen. A container
100
holds a proton transport membrane
102
. The transport membrane
102
can be, for example, a sulfonated styrene/ethylene/butylene-styrene triblock copolymer from DAIS. The membrane
102
is flanked by a porous cathode
104
and a porous anode
106
. (These are made of a porous conductive material, e.g. carbon fibers.) Hydrogen, supplied to fuel manifold
110
through inlet
114
, is catalytically ionized at the interface between anode
106
and membrane
102
. Hydrogen can then be transported through membrane
102
as protons (hydrogen ions). Similarly, oxygen is introduced through inlet
116
into oxidant manifold
112
, and is absorbed at the interface between membrane
102
and cathode
104
, to form oxygen ions within membrane
102
. The oxygen ions and protons react to form water, which is exuded into the oxidant manifold. Typically an excess of air is pumped into inlet
116
, so the exhaust port
118
carries air which is only partly deoxygenated, as well as moisture from the reaction. The free energy from the reaction can be extracted electrically at terminals V+ and V−. The voltage per cell will be in the neighborhood of 0.6 V to 1.1 V, depending on load characteristics and cell design.
The drawing of
FIG. 1
is highly simplified. Since the membrane
102
generates only a small current per square inch, the membrane is typically folded back and forth many times. Thus the manifolds
110
and
112
will typically be long meandering passages, where condensed water can easily block gas flow. Additional pressure is therefore applied to the inputs occasionally, to produce a puff at the exhaust port which vents excess water.
Additional background on fuel cell technology can be found in Kordesh and Simader, F
UEL
C
ELLS AND
T
HEIR
A
PPLICATIONS
(1996); the H
ANDBOOK OF
B
ATTERIES AND
F
UEL
C
ELLS
(ed. Linden 1984); in the proceedings of the Grove Fuel Cell Symposia; and in the proceedings of the Annual Battery Conference on Applications and Advances; all of which are hereby incorporated by reference.
Innovative Portable Fuel Cell System
The present invention provides a portable fuel cell-powered system in which the water by-product is disposed of by ultrasonic vaporization. Users will object to the presence of liquid water (or to the presence of steam), but ultrasonic vaporization provides a very convenient way to expel H
2
O without the difficulties of handling liquid water in an office environment. Preferably a piezoelectric element is used to vaporize the water by-product, and a small port is used to eject the vapor thus produced.
In one class of embodiments, a heated airstream is combined with the water vapor exhaust port to reduce the chances of liquid water accumulating.
In another class of embodiments, the water byproduct is transported as a very-low-volume liquid flow to a vaporization orifice on the exterior of the system, where an ultrasonic transducer atomizes and expels the water.
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Freiman Joseph F.
Mitchell Nathan
Compaq Computer Corporation
Cuchlinski Jr. William A.
Fletcher Yoder & Van Someren
Marc McDieunel
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