Measuring and testing – Specific gravity or density of liquid or solid – Freely vertical reciprocable float with carried indicium
Reexamination Certificate
2002-01-11
2004-09-14
Kwok, Helen C. (Department: 2856)
Measuring and testing
Specific gravity or density of liquid or solid
Freely vertical reciprocable float with carried indicium
C429S006000
Reexamination Certificate
active
06789421
ABSTRACT:
TECHNICAL FIELD
The present invention relates to fuel cells, and, in particular, to a density-based fuel indicator system for use with fuel cells.
BACKGROUND OF THE INVENTION
Fuel cells produce electrical energy by reacting a fuel with an oxidant, usually in the presence of a catalyst. Typically, fuel cells consist of a fuel electrode, or anode, and a reducing electrode, or cathode, separated by an ion-conducting electrolyte. An external conductor connects the electrodes to an electrical circuit, or load. In the conductor, current is transported by the flow of electrons. In the electrolyte, current is transported by the flow of ions.
Any number of hydrogen rich fuels may be used as a fuel source, such as methanol, ethanol, butane, and propane.
FIG. 1
is a diagram of a methanol fuel cell. A reservoir that includes the anode, or anode reservoir
102
, contains a methanol-water solution
104
. The methanol fuel cell generally is in a charged state when the percentage of methanol in the methanol-water solution is relatively large. As methanol is oxidized and electricity is generated by the fuel cell, the percentage of methanol in the methanol-water solution decreases and the fuel cell becomes depleted.
The methanol contained within the methanol-water solution is oxidized, usually in the presence of a catalyst, producing hydrogen ions
106
, electrons
108
, and carbon dioxide
116
. This oxidation reaction occurs inside the anode reservoir
102
of the fuel cell. A primary anode oxidation reaction is shown below:
CH
3
OH+H
2
O→CO
2
+6H
+
+6
e
−
Note that, since the electrolyte is a relatively poor electrical conductor, electrons
108
flow away from the anode via an external circuit
110
. Simultaneously, hydrogen ions
106
travel through the electrolyte, or membrane
112
, to the cathode
114
. Commonly used membranes include Nafion 112®, Nafion 117®, and polybenzimidazole.
At the cathode
114
of a fuel cell, oxygen
118
is reduced by hydrogen ions
106
migrating through the electrolyte
112
and incoming electrons
108
from the external circuit
110
to produce water
120
. The primary cathode reaction is shown below:
3/2O
2
+6H
+
+6
e
−
→3H
2
O
The individual electrode reactions, described above as primary anode and primary cathode reactions, result in an overall methanol-fuel-cell reaction shown below:
2CH
3
OH+3O
2
→2CO
2
+4H
2
O+electricity
Additional minor chemical reactions may occur, and thermal energy is generally produced.
Modern fuel cells can continuously produce electrical current for long periods of time without the need for recharging. However, fuel cells produce electrical charge only when fuel is present in the anode reservoir above a threshold concentration. Therefore, in order to ensure continuous operation of a fuel cell, an indication of the amount of fuel remaining in the fuel cell needs to be easily obtainable. Fuel cells commonly provide no convenient, cost-efficient means for reliably determining the amount of available fuel remaining in the fuel cell. Therefore, designers, manufacturers, and users of fuel cells have recognized the need for a convenient, cost-efficient means for determining the amount of fuel remaining in a fuel cell.
SUMMARY OF THE INVENTION
One embodiment of the present invention provides a means for determining the concentration of methanol within an anode reservoir of a methanol-based fuel cell. The methanol concentration is determined through the use of a float that responds to the density of the methanol-water solution. As methanol is consumed during normal operation of the fuel cell, the methanol concentration of the methanol-water solution decreases and the density of the methanol-water solution correspondingly increases. The float is fabricated to have a density such that, as methanol is consumed, the float rises from a lower position within the anode reservoir, or within a float chamber in fluid communication with the anode reservoir, to a higher position in the anode reservoir or float chamber. A fuel scale may be included with the fuel cell to facilitate determination of the methanol concentration by visual comparison of the float position with markings on the fuel scale corresponding to fuel concentrations. Additionally, a valve responsive to the position of the float may act to control fuel delivery. Alternative embodiments may employ different types of hydrogen-rich fuels.
REFERENCES:
patent: 3808893 (1974-05-01), Jinno et al.
patent: 3952761 (1976-04-01), Friedland
patent: 4061839 (1977-12-01), Kubler
patent: 4353253 (1982-10-01), Callahan
patent: 4400978 (1983-08-01), Guay et al.
patent: 4442700 (1984-04-01), Swoboda
patent: 4443424 (1984-04-01), Olson
patent: 4496637 (1985-01-01), Shimada et al.
patent: 4650729 (1987-03-01), Nakamura et al.
patent: 4700580 (1987-10-01), Kamin
patent: 4967595 (1990-11-01), Olson
patent: 5518831 (1996-05-01), Tou et al.
patent: 5534363 (1996-07-01), Sprouse et al.
patent: 5824885 (1998-10-01), Lekholm
patent: 6408694 (2002-06-01), Lin et al.
patent: 6506513 (2003-01-01), Yonetsu et al.
patent: 2-37881 (1987-02-01), None
Gore Makarand P.
Mann L. Chris
Hewlett--Packard Development Company, L.P.
Kwok Helen C.
LandOfFree
Density-based fuel indicator system for fuel cells does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Density-based fuel indicator system for fuel cells, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Density-based fuel indicator system for fuel cells will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3263503