| Fuel cell coolant bubble control -> Monitor Keywords |
|
|
 
Fuel cell coolant bubble controlRelated Patent Categories: Chemistry: Electrical Current Producing Apparatus, Product, And Process, Fuel Cell, Subcombination Thereof Or Methods Of Operating, Process Of OperatingFuel cell coolant bubble control description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070154744, Fuel cell coolant bubble control. Brief Patent Description - Full Patent Description - Patent Application Claims
TECHNICAL FIELD [0001] This invention relates to reducing gas bubble blockage in small, low flow coolant passageways of fuel cells, by means of gas segregating passageway configurations, and/or layers of liquiphilic and liquiphobic material adjacent to reactant gas flow field plates. BACKGROUND ART [0002] In order to reduce the exposure of proton exchange membrane (PEM) fuel cells to problems resulting from freezing temperatures, and to reduce reliance on water pumps and other plumbing as accessories to the fuel cells, the total volume of coolant in the fuel cells may be reduced. [0003] However, in systems which do not use either a coolant pump or a gas venting micropump, and have minimal external water plumbing, the flow rate of coolant in the cells is quite low. If only gas is vented from the coolarit passageways, water flow is limited to that which evaporates into the reactant gases. With small passageways and low water flow, gas bubbles may join together (aggregate) and block water flow from large areas of the water channels, sometimes referred to as "gas breakthrough" of the reactant gas flow field plates, thereby causing localized heating and dehydration of the membrane at various spots, resulting in degradation of components and reduced performance. [0004] Systems employing between-cell coolant plates, which have glycol or other coolants, may have extremely small, in-cell water passageways to provide low flows of water to the anode side of the fuel cells for hydration, with insignificant cooling resulting from the water flow. DISCLOSURE OF INVENTION [0005] Aspects of the invention include: assuring coolant flow in small fuel cell coolant passageways; mitigating bubble blockage of coolant flowing at a low flow rate in fuel cell coolant passageways; assisting gas bubbles to flow through coolant passageways from PEM fuel cells; improved venting of gas in PEM fuel cell coolant passageways; reducing or eliminating ingestion of gas into fuel cell coolant passageways; increasing gas flow toward a vent in PEM fuel cells; improved hydration in PEM fuel cells; and improved evaporative cooling in PEM fuel cells. [0006] Although the ultimate purpose herein is to assure that coolant flow will not be blocked in small coolant passageways of a fuel cell, the removal of coolant-blocking gas bubbles is achieved by addressing the gas flow characteristics of the coolant passageways. This invention is predicated on the realization that gas, typically gas bubbles, may be present in small fuel cell coolant passageways having low coolant flow rates, and that properly designed passageways will assure sufficient flow of coolant to propel gas bubbles through the coolant passageways to the vents, thereby assuring an adequate flow of coolant for operational purposes, rather than blockage of coolant by gas bubbles. [0007] As coolant flow passageways become smaller, they become more prone to being blocked by bubbles of any gas therein. For a given cross sectional area of a prior art coolant passageway, there is a threshold coolant flow rate at or below which bubbles will block the coolant passageways if gas is present in the coolant; at coolant flow rates above the threshold, bubbles will be swept along by the flow of coolant, and will not block the coolant passageway. [0008] As used herein, the term "fuel cell" may mean the apparatus for a complete, operative fuel cell capable of producing electricity from oxidant and fuel reactant gases, or where the context so requires, that term may mean the portion of a fuel cell exclusive of layers that provide coolant to the fuel cells, which may be disposed between adjacent ones of said fuel cell portions. [0009] As used herein, the term "liquid coolant" means a coolant which is in the liquid state when the fuel cell is operating, even though such liquid coolant may freeze and become a solid when the fuel cell is not operating and the ambient temperature is below the freezing point of the coolant. The coolant may be water or other liquid; herein, "liquiphobic" is defined as having an aversion to the coolant, or lacking an affinity for the coolant, and "liquiphilic" is defined as having an affinity for, or lacking an aversion to, the coolant. The coolant flow assisted by the invention may, in some cases, be used primarily for hydration, with minimal cooling effect. Coolant flow paths and passageways herein are distinct from fuel and oxidant reactant gas flow field channels. [0010] As used herein, the term "coolant passageways" refers to those portions of the coolant flow path in a fuel cell stack which are substantially coextensive with the planform (the in-plane outline) of the fuel cells. [0011] According to the present invention, gas tolerant coolant passageways of fuel cells promote flow of coolant within such passageways with or without the presence of gas. In accordance further with the present invention, the gas tolerant configurations are provided along substantially the entire length of coolant passageways, thereby to provide a contiguous gas flow capability from inlets of said passageways to outlets thereof. [0012] In accordance with one form of the invention, gas tolerant fuel cell coolant passageways are configured to provide portions for which gas has an affinity, that is, a propensity to migrate to such portions and to flow therein, in contrast with other portions of the passageways where coolant may flow without interference from gas, thereby to assure that there is room for coolant to flow without being blocked by gas bubbles. [0013] According further to the invention, coolant passageways having gas tolerant cross sections may comprise first portions conducive to presence of gas preferentially in comparison with second portions which are less conducive to the presence of gas than the first portions. [0014] Gas tolerant passageways of the invention may comprise first and second portions within the same passageways: the first portions may be adjacent to a wall of a passageway which is liquiphobic; the first portions may each comprise a corner which subtends more than 90.degree. between two walls of a passageway; the first portions may comprise a portion of a triangle, a trapezoid or other polygon away from acute angular areas thereof; or they may comprise combinations of the foregoing. Gas tolerant passageways of the invention may comprise channels extending from surfaces of reactant gas flow field plates opposite to those surfaces from which reactant gas flow field channels extend. The gas tolerant coolant passageways may comprise intersecting polygons, or other closed plane figures bounded by lines, at least some of which may not be straight, of the same or a different shape in the same or adjacent flow field plates; for instance, the gas tolerant coolant passageways may comprise two channels, one larger than the other, or of two different cross sections, extending inwardly from one of the fuel reactant gas flow field plates, or one extending from a surface of a reactant gas flow field plate of one fuel cell, and the other extending from a surface of a reactant gas flow field plate of an adjoining fuel cell. [0015] In further accord with the present invention, gas tolerant passageways of the invention may comprise liquiphilic and/or liquiphobic layers disposed between and extending across substantially the entire planform of the reactant gas flow field plates of adjacent fuel cells. In one form, a layer which has high coolant permeability is disposed between coolant passageways and a reactant gas flow field plate in a proton exchange membrane fuel cell. According to the invention, the highly permeable layer may be adjacent conventional, rectangular coolant channels, or may be adjacent gas tolerant coolant channels, such as T-shaped channels or triangular shaped channels, or otherwise. This form of the invention may be implemented with liquiphilic permeable sheets such as carbon fiber paper treated with tin, in a conventional fashion. Disposing the layer of material with high coolant permeability adjacent the fuel reactant gas flow fields prevents dryout and subsequent gas ingestion toward the membrane through the fuel reactant gas flow field plates, and also reduces the amount of gas ingested into the coolant channels (flowing away from the membrane). [0016] In another form, the gas tolerant coolant passageways comprise either a sandwich of a liquiphobic layer between liquiphilic layers, or a liquiphilic layer adjacent to a layer which is both liquiphilic and liquiphobic, the layers being disposed between adjacent fuel cells. In one embodiment, the liquiphilic/liquiphobic layer may comprise a layer that is first formed to be entirely liquiphobic, thereafter treated to form non-liquiphobic regions; or the layer may simply have holes through it to conduct coolant. [0017] Gas tolerant passageways may comprise a combination of first channels having a first cross sectional area or shape and other channels, interspersed with said first channels, having a cross sectional area or shape different than said first cross sectional area or shape. A particular embodiment has channels of a larger cross section interspersed with separate channels of a smaller cross section, in pairs. [0018] The flow of coolant is the purpose, rather than the flow of gas; however, the control of gas flow is accomplished by affecting the characteristics of the coolant channels with respect to gas: that is, while the coolant flow characteristics at low flow rates are essentially the same in one portion of the gas tolerant coolant passageways as in other portions thereof, the invention provides certain portions of gas tolerant channels for which gas has an affinity. For instance, gas prefers the larger channel of an intersecting channel configuration, and gas prefers the areas adjacent obtuse angles rather than acute angles in a triangular configuration. Therefore, affecting the location of gas within the passageway accomplishes the flow of coolant within the passageway, whether or not gas is present. [0019] Other aspects, features and advantages of the present invention will become more apparent in the light of the following detailed description of exemplary embodiments thereof, as illustrated in the accompanying drawing. BRIEF DESCRIPTION OF THE DRAWINGS [0020] FIG. 1 is a simplified, stylized block diagram of an evaporatively cooled fuel cell system, which may be modified to employ the present invention. Continue reading about Fuel cell coolant bubble control... Full patent description for Fuel cell coolant bubble control Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Fuel cell coolant bubble control patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. Start now! - Receive info on patent apps like Fuel cell coolant bubble control or other areas of interest. ### Previous Patent Application: Rechargeable battery and its fabrication method Next Patent Application: Fuel cell coolant bubble control Industry Class: Chemistry: electrical current producing apparatus, product, and process ### FreshPatents.com Support Thank you for viewing the Fuel cell coolant bubble control patent info. IP-related news and info Results in 0.12453 seconds Other interesting Feshpatents.com categories: Qualcomm , Schering-Plough , Schlumberger , Seagate , Siemens , Texas Instruments , 174 |
 * Protect your Inventions * US Patent Office filing 
PATENT INFO |
|
