Fuel cell coolant bubble control

Abstract

To mitigate bubble blockage in water passageways (78, 85), in or near reactant gas flow field plates (74, 81) of fuel cells (38), passageways are configured with (a) intersecting polygons, obtuse angles including triangles, trapezoids, or (b) hydrophobic surfaces (111), or (c) differing adjacent channels (127, 128), or (d) water permeable layers (93, 115, 116, 119) adjacent to water channels or hydrophobic / hydrophilic layers (114, 120).

Description

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 wa...

AI Technical Summary

Benefits of technology

[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.

[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.

[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).

Problems solved by technology

As coolant flow passageways become smaller, they become more prone to being blocked by bubbles of any gas therein.

Images