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Author:Nikiforow, Kaj
Title:Optimization of polymer elctrolyte membrane fuel cell systems - Applied study of hydrogen recirculation
Polymeeripolttokennojärjestelmän optimointi - Vedyn kierrätyksen soveltava tarkastelu
Publication type:Master's thesis
Publication year:2010
Pages:xiv + 87      Language:   eng
Department/School:Kemian laitos
Main subject:Kemian laitetekniikka   (Kem-42)
Supervisor:Alopaeus, Ville
Instructor:Ihonen, Jari ; Kallio, Tanja
Electronic version URL: http://urn.fi/URN:NBN:fi:aalto-201203151566
OEVS:
Electronic archive copy is available via Aalto Thesis Database.
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Location:P1 Ark Aalto  3159   | Archive
Keywords:PEMFC
hydrogen recirculation
ejector model
nitrogen build-up
vedyn kierrätys
ejektorimalli
typen rikastuminen
Abstract (eng): The goal of this thesis was to investigate the effects of hydrogen recirculation in a polymer electrolyte membrane fuel cell (PEMFC) on hydrogen stoichiometry and on the build-up of nitrogen in the re circulated stream as well as the effects of nitrogen build-up on the fuel cell performance.
Recirculation of hydrogen has a remarkable effect on the overall efficiency of a fuel cell system, as recirculation affects not only the performance of the fuel cell through hydrogen stoichiometry and water balance but also the consumption of fuel.
However, recirculation of hydrogen consumes energy and causes impurities to build up in the re circulated stream.

In this work, recirculation of hydrogen was studied by simulating an ejector model as well as through experimental work conducted on an 8-kWe PEMFC system.
The ejector model presented in this work was based on the assumptions of one-dimensional flow in steady state as well as constant area and constant pressure mixing.
In the experimental part of this work, the build-up of nitrogen in the re circulated stream was monitored using a hydrogen sensor which measured the partial pressure of hydrogen.

Based on the simulations with the ejector model, it was found that the achievable recirculation rate strongly depends on several factors, such as the flow resistance of the stack, the dimensions of the ejector, and the hydrogen feed pressure.
The results from the experimental work revealed that the build-up of nitrogen has a profound effect on cell voltages, depending strongly, however, on the conditions of the cells.
Hence, the condition of the cells must be taken into account when optimizing the fuel supply in a PEMFC.
Abstract (fin): Tämän diplomityön tavoitteena oli tutkia vedyn kierrättämisen vaikutusta polymeeripolttokennossa vedyn stoikiometriseen kertoimeen ja typen rikastumiseen vetykierrossa sekä typen rikastumisen vaikutusta polttokennon suorituskykyyn.

Vedyn kierrättämisellä on merkittävä vaikutus polttokennojärjestelmän kokonaishyötysuhteeseen.
Kierrätyksellä voidaan parantaa polttokennon suorituskykyä vaikuttamalla vedyn stoikiometriseen kertoimeen ja veden hallintaan, joilla on edelleen vaikutusta polttoaineen käyttöasteeseen.
Vedyn kierrättäminen kuitenkin kuluttaa energiaa ja johtaa epäpuhtauksien rikastumiseen vetykierrossa.

Tässä työssä vedyn kierrätystä tutkittiin sekä mallintamalla vety-ejektoria että suorittamalla kokeita 8 kWe polymeeripolttokenno-järjestelmällä.
Työssä esitetyssä ejektorimallissa oletettiin 1-uloitteinen stationaarinen virtaus sekä vakio pinta-ala- ja vakio paine-sekoittuminen.
Työn kokeellisessa osassa typen rikastumista kierrätetyssä kaasussa tutkittiin vetyanturin avulla, joka mittasi vedyn osapainetta.

Ejektori-mallin simulointitulosten perusteella voitiin todeta, että saavutettavaan kierrätysnopeuteen vaikuttaa merkittävästi polttokennoston virtausvastus, ejektorin mitat sekä vedyn syöttöpaine.
Kokeelliset tulokset osoittivat että typen rikastuminen vetykiertoon vaikuttaa merkittävästi kennojännitteisiin, kuitenkin voimakkaasti riippuen siitä miten kennot ovat vanhentuneet.
Näin ollen kennojen kunto on otettava huomioon optimoitaessa polttoaineen syöttöä polymeeripolttokennossa.
ED:2010-12-20
INSSI record number: 41462
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