JP2004031096A - Fuel cell and electric equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel cell with a large capacity or a high output capable of keeping the outside of a body of equipment and the inside of a fuel tank in proper temperatures by dissipating heat generated from an electricity generating cell outside. <P>SOLUTION: For the fuel cell comprising at least a fuel tank storing fuel inside, an electricity generating cell generating electricity utilizing the fuel guided from the fuel tank, and a body of equipment covering the fuel tank and the electricity generating cell, a heat insulating structure is formed in the fuel tank, or a heat conduction structure having thermal resistance lower than that of natural heat radiation by air is formed between the electricity generating cell and the body of equipment thereof. <P>COPYRIGHT: (C)2004,JPO

Description

【００４１】
【表２】

【００４２】
表２から分かるように、燃料タンク内の温度が５０℃を超えると、タンク内圧は０．４ＭＰａ（約４ａｔｍ）を超えてしまう。燃料タンクが、このような高圧になることは、破裂の危険性が高まるだけでなく、燃料の流量を制御するバルブが正常に動作しなくなる原因となる。従って、燃料タンクの圧力上昇を防ぐためには、発電に伴って発生する熱や外部からの熱が燃料タンクに伝わらないようにすることが必要である。本発明においては、燃料タンク内壁３６、および燃料電池セル１と燃料タンク３１との隔壁６３に断熱機構を有する。断熱機構には、断熱性を有する材料を用いて構成する方法と、断熱性の高い構造を具備する方法がある。断熱性を有する材料には、ポリエチレン、ポリスチレン、ポリアクリル、ポリカーボネートなどのプラスチック類、ウレタンゴム、シリコーンゴム、フッ素ゴムなどのゴム類、ガラス、シリコンカーバイド、窒化シリコン、アモルファスカーボン、木材、コルク、紙、陶磁器などがあり、必要とされる加工性、強度などから最適な材料を選択することができる。また、断熱性の高い構造としては、断熱部分に真空室を設ける方法がある。
【００４３】
一方、表１に示すように、一般に水素吸蔵合金は温度が上がると解離速度が上昇する。また、水素吸蔵合金の水素放出反応は吸熱反応であるため、水素の放出に伴い、燃料タンク内の温度は低下する。そこで、水素吸蔵合金の種類によっては、発電に必要な水素をタンクから放出させるためには、タンクを暖める必要が有る場合がある。上記燃料タンク内壁３６および上記隔壁６３の熱伝導性を最適に選ぶことで、燃料タンクの温度を発電に最適な状態に保つことも可能である。
【００４４】
次に、セル部１について説明する。本実施例の燃料電池セルは起電力０．８Ｖ、電流密度３００ｍＡ／ｃｍ^２　であり、単位セルの大きさは１．２ｃｍ×２ｃｍである。この燃料電池セルを８枚直列につなぐことで、電池全体の出力は６．４Ｖ、７２０ｍＡで４．６Ｗである。固体高分子型燃料電池の発電効率は概ね５０％程度であり、発電量と同量程度の熱が発生する。従って、本実施例の燃料電池もセル部において、５Ｗ程度の発熱がある。
【００４５】
発電セル筐体６１のみから、外部への放熱を行う場合を考える。
図８に示すように、発電セルの発熱量をＱ［Ｗ］、発電セル筐体表面積をＡ_ｗ［ｍ^２　］、外気温度をＴ_０　［℃］、発電セル筐体温度をＴ_ｗ　［℃］、また空気の熱伝達率ｈ_ａ　［Ｗ／ｍ^２　・Ｋ］とすると、
【００４６】
【数１】
Ｔ_ｗ　−Ｔ_０　＝Ｑ／（ｈ_ａ　Ａ_ｗ　）
で表される。また、Ｔ_ｃ　は発電セル温度を示す。
【００４７】
ｈ_ａ　＝４０［Ｗ／ｍ^２　・Ｋ］、Ａ_ｗ　＝２．３×１０^−３［ｍ^２　］、Ｑ＝５［Ｗ］
のとき、
【００４８】
【数２】
Ｔ_ｗ　−Ｔ_０　＝５４．３
となる。
従って、外気温度Ｔ_０　＝２５℃とすると、Ｔ_ｗ　＝７９．３℃となる。
【００４９】
燃料電池をデジタルカメラなどの小型電気機器に搭載して使用することを想定した場合、これらの小型電気機器は手に持つなど肌に近いところで使用する可能性が高く、発電セル筐体が８０℃近くになることは好ましくない。また、電気機器の動作の安定性という点からも、発電セル筐体の温度は低いことが望ましい。
【００５０】
そこで、より効率よく発電セル筐体からの放熱を行うために、発電セル筐体の熱を燃料タンク筐体に伝えることで、発電セル筐体および燃料タンク筐体の表面から外気への放熱を行う。これにより、放熱面の表面積が増大し、大きな放熱効果が得られる。
【００５１】
発電セル筐体、燃料タンク筐体の表面で、熱を効率よく伝えるための材料としては、ステンレス、アルミニウム、チタン、マグネシウム合金、金、銀、銅などの金属やグラファイト、アルミナ、シリコン、ゲルマニウム、ダイヤモンドなどが挙げられる。加工性や強度などを考慮すると、ステンレス、チタン、アルミニウム、マグネシウム合金などが好ましい。
【００５２】
燃料タンクでの放熱を利用する場合、発電セル筐体および燃料電池筐体の表面積の合計は、４．６×１０^−３［ｍ^２　］となる。従って、
【００５３】
【数３】
Ｔ_ｗ　−Ｔ_０　＝２７．１
となる。従って、外気温度Ｔ_０　＝２５℃とすると、Ｔ_ｗ　＝５２．１℃となり、燃料電池筐体の温度をより効率よく下げることができる。また、前述のように、燃料タンク内壁は断熱材料によりなるため、燃料タンク筐体に伝わった熱は、燃料タンク内部には伝わらない。
【００５４】
さらに大きな放熱効果を得るためには、例えば、燃料電池筐体にヒートシンクを設けて表面積を増大させたり、冷却ファンやヒートパイプなどを用いてより積極的に放熱を行うことも可能である。
【００５５】
発電セル筐体から燃料タンク筐体表面への伝熱を発電セル筐体の温度が高い場合にのみ行うことで、発電セル表面の温度を必要以上に下げることなく、より効率よく発電を行うことができる。この機能は、例えば以下のようにして実現することができる。
【００５６】
図９に示すように、発電セル筐体６１に熱膨張率が高く、熱伝導率が高い材料からなる接続部材８を設けておき、温度が低い状態では発電セル筐体６１と燃料タンク筐体６２とは熱的に接続されておらず、発電セル筐体の温度が上昇するに伴い、該接続部材８が熱膨張し、燃料タンク筐体と接触することで、熱が伝わるようになる。熱膨張率が高く、熱伝導率が高い材料としては、アルミニウムなどが挙げられる。材料の線膨張率をα［Ｋ^−１］、長さをｌ_０　［ｃｍ］とすると、温度がΔＴ［Ｋ］変化したときの接続部の伸びΔｌ［ｃｍ］は以下のように表される。
【００５７】
【数４】
Δｌ＝ｌ_０　αΔＴ
例えば、発電セル筐体にチタンを用い、接続部材の材料としてアルミニウムを用いた場合、チタンの線膨張率が８．６×１０^−６［Ｋ^−１］であり、アルミニウムの線膨張率が２３．１×１０^−６［Ｋ^−１］であることから、長さｌ_０　を２．５［ｃｍ］とすると、ΔＴ＝３０［Ｋ］では、発電セルと発電セル筐体との伸びの差は、２．５×（２３．１−８．６）×１０^−６×３０＝１．０８×１０^−３［ｃｍ］である。従って、接続部材と燃料タンク筐体との間隔を１．０８×１０^−３［ｃｍ］離して設計すれば、室温を２５℃とすると、発電セル筐体温度が５５℃を超えた時にのみ、発電セル筐体から、燃料タンク筐体への放熱が行われる。
【００５８】
以上の設計指針に従い、接続部の材料と長さ、および接続部と燃料タンク筐体の間隔を設計することにより、所定の温度を超えた時にのみ、発電セル筐体から、燃料タンク筐体への放熱が行われるようにすることができる。
【００５９】
燃料電池の発電においては、燃料電池セル温度が６０℃〜８０℃程度の場合に最も効率よく発電を行うことが可能である。また、発電セル温度が１００℃を超えてしまうと、発電性能は著しく低下する。従って、発電において、発電セル温度が上記温度範囲にあることが好ましい。
【００６０】
まず、発電セル筐体面に対向している発電セルの放熱を考える。発電セルと発電セル筐体との間の伝熱が空気の自然対流のみであるとすると、発電セルから発電セル筐体表面までの熱抵抗Ｒは以下のように表される。
【００６１】
【数５】
Ｒ＝１／（ｈ_ａ　Ａ_ｃ　）＋ｔ_ｗ　／（λ_ｗ　Ａ_ｗ　）
ただし、ｈ_ａ　は空気の熱伝達率、Ａ_ｃ　は発電セル筐体面に対抗している発電セル部の面積、λ_ｗ　は発電セル筐体の熱伝導率、Ａ_ｗ　は発電セル筐体の表面積、ｔ_ｗ　は発電セル筐体の厚さである。
【００６２】
Ａ_ｃ　を７．５×１０^−４［ｍ^２　］、発電セル筐体の肉厚ｔ_ｗ　を１［ｍｍ］、材料をステンレス（λ_ｗ　＝１６．３［Ｗ／ｍ・Ｋ］）とすると、
Ｒ＝３３．３［Ｋ／Ｗ］
となる（空気部分の熱抵抗は３３．３［Ｋ／Ｗ］、筐体部分の熱抵抗は０．０２７［Ｋ／Ｗ］）。
【００６３】
また、発電セルと発電セル筐体との距離が非常に近いため、空気での伝熱が熱伝導であるとした場合、熱抵抗Ｒは以下のように表される。
【００６４】
【数６】
Ｒ＝ｔ_ａ　／（λ_ａ　Ａ_ｃ　）＋ｔ_ｗ　／（λ_ｗ　Ａ_ｗ　）
ただし、ｔ_ａ　は発電セルと発電セル筐体との距離、λ_ａ　は空気の熱伝導率である。
【００６５】
ｔ_ａ　を１［ｍｍ］、λ_ａ　＝２５×１０^−３［Ｗ／ｍ・Ｋ］とすると、
Ｒ＝５３．３［Ｋ／Ｗ］
となる（空気部分の熱抵抗は５３．３［Ｋ／Ｗ］、筐体部分の熱抵抗は０．０２７［Ｋ／Ｗ］）。
【００６６】
発電セル温度をＴ_ｃ　とすると、
【００６７】
【数７】
Ｔ_ｃ　−Ｔ_ｗ　＝ｑ_１　Ｒ
である。ただし、ｑ_１　は発電セル筐体片面に対向している発電セルの発熱量である。
ここで、ｑ_１　を１．２５［Ｗ］とすると、
Ｔ_ｃ　−Ｔ_ｗ　＝４１．６℃（自然対流）
Ｔ_ｃ　−Ｔ_ｗ　＝６６．６℃（熱伝導）
【００６８】
発電セル筐体表面と燃料タンク筐体表面の両方で放熱を行う場合、Ｔ_ｗ　＝５２．１℃であるから、
Ｔ_ｃ　＝９３．７℃（自然対流）
Ｔ_ｃ　＝１１８．７℃（熱伝導）
となり、発電セル表面温度は１００℃以上にまで上昇するおそれがある。
そこで、発電セルから発電セル筐体へ効率よく熱を伝える方法が必要となる。
【００６９】
発電セルから発電セル筐体へ効率よく熱を伝える第一の方法は、図１０に示すように、発電セル１と発電セル筐体６１との間に、高い熱伝導率を示す材料からなる伝熱部材９によって接続する方法である。高い熱伝導率を持つ材料としては、ステンレス、アルミニウム、チタン、マグネシウム合金、金、銀、銅などの金属やグラファイト、アルミナ、シリコン、ゲルマニウム、ダイヤモンドなどが挙げられる。加工性や強度などを考慮すると、ステンレス、チタン、アルミニウム、マグネシウム合金などが良い。特に、発電した電力を外に逃がさないようにするためには、上記部材が絶縁体（半導体）であることが好ましい。絶縁体（半導体）であり、かつ、熱伝導率が高い部材には、アルミナ、シリコン、ゲルマニウムなどがある。
【００７０】
一方、上記伝熱部材に導体を用いる場合には、発電セル筐体を絶縁体材料で作製することにより、発電した電気を外に漏れないようにすることが可能である。また、この場合、図１１に示すように、発電セル筐体６１と上記伝熱部材９が接している部分に導体材料からなる配線部材９１を設け、該配線部材９１が、燃料電池の電力取りだし用電極５３に電気的に接続されるようにすることで、配線を効率よく行うことが可能である。
【００７１】
また、上記伝熱部材は、発電セルと発電セル筐体とを固定する支持部材としての機能も兼ね備えることができる。この場合、支持部材の配置位置としては、図１０（ａ）のように伝熱部材９を発電セル１と発電セル筐体６１との間に間隔を設けて配置したものが挙げられる。これにより、発電セルと発電セル筐体とを固定することができ、また、酸化剤極と燃料極との差圧により、電解質膜がたわんだり、はがれたりすることを防ぐことができる。
【００７２】
また、上記伝熱部材は多孔質状のものを用いたり、通気口を具備したりすることにより、酸化剤極により効率よく外気を供給することができる。
【００７３】
上記伝熱部材として、ガス透過性がよく熱伝導性の高い材料としては、絶縁体ではシリコン、アルミナをポーラス状、あるいはウィスカー状に加工したものなど、導体では、グラファイト構造を有するポーラスカーボンなどがある。このような多孔質な部材を用いる場合、ガス透過性が高いため、図１０（ｂ）に示すように、シート状の伝熱部材９を発電セル１と発電セル筐体６１との間に挟むことも可能である。
【００７４】
図１０（ａ）のように、伝熱部材９としてアルミナ材料からなる部材を配置した場合の伝熱について述べる。
【００７５】
アルミナの熱伝導率λ_Ａｌ＝３６［Ｗ／ｍ・Ｋ］、部材の発電セルと接する部分の面積をＡ_Ａｌ（部材を２［ｍｍ］）、厚さをｔ_Ａｌ＝１［ｍｍ］とすると、
熱抵抗Ｒ_１　は、
【００７６】
【数８】
Ｒ_１＝ｔ_Ａｌ／（λ_ＡｌＡ_Ａｌ）
Ｒ_１＝１．０×１０^−３÷（３６×（３×２．５−２．６×２．１）×１０^−４）＝０．１４
従って、Ｔ_ｃ　−Ｔ_ｗ　＝ｑ_１　Ｒ_１　＝１．２５×（０．１４＋０．０２７）＝０．２０より、Ｔ_ｃ　＝５２．３℃である。
【００７７】
すなわち、高熱伝導率を有する材料からなる部材によって、発電セルから発電セル筐体に反応熱を伝え、発電セルが加熱しすぎるのを防ぐことができる。また、部材の材料や形状、大きさを上記指針に従って設計することにより、発電セルを発電に最適な温度に保つことも可能である。
【００７８】
発電セルから発電セル筐体へ効率よく熱を伝える第二の方法は図１２（ａ）に示すように、発電によって、酸化剤極で生成する水の気化を利用する方法である。水の蒸発に伴う熱伝達率は１×１０^４　［Ｗ／ｍ^２　Ｋ］程度である。これは自然対流における空気の熱伝達率の約１０００倍である。従って、発熱に伴って発生する水の量は微量ではあるが、十分に発電セルから発電セル筐体へ熱を伝えることが可能である。
【００７９】
発電セルから発電セル筐体へ効率よく熱を伝える第三の方法は図１３（ａ）に示すように、ファンなどを用いて、発電セルと発電セル筐体との間の空気を強制的に対流させる方法である。この場合、酸化剤極により積極的に空気を供給できるようになるため、発電効率をさらに高めることができるという利点も有する。空気の強制対流の熱伝達率は１×１０^２　［Ｗ／ｍ^２　Ｋ］程度である。これは自然対流における空気の熱伝達率の約１０倍である。従って、自然対流に比べて効率よく発電セルから発電セル筐体へ熱を伝えることが可能である。
【００８０】
また、ファンを駆動するモーターの電力を燃料電池の発電電力から供給するように配線することにより、発電量が増えるほど、すなわち、発熱量が増えるほど、モーターの回転速度が増加するようにすることができ、発熱量に合わせた冷却を行うことが可能になる。
【００８１】
次に発電セル間の伝熱について述べる。
発電セル全体の大きさを小さくし、かつ、大きな発電量を得るためには、複数のセルを積層して使用する方法が有効である。複数のセルを積層すると、発電セル筐体に直接対向していない発電セルが存在する場合がある。発電セルの温度を最適に保つためには、発電セル筐体に直接対向していない発電セルから効率よく放熱を行う必要がある。
【００８２】
発電セル筐体に直接対向していない発電セルから効率よく放熱を行う第一の方法は、図１４に示すように発電セルと発電セル間を、高い熱伝導率を示す材料からなる部材によって接続する方法である。高い熱伝導率を持つ材料としては、ステンレス、アルミニウム、チタン、マグネシウム合金、金、銀、銅などの金属やグラファイト、アルミナ、シリコン、ゲルマニウム、ダイヤモンドなどが挙げられる。
【００８３】
発電セルを図１５に示すように酸化剤極、高分子電解質膜、燃料極、セパレータの順で積層する方式においては、上記高熱伝導率部材に導電性をもつ材料を用いることによって、各発電セルを電気的に直列に接続することが可能である。一方、図２に示すように、同極同士が対向するような積層構造を有する場合、上記高熱伝導率部材に導電性をもつ材料を用いれば、各発電セルを電気的に並列に接続することができ、絶縁性を持つ材料を用いれば、各セルの配線を別途行うことで、各発電セルを電気的に直列に接続することができる。
【００８４】
また、上記部材は、発電セルと発電セルとの接触を防ぎ、また燃料極室と酸化剤極室の圧力差による発電セルのたわみを防ぐ支持部材としての機能も兼ね備えることができる。この場合、支持部材の配置位置としては、図１４（ａ）のようなものが、挙げられる。これにより、発電セルと発電セル筐体とを固定することができ、また、酸化剤極と燃料極との差圧により、電解質膜がたわんだり、はがれたりすることを防ぐことができる。
【００８５】
特に、図２のような酸化剤極に空気を用いる外気開放型の燃料電池においては、酸化剤極に接する支持部材としては、通気性（ガス透過性）の良いものを、一方、燃料極に接する支持部材としては、燃料が外に漏れないように密封性の高いものを用いるのが好ましい。
【００８６】
導体であり、かつ、熱伝導率が高い部材にはステンレス、アルミニウム、チタン、マグネシウム合金、金、銀、銅などの金属やグラファイトなどがある。絶縁体であり、かつ、熱伝導率が高い部材には、アルミナ、シリコン、ゲルマニウムなどがある。
【００８７】
また、ガス透過性がよく熱伝導性の高い材料としては、絶縁体ではシリコン、アルミナをポーラス状、あるいはウィスカー状に加工したものなど、導体では、グラファイト構造を有するポーラスカーボンなどがある。このような多孔質な部材を用いる場合、ガス透過性が高いため、図１４（ｂ）に示すように、シート状の伝熱部材を発電セル間に挟むことも可能である。ガス密封性がよく、熱伝導性の高い材料としては、絶縁体では、シリコン、アルミナ、ゲルマニウムなどがあり、導体ではステンレス、アルミニウム、チタン、マグネシウム合金、金、銀、銅などの金属やグラファイトなどがある。
【００８８】
発電セル筐体に直接対向していない発電セルから効率よく放熱を行う第二の方法は、図１２（ｂ）に示すように、発電によって、酸化剤極で生成する水の気化を利用して発電セル間の伝熱効率を高める方法である。水の蒸発に伴う熱伝達率は１×１０^４　［Ｗ／ｍ^２　Ｋ］程度である。これは自然対流における空気の熱伝達率の約１０００倍である。従って、発熱に伴って発生する水の量は微量ではあるが、十分に発電セル間で熱を伝えることが可能である。
【００８９】
発電セル筐体に直接対向していない発電セルから効率よく放熱を行う第三の方法は、図１３（ｂ）に示すように、ファンなどを用いて、発電セルと発電セル筐体との間の空気を強制的に対流させる方法である。この場合、酸化剤極により積極的に空気を供給できるようになるため、発電効率をさらに高めることができるという利点も有する。空気の強制対流の熱伝達率は１×１０^２　［Ｗ／ｍ^２　Ｋ］程度である。これは自然対流における空気の熱伝達率の約１０倍である。従って、自然対流に比べて効率よく放熱を行うことが可能である。
【００９０】
また、ファンを駆動するモーターの電力を燃料電池の発電電力から供給するように配線することにより、発電量が増えるほど、すなわち、発熱量が増えるほど、モーターの回転速度が増加するようにすることができ、発熱量に合わせた冷却を行うことが可能になる。
【００９１】
また、燃料の流れを利用して効率よく熱を伝えることも可能である。本実施例の燃料電池では、１１４［ｍｍ^３　／ｓ］の流量の燃料が、燃料極に供給される。燃料タンクは断熱されているので、発電によっても、タンク内の燃料はほとんど温度が上がらない。そこで、この燃料の流れを利用することにより、発電セルを冷却し、また、熱の循環を効率よく行うことができる。
【００９２】
本発明の燃料電池は、デジタルカメラ、デジタルビデオカメラ、小型プロジェクタ、小型プリンタ、ノート型パソコンなどの持ち運び可能な小型電気機器に特に好適に用いられることができる。
【００９３】
【発明の効果】
以上のように、本発明の燃料電池は、大容量あるいは高出力であっても、その燃料電池セル、筐体外部、燃料タンク内部の温度を最適に保つことが可能であり、これを用いた電気機器に好適である。特に、持ち運んで使用できるような小型の電気機器に、より好適である。
【図面の簡単な説明】
【図１】本発明の燃料電池システムを示す概略図である。
【図２】本発明の燃料電池セルと燃料タンクの位置関係を示す概略図である。
【図３】図２（ａ）の燃料電池の概観を表す斜視図である。
【図４】図２（ａ）の燃料電池の平面図である。
【図５】図２（ａ）の燃料電池の正面図である。
【図６】図２（ａ）の燃料電池の側面図である。
【図７】図２（ａ）の燃料電池の燃料タンクを示す概略図である。
【図８】本発明の燃料電池の各部の温度パラメータを示す図である。
【図９】本発明の燃料電池の熱的接続部材を示す説明図である。
【図１０】本発明の燃料電池の発電セルと発電セル筐体間の伝熱部材を示す説明図である。
【図１１】本発明の燃料電池の発電セルと発電セル筐体間の配線部材を示す説明図である。
【図１２】本発明の燃料電池の発電セルと発電セル筐体間の水による伝熱を示す説明図である。
【図１３】本発明の燃料電池の発電セルと発電セル筐体間のファンによる伝熱を示す説明図である。
【図１４】本発明の燃料電池の発電セル間の伝熱部材を示す説明図である。
【図１５】本発明の燃料電池の酸化剤極、高分子電解質膜燃料極、セパレータの順での発電セルの積層方式を示す図である。
【図１６】本発明の燃料電池をデジタルカメラに搭載した状態を示す概要図である。
【符号の説明】
１　セル部
１１　酸化剤極
１２　高分子電解質膜
１３　燃料極
３　燃料タンク部
３１　燃料タンク
３２　燃料注入口
３３　注入弁
３４　燃料放出口
３５　放出弁
３６　燃料タンク内壁
３７　燃料タンク外壁
４　燃料供給部
５　配線部
５３　電極
６１　発電セル筐体
６２　燃料タンク筐体
６３　隔壁
７　通気孔
７１　ファン
８　接続部材
９　伝熱部材
９１　配線部材
９２　燃料電池
９３　デジタルカメラ
９４　水滴
１０　保水部材[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fuel cell and an electric device using the same.
[0002]
[Prior art]
Conventionally, various primary batteries and secondary batteries have been used to use electric equipment. However, with the recent high performance of small electric devices, power consumption has increased, and primary batteries have become smaller and lighter and cannot supply sufficient energy. On the other hand, secondary batteries have the advantage of being able to be repeatedly charged and used, but the energy that can be used in a single charge is even less than that of primary batteries. In order to charge the secondary battery, a separate power source is required, and charging usually takes tens of minutes to several hours, and it is difficult to use the secondary battery anytime and anywhere. In the future, as electric devices are becoming smaller and lighter, and the wireless network environment is in place, the tendency to carry and use the devices is increasing, and conventional primary and secondary batteries are sufficient for driving devices. It is difficult to supply sufficient energy.
[0003]
As a solution to such a problem, attention has been paid to a fuel cell. Fuel cells have been developed as drive sources for large generators and automobiles. This is mainly because fuel cells have higher power generation efficiency and cleaner waste than conventional power generation systems. On the other hand, the reason why a fuel cell is useful as a drive source for a small electric device is that the amount of energy that can be supplied per volume and per weight is several to nearly ten times that of a conventional battery. Furthermore, since the fuel cell can be used continuously if only the fuel is exchanged, it does not take much time to charge the battery unlike other secondary batteries.
[0004]
Various types of fuel cells have been invented, but a polymer electrolyte fuel cell is suitable for small electric equipment, especially for portable equipment. This is because it can be used at a temperature close to normal temperature, and has an advantage that it can be carried safely because the electrolyte is not a liquid but a solid.
[0005]
As a fuel for a fuel cell for a small electric device, a methanol type fuel has been studied. This is mainly because methanol is a fuel that is easy to store and readily available.
[0006]
For a fuel cell for obtaining a large output, it is effective to use hydrogen as a fuel. As a method of storing gaseous hydrogen under normal pressure, the first method is a method of compressing hydrogen and storing it as a high-pressure gas. The second method is a method in which hydrogen is cooled to a low temperature and stored as a liquid. A third method is to store hydrogen using a hydrogen storage alloy. In the fourth method, there is a method in which methanol, gasoline, or the like is loaded in a fuel tank, reformed, converted into hydrogen, and used. Recently, attention has been paid to carbon-based materials such as carbon nanotubes, graphite nanofibers, and carbon nanohorns as a fifth method. This is because these carbon-based materials may be able to store about 10 wt% of hydrogen per weight.
[0007]
On the other hand, the power generation of the polymer electrolyte fuel cell is performed as follows. For the polymer electrolyte membrane, a perfluorosulfonic acid-based cation exchange resin is often used. For example, Nafyon of DuPont is well known as such a film. The power generation cell is a membrane electrode assembly in which the solid polymer electrolyte membrane is sandwiched between a pair of porous electrodes carrying a catalyst such as platinum, that is, a fuel electrode and an oxidant electrode. By supplying an oxidizing agent to the oxidizing agent electrode and a fuel to the fuel electrode, protons move in the polymer electrolyte membrane to generate electric power. This power generation reaction is most efficient when performed in a temperature range of about 60 ° C to 100 ° C. However, the polymer electrolyte membrane has a property that when it exceeds 100 ° C., the power generation performance is significantly reduced. Further, the polymer electrolyte membrane is usually used after being moistened, but at a temperature of 100 ° C. or higher, moisture in the polymer electrolyte membrane evaporates. Therefore, it is not preferable that the temperature of the power generation cell be 100 ° C. or higher in power generation.
[0008]
On the other hand, the power generation efficiency of the polymer electrolyte fuel cell is about 50%, and the same amount of heat is generated as the amount of power generation. Therefore, in power generation, it is necessary to keep the fuel cell at an appropriate temperature.
[0009]
As an attempt to increase the power generation efficiency by heating the power generation cell and to control the power generation cell temperature to be optimal, a method using a heat exchanger has been conventionally adopted. Further, as disclosed in JP-A-8-64218, a method of controlling the temperature without using a heat exchanger by heating or cooling when humidifying the fuel has been attempted. Also, in JP-A-2000-353536 and JP-A-10-340734, a large-sized control device is not required by using a cooling device using a heat pipe and a fin.
[0010]
[Problems to be solved by the invention]
However, the configuration of the conventional fuel cell described above does not consider a configuration for mounting on a small electric device or a configuration necessary for downsizing. Furthermore, as the integration of fuel cells progresses, the heat value per unit volume also increases, and accordingly, the heat value also increases.
[0011]
For example, small electric devices such as digital cameras are often used in contact with the human body, such as in a hand, and it is not preferable that the temperature of the fuel cell housing be higher than 100 ° C.
[0012]
In addition, if the periphery of the power generation cell is covered by the housing, heat is trapped, and the temperature of the power generation cell tends to become high. The power generation cell has a property that it does not operate normally at a high temperature exceeding 100 ° C.
[0013]
However, using a large-sized cooling device is not preferable in reducing the size of the system.
[0014]
Further, when the whole fuel cell is miniaturized, the distance between the fuel tank and the power generation cell becomes shorter, and the heat generated by the power generation is easily transmitted to the inside of the fuel tank. However, this causes an increase in the internal pressure in the tank, which is not preferable.
[0015]
The present invention has been made in order to solve such problems of the prior art, and has a large capacity or a high output capable of maintaining the temperature of the fuel cell, the outside of the housing, and the inside of the fuel tank at an optimum level. And an electric device using the same.
[0016]
[Means for Solving the Problems]
That is, the first invention of the present invention provides a fuel tank having at least fuel therein, a power generation cell for generating power using fuel guided from the fuel tank, and a fuel tank and a power generation cell. A fuel cell having a casing to cover, wherein the fuel cell has a heat insulating structure inside the casing of the fuel tank.
[0017]
It is preferable that a heat insulating structure is provided inside the fuel tank housing, and a member having lower thermal resistance than the heat insulating structure inside the fuel tank housing is provided outside the fuel tank housing.
It is preferable that the power generation cell casing is made of a member having a lower heat dissipation resistance to air and a lower heat resistance than a heat insulating member provided inside the fuel tank casing.
It is preferable that the power generation cell housing and the outer wall of the fuel tank housing have a portion for thermal connection.
[0018]
It is preferable that the thermal connection between the power generation cell housing and the outer wall of the fuel tank housing be made at a predetermined temperature or higher.
It is preferable that the thermal connection is performed by utilizing thermal expansion of a connection member in contact with the power generation cell housing.
It is preferable that a heat insulating structure is provided between the fuel tank and the fuel cell.
It is preferable that a partition made of a heat insulating material is provided between the power generation cell and the fuel tank.
[0019]
A second invention of the present invention includes a fuel tank holding at least fuel therein, a power generation cell that generates power using fuel guided from the fuel tank, and a housing that covers the power generation cell. The fuel cell according to claim 1, further comprising a heat transfer mechanism between the power generation cell and the power generation cell housing, the heat transfer mechanism having a smaller thermal resistance than a thermal resistance in natural heat radiation by air.
[0020]
It is preferable that the power generation cell housing is made of a material having a thermal conductivity that is smaller than a heat radiation resistance to air.
In the heat transfer mechanism, it is preferable that the power generation cell and the power generation cell housing are connected by a member having a smaller thermal resistance than that of natural heat radiation by air.
It is preferable that the member having a heat resistance smaller than the heat resistance in the natural heat radiation by the air has air permeability.
It is preferable that the member having a thermal resistance smaller than the thermal resistance in the natural heat radiation by the air is a power generation cell housing, a power generation cell, or a support member for fixing the power generation cells to each other.
[0021]
It is preferable that the member having a thermal resistance smaller than the thermal resistance in the natural heat radiation by the air is an electrical insulator.
It is preferable that the member having a smaller thermal resistance than the natural thermal radiation by the air is a conductor and is insulated from the outside of the power generation cell housing.
It is preferable that the power generation cell housing is made of an insulator material.
A wiring portion made of a conductive material is provided at a junction between the member having a thermal resistance smaller than the thermal resistance in the natural heat radiation by the air and the power generation cell housing, and the wiring portion is electrically connected to a power extraction electrode of the fuel cell. It is preferable that they are connected electrically.
[0022]
Preferably, the heat transfer mechanism is realized by utilizing evaporation of water generated by power generation.
It is preferable that the heat transfer mechanism is realized by convection of air in the power generation cell housing.
Preferably, the convection means is a fan for supplying air or oxygen to the oxidizer electrode of the fuel cell.
[0023]
According to a third aspect of the present invention, there is provided a fuel cell having a plurality of power generation cells, wherein a fuel transfer mechanism having a heat resistance smaller than a heat resistance in natural heat radiation by air is provided between the power generation cells. Battery.
[0024]
It is preferable that the heat transfer mechanism is connected between the power generation cells by a member having a smaller thermal resistance than that of natural heat radiation by air.
It is preferable that the member having a thermal resistance smaller than the thermal resistance in the natural heat radiation by the air has an insulating property.
It is preferable that the member having a heat resistance smaller than the heat resistance in the natural heat radiation by the air has air permeability.
It is preferable that a member having a thermal resistance smaller than the thermal resistance in the natural heat radiation by the air also serves as a partition of the oxidant electrode chamber of the fuel cell.
[0025]
It is preferable that the member having a heat resistance smaller than the heat resistance in the natural heat radiation by the air has gas tightness.
It is preferable that the member having a smaller thermal resistance than the thermal resistance in the natural heat radiation by the air also serves as a partition of the fuel electrode chamber of the fuel cell.
It is preferable that the member having a smaller thermal resistance than the thermal resistance in the natural heat radiation by the air has conductivity.
It is preferable that the member having a heat resistance smaller than the heat resistance in the natural heat radiation by the air has air permeability.
[0026]
It is preferable that a member having a thermal resistance smaller than the thermal resistance in the natural heat radiation by the air also serves as a partition of the oxidant electrode chamber of the fuel cell.
It is preferable that the member having a heat resistance smaller than the heat resistance in the natural heat radiation by the air has airtightness.
It is preferable that the member having a smaller thermal resistance than the thermal resistance in the natural heat radiation by the air also serves as a partition of the fuel electrode chamber of the fuel cell.
Preferably, the heat transfer mechanism utilizes evaporation of water generated by power generation.
[0027]
It is preferable that the heat transfer mechanism is realized by convection of air in the power generation cell housing.
Preferably, the convection means is a fan for supplying air or oxygen to the oxidizer electrode of the fuel cell.
Preferably, the heat transfer mechanism is realized by a fuel flow.
[0028]
Further, a fourth invention of the present invention is an electric device using the above fuel cell.
[0029]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, features of the fuel cell of the present invention will be described.
The fuel cell according to the present invention includes a fuel tank having at least fuel therein, a power generation cell that generates power using fuel guided from the fuel tank, and a housing that covers the fuel tank and the power generation cell. In the fuel cell having the fuel tank, a heat insulating structure is provided inside the fuel tank, and by insulating the inside of the fuel tank from the outside, heat generated by power generation and heat from an external environment are hardly transmitted to the fuel tank, and the fuel It is possible to prevent the fuel pressure in the tank from rising.
[0030]
Further, the fuel cell of the present invention has at least a fuel tank that holds fuel therein, a power generation cell that generates power using fuel guided from the fuel tank, and a housing that covers the power generation cell. In the fuel cell, characterized by comprising a heat transfer mechanism having a smaller thermal resistance than the thermal resistance in the natural heat radiation by air between the power generation cell and the power generation cell housing, between the power generation cell and the power generation cell housing By increasing the heat transfer efficiency, it is possible to prevent the temperature of the power generation cell from becoming too high.
[0031]
Further, the fuel cell according to the present invention is characterized in that, in the fuel cell having a plurality of power generation cells, a heat transfer mechanism having a heat resistance smaller than a heat resistance in natural heat radiation by air is provided between the power generation cells, By increasing the heat transfer efficiency between the cells, it is possible to prevent the temperature of the power generation cell from becoming too high.
[0032]
Furthermore, by connecting the outer surface of the fuel tank and the power generation cell housing in a conductive manner, the internal heat can be radiated not only from the power generation cell housing but also from the outer surface of the fuel tank housing. Can be enhanced.
Further, by controlling the above-mentioned thermal connection according to the heat generation state of the fuel cell, the temperature of the fuel cell unit can be maintained at an optimum value.
Further, the present invention can provide an electric device using a fuel cell which can control heat generated by the heat generated from the power generation cell and keep the temperature at an optimum value.
[0033]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.
FIG. 1 is a schematic diagram showing a fuel cell system of the present invention.
[0034]
The fuel cell of this embodiment has ventilation holes 7 on the upper, lower, and side surfaces for taking in the oxygen used for the reaction as the oxidant from the outside air. The vent hole 7 also has a function of releasing generated water as water vapor to the outside. On one side, there is an electrode 53 for extracting electricity. Inside, a cell portion 1 composed of a polymer electrolyte membrane 12, an oxidant electrode 11, a fuel electrode 13, and a catalyst of a cell electrode, a fuel tank portion 3 for storing fuel, and the pressure of fuel from the fuel tank are reduced. And a wiring section 5 for collecting electricity generated in each cell.
[0035]
In the present embodiment, in miniaturizing the fuel cell, the fuel tank volume for obtaining a sufficient cell capacity, the fuel cell area for obtaining a sufficient output, and the efficient supply of an oxidant to the fuel cell are provided. The positional relationship between the vent holes and the fuel cells is optimized. FIGS. 2A and 2B are views showing the positional relationship among the fuel cell unit, the fuel tank, and the vent. In FIG. 2A, the fuel cell unit 1 and the fuel tank unit 3 are arranged in series, and the fuel tank 31 exists on the side surface of the fuel cell. In addition, the surface of the power generation cell housing 61 having the ventilation holes 7 is located at a position facing the fuel cell surface.
[0036]
FIG. 2B shows a state in which the ventilation holes 7 are arranged on the surface where the surface area of the fuel cell casing is maximized, and the fuel cell 1 is arranged at a position opposite to the surface having the ventilation holes 7. The fuel tank 31 is arranged at the bottom. When the fuel cell is thin, the system shown in FIG. 2A is effective for increasing the fuel tank volume. On the other hand, the method shown in FIG. 2B is effective for more efficiently taking in the oxidant from the air holes and supplying it to the oxidant electrode. In each case, the fuel cell housing is divided into a power generation cell housing 61 and a fuel tank housing 62, and the power generation cell and the fuel tank are separated by a partition 63.
[0037]
FIG. 3 is a perspective view showing an overview of the fuel cell having the arrangement relationship shown in FIG. FIG. 4 is a plan view of the fuel cell having the arrangement shown in FIG. FIG. 5 is a front view of the fuel cell having the arrangement shown in FIG. FIG. 6 is a side view of the fuel cell having the arrangement shown in FIG. The outer dimensions of the fuel cell are 50 mm wide × 30 mm long × 10 mm high, which are almost the same as the size of a lithium ion battery usually used in a compact digital camera. FIG. 16 is a schematic diagram when a fuel cell 92 of the present invention is mounted on a digital camera 93. As described above, since the digital camera of the present invention is small and integrated, it has a shape that can be easily incorporated into a portable device.
[0038]
Hereinafter, each part of the fuel cell of the present invention will be described in detail.
The fuel tank 3 will be described. FIG. 7 is a schematic diagram showing an outline of the fuel tank. In this embodiment, hydrogen is used as fuel. A case where the inside of the tank is filled with a hydrogen storage alloy will be described. In general, the pressure resistance of a polymer electrolyte membrane used in a fuel cell is 0.3 to 0.5 MPa, so that it is necessary to use the polymer electrolyte membrane in a range of a pressure difference from outside air within 0.1 MPa. For this reason, in order to simplify the system, as a hydrogen storage alloy having a hydrogen release pressure of 0.2 MPa at room temperature, for example, LaNi ₅ It is preferable to use such as. Assuming that the volume of the fuel tank is half of the entire fuel cell and the thickness of the tank is 1 mm, the volume of the fuel tank is 5.2 cm. ³ become. LaNi ₅ Can absorb and desorb 1.1 wt% of hydrogen per weight, the amount of hydrogen stored in the fuel tank is 0.4 g, and the energy that can be generated is about 11.3 [W · hr]. It is about four times that of the lithium-ion battery.
[0039]
Further, a relief valve can be provided in the fuel tank in order to prevent the fuel pressure from excessively increasing due to a temperature change or the like. In general, the dissociation pressure of hydrogen increases as the temperature of a hydrogen storage alloy increases. Table 1 shows LaNi ₅ Table 2 shows the change in the rate of release of hydrogen depending on the temperature of LaNi. ₅ 3 shows the change in the dissociation pressure of hydrogen depending on the temperature.
[0040]
[Table 1]

[0041]
[Table 2]

[0042]
As can be seen from Table 2, when the temperature in the fuel tank exceeds 50 ° C., the tank internal pressure exceeds 0.4 MPa (about 4 atm). Such high pressure in the fuel tank not only increases the risk of rupture, but also causes the valve that controls the fuel flow rate to malfunction. Therefore, in order to prevent the pressure in the fuel tank from increasing, it is necessary to prevent heat generated from power generation or external heat from being transmitted to the fuel tank. In the present invention, the fuel tank inner wall 36 and the partition 63 between the fuel cell 1 and the fuel tank 31 have a heat insulating mechanism. As the heat insulating mechanism, there are a method of using a material having heat insulating properties and a method of providing a structure with high heat insulating properties. Materials with heat insulation properties include plastics such as polyethylene, polystyrene, polyacryl, and polycarbonate; rubbers such as urethane rubber, silicone rubber, and fluororubber; glass, silicon carbide, silicon nitride, amorphous carbon, wood, cork, and paper. , Ceramics and the like, and an optimum material can be selected from required workability, strength and the like. As a structure having high heat insulating properties, there is a method of providing a vacuum chamber in the heat insulating portion.
[0043]
On the other hand, as shown in Table 1, the dissociation rate of a hydrogen storage alloy generally increases as the temperature increases. Further, since the hydrogen release reaction of the hydrogen storage alloy is an endothermic reaction, the temperature in the fuel tank decreases with the release of hydrogen. Therefore, depending on the type of the hydrogen storage alloy, it may be necessary to heat the tank in order to release hydrogen required for power generation from the tank. By optimally selecting the thermal conductivity of the fuel tank inner wall 36 and the partition 63, it is possible to keep the temperature of the fuel tank in an optimal state for power generation.
[0044]
Next, the cell section 1 will be described. The fuel cell of this embodiment has an electromotive force of 0.8 V and a current density of 300 mA / cm. ² And the size of the unit cell is 1.2 cm × 2 cm. By connecting eight fuel cells in series, the output of the entire cell is 6.4 V, 4.6 W at 720 mA. The power generation efficiency of the polymer electrolyte fuel cell is about 50%, and the same amount of heat as the power generation is generated. Therefore, the fuel cell of this embodiment also generates about 5 W of heat in the cell section.
[0045]
A case where heat is radiated to the outside only from the power generation cell housing 61 will be considered.
As shown in FIG. 8, the heat generation amount of the power generation cell is Q [W], and the power generation cell housing surface area is A. _w [M ² ], The outside air temperature is T ₀ [° C], the power generation cell case temperature is T _w [° C] and the heat transfer coefficient h of air _a [W / m ² ・ K]
[0046]
(Equation 1)
T _w -T ₀ = Q / (h _a A _w )
Is represented by Also, T _c Indicates the power generation cell temperature.
[0047]
h _a = 40 [W / m] ² ・ K] 、 A _w = 2.3 × 10 ^-3 [M ² ], Q = 5 [W]
When,
[0048]
(Equation 2)
T _w -T ₀ = 54.3
It becomes.
Therefore, the outside air temperature T ₀ = 25 ° C, T _w = 79.3 ° C.
[0049]
When it is assumed that a fuel cell is mounted on a small electric device such as a digital camera and used, these small electric devices are likely to be used near the skin, such as in a hand, and the power generation cell housing is at 80 ° C. It is not desirable to be close. It is also desirable that the temperature of the power generation cell housing be low from the viewpoint of the stability of the operation of the electric equipment.
[0050]
Therefore, in order to more efficiently dissipate heat from the power generation cell housing, the heat of the power generation cell housing is transmitted to the fuel tank housing, thereby releasing heat from the surfaces of the power generation cell housing and the fuel tank housing to the outside air. Do. Thereby, the surface area of the heat radiating surface increases, and a large heat radiating effect can be obtained.
[0051]
Materials for efficiently transmitting heat on the surfaces of the power generation cell housing and the fuel tank housing include metals such as stainless steel, aluminum, titanium, magnesium alloy, gold, silver, and copper, graphite, alumina, silicon, germanium, and the like. Diamond and the like. Considering workability and strength, stainless steel, titanium, aluminum, magnesium alloy, and the like are preferable.
[0052]
When utilizing the heat radiation in the fuel tank, the total surface area of the power generation cell casing and the fuel cell casing is 4.6 × 10 ^-3 [M ² ]. Therefore,
[0053]
[Equation 3]
T _w -T ₀ = 27.1
It becomes. Therefore, the outside air temperature T ₀ = 25 ° C, T _w = 52.1 ° C., and the temperature of the fuel cell housing can be more efficiently reduced. Further, as described above, since the inner wall of the fuel tank is made of a heat insulating material, heat transmitted to the fuel tank housing is not transmitted to the inside of the fuel tank.
[0054]
In order to obtain a greater heat radiation effect, for example, a heat sink may be provided in the fuel cell housing to increase the surface area, or heat radiation may be more actively performed using a cooling fan, a heat pipe, or the like.
[0055]
By conducting heat transfer from the power generation cell housing to the fuel tank housing surface only when the temperature of the power generation cell housing is high, power can be generated more efficiently without lowering the temperature of the power generation cell surface more than necessary. Can be. This function can be realized, for example, as follows.
[0056]
As shown in FIG. 9, a connection member 8 made of a material having a high thermal expansion coefficient and a high thermal conductivity is provided in the power generation cell housing 61, and the power generation cell housing 61 and the fuel tank housing are provided when the temperature is low. The connecting member 8 is not thermally connected to the fuel cell housing 62, and as the temperature of the power generation cell housing rises, the connecting member 8 expands thermally and comes into contact with the fuel tank housing, so that heat is transmitted. Examples of the material having a high thermal expansion coefficient and a high thermal conductivity include aluminum. The coefficient of linear expansion of the material is α [K ^-1 ], Length is l ₀ [Cm], the elongation Δl [cm] of the connection portion when the temperature changes by ΔT [K] is expressed as follows.
[0057]
(Equation 4)
Δl = 1 ₀ αΔT
For example, when titanium is used for the power generation cell casing and aluminum is used as the material of the connection member, the linear expansion coefficient of titanium is 8.6 × 10 ^-6 [K ^-1 And the coefficient of linear expansion of aluminum is 23.1 × 10 ^-6 [K ^-1 ], The length l ₀ Is 2.5 [cm], at ΔT = 30 [K], the difference in elongation between the power generation cell and the power generation cell housing is 2.5 × (23.1-8.6) × 10 ^-6 × 30 = 1.08 × 10 ^-3 [Cm]. Therefore, the distance between the connecting member and the fuel tank housing is set to 1.08 × 10 ^-3 If designed at a distance of [cm] and the room temperature is set to 25 ° C., heat is released from the power generation cell housing to the fuel tank housing only when the power generation cell housing temperature exceeds 55 ° C.
[0058]
By designing the material and length of the connection part and the distance between the connection part and the fuel tank housing in accordance with the above design guidelines, the power generation cell housing can be moved from the fuel cell housing to the fuel tank housing only when a predetermined temperature is exceeded. Can be dissipated.
[0059]
In power generation of a fuel cell, power generation can be performed most efficiently when the temperature of the fuel cell unit is about 60 ° C to 80 ° C. Further, when the temperature of the power generation cell exceeds 100 ° C., the power generation performance is significantly reduced. Therefore, in power generation, it is preferable that the power generation cell temperature be in the above temperature range.
[0060]
First, consider the heat radiation of the power generation cell facing the power generation cell housing surface. Assuming that the heat transfer between the power generation cell and the power generation cell housing is only natural convection of air, the thermal resistance R from the power generation cell to the surface of the power generation cell housing is expressed as follows.
[0061]
(Equation 5)
R = 1 / (h _a A _c ) + T _w / (Λ _w A _w )
Where h _a Is the heat transfer coefficient of air, A _c Is the area of the power generation cell portion facing the power generation cell housing surface, λ _w Is the thermal conductivity of the power generation cell case, A _w Is the surface area of the power generation cell case, t _w Is the thickness of the power generation cell housing.
[0062]
A _c Is 7.5 × 10 ^-4 [M ² ], The thickness t of the power generation cell housing _w Is 1 mm, and the material is stainless steel (λ _w = 16.3 [W / m · K])
R = 33.3 [K / W]
(The thermal resistance of the air portion is 33.3 [K / W], and the thermal resistance of the housing portion is 0.027 [K / W]).
[0063]
In addition, since the distance between the power generation cell and the power generation cell housing is very short, if the heat transfer in the air is heat conduction, the thermal resistance R is expressed as follows.
[0064]
(Equation 6)
R = t _a / (Λ _a A _c ) + T _w / (Λ _w A _w )
Where t _a Is the distance between the power generation cell and the power generation cell case, λ _a Is the thermal conductivity of air.
[0065]
t _a Is 1 mm, λ _a = 25 × 10 ^-3 [W / m · K],
R = 53.3 [K / W]
(The thermal resistance of the air portion is 53.3 [K / W], and the thermal resistance of the housing portion is 0.027 [K / W]).
[0066]
Set the power generation cell temperature to T _c Then
[0067]
(Equation 7)
T _c -T _w = Q ₁ R
It is. Where q ₁ Is the calorific value of the power generation cell facing one side of the power generation cell housing.
Where q ₁ Is 1.25 [W],
T _c -T _w = 41.6 ° C (natural convection)
T _c -T _w = 66.6 ° C (thermal conduction)
[0068]
When radiating heat on both the power generation cell housing surface and the fuel tank housing surface, T _w = 52.1 ° C,
T _c = 93.7 ° C (natural convection)
T _c = 118.7 ° C (thermal conduction)
And the power generation cell surface temperature may rise to 100 ° C. or higher.
Therefore, a method for efficiently transmitting heat from the power generation cell to the power generation cell housing is required.
[0069]
As shown in FIG. 10, a first method of efficiently transmitting heat from a power generation cell to a power generation cell housing is a method of transferring heat between a power generation cell 1 and a power generation cell housing 61 using a material having high thermal conductivity. This is a method of connecting with the heat member 9. Examples of materials having high thermal conductivity include metals such as stainless steel, aluminum, titanium, magnesium alloy, gold, silver, and copper, graphite, alumina, silicon, germanium, and diamond. Considering workability and strength, stainless steel, titanium, aluminum, magnesium alloy and the like are preferable. In particular, it is preferable that the above-mentioned member is an insulator (semiconductor) in order to prevent the generated power from leaking outside. Alumina, silicon, germanium, and the like are members that are insulators (semiconductors) and have high thermal conductivity.
[0070]
On the other hand, when a conductor is used for the heat transfer member, it is possible to prevent the generated electricity from leaking outside by forming the power generation cell casing with an insulating material. In this case, as shown in FIG. 11, a wiring member 91 made of a conductive material is provided at a portion where the power generation cell casing 61 and the heat transfer member 9 are in contact with each other, and the wiring member 91 takes out power of the fuel cell. By electrically connecting to the electrode 53 for use, wiring can be efficiently performed.
[0071]
The heat transfer member can also have a function as a support member for fixing the power generation cell and the power generation cell housing. In this case, as an arrangement position of the support member, a member in which the heat transfer member 9 is arranged with a space between the power generation cell 1 and the power generation cell housing 61 as illustrated in FIG. Thus, the power generation cell and the power generation cell housing can be fixed, and the electrolyte membrane can be prevented from being bent or peeled off due to the differential pressure between the oxidant electrode and the fuel electrode.
[0072]
In addition, by using a porous heat transfer member or by providing a vent, the outside air can be more efficiently supplied to the oxidizer electrode.
[0073]
As the heat transfer member, as a material having good gas permeability and high thermal conductivity, silicon and alumina are processed into a porous or whisker-like insulator, and porous carbon having a graphite structure is used as a conductor. is there. When such a porous member is used, since the gas permeability is high, the sheet-shaped heat transfer member 9 is sandwiched between the power generation cell 1 and the power generation cell housing 61 as shown in FIG. It is also possible.
[0074]
The heat transfer in the case where a member made of an alumina material is arranged as the heat transfer member 9 as shown in FIG.
[0075]
Thermal conductivity λ of alumina _Al = 36 [W / m · K], and the area of the part of the member in contact with the power generation cell is A _Al (The member is 2 [mm]) and the thickness is t _Al = 1 [mm]
Thermal resistance R ₁ Is
[0076]
(Equation 8)
R ₁ = T _Al / (Λ _Al A _Al )
R ₁ = 1.0 × 10 ^-3 ÷ (36 × (3 × 2.5-2.6 × 2.1) × 10 ^-4 ) = 0.14
Therefore, T _c -T _w = Q ₁ R ₁ = 1.25 × (0.14 + 0.027) = 0.20, T _c = 52.3 ° C.
[0077]
In other words, a member made of a material having a high thermal conductivity can transfer reaction heat from the power generation cell to the power generation cell casing, thereby preventing the power generation cell from being overheated. Further, by designing the material, shape, and size of the members in accordance with the above guidelines, it is possible to keep the power generation cell at an optimal temperature for power generation.
[0078]
As shown in FIG. 12A, the second method of efficiently transmitting heat from the power generation cell to the power generation cell housing is a method utilizing vaporization of water generated at the oxidant electrode by power generation. Heat transfer coefficient due to water evaporation is 1 × 10 ⁴ [W / m ² K]. This is about 1000 times the heat transfer coefficient of air in natural convection. Therefore, although the amount of water generated by heat generation is very small, it is possible to sufficiently transfer heat from the power generation cell to the power generation cell casing.
[0079]
As shown in FIG. 13A, a third method of efficiently transmitting heat from the power generation cell to the power generation cell casing is to forcibly force air between the power generation cell and the power generation cell casing using a fan or the like. It is a method of convection. In this case, since air can be more positively supplied to the oxidant electrode, there is an advantage that power generation efficiency can be further increased. Heat transfer coefficient of forced convection of air is 1 × 10 ² [W / m ² K]. This is about ten times the heat transfer coefficient of air in natural convection. Therefore, it is possible to transfer heat from the power generation cell to the power generation cell casing more efficiently than in natural convection.
[0080]
Also, by wiring so that the electric power of the motor for driving the fan is supplied from the electric power generated by the fuel cell, the rotational speed of the motor increases as the amount of generated power increases, that is, as the amount of generated heat increases. It is possible to perform cooling in accordance with the amount of heat generated.
[0081]
Next, heat transfer between the power generation cells will be described.
In order to reduce the size of the entire power generation cell and obtain a large power generation amount, a method of stacking and using a plurality of cells is effective. When a plurality of cells are stacked, there may be a power generation cell that does not directly face the power generation cell housing. In order to keep the temperature of the power generation cell at the optimum, it is necessary to efficiently radiate heat from the power generation cell that is not directly opposed to the power generation cell housing.
[0082]
A first method for efficiently dissipating heat from a power generation cell that is not directly opposed to the power generation cell housing is to connect the power generation cells with each other by a member made of a material having high thermal conductivity as shown in FIG. How to Examples of materials having high thermal conductivity include metals such as stainless steel, aluminum, titanium, magnesium alloy, gold, silver, and copper, graphite, alumina, silicon, germanium, and diamond.
[0083]
In the system in which the power generation cells are stacked in the order of the oxidizer electrode, the polymer electrolyte membrane, the fuel electrode, and the separator as shown in FIG. 15, each of the power generation cells is formed by using a conductive material for the high thermal conductivity member. Can be electrically connected in series. On the other hand, as shown in FIG. 2, in the case of a laminated structure in which the same poles face each other, if a material having conductivity is used for the high thermal conductivity member, the power generation cells can be electrically connected in parallel. If a material having an insulating property is used, the power generation cells can be electrically connected in series by separately wiring the cells.
[0084]
Further, the above member can also have a function as a support member for preventing contact between the power generation cell and the power generation cell and for preventing bending of the power generation cell due to a pressure difference between the fuel electrode chamber and the oxidant electrode chamber. In this case, as an arrangement position of the support member, a position as shown in FIG. Thus, the power generation cell and the power generation cell housing can be fixed, and the electrolyte membrane can be prevented from being bent or peeled off due to the differential pressure between the oxidant electrode and the fuel electrode.
[0085]
In particular, in an open-air fuel cell using air as the oxidant electrode as shown in FIG. 2, a support member having good air permeability (gas permeability) is used as a support member in contact with the oxidant electrode. It is preferable to use a support member having a high sealing property so that the fuel does not leak outside.
[0086]
Examples of members that are conductors and have high thermal conductivity include metals such as stainless steel, aluminum, titanium, magnesium alloys, gold, silver, and copper, and graphite. Alumina, silicon, germanium, and the like are examples of members that are insulators and have high thermal conductivity.
[0087]
Examples of the material having good gas permeability and high heat conductivity include silicon or alumina processed into a porous shape or a whisker shape as an insulator, and porous carbon having a graphite structure as a conductor. When such a porous member is used, since the gas permeability is high, a sheet-like heat transfer member can be interposed between the power generation cells as shown in FIG. Materials with good gas sealing properties and high thermal conductivity include insulators such as silicon, alumina and germanium, and conductors such as metals such as stainless steel, aluminum, titanium, magnesium alloys, gold, silver and copper, and graphite. There is.
[0088]
A second method for efficiently dissipating heat from a power generation cell that is not directly opposed to the power generation cell housing utilizes vaporization of water generated at an oxidant electrode by power generation, as shown in FIG. This is a method of increasing the heat transfer efficiency between the power generation cells. Heat transfer coefficient due to water evaporation is 1 × 10 ⁴ [W / m ² K]. This is about 1000 times the heat transfer coefficient of air in natural convection. Therefore, although the amount of water generated due to heat generation is very small, it is possible to sufficiently transfer heat between the power generation cells.
[0089]
A third method for efficiently dissipating heat from a power generation cell that is not directly opposed to the power generation cell housing is to use a fan or the like to connect the power generation cell to the power generation cell housing as shown in FIG. This is a method of forcibly convection air. In this case, since air can be more positively supplied to the oxidant electrode, there is an advantage that power generation efficiency can be further increased. Heat transfer coefficient of forced convection of air is 1 × 10 ² [W / m ² K]. This is about ten times the heat transfer coefficient of air in natural convection. Therefore, heat can be efficiently radiated as compared with natural convection.
[0090]
Also, by wiring so that the electric power of the motor for driving the fan is supplied from the electric power generated by the fuel cell, the rotational speed of the motor increases as the amount of generated power increases, that is, as the amount of generated heat increases. It is possible to perform cooling in accordance with the amount of heat generated.
[0091]
It is also possible to efficiently transfer heat using the flow of fuel. In the fuel cell of this embodiment, 114 [mm ³ / S] is supplied to the fuel electrode. Since the fuel tank is insulated, the temperature of the fuel in the tank hardly rises even by power generation. Therefore, by utilizing the flow of the fuel, the power generation cell can be cooled and heat can be efficiently circulated.
[0092]
The fuel cell of the present invention can be particularly suitably used for a portable small electric device such as a digital camera, a digital video camera, a small projector, a small printer, and a notebook computer.
[0093]
【The invention's effect】
As described above, the fuel cell of the present invention can maintain the temperature inside the fuel cell, the outside of the housing, and the inside of the fuel tank even at a large capacity or a high output. Suitable for electrical equipment. In particular, the present invention is more suitable for a small electric device which can be carried and used.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a fuel cell system of the present invention.
FIG. 2 is a schematic diagram showing a positional relationship between a fuel cell unit and a fuel tank of the present invention.
FIG. 3 is a perspective view showing an overview of the fuel cell shown in FIG.
FIG. 4 is a plan view of the fuel cell of FIG. 2 (a).
FIG. 5 is a front view of the fuel cell of FIG. 2 (a).
FIG. 6 is a side view of the fuel cell of FIG. 2 (a).
FIG. 7 is a schematic diagram showing a fuel tank of the fuel cell of FIG. 2 (a).
FIG. 8 is a diagram showing temperature parameters of each part of the fuel cell according to the present invention.
FIG. 9 is an explanatory view showing a thermal connection member of the fuel cell of the present invention.
FIG. 10 is an explanatory view showing a heat transfer member between a power generation cell and a power generation cell housing of the fuel cell of the present invention.
FIG. 11 is an explanatory view showing a wiring member between a power generation cell and a power generation cell housing of the fuel cell of the present invention.
FIG. 12 is an explanatory diagram showing heat transfer by water between a power generation cell and a power generation cell housing of the fuel cell of the present invention.
FIG. 13 is an explanatory diagram showing heat transfer by a fan between a power generation cell and a power generation cell housing of the fuel cell of the present invention.
FIG. 14 is an explanatory view showing a heat transfer member between power generation cells of the fuel cell of the present invention.
FIG. 15 is a diagram showing a stacking system of power generation cells in the order of an oxidizer electrode, a polymer electrolyte membrane fuel electrode, and a separator of the fuel cell of the present invention.
FIG. 16 is a schematic diagram showing a state where the fuel cell of the present invention is mounted on a digital camera.
[Explanation of symbols]
1 cell part
11 Oxidizer electrode
12 polymer electrolyte membrane
13 Fuel electrode
3 Fuel tank
31 Fuel tank
32 Fuel inlet
33 injection valve
34 Fuel outlet
35 Release valve
36 Fuel tank inner wall
37 Fuel tank outer wall
4 Fuel supply section
5 Wiring section
53 electrodes
61 Power generation cell housing
62 Fuel tank housing
63 partition
7 Vent
71 fans
8 Connecting members
9 Heat transfer members
91 Wiring member
92 Fuel cell
93 Digital Camera
94 Water Drop
10 Water retention members

Claims (37)

In a fuel cell including at least a fuel tank holding fuel therein, a power generation cell for generating electric power using fuel guided from the fuel tank, and a casing covering the fuel tank and the power generation cell, A fuel cell having a heat insulating structure inside a housing. The fuel tank according to claim 1, further comprising a heat insulating structure inside the fuel tank housing, and a member having a lower thermal resistance than the heat insulating structure inside the fuel tank housing outside the fuel tank housing. The fuel cell as described. 3. The fuel cell according to claim 1, wherein the power generation cell housing is made of a member having a lower heat dissipation resistance to air and a lower heat resistance than a heat insulating member provided inside the fuel tank housing. 4. The fuel cell according to claim 3, further comprising a portion for thermally connecting the power generation cell housing and an outer wall of the fuel tank housing. The fuel cell according to claim 4, wherein a thermal connection between the power generation cell housing and an outer wall of the fuel tank housing is connected at a predetermined temperature or higher. The fuel cell according to claim 5, wherein the thermal connection is performed by utilizing thermal expansion of a connection member in contact with the power generation cell housing. The fuel cell according to any one of claims 1 to 6, further comprising a heat insulating structure between the fuel tank and the fuel cell. The fuel cell according to claim 7, further comprising a partition wall made of a heat insulating material between the power generation cell and the fuel tank. A fuel tank having at least fuel therein, a power generation cell for generating power using the fuel guided from the fuel tank, and a fuel cell having a housing covering the power generation cell; A fuel cell, comprising: a heat transfer mechanism having a smaller thermal resistance than a thermal resistance in natural heat radiation by air between the fuel cell and a cell housing. 10. The fuel cell according to claim 9, wherein the power generation cell housing is made of a material having a thermal conductivity that is smaller than a heat radiation resistance to air. 11. The fuel cell according to claim 9, wherein the heat transfer mechanism includes a power generation cell and a power generation cell housing connected by a member having a thermal resistance smaller than a thermal resistance in natural heat radiation by air. 12. The fuel cell according to claim 11, wherein the member having a thermal resistance smaller than the thermal resistance in the natural heat radiation by the air has air permeability. The member having a thermal resistance smaller than the thermal resistance in the natural heat radiation by the air is a power generation cell housing, a power generation cell, or a support member for fixing the power generation cells to each other. Fuel cell. The fuel cell according to any one of claims 11 to 13, wherein the member having a smaller thermal resistance than the natural thermal radiation by air is an electrical insulator. The member according to any one of claims 11 to 14, wherein the member having a smaller thermal resistance than the natural thermal radiation by air is a conductor, and is insulated from the outside of the power generation cell housing. The fuel cell as described. The fuel cell according to claim 15, wherein the power generation cell housing is made of an insulator material. A wiring portion made of a conductive material is provided at a junction between the member having a thermal resistance smaller than the thermal resistance in the natural heat radiation by the air and the power generation cell housing, and the wiring portion is electrically connected to a power extraction electrode of the fuel cell. 17. The fuel cell according to claim 16, wherein the fuel cell is electrically connected. The fuel cell according to claim 9, wherein the heat transfer mechanism is realized by utilizing evaporation of water generated by power generation. The fuel cell according to claim 9, wherein the heat transfer mechanism is realized by convection of air in a power generation cell housing. 20. The fuel cell according to claim 19, wherein the convection means is a fan for supplying air or oxygen to an oxidizer electrode of the fuel cell. A fuel cell having a plurality of power generation cells, wherein a heat transfer mechanism having a heat resistance smaller than that of natural heat radiation by air is provided between the power generation cells. 22. The fuel cell according to claim 21, wherein the heat transfer mechanism is realized by connecting the power generation cells by a member having a thermal resistance smaller than that of natural heat radiation by air. 23. The fuel cell according to claim 22, wherein the member having a thermal resistance smaller than the thermal resistance in the natural heat radiation by the air has an insulating property. 24. The fuel cell according to claim 22, wherein the member having a heat resistance smaller than the heat resistance in the natural heat radiation by the air has air permeability. 25. The fuel cell according to claim 24, wherein the member having a smaller thermal resistance than the natural thermal radiation by the air also serves as a partition wall of the oxidant electrode room of the fuel cell. 26. The fuel cell according to claim 25, wherein the member having a smaller thermal resistance than the natural thermal radiation by air has gas tightness. 27. The fuel cell according to claim 26, wherein the member having a smaller thermal resistance than the thermal resistance in the natural heat radiation by the air also serves as a partition of the fuel electrode chamber of the fuel cell. 28. The fuel cell according to claim 27, wherein the member having a smaller thermal resistance than the natural thermal radiation by air has conductivity. 29. The fuel cell according to claim 28, wherein the member having a smaller thermal resistance than the natural thermal radiation by air has air permeability. 30. The fuel cell according to claim 29, wherein the member having a thermal resistance smaller than the thermal resistance in the natural heat radiation by the air also serves as a partition wall of the oxidant electrode room of the fuel cell. 29. The fuel cell according to claim 28, wherein the member having a smaller thermal resistance than the natural thermal radiation by air has airtightness. 32. The fuel cell according to claim 31, wherein a member having a smaller thermal resistance than the thermal resistance in the natural heat radiation by the air also serves as a partition of a fuel electrode chamber of the fuel cell. 22. The fuel cell according to claim 21, wherein the heat transfer mechanism is realized by utilizing evaporation of water generated by power generation. 22. The fuel cell according to claim 21, wherein the heat transfer mechanism is realized by convection of air in a power generation cell housing. 35. The fuel cell according to claim 34, wherein the convection means is a fan for supplying air or oxygen to an oxidizer electrode of the fuel cell. 22. The fuel cell according to claim 21, wherein the heat transfer mechanism is realized by a flow of fuel. An electric device using the fuel cell according to any one of claims 1 to 36.

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