JP4777536B2

JP4777536B2 - Porous thermoelectric generator

Info

Publication number: JP4777536B2
Application number: JP2001146886A
Authority: JP
Inventors: 三千郎小堤
Original assignee: オパーツ株式会社
Priority date: 2001-05-16
Filing date: 2001-05-16
Publication date: 2011-09-21
Anticipated expiration: 2021-05-16
Also published as: JP2002345271A

Description

【０００１】
【産業上の利用分野】
本発明は、異種の金属板または金属箔を積層した多孔体中でのガス燃焼による温度勾配を利用したガス燃焼型の多孔体熱電発電素子に関する。
【０００２】
【従来の技術】
原子力発電は放射性廃棄物等の問題を抱え、一部の先進国では廃止の方向にあり、さらにエネルギーの有効利用を図るため、大規模集中型発電から送電ロスのない小型分散型の発電装置の必要性も強くなっている。また、大都市での健康への影響さらに地球環境への影響を配慮して排気ガスの少ない電気自動車の開発が急がれている。こういった状況の中で、幾多の発電方式が提案され、開発されており、最近では電気自動車・分散発電装置用途として燃料電池の開発も進んでいる。しかし水素と酸素の反応を直接利用する燃料電池は、燃料が水素に限られるため、メタン・エタン等の天然ガス，ＬＰＧ等の燃料ガス，ガソリン等の石油製品を直接使用できず、別途のエネルギーを投入して水素に変換（改質）する必要がある。
【０００３】
一方、異種の金属または半導体を二ヶ所で接続し、二ヶ所の接点に温度差を与えると、ゼーベック効果によって起電力が発生し、電流が流れる。この現象を利用して熱を電気に直接変換する発電装置は、熱の発生源ならばメタン・エタン等の天然ガス，ＬＰＧ等の燃料ガス，アルコール，ガソリン等の石油製品を直接使用でき、さらにエンジン式発電機等に比べ、設備構成がシンプルであり可動部分がないので、耐久性がある，騒音が少ない，保守が容易，小型に作れる等の長所を持っている。
【０００４】
そのため、熱電変換効率の高い素材の研究が永年行われているが、未だに宇宙等特殊用途分野で利用されるだけで工業用や民生用にはほとんど利用されていない。その理由は、起電力（熱電能）の高い組み合わせの材料の例では、ＰｂやＴｅ，Ｂｉ，Ｓｂ等のように低融点であったり、毒性が強かったりで使いにくい材料が多いため等が考えられる。その上、接続された二ヶ所（高温接点及び低温接点）の温度差を効率よく発生させるため熱伝導率が低い必要があり、発生した起電力を外部に取出すためには、逆に電気伝導率が高い必要がある、と言う材料にとって相矛盾する性質が要求される。永年の研究にもかかわらず高起電力，低熱伝導率，高電気伝導率で、環境に優しく、低コストの材料はなかなか見つかっていないといえる。
【０００５】
一方、超断熱効果をもつ通気性の多孔体内でのガス燃焼によって発生する温度勾配を利用する熱電発電が提唱された。この考え方によれば、温度勾配は投入する熱量と物質の熱伝導率によって決まるものではなく、多孔体としての超断熱性能によって決まる。そこで、本発明者は特殊な素材を用いず、一般的な材料である熱電対用等の起電力をもつ組合せの金属を用いた多孔体の超断熱効果を利用して発電を行うことのできる熱電発電素子を発明し、特開平８−２５１９５７号公報で紹介した。
【０００６】
この熱電発電素子は、熱電対の関係にある２種の金属箔の縦横方向に波型を形成すると共に開孔を設け、この金属箔をツヅラ折状に互い違いに接続・積層し、全体として通気性の多孔体とした素子である。ガスをこの多孔体内に導き、通過・燃焼させることによって、多孔体内に超断熱効果による温度勾配を発生させ、ツヅラ折状に接続した熱電対材料の両端から電力を取出す。また、通常は自燃しないような、塗装工場等から排気される希薄な可燃ガスを含んだ気体を助燃ガスを要せずに燃焼させることが出来る、往復燃焼排気処理装置に利用できることも多孔体内の超断熱効果を利用した燃焼方式の利点である。
【０００７】
この方式によれば、発生する温度差又は温度勾配は原理的に、高温側接合部に供給される熱量と材料の熱伝導率のみによって決まるものではなく、多孔体を構成する固体表面の局部的な熱吸収率や多孔体を構成する固体と気体（ガス）との熱交換効率、また輻射熱の通りにくさ等に支配される多孔体としての性能（超断熱効果を効率よく起こす性能）によって決まる。多孔体の性能さえ良ければ、投入した熱量と熱電材料の熱伝導率のみによって決まる従来の熱電発電システム以上の温度勾配が得られるので、採用できる材料の自由度が高くなる。すなわち、素材として、Ｆｅ，Ｎｉ，Ｃｒ，Ａｌ，Ｃｕ等といった熱伝導率の高い金属又はこれらの合金も使用可能となり、これらの金属又は合金は毒性も弱く、歴史が永く十分熟しきった製造・加工技術を適用することができる。
【０００８】
前記公報でも紹介した越後教授らの論文Int.J.Mass.Transfer., vol.36, No.13, pp.3201-3209(1993)によれば、燃焼熱を閉じこめる多孔体の超断熱効果は、多孔体の性能としての放射の自由行路が短いほど高くなり、大きい温度勾配が得られる。すなわち、ガスの燃焼により発生した熱量が高温のガスから発する熱放射により温度の低い方向へ移動するのを、近傍の固体が吸収することにより阻止し、温度の低い方向から流れてくるガスに固体−気体間の接触による熱伝導によりその熱量を与えることで、燃焼熱量と多孔体を構成する固体の熱伝導で決まる温度勾配以上の温度勾配が得られる。
【０００９】
このとき、高温のガスから温度の低い方向へ熱放射により熱量が移動する距離が短いほど、また固体が放射熱を吸収し易いほど、また固体から気体へ熱量が移動しやすいほど、小さい空間に局部的に熱量が保存されて温度が上がり、温度勾配が高くなる。すなわち高い超断熱効果が得られる。同時に温度の低い方向から流れて来たガスは、固体から熱量を貰って十分に加熱され燃焼温度に達する。温度勾配が大きければ、短い距離で大きい温度差が得られ熱電発電体の内部抵抗は低くなり起電力は大きくなるため発電効率が高くなる。
【００１０】
上記の発電方式は超断熱効果を利用したものであるため、発電多孔体はその多孔体内で熱の放射の自由行路が出来るだけ短くなるように設計・製作をする。多孔体の内部構造としての観点からは、放射の自由行路は、多孔体内のある点からある方向を見たとき、見通せる距離が短く断面積が少ないほど短いと言える。見通せる断面積が多い（放射の自由行路が長い）と、それだけ遠くまで放射熱が伝わってしまうので超断熱効果が低くなり温度勾配が得られない。見通せる距離が短く、見通せる断面積が少ない（放射の自由行路が短い）と、温度の低い方向に放射された輻射熱は直ちに近傍の多孔体を構成する固体に吸収され、温度の低い方向から流れてきた気体に接触による熱伝導で熱を与える。
【００１１】
【発明が解決しようとする課題】
本発明は、前記特開平８−２５１９５７号公報に紹介した、数々の長所をもつ金属箔を用いた多孔体熱電発電素子をその基本原理に基づいて詳細に検討し、発電効率（熱電変換効率）を高めた発電素子を提供することを目的とする。
【００１２】
【課題を解決するための手段】
すなわち、本発明では、前記熱電発電素子を構成する金属又は合金の箔の表面の熱吸収率及び金属又は合金の箔と気体との熱交換率を高くすることで温度勾配を高くし、さらに、熱電発電素子内でガス流動方向と直角の方向の温度を均一にし、外部に取出せない無効な電流成分を抑制するような多孔体の構造・形状とすることにより、発電効率を向上する事を目的とする。
【００１３】
本発明の多孔体熱電発電素子は、上記目的を達成するため、熱電対の関係にある２種の金属又は合金の箔を積層し、第１の金属又は合金の箔の一端を隣合う第２の金属又は合金の箔の一端に接合することにより多数の直列接続された熱電対をツヅラ折状に構成し、接合部以外の個所で第１の金属又は合金の箔と第２の金属又は合金の箔とを電気的に絶縁し、燃焼ガスが通過する複数の細孔が第１及び／又は第２の金属又は合金の箔に穿設され、第１及び／又は第２の金属又は合金の箔の表面に放射熱吸収率の高い耐熱性皮膜が設けられてなり、前記２種の金属又は合金の箔の少なくとも一方に、後述するような縦横方向の波型が異なる形状で形成されている。前記金属又は合金の箔の表面に形成された放射熱吸収率の高い耐熱性皮膜は、高温の燃焼ガスから輻射される放射熱をよく吸収するため超断熱効果を高める。
【００１４】
熱電対の関係にある２種の金属又は合金の箔を積層し、第１の金属又は合金の箔の一端を隣合う第２の金属又は合金の箔の一端に接合することにより多数の直列接続された熱電対をツヅラ折状に構成し、接合部以外の個所で第１の金属又は合金の箔と第２の金属又は合金の箔とを電気的に絶縁し、燃焼ガスが通過する複数の細孔が第１及び／又は第２の金属又は合金の箔に穿設され、ガス流動方向に直角な方向に沿った放射の自由行路がガス流動方向に沿った放射の自由行路よりも長くし、前記２種の金属又は合金の箔の少なくとも一方に、後述するような縦横方向の波型が異なる形状で形成されるようにすることも、ガス流動方向に直角な方向に沿った温度分布を均一にするため接合部での無効電流を抑制し、発電効率を向上できる。
【００１５】
前記２種の金属又は合金の箔の少なくとも一方には、縦横方向の波型が異なる形状で形成されるが、そのような構造では、放射の自由行路の長さを波型の振幅や周期で調整できる。すなわち、ガス流動方向と直角な方向の波型の振幅をガス流動方向の波型の振幅より小さくし、及び／又はガス流動方向と直角な方向の波型の周期をガス流動方向の波型の周期より大きくなるようにすればよい。
【００１６】
前記縦横方向の波型の形成に際しては、表面に設けられた複数の突起が等ピッチで１列ごとに交互に整列するようになっている２個のロールを用い、金属又は合金の箔材を、前記複数の突起が前記金属又は合金の箔材の表裏から交互に突き刺さるように、前記２個のロールの間に通すことにより、前記金属又は合金の箔に細孔の形成と同時に波型が縦横方向異なる形状に形成される。前記の場合において、前記２個のロール表面に設けられた複数の突起の間に小突起を整列して配置すれば、前記金属又は合金の箔における大きい波型の間に小さい波型が形成された状態になって、箔と気体との熱交換効率が上がる。
【００１７】
また、前記２種の金属又は合金の箔の少なくとも一方の表面上に、ガス流動方向と直角な方向に長い形状の突出部を設けることによって、ガス流動方向と直角な方向の放射の自由行路を短くすることなく、ガス流動方向の放射の自由行路を短くすることもでき、さらに前記突出部が通気性の多孔体素材でできていれば、さらに気体と固体の熱交換がしやすくなり、多孔体熱電発電素子としての性能を向上できる。
【００１８】
【作用】
本発明者は、前記特開平８−２５１９５７号公報に紹介された熱電発電素子の発電効率を高める方法について鋭意検討を重ねた。なお、本明細書では金属又は合金の薄板を一般に箔又は金属箔と称し、その厚みに制限が与えられているものではない。
前記公報に紹介された技術に基づき、図１（ａ）に示すように、縦横方向に波型に形成された厚み５０μｍ程度のアルメル（Ｎｉ＋２％Ａｌ合金）の箔Ａ及びクロメル（Ｎｉ＋１０％Ｃｒ合金）の箔Ｂを、高温側接合部２Ｈ及び低温側接合部２Ｌで交互に接続し、空気中で加熱することにより金属箔Ａ，Ｂの表面に絶縁膜を形成し、全体として多孔体ブロックを成す状態にし、ツヅラ折状の両側にあたる低温側接合部２Ｌに取り出し電極３を接続し、発電素子１を作成した。
【００１９】
作成した発電素子１を、図１（ｂ）に示すように石英ガラス製の燃焼器１０（内寸法：４×４ｃｍ）にセットした。発電素子１と燃焼器１０の間にはアスベスト等の耐熱材を挟んだ。ＬＰＧと空気をそれぞれ、送気口１１，１２に送り込み、発電素子１を燃焼ガスが通過したところで点火し、その後ＬＰＧと空気の送入量を調節すると炎は次第に後退し、ＬＰＧは多孔体内で燃焼するようになり、その状態で発電が起きた。無負荷状態で開放電圧Ｅｏを測定し、出力端子を短絡して短絡電流Ｉｏを測定し、内部抵抗Ｒｉ＝Ｅｏ／Ｉｏから最大取り出し電力Ｐ＝Ｅｏ²／Ｒｉを計算した。
【００２０】
従来方法で作成された発電素子１の箔表面は、加熱により絶縁膜（酸化クロム等の酸化物）が形成され、加熱前の金属光沢を多少失っていたが、なお高い光反射率をもっていた。そこで、水で擦った書道用の墨を箔に塗布・乾燥して実験したところ、燃焼開始初期には可燃成分（ニカワと考えられる）が燃焼して煙が発生したが、出力は約２５０ｍＷと従来の１．２５倍となった。多孔体を形成する箔の表面に炭素粒子（スス）が付着して放射熱を吸収しやすくなり、温度勾配が大きくなり出力が上昇したものと考えられる。実用的には、炭素粒子付着の外、金属酸化物，セラミックス等の耐熱黒色顔料、理想的にはゴールドブラック（最も完全黒体に近い）等を適宜の手段で箔の表面に付着させる。
【００２１】
さらに、実験を進めるうちに、箔表面の変色状態等から図２（ａ）に等温線で示すような箔の面内温度分布があることがわかった。すなわち、１枚１枚の箔の面内で燃焼器１０に近い両側の温度が低く、中央での温度が高くなって、水平方向の温度不均一性が生じていると推測された。これは、断熱材を介して燃焼器１０に接している多孔体の両側で石英ガラスへの熱伝導により熱が逃げてしまっているのが主原因と考えられる。
【００２２】
図２（ａ）に示すような箔の面内温度分布があると、高温側接合部２Ｈの領域で温度差が発生し、温度差による発電電流は温度勾配に沿って高温側接合部２Ｈの領域部分のみに流れ、外部に取り出せない無効電流Ｉとなってしまう（図２ｂ）。低温側接合部２Ｌの領域部分でも同様に温度差ができ、外部に取り出せない無効電流が発生する。その結果、全体として外部に取り出し可能な電流は高温側接合部２Ｈの最も低温の部分（端部）と低温側接合部２Ｌの最も高温の部分（中央部）との温度差に基づく電流になってしまう。すなわち、水平方向の温度分布（温度不均一性）は、発電効率を大きく低下させる原因となる。このことは、金属多孔体と燃焼器の間に断熱材を設けることによりこの水平方向の温度分布をある程度解消でき、発電効率に一定の効果が認められたことからも伺える。
【００２３】
本発明者は、本発電方式の基本原理に戻って、多孔体発電素子としての性能向上を検討した結果、発電効率の向上のためガス流方向にはできるだけ急峻な温度勾配が必要なので放射の自由行路をできるだけ短くする必要があるが、それに直角な方向には逆に熱伝導が促進されるように放射の自由行路をできるだけ長くするように、多孔体の構造を構成することに思い至った。
【００２４】
放射の自由行路とは前述のように、多孔体を構成する固体物質の気体との熱交換効率や輻射熱の吸収係数等の材料物性によっても左右されるが、構造・形状的な要因としては、一般に多孔体のある位置からある方向を眺めたとき、多孔体内の空隙部分を通して見通しにくい場合には短く、よく見通せる場合には長いと理解できる。したがって、本発明の発電多孔体では、ガス流動方向に直角な方向によく見通せるようにすることで放射の自由行路を長くし、この方向の温度分布（温度差）を少なくする。金属箔の面内で、このガス流動方向に直角な方向の温度分布（温度差）を少なくすることによって、高温側接合部２Ｈや低温側接合部２Ｌの内部に流れる無効電流を抑制し、ガス流方向のみの温度分布から外部に効率的に電流を取り出せるようにできる。
【００２５】
このような多孔体特性の異方性を、例えばセラミック粒子等の焼結多孔体等で実現しようとすると非常に困難であることが予想できるが、機械加工等で一定の形状を付与された金属箔を積層することで多孔体を構成する本発明の方式においては比較的容易である。
【００２６】
すなわち、図３に示したように、金属箔Ａ，Ｂを波型加工する際、ガス流動方向には金属箔の波型形状の振幅を大きくし、ガス流動方向と直角な方向には波型形状の振幅を小さくする（図３では簡単のため、ガス流動方向と直角な方向に振幅ゼロつまりガス流動方向Ｇのみに波型を付けた例を示している）。すると、ガス流動方向には放射の自由行路が短くなり、ガス流動方向に直角な方向には放射の自由行路が長くなる。そのため、ガス流動方向には温度差が発生しやすく、ガス流動方向に直角な方向には温度差が発生しにくくなる。同様の効果は、ガス流動方向には金属箔の波型形状の周期を小さくし、ガス流動方向と直角な方向には波型形状の周期を大きくすることでも得られる。
【００２７】
この効果は、図４（ａ）に示すように、金属箔Ａ，Ｂの表面に熱伝導性の良いセラミック等の素材で、ガス流動方向に直角な方向に細長い突出部Ｔを設けることでさらに効果的になる。勿論、突出部Ｔを設ける場合、金属箔Ａ，Ｂを波型加工せず平板を用いても（図４ｂ）、金属箔Ａ，Ｂの積層体は本発明に従った多孔体になる。すなわち、図５（ａ）で判るように、ガス流動方向Ｇには放射の自由行路は短くなる。ガスそのものは矢印ｇで示すように、突出部Ｔの間隙を、突出部Ｔに衝突・熱伝導を繰返しながら、乱流状態で多孔体内をガス流動方向Ｇに通過する。ガス流動方向に直角な方向Ｈには、図５（ｂ）に断面図を示すようによく見通せるため、放射の自由行路が長くなる。勿論、完全に見通せなくても見通せる距離が長ければよい。
【００２８】
該突出部Ｔは、気体との熱交換の容易なように、突出部Ｔ自体が、例えばスポンジ状の通気性の多孔体であることが好ましい。さらに、該突出部が絶縁体であれば隣接する箔同士の電気絶縁を確保するための箔表面上の絶縁膜形成の必要が無く、また突出部Ｔの高さで決まる金属箔同士の間隔（開孔）を安定にする。
【００２９】
【実施の形態】
本発明の発電素子は例えば、前記のように熱電対の関係にあるアルメル及びクロメルの金属箔Ａ，Ｂを用いる。アルメル及びクロメルはＮｉ基合金であり、耐熱性，耐久性は高く、燃焼反応に際しての触媒作用も期待できる。アルメル及びクロメル以外にも、鉄及びコンスタンタン（銅合金）等が考えられるが、温度計測用のように温度・起電力間の直線性は必要でないので、温度計測用に比べ熱電対材料の選択自由度は高い。動作温度や起電力，耐久性，コストなどを勘案して最適な材料が選択される。
【００３０】
金属箔Ａ，Ｂの表面に塗布又は付着される放射熱吸収率の高い耐熱性皮膜の形成方法には、箔材料に応じて高温酸化や薬品による表面処理・化学処理や、炭素粒子，金属酸化物等の耐熱性黒色顔料等を塗装等により付着させる方法がある。
塗装は、浸漬，ロールコーティング，スピンコーティング，吹き付け等が採用可能である。
箔の材質によっては、例えば適当な露点に調整された水蒸気雰囲気中、処理温度：５００℃程度、均熱時間：数１０分程度の熱処理で表面を黒化することもできる。鉄基合金の場合は、いわゆる黒さびを表面に形成するとよい。
【００３１】
炭素粒子の場合、発電時の温度レベルや酸化雰囲気等によっては燃えてしまって損耗することが考えられる。この点、耐熱性の無機顔料等が適当である。放射熱吸収率の高いものは一般的には黒色であるが、放射熱（赤外〜遠赤外線）を吸収する限り、白色でも採用可能である。放射熱の吸収性から言えば、窒素雰囲気中で金を加熱蒸着することにより得られる金黒（ゴールドブラック）を付着させるのが最も好ましい。
放射熱吸収率の高い耐熱性皮膜の形成は、金属箔の形状加工前に行ってもよいが、加工による皮膜の脱落等を避けるため、形状加工後に行うのがよい。
【００３２】
金属箔Ａ，Ｂに付けられる波型の形状は、ガス流動方向の超断熱性能の観点から、気体との接触面積を大きくするため金属箔の厚みは出来るだけ薄くして枚数を多くし、ガス流動方向に放射の自由行路（見通せる距離）を短くするため、金属箔Ａ，Ｂにつけられる波型の周期は出来るだけ小さく、波型の振幅は大きくするのが良い。そのうえで、ガス流動方向に直角な方向には放射の自由行路が長くなるように、波型をつけないか、適宜波型の周期を大きく、振幅を小さくする。
【００３３】
このような波型を形成する方法のひとつに、周面にスパイク状の鋭い突起Ｓａ，Ｓｂを備えた２個のロールＲａ，Ｒｂの間に帯状の箔材Ｗを通す方法がある（図６）。この方法によると、箔材Ｗは表裏反対方向から突起Ｓａ及びＳｂにより変形し，同時に穿孔されるので、金属箔に要求される細孔と波型を同時に付けることが出来る。この突起Ｓａ，Ｓｂの間隔，配置を変えることにより金属箔の形状を変化させることが出来る。すなわち、縦横等ピッチで、突起Ｓａ，Ｓｂを通板方向Ｒに１列ごとに互い違いに整列（図７ａ）させると、縦横両方向に略同形の波型がつけられる。突起Ｓａ，Ｓｂを通板方向Ｒに直角な方向に１列ごとに並べた配置（図７ｂ）では通板方向Ｒに直角な方向の波型の振幅が大きくなる。図７（ｃ）のように配置すると通板方向Ｒの波型の振幅が大きくなる。図７（ｄ）のように通板方向Ｒに直角な方向のピッチＰｌを通板方向のピッチＰｈより大きくすれば、この方向の波型の周期を大きくし、振幅も小さく出来、細孔の数も減らせる。
【００３４】
波型と同時に穿孔される細孔は、周囲にバリが残される状態になるので、気体との接触面積が増え気体の乱流が発生し、気体・固体間の熱交換効率が高くなる。突起Ｓａ，Ｓｂによる金属箔に付けられる凹凸は互いに逆になり、バリの出る方向も互いに逆になる。穿孔により金属箔の全体としての電気抵抗が上がるが、電気抵抗が上がることを極力防ぐため、例えば突起Ｓａ，Ｓｂの高さを一つおきに低くすること等で、細孔のサイズを変えたり、突起Ｓａ，Ｓｂの低いところでは穿孔せず凹凸のみを付けることも可能である。
【００３５】
気体に乱流を起こさせ、気体との接触面積を大きくするため、金属箔の表面が細かい凹凸を有するとさらに好ましい。突起Ｓａ，Ｓｂの間に小突起Ｓｓを多数設ければ（図７ｅ）、細孔を伴う主たる波型の間にさざなみ状の形状をもった断面（図７ｆ）が形成される。
このように、この加工方法では２個のロールＲａ，Ｒｂのスパイク状の鋭い突起Ｓａ，Ｓｂのロール面上の配置や高さを適宜変えたり、またロールＲａ，Ｒｂ間の距離を変えることにより、金属箔に付けられる波型が調整でき、ひいては発電多孔体の性能を調整できる。加工技術にもよるが現状では、金属箔の厚み：５０μｍ程度，波型の周期（スパイクの間隔で決まる）・振幅：各１ｍｍ前後が現実的である。
【００３６】
ガス流動方向の波型の付いた金属箔Ａ，Ｂの組合せは、図８（ａ）に示すように位相を一にして組合せても良いし、図８(ｂ)のように位相を１８０度ずらせ、波型の山部と山部を付合わせても良い。図８（ａ）の場合は、金属箔Ａ，Ｂの間隙を確保する意味でも、前記突出部Ｔをスペーサを兼ねて設けるのが好ましい。
図８(ｂ)の場合にも、付合わせられる波型の山部同士で電気的な短絡が発生しやすいので、絶縁を兼ねて前記突出部Ｔを設けるのが好ましい。この場合、山部の付合わせ部分でガス流れを確保するように突出部には適宜、切れ目が設けられる。図８(ｃ)のように、金属箔Ａ，Ｂに付けられる波型を適宜傾斜させ、金属箔Ａ，Ｂをそれぞれ波型の傾斜が反対方向になるように組合せると、各波型の山部の付合わせ部分が、図８(ｄ)のようにポイントｐとなり、このポイント以外の部分ではガス流が確保でき、同時に金属箔Ａ，Ｂ同士の間隔も確保できる。
【００３７】
以上のように準備されたアルメル及びクロメルの金属箔Ａ，Ｂは、定寸に切断され図３のように、それぞれ上端および下端が溶接，ロウ付け等の適宜の手段で、互い違いにツヅラ折状に接続される。低温側接合部２Ｌ，２Ｌ，．．のツヅラ折状の最両端に、ニッケル帯等の取出し電極３，３が接続される。必要に応じて酸化処理により金属表面に絶縁膜が形成され、本発明に従った発電素子となる。
【００３８】
熱電対の金属箔Ａ，Ｂ上に設けられる突出部Ｔは、金属箔Ａ，Ｂと同様に気体との熱交換が良いようにスポンジ状で通気性があり、熱伝導性に富み、放射熱吸収率のよい素材が好ましく、Ｗ，Ｍｏ，Ｔｉ等の高融点金属やシリカ，アルミナ，サファイア，炭化ケイ素，窒化珪素等のセラミックス材料及びこれらの混合物が考えられる。これらの粉末や繊維の焼結・圧着等により金属箔Ａ，Ｂ上に形成される。突出部Ｔの形成には、半導体の微細加工技術，機械の精密加工技術等も採用できる。勿論、突出部Ｔの表面を放射熱吸収率の高い耐熱性皮膜で覆うこともできる。
【００３９】
放射の自由行路を小さくするため突出部Ｔのガス流動方向の幅・配置ピッチは小さいほど良いが、加工・成型技術にもより、０．１〜数ｍｍ程度が現実的である。突出部Ｔのガス流動方向に直角方向の長さは、発電素子のガス流動方向の通気性（低圧損）が確保できる範囲で長いほど良い。
【００４０】
このように作成された多孔体熱電発電素子は通気性であり、低温側接合部２Ｌ側から高温側接合部２Ｈに向けて混合可燃ガスを導入し、多孔体内で燃焼させると、高温側接合部２Ｈは燃焼熱によって加熱され、低温側接合部２Ｌは続けて補給される低温（常温）の可燃ガスによって冷却される。逆に可燃ガスは多孔体内を移動するうちに加熱され、燃焼領域に到達する時点では十分に温度が上がってスムーズな燃焼反応が起きる。結果として低温側接合部２Ｌと高温側接合部２Ｈとの間に急峻な温度勾配が発生し、ツヅラ折り状に構成され多数の熱電対が直列接続された多孔体の両取出し電極から、高い効率で電力が取り出せる。
【００４１】
実際の装置では、燃焼済みの高温排気ガスは熱の有効利用の観点から、湯を沸かす等の仕事をさせることも考えられる。しかし、発電装置として発電効率向上の観点からは、燃焼済みの高温排気ガスは、排気側に対向配置された第２の多孔体熱電発電素子又は超断熱多孔体を通して排気するのが好ましい。この時、排気ガスはこの多孔体に熱量を伝達して冷却されてから大気に開放されるので、この配置により両多孔体の間の空間は高温に維持される。さらには、前掲の越後教授の論文に紹介されたような、往復燃焼システムとすることも考えられる。
なお、この発電素子を用いた発電装置の最初の予備加熱は、前記実験のようにガスに点火した後、ガス量を調整してもよいが、この多孔体に外部から電流を流してやることで容易に多孔体を加熱できる。
【００４２】
【発明の効果】
本発明の多孔体熱電発電素子は、以上に説明したように多孔体を構成する金属箔の表面を放射熱吸収率の高い耐熱性皮膜で覆っている。そのため、ガス流動方向に温度勾配がつきやすく、高い起電力が得られる。また、多孔体の放射の自由行路をガス流動方向に直角の方向には長く設定し、ガス流動方向には短く設定するとき、ガス流動方向に直角の方向には温度の均一性が図られるため、接合部分での無効電流を抑制する。発生した急峻な温度勾配を有効利用できるので発電の効率を向上させることが可能となる。
この発電方式によれば、アルコール，メタン，エタン等の燃料を直接利用でき燃料電池等のように燃料の改質の必要もない。さらに、超断熱効果を利用するため、例えば塗装工場等から排出される希薄燃焼ガスを別途の助燃ガスを必要とせず燃焼できる往復燃焼排気処理装置にも適用できる。
【図面の簡単な説明】
【図１】は多孔体熱電発電素子の従来例（ａ）及び多孔体熱電発電素子を用いた発電実験装置（ｂ）。
【図２】は従来の多孔体熱電発電素子を用いた発電時の金属箔の温度分布を等温線で示した図（ａ）及び高温側接合部内で発生する無効電流を説明する断面図（ｂ）。
【図３】は本発明に従った一実施例。
【図４】は本発明に従った他の実施例。
【図５】は本発明の突出部の作用を説明する図。
【図６】は金属箔に波型を付ける方法の一例。
【図７】はロール上でのスパイク状突起の配置例を示す図（ａ〜ｅ）及び波型を付けた金属箔の断面図（ｆ）。
【図８】はガス流動方向のみに波型を付けた金属箔Ａ，Ｂの突合せ方法を示す図（ａ，ｂ）及び波型の方向をわずかに傾斜させた金属箔Ａ，Ｂを示す図（ｃ，ｄ）。
【符号の説明】
１：発電素子
２Ｈ：高温側接合部
２Ｌ：低温側接合部
３：取り出し電極
１０：燃焼器
１１，１２：送気口

Ａ，Ｂ：熱電対の関係にある２種の金属の箔
Ｔ：突出部
ｇ：ガス
Ｇ：ガス流動方向
Ｈ：ガス流動方向に直角な方向
Ｒａ，Ｒｂ：ロール
Ｓａ，Ｓｂ：スパイク状突起
Ｗ：箔材
Ｒ：通板方向
Ｐｈ：通板方向のピッチ
Ｐｌ：通板方向に直角な方向のピッチ
ｐ：各波型の山部の付合わせ部分（ポイント） [0001]
[Industrial application fields]
The present invention relates to a gas combustion type porous thermoelectric power generation element using a temperature gradient due to gas combustion in a porous body in which different types of metal plates or metal foils are laminated.
[0002]
[Prior art]
Nuclear power generation has problems such as radioactive waste, is being abolished in some developed countries, and in order to make more efficient use of energy, a large-scale centralized power generation is a small distributed power generation system with no transmission loss. The need is getting stronger. In addition, there is an urgent need to develop an electric vehicle with less exhaust gas in consideration of the impact on health in large cities and the impact on the global environment. Under such circumstances, a number of power generation methods have been proposed and developed, and recently, fuel cells are being developed for use in electric vehicles and distributed power generation devices. However, fuel cells that directly use the reaction between hydrogen and oxygen are limited to hydrogen, so natural gas such as methane and ethane, fuel gas such as LPG, and petroleum products such as gasoline cannot be used directly. Must be converted to hydrogen (reform).
[0003]
On the other hand, when different metals or semiconductors are connected at two locations and a temperature difference is given to the two contacts, an electromotive force is generated due to the Seebeck effect and current flows. A power generator that directly converts heat into electricity using this phenomenon can directly use natural gas such as methane and ethane, fuel gas such as LPG, petroleum products such as alcohol and gasoline, etc. Compared to engine generators, etc., the equipment configuration is simple and there are no moving parts, so it has advantages such as durability, low noise, easy maintenance, and small size.
[0004]
For this reason, research on materials with high thermoelectric conversion efficiency has been carried out for many years, but they are still used only in special fields such as space and are hardly used for industrial or consumer use. The reason is that in the case of materials with high electromotive force (thermoelectricity), there are many materials that have a low melting point, such as Pb, Te, Bi, Sb, etc., or are highly toxic and difficult to use. It is done. In addition, the thermal conductivity needs to be low in order to efficiently generate the temperature difference between the two connected places (high temperature contact and low temperature contact), and in order to extract the generated electromotive force to the outside, the electrical conductivity is reversed. For materials that need to be high, conflicting properties are required. Despite many years of research, it has been difficult to find materials that are high in electromotive force, low thermal conductivity, high electrical conductivity, and are environmentally friendly and low in cost.
[0005]
On the other hand, thermoelectric power generation using a temperature gradient generated by gas combustion in a breathable porous body having a super-insulating effect was proposed. According to this concept, the temperature gradient is not determined by the amount of heat input and the thermal conductivity of the substance, but by the super-insulation performance as a porous body. Therefore, the present inventor can generate power using the super-insulating effect of a porous body using a combination metal having an electromotive force such as for a thermocouple which is a general material without using a special material. A thermoelectric generator was invented and introduced in JP-A-8-251957.
[0006]
This thermoelectric power generation element forms corrugations in the vertical and horizontal directions of two types of metal foils that are related to thermocouples, and is provided with openings, and the metal foils are alternately connected and stacked in a spiral shape to ventilate as a whole. It is an element made of a porous material. A gas is introduced into the porous body, passed, and burned to generate a temperature gradient due to the super-insulating effect in the porous body, and electric power is taken out from both ends of the thermocouple material connected in a spiral shape. In addition, it can be used in a reciprocating combustion exhaust treatment device that can burn a gas containing a lean combustible gas exhausted from a paint factory or the like that normally does not self-combust without requiring an auxiliary combustion gas. This is an advantage of the combustion method using the super-insulation effect.
[0007]
According to this method, the generated temperature difference or temperature gradient is not determined solely by the amount of heat supplied to the high-temperature side joint and the thermal conductivity of the material, but is locally determined by the solid surface forming the porous body. It is determined by the heat absorption rate, the heat exchange efficiency between the solid and gas (gas) constituting the porous body, and the performance as a porous body governed by the difficulty of the radiant heat (the ability to efficiently generate the superadiabatic effect) . As long as the performance of the porous body is good, a temperature gradient higher than that of a conventional thermoelectric power generation system determined only by the amount of heat input and the thermal conductivity of the thermoelectric material can be obtained. That is, as a material, metals having high thermal conductivity such as Fe, Ni, Cr, Al, Cu, etc., or alloys thereof can be used. These metals or alloys have low toxicity and have a long history and are fully ripe. Processing techniques can be applied.
[0008]
According to Int. J. Mass. Transfer., Vol.36, No.13, pp.3201-3209 (1993), which was also introduced in the above-mentioned publication, the super-insulation effect of the porous body that traps the heat of combustion is The shorter the free path of radiation as the performance of the porous body, the higher, and a large temperature gradient can be obtained. That is, the amount of heat generated by the combustion of the gas is prevented from moving in the direction of lower temperature by the heat radiation emitted from the hot gas by the absorption of the nearby solid, and the gas flowing from the direction of lower temperature is solid. -By providing the amount of heat by heat conduction by contact between gases, a temperature gradient greater than the temperature gradient determined by the amount of combustion heat and the heat conduction of the solid constituting the porous body can be obtained.
[0009]
At this time, the smaller the distance that the amount of heat moves from the high-temperature gas to the lower temperature direction due to heat radiation, the more easily the solid absorbs radiant heat, and the more easily the amount of heat moves from the solid to the gas, the smaller the space. The amount of heat is stored locally, the temperature rises, and the temperature gradient increases. That is, a high super-insulation effect can be obtained. At the same time, the gas flowing from the direction of lower temperature reaches the combustion temperature by being sufficiently heated from the solid through the amount of heat. If the temperature gradient is large, a large temperature difference is obtained at a short distance, the internal resistance of the thermoelectric generator is lowered, and the electromotive force is increased, so that the power generation efficiency is increased.
[0010]
Since the above power generation method utilizes the super-insulation effect, the power generation porous body is designed and manufactured so that the free path of heat radiation within the porous body is as short as possible. From the viewpoint of the internal structure of the porous body, it can be said that the free path of radiation is shorter as the distance that can be seen from a certain point in the porous body is shorter and the cross-sectional area is smaller. If the cross-sectional area that can be seen is large (the radiation free path is long), the radiant heat is transmitted to that distance, so the superadiabatic effect is reduced and a temperature gradient cannot be obtained. If the distance that can be seen is short and the cross-sectional area that can be seen is small (the free path of radiation is short), the radiant heat radiated in the lower temperature direction is immediately absorbed by the solids that make up the nearby porous body and flows from the lower temperature direction. Heat is given to the gas by heat conduction by contact.
[0011]
[Problems to be solved by the invention]
In the present invention, a porous thermoelectric power generation element using a metal foil having a number of advantages introduced in JP-A-8-251957 is examined in detail based on its basic principle, and power generation efficiency (thermoelectric conversion efficiency) An object of the present invention is to provide a power generation element with improved resistance.
[0012]
[Means for Solving the Problems]
That is, in the present invention, the temperature gradient is increased by increasing the heat absorption rate of the surface of the metal or alloy foil constituting the thermoelectric power generation element and the heat exchange rate between the metal or alloy foil and the gas, The purpose is to improve the power generation efficiency by making the temperature and the direction perpendicular to the gas flow direction uniform in the thermoelectric power generation element and making it a porous structure and shape that suppresses invalid current components that cannot be extracted outside. And
[0013]
In order to achieve the above object, the porous thermoelectric power generation element of the present invention laminates two types of metal or alloy foils having a thermocouple relationship, and adjoins one end of the first metal or alloy foil. A large number of series-coupled thermocouples are formed in a spiral shape by joining to one end of the metal or alloy foil of the first metal or alloy, and the first metal or alloy foil and the second metal or alloy are provided at a place other than the joint. A plurality of pores through which combustion gas passes are formed in the first and / or second metal or alloy foil, and the first and / or second metal or alloy A heat-resistant film with a high radiant heat absorption rate is provided on the surface of the foil.And at least one of the two types of metal or alloy foils are formed in different shapes in the vertical and horizontal directions as described later..Of the metal or alloyThe heat-resistant film having a high radiant heat absorption rate formed on the surface of the foil absorbs the radiant heat radiated from the high-temperature combustion gas well, thereby enhancing the super-insulation effect.
[0014]
Multiple series connections by laminating two metal or alloy foils in a thermocouple relationship and joining one end of a first metal or alloy foil to one end of an adjacent second metal or alloy foil The thermocouple is configured in a fold-like shape, and the first metal or alloy foil and the second metal or alloy foil are electrically insulated at locations other than the joint, and a plurality of combustion gases pass through. The pores are drilled in the first and / or second metal or alloy foil, and the free path of radiation along the direction perpendicular to the gas flow direction is longer than the free path of radiation along the gas flow direction.And, at least one of the two kinds of metal or alloy foils is formed in different shapes in the vertical and horizontal directions as described later.Also, since the temperature distribution along the direction perpendicular to the gas flow direction is made uniform, the reactive current at the junction can be suppressed and the power generation efficiency can be improved.
[0015]
At least one of the two types of metal or alloy foils is formed in a shape having different vertical and horizontal corrugations. In such a structure, the length of the free path of radiation is reduced.It can be adjusted with the amplitude and period of the waveform. That is, the wave shape amplitude in the direction perpendicular to the gas flow direction is smaller than the wave shape amplitude in the gas flow direction.And / orThe wave period in the direction perpendicular to the gas flow direction may be made larger than the wave period in the gas flow direction.
[0016]
In forming the vertical and horizontal corrugations,Using two rolls in which a plurality of protrusions provided on the surface are arranged alternately at regular intervals for each row,Metal or alloy foil material, the plurality of protrusions areMetal or alloy foilMaterialAs you pierce from the front and back alternately,Said2 rollsofwhilePass throughBySaidSimultaneously with the formation of the pores in the metal or alloy foil, the corrugations are formed in different shapes in the vertical and horizontal directions.In the above case,If the small protrusions are aligned and arranged between the plurality of protrusions provided on the two roll surfaces,SaidFor metal or alloy foilCanA small wave shape is formed between the large wave shapes, and the heat exchange efficiency between the foil and the gas increases.
[0017]
Also, at least one of the two metal or alloy foilsOn the surface, in a direction perpendicular to the gas flow directionlongProviding a shape-shaped protrusionthingWithout shortening the free path of radiation in the direction perpendicular to the gas flow direction.,Shorten the free path of radiation in the gas flow directionthingCan alsoFurthermore,ProtrusionPartIf it is made of a breathable porous material, heat exchange between gas and solid is further facilitated, and the performance as a porous thermoelectric generator can be improved.
[0018]
[Action]
The inventor has intensively studied a method for increasing the power generation efficiency of the thermoelectric power generation element introduced in the above-mentioned JP-A-8-251957. In the present specification, a thin plate of metal or alloy is generally referred to as a foil or a metal foil, and the thickness thereof is not limited.
Based on the technique introduced in the above publication, as shown in FIG. 1 (a), a foil A and chromel (Ni + 10% Cr alloy) of about 50 μm thick alumel (Ni + 2% Al alloy) formed in a wave shape in the vertical and horizontal directions. ) Foil B is alternately connected at the high temperature side joint 2H and the low temperature side joint 2L, and heated in the air to form an insulating film on the surfaces of the metal foils A and B, and the porous body block as a whole. The power generation element 1 was created by connecting the take-out electrode 3 to the low-temperature side joints 2 </ b> L on both sides of the hook fold.
[0019]
The created power generation element 1 was set in a combustor 10 (internal dimensions: 4 × 4 cm) made of quartz glass as shown in FIG. A heat-resistant material such as asbestos was sandwiched between the power generation element 1 and the combustor 10. LPG and air are respectively sent to the air inlets 11 and 12 and ignited when the combustion gas passes through the power generation element 1, and then the flame gradually recedes when the LPG and air feed amount is adjusted. It began to burn, and power generation occurred in that state. The open circuit voltage Eo is measured in the no-load state, the output terminal is short-circuited, the short-circuit current Io is measured, and the maximum output power P = Eo is calculated from the internal resistance Ri = Eo / Io.²/ Ri was calculated.
[0020]
The foil surface of the power generating element 1 produced by the conventional method was formed with an insulating film (oxide such as chromium oxide) by heating and lost some metallic luster before heating, but still had high light reflectance. So, when we experimented by applying and drying calligraphy ink rubbed with water on the foil, combustible components (considered to be glue) burned at the beginning of combustion and smoke was generated, but the output was about 250 mW It became 1.25 times the conventional one. It is considered that carbon particles (soot) adhere to the surface of the foil forming the porous body and easily absorb the radiant heat, the temperature gradient increases, and the output increases. Practically, heat-resistant black pigments such as metal oxides and ceramics, ideally gold black (closest to the complete black body), and the like are adhered to the surface of the foil by appropriate means in addition to carbon particle adhesion.
[0021]
Further, as the experiment proceeded, it was found that there was an in-plane temperature distribution of the foil as shown by the isotherm in FIG. That is, it was estimated that the temperature on both sides close to the combustor 10 in the plane of each sheet of foil was low and the temperature at the center was high, resulting in temperature nonuniformity in the horizontal direction. The main cause of this is considered to be that heat escapes due to heat conduction to the quartz glass on both sides of the porous body that is in contact with the combustor 10 via the heat insulating material.
[0022]
When there is an in-plane temperature distribution of the foil as shown in FIG.HA temperature difference occurs in the region of, and the generated current due to the temperature difference follows the temperature gradient on the high temperature side junction 2.HThis results in a reactive current I that cannot be extracted outside (FIG. 2b). Low temperature side joint2LSimilarly, a temperature difference is generated in the region of, and a reactive current that cannot be taken out is generated. As a result, the current that can be taken out as a whole is the high-temperature side junction 2.HThe coldest part (end part) and the low-temperature side joint2LThe current is based on the temperature difference from the hottest part (center part). That is, the temperature distribution in the horizontal direction (temperature nonuniformity) causes a significant decrease in power generation efficiency. This is also because the horizontal temperature distribution can be eliminated to some extent by providing a heat insulating material between the porous metal body and the combustor, and a certain effect on the power generation efficiency has been recognized.
[0023]
The present inventor returned to the basic principle of the power generation method, and as a result of studying the performance improvement as a porous body power generation element, the steepest temperature gradient in the gas flow direction is necessary in order to improve the power generation efficiency. Although it is necessary to make the path as short as possible, the inventors have come up with the idea of constructing the porous structure so that the free path of radiation is as long as possible so that heat conduction is promoted in the direction perpendicular to it.
[0024]
As described above, the free path of radiation depends on material properties such as the heat exchange efficiency with the gas of the solid substance constituting the porous body and the absorption coefficient of radiant heat, but as structural and shape factors, In general, when looking in a certain direction from a certain position of the porous body, it can be understood that it is short when it is difficult to see through the voids in the porous body and long when it can be seen well. Therefore, in the power generation porous body of the present invention, the free path of radiation is lengthened by making it well visible in the direction perpendicular to the gas flow direction, and the temperature distribution (temperature difference) in this direction is reduced. By reducing the temperature distribution (temperature difference) in the direction perpendicular to the gas flow direction in the plane of the metal foil, the high-temperature side joint 2HAnd low temperature side joints2LIt is possible to suppress the reactive current flowing in the interior of the chamber and efficiently extract the current from the temperature distribution only in the gas flow direction.
[0025]
Such anisotropy of the characteristics of the porous material can be expected to be very difficult when trying to realize a sintered porous material such as ceramic particles, but a metal that has been given a certain shape by machining or the like In the method of the present invention in which the porous body is formed by laminating foils, it is relatively easy.
[0026]
That is, as shown in FIG. 3, when corrugating the metal foils A and B, the amplitude of the corrugated shape of the metal foil is increased in the gas flow direction, and the corrugation is performed in the direction perpendicular to the gas flow direction. The amplitude of the shape is reduced (in FIG. 3, for the sake of simplicity, an example is shown in which a waveform is attached only to the zero amplitude in the direction perpendicular to the gas flow direction, that is, the gas flow direction G). Then, the free radiation path becomes shorter in the gas flow direction, and the free radiation path becomes longer in the direction perpendicular to the gas flow direction. Therefore, a temperature difference is likely to occur in the gas flow direction, and a temperature difference is less likely to occur in a direction perpendicular to the gas flow direction. The same effect is that the period of the corrugated shape of the metal foil is reduced in the gas flow direction, and the period of the corrugated shape is increased in the direction perpendicular to the gas flow direction.thingBut you can get it.
[0027]
As shown in FIG. 4 (a), this effect is further achieved by providing an elongated protrusion T in the direction perpendicular to the gas flow direction with a material such as ceramic having good thermal conductivity on the surfaces of the metal foils A and B. Become effective. Of course, when the protrusion T is provided, even if the metal foils A and B are not corrugated and a flat plate is used (FIG. 4b), the laminate of the metal foils A and B becomes a porous body according to the present invention. That is, as can be seen in FIG. 5A, the free path of radiation is shorter in the gas flow direction G. As indicated by an arrow g, the gas itself passes through the porous body in the gas flow direction G in a turbulent state while repeatedly colliding and thermally conducting the projection T through the gap of the projection T. In the direction H perpendicular to the gas flow direction, as shown in the cross-sectional view of FIG. Of course, it is sufficient if the distance that can be seen is long even if it cannot be seen completely.
[0028]
It is preferable that the protrusion T itself is, for example, a sponge-like air-permeable porous body so that the heat exchange with the gas is easy. Furthermore, if the protrusion is an insulator, there is no need to form an insulating film on the foil surface to ensure electrical insulation between adjacent foils, and the distance between metal foils determined by the height of the protrusion T ( Stabilize the opening).
[0029]
Embodiment
The power generating element of the present invention uses, for example, the metal foils A and B of alumel and chromel that have a thermocouple relationship as described above. Alumel and chromel are Ni-based alloys, have high heat resistance and durability, and can be expected to have a catalytic action during a combustion reaction. In addition to alumel and chromel, iron, constantan (copper alloy), etc. can be considered, but the linearity between temperature and electromotive force is not required as in temperature measurement, so the thermocouple material can be freely selected compared to temperature measurement. The degree is high. The optimum material is selected in consideration of the operating temperature, electromotive force, durability, and cost.
[0030]
Depending on the foil material, high-temperature oxidation, chemical surface treatment / chemical treatment, carbon particles, metal oxidation can be used to form heat-resistant films with high radiant heat absorption rate that are applied to or attached to the surfaces of metal foils A and B. There is a method of attaching a heat-resistant black pigment such as an object by painting or the like.
Dipping, roll coating, spin coating, spraying, etc. can be used for painting.
Depending on the material of the foil, for example, the surface can be blackened by a heat treatment in a steam atmosphere adjusted to an appropriate dew point, with a treatment temperature of about 500 ° C. and a soaking time of about several tens of minutes. In the case of an iron-based alloy, so-called black rust may be formed on the surface.
[0031]
In the case of carbon particles, it may be burned and worn out depending on the temperature level during power generation, the oxidizing atmosphere, and the like. In this respect, heat-resistant inorganic pigments are suitable. A material having a high radiant heat absorption rate is generally black. However, as long as it absorbs radiant heat (infrared to far-infrared), white can be used. In terms of the absorption of radiant heat, it is most preferable to deposit gold black obtained by heating and depositing gold in a nitrogen atmosphere.
The heat-resistant film having a high radiant heat absorption rate may be formed before the shape processing of the metal foil. However, in order to avoid dropping of the film due to the processing, the heat-resistant film may be formed after the shape processing.
[0032]
The corrugated shape attached to the metal foils A and B is from the viewpoint of super-insulation performance in the gas flow direction, in order to increase the contact area with the gas, the thickness of the metal foil is made as thin as possible to increase the number of gas, In order to shorten the free path of radiation (visible distance) in the flow direction, it is preferable that the corrugated period applied to the metal foils A and B is as small as possible and the corrugated amplitude is increased. In addition, a wave shape is not added or the wave cycle is appropriately increased and the amplitude is decreased so that the free path of radiation becomes longer in the direction perpendicular to the gas flow direction.
[0033]
One method of forming such a corrugation is to pass a strip-shaped foil material W between two rolls Ra and Rb having spike-shaped sharp protrusions Sa and Sb on the peripheral surface (FIG. 6). ). According to this method, since the foil material W is deformed by the projections Sa and Sb from the opposite directions, and is simultaneously perforated, the pores and corrugations required for the metal foil can be attached at the same time. The shape of the metal foil can be changed by changing the interval and arrangement of the protrusions Sa and Sb. In other words, when the protrusions Sa and Sb are alternately arranged in the plate direction R every row at regular pitches in the vertical and horizontal directions (FIG. 7a), substantially the same wave shape is applied in both the vertical and horizontal directions. In the arrangement in which the protrusions Sa and Sb are arranged in a line in a direction perpendicular to the plate passing direction R (FIG. 7b), the waveform amplitude in the direction perpendicular to the plate passing direction R increases. If it arrange | positions like FIG.7 (c), the waveform amplitude of the sheet passing direction R will become large. As shown in FIG. 7D, the pitch Pl in the direction perpendicular to the sheet passing direction R is set toFrom pitch Ph in the plate directionIf it is increased, the wave period in this direction can be increased, the amplitude can be decreased, and the number of pores can be decreased.
[0034]
The pores that are drilled simultaneously with the corrugations are in a state where burrs are left around, so that the contact area with the gas increases, turbulence of the gas occurs, and the heat exchange efficiency between the gas and the solid increases. Concavities and convexities attached to the metal foil by the protrusions Sa and Sb are opposite to each other, and the direction in which burrs appear is also opposite to each other. Although the electrical resistance of the metal foil as a whole is increased by perforation, in order to prevent the electrical resistance from increasing as much as possible, for example, the heights of the protrusions Sa and Sb are lowered every other.thingFor example, it is possible to change the size of the pores or to provide only irregularities without drilling in the places where the protrusions Sa and Sb are low.
[0035]
In order to cause turbulent flow in the gas and increase the contact area with the gas, it is more preferable that the surface of the metal foil has fine irregularities. If a large number of small protrusions Ss are provided between the protrusions Sa and Sb (FIG. 7e), a cross-section (FIG. 7f) having a ripple shape is formed between main corrugations with pores.
As described above, in this processing method, the arrangement and height of the spike-shaped sharp projections Sa and Sb of the two rolls Ra and Rb on the roll surface are appropriately changed, and the distance between the rolls Ra and Rb is changed. The corrugation attached to the metal foil can be adjusted, so that the performance of the power generating porous body can be adjusted. Although it depends on the processing technique, at present, the thickness of the metal foil is about 50 μm, the wave period (determined by the interval between spikes), and the amplitude: about 1 mm each is realistic.
[0036]
The combination of the metal foils A and B with corrugations in the gas flow direction may be combined with the same phase as shown in FIG. 8A, or 180 degrees as shown in FIG. 8B. It is also possible to add a wave-shaped peak and a peak. In the case of FIG. 8A, it is preferable to provide the protruding portion T also as a spacer in order to secure a gap between the metal foils A and B.
Also in the case of FIG. 8B, an electrical short circuit is likely to occur between corrugated ridges to be attached. Therefore, it is preferable to provide the protruding portion T also for insulation. In this case, the protrusion is appropriately provided with a cut so as to ensure the gas flow at the ridge portion. When the corrugations attached to the metal foils A and B are appropriately inclined as shown in FIG. 8C, and the metal foils A and B are combined so that the inclinations of the corrugations are opposite to each other, As shown in FIG. 8 (d), the ridged portion is a point p, and a gas flow can be secured at portions other than this point, and at the same time, the interval between the metal foils A and B can be secured.
[0037]
The alumel and chromel metal foils A and B prepared as described above are cut to a fixed size, and as shown in FIG. 3, the upper end and the lower end are alternately folded in a spiral shape by appropriate means such as welding and brazing. Connected to. Low temperature side joints 2L, 2L,. . Extraction electrodes 3 and 3 such as a nickel band are connected to the outermost ends of the fold-like shape. If necessary, an insulating film is formed on the metal surface by oxidation treatment, and the power generation element according to the present invention is obtained.
[0038]
The protrusions T provided on the metal foils A and B of the thermocouple are sponge-like and air-permeable so that heat exchange with gas is good like the metal foils A and B. A material having a high absorption rate is preferable, and high melting point metals such as W, Mo, Ti, ceramic materials such as silica, alumina, sapphire, silicon carbide, silicon nitride, and mixtures thereof are conceivable. These powders and fibers are formed on the metal foils A and B by sintering or pressure bonding. For the formation of the projecting portion T, a semiconductor micromachining technique, a machine precision machining technique, or the like can be employed. Of course, the surface of the protrusion T can be covered with a heat-resistant film having a high radiant heat absorption rate.
[0039]
In order to reduce the free path of radiation, the smaller the width / arrangement pitch in the gas flow direction of the protrusion T, the better. However, about 0.1 to several mm is practical depending on the processing / molding technique. The length of the protrusion T in the direction perpendicular to the gas flow direction is preferably as long as the air permeability (low pressure loss) in the gas flow direction of the power generation element can be secured.
[0040]
The porous thermoelectric generator produced in this way is air permeable. When mixed flammable gas is introduced from the low temperature side joint 2L toward the high temperature side joint 2H and burned in the porous body, the high temperature side joint 2H is heated by combustion heat, and the low temperature side joint 2L is cooled by a low temperature (normal temperature) combustible gas that is continuously replenished. Conversely, the combustible gas is heated while moving through the porous body, and when it reaches the combustion region, the temperature rises sufficiently to cause a smooth combustion reaction. As a result, a steep temperature gradient is generated between the low-temperature side junction 2L and the high-temperature side junction 2H, and high efficiency is obtained from the two extraction electrodes of the porous body that is configured in a fold-like shape and has a large number of thermocouples connected in series. Power can be taken out with.
[0041]
In an actual apparatus, the burned hot exhaust gas may be allowed to perform work such as boiling water from the viewpoint of effective use of heat. However, from the viewpoint of improving power generation efficiency as a power generation device, it is preferable that the combusted high-temperature exhaust gas is exhausted through the second porous thermoelectric power generation element or the superadiabatic porous body disposed to face the exhaust side. At this time, the exhaust gas is cooled by transferring heat to the porous body and then released to the atmosphere, so that the space between the porous bodies is maintained at a high temperature by this arrangement. Furthermore, a reciprocating combustion system as introduced in the above-mentioned paper by Prof. Echigo can be considered.
Note that the initial preheating of the power generation device using this power generation element may be adjusted by adjusting the gas amount after igniting the gas as in the above-mentioned experiment. The porous body can be easily heated.
[0042]
【The invention's effect】
As described above, the porous thermoelectric power generating element of the present invention covers the surface of the metal foil constituting the porous body with a heat-resistant film having a high radiant heat absorption rate. For this reason, a temperature gradient tends to occur in the gas flow direction, and a high electromotive force can be obtained. In addition, when the free path of radiation of the porous body is set long in the direction perpendicular to the gas flow direction and short in the gas flow direction, temperature uniformity is achieved in the direction perpendicular to the gas flow direction. Suppresses the reactive current at the junction. Since the generated steep temperature gradient can be used effectively, the efficiency of power generation can be improved.
According to this power generation method, fuel such as alcohol, methane, and ethane can be directly used, and there is no need to reform the fuel as in a fuel cell. Furthermore, since the super-insulating effect is utilized, the present invention can be applied to a reciprocating combustion exhaust treatment apparatus that can burn, for example, a lean combustion gas discharged from a painting factory or the like without requiring a separate auxiliary combustion gas.
[Brief description of the drawings]
FIG. 1 shows a conventional example (a) of a porous thermoelectric generator and a power generation experiment apparatus (b) using the porous thermoelectric generator.
FIG. 2A is a diagram showing the temperature distribution of a metal foil during power generation using a conventional porous thermoelectric power generation element as an isotherm, and FIG. 2B is a cross-sectional view explaining a reactive current generated in a high-temperature side junction ).
FIG. 3 is an embodiment according to the present invention.
FIG. 4 is another embodiment according to the present invention.
FIG. 5 is a diagram for explaining the operation of the protrusion of the present invention.
FIG. 6 is an example of a method of corrugating a metal foil.
FIG. 7 is a diagram (a to e) showing an example of the arrangement of spike-like projections on a roll, and a cross-sectional view (f) of a corrugated metal foil.
FIG. 8 is a diagram (a, b) showing a method for abutting metal foils A, B with corrugations only in the gas flow direction, and a diagram showing metal foils A, B with the corrugation directions slightly inclined. (C, d).
[Explanation of symbols]
1: Power generation element
2H: High temperature side joint
2L: Low temperature side joint
3: Extraction electrode
10: Combustor
11, 12: Air inlet

A, B: Two types of metal foils in a thermocouple relationship
T: Projection
g: Gas
G: Gas flow direction
H: Direction perpendicular to the gas flow direction
Ra, Rb: Roll
Sa, Sb: Spike-like projection
W: Foil material
R: Plate direction
Ph: Pitch in the plate passing direction
Pl: Pitch in a direction perpendicular to the plate passing direction
p: Attached part (point) of each wave type peak

Claims

熱電対の関係にある２種の金属又は合金の箔を積層し、第１の金属又は合金の箔の一端を隣合う第２の金属又は合金の箔の一端に接合することにより多数の直列接続された熱電対をツヅラ折状に構成し、接合部以外の個所で第１の金属又は合金の箔と第２の金属又は合金の箔とを電気的に絶縁し、燃焼ガスが通過する複数の細孔が第１及び／又は第２の金属又は合金の箔に穿設され、第１及び／又は第２の金属又は合金の箔の表面に放射熱吸収率の高い耐熱性皮膜が設けられた多孔体熱電発電素子であって、前記２種の金属又は合金の箔の少なくとも一方に波型が縦横方向に形成され、ガス流動方向と直角な方向の波型の振幅がガス流動方向の波型の振幅より小さく形成され、及び／又はガス流動方向と直角な方向の波型の周期がガス流動方向の波型の周期より大きく形成され、且つ前記縦横方向の波型の形成に際して、金属又は合金の箔材を、２個のロールの表面に等ピッチで１列ごとに交互に整列して設けられた複数の突起が前記金属又は合金の箔材の表裏から交互に突き刺さるように、前記２個のロールの間に通すことにより、縦横方向の波型が異なる形状に形成されたことを特徴とする多孔体熱電発電素子。Multiple series connections by laminating two metal or alloy foils in a thermocouple relationship and joining one end of a first metal or alloy foil to one end of an adjacent second metal or alloy foil The thermocouple is configured in a fold-like shape, and the first metal or alloy foil and the second metal or alloy foil are electrically insulated at locations other than the joint, and a plurality of combustion gases pass through. Fine pores were drilled in the first and / or second metal or alloy foil, and a heat-resistant film having a high radiant heat absorption rate was provided on the surface of the first and / or second metal or alloy foil. A porous thermoelectric power generation element, wherein a corrugation is formed in at least one of the two metal or alloy foils in a longitudinal and transverse direction, and the corrugation amplitude in a direction perpendicular to the gas flow direction is a corrugation in the gas flow direction. And / or a wave-like period in a direction perpendicular to the gas flow direction. When forming the corrugations in the vertical and horizontal directions, metal or alloy foil materials are alternately arranged on the surface of two rolls at equal pitches for each row. A plurality of protrusions are inserted into the two rolls so that the protrusions are alternately pierced from the front and back of the metal or alloy foil material. Porous thermoelectric generator.

熱電対の関係にある２種の金属又は合金の箔を積層し、第１の金属又は合金の箔の一端を隣合う第２の金属又は合金の箔の一端に接合することにより多数の直列接続された熱電対をツヅラ折状に構成し、接合部以外の個所で第１の金属又は合金の箔と第２の金属又は合金の箔とを電気的に絶縁し、燃焼ガスが通過する複数の細孔が第１及び／又は第２の金属又は合金の箔に穿設され、ガス流動方向に直角な方向に沿った放射の自由行路がガス流動方向に沿った放射の自由行路よりも長い多孔体熱電発電素子であって、前記２種の金属又は合金の箔の少なくとも一方に波型が縦横方向に形成され、ガス流動方向と直角な方向の波型の振幅がガス流動方向の波型の振幅より小さく形成され、及び／又はガス流動方向と直角な方向の波型の周期がガス流動方向の波型の周期より大きく形成され、且つ前記縦横方向の波型の形成に際して、金属又は合金の箔材を、２個のロールの表面に等ピッチで１列ごとに交互に整列して設けられた複数の突起が前記金属又は合金の箔材の表裏から交互に突き刺さるように、前記２個のロールの間に通すことにより、縦横方向の波型が異なる形状に形成されたことを特徴とする多孔体熱電発電素子。Multiple series connections by laminating two metal or alloy foils in a thermocouple relationship and joining one end of a first metal or alloy foil to one end of an adjacent second metal or alloy foil The thermocouple is configured in a fold-like shape, and the first metal or alloy foil and the second metal or alloy foil are electrically insulated at locations other than the joint, and a plurality of combustion gases pass through. pores are formed in the foil of the first and / or second metal or alloy, longer porous than the free path of the radiation free path of the radiation along the direction perpendicular to the gas flow direction along the gas flow direction A thermoelectric power generation element, wherein a corrugation is formed in at least one of the two metal or alloy foils in a longitudinal and transverse direction, and the corrugation amplitude in a direction perpendicular to the gas flow direction is a corrugation in the gas flow direction. A wave-like period formed in a direction smaller than the amplitude and / or perpendicular to the gas flow direction When forming the corrugation in the longitudinal and transverse directions, the metal or alloy foil material is alternately arranged on the surface of the two rolls at equal pitches in each row. The corrugations in the vertical and horizontal directions are formed in different shapes by passing between the two rolls so that the plurality of provided protrusions are alternately inserted from the front and back of the metal or alloy foil material. A porous thermoelectric power generation element.

前記金属又は合金の箔材を、表面に等ピッチで整列して設けられた複数の突起の間に小突起が整列して設けられた２個のロールの間に通すことにより、小さな波型が前記縦横方向の波型の形成と同時に形成された金属又は合金の箔を用いる請求項１又は２に記載の多孔体熱電発電素子。By passing the metal or alloy foil material between two rolls in which small protrusions are arranged between a plurality of protrusions arranged on the surface at an equal pitch, a small corrugation is obtained. porous thermoelectric power generation element according to claim 1 or 2 using the foil of the vertical and horizontal directions of the corrugated simultaneously formed metal or alloy and formation of.

前記２種の金属又は合金の箔の少なくとも一方の表面上に、ガス流動方向と直角な方向に長い形状の突出部が設けられている請求項１〜３の何れかに記載の多孔体熱電発電素子。On at least one surface of the foil of the two metals or alloys, porous thermoelectric generator according to claim 1, protrusions elongated in a direction perpendicular with the gas flow direction is provided element.

前記突出部が通気性の多孔体素材からなる請求項４に記載の多孔体熱電発電素子。The porous thermoelectric generator according to claim 4 , wherein the protruding portion is made of a breathable porous material.