JP2004349116A - Dielectric heating apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dielectric heating apparatus capable of preventing the local heating of heated objects such as indefinite-shaped foods or the like, and minimizing the variations of load impedance between electrodes, and further achieving a downsizing, a cost reduction and an energy-saving of a matching unit. <P>SOLUTION: The high-frequency dielectric heating apparatus produces a dielectric heat to a frozen tuna 6 placed and held between a pair of opposed high voltage side electrodes 4 and an earth side electrode 5, by causing an electric field to be applied to the high voltage side electrodes 4 and the earth side electrode 5. The frozen tuna 6 is covered by intercalated objects 8, 50 having a dielectric constant that is equivalent to or more than equivalent to a dielectric constant of the frozen tuna 6. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０００９】
また、上記特許文献２のものの場合、２枚の平行電極間の電気特性（抵抗、静電容量）は、被加熱体の材料や量、温度状態に合わせて大きく変動するため、可変インダクタンスやバリコンの調整範囲は広くて複雑になり、整合器が大型化するとともに高価となり、さらに整合器で消費されるエネルギー損失も大きくなってしまうという問題点もあった。
なお、上記特許文献１において用いられるゴム、ウレタン、シリコンゴム等は比誘電損失が比較的大きな材料であり、エネルギー損失の観点からも必ずしもよい選択とはいえない。
【００１０】
この発明は、上記のような問題点を解決することを課題とするものであって、不定形状の食品等の被加熱体の局部加熱を防止できる誘導加熱装置を得ることを目的とする。
【００１１】
また、電極間の負荷インピーダンスの変動を小さくでき、整合器の小型化、低コスト化および省エネルギー化を図ることができる誘導加熱装置を得ることを目的とする。
【００１２】
【課題を解決するための手段】
この発明に係る誘電加熱装置では、対向した一対の電極間に載置される被加熱体を、前記電極間に電界を印加させて誘電加熱する誘電加熱装置において、前記被加熱体は、被加熱体の比誘電率と同等もしくは同等以上である比誘電率の介在体で覆われている。
【００１３】
この発明に係る誘電加熱装置では、被加熱体はマイクロ波が照射される電界空間に載置され、誘電加熱される誘電加熱装置において、前記被加熱体は、被加熱体の比誘電率と同等もしくは同等以上である比誘電率の介在体で覆われている。
【００１４】
【発明の実施の形態】
以下、この発明の各実施の形態について説明するが、同一、または相当部材、部位については、同一符号を付して説明する。
実施の形態１．
図１は、この発明の実施の形態１における高周波誘電加熱装置の構成図である。
この高周波誘導加熱装置は、高周波電源１と、この高周波電源１と接続された整合器２と、この整合器２と同軸ケーブル３、中心導体３ａを介して電気的に接続された高圧側電極４と、この高圧側電極４と対向しているとともにアース１１にスライド式導体１２を介して接続されたアース側電極５と、このアース側電極５を載置しているとともにアース側の電極５を搬送するローラ式ベルト１３と、高圧側電極４を上下動させる可変機１４とを備えている。
【００１５】
高圧側電極４とアース側電極５との間には、例えば被加熱体である冷凍マグロ６が載置される。この冷凍マグロ６は高分子フィルムからなるラップ７で包まれる。
冷凍マグロ６とアース側電極５との間には、変形自在な第１の介在体８が介在している。この第１の介在体８は、高誘電体である二酸化チタンからなり直径が２〜３ｍｍの複数個の小さな球体８ａがポリエチレンからなる袋８ｂに詰められて構成されている。
冷凍マグロ６と高圧側電極４との間には、変形自在な第２の介在体５０が介在している。この第２の介在体５０も、高誘電体である二酸化チタンからなり直径が２〜３ｍｍの複数個の小さな球体５０ａがポリエチレンからなる房袋５０ｂに詰められて構成されている。この小さな房袋５０ｂは、高圧側電極４から垂れ下がった複数個の房芯ロープ１０に多数房状に接続されている。
第１の介在体８および第２の介在体５０では、冷凍マグロ６の比誘電率と同程度になるように空隙率が調整されるようになっている。
【００１６】
上記構成の高周波誘電加熱装置では、先ず、被加熱体を第１の介在体８を介してアース側電極５上に載置する。この後、ローラ式ベルト１３の駆動によって冷凍マグロ６を第２の介在体５０の直下まで移動させる。このとき、アース側電極５はアース１１とスライド式導体１２ｄを介して接続された状態は保持されている。
次に、高圧側電極４を可変機１４で降下することで、周囲が第１の介在体８および第２の介在体５０で覆われた状態の冷凍マグロ６を高圧側電極４とアース側電極５との間に挟む。その後、高周波電源１の駆動により高圧側電極４とアース側電極５との間に高周波電力を供給し、冷凍マグロ６に高周波電界を印加して冷凍マグロ６を誘電加熱する。
なお、高周波電力の供給では、整合器２により高周波電源１の出力インピーダンスと負荷インピーダンスとの整合が図られている。
【００１７】
本願発明者は、上記の手順に従って短冊状の２２０ｇの冷凍マグロ６をラップ７で包んだ状態で高周波解凍試験を行い、そのときの温度分布を測定した。
なお、袋８ｂおよび房袋５０ｂ内に袋詰めされた二酸化チタンの空隙率は約５０％であり、この場合の平均比誘電率は約１０と予測される（著基木洋一「ファインセラミック」、技報堂（１９７８）ｐ７７５、参照）。
図２（ａ）は装置内の冷凍マグロ６の平面図、（ｂ）はその正面図、（ｃ）はその右側面図であり、各図において○印、点線の○は冷凍マグロ６の測定点を示す。
【００１８】
図３はそのときの温度分布の経時変化を示す図である。図４は比較例１として、冷凍マグロ６を高誘電体である第１の介在体８および第２の介在体５０で覆わない状態で高周波解凍した場合の温度分布の経時変化を示す図である。
【００１９】
高周波電源１は４１ＭＨｚ、最大５０Ｗ出力であり、全ての測定点イ〜トにおいて−２０℃の状態からスタートし、０℃以下の半解凍状態までは５０Ｗ出力で、その後は２０Ｗ出力に切り替え、さらに内部の測定点が０℃以上になった時点で１０Ｗ出力に切り替え、中心部ロも２℃以上に到達し、全ての測定点が２℃以上に到達した時点で解凍を終了した。
【００２０】
表２は図３と図４から解凍に要した時間と高周波加熱効率（＝マグロ解凍に要する熱量÷高周波電源出力）を比較した表である。
この表から、実施の形態１のものが比較例１のものと比較して解凍時間が短く、かつ高周波加熱効率も良いことが分かる。
【００２１】
【表２】

【００２２】
以上のようにこの実施の形態１によると、被加熱体である冷凍マグロ６が０℃以下の半解凍状態では、全体をほぼ均一に加熱でき、かつ解凍時間の短縮化も図れることが分かった。
また、肉眼観察によると、スパークによる冷凍マグロ６の損傷は発見されなかった。
さらに、解凍の進行に伴う電極４、５間の静電容量の変化は小さくなり、整合器２のバリコンの静電容量が回路全体に占める割合も小さくなり、電極４、５間以外で消費されるエネルギー損失も低減された。
【００２３】
なお、上記実施の形態１では、第１の介在体８および第２の介在体５０は、ポリエチレン袋８ｂおよび房袋５０ｂ内に高誘電体である小粒状の二酸化チタンを袋詰めしたものであったが、袋詰めした状態で被加熱体の形状に合わせて変形自在なものとして、中にペレット状、チップ状に加工した誘電体材料の集合体を袋詰めするようにしてもよい。
但し、空隙率によって平均比誘電率は変化するので、被加熱体の比誘電率と同程度またはそれ以上になるように空隙率を調整する必要がある。
【００２４】
例えば、上記表１から、キハダマグロの比誘電率は、冷凍状態（−１５℃）で約１０程度、半解凍状態（−５℃）で２０〜４０程度、解凍した状態では約５０〜６０程度に上昇するが、高誘電体材料として、ルチル型の二酸化チタン（比誘電率１２０）を用いた場合、平均比誘電率を１０以上にするには、空隙率５０％以下にしなければ期待する効果は得られない。
なお、高誘電率材料を低誘電率材料で薄めた場合の平均比誘電率は、「著基木洋一「ファインセラミック」、技報堂（１９７８）ｐ７７５参照」に示された式により得られる。
【００２５】
実施の形態２．
図５は実施の形態２における高周波誘電加熱装置の構成図である。
この実施の形態２では、冷凍マグロ６の周囲が介在体である高誘電体材料の粉末１７で覆われている。
本願発明者は、冷凍マグロ６の周囲を覆った高誘電体材料の粉末１７についての効果を比較するために、高誘電体材料の粉末１７を換えて、実施の形態１と同様の試験を行った。即ち、短冊状の冷凍マグロ２２０ｇを高周波（４１ＭＨｚ、最大５０Ｗ出力）で解凍する試験で、そのときの温度分布の経時変化を測定した。
【００２６】
この実施の形態では、解凍試験をする前に、まずポリプロピレン容器であるタッパ１９の中にラップ（商標名、旭化成製、ポリ塩化ビニリデン）７に包んだ被加熱体である冷凍マグロ６をその周囲が粉末１７で覆った状態で収めた。このとき、粉末１７の周囲は断熱発砲材１８で囲まれている。
【００２７】
比較的大きな比誘電率を示す高誘電体材料の粉末１７としては、二酸化チタン、チタン酸塩化合物（チタン酸ストロンチウム、チタン酸カルシウム、チタン酸バリウム、チタン酸鉛、チタン酸マグネシウム等）、ジルコニア、ジルコン酸塩化合物、その他金属酸化物（アルミナ等）、その他酸化物系磁器、酸化炭化ケイ素、窒化ケイ素等と、これら混合物の固溶体、例えば、チタン酸塩とジルコン酸塩の固溶体（ＰＺＴ、ＰＺＬ）等である。
【００２８】
表３に各種高誘電体材料単体の誘電特性、およびその中からいくつかの材料についての実際の解凍試験結果について示す。
【００２９】
【表３】

【００３０】
【表４】

【００３１】
なお、これらの値は、「静電気学会、「静電気ハンドブック」、オーム社（１９９８年）ｐ５９５〜ｐ５９７」および「多機能フィルム膜編集委員会、「多機能フィルム・膜活用ノート」、工業調査会（１９９１年）ｐ７５〜ｐ８３」から抽出したものである。
表３において、比較例１は介在体である粉末１７が存在せず、冷凍マグロ６の周囲が空気層で覆われた状態の場合である。比較例２は冷凍マグロ６の周囲がシリコンゴムで覆われた状態の場合である。
【００３２】
冷凍マグロ６の比誘電率は約１０程度と予測されるが、表３から、粉末１７の平均比誘電率がこれと同等もしくは同等以上の比誘電率を有する材料（二酸化チタン、チタン酸塩（ストロンチウム、カルシウム、亜鉛、マグネシウム等）、ニオブ酸リチウム、ジルコニア）の場合には、比較例１、比較例２と比較して均一に加熱でき、また解凍時間も短縮できることが分かった。また、高周波加熱効率も改善されたことが分かった。
【００３３】
また、望ましい誘電特性として、温度条件で誘電特性変化が少ないこと、比誘電損失が小さいことが要求されるが、この場合には、例えば、二酸化チタンに、希土類元素（Ｌａ、Ｃｅ，Ｚｒ，Ｔｈ）酸化物およびＳｎ、Ｍｇ，Ｚｎの酸化物を添加して、温度係数を小さくしたものがよく知られており、これらのものを用いることで、解凍時間もより短縮でき、また高周波加熱効率もより改善される（（著基木洋一「ファインセラミック」、技報堂（１９７８）ｐ７８３参照）。
また、粉末１７は冷凍マグロ６の比誘電率と同程度であることが望ましいので、誘電率が著しく大きい材料（チタン酸ストロンチウム、チタン酸バリウム、ジルコン酸鉛、ＰＺＴなど）については、空隙率が大きくするようにすればよい。
【００３４】
実施の形態３．
図６はこの発明の実施の形態３における高周波誘電加熱装置の電極４、５間の構成を示す説明図である。
この実施の形態では、被加熱体である蒲鉾２０が第１の介在体２１ａ、第２の介在体２１ｂで覆われている。
蒲鉾２０は、蒲鉾すりみ２０ａの下側に板２０ｂがついており、全体がラップ２０ｃで包装されている。
【００３５】
第１の介在体２１ａ、第２の介在体２１ｂは、実施の形態２に示した高誘電体材料の粉末１７を高温焼結させた定形体である。なお、エチルセルロースやアクリル粉で粉末を接着乾燥させて第１の介在体２１ａ、第２の介在体２１ｂを製造することもできる。
また、この実施の形態でも、実施の形態１および２と同様に、誘電特性として、温度条件で誘電特性変化が少ないこと、比誘電損失が小さいことが要求される。
【００３６】
また、例えば、二酸化チタンの場合、焼結温度（１４００℃）は高温となり、誘電正接が大きい組成になるため、焼結温度を下げる必要性があり、そのための溶剤としてアルカリ土金属や粘土が用いられる。また、二酸化チタンにＺｒＯ_２を添加すると誘電正接が低下できる。また、温度係数を調整するための添加剤として、ＭｇＯ、ＢａＯ、チタン酸塩、Ｃａ−Ｔｉ酸塩、共融物ＳｉＯ_２、Ａｌ_２Ｏ_３、粘土等を用いればよい（著基木洋一「ファインセラミック」、技報堂（１９７８）ｐ７７６参照）。
【００３７】
上記の高周波誘電加熱装置では、複数個の蒲鉾２０をニ酸化チタンを主成分とする定形体である第１の介在体２１ａ、第２の介在体２１ｂで覆った状態で、高圧側電極４とアース側電極５との間に載置し、高周波電源１の駆動により高圧側電極４とアース側電極５との間に高周波電界を印加して蒲鉾２０を誘電加熱して、複数個の冷凍した蒲鉾を同時に解凍したところ、局部過熱することなく均一加熱による解凍がなされた。また、高周波加熱効率も改善された。
【００３８】
実施の形態４．
図７はこの発明の実施の形態４における高周波誘電加熱装置の構成図である。
この実施の形態では、冷凍マグロ６の上面が高誘電体シート２４で覆われている。この高誘電体シート２４は高誘電性セラミックス（例えば、ＰＺＴ（ジルコン酸塩とチタン酸塩の固溶体、Ｃｌｅｖｉｔｅ社の商標名）の粉末を高誘電性の高分子フィルム（例えば、ポリフッ化ビニリデン（ＰＶＤＦ））に分散してポットプレスした複合体であって、比誘電率は約１００である（静電気学会、「静電気ハンドブック」、オーム社（１９９８）ｐ５９５〜ｐ５９７、参照）。
また、第２の介在体２５は、高誘電体材料を細かく無数に切断して糸状のものであり、高圧側電極４に垂れ下げられている。空隙率は約５０％であり、平均比誘電率は約１０と予測される。
【００３９】
また、第１の介在体８は、高誘電体率で低誘電損失のセラミック材料の受け皿２６に載置されている。アース側電極５は、絶縁体２８を介して回転モータ２７に接続されており、回転モータ２７の駆動によって回転し、電界分布のばらつきによって冷凍マグロ６である被加熱体に生じる加熱むらを低減している。外部導体容器３０と中心導体３ａとは絶縁体２９（ＰＴＦＥなど）により絶縁状態が確保されている。
他の構成は実施の形態１と同様である。
【００４０】
本願発明者は、この実施の形態４における高周波誘電加熱装置について、実施の形態１の高周波誘電加熱装置と同様に２２０ｇの冷凍マグロ６をラップ７で包んだ状態で高周波解凍試験を行い、そのときの温度分布の経時変化を測定した。
その試験結果では、解凍時間がほぼ実施の形態１と同様な効果が得られた。
【００４１】
なお、表４に各種高分子フィルム材料（圧電性高分子）単体および高誘電体粉末材料を組み合わせた場合の誘電特性値を示す。
【００４２】
【表５】

【００４３】
【表６】

【００４４】
なお、これらの値は、「著基木洋一「ファインセラミック」、技報堂（１９７８年）」、「Ａ．Ｒ．Ｖｏｎ Ｈｉｐｐｅｌ：”Ｄｉｅｌｅｃｔｒｉｃ Ｍａｔｅｒｉａｌｓ ａｎｄ Ａｐｐｌｉｃａｔｉｏｎ”，ＭＩＴ Ｐｒｅｓｓ（１９５４）」、「Ｄａｖｉｄ Ｒ．Ｌｉｄｅ：”ＣＲＣ Ｈａｎｄｂｏｏｋ ｏｆ Ｃｈｅｍｉｓｔｒｙ ａｎｄ Ｐｈｙｓｉｃｓ”ＣＲＣ Ｐｒｅｓｓ（１９９６）」、「日本化学会、「化学便覧基礎編（改定４版）Ｉ」、丸善（１９９３）、ｐ−５５６〜ｐ５６７」および「角田誠、“高分子材料のマイクロ波誘電特性”、ＳＨＭ会誌、Ｖｏｌ９、Ｎｏ（１９９３）ｐ４３〜ｐ４４」から抽出したものである。
【００４５】
本願発明者は、そのうちのいくつかの組み合わせについて、高誘電体シート２４、第１の介在体８および第２の介在体２５を用いて、実施の形態１と同様に冷凍マグロ６の高周波解凍試験を行い、そのときの温度分布の経時変化を測定した。
【００４６】
高誘電体粉末材料としては、上記表３のうちでも特に比誘電率の高い材料が望ましい。その材料として、チタン酸ストロンチウム、チタン酸塩とジルコン酸塩の固溶体（ＰＺＴ、ＰＬＺＴ）、Ｂａ−Ｐｂのジルコン酸塩等がある。
高分子フィルム材料として、それ自体の比誘電率が（３〜１０程度、１ＭＨｚで）比較的高い圧電性高分子（フッ化ビニリデン、ポリフッ化ビニリデン、酢酸セルロース、ナイロン、ポリウレタンなど）であってもよいし、それ自体の比誘電率が高くない高分子材料、ポリエチレンテレフタレート、ポリプロピレン、ポリスチレン、ポリテトラフルオロエチレンなどであってもよい。
例えば、本願発明者は、Ｂａ−Ｐｂのジルコン酸塩の粉末をビニロン（ポリ塩化ビニリデンアセテートの代表的商品名）に分散させた高誘電体シート２４と毛玉状の高誘電体を用いて、冷凍マグロ６の高周波解凍試験を行った結果、解凍時間の短縮と高周波加熱効率の改善が確認された。
【００４７】
さらに、チタン酸バリウム、ジルコン酸鉛等の粉末材料のキューリ点（誘電率が著しく変化する温度）を０℃〜２０℃程度に設計し（例えば、著基木洋一「ファインセラミック」、技報堂（１９７８）ｐ８０４参照）、これを分散させて構成された高誘電体シート２４は、冷凍食品が固体から液体に相変化し比誘電率の増加に追従して、比誘電率が増加することになり、食品等対象物と同程度の比誘電率を保つことができる。
【００４８】
なお、図８に示すように、複数個の被加熱体を同時に誘導加熱するように、第１の介在体８上に複数個の被加熱体を載置するようにしてもよい。
【００４９】
また、図９に示すように、この第２の介在体２５の換わりに、実施の形態１の高周波誘電加熱装置の第２の介在体５０を用い、また複数個の被加熱体を同時に誘導加熱するようにしてもよい。
【００５０】
なお、上記実施の形態１〜４では、電極４、５は、最も一般的な平板電極であったが、勿論このものに限定されない。例えば、グリッド電極、ローラ電極、移動式電極等であってもよい（大森豊明、「電磁波と食品」、光琳（１９９３年）ｐ４６〜ｐ５３、参照）。
これらの電極を用いた場合でも、被加熱体を覆うように高誘電体物質を配置することによって、空気層の影響が小さくなり、局部過熱を抑えて、均一な加熱が実現できる。
【００５１】
また、上記実施の形態１〜４では、電極４、５間の負荷インピーダンスと高周波電源１の出力インピーダンスとを整合させる整合器２が用いられているが、電極４、５間の静電容量のうちで、食品等対象物以外の静電容量の割合が十分大きい場合には、整合器２のバリコン調整は不要であり、さらには整合器２自体を用いることなく、高周波誘電加熱をすることも可能である。
【００５２】
実施の形態５．
図１０はこの発明の実施の形態５におけるマイクロ波加熱装置の構成を示す説明図である。
この実施の形態における誘電加熱装置であるマイクロ波誘電加熱装置では、マグネトロン３３で発生したマイクロ波は導波管３４を通って、高電界空間３５内に照射されて、マイクロ波が乱反射して、冷凍マグロ６が加熱されるようになっている。
被加熱体である冷凍マグロ６の周囲は介在体である高誘電体材料の粉末１７で覆われている。
冷凍マグロ６が入ったタッパ１９は高誘電体の受け皿２６を介してターンテーブル３６に載置されている。ターンテーブル３６は、絶縁体２８を介して回転モータ２７に接続されている。このターンテーブル３６は、回転モータ２７の駆動により、冷凍マグロ６６に印加される電界のばらつきは低減される。
【００５３】
本願発明者は、このマイクロ波加熱装置において高誘電体の粉末１７の有無の効果を確認するために、冷凍マグロ６の解凍時間、マイクロ波加熱効率を測定した。
実際には、２２０ｇの冷凍マグロ６をマイクロ波１０Ｗ出力一定条件解凍して、解凍時間（中心部が−２０℃から２℃に到達するまでの時間）とマイクロ波加熱効率を測定した。
表５にその測定結果を示す。この表５から、被加熱体を高誘電体粉末１７で覆った場合のほうが、解凍時間が短縮し、またマイクロ波加熱効率（＝被加熱体に与えた熱量／マイクロ波電源出力）が改善したことが分かる。
【００５４】
【表７】

【００５５】
以上のように、マイクロ波加熱においても、高電界空間内におかれた冷凍マグロ６を高誘電体の粉末１７で覆うことのよって、マイクロ波加熱効率が改善され、省エネ化が図られることが確認できた。
【００５６】
なお、上記実施の形態１ないし実施の形態５では、冷凍食品である冷凍マグロ６を誘電加熱して解凍した場合について説明したが、実施の形態１ないし実施の形態５で説明した誘電加熱手段を、例えば特開２００１−２４５６４５号公報に開示されている冷凍方法に適用できる。
即ち、食品等の冷凍対象物を前記誘電加熱手段で誘電加熱し、誘電加熱により冷凍対象物に吸収されるエネルギーよりも大きなエネルギーで冷却して、冷凍対象物を凍結させることによって、生鮮食品等を高鮮度に冷凍することができる。
【００５７】
また、上記実施の形態１ないし実施の形態５では、被加熱体として冷凍食品である冷凍マグロ６について説明したが、勿論このものに限定されない。例えば食品以外の医療関係の被加熱体として、臓器、細胞、薬品、人体、動物、植物等であってもよい。また、工業用途の被加熱体物として、木材、繊維品、樹脂成形品、陶磁器等であってもよい。
【００５８】
【発明の効果】
以上説明したように、この発明に係る誘電加熱装置によれば、対向した一対の電極間に載置される被加熱体を、前記電極間に電界を印加させて誘電加熱する誘電加熱装置において、前記被加熱体は、被加熱体の比誘電率と同等もしくは同等以上である比誘電率の介在体で覆われているので、電極間の空気層の影響が低く抑えられ、例えば不定形上の食品等の被加熱体の局部過熱を防止でき、解凍時間も短縮できる。
また、電極間の負荷インピーダンスの変動を小さくでき、整合器の小型化、低コスト化および省エネルギー化を図ることができる。
【００５９】
また、この発明に係る誘電加熱装置によれば、被加熱体はマイクロ波が照射される電界空間に載置され、誘電加熱される誘電加熱装置において、前記被加熱体は、被加熱体の比誘電率と同等もしくは同等以上である比誘電率の介在体で覆われているので、電界空間の空気層の影響が低く抑えられ、不定形上の食品等の被加熱体の局部過熱を防止でき、解凍時間も短縮できる。
【図面の簡単な説明】
【図１】この発明の実施の形態１による高周波誘電加熱装置の構成図である。
【図２】この発明の実施の形態１を検証する解凍試験で用いた冷凍マグロの形状と温度分布測定点を示す説明図である。
【図３】この発明の実施の形態１に基づいて冷凍マグロを高誘電体で覆った状態で高周波解凍した場合の温度分布の経時変化を示す図である。
【図４】実施の形態１との比較例１として冷凍マグロを高誘電体で覆わない状態で高周波解凍した場合の温度分布の経時変化を示す図である。
【図５】この発明の実施の形態２による高周波誘電加熱装置の電極の構成図である。
【図６】この発明の実施の形態３による高周波誘電加熱装置の電極の構成図である。
【図７】この発明の実施の形態４による高周波誘電加熱装置の構成図である。
【図８】図７の高周波誘電加熱装置の別の例を示す要部構成図である。
【図９】図７の高周波誘電加熱装置の別の例を示す要部構成図である。
【図１０】この発明の実施の形態５によるマイクロ波誘電加熱装置の構成図である。
【符号の説明】
１ 高周波電源、２ 整合器、４ 高圧側電極、５ アース側電極、６ 冷凍マグロ（被加熱体）、８ 第１の介在体、１７ 粉末（介在体）、２０ 蒲鉾（被加熱体）、２１ａ 第１の介在体、２１ｂ 第２の介在体、２４ 高誘電体シート、２５ 第２の介在体、３５ 高電界空間。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a dielectric heating device that dielectrically heats and defrosts an object to be heated such as frozen food.
[0002]
[Prior art]
The high-frequency dielectric heating device is a dielectric heating device using electromagnetic waves in a frequency band of 0.3 MHz to 300 MHz, and the microwave dielectric heating device is a dielectric heating device using electromagnetic waves in a frequency band of 300 MHz to 30 GHz.
The high-frequency dielectric heating device has a feature that it has a longer wavelength, higher internal permeability, and is more excellent in heating a thick object to be heated from inside and outside as compared with microwave heating. For example, it is used in the food industry to defrost blocks such as frozen tuna 6 and frozen meat.
According to Non-Patent Document 1, a high-temperature power source (13 MHz) is driven while a heated object, which is a frozen food, is placed between two parallel electrodes, and a low-temperature atmosphere is adjusted by a cooler, to about 0 ° C. Thawing is described.
[0003]
However, in this high-frequency dielectric heating device, there is an air layer between the frozen food or the like to be heated and the electrode, so that a sharp potential difference is generated between the surface of the heated body and the electrode, and for example, an irregular shape In the case of food, the air layer between the electrode and the surface of the food is non-uniform, electromagnetic waves are concentrated on the parts and corners close to the electrode, and uneven heating and local overheating occur, There is a problem that sparks may be generated and the food surface may be damaged.
[0004]
As a method for solving the above-mentioned problem, a heated conductor side of a flexible conductor (metal mesh or metal foil or the like) is replaced with a flexible low dielectric substance (rubber, urethane, silicon rubber, or a foam thereof). And the like, and an integrally formed flexible electrode that covers the upper surface of the object to be heated is disclosed (for example, see Patent Document 1).
[0005]
In addition, in the high-frequency dielectric heating apparatus, for example, if the material of the frozen food is constant, the load impedance is constant, and it is not necessary to adjust the impedance by the load. , The load impedance also varies, and it is necessary to adjust the matching between the load impedance and the output impedance of the high-frequency power supply. In order to achieve this matching, a matching device is interposed between the high-frequency power supply and the electrode, and a variable inductance and a variable capacitor (varicon) constituting the matching device are adjusted (for example, see Patent Document 2). .
[0006]
[Non-patent document 1]
Aso, "High-Frequency Thawing Device," Frozen, Vol.
[Patent Document 1]
Japanese Utility Model Publication No. 56-129293
[Patent Document 2]
JP-A-10-134953
[0007]
[Problems to be solved by the invention]
In the case of the above-mentioned Patent Document 1, although the effect of reducing the ratio of the air layer between the flexible electrode and the object to be heated is small, as can be seen from Table 1, rubber, urethane, silicon rubber, etc. The relative dielectric constant is only about 3 at most, which is smaller than the relative dielectric constant (for example, about 10 or more) of a body to be heated such as food, and there is a problem that local heating of food or the like cannot be sufficiently prevented.
[0008]
[Table 1]

[0009]
In the case of Patent Document 2, the electrical characteristics (resistance, capacitance) between the two parallel electrodes greatly vary depending on the material, amount, and temperature of the object to be heated. However, there is a problem in that the adjustment range is wide and complicated, the matching device becomes large and expensive, and the energy consumed by the matching device also increases.
Note that rubber, urethane, silicon rubber, and the like used in Patent Document 1 are materials having relatively large relative dielectric losses, and are not necessarily a good choice from the viewpoint of energy loss.
[0010]
An object of the present invention is to solve the above-described problems, and an object of the present invention is to provide an induction heating device that can prevent local heating of a body to be heated such as an irregularly shaped food or the like.
[0011]
It is another object of the present invention to provide an induction heating device capable of reducing the variation in load impedance between electrodes and reducing the size, cost, and energy consumption of the matching device.
[0012]
[Means for Solving the Problems]
In the dielectric heating apparatus according to the present invention, in the dielectric heating apparatus for performing dielectric heating by applying an electric field between the electrodes, the heated body placed between the pair of opposed electrodes is heated. It is covered with an intermediate having a dielectric constant equal to or greater than the dielectric constant of the body.
[0013]
In the dielectric heating device according to the present invention, the object to be heated is placed in an electric field space irradiated with microwaves, and in the dielectric heating device to be subjected to dielectric heating, the object to be heated is equivalent to the relative dielectric constant of the object to be heated. Alternatively, it is covered with an intermediate having a dielectric constant equal to or higher than the equivalent.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, each embodiment of the present invention will be described, but the same or corresponding members and portions will be described with the same reference numerals.
Embodiment 1 FIG.
FIG. 1 is a configuration diagram of a high-frequency dielectric heating device according to Embodiment 1 of the present invention.
The high-frequency induction heating apparatus includes a high-frequency power supply 1, a matching device 2 connected to the high-frequency power supply 1, a high-voltage side electrode 4 electrically connected to the matching device 2, a coaxial cable 3, and a center conductor 3a. A ground-side electrode 5 facing the high-voltage side electrode 4 and connected to the ground 11 via a sliding conductor 12; and mounting the ground-side electrode 5 and connecting the ground-side electrode 5 to the ground-side electrode 5. The apparatus includes a roller-type belt 13 that conveys and a variable device 14 that moves the high-voltage side electrode 4 up and down.
[0015]
Between the high-voltage side electrode 4 and the earth-side electrode 5, for example, a frozen tuna 6, which is a body to be heated, is placed. The frozen tuna 6 is wrapped in a wrap 7 made of a polymer film.
A deformable first intervening body 8 is interposed between the frozen tuna 6 and the ground electrode 5. The first intervening body 8 is formed by packing a plurality of small spheres 8a having a diameter of 2 to 3 mm made of titanium dioxide, which is a high dielectric substance, in a bag 8b made of polyethylene.
Between the frozen tuna 6 and the high-pressure side electrode 4, a deformable second intervening body 50 is interposed. The second intervening body 50 is also formed by packing a plurality of small spheres 50a having a diameter of 2 to 3 mm made of titanium dioxide, which is a high dielectric substance, into a bladder 50b made of polyethylene. The small tufts 50b are connected to a plurality of tuft core ropes 10 hanging from the high-voltage side electrode 4 in a large number of tufts.
The porosity of the first and second intervening bodies 8 and 50 is adjusted so as to be substantially equal to the relative dielectric constant of the frozen tuna 6.
[0016]
In the high-frequency dielectric heating device having the above configuration, first, the object to be heated is placed on the ground electrode 5 via the first intervening body 8. Thereafter, the frozen tuna 6 is moved to a position immediately below the second intermediary body 50 by driving the roller belt 13. At this time, the state in which the earth-side electrode 5 is connected to the earth 11 via the slide-type conductor 12d is maintained.
Next, the high-pressure side electrode 4 is lowered by the variable machine 14, so that the frozen tuna 6 whose surroundings are covered with the first intervening body 8 and the second intervening body 50 are separated from the high-pressure side electrode 4 and the ground side electrode. 5 between. Thereafter, high-frequency power is supplied between the high-voltage side electrode 4 and the earth-side electrode 5 by driving the high-frequency power supply 1, and a high-frequency electric field is applied to the frozen tuna 6 to dielectrically heat the frozen tuna 6.
In supplying the high-frequency power, the matching between the output impedance of the high-frequency power supply 1 and the load impedance is achieved by the matching device 2.
[0017]
The inventor of the present application performed a high-frequency thawing test with the strip-shaped 220 g of frozen tuna 6 wrapped in the wrap 7 in accordance with the above procedure, and measured the temperature distribution at that time.
The porosity of the titanium dioxide packed in the bag 8b and the bladder 50b is about 50%, and the average relative dielectric constant in this case is predicted to be about 10 (Yoichi Kiyoshi "Fine Ceramic", Gihodo (1978) p. 775).
2A is a plan view of the frozen tuna 6 in the apparatus, FIG. 2B is a front view thereof, and FIG. 2C is a right side view thereof. Indicates a point.
[0018]
FIG. 3 is a diagram showing a temporal change of the temperature distribution at that time. FIG. 4 is a diagram showing a time-dependent change in the temperature distribution when the frozen tuna 6 is subjected to high-frequency thawing in a state where the frozen tuna 6 is not covered with the first and second intervening bodies 8 and 50 which are high dielectric substances. .
[0019]
The high frequency power supply 1 has a maximum output of 41 MHz and a maximum output of 50 W, and starts from a state of −20 ° C. at all measurement points to 50 W output until a half-thaw state of 0 ° C. or less, and then switches to a 20 W output. The output was switched to 10 W when the internal measurement points reached 0 ° C. or higher, and the central part also reached 2 ° C. or higher, and the thawing was terminated when all the measurement points reached 2 ° C. or higher.
[0020]
Table 2 is a table comparing the time required for thawing and the high-frequency heating efficiency (= heat amount required for tuna thawing / high-frequency power supply output) from FIGS. 3 and 4.
From this table, it can be seen that the first embodiment has a shorter thawing time and a higher high-frequency heating efficiency than the first comparative example.
[0021]
[Table 2]

[0022]
As described above, according to the first embodiment, when the frozen tuna 6 to be heated is in a semi-thawed state at 0 ° C. or lower, the whole can be almost uniformly heated, and the thawing time can be shortened. .
Further, according to the visual observation, no damage to the frozen tuna 6 due to the spark was found.
Furthermore, the change in the capacitance between the electrodes 4 and 5 due to the progress of the thawing becomes small, and the ratio of the capacitance of the variable condenser of the matching unit 2 to the whole circuit also becomes small. Energy loss has also been reduced.
[0023]
In the first embodiment, the first intervening body 8 and the second intervening body 50 are formed by packing small granular titanium dioxide, which is a high dielectric substance, in the polyethylene bag 8b and the bladder 50b. However, an assembly of a dielectric material processed into a pellet or a chip may be packed in a bag as a material that can be deformed according to the shape of the object to be heated in the bag.
However, since the average relative dielectric constant changes depending on the porosity, it is necessary to adjust the porosity so as to be equal to or higher than the relative dielectric constant of the object to be heated.
[0024]
For example, from Table 1 above, the relative permittivity of yellowfin tuna is about 10 in a frozen state (-15 ° C), about 20-40 in a half-thawed state (-5 ° C), and about 50-60 in a thawed state. When the rutile-type titanium dioxide (dielectric constant: 120) is used as the high dielectric material, the expected effect is required if the porosity is not less than 50% in order to increase the average relative dielectric constant to 10 or more. I can't get it.
The average relative dielectric constant when the high dielectric constant material is thinned with the low dielectric constant material is obtained by the equation shown in “Yoichi Kigi“ Fine Ceramic ”, Gihodo (1978), p. 775”.
[0025]
Embodiment 2 FIG.
FIG. 5 is a configuration diagram of the high-frequency dielectric heating device according to the second embodiment.
In the second embodiment, the periphery of the frozen tuna 6 is covered with a powder 17 of a high dielectric material as an intervening body.
In order to compare the effects of the powder 17 of the high dielectric material covering the periphery of the frozen tuna 6, the present inventor performed a test similar to that of the first embodiment by changing the powder 17 of the high dielectric material. Was. That is, in a test in which 220 g of a strip-shaped frozen tuna was thawed at a high frequency (41 MHz, maximum output of 50 W), a temporal change in the temperature distribution at that time was measured.
[0026]
In this embodiment, before performing a thawing test, first, a frozen tuna 6 to be heated which is wrapped in a wrap (trade name, manufactured by Asahi Kasei Corporation, polyvinylidene chloride) 7 in a tapper 19 which is a polypropylene container is surrounded by a tapper 19. Was covered with powder 17. At this time, the periphery of the powder 17 is surrounded by the adiabatic foam material 18.
[0027]
Examples of the powder 17 of a high dielectric material exhibiting a relatively large relative dielectric constant include titanium dioxide, titanate compounds (such as strontium titanate, calcium titanate, barium titanate, lead titanate, and magnesium titanate), zirconia, Solid solutions of zirconate compounds, other metal oxides (such as alumina), other oxide-based porcelain, silicon oxycarbide, silicon nitride, and mixtures thereof, for example, solid solutions of titanate and zirconate (PZT, PZL) And so on.
[0028]
Table 3 shows the dielectric properties of various high dielectric materials alone and the results of actual thawing tests on some of the materials.
[0029]
[Table 3]

[0030]
[Table 4]

[0031]
In addition, these values are described in “Electrostatics Society,“ Electrostatics Handbook ”, Ohmsha (1998) p595 to p597”, “Multifunctional Film Membrane Editing Committee,“ Multifunctional Film / Membrane Utilization Note ”, 1991) p75-p83 ".
In Table 3, Comparative Example 1 is a case where the powder 17 as an intervening body is not present and the periphery of the frozen tuna 6 is covered with an air layer. Comparative Example 2 is a case where the periphery of the frozen tuna 6 is covered with silicone rubber.
[0032]
The relative permittivity of the frozen tuna 6 is expected to be about 10, and from Table 3, it is understood from Table 3 that materials having an average relative permittivity of the powder 17 equal to or greater than this (titanium dioxide, titanate ( In the case of strontium, calcium, zinc, magnesium, etc.), lithium niobate, and zirconia), it was found that compared to Comparative Examples 1 and 2, uniform heating was possible and the thawing time was also shortened. It was also found that the high-frequency heating efficiency was improved.
[0033]
Desirable dielectric characteristics include a small change in dielectric characteristics under temperature conditions and a small relative dielectric loss. In this case, for example, a rare earth element (La, Ce, Zr, Th) is added to titanium dioxide. It is well known that oxides and oxides of Sn, Mg, and Zn are added to reduce the temperature coefficient, and by using these oxides, the thawing time can be further reduced and the high-frequency heating efficiency can be reduced. It is further improved (see Yoichi Kimoto "Fine Ceramic", Gihodo (1978) p783).
Since the powder 17 is desirably about the same as the relative permittivity of the frozen tuna 6, the porosity of a material having a remarkably high permittivity (such as strontium titanate, barium titanate, lead zirconate, or PZT) is reduced. What is necessary is just to make it large.
[0034]
Embodiment 3 FIG.
FIG. 6 is an explanatory diagram showing a configuration between the electrodes 4 and 5 of the high-frequency dielectric heating device according to Embodiment 3 of the present invention.
In this embodiment, a kamaboko 20, which is a body to be heated, is covered with a first intervening body 21a and a second intervening body 21b.
The kamaboko 20 has a board 20b below the kamabori surimi 20a, and is entirely wrapped with a wrap 20c.
[0035]
The first intervening body 21a and the second intervening body 21b are shaped bodies obtained by sintering the powder 17 of the high dielectric material shown in the second embodiment at a high temperature. The first intervening body 21a and the second intervening body 21b can be manufactured by bonding and drying the powder with ethyl cellulose or acrylic powder.
Also in this embodiment, as in the first and second embodiments, the dielectric characteristics are required to have a small change in dielectric characteristics under temperature conditions and a small relative dielectric loss.
[0036]
Further, for example, in the case of titanium dioxide, the sintering temperature (1400 ° C.) is high, and the composition has a large dielectric loss tangent. Therefore, it is necessary to lower the sintering temperature, and an alkaline earth metal or clay is used as a solvent therefor. Can be ZrO is added to titanium dioxide. ₂ When added, the dielectric loss tangent can be reduced. Further, as additives for adjusting the temperature coefficient, MgO, BaO, titanate, Ca—Ti salt, eutectic SiO ₂ , Al ₂ O ₃ And clay or the like (refer to Yoichi Kiki "Fine Ceramic", Gihodo (1978), p. 776).
[0037]
In the above high-frequency dielectric heating apparatus, the high voltage side electrode 4 and the plurality of Kamaboko 20 are covered with the first intermediate body 21a and the second intermediate body 21b, which are fixed bodies mainly composed of titanium dioxide. It was placed between the earth side electrode 5 and the high frequency power supply 1 was driven to apply a high frequency electric field between the high voltage side electrode 4 and the earth side electrode 5 to dielectrically heat the kamaboko 20 to freeze a plurality of pieces. When the kamaboko was thawed at the same time, it was thawed by uniform heating without local overheating. Also, the high frequency heating efficiency was improved.
[0038]
Embodiment 4 FIG.
FIG. 7 is a configuration diagram of a high-frequency dielectric heating device according to Embodiment 4 of the present invention.
In this embodiment, the upper surface of the frozen tuna 6 is covered with the high dielectric sheet 24. The high dielectric sheet 24 is made of a powder of a high dielectric ceramic (for example, PZT (a solid solution of zirconate and titanate, trade name of Clevite)) and a high dielectric polymer film (for example, polyvinylidene fluoride (PVDF)). )) And a pot-pressed composite having a relative dielectric constant of about 100 (refer to the Electrostatics Society of Japan, “Electrostatic Handbook”, Ohmsha (1998) p595 to p597).
Further, the second intervening body 25 is a thread-like material obtained by finely cutting the high dielectric material into countless pieces, and is hung on the high-voltage side electrode 4. The porosity is about 50% and the average relative dielectric constant is expected to be about 10.
[0039]
The first intervening body 8 is placed on a tray 26 made of a ceramic material having a high dielectric constant and a low dielectric loss. The earth side electrode 5 is connected to a rotation motor 27 via an insulator 28, rotates by driving the rotation motor 27, and reduces uneven heating of the frozen tuna 6 which is a heated object due to variation in electric field distribution. ing. The outer conductor container 30 and the center conductor 3a are insulated from each other by an insulator 29 (such as PTFE).
Other configurations are the same as in the first embodiment.
[0040]
The inventor of the present application performed a high-frequency thawing test on the high-frequency dielectric heating apparatus according to the fourth embodiment in the same manner as the high-frequency dielectric heating apparatus according to the first embodiment, with 220 g of frozen tuna 6 wrapped in wrap 7. Of the temperature distribution over time was measured.
According to the test result, the same effect as that of the first embodiment was obtained.
[0041]
Table 4 shows the dielectric characteristic values when various polymer film materials (piezoelectric polymers) alone and high dielectric powder materials are combined.
[0042]
[Table 5]

[0043]
[Table 6]

[0044]
In addition, these values are described in "Yoichi Motoki" Fine Ceramic ", Gihodo (1978)", "AR Von Hippel:" Dielectric Materials and Application ", MIT Press (1954)", "David R. Lide: “CRC Handbook of Chemistry and Physics” CRC Press (1996), “The Chemical Society of Japan,“ Chemical Handbook Basic Edition (Revised 4th Edition) I ”, Maruzen (1993), p-556 to p567, and“ Makoto Kakuda ” , “Microwave dielectric properties of polymer materials”, SHM Journal, Vol 9, No. (1993) p43-p44.
[0045]
The inventor of the present application used a high dielectric sheet 24, a first intervening body 8 and a second intervening body 25 for some of the combinations, and conducted a high-frequency thawing test of the frozen tuna 6 in the same manner as in the first embodiment. Was performed, and the change with time in the temperature distribution at that time was measured.
[0046]
As the high dielectric powder material, a material having a particularly high relative dielectric constant in Table 3 is preferable. Examples of the material include strontium titanate, a solid solution of titanate and zirconate (PZT, PLZT), and zirconate of Ba-Pb.
Even as a polymer film material, even a piezoelectric polymer (vinylidene fluoride, polyvinylidene fluoride, cellulose acetate, nylon, polyurethane, etc.) having a relatively high relative dielectric constant (at about 3 to 1 at 1 MHz) is used. Alternatively, a polymer material having a low relative dielectric constant per se, such as polyethylene terephthalate, polypropylene, polystyrene, or polytetrafluoroethylene may be used.
For example, the present inventor uses a high dielectric sheet 24 in which Ba-Pb zirconate powder is dispersed in vinylon (a typical trade name of polyvinylidene chloride acetate) and a pill-shaped high dielectric to prepare frozen tuna. As a result of performing the high-frequency thawing test of No. 6, it was confirmed that the thawing time was shortened and the high-frequency heating efficiency was improved.
[0047]
Furthermore, the Curie point (the temperature at which the dielectric constant changes remarkably) of powder materials such as barium titanate and lead zirconate is designed to be about 0 ° C. to 20 ° C. (for example, Yoichi Kiki "Fine Ceramic", Gihodo (1978) ) P804), the high dielectric sheet 24 formed by dispersing the same, the frozen food changes its phase from solid to liquid and follows the increase of the relative dielectric constant, and the relative dielectric constant increases. It is possible to maintain the same relative dielectric constant as that of an object such as food.
[0048]
Note that, as shown in FIG. 8, a plurality of objects to be heated may be placed on the first intervening body 8 so that a plurality of objects to be heated are induction-heated at the same time.
[0049]
As shown in FIG. 9, instead of this second intervening body 25, a second intervening body 50 of the high-frequency dielectric heating apparatus according to the first embodiment is used, and a plurality of objects to be heated are simultaneously subjected to induction heating. You may make it.
[0050]
In the first to fourth embodiments, the electrodes 4 and 5 are the most common plate electrodes, but are not limited to these electrodes. For example, it may be a grid electrode, a roller electrode, a movable electrode, or the like (see Toyoaki Omori, “Electromagnetic Waves and Foods”, Korin (1993) pp. 46-53).
Even when these electrodes are used, by arranging the high dielectric substance so as to cover the object to be heated, the influence of the air layer is reduced, local overheating can be suppressed, and uniform heating can be realized.
[0051]
In the first to fourth embodiments, the matching device 2 that matches the load impedance between the electrodes 4 and 5 and the output impedance of the high-frequency power supply 1 is used. In the case where the ratio of the capacitance other than the object such as food is sufficiently large, the variable condenser adjustment of the matching box 2 is unnecessary, and high-frequency dielectric heating can be performed without using the matching box 2 itself. It is possible.
[0052]
Embodiment 5 FIG.
FIG. 10 is an explanatory diagram illustrating a configuration of a microwave heating apparatus according to Embodiment 5 of the present invention.
In the microwave dielectric heating device which is the dielectric heating device in this embodiment, the microwave generated by the magnetron 33 passes through the waveguide 34 and is irradiated into the high electric field space 35, and the microwave is irregularly reflected. The frozen tuna 6 is heated.
The periphery of the frozen tuna 6 which is the object to be heated is covered with a powder 17 of a high dielectric material which is an intervening body.
The tapper 19 containing the frozen tuna 6 is placed on a turntable 36 via a tray 26 made of a high dielectric material. The turntable 36 is connected to the rotation motor 27 via the insulator 28. In the turntable 36, the variation of the electric field applied to the frozen tuna 66 is reduced by the driving of the rotary motor 27.
[0053]
The inventor of the present application measured the thawing time of the frozen tuna 6 and the microwave heating efficiency in order to confirm the effect of the presence or absence of the high dielectric powder 17 in the microwave heating device.
Actually, 220 g of frozen tuna 6 was thawed under a constant microwave output of 10 W under a constant condition, and the thawing time (time required for the center to reach -20 ° C. to 2 ° C.) and microwave heating efficiency were measured.
Table 5 shows the measurement results. From Table 5, when the object to be heated is covered with the high dielectric powder 17, the thawing time is shortened, and the microwave heating efficiency (= the amount of heat applied to the object to be heated / microwave power output) is improved. You can see that.
[0054]
[Table 7]

[0055]
As described above, even in the microwave heating, by covering the frozen tuna 6 placed in the high electric field space with the powder 17 of the high dielectric substance, the microwave heating efficiency can be improved and energy saving can be achieved. It could be confirmed.
[0056]
In the first to fifth embodiments, the case where the frozen tuna 6, which is a frozen food, is thawed by dielectric heating has been described. However, the dielectric heating means described in the first to fifth embodiments may be replaced by the dielectric heating means. For example, the present invention can be applied to a refrigeration method disclosed in JP-A-2001-245645.
That is, the frozen object such as food is dielectrically heated by the dielectric heating means, cooled with energy larger than the energy absorbed by the frozen object due to the dielectric heating, and the frozen object is frozen to produce fresh food or the like. Can be frozen to a high degree of freshness.
[0057]
Further, in the first to fifth embodiments, the frozen tuna 6 which is a frozen food is described as the object to be heated, but is not limited to this. For example, a medical-related heated body other than food may be an organ, a cell, a medicine, a human body, an animal, a plant, or the like. In addition, the object to be heated for industrial use may be wood, a fiber product, a resin molded product, a ceramic, or the like.
[0058]
【The invention's effect】
As described above, according to the dielectric heating device according to the present invention, in the dielectric heating device that performs the dielectric heating by applying an electric field between the electrodes to be heated, which is placed between the pair of opposed electrodes, Since the object to be heated is covered with an intermediate having a relative dielectric constant that is equal to or greater than the relative dielectric constant of the object to be heated, the influence of an air layer between the electrodes is suppressed to a low level. Local overheating of the object to be heated such as food can be prevented, and the thawing time can be reduced.
In addition, the variation of the load impedance between the electrodes can be reduced, and the size, the cost, and the energy saving of the matching device can be reduced.
[0059]
Further, according to the dielectric heating device of the present invention, the object to be heated is placed in the electric field space irradiated with microwaves, and in the dielectric heating device to be dielectrically heated, the object to be heated has a ratio of the object to be heated. Since it is covered with an intermediate having a dielectric constant equal to or higher than the dielectric constant, the effect of the air layer in the electric field space can be kept low, and it is possible to prevent local overheating of the heated object such as irregular shaped foods. Also, the thawing time can be shortened.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a high-frequency dielectric heating device according to a first embodiment of the present invention.
FIG. 2 is an explanatory diagram showing the shape and temperature distribution measurement points of frozen tuna used in a thawing test for verifying Embodiment 1 of the present invention.
FIG. 3 is a diagram showing a time-dependent change of a temperature distribution when high-frequency thawing is performed in a state where frozen tuna is covered with a high dielectric substance according to Embodiment 1 of the present invention.
FIG. 4 is a diagram illustrating a temporal change of a temperature distribution when frozen tuna is thawed at a high frequency without being covered with a high dielectric substance as Comparative Example 1 with the first embodiment.
FIG. 5 is a configuration diagram of electrodes of a high-frequency dielectric heating device according to a second embodiment of the present invention.
FIG. 6 is a configuration diagram of electrodes of a high-frequency dielectric heating device according to Embodiment 3 of the present invention.
FIG. 7 is a configuration diagram of a high-frequency dielectric heating device according to a fourth embodiment of the present invention.
8 is a main part configuration diagram showing another example of the high-frequency dielectric heating device of FIG. 7;
FIG. 9 is a main part configuration diagram showing another example of the high-frequency dielectric heating device of FIG. 7;
FIG. 10 is a configuration diagram of a microwave dielectric heating device according to a fifth embodiment of the present invention.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 high-frequency power supply, 2 matching box, 4 high-voltage side electrode, 5 ground-side electrode, 6 frozen tuna (heated body), 8 first intervening body, 17 powder (intervened body), 20 kamaboko (heated body), 21a 1st interposed body, 21b 2nd interposed body, 24 high dielectric sheet, 25 2nd interposed body, 35 high electric field space.

Claims (8)

In a dielectric heating apparatus that performs dielectric heating by applying an electric field between the electrodes to be heated, which is placed between a pair of opposed electrodes,
A dielectric heating apparatus, wherein the object to be heated is covered with an intermediate having a dielectric constant equal to or greater than the relative dielectric constant of the object to be heated. The object to be heated is placed in an electric field space where microwaves are irradiated, and in a dielectric heating device in which dielectric heating is performed,
A dielectric heating apparatus, wherein the object to be heated is covered with an intermediate having a dielectric constant equal to or greater than the relative dielectric constant of the object to be heated. 2. The pair of electrodes and a high-frequency power supply that applies an electric field between the electrodes are electrically connected to matching devices that match a load impedance between the electrodes and an output impedance of the high-frequency power supply. 3. 3. The dielectric heating device according to claim 1. The dielectric heating device according to claim 1, wherein the intervening body is deformable along an outer surface of the object to be heated. The dielectric heating device according to claim 1, wherein the intervening body includes a gap, and the relative permittivity is adjusted by adjusting a ratio of the gap. Between the object to be heated and the intervening body, a powder of a high dielectric material whose relative dielectric constant is higher than that of the object to be heated is dispersed in a polymer film having a higher relative dielectric constant than the object to be heated. The dielectric heating device according to any one of claims 1 to 5, wherein a high dielectric sheet configured as described above is interposed. The high-dielectric sheet follows an increase in relative dielectric constant due to a phase change from a solid to a liquid of the object to be heated, so that a relative dielectric constant similar to the relative dielectric constant of the object to be heated is ensured. 7. The dielectric heating device according to claim 6, wherein The dielectric heating device according to claim 1, wherein a plurality of the objects to be heated are placed inside.

Images