JP2004077021A

JP2004077021A - Gas cooler

Info

Publication number: JP2004077021A
Application number: JP2002238085A
Authority: JP
Inventors: Shigeto Yamaguchi; 山口　成人; Shoichi Yokoyama; 横山　昭一
Original assignee: Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Holdings Corp
Priority date: 2002-08-19
Filing date: 2002-08-19
Publication date: 2004-03-11

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem of a gas cooler: wherein, if the temperature of refrigerant has a condition characteristic of sensible heat changes with a temperature gradient in a supercritical area without phase changes at all times during the radiation process of the gas cooler, the heat transfer performance of a heat exchanger cannot be enhanced effectively, resulting in a decrease in the performance of a refrigerating cycle device and increases in the size and cost of the heat exchanger. <P>SOLUTION: In the gas cooler, fins making close contact with the outer surface of a heat transfer pipe are densely spaced apart where the temperature difference between air and refrigerant is lowest so as to increase heat efficiency. Thus, the effective gas cooler can be provided even if the temperature of the refrigerant has a condition characteristic of latent heat changes with a temperature gradient in the supercritical area. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、高圧側の冷媒圧力が冷媒の臨界圧力以上となる超臨界蒸気圧縮式冷凍サイクルに関するものであり、空気調和装置に適用して有効なものである。
【０００２】
【従来の技術】
従来、オゾン層破壊、地球温暖化など地球環境側面から特定フロンであるＨＣＦＣ系の冷媒から、ＨＦＣ系の代替冷媒がへの変更がなされている。しかし、これらの冷媒でも、地球温暖化係数が十分に小さいものでない為、近年、温暖化係数が小さく、工夫次第では成績係数も向上して期待が持たれる二酸化炭素が注目を浴びてきている。
【０００３】
しかし、二酸化炭素においては、臨界温度が一般的に、約３１．０５℃といわれており、従来のＨＣＦＣ系冷媒Ｒ２２（臨界温度約９６℃）やＨＦＣ系冷媒Ｒ４１０Ａ（臨界温度約７２℃）に対してかなり低い温度となっている。また、凝縮過程においては、従来のＨＦＣ系冷媒やＨＣＦＣ系冷媒では顕熱と潜熱変化が混在していたが、二酸化炭素においては、凝縮過程に相当する過程において、熱力学的特性から既に臨界温度と臨界圧力を超えた超臨界領域で作動する流体となり、超臨界領域での顕熱変化だけ起こるという作動となる特徴がある。
【０００４】
図１６は、従来のＨＦＣ系冷媒等が熱交換器（ガスクーラー）における冷媒と空気の温度状態を簡易的に示したものであり、縦軸に冷媒と空気の温度Ｔ、横軸に冷媒のエンタルピーｈを示し、実線が熱交換器内部の伝熱管を流れる冷媒の温度変化状態を示し、破線が空気の温度変化状態を示したものであり、冷媒と空気が対向流的な流れ方で熱交換した場合の状態を示したものである。ここでは、常に温度変化が小さく、熱伝達率の高い潜熱変化を有する気液二相領域が熱交換器の大部分を占めて支配的であり、空気側との熱交換性能を向上させる為には、性能向上効果が大きく、かつ顕熱変化を起こして冷媒側熱伝達率が低下する熱交換器出口（ガスクーラー出口）近傍に限定して熱交換性能を向上させる工夫がなされ、更に最も冷媒の温度差の大きい熱交換器出入り口の伝熱管が空気の流れに対して対向流的な流れになるように配置していた。
【０００５】
次に、図１７には、超臨界領域で動作する二酸化炭素が、熱交換器（放熱器）で放熱する場合の冷媒と空気の温度状態を簡易的に示す。この図１７では、熱交換器の入口で空気と冷媒の温度差が最も大きかったが、冷媒と空気の熱交換が進むにつれて温度差が小さくなり、熱交換の途中であっても、空気と冷媒がお互いに顕熱変化を起こし温度差が最小になる領域が図１６に示す従来のＨＦＣ系冷媒等を用いた場合よりも多く存在するため、二酸化炭素を冷媒として用いた場合は特開昭６３−３１８８号公報や特開２０００−３０４３８０号公報に示されように対向流的に冷媒と空気を流し、コストをかけて熱交換器全体の高性能化、特にフィンの形状や伝熱管のパス数等を減少させて改善することが行なわれていた。
【０００６】
【発明が解決しようとする課題】
しかしながら、二酸化炭素等を用いた冷凍サイクルにおいて、熱交換器の放熱過程において熱交換器の出入口で数十℃の最大温度差を発生しながら常に相変化を伴わないで超臨界領域で、温度勾配をもつ顕熱変化特有の冷媒温度状態を有する場合に、上記従来例に示すように熱交換器全体の改善をすると効果的な熱交換器の伝熱性能も向上が図れないばかりか、冷凍サイクル装置自身の性能が低下し、通風抵抗が増えることによる騒音の増大、熱交換器の巨大化、高コストになるという課題を有していた。
【０００７】
本発明はこのような従来の課題を解決するものであり、熱交換器内部で温度勾配を有し且つ超臨界領域で作動する冷媒を使用した場合でも、従来の冷媒を超臨界領域以下で使用した場合と同等以上に高性能化を図ることにより、効果的に低コストで熱交換効率の高い熱交換器を提供することを目的とする。
【０００８】
【課題を解決するための手段】
上記課題を解決するために請求項１記載の発明は、臨界圧力以上となる冷媒が流通するガスクーラーであって、前記ガスクーラーの伝熱管の外面に密着するフィンのピッチを空気と冷媒の温度差が小さくなった部分を密にしたことを特徴とする。
【０００９】
また、請求項２記載の発明は、臨界圧力以上となる冷媒が流通するガスクーラーであって、前記ガスクーラーの伝熱管の外面に密着するフィンの切り起し数を空気と冷媒の温度差が小さくなった部分を増加させたことを特徴とする。
【００１０】
また、請求項３記載の発明は、臨界圧力以上となる冷媒が流通するガスクーラーであって、前記ガスクーラーの伝熱管の外面に密着するフィンの切り起こし高さを空気と冷媒の温度差が小さくなった部分を高くしたことを特徴とする。
【００１１】
また、請求項４記載の発明は、臨界圧力以上となる冷媒が流通するガスクーラーであって、前記ガスクーラーの伝熱管のピッチを空気と冷媒の温度差が小さくなった部分を密にしたことを特徴とする。
【００１２】
また、請求項５記載の発明は、臨界圧力以上となる冷媒流通するガスクーラーであって、前記ガスクーラーの伝熱管の直径とピッチを、空気と冷媒の温度差が小さくなった部分において、直径を小さくし、ピッチを密にしたことを特徴とする。
【００１３】
また、請求項６記載の発明は、臨界圧力以上となる冷媒が流通するガスクーラーであって、前記ガスクーラーの伝熱管の内面フィンを空気と冷媒の温度差が小さくなった部分を高しくたことを特徴とする。
【００１４】
また、請求項７記載の発明は、臨界圧力以上となる冷媒が流通するガスクーラーであって、前記ガスクーラーの伝熱管の内面フィンのピッチを空気と冷媒の温度差が小さくなった部分を密にしたことを特徴とする。
【００１５】
また、請求項８記載の発明は、請求項１〜７記載のガスクーラーにおいて、併せてガスクーラーの出入口部も変化させたことを特徴とする。
【００１６】
また、請求項９記載の発明は、前記空気と冷媒が対向流的に熱交換を行うことを特徴とする。
【００１７】
また、請求項１０記載の発明は、前記冷媒が二酸化炭素であることを特徴とする。
【００１８】
【発明の実施の形態】
以下本発明の実施の形態について図面を参照して説明する。
【００１９】
（実施の形態１）
図１、図２においては、例えば、超臨界領域で動作する二酸化炭素等の冷媒と空気が熱交換を行なう室内ユニット１と室外ユニット５の構成概略を側面側から見た図であり、空気と冷媒の熱交換を行なう為に、図１の室内ユニット１では室内送風ファン２と冷媒が通過する伝熱管４が組み合わさった室内熱交換器で構成され、図２の室外ユニット４は室外送風ファン７と室外熱交換器６で構成される。
【００２０】
また、本発明第１の実施の形態では冷房運転時の室外熱交換器６が、暖房運転時の室内熱交換器３と同じように冷媒を放熱する役目をするので、室外熱交換器６の作用については割愛し、以下にはガスクーラーとして作用する室内熱交換器３を中心に説明する。
【００２１】
図４は、室内ユニット１での室内熱交換器３を長手方向となる正面側から見た図であり、図５は、図４に示す室内熱交換器３のア−アの線で示した矢視断面図である。
【００２２】
また、図７は、図４における室内熱交換器３のフィン群ＡのＸ−Ｘ´線を結ぶ拡大概略図であり、フィンピッチがα１（例えば３ｍｍ）であり、図８は、同じく図４に示すフィン群ＢのＹ−Ｙ´線を結ぶ拡大概略図であり、フィンピッチはα１よりも小さいα２（例えば１．５ｍｍ）となり、密になっている。
【００２３】
図３は、図４または図５で放熱される二酸化炭素の冷媒が、暖房運転時に室内ユニット１の室内熱交換器３で放熱する場合の冷媒と空気の温度状態を簡易的に示したものである。
【００２４】
図３では、縦軸に冷媒と空気の温度Ｔ、横軸に冷媒のエンタルピーｈを示す。
実線が室内熱交換器３内部の伝熱管４を流れる冷媒の温度変化状態を示し、破線が空気の温度変化状態を示したものであり、対向流的な流れ方で熱交換した場合の状態を示したものである。また、伝熱管４に密着して空気側との熱交換を促進させる放熱フィン７（フィンピッチの広いフィン群Ａとフィンピッチの狭いフィン群Ｂに分けて構成）により空気側に放熱されるが、まず、点Ａ（４ａ）は室内熱交換器３の入口の伝熱管４ａの冷媒温度Ｔａ（例えば１００℃）であり、点Ｂ（４ｂ）から点Ｃ（４ｃ）は、伝熱管４ｂから４ｃの伝熱管までの冷媒の温度Ｔｂ（例えば６０℃）とＴｃ（例えば５５℃）である。この伝熱管４ｂから４ｃまでを冷媒が流れながら空気側と熱交換する際に、図３にハッチングして示すように、空気側との温度差が最も小さくなる最小温度差ΔＴ（例えば５ｄｅｇ）領域部分であると同時に冷媒と空気の熱交換性能が最も低下する領域が大きく存在する。この領域を通過した冷媒は図５に示す空気側の風上になる伝熱管４を通過し、点Ｄ（４ｄ）は室内熱交換器３の出口である伝熱管４ｄの冷媒の温度Ｔｄ（例えば２５℃）を示す点である。
【００２５】
尚、以下に説明する伝熱管４は、室内熱交換器３の冷媒入口に挿入されている最初の伝熱管を４ａ、空気と冷媒の温度差が最小となり、室内熱交換器３の熱交換性能が低下する領域を示すフィンに挿入されている最初の伝熱管４を伝熱管４ｂ、領域の終りを伝熱管４ｃと呼び、室内熱交換器３の冷媒出口の伝熱管を４ｄとし、それ以外は総称して伝熱管４と呼ぶ。
【００２６】
従来のＨＦＣ系等の冷媒よりも大きく生じた場合でも、空気とフィンの接触する伝熱面積が大きくなり熱交換率が向上する。図３に示すように、ここでは熱交換器の入口で空気と冷媒の温度差が最も大きかったが、熱交換が進むにつれて小さくなり、放熱過程の途中、部分的に空気と冷媒の温度差が取れにくい状態が発生し、ここでは熱交換効率が低下してしまう領域があり、従来の潜熱変化を起していたＨＦＣ系等の冷媒よりもその領域は大きくなる。
【００２７】
よって、図４および図５に示す点Ｂから点Ｃの間、即ち、伝熱管４ｂから４ｃの間の伝熱管４に密着するフィン７のピッチを図７に示すようにピッチを部分的にα２（例えば１．５ｍｍ）に小さくすることにより、フィンの伝熱面積が大きくなるので図３に示す放熱過程において、部分的に空気と冷媒の温度差が取れにくい状態で熱交換効率が低下してしまう領域が大きく存在しても、この実施の形態によれば、部分的にフィンピッチを密にすることにより、フィンの投入量を増加させるだけで効果的に低コストで簡単に室内熱交換器の熱交換率を向上させ、超臨界で温度変化する二酸化炭素を冷媒に用いた場合でも、高性能の室内熱交換器を提供できる。
【００２８】
なお、上記室内熱交換器のフィンピッチを密にする部分は、図４に示すような形態を問わず、部分的に熱交換器の１箇所だけでなく、冷媒と空気の温度差が小さくなる室内熱交換器の出口も合わせて２箇所以上のフィンピッチを密にして熱交換効率を向上させても構わない。さらに、２箇所以上のフィンピッチは各々、同じ値でなくても構わない。
【００２９】
また、フィンピッチを密にする部分は製造上困難で、コストがかさむ場合や、その他の不具合が生じる場合は低コスト化等のメリットが図れるように、冷媒と空気の温度差が取れている領域まで広がっても構わず、必ずしも図４，５の形態をとる熱交換器でなくても良い。
【００３０】
（実施の形態２）
本発明第２の実施の形態では、図８には、図４、５に示すようにフィン群Ａ，Ｂのフィン７の切り起こし形状と数を拡大した概略図であり、台形ルーバ７ｂが切り起こされており、空気側と積極的に熱交換するようにしている。図４、５では、空気側との温度差が最も小さくなり熱交換性能が低下するフィン群Ｂに相当するところに、空気側の熱交換性能を向上させる為に、図９に示すように台形ルーバ７ｂの数を増大させたフィン７ａを用いることで、図３での放熱過程の途中、空気と冷媒の温度差が取れにくい状態で熱交換効率が低下してしまう領域が、従来のＨＦＣ系等の冷媒よりも大きく生じた場合でも、この実施の形態によれば空気と台形ルーバ７ｂの数を増大させることにより、フィンと空気が接触する伝熱面積が大きくなり熱交換効率が向上する。
【００３１】
従って、簡単に室内熱交換器の熱交換効率を向上させ、超臨界で温度変化する二酸化炭素を冷媒に用いた場合でも、高性能の室内熱交換器を提供できる。
【００３２】
また、図１０は図８に示すフィン７のイ−イの線で示した矢視断面図である。
図１０に示すように、熱交換器が部分的に熱交換性能が低下するフィン群７２に相当するところにフィン７の台形ルーバ７ｂの切り起し高さを従来よりの所定高さｈ（例えば０．７ｍｍ）よりΔｈ（０．３ｍｍ）高い、フィン高さβ（例えば１．０ｍｍ）にしてフィンピッチを密にすることで同様に図３に示すように、放熱過程の途中、部分的に空気と冷媒の温度差が取れにくい状態で熱交換効率が低下してしまう領域が、従来のＨＦＣ系等の冷媒よりも大きく生じた場合でも、この実施の形態によればにより、フィン７の台形ルーバ７ｂの切り起し高さを従来よりの所定高くすることによりフィンと空気が接触する伝熱面積が大きくなり熱交換率が向上し、更に高性能の室内熱交換器を提供できる。
【００３３】
よって、本発明第２の実施の形態と同様に、熱交換性能が低下する領域においてフィンの切り起こし数および高さを高くすることにより、空気と冷媒の温度差が取れにくい状態で熱交換効率が低下してしまう領域において、空気と台形ルーバ７ｂの切り起し数と高さを大きくして伝熱面積を増大させることにより、フィンと空気が接触する伝熱面積が大きくなり熱交換効率が向上する。
【００３４】
また、効果的に低コストで簡単に室内熱交換器の熱交換効率を向上させ、超臨界で温度変化する二酸化炭素を冷媒に用いた場合でも、高性能の室内熱交換器を提供できる。
【００３５】
また、高性能化を図ることができれば、フィンの形状を変えたり、フィンの高さや数等は、上記実施の形態にこだわらず変えても構わない。
【００３６】
さらに、高性能化を図ることができればフィンの形状や高さや、数を変えるだけで、フィン群Ａとフィン群Ｂは同ピッチのままでも構わない。
【００３７】
（実施の形態３）
本発明第３の実施の形態では、図１１には、図４、５に示すように空気側との温度差が最も小さくなり室内熱交換器が部分的に熱交換性能が低下するフィン群Ｂに相当するところ、即ち伝熱管４ｂから４ｃが挿入されている部分のブロックを中心に拡大した概略図であり、図１１に示すように図５の伝熱管４ｂから４ｃの間の伝熱管４を２本増やして、伝熱管４のピッチを風上の上流側の伝熱管４のピッチγ１（例えば１５ｍｍ）より小さいγ２（例えば１０ｍｍ）に密にすることにより、伝熱管の本数が増加したことにより管内の伝熱面積が増大し、熱交換器の熱交換効率を向上させることが可能となる。また、同様に図１２に示すように、図１１の伝熱管４ｂから４ｃ間の伝熱管の間に伝熱管４の直径Ｄ１（例えば７．５ｍｍ）を小さくした直径Ｄ２（例えば４ｍｍ）の細管伝熱管４１を挿入して、細管電伝熱管４１のピッチをγ３（例えば７ｍｍ）にして密にすることにより、同一フィン群Ｂに挿入されている細管伝熱管４１の本数も増えて管内伝熱面積が増えると共に、伝熱管４の直径を小さくして断面積を縮小したことで冷媒の流速が増して冷媒の熱伝達率も向上し、二酸化炭素のような低圧力損失の特徴を持つ冷媒を用いることで、冷凍サイクル装置の性能を低下させることなく、効果的に冷媒側の熱交換率が向上する。
【００３８】
よって、超臨界で温度変化する二酸化炭素を冷媒に用いた場合でも、図３に示すように、放熱過程の途中で、部分的に空気と冷媒の温度差が取れにくい状態で熱交換効率が低下してしまう領域が、従来のＨＦＣ系等の冷媒よりも大きく生じた場合でも、伝熱管のピッチを小さくし、細管伝熱管を挿入させることにより、管内の伝熱面積が大きくなると共に、冷媒側の熱伝達率も上がり、熱交換率が向上する。
【００３９】
また、高性能化を図ることができれば、伝熱管の本数や管直径およびピッチ等は上記実施の形態にこだわらない、さらに、伝熱管に密着するフィンは上記実施の形態２のフィンを組合せても構わない。
【００４０】
（実施の形態４）
図１３には、図４、５に示す伝熱管４の内面フィン８の形状を拡大したものであり、図１４は更に、図１３の内面フィン８の部分を拡大しものである。図１５におけるフィン８の山高さｈ１（例えば０．３ｍｍ）とフィンのピッチｐ１（例えば０．２ｍｍ）を示すものであるが、図４、５に示すように空気側との温度差が最も小さくなり室内熱交換器が部分的に熱交換性能が低下するフィン群Ｂに相当するところに、特に図５に示す伝熱管４ｂから４ｃが挿入されている部分に、図１５に示すような、フィン８の山高さｈ２（例えば０．５ｍｍ）とフィンのピッチｐ２（例えば０．１ｍｍ）にすることにより、伝熱管内のフィンの伝熱面積が大きくなるので図３に示すように、放熱過程において、部分的に空気と冷媒の温度差が取れにくい状態で熱交換効率が低下してしまう領域が大きく存在しても、本実施の形態によれば、管内フィンのピッチを小さくし、管内フィンの山高さを高くすることにより、管内フィンと冷媒が接触する面積が大きくなると共に、冷媒側の熱伝達率も上がり、熱交換率が向上し、超臨界で温度変化する二酸化炭素を冷媒に用いた場合でも、高性能の室内熱交換器を提供できる。
【００４１】
また、高性能化を図ることができれば、伝熱管の内面フィンの高さやピッチ、および、伝熱管の本数や管直径およびピッチ等に関係なく、変更しても構わない。
【００４２】
また、内面フィンの形状や内面フィンの高さが部分的に変化したり、上記実施の形態と、異なっても構わない。
【００４３】
【発明の効果】
上記から明らかなように、請求項１に記載の発明は、冷媒と空気が最小温度差となり熱交換性能が低下する部分のフィンピッチを密にすることにより、超臨界で温度変化するを冷媒に用いた場合でも、的確に高性能のガスクーラーを提供できる。
【００４４】
請求項２に記載の発明は、冷媒と空気が最小温度差となり熱交換性能が低下する部分のフィン切り起こし数を多くすることにより、超臨界で温度変化する冷媒を用いた場合でも、低コストで容易に高性能のガスクーラーを提供できる。
【００４５】
請求項３に記載の発明は、冷媒と空気が最小温度差となり熱交換性能が低下する部分のフィンの高さを高くすることにより、空気側の伝熱面積が増大し、超臨界で温度変化する冷媒を用いた場合でも、低コストで容易に高性能のガスクーラーを提供できる。
【００４６】
請求項４に記載の発明は、冷媒と空気が最小温度差となり熱交換性能が低下する部分の室内伝熱管のピッチを密にして、本数を増やしたことで冷媒側の伝熱面積が増大し、超臨界で温度変化する冷媒を用いた場合でも、フィンの変更を伴うことなく低コストで容易に高性能のガスクーラーを提供できる。
【００４７】
請求項５に記載の発明は、冷媒と空気が最小温度差となり熱交換性能が低下する部分の室内伝熱管との管直径を小さくしたことで、冷媒の流速向上に伴う冷媒熱伝達性能も向上し、ピッチを密にして数を増やしたことにより、フィンの変更を伴うことなく低コストで容易に高性能のガスクーラーを提供できる。
【００４８】
請求項６に記載の発明は、冷媒と空気が最小温度差となり熱交換性能が低下する部分の室内伝熱管の内面フィンの高さを高くして冷媒側の熱伝達性能を高いものにすることで、フィンの変更を伴うことなく、さらに伝熱管の使用本数を抑えることで、さらなる低コストで容易に高性能のガスクーラーを提供できる。
【００４９】
請求項７に記載の発明は、冷媒と空気が最小温度差となり熱交換性能が低下する部分の室内伝熱管の内面フィンのピッチを密にして冷媒側の熱伝達性能を高いものにすることで、フィンの変更を伴うことなく、さらに伝熱管の使用本数を抑えるとともに、工法上、加工しやすくなる為に、さらなる低コストで容易に高性能のガスクーラーを提供できる。
【００５０】
請求項８に記載の発明は、ガスクーラーの出入口も変化することにより、超臨界で温度変化する冷媒に用いた場合でも、更に効果的に高性能化の室内熱交換器を提供できる。
【図面の簡単な説明】
【図１】本発明の一実施例を示す室内ユニットの概略断面図
【図２】本発明の一実施例を示す室外ユニットの概略断面図
【図３】本発明の一実施例を示す熱交換器での二酸化炭素と空気の温度状態図
【図４】本発明の一実施例を示す室内熱交換器の正面概略図
【図５】本発明の一実施例を示す室内熱交換器の概略断面図
【図６】本発明の一実施例を示す図４のＸ−Ｘ´の矢視断面図
【図７】本発明の一実施例を示す図４のＹ−Ｙ´の矢視断面図
【図８】本発明の一実施例を示す室内熱交換器ルーバフィンの拡大概略図
【図９】本発明の一実施例を示す室内熱交換器の台形ルーバを増加したフィンの拡大概略図
【図１０】本発明の一実施例を示す図８のイ−イ矢視断面図
【図１１】本発明の一実施例を示す室内熱交換器フィン群Ｂの伝熱管ピッチの関係を示した概略断面図
【図１２】本発明の一実施例を示す室内熱交換器フィン群Ｂの伝熱管ピッチと管径を示した概略断面図
【図１３】本発明の一実施例を示す図４，５の伝熱管の内面フィンの拡大断面図
【図１４】本発明の一実施例を示す図１３の伝熱管の内面フィンの拡大詳細図
【図１５】本発明の一実施例を示す図１３の伝熱管内面フィンの山高さを高くして、ピッチを密にした拡大詳細図
【図１６】従来のＨＦＣ系冷媒と空気の温度状態図
【図１７】二酸化炭素冷媒と空気の温度状態図
【符号の説明】
１　室内ユニット
２　室内送風ファン
３　室内熱交換器
４　伝熱管
４１　細管伝熱管
４ａ　伝熱管
４ｂ　伝熱管
４ｃ　伝熱管
４ｄ　伝熱管
５　室外ユニット
６　室外熱交換器
７、７ａ　フィン
７ｂ　台形ルーバ
８　伝熱管内面フィン[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a supercritical vapor compression refrigeration cycle in which the refrigerant pressure on the high pressure side is equal to or higher than the critical pressure of the refrigerant, and is effective when applied to an air conditioner.
[0002]
[Prior art]
Conventionally, from the aspect of the global environment such as ozone layer depletion and global warming, the HCFC-based refrigerant, which is a specific freon, has been changed to an HFC-based alternative refrigerant. However, even with these refrigerants, since the global warming potential is not sufficiently small, in recent years, carbon dioxide, which has a low global warming potential and an improved coefficient of performance depending on the device, has attracted attention.
[0003]
However, the critical temperature of carbon dioxide is generally said to be about 31.05 ° C., which is lower than that of the conventional HCFC-based refrigerant R22 (critical temperature of about 96 ° C.) or HFC-based refrigerant R410A (critical temperature of about 72 ° C.). On the other hand, the temperature is quite low. In the condensing process, sensible heat and latent heat change were mixed in the conventional HFC-based refrigerant and HCFC-based refrigerant. However, in the process corresponding to the condensing process, the critical temperature of the carbon dioxide was already critical temperature due to the thermodynamic characteristics. And a fluid that operates in a supercritical region exceeding the critical pressure, and is characterized in that only a sensible heat change occurs in the supercritical region.
[0004]
FIG. 16 schematically shows the temperature state of the refrigerant and the air in the heat exchanger (gas cooler) of the conventional HFC-based refrigerant and the like. The vertical axis represents the temperature T of the refrigerant and the air, and the horizontal axis represents the temperature of the refrigerant. The enthalpy h is shown, the solid line shows the temperature change state of the refrigerant flowing through the heat transfer tube inside the heat exchanger, and the broken line shows the temperature change state of the air. This shows a state in the case of replacement. Here, the gas-liquid two-phase region having a small temperature change and a latent heat change having a high heat transfer coefficient occupies most of the heat exchanger and is dominant, and in order to improve the heat exchange performance with the air side. Has been devised to improve the heat exchange performance only in the vicinity of the heat exchanger outlet (gas cooler outlet) where the performance improvement effect is large and the sensible heat change causes a decrease in the heat transfer coefficient on the refrigerant side. The heat transfer tubes at the entrance and exit of the heat exchanger having a large temperature difference are arranged so as to be countercurrent to the flow of air.
[0005]
Next, FIG. 17 simply shows the temperature states of the refrigerant and the air when carbon dioxide operating in the supercritical region radiates heat in the heat exchanger (radiator). In FIG. 17, the temperature difference between the air and the refrigerant at the inlet of the heat exchanger was the largest, but the temperature difference became smaller as the heat exchange between the refrigerant and the air progressed. There are more areas where sensible heat changes occur and the temperature difference is minimized as compared with the case where the conventional HFC-based refrigerant or the like shown in FIG. 16 is used. As disclosed in JP-A-3188 / 2000 and JP-A-2000-304380, refrigerant and air are caused to flow in countercurrent to increase the performance of the entire heat exchanger at a high cost, especially the shape of the fins and the number of passes of the heat transfer tubes. And so on.
[0006]
[Problems to be solved by the invention]
However, in a refrigeration cycle using carbon dioxide, etc., a temperature gradient of several tens of degrees Celsius is generated at the entrance and exit of the heat exchanger during the heat radiation process of the heat exchanger, and the temperature gradient is always in the supercritical region without phase change. In the case of having a refrigerant temperature state peculiar to sensible heat change, when the entire heat exchanger is improved as shown in the above-described conventional example, not only the effective heat transfer performance of the heat exchanger cannot be improved, but also the refrigeration cycle. There is a problem that the performance of the apparatus itself is reduced, the noise is increased due to an increase in ventilation resistance, the heat exchanger is enlarged, and the cost is increased.
[0007]
The present invention solves such a conventional problem. Even when a refrigerant having a temperature gradient inside a heat exchanger and operating in a supercritical region is used, the conventional refrigerant is used below the supercritical region. It is an object of the present invention to provide a heat exchanger having high heat exchange efficiency at low cost effectively by improving the performance to be equal to or higher than that of the heat exchanger.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the invention according to claim 1 is a gas cooler through which a refrigerant having a critical pressure or higher flows, wherein the pitch of the fins closely contacting the outer surface of the heat transfer tube of the gas cooler is controlled by the temperature of the air and the refrigerant. It is characterized in that the portion where the difference is small is made dense.
[0009]
Further, the invention according to claim 2 is a gas cooler through which a refrigerant having a critical pressure or more flows, wherein the number of cut and raised fins in close contact with the outer surface of the heat transfer tube of the gas cooler is such that the temperature difference between the air and the refrigerant is reduced. It is characterized in that the reduced portion is increased.
[0010]
Further, the invention according to claim 3 is a gas cooler through which a refrigerant having a critical pressure or higher flows, wherein the cut-and-raised height of the fin that is in close contact with the outer surface of the heat transfer tube of the gas cooler is such that the temperature difference between the air and the refrigerant is reduced. It is characterized in that the smaller portion is raised.
[0011]
The invention according to claim 4 is a gas cooler through which a refrigerant having a critical pressure or higher flows, wherein the pitch of the heat transfer tubes of the gas cooler is made denser at a portion where the temperature difference between the air and the refrigerant is reduced. It is characterized by.
[0012]
Further, the invention according to claim 5 is a gas cooler through which a refrigerant circulates at a critical pressure or higher, wherein a diameter and a pitch of the heat transfer tube of the gas cooler are changed at a portion where a temperature difference between the air and the refrigerant is reduced. And the pitch is made denser.
[0013]
Further, the invention according to claim 6 is a gas cooler through which a refrigerant having a critical pressure or higher flows, wherein an inner fin of a heat transfer tube of the gas cooler is raised at a portion where a temperature difference between air and the refrigerant is reduced. It is characterized by the following.
[0014]
The invention according to claim 7 is a gas cooler in which a refrigerant having a critical pressure or higher flows, wherein the pitch of the inner fins of the heat transfer tube of the gas cooler is reduced by reducing the temperature difference between the air and the refrigerant. It is characterized in that.
[0015]
According to an eighth aspect of the present invention, in the gas cooler according to the first to seventh aspects, an inlet / outlet portion of the gas cooler is also changed.
[0016]
The invention according to claim 9 is characterized in that the air and the refrigerant perform heat exchange in a countercurrent manner.
[0017]
The invention according to claim 10 is characterized in that the refrigerant is carbon dioxide.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0019]
(Embodiment 1)
FIGS. 1 and 2 are schematic views of a configuration of an indoor unit 1 and an outdoor unit 5 in which air and a refrigerant such as carbon dioxide that operate in a supercritical region exchange heat, as viewed from the side. In order to perform heat exchange of the refrigerant, the indoor unit 1 of FIG. 1 is configured by an indoor heat exchanger in which an indoor blower fan 2 and a heat transfer tube 4 through which the refrigerant passes are combined, and the outdoor unit 4 of FIG. 7 and an outdoor heat exchanger 6.
[0020]
In the first embodiment of the present invention, the outdoor heat exchanger 6 during the cooling operation serves to radiate the refrigerant similarly to the indoor heat exchanger 3 during the heating operation. The operation will be omitted, and the following description will focus on the indoor heat exchanger 3 acting as a gas cooler.
[0021]
FIG. 4 is a view of the indoor heat exchanger 3 in the indoor unit 1 as viewed from the front side, which is a longitudinal direction, and FIG. 5 is indicated by an air line of the indoor heat exchanger 3 shown in FIG. It is arrow sectional drawing.
[0022]
FIG. 7 is an enlarged schematic view of the fin group A of the indoor heat exchanger 3 in FIG. 4 that connects the XX 'lines. The fin pitch is α1 (for example, 3 mm), and FIG. 3 is an enlarged schematic diagram connecting the YY ′ line of the fin group B shown in FIG. 2, and the fin pitch is α2 (for example, 1.5 mm) smaller than α1 and is dense.
[0023]
FIG. 3 simply shows the temperature state of the refrigerant and air when the refrigerant of carbon dioxide radiated in FIG. 4 or 5 radiates heat in the indoor heat exchanger 3 of the indoor unit 1 during the heating operation. is there.
[0024]
In FIG. 3, the vertical axis shows the temperature T of the refrigerant and the air, and the horizontal axis shows the enthalpy h of the refrigerant.
The solid line shows the temperature change state of the refrigerant flowing through the heat transfer tubes 4 inside the indoor heat exchanger 3, and the broken line shows the temperature change state of the air. It is shown. Further, heat is dissipated to the air side by radiation fins 7 (constituted into a fin group A having a wide fin pitch and a fin group B having a narrow fin pitch) which are in close contact with the heat transfer tube 4 and promote heat exchange with the air side. First, a point A (4a) is the refrigerant temperature Ta (for example, 100 ° C.) of the heat transfer tube 4a at the entrance of the indoor heat exchanger 3, and a point B (4b) to a point C (4c) is a heat transfer tube 4b to 4c. Are the temperatures Tb (eg, 60 ° C.) and Tc (eg, 55 ° C.) of the refrigerant up to the heat transfer tube. When heat exchanges with the air side while the refrigerant flows through the heat transfer tubes 4b to 4c, as shown by hatching in FIG. 3, a minimum temperature difference ΔT (for example, 5 deg) region where the temperature difference with the air side becomes smallest. At the same time, there is a large region where the heat exchange performance between the refrigerant and the air is most reduced. The refrigerant that has passed through this region passes through the heat transfer tube 4 that becomes windward on the air side shown in FIG. 5, and a point D (4d) is the temperature Td of the refrigerant in the heat transfer tube 4d that is the outlet of the indoor heat exchanger 3 (for example, 25 ° C.).
[0025]
The heat transfer tube 4 described below has the first heat transfer tube 4a inserted into the refrigerant inlet of the indoor heat exchanger 3 and the temperature difference between air and refrigerant is minimized, and the heat exchange performance of the indoor heat exchanger 3 The first heat transfer tube 4 inserted in the fin indicating the region where the temperature decreases is called a heat transfer tube 4b, the end of the region is called a heat transfer tube 4c, and the heat transfer tube at the refrigerant outlet of the indoor heat exchanger 3 is 4d. The heat transfer tubes 4 are collectively called.
[0026]
Even when the heat generated is larger than that of a conventional refrigerant such as an HFC system, the heat transfer area where the air and the fins come into contact increases, and the heat exchange rate improves. As shown in FIG. 3, here, the temperature difference between the air and the refrigerant at the inlet of the heat exchanger was the largest, but it decreased as the heat exchange progressed, and the temperature difference between the air and the refrigerant partially increased during the heat radiation process. There is a region where it is difficult to remove the heat, and there is a region where the heat exchange efficiency is reduced. The region is larger than that of a conventional refrigerant such as an HFC system which has caused a change in latent heat.
[0027]
Therefore, the pitch of the fins 7 that are in close contact with the heat transfer tube 4 between the points B and C shown in FIGS. 4 and 5, ie, between the heat transfer tubes 4b and 4c, is partially changed to α2 as shown in FIG. (For example, 1.5 mm), the heat transfer area of the fins increases, so that in the heat release process shown in FIG. According to this embodiment, even if a large area exists, the indoor heat exchanger can be effectively and simply manufactured at a low cost simply by increasing the fin input amount by partially increasing the fin pitch. And a high-performance indoor heat exchanger can be provided even when carbon dioxide that is supercritical and changes in temperature is used as a refrigerant.
[0028]
In addition, the part which makes the fin pitch of the indoor heat exchanger dense is not limited to only one part of the heat exchanger irrespective of the form as shown in FIG. 4, but the temperature difference between the refrigerant and the air becomes small. The heat exchange efficiency may be improved by making the fin pitches of two or more places dense, including the outlet of the indoor heat exchanger. Further, the fin pitches at two or more locations need not be the same.
[0029]
Also, the area where the fin pitch is high is difficult to manufacture, and when the cost is high or other problems occur, the temperature difference between the refrigerant and the air is taken so that the merit such as cost reduction can be achieved. The heat exchanger may be expanded to the extent shown in FIGS.
[0030]
(Embodiment 2)
In the second embodiment of the present invention, FIG. 8 is a schematic diagram in which cut-and-raised shapes and numbers of the fins 7 of the fin groups A and B are enlarged as shown in FIGS. It is awake and actively exchanges heat with the air side. In FIGS. 4 and 5, a trapezoidal shape as shown in FIG. 9 is used to improve the heat exchange performance on the air side where the temperature difference from the air side is the smallest and the heat exchange performance is reduced. By using the fins 7a in which the number of the louvers 7b is increased, the area where the heat exchange efficiency is reduced due to the difficulty in obtaining the temperature difference between the air and the refrigerant during the heat radiation process in FIG. According to this embodiment, even when the refrigerant is larger than the refrigerant such as the above, by increasing the number of the air and the trapezoidal louvers 7b, the heat transfer area where the fin and the air come into contact is increased, and the heat exchange efficiency is improved.
[0031]
Therefore, it is possible to easily improve the heat exchange efficiency of the indoor heat exchanger and to provide a high-performance indoor heat exchanger even when using supercritical carbon dioxide whose temperature changes.
[0032]
FIG. 10 is a cross-sectional view of the fin 7 shown in FIG.
As shown in FIG. 10, when the heat exchanger partially corresponds to the fin group 72 in which the heat exchange performance is reduced, the cut-and-raised height of the trapezoidal louver 7b of the fin 7 is set to a predetermined height h (for example, By increasing the fin pitch by setting the fin height β (for example, 1.0 mm) to Δh (0.3 mm) higher than 0.7 mm), as shown in FIG. According to this embodiment, the trapezoidal shape of the fin 7 can be obtained even when the region where the heat exchange efficiency is reduced in a state where the temperature difference between the air and the refrigerant is difficult to be obtained is larger than that of the conventional refrigerant such as the HFC system. By setting the cut-and-raised height of the louver 7b to a predetermined height as compared with the conventional case, the heat transfer area where the fin and the air come into contact is increased, the heat exchange rate is improved, and a further high-performance indoor heat exchanger can be provided.
[0033]
Therefore, similarly to the second embodiment of the present invention, by increasing the number and height of the fins in a region where the heat exchange performance is reduced, the heat exchange efficiency is reduced in a state where the temperature difference between the air and the refrigerant is difficult to be obtained. The heat transfer area where the fins and the air come into contact with each other is increased by increasing the number of cut and raised portions and the height of the trapezoidal louver 7b in the area where the fins and the air are reduced. improves.
[0034]
Further, the heat exchange efficiency of the indoor heat exchanger can be effectively improved easily at low cost, and a high-performance indoor heat exchanger can be provided even when supercritical carbon dioxide that changes in temperature is used as a refrigerant.
[0035]
Further, as long as high performance can be achieved, the shape of the fins may be changed, and the height and number of the fins may be changed without being limited to the above embodiment.
[0036]
Further, if high performance can be achieved, the fin group A and the fin group B may be kept at the same pitch only by changing the shape, height, and number of the fins.
[0037]
(Embodiment 3)
In the third embodiment of the present invention, FIG. 11 shows a fin group B in which the temperature difference from the air side is the smallest and the indoor heat exchanger partially reduces the heat exchange performance as shown in FIGS. 11, that is, a schematic view in which the heat transfer tubes 4b to 4c are inserted, and the block in which the heat transfer tubes 4b to 4c are inserted is enlarged. As shown in FIG. 11, the heat transfer tubes 4 between the heat transfer tubes 4b to 4c in FIG. The number of heat transfer tubes 4 is increased by increasing the number of heat transfer tubes 4 by making the pitch of the heat transfer tubes 4 denser to γ2 (for example, 10 mm) smaller than the pitch γ1 (for example, 15 mm) of the heat transfer tubes 4 on the upstream side on the windward side. The heat transfer area in the tube increases, and the heat exchange efficiency of the heat exchanger can be improved. Also, as shown in FIG. 12, a thin tube tube having a diameter D2 (for example, 4 mm) obtained by reducing the diameter D1 (for example, 7.5 mm) of the heat transfer tube 4 between the heat transfer tubes between the heat transfer tubes 4b to 4c in FIG. By inserting the heat tubes 41 and setting the pitch of the thin tube heat transfer tubes 41 to γ3 (for example, 7 mm) to make them dense, the number of the thin tube heat transfer tubes 41 inserted in the same fin group B also increases, and the heat transfer area in the tube is increased. As the diameter of the heat transfer tube 4 is reduced and the cross-sectional area is reduced, the flow rate of the refrigerant increases, the heat transfer coefficient of the refrigerant improves, and a refrigerant having a low pressure loss characteristic such as carbon dioxide is used. This effectively increases the heat exchange rate on the refrigerant side without lowering the performance of the refrigeration cycle device.
[0038]
Therefore, even when carbon dioxide, which changes its temperature in the supercritical state, is used as the refrigerant, the heat exchange efficiency is reduced in a state where the temperature difference between the air and the refrigerant is partially hard to be obtained during the heat radiation process, as shown in FIG. Even when the area of the heat transfer is larger than that of the conventional HFC-based refrigerant, the heat transfer area in the pipe is increased by reducing the pitch of the heat transfer tubes and inserting the thin tube heat transfer tubes. The heat transfer coefficient is also increased, and the heat exchange rate is improved.
[0039]
Further, if high performance can be achieved, the number of heat transfer tubes, the tube diameter, the pitch, and the like are not limited to the above-described embodiment, and the fins that are in close contact with the heat transfer tubes may be combined with the fins of the above-described second embodiment. I do not care.
[0040]
(Embodiment 4)
FIG. 13 is an enlarged view of the shape of the inner fin 8 of the heat transfer tube 4 shown in FIGS. 4 and 5, and FIG. 14 is an enlarged view of the inner fin 8 of FIG. FIG. 15 shows the peak height h1 (for example, 0.3 mm) of the fin 8 and the pitch p1 (for example, 0.2 mm) of the fins in FIG. 15, and as shown in FIGS. Where the indoor heat exchanger partially corresponds to the fin group B in which the heat exchange performance is deteriorated, in particular, in the portion where the heat transfer tubes 4b to 4c shown in FIG. 5 are inserted, fins as shown in FIG. By setting the peak height h2 (for example, 0.5 mm) and the pitch p2 (for example, 0.1 mm) of the fins to 8, the heat transfer area of the fins in the heat transfer tube becomes large, and as shown in FIG. However, according to this embodiment, the pitch of the in-tube fins is reduced, and the Raising the mountain height This increases the area of contact between the fins in the pipe and the refrigerant, increases the heat transfer coefficient on the refrigerant side, improves the heat exchange rate, and achieves high performance even when using carbon dioxide that changes temperature in a supercritical state. An indoor heat exchanger can be provided.
[0041]
Further, if high performance can be achieved, it may be changed regardless of the height and pitch of the inner fins of the heat transfer tube, and the number, diameter and pitch of the heat transfer tube.
[0042]
Further, the shape of the inner fin and the height of the inner fin may be partially changed, or may be different from the above embodiment.
[0043]
【The invention's effect】
As is evident from the above, the invention according to claim 1 is characterized in that the refrigerant and the air have the minimum temperature difference, and the fin pitch of the portion where the heat exchange performance is reduced is made dense, so that the supercritically temperature-changed refrigerant is produced. Even when used, a high-performance gas cooler can be provided accurately.
[0044]
According to the second aspect of the present invention, the refrigerant and the air have a minimum temperature difference, and the number of fins raised and raised in a portion where the heat exchange performance is reduced is increased. And can easily provide a high-performance gas cooler.
[0045]
According to the third aspect of the present invention, the heat transfer area on the air side is increased by increasing the height of the fin in a portion where the refrigerant and the air have a minimum temperature difference and the heat exchange performance is reduced, thereby increasing the temperature in the supercritical state. Even when a cooling medium is used, a high-performance gas cooler can be easily provided at low cost.
[0046]
In the invention according to claim 4, the refrigerant and the air have a minimum temperature difference, and the pitch of the indoor heat transfer tubes in the portion where the heat exchange performance is reduced is increased, and the heat transfer area on the refrigerant side is increased by increasing the number thereof. In addition, even when a supercritical refrigerant whose temperature changes is used, a high-performance gas cooler can be easily provided at low cost without changing the fins.
[0047]
According to the fifth aspect of the present invention, the heat transfer performance of the refrigerant accompanying the flow rate of the refrigerant is improved by reducing the diameter of the refrigerant and the air at the portion where the heat exchange performance is reduced due to the minimum temperature difference between the refrigerant and the air. However, by increasing the number of pitches by increasing the pitch, it is possible to easily provide a high-performance gas cooler at low cost without changing fins.
[0048]
The invention according to claim 6 is to increase the height of the inner fins of the indoor heat transfer tube in the portion where the heat exchange performance is reduced due to the minimum temperature difference between the refrigerant and the air, thereby increasing the heat transfer performance on the refrigerant side. Therefore, a high-performance gas cooler can be easily provided at lower cost by further reducing the number of heat transfer tubes used without changing the fins.
[0049]
The invention according to claim 7 is to increase the heat transfer performance on the refrigerant side by increasing the pitch of the inner fins of the indoor heat transfer tube in the portion where the heat exchange performance is reduced due to the minimum temperature difference between the refrigerant and the air. In addition, the number of heat transfer tubes used can be further reduced without changing the fins, and the processing method can be easily processed. Therefore, a high-performance gas cooler can be easily provided at a lower cost.
[0050]
The invention described in claim 8 can provide a more efficient indoor heat exchanger even when used as a supercritical refrigerant whose temperature changes by changing the inlet and outlet of the gas cooler.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of an indoor unit showing one embodiment of the present invention. FIG. 2 is a schematic sectional view of an outdoor unit showing one embodiment of the present invention. FIG. 3 is a heat exchange showing one embodiment of the present invention. FIG. 4 is a front view of an indoor heat exchanger showing one embodiment of the present invention. FIG. 5 is a schematic cross-sectional view of an indoor heat exchanger showing one embodiment of the present invention. FIG. 6 is a sectional view taken along the line XX ′ of FIG. 4 showing one embodiment of the present invention. FIG. 7 is a sectional view taken along the line YY ′ of FIG. 4 showing one embodiment of the present invention. FIG. 8 is an enlarged schematic view of an indoor heat exchanger louver fin showing one embodiment of the present invention. FIG. 9 is an enlarged schematic view of a fin with an increased trapezoidal louver of the indoor heat exchanger showing one embodiment of the present invention. FIG. 8 is a cross-sectional view taken along the line II of FIG. 8 showing one embodiment of the present invention. FIG. 11 is the pitch of the heat transfer tubes of the indoor heat exchanger fin group B showing one embodiment of the present invention. FIG. 12 is a schematic sectional view showing a heat transfer tube pitch and a tube diameter of the indoor heat exchanger fin group B showing an embodiment of the present invention. FIG. 13 is an embodiment of the present invention. FIG. 14 is an enlarged sectional view of the inner fin of the heat transfer tube of FIGS. 4 and 5 showing an embodiment of the present invention. FIG. 15 is an enlarged detailed view of the inner fin of the heat transfer tube of FIG. 13 showing one embodiment of the present invention. 13 is an enlarged detailed view in which the fin height of the inner surface fin of the heat transfer tube in FIG. 13 is increased to make the pitch denser. FIG. 16 is a temperature state diagram of a conventional HFC-based refrigerant and air. Temperature state diagram [Explanation of symbols]
Reference Signs List 1 indoor unit 2 indoor blower fan 3 indoor heat exchanger 4 heat transfer tube 41 thin tube heat transfer tube 4a heat transfer tube 4b heat transfer tube 4c heat transfer tube 4d heat transfer tube 5 outdoor unit 6 outdoor heat exchanger 7, 7a fin 7b trapezoidal louver 8 heat transfer tube inner surface fin

Claims

A gas cooler through which a refrigerant having a critical pressure or higher flows, wherein the pitch of the fins closely contacting the outer surface of the heat transfer tube of the gas cooler is made denser at a portion where the temperature difference between the air and the refrigerant is reduced. Gas cooler.

A gas cooler through which a refrigerant having a critical pressure or higher flows, wherein the number of cut-and-raised fins in close contact with the outer surface of the heat transfer tube of the gas cooler increases the portion where the temperature difference between the air and the refrigerant is reduced. Characterized gas cooler.

A gas cooler through which a refrigerant having a critical pressure or higher flows, wherein the cut-and-raised height of the fin that is in close contact with the outer surface of the heat transfer tube of the gas cooler is increased at a portion where the temperature difference between the air and the refrigerant is reduced. And gas cooler.

A gas cooler through which a refrigerant having a critical pressure or higher flows, wherein a pitch of a heat transfer tube of the gas cooler is increased in a portion where a temperature difference between the air and the refrigerant is small.

A gas cooler through which a refrigerant circulating at or above the critical pressure flows, wherein the diameter and pitch of the heat transfer tube of the gas cooler are reduced in the portion where the temperature difference between air and the refrigerant is reduced, and the pitch is increased. A gas cooler.

A gas cooler through which a refrigerant having a critical pressure or higher flows, wherein an inner fin of a heat transfer tube of the gas cooler is increased in a portion where a temperature difference between air and the refrigerant is small.

A gas cooler through which a refrigerant having a critical pressure or higher flows, wherein the pitch of inner fins of a heat transfer tube of the gas cooler is made dense at a portion where a temperature difference between the air and the refrigerant is small.

The gas cooler according to any one of claims 1 to 7, wherein an inlet / outlet portion of the gas cooler is also changed.

The gas cooler according to any one of claims 1 to 8, wherein the air and the refrigerant perform heat exchange in a countercurrent flow.

The gas cooler according to any one of claims 1 to 9, wherein the refrigerant is carbon dioxide.