Name: evolution of staircase structures in diffusive convection
Uploaded: 2018-09-05T15:30:00.000+00:00
Duration: 7 min 28 s
Description: Watch this Scientific Journal Video about Evolution of Staircase Structures in Diffusive Convection at JoVE.com

この作品は、中国の NSF の補助金 (41706033、91752108、41476167)、(2017A030313242 と 2016A030311042) Grangdong NSF の補助金および LTO 補助金 (LTOZZ1801) によって支えられました。

1. ワーキング タンク
注: 実験は長方形タンクで実施です。タンクは、上部と下部のプレートと側壁に含まれます。上部と下部プレートは、めっき表面の銅から成っています。トップ プレートの中で水室があります。電気加熱パッドは、底板に挿入されます。側の壁は透明なプレキシ グラス製です。水槽サイズは Lx 257 mm (長さ)、Lyを = = 65 mm (幅)、Lz = 257 mm (高さ)。側壁の厚さ 9.5 mm です。
<ol><li>銅のプレートと蒸留水で慎重にプレキシ ガラス側壁をきれい。</li>
	<li>タンクは水が漏らないようにネジを使用してタンクを組み立てます。</li>
	<li>光学テーブルのステンレス製サポート フレーム (高さ 150 mm) を設定し、テーブルに現用戦車からの熱漏れを制限するスラブ断熱の間にフレームの上タンクを修正します。</li>
	<li>各プレートに 3 つのサーミスタ (0.01 ° C の温度の安定性) を挿入し、デジタルマルチメータに接続します。上部と下部の板の温度を監視するこれらのサーミスタを使用に注意してください。</li>
	<li>タンク内微小導電率と温度計測器 (MSCTI) を配置、多機能データ集録 (MDA) に接続します。モーターを備えられた高精度翻訳段階 (MPTS) に MSCTI を修正します。 注: 作動流体の水温・塩分プロファイルを達成できるように、MSCTI が垂直方向に移動して、上下に移動できます注意してください。ここで、MSCTI、0.01 ° C と塩分の安定性は 1% の温度安定性です。MPTS が 0.005 mm の位置精度です。</li>
	<li>デジタルマルチメータと多機能データ集録、サンプリング レート、データ集録チャンネル ストレージ パスなどの対応するソフトウェア プログラムでパラメーターを設定します。ここでは、それぞれ 1.0 と 128 Hz としてデジタル マルチ メーターとマルチファンクションのデータ集録のサンプリング レートを設定します。</li>
	<li>MPTS、初期位置を含む最低と最高の位置、移動速度、加速度、MSCTI のソフトウェア プログラムで移動パラメーターを設定します。ここでは、1 mm/秒と 0.5 mm/s2、移動の速度と加速度を設定し、20 と 220 mm 底板上に最小値と最大位置を設定します。これは 404 の MPTS の期間につながる上下測定のための s。低い位置で、MSCTI の初期位置を設定します。</li>
	<li>部屋の温度にほぼ一定な 2 つの高出力のエアコン (3000 W の作業力) 約 24 ° C に保ちます。</li>
</ol>2. 光学機器
注: 実験中に DC 階段の進化が監視と満たされる影絵の手法をプロシージャの下
<ol><li>タンクの外側のトレーシング ペーパー (25.7 cm × 25.7 cm) の一部を添付します。</li>
	<li>狭いビームの LED ランプを光源として使用します。ほぼ平行光を生成することができますように、タンクの反対側から約 5 m の光のソースを配置します。了承 DC 実験中に流体構造の層が流体の密度変化 (屈折率の変化に対応する) のためトレーシング ペーパーに点灯します。</li>
	<li>高速ビデオカメラを透写紙の同じ側に配置します。フルサイズのタンクを持つ層状構造を記録できるので、タンクから約 1 m です。</li>
	<li>ビデオカメラのサンプリング レートを設定します。サンプリング レートが階段の進化の詳細をキャプチャして適切なする必要がありますに注意してください。ここでは、ビデオカメラのサンプリング レートは、25 Hz です。</li>
	<li>電源ランプとビデオカメラと若干のポーションや距離を調整、画像をオフにするようにビデオカメラで取り込むことができます。</li>
</ol>3. 作動流体
<ol><li>2 つのタンクで生理食塩水と新鮮な水を準備します。<ol>
<li>それぞれの底からフレキシブル チューブ (外径 10 mm、内径 6 mm、長さ 10 cm) で 2 つの同じ長方形タンク (タンクおよびタンク B) に参加します。</li>
		<li>塗りタンク塩水、塩 (すなわち、塩分濃度) の質量濃度は、この例では 60 g/kg です。</li>
		<li>逆に包まれた新鮮な水の等量でタンク B を満たすし、電気磁気攪拌機を使用して連続的に流体を均一します。</li>
		<li>両方のタンク内初期流体温度の室温 (24 ° C) と同じにしてください。</li>
	</ol>
</li>
	<li>現用戦車で線形密度成層を確立します。<ol>
<li>二重タンク法29を使用すると、現用戦車の塩水の初期の線形階層を確立できます。</li>
		<li>現用戦車より高い 30 cm は、同じ高さにタンク A と B を配置します。お尻からタンク B と別の柔軟な管 (内径 2 mm、外径 5 mm、長さ 50 cm) の現用戦車に参加します。これらの 2 つのタンクで液圧差タンク B 内の液体は現用戦車にゆっくりと注入することができます。</li>
		<li>0.45 mL で蠕動ポンプの流れの速度を制御/s. 注作業槽水充填の全体の時間は約 3 h29に基づいて作業タンクの下部に塩分計算 <img alt="Equation 1" src="/files/ftp_upload/58316/58316eq1.jpg">(1) ここ SA, V, V0タンク、現用戦車の最終液量とタンク A (または B) の初期の液量の塩分濃度は、それぞれ。SB下部と上部に新鮮な水に塩分を使用して、初期階層 N0の浮力の周波数は、します。 <img alt="Equation 2" src="/files/ftp_upload/58316/58316eq2.jpg">(2) g は重力加速度、ρ0は参照密度、β は塩分収縮係数。注 N0は、この例では 1.14 rad/秒として計算されます。</li>
	</ol>
</li>
</ol>4. 実験を実行しています。
<ol><li>現用戦車の境界条件を設定します。<ol>
<li>トップ プレートの水室部を 8 等分プラスチック軟管 (内径 10 mm 外径 15 mm、長さ 150 cm) を使用した冷凍サーキュレータに接続します。トップ プレートの温度が冷蔵サーキュレータの温度に依存することに注意してください。部屋の温度 (24 ° C) と同じようにトップ プレートの温度を設定します。</li>
		<li>底板内部電気加熱パッドを接続すると、直流電流を供給します。うに計算されるこの実験中にメモ一定熱流束は作動流体に提供されて <img alt="Equation 3" src="/files/ftp_upload/58316/58316eq3.jpg">(3) U、R、および A は供給電圧、電気抵抗、電気暖房の有効面積パッド、それぞれ。この例では抵抗と有効面積は、44.12 オームと 1.89 × 10-2 m2。60 V、総熱量を Fh 4317 W/m2供給電圧を設定します。</li>
	</ol>
</li>
	<li>フロー パターンを記録するビデオカメラを入れます。</li>
	<li>デジタルマルチメータ、上部と下部のプレートと温度の温度と、MSCTI を使用して液の塩分濃度を監視する多機能データ集録を入れます。</li>
	<li>作動流体の温度と塩分濃度のプロファイルを達成するために上下に MSCTI を移動する MPTS を入れます。</li>
	<li>冷蔵サーキュレータと作動流体の上部と下部の境界条件を達成するために直流電源を入れます。 メモ全体の実験は生成、開発、没入、および DC 階段の消失を経験し、それが続く約 5 時間。DC の階段の消失後、電源を切り、直流を供給、冷蔵サーキュレータ、MPTS、デジタルマルチメータ、多機能データ集録、ビデオカメラ順番。</li>
</ol>5 データ処理
<ol><li>影絵のイメージ<ol>
<li>Matlab プログラムを使用して、さらなる分析のための連続画像をビデオカメラで記録されたビデオを変換します。タンク内のフロー パターンを強調するためにこれらのイメージを調整します。どこ私として (x, z) は、デジタル画像の輝度を設定 (x, z) イメージの左下隅を原点との水平および垂直座標を示します。(X, z) に変化に注意してください (0, 1) 256 のグレーのレベルで。30として各画像で背景イメージを正規化します。 <img alt="Equation 4" src="/files/ftp_upload/58316/58316eq4.jpg">(4) どこ<img alt="Equation 5" src="/files/ftp_upload/58316/58316eq5.jpg">冷・暖房適用されて前に撮影した 10 の画像の平均輝度は、 <img alt="Equation 6" src="/files/ftp_upload/58316/58316eq6.jpg"> i の強度を示すthイメージ。この方法で画像の静止した欠陥を削除できます。DC パターンの時間発展を検討するために各イメージを単一の縦強度変動プロファイルに変換できる<img alt="Equation 7" src="/files/ftp_upload/58316/58316eq7.jpg">、(すなわち強度の二乗) に沿ってイメージ強度変動を計算することによって、水平方向<img alt="Equation 7" src="/files/ftp_upload/58316/58316eq7.jpg">。強度変動分布をプロット<img alt="Equation 7" src="/files/ftp_upload/58316/58316eq7.jpg">DC 階段の進化を見るには時間の増加と共に連続画像。</li>
	</ol>
</li>
	<li>水温・塩分プロファイル<ol>
<li>この実験では上下移動 MSCTI で温度の鉛直分布と加工液の塩分濃度測定に注意してください。一時的な高さ、移動速度 w、時間 t、(最も低い位置に対応する) 開始時間 t0 、最も低い位置 hL平均値を持つ MSCTI の時間 (t) を計算し、最高 hH、として配置 <img alt="Equation 8" src="/files/ftp_upload/58316/58316eq8.jpg">(5) どこ<img alt="Equation 9" src="/files/ftp_upload/58316/58316eq9.jpg">は、MSCTI 期間最低 (最高値) から最高 (最低) の位置から移動、n そして δ は、それぞれ整数部と小数部。計算として一時的な高さの場合 <img alt="Equation 10" src="/files/ftp_upload/58316/58316eq10.jpg">(6) 方程式 (6)、n が偶数の場合のノートで、MSCTI は移動です。それ以外の場合、MSCTI は下に移動です。時間シリーズ温度 T(t) と垂直方向の水温・塩分プロファイルを取得する高さの場合の面で塩分 S(t) をプロットします。</li>
	</ol>
</li>
</ol>

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S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+coupled+turbulent+transports+of+salt+and+heat+across+a+sharp+density+interface.">The coupled turbulent transports of salt and heat across a sharp density interface.</a> International Journal of Heat and Mass Transfer. 8 (5), 759-767 (1965).</li><li>Hill, D. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=General+density+gradients+in+general+domains:+the+&amp;#34;two-tank&amp;#34;+method+revisited.">General density gradients in general domains: the &amp;#34;two-tank&amp;#34; method revisited.</a> Experiments in Fluids. 32 (4), 434-440 (2002).</li><li>Zhou, S. Q., Ahlers, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spatiotemporal+chaos+in+electroconvection+of+a+homeotropically+aligned+nematic+liquid+crystal.">Spatiotemporal chaos in electroconvection of a homeotropically aligned nematic liquid crystal.</a> Physical Review E. 74 (4), 046212 (2006).</li></ol>

著者が明らかに何もありません。

本稿で詳細な実験的プロトコルは矩形容器内熱塩 DC 階段構造をシミュレートに記載されます。作動流体の初期密度成層は、2 つのタンクのメソッドを使用して構築されます。トップ プレートは、一定の温度と熱流束一定の 1 つ下で保持されます。DC の階段は、生成、発展、没入、消失などの全体の進化プロセスは、影絵を用いた可視化し、高精度プローブにより温度と塩分濃度の差異を記録...

二重拡散対流 (DDC) は、最も重要な垂直混合プロセスのひとつです。それは、層状水の列の垂直方向の密度分布がコンポーネントが異なる分子拡散1をある反対の方向の 2 つ以上のスカラー部品勾配によって制御されるときに発生します。それは広く海洋2雰囲気3、地質学4、天体物理学5、材料科学6冶金7、および建築工学8で発生します。DDC は、世界の海洋のほとんど半分で現在、海洋のマルチ スケール プロセスとも気候変動9に対する重要な効果です。
DDC の主に 2 つのモードがある: 塩の指 (SF) と拡散対流 (DC)。SF は、暖かく、塩辛い水固まり成層環境でクーラー、新鮮な水を覆います。暖かく、塩辛い水は冷たい、新鮮な水の下にある、DC が形成されます。DC の顕著な特徴は、水温・塩分・密度の鉛直分布が階段のようより均一に対流する層と薄く、強く成層界面によって構成されることです。DC は高緯度の海や北極海や南極海などのいくつかの内部の salt 湖で主にオホーツク海、紅海、アフリカのキブ湖10発生します。北極海の流域と永続的な DC 階段上部と深い海11,12が存在します。それは深層海洋上層の混合に重要な影響を及ぼすし、氷の融解、最近海洋コミュニティ13より多くの興味をそそりますに大きく影響があります。
DC 階段構造最初 1969年14で、北極海で発見されました。その、パッドマン ・ ディロン15後、ティンメルマンスら。11、Sirevaag & Fer16周・魯12、ガスリーら。17Bebieva ・ ティンメルマンスは18、およびワイスマンら。19測定垂直方向を含む北極海の異なる流域で DC 階段と対流層とインターフェイス、深さと、階段の総厚さの水平スケール垂直伝で DC プロセスメソ渦と階段構造の時空変遷。シュミットら。20ゾンマーら21は、キブ湖の微細構造プロファイラーを用いて DC 階段を観察しました。彼らは主要な構造機能および DC の熱流束を報告、既存のパラメトリック式で測定した熱フラックスを比較します。コンピューターの処理速度を向上させると DC のシミュレーションが行われている最近、たとえば、インターフェイスを確認する構造と不安定性、インターフェイスを通じて熱伝達層の結合イベント22,23,24。
フィールド観測、海洋学者の海 DC の理解を大幅に強化が、測定は強く中間海洋流れ環境と楽器によって制限されます。たとえば、DC インターフェイスは、非常に小型の垂直方向のスケールをいくつか湖や海で25、0.1 m よりも薄いといくつかの特別な高解像度の器具が必要があります。実験では、DC の基本的な動的・熱力学的法則を探究することに独特な利点を示しています。室内実験と DC 階段の進化を観察、温度と塩分濃度測定、海洋アプリケーション26,27のいくつかのパラメーター化を提案できます。さらに、研究室の実験では、制御パラメーターと条件が容易に調整必要に応じて。たとえば、ターナーは最初 1965 年に実験室で DC 階段をシミュレートし、頻繁に更新され、その場で海洋観測28 で広く使用されて拡散界面熱伝達のパラメーター化を提案.
本稿で詳細な実験的プロトコルと DC 階段を下から加熱成層の食塩水で生成、開発および消失を含むの進化プロセスをシミュレートする説明です。水温・塩分は、影絵を用いた監視されている DC 階段と同様、マイクロ スケール装置によって測定されます。実験のセットアップ、進化プロセス、データ分析、および結果の検討は、詳細で説明されます。初期と境界条件を変えることによって現在の実験設定とメソッドを海洋の水平対流、深海熱水噴火、表層混合層の深化の効果などの他の海洋現象をシミュレートするために使用できます。潜水艦が海洋循環上の地熱です。

<table><tbody><tr><td>Rectangular tank</td><td></td><td></td><td>Custom made part</td></tr><tr><td>Plexiglas</td><td></td><td></td><td>Custom made part</td></tr><tr><td>Electric heating pad</td><td></td><td></td><td>Custom made part</td></tr><tr><td>Distilled water</td><td></td><td></td><td>Multiple suppliers</td></tr><tr><td>Optical table</td><td>Liansheng Inc.</td><td>MRT-P/B</td><td></td></tr><tr><td>Thermiostors</td><td></td><td></td><td>Custom made part</td></tr><tr><td>Digital multimeter</td><td>Keithley Inc</td><td>Model 2700</td><td></td></tr><tr><td>Micro-scale conductivity and temperature instrument (MSCTI)</td><td>PME. Inc.</td><td>Model 125</td><td></td></tr><tr><td>Multifunction data acquisition (MDA)</td><td>MCC. Inc.</td><td>USB-2048</td><td></td></tr><tr><td>Motorized precision translation stage (MPTS)</td><td>Thorlabs Inc.</td><td>LTS300</td><td></td></tr><tr><td>Tracing paper</td><td></td><td></td><td>Multiple suppliers</td></tr><tr><td>LED lamp</td><td></td><td></td><td>Multiple suppliers</td></tr><tr><td>Camcorder</td><td>Sony Inc.</td><td>XDR-XR550</td><td></td></tr><tr><td>De-gassed fresh water</td><td></td><td></td><td>Custom made part</td></tr><tr><td>Saline water</td><td></td><td></td><td>Custom made part</td></tr><tr><td>Flexible tube</td><td></td><td></td><td>Multiple suppliers</td></tr><tr><td>Electric magnetic stirrer&amp;nbsp;</td><td>Meiyingpu Inc.</td><td>MYP2011-100</td><td></td></tr><tr><td>Peristaltic pump</td><td>Zhisun Inc.</td><td>DDBT-201</td><td></td></tr><tr><td>Refrigerated circulator</td><td>Polyscience Inc.</td><td>Model 9702</td><td></td></tr><tr><td>Plastic soft tube</td><td></td><td></td><td>Multiple suppliers</td></tr><tr><td>Direct-current power supply</td><td>GE Inc.</td><td>GPS-3030</td><td></td></tr><tr><td>Matlab</td><td>MathWorks Inc.</td><td>R2012a</td><td></td></tr></tbody></table>

evolution of staircase structures in diffusive convection

拡散対流 (DC) 密度が 2 つの異なる分子拡散スカラーのグラデーションに反対によって制御されより大きいと、小さい-拡散スカラー勾配が正と負の垂直層状するときに発生します密度分布のための貢献それぞれ。DC は、多くの自然のプロセスと工学的応用、海洋学、天体物理学、冶金などで発生します。海洋の DC の最も顕著な特徴の 1 つは鉛直水温・塩分分布が厚い均一対流層と比較的薄いと高勾配インタ フェース連続ステップの階段のような構造であることです。DC 階段は北極と南極海を中心に、いろいろな海で観察されているし、海洋循環と気候変動に重要な役割を果たします。北極海における上部と深い海の流域と永続的な DC の階段が存在します。DC プロセスは深層海洋上層の混合に重要な影響を及ぼすし、表面の氷の融解に大きく影響があります。実験観測の制限に比べると、そのユニークな利点 dc、動的・熱力学的プロセスを効果的に調べる境界条件と制御のパラメーターを厳密に調整できますのでを示しています。ここでは、詳細なプロトコルと成層の食塩水で満たされた長方形タンクの生成、開発および消失を含む DC 階段構造の進化プロセスをシミュレートする説明です。実験のセットアップ、進化プロセス、データ分析、および結果の検討は、詳細で説明されます。

実験装置の概略図を図 1に示します。そのコンポーネントは、プロトコルのとおりです。主要部品、図 1 aに示すように、詳細な現用戦車は図 1 bに示すように。図 2は、下部 (Tb、赤色の曲線) と (Tt、黒の曲線) トップ プレートの温度変化を示しています。それは 2 つのプレートの温度は?...

Watch this Scientific Journal Video about Evolution of Staircase Structures in Diffusive Convection at JoVE.com

Evolution of Staircase Structures in Diffusive Convection

拡散対流 (DC) は広く自然のプロセスと同種の対流層と成層界面と階段の連続によって特徴付けられる、エンジニア リング アプリケーションで発生します。実験手順、長方形タンクの生成、開発および消失を含む、DC 階段構造の進化プロセスをシミュレートする説明します。

拡散対流における階段形状の進化

Diffusive convection (DC) occurs when the vertical stratified density is controlled by two opposing scalar gradients that have distinctly different ...

evolution-of-staircase-structures-in-diffusive-convection

Research

JoVE Journal

Environment

6.4K ビュー.  Chinese Academy of Sciences. 拡散対流 (DC) は広く自然のプロセスと同種の対流層と成層界面と階段の連続によって特徴付けられる、エンジニア リング アプリケーションで発生します。実験手順、長方形タンクの生成、開発および消失を含む、DC 階段構造の進化プロセスをシミュレートする説明します。

ビデオ: Evolution of Staircase Structures in Diffusive Convection

Ice Generation and the Heat and Mass Transfer Phenomena of Introducing Water to a Cold Bath of Brine

We demonstrate a method for the study of the heat and mass transfer and of the freezing phenomena in a subcooled brine environment. Our experiment showed that, under the proper conditions, ice can be produced when water is introduced to a bath of cold brine. To make ice form, in addition to having the brine and water mix, the rate of heat transfer must bypass that of mass transfer. When water is introduced in the form of tiny droplets to the brine surface, the mode of heat and mass transfer is by diffusion. The buoyancy stops water from mixing with the brine underneath, but as the ice grows thicker, it slows down the rate of heat transfer, making ice more difficult to grow as a result. When water is introduced inside the brine in the form of a flow, a number of factors are found to influence how much ice can form. Brine temperature and concentration, which are the driving forces of heat and mass transfer, respectively, can affect the water-to-ice conversion ratio; lower bath temperatures and brine concentrations encourage more ice to form. The flow rheology, which can directly affect both the heat and mass transfer coefficients, is also a key factor. In addition, the flow rheology changes the area of contact of the flow with the bulk fluid.

Here, we present a protocol to demonstrate the generation of ice when water is introduced to a cold bath of brine, as a secondary refrigerant, at a range of temperatures well below the freezing point of water. It can be used as an alternative way of producing ice for industry.

塩水の冷浴に水を導入するアイス生成と熱・物質移動現象

We demonstrate a method for the study of the heat and mass transfer and of the freezing phenomena in a subcooled brine environment. Our experiment showed ...

工学

Experimental Investigation of Secondary Flow Structures Downstream of a Model Type IV Stent Failure in a 180&#176; Curved Artery Test Section

The arterial network in the human vasculature comprises of ubiquitously present blood vessels with complex geometries (branches, curvatures and tortuosity). Secondary flow structures are vortical flow patterns that occur in curved arteries due to the combined action of centrifugal forces, adverse pressure gradients and inflow characteristics. Such flow morphologies are greatly affected by pulsatility and multiple harmonics of physiological inflow conditions and vary greatly in size-strength-shape characteristics compared to non-physiological (steady and oscillatory) flows 1 - 7.
Secondary flow structures may ultimately influence the wall shear stress and exposure time of blood-borne particles toward progression of atherosclerosis, restenosis, sensitization of platelets and thrombosis 4 - 6, 8 - 13. Therefore, the ability to detect and characterize these structures under laboratory-controlled conditions is precursor to further clinical investigations.
A common surgical treatment to atherosclerosis is stent implantation, to open up stenosed arteries for unobstructed blood flow. But the concomitant flow perturbations due to stent installations result in multi-scale secondary flow morphologies 4 - 6. Progressively higher order complexities such as asymmetry and loss in coherence can be induced by ensuing stent failures vis-&#224;-vis those under unperturbed flows 5. These stent failures have been classified as &#34;Types I-to-IV&#34; based on failure considerations and clinical severity 14.
This study presents a protocol for the experimental investigation of the complex secondary flow structures due to complete transverse stent fracture and linear displacement of fractured parts (&#34;Type IV&#34;) in a curved artery model. The experimental method involves the implementation of particle image velocimetry (2C-2D PIV) techniques with an archetypal carotid artery inflow waveform, a refractive index matched blood-analog working fluid for phase-averaged measurements 15 - 18. Quantitative identification of secondary flow structures was achieved using concepts of flow physics, critical point theory and a novel wavelet transform algorithm applied to experimental PIV data 5, 6, 19 - 26.

Stent implants in stenosed arterial curvatures are prone to "Type IV" failures involving the complete transverse fracture of stents and linear displacement of the fractured parts. We present a protocol for detection of secondary flow (vortical) structures in a curved artery model, downstream of clinically relevant "Type IV" stent failures.

180°湾曲動脈テストセクションにおけるモデルIV型ステントの失敗の下流に二次流れ構造に関する実験的研究

The arterial network in the human vasculature comprises of ubiquitously present blood vessels with complex geometries (branches, curvatures and ...

生物工学

The Diffusion of Passive Tracers in Laminar Shear Flow

A simple method to experimentally observe and measure the dispersion of a passive tracer in a laminar fluid flow is described. The method consists of first injecting fluorescent dye directly into a pipe filled with distilled water and allowing it to diffuse across the cross-section of the pipe to obtain a uniformly distributed initial condition. Following this period, the laminar flow is activated with a programmable syringe pump to observe the competition of advection and diffusion of the tracer through the pipe. Asymmetries in the tracer distribution are studied and correlations between the pipe cross-section and the shape of the distribution is shown: thin channels (aspect ratio &#60;&#60; 1) produce tracers arriving with sharp fronts and tapering tails (front-loaded distributions), while thick channels (aspect ratio ~1) present the opposite behavior (back-loaded distributions). The experimental procedure is applied to capillary tubes of various geometries and is particularly relevant to microfluidic applications by dynamical similarity.

A protocol for the study of the diffusion of passive tracers in laminar pressure-driven flow is presented. The procedure is applicable to various capillary pipe geometries.

層間せん断流中のトレーサーの拡散

A simple method to experimentally observe and measure the dispersion of a passive tracer in a laminar fluid flow is described. The method consists of ...

Simulation of Early Earth Hydrothermal Chimneys in a Thermal Gradient Environment

Deep sea hydrothermal vents are self-organizing precipitates generated from geochemical disequilibria and have been proposed as a possible setting for the emergence of life. The growth of hydrothermal chimneys in a thermal gradient environment within an early Earth vent system was successfully simulated by using different hydrothermal simulants, such as sodium sulfide, which were injected into an early Earth ocean simulant containing dissolved ferrous iron. Moreover, an apparatus was developed to sufficiently cool the ocean simulant to near 0 &#176;C in a condenser vessel immersed in a cold water bath while injecting a sulfide solution at hot to room temperatures, effectively creating an artificial chimney structure in a temperature gradient environment over a period of a few hours. Such experiments with different chemistries and variable temperature&#160;gradients resulted in a variety of morphologies in the chimney structure. The use of ocean and hydrothermal fluid simulants at room temperature resulted in vertical chimneys, whereas the combination of a hot hydrothermal fluid and cold ocean simulant inhibited the formation of robust chimney structures. The customizable 3D printed condenser created for this study acts as a jacketed reaction vessel that can be easily modified and used by different researchers. It will allow the careful control of injection rate and chemical composition of vent and ocean simulants, which should help accurately simulate prebiotic reactions in chimney systems with thermal gradients similar to those of natural systems.

The goal of this protocol is to form simulated hydrothermal chimneys via chemical garden injection experiments and introduce a thermal gradient across the inorganic precipitate membrane, using a 3D printable condenser that can be reproduced for educational purposes.

熱勾配環境における初期の地球熱水煙突のシミュレーション

Deep sea hydrothermal vents are self-organizing precipitates generated from geochemical disequilibria and have been proposed as a possible setting for the ...

環境学

Scalable Stamp Printing and Fabrication of Hemiwicking Surfaces

Hemiwicking is a process where a fluid wets a patterned surface beyond its normal wetting length due to a combination of capillary action and imbibition. This wetting phenomenon is important in many technical fields ranging from physiology to aerospace engineering. Currently, several different techniques exist for fabricating hemiwicking structures. These conventional methods, however, are often time consuming and are difficult to scale-up for large areas or are difficult to customize for specific, nonhomogeneous patterning geometries. The presented protocol provides researchers with a simple, scalable, and cost-effective method for fabricating micro-patterned hemiwicking surfaces. The method fabricates wicking structures through the use of stamp printing, polydimethylsiloxane (PDMS) molding, and thin-film surface coatings. The protocol is demonstrated for hemiwicking with ethanol on PDMS micropillar arrays coated with a 70 nm thick aluminum thin-film.

A simple protocol is provided for the fabrication of hemiwicking structures of varying sizes, shapes, and materials. The protocol uses a combination of physical stamping, PDMS molding, and thin-film surface modifications via common materials deposition techniques.

Hemiwicking 表面の作製とスケーラブルなスタンプ印刷

Hemiwicking is a process where a fluid wets a patterned surface beyond its normal wetting length due to a combination of capillary action and imbibition. ...

Thermocapillary Convection Space Experiment on the SJ-10 Recoverable Satellite

Thermocapillary convection is an important research subject in microgravity fluid physics. The experimental study on surface waves of thermocapillary convection in an annular liquid pool is one of the 19 scientific experimental projects on the SJ-10 recoverable satellite. Presented is a design for a payload for space experimental study on thermocapillary convection that includes the experimental model, measurement system, and control system. The specifics for the construction of an experimental model of an annular liquid pool with variable volume ratios is provided. The fluid temperatures are recorded by six thermocouples with a high sensitivity of 0.05 &#176;C at different points. The temperature distributions on the liquid free surface are captured by means of an infrared thermal camera. The free surface deformation is detected by a displacement sensor with a high accuracy of 1 &#181;m. The experimental process is fully automated. The research is focused on thermocapillary oscillation phenomena on the liquid-free surface and convective pattern transitions through analyses of experimental data and images. This research will be helpful to understand the mechanism of thermocapillary convection and will offer further insights into the nonlinear characteristics, flow instability, and bifurcation transitions of thermocapillary convection.

A protocol for the space payload design, the space experiment on thermocapillary convection, and analyses of experimental data and images are presented in this paper.

SJ-10回収衛星における熱キャピラリー対流宇宙実験

Thermocapillary convection is an important research subject in microgravity fluid physics. The experimental study on surface waves of thermocapillary ...

Preparation of Free-Surface Hyperbolic Water Vortices

Free surface vortices are present in industry in flow regulation, energy dissipation, and energy generation. Although investigated extensively, detailed experimental data regarding free surface vortices are lacking, particularly regarding the turbulence at the interface. The present paper reports on a special type of free surface vortex first proposed by Walter Schauberger in the 1960s that has an oxygen volumetric mass transfer coefficient exceeding the value of similar systems. This special type of vortex forms in a hyperbolic funnel. Different stable regimes can be stabilized with different hydraulic characteristics. Other advantages of this technology are its energy efficiency, simple design, and scalability. The flow in this hyperbolic funnel is characterized by strong turbulence and an increased surface area of the air-water interface. The local pressure strongly varies along the surface, resulting in a pronounced wavey air-water boundary layer. Due to the helical flow, these perturbations move inward, pulling the boundary layer with them. The resultant pressure gradient draws a certain air volume into the water vortex. The construction of the basic hyperbolic funnel setup and operational examples, including high-speed visualization for three different stable regimes, are presented in this work.

This paper describes how three different water vortex regimes in a hyperbolic Schauberger funnel can be created, their most important characteristics, and how associated parameters such as the oxygen transfer rates can be calculated.

自由表面双曲水渦の作製

Free surface vortices are present in industry in flow regulation, energy dissipation, and energy generation. Although investigated extensively, detailed ...

Flow Visualization in a Water Tunnel: Observing the Leading-edge Vortex Over a Delta Wing

Source: Jose Roberto Moreto, Gustaaf Jacobs and Xiaofeng Liu, Department of Aerospace Engineering, San Diego State University, San Diego, California
The delta wing, shown in Figure 1D, is a popular design in high-speed airplanes due to its superb performance in transonic and supersonic flight regimes. This type of wing has a small aspect ratio and high sweep angle, which reduces drag at high subsonic, transonic and supersonic flight regimes. The aspect ratio is defined as the wing span divided by the average chord <img align="middle" src="/files/ftp_upload/10459/10459eq1a.jpg" />.
An important advantage of the delta wing is its high stall angle. The stall of a delta wing is delayed compared to the stall of a high aspect ratio wing. This is because the lift of a delta wing is enhanced by the leading-edge vortex over the wing.
An effective way to observe this vortex flow phenomenon and study the vortex breakdown in a delta wing is by visualizing the flow in a water tunnel. By injecting dye in the flow surrounding a model from dye ports on the leading-edge, the vortex development and breakdown can be observed and its position measured. The data can also be used to estimate the stall angle.
<img src="/files/ftp_upload/10459/10459fig1.jpg" />
Figure 1. Typical wing planform shapes: A) Rectangular, with constant chord along span, B) elliptical, C) tapered, with variable chord along the span, and D) delta wing, an aft-swept wing with zero taper ratio.

Flow in a Water Tunnel: Leading-edge Vortex over a Delta Wing

水洞における流れの可視化:デルタウィング上の最先端渦の観察

Source: Jose Roberto Moreto, Gustaaf Jacobs and Xiaofeng Liu, Department of Aerospace Engineering, San Diego State University, San Diego, California
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JoVE Science Education

航空工学

Steady, Laminar Flow Between Parallel Plates

Understanding steady, laminar flow between parallel plates is essential for analyzing and designing flow in narrow rectangular channels, commonly found in various water conveyance and drainage systems. The Navier-Stokes equations govern fluid motion and are generally challenging to solve due to their nonlinearity. However, simplifications are possible in certain cases, like the steady laminar flow between parallel plates. For this scenario, we assume steady, incompressible, laminar flow.
Considering two horizontal plates aligned along the x-axis and spaced a distance &#39;2h&#39; apart, with the y-axis perpendicular to the plates, fluid motion is assumed to be parallel. Here, the continuity equation indicates no change in velocity along the x-axis, and the Navier-Stokes equations reduce as follows:
<img alt="Equation 1" src="/files/ftp_upload/18063/18063_Equation_1.svg" style="text-align: center; height: 30px;" />
The equations in the y and z directions show no pressure gradient along these axes, indicating that pressure varies hydrostatically in the y-direction, allowing integration to yield:
<img alt="Equation 2" src="/files/ftp_upload/18063/18063_Equation_2.svg" style="text-align: center; height: 12px;" />
For parallel plates with a pressure gradient along the x-axis, the equation simplifies:
<img alt="Equation 3" src="/files/ftp_upload/18063/18063_Equation_3.svg" style="text-align: center; height: 30px;" />
By integrating twice and applying boundary conditions (u = 0 at y = +h and y = -h), we obtain:
<img alt="Equation 4" src="/files/ftp_upload/18063/18063_Equation_4.svg" style="text-align: center; height: 30px;" />
This expression reveals that the velocity profile across the gap between the plates is parabolic, with maximum velocity at y = 0, midway between the plates. The volumetric flow rate through a unit width of the plates is obtained by integrating the velocity profile across the gap.
Understanding laminar flow between parallel plates has practical applications in groundwater flow, wastewater treatment, and lubrication. For instance, this model can approximate flow in soil layers, where water moves between soil particles like flow between plates. Knowing the flow rate and velocity distribution helps engineers design efficient drainage systems and predict groundwater movement.

平行プレート間の安定した層流

Steady, laminar flow between two parallel plates describes fluid movement in a narrow, confined channel, often used to model simple fluid systems.
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JoVE Core

Civil Engineering

Unit 1

Differential Analysis of Fluid Flow

KEY TERMS AND CONCEPTS

Steady, Laminar Flow in Circular Tubes

Hagen-Poiseuille flow describes a viscous fluid&#39;s steady, incompressible flow through a cylindrical tube with a constant radius R. This flow profile is often applied to understand fluid transport in narrow channels, such as capillaries. It serves as a foundational example of laminar flow. In this model, cylindrical coordinates (r,&#952;,z) are used to describe the radial (r), angular (&#952;), and axial (z) dimensions within the tube. For Hagen-Poiseuille flow, the velocity profile is purely axial, meaning the velocity vector points only along the z-axis and varies solely with the radial distance r from the center of the tube.
The governing equations for fluid motion, the Navier-Stokes equations, simplify under these conditions. Without angular or radial velocity components, the axial velocity vz(r) emerges as a function of r alone. Solving the reduced Navier-Stokes equations yields a parabolic velocity profile:
<img alt="Equation 1" src="/files/ftp_upload/18065/18065_Equation 1.svg" style="text-align: center; height: 27px;" />
This profile demonstrates that viscous drag decreases the fluid velocity from the maximum at the center to zero at the tube wall. This zero velocity at the boundary, known as the no-slip condition, results from the friction between the fluid and the tube wall. Consequently, the flow is laminar, with fluid particles moving in parallel layers without lateral mixing.
Integrating the velocity profile over the cross-sectional area of the tube yields the volumetric flow rate Q, known as Poiseuille&#39;s law:
<img alt="Equation 2" src="/files/ftp_upload/18065/18065_Equation 2.svg" style="text-align: center; height: 27px;" />
Where &#916;P is the pressure difference across the length L &#160;of the tube, and &#956; is the fluid&#39;s dynamic viscosity. This relation shows that Q is highly sensitive to the tube&#39;s radius, increasing with the fourth power of R. It follows that even a slight increase in radius significantly boosts the flow rate, a principle critical in fluid transport applications.
From Poiseuille&#39;s law, the mean velocity V of the fluid can be expressed as:
<img alt="Equation 3" src="/files/ftp_upload/18065/18065_Equation 3.svg" style="text-align: center; height: 27px;" />
This average velocity is precisely half of the maximum velocity at the tube&#39;s center, confirming the parabolic velocity distribution and demonstrating the predictable, layered nature of laminar flow in a cylindrical tube.

円形チューブ内の安定した層流

Consider steady, incompressible flow through a straight cylindrical tube of constant radius R, known as Hagen&#8211;Poiseuille flow.
The cylindrical ...