The authors gratefully acknowledge funding support from the Ministry of Science and Technology, MOST (project numbers: MOST 104-2218-E-002 -004, MOST 105-2218-E-002-019, MOST 105-2221-E-002 -107 -MY3, MOST 102-2221-E-002 -133 -MY3, and MOST 102-2221-E-002 -088 -MY3).

1. Herstellung der modifizierten Oberflächen <ol><li> Polieren manuell das Prüfstück (hohlen Kupferzylinder mit einer 40-mm - Länge (l) in einem 25-mm Außendurchmesser (d o), und ein 18-mm - Innendurchmesser (d i)) für 15 min unter Verwendung eines # 2000 Emery unter Verwendung Papier. Reinigen Sie die polierte Oberfläche indem sie sie mit Aceton, gefolgt von DI-Wasser gespült. </li><li> Platzieren Sie das polierte Teststück in einem Ofen für 2 Stunden bei einer konstanten Temperatur von 120 ° C. </li><li> Vorbereiten einer superhydrophilen SiO 2 Nanopartikellösung die folgenden Schritte verwendet wird . <ol><li> Bereiten Lösung A durch Mischen von 1: 4 Molverhältnisse von Tetraethoxysilan und DI-Wasser. 2 Tropfen 37% konzentrierte HCl zur Lösung A hinzu und rührt 2 Stunden. </li><li> Make-Lösung B durch ein 1 Mischen: 3 Molverhältnis von Ethanol und DI-Wasser. </li><li> Mix 1 ml Lösung A und 80 ml Lösung B hinzu und rühre 2 Stunden. </li><li> Fügen Sie 32 g SiO 2 -Nanopartikel (40 nm Durchmesser) auf die vorbereitete solution und rühre 1 h. </li></ol></li><li> Tauchen des Prüfkörpers in der vorbereiteten Lösung durch die Tauchbeschichtungsvorrichtung mit einer Geschwindigkeit von 5 mm / min verwendet. Halten Sie das beschichtete Teststück in einem Ofen bei 120 ° C für 1 h. </li><li> Bereiten 2, 4, 8 und wattierte Hybridmuster mit unterschiedlichen Orientierungen entlang der axialen Richtung mit Hilfe der folgenden Schritte (wie in Abbildung 1 gezeigt). <ol><li> Maskiert den Bereich unbeschichtet sein, mit dem Isolierband entsprechend die erforderlichen Anzahl von Zwischenzeilen mit der richtigen Orientierung (für die 2-Interline-Oberfläche bei einer 0 ° Orientierung, stellen Zwischenzeilen in der Mitte und der superhydrophilen Bereich (Bereich zu beschichtende) auf die Oberseite. Andererseits seits~~POS=HEADCOMP wird für die Ausrichtung 90 °, stellt eine Zwischenzeile am oberen Ende und ein anderen am unteren Ende und für die 180 ° -Ausrichtung, superhydrophilen Bereich auf der Unterseite und die Zwischenzeilen in der Mitte eingestellt wird. in ähnlicher Weise justiert die Position der 4, 8 wattierten Oberflächen mit der verschiedenen orientation wie in Abbildung 1 gezeigt). </li><li> Tauchen des maskierten Prüfstück in der hergestellten Lösung, die durch eine Tauchbeschichtungsvorrichtung verwendet wird, bei einer hohen dip Tauchgeschwindigkeit und Anstieg bei einer langsamen Geschwindigkeit von 5 mm / min. Halten Sie das beschichtete Teststück in einem Ofen bei 120 ° C für 1 h. </li><li> Entfernen Sie das Isolierband aus dem maskierten Bereich die erforderlichen Anzahl von Zwischenzeilen mit der richtigen Orientierung zu erhalten. </li></ol></li></ol><img alt="Abbildung 1" src="/files/ftp_upload/55387/55387fig1.jpg" /> Abbildung 1. Auswahl von verschiedenen wattierte Oberflächen. (a) Schematische Darstellung der verschiedenen wattierte Flächen mit unterschiedlichen Orientierungen. Das Flächenverhältnis einer glatten Kupferoberfläche und eine superhydrophile Oberfläche ist, von 1: 1 unter allen Bedingungen. (b) Ausrichtung Auswahlkriterien. (c) isometrische Ansicht der 2 Interline 0 ° Winkel orientiert Oberfläche. Die Orientierung wird als der Winkel zwischen der Basislinie ausgewählt und BeschichtungsMittellinie des ersten hydrophilen Musters von der oberen Seite, und es wird im Uhrzeigersinn gemessen. <a href="http://ecsource.jove.com/files/ftp_upload/55387/55387fig1large.jpg" target="_blank">Bitte klicken Sie hier</a> , um <a href="http://ecsource.jove.com/files/ftp_upload/55387/55387fig1large.jpg" target="_blank">eine größere Version dieser Figur zu sehen.</a> 2. Experimentelles Verfahren <ol><li> Unter Verwendung des Isolierband, fixieren ein Glasrohr an jeder kreisförmigen Basis des beschichteten Teststücks. </li><li> Horizontal fixiert diese Baugruppe in der 140- 140- x x 160 mm-Kammer unter Verwendung von Silikonpaste nach der gewünschten Position der Zwischenzeilen (wie in Abbildung 2 gezeigt). </li><li> Legen Sie eine 550-W, 18 mm Durchmesser und 40 mm langen Heizpatrone mit einem dünnen Film aus Wärmeleitpaste auf der Umfangsfläche in das Loch des Prüflings. </li><li> Verbinden Sie die Heizpatrone in einen Gleichstrom (DC) Energieversorgungseinheit. </li><li> Ort T-Typ - Thermoelemente in die 8 gleich beabstandeten Löcher von 1 mm, mit abwechselnden Tiefen von 5 mm und 7 mm , wie gezeigt in Fig3 Schließen Sie sie an den Datenlogger. </li><li> Einsetzen und fixieren Widerstandstemperaturdetektoren (RTD), einen Rückflusskühler und einen Zuheizer in den auf der oberen Abdeckung vorgesehen Flächen. Fix sie über die Siedekammer. </li><li> Füllen Sie 1400 ml DI-Wasser in den Pool-Siedekammer. </li><li> Schließen Sie den Rückflußkühler in eine Kühlkammer, die bei 5 ° C gehalten wird. </li><li> Vor dem Experiment, kochen kräftig das DI-Wasser in den Pool-Siedekammer für 30 min, um die Zusatzheizung verwendet wird. </li><li> Halten Sie das DI-Wasser im gesättigten siedenden Zustand durch die Zusatzheizung verwendet wird. Anschließend schalt die Stromversorgung und einen ersten Strom von 0,1 A. </li><li> Warten für 2 min, um einen stabilen Zustand zu erreichen. Dann erhöht den elektrischen Strom in Schritten von 0,3 A. </li><li> Aufzeichnen die Temperatur an jedem Stromeingang durch den Datenlogger verwendet. Weiter das Experiment, bis ein Maximalstrom von 4 A erreicht ist. Inzwischen notieren Sie die Blasendynamik f<html> oder jeder Stromeingang von einer CCD-Kamera angeordnet vor den Pool-Siedekammer, die auf dem Teststück fokussiert wird. </li></ol><img alt="Figur 2" src="/files/ftp_upload/55387/55387fig2.jpg" /> Abbildung 2. Schematische Darstellung des Pool-Siedekammer. Glasrohre sind an beiden Seiten des hohlen Kupferzylinders mit Silikonpaste verbunden. Dies wird mit Silikonpaste zum Pool-Siedekammer befestigt. <a href="http://ecsource.jove.com/files/ftp_upload/55387/55387fig2large.jpg" target="_blank">Bitte klicken Sie hier</a> , um <a href="http://ecsource.jove.com/files/ftp_upload/55387/55387fig2large.jpg" target="_blank">eine größere Version dieser Figur zu sehen.</a> <img alt="Abbildung 3" src="/files/ftp_upload/55387/55387fig3.jpg" /> Abbildung 3. Thermoelement Positionierung. 8-Thermoelemente sind in den Bohrungen von 1 mm Durchmesser in Umfangsrichtung in dem Prüfstück Ort bei einem Durchmesser von 20 mm platziert. Die Tiefen von abwechselnden 1 mm Durchmesser Löcher werden bei 5 mm und 7 mm bzw. fixiert./files/ftp_upload/55387/55387fig3large.jpg“target =‚_ blank‘&gt; Bitte hier klicken, um eine größere Version dieser Figur zu sehen. 3. Datenreduktion <ol><li> Berechnen Sie die Wärmezufuhr (Q) durch die folgende Gleichung unter Verwendung von 19 Q = I V (1) HINWEIS: I und V ist der Eingangsstrom in Ampere und die Spannung in Volt, respectively. </li><li> Schätzen , um den Wärmeverlust (Q Verlust) von den beiden Seitenflächen mit Hilfe der Formel 19: <img alt="Gleichung 2" src="/files/ftp_upload/55387/55387eq2.jpg" /> (2) HINWEIS: k ist die thermische Leitfähigkeit von Kupfer; T 7 mm T 5 mm und sind die Mittelwerte der Temperatur in einer Tiefe von 7 mm und 5 mm sind; &amp; Dgr; x (2 mm) ist der Unterschied zwischen der Tiefe; und <img alt="Gleichung 2B" src="/files/ftp_upload/55387/55387eq2b.jpg" /> ist die Querschnittsfläche des Test p<html> IECE. </li><li> Bestimmen Sie den Wärmefluß (q ‚‘) unter Verwendung der folgenden Formel 19: <img alt="Gleichung 3" src="/files/ftp_upload/55387/55387eq3.jpg" /> (3) HINWEIS: A = π d o l ist der Umfangsbereich des Prüflings. </li><li> Berechnen der Wandüberhitzung (unter Verwendung der folgenden Gleichung 19: <img alt="Gleichung 4" src="/files/ftp_upload/55387/55387eq4.jpg" /> (4) HINWEIS: Die T m ist der Durchschnitt der T 7 mm und T 5 mm ist die Länge des Prüfkörpers, r o (12,5 mm) Außenradius des Prüfkörpers, r m (10 mm) Radius des Prüfstücks bei der Löcher zu messen und T sat die Sättigungstemperatur von DI - Wasser , wie in Abbildung 4 dargestellt. </li><li> Berechnen Sie die HTC (α) mit der folgenden Formel 19: pload / 55387 / 55387eq5.jpg“/&gt; (5) </li></ol><img alt="Abbildung 4" src="/files/ftp_upload/55387/55387fig4.jpg" /> Abbildung 4. Schematische Darstellung der Wandtemperatur - Analyse. Wandtemperatur wird unter Verwendung des gemessenen Durchschnittstemperatur und bekannten zylindrischen Wärmewiderstand errechnet. <a href="http://ecsource.jove.com/files/ftp_upload/55387/55387fig4large.jpg" target="_blank">Bitte klicken Sie hier</a> , um <a href="http://ecsource.jove.com/files/ftp_upload/55387/55387fig4large.jpg" target="_blank">eine größere Version dieser Figur zu sehen.</a>

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The authors declare that they have no competing financial interests.

The main goal of this investigation was to develop a pool-boiling heat sink for high heat dissipation applications, such as nuclear reactors, boilers, and heat pipes, by introducing the hybrid wettable surface, as described in the protocol section. These surfaces can produce better pool-boiling performances than homogeneous wettable surfaces (hydrophilic and hydrophobic). The improvement in the boiling heat-transfer performance is due to an increase in active nucleation sites and the easy detachment of the formed bubbles...

Ein hoher Wärmefluß erhaltKühlSystems im Bereich von 10 bis 10 Mai W Bereitstellung / cm 2 wird in den Schwellen Bereichen Elektronik, Verteidigungs-, Avionik und Kerngeräteentwicklung erforderlich. Herkömmliche Kühlung mit Luft nicht ausreichend ist für diese Anwendungen aufgrund der geringen Wärmeübertragungskoeffizienten (HTC) sowohl für Frei und erzwungener Konvektion Bedingungen. Die Phasenänderung-basierten Kühltechniken, wie Pool Sieden und Sieden fließen, sind gut genug , um hohe Wärmeströme in der Größenordnung von 10 zu entfernen - 1.000 W / cm 2 1. Da der Zwei-Phasen-Wärmeübertragungsvorgang isotherm ist, wird die gekühlte Gerätetemperatur über seine Oberfläche nahezu konstant. Aufgrund der vernachlässigbaren Variation der Temperatur entlang der Oberfläche, kann der thermische Schock der Vorrichtung beseitigt werden. Allerdings ist die Hauptbegrenzungs Parameter in siedendem Wärmeübertragungs der kritische Wärmefluss (CHF), die einen anormalen Temperaturanstieg verursacht 2 </sup&gt;. In den letzten Jahrzehnten wurde umfangreiche Forschung durchgeführt , die CHF zu verbessern , indem die Oberflächenmodifikation unter Verwendung Nanoflüssigkeiten und Oberflächenbeschichtungen , 3, 4, 5, 6, 7, 8, 9, 10, 11. Unter den verschiedenen Methoden, Oberflächenbeschichtungen die beste Methode zur Verbesserung der CHF aufgrund der erheblichen Zunahme der Oberfläche befunden werden. Oberflächenbeschichtungen erhöhen im allgemeinen die Wärmeübertragung durch fin Aktion, Porosität Effekte und Oberflächenbenetzbarkeit 12. Benetzbarkeit der Oberfläche spielt eine bedeutende Rolle Wärmetransfer in siedendem. Frühere Studien zeigen bei niedrigeren Wärmeflussbedingungen, dass die hydrophobe Oberfläche besser HTC aufgrund der frühen Keimbildung zeigt. Doch beihöherer Wärmefluss ist die Ablösung der gebildeten Blasen langsam aufgrund der geringen Affinität von Wasser in Richtung der Oberfläche. Dies führt zu einer Blasenvereinigung und führt zu einem geringeren 3 CHF. Auf der anderen Seite erzeugt eine hydrophile Oberfläche eine höhere CHF, wegen der schnellen Ablösung der gebildeten Blase, aber es gibt eine geringere HTC bei niedrigen Wärmeflüssen, aufgrund der Verzögerung in Blasennukleierung 13. Die Hybridstrukturen zeigen eine bemerkenswerte Verbesserung Wärmeübertragung für alle Wärmeflüsse aufgrund der kombinierten Wirkung der Hydrophobie und Hydrophilie 14, 15, 16 in sieden. Hsu et al. hergestellte heterogene benetzbare Oberfläche superhydrophilen Si durch Beschichtung Nanopartikel auf einer maskierte Kupferoberfläche. Sie erreichten unterschiedliche Benetzbarkeit Verhältnisse durch die Beschichtungszeit variiert. Der Beginn des Kochens aufgetreten früher auf den heterogenen Oberflächen im Vergleich zu dem Homogeneous Oberfläche, die im wesentlichen die Wand 17 verringert hitzen. Jo et al. Blasensieden Wärmeübertragungs Studien auf hydrophile, hydrophobe und heterogenen Benetzungsflächen durchgeführt. Die heterogene Benetzungsfläche wurde aus hydrophoben gemusterten Punkten auf der hydrophilen Oberfläche bestehen. Sie haben höhere HTCs und die gleiche CHF für die heterogene Oberfläche im Vergleich zu der hydrophilen Oberfläche. Eine Verbesserung in der Siedehitze Übertragung hängt direkt von der Anzahl der Punkte auf der Oberfläche und auf die Siedebedingungen 18. In dieser Studie axiale hybrid benetzbar Muster wurden auf einer zylindrischen Kupferoberfläche unter Verwendung der Tauchbeschichtungstechnik hergestellt. Pool siedende Wärmeübertragungs Studien wurden durchgeführt, um die Auswirkungen der Reihe von Zwischenzeilen und der Orientierung des Hybrids benetzbar Muster zu bestimmen. Boiling Wärmefluss, HTC, und Blasendynamik wurden für die alle beschichteten Substrate analysiert und wirerneut gegenüber dem Kupfersubstrat.

<table><tbody><tr><td>Deionized water</td><td></td><td></td><td></td></tr><tr><td>Silica nanopowder,40 nm</td><td>UniRegion Bio-Tech</td><td>60676860</td><td></td></tr><tr><td>Ethanol</td><td>ECHO Chemical co. Ltd</td><td>64175</td><td></td></tr><tr><td>Hydrochloric acid</td><td>SHOWA Chemical co. Ltd.</td><td>7647010</td><td></td></tr><tr><td>Tetraethoxysilane</td><td>SHOWA Chemical co. Ltd.</td><td>78104</td><td></td></tr><tr><td>Acetone</td><td>UNI-ONWARD CORP.</td><td>67641</td><td></td></tr><tr><td>Cartridge Heater</td><td>Chung Shun Heater &amp;amp; Instrument Co, Ltd.</td><td></td><td></td></tr><tr><td>Pyrex glass&amp;nbsp;</td><td>Automotive Glass service , Taiwan</td><td></td><td></td></tr><tr><td>Ordinary toughened glass</td><td>Automotive Glass service , Taiwan</td><td></td><td></td></tr><tr><td>Thermal paste</td><td>Electrolube</td><td>EG-30&amp;nbsp;</td><td></td></tr><tr><td>Insulation Tape</td><td>Chuan Chi Trading Co. Ltd</td><td>Kapton Tape</td><td></td></tr><tr><td>Sandpaper</td><td>Chuan Chi Trading Co. Ltd</td><td>#2000</td><td></td></tr><tr><td>Heating furnace</td><td>Chung Chuan</td><td>Hong Sen HS-101</td><td></td></tr><tr><td>Electronic scales</td><td>A&amp;amp;D co. Ltd</td><td>GX400</td><td></td></tr><tr><td>Ultrasonic cleaner</td><td>Bransonic</td><td>Bransonic 3510</td><td></td></tr><tr><td>Magnet stirrer</td><td>Yellow line</td><td>MST D S1</td><td></td></tr><tr><td>Data logger&amp;nbsp;</td><td>Yokogawa</td><td>MX-100</td><td></td></tr><tr><td>CCD camera</td><td>JVC</td><td>LY35862-001A</td><td></td></tr><tr><td>Silicon paste</td><td>Permatex</td><td>599BR</td><td></td></tr><tr><td>Power supply</td><td>Gwinstek</td><td>GPR-20H50D</td><td></td></tr><tr><td>Teflon tape&amp;nbsp;</td><td>Chuan Chi Trading Co. Ltd</td><td>CS170000</td><td></td></tr><tr><td>Contact Angle Goniometer</td><td>Sindatek</td><td>Model 100SB</td><td></td></tr><tr><td>Auxiliary Heater</td><td>Chuan Chi Trading Co. Ltd</td><td></td><td></td></tr><tr><td>T- type thermocouples</td><td>Chuan Chi Trading Co. Ltd</td><td></td><td></td></tr><tr><td>Reflux Condenser&amp;nbsp;</td><td>Chuan Chi Trading Co. Ltd</td><td></td><td></td></tr><tr><td>Fiber glass</td><td>Professional Plastics, Taiwan</td><td></td><td></td></tr></tbody></table>

pool-boiling heat-transfer enhancement on cylindrical surfaces with hybrid wettable patterns

In this study, pool-boiling heat-transfer experiments were performed to investigate the effect of the number of interlines and the orientation of the hybrid wettable pattern. Hybrid wettable patterns were produced by coating superhydrophilic SiO2 on a masked, hydrophobic, cylindrical copper surface. Using de-ionized (DI) water as the working fluid, pool-boiling heat-transfer studies were conducted on the different surface-treated copper cylinders of a 25-mm diameter and a 40-mm length. The experimental results showed that the number of interlines and the orientation of the hybrid wettable pattern influenced the wall superheat and the HTC. By increasing the number of interlines, the HTC was enhanced when compared to the plain surface. Images obtained from the charge-coupled device (CCD) camera indicated that more bubbles formed on the interlines as compared to other parts. The hybrid wettable pattern with the lowermost section being hydrophobic gave the best heat-transfer coefficient (HTC). The experimental results indicated that the bubble dynamics of the surface is an important factor that determines the nucleate boiling.

Pool siedenden Wärmeübertragungsexperimente wurden auf einer Hybrid - benetzbaren zylindrischen Oberfläche durchgeführt unter Verwendung des experimentellen Aufbaus , deren schematischen wird in 5 gezeigt. Der Pool siedende experimentelle Verfahren erläutert in Schritt 2 des Protokolls Abschnitt wurde erfolgreich durchgeführt, während die Wirkung der Anzahl von Zwischenzeilen und der Orientierung des Hybrids benetzbar Muster auf dem Pool siedende Leistung zu unter...

Watch this Scientific Journal Video about Pool-Boiling Heat-Transfer Enhancement on Cylindrical Surfaces with Hybrid Wettable Patterns at JoVE.com

Pool-Boiling Heat-Transfer Enhancement on Cylindrical Surfaces with Hybrid Wettable Patterns

Pool siedenden Wärmeübertragungs Experimente wurden durchgeführt, um die Auswirkungen von Hybrid-Spritzmuster auf dem Wärmeübertragungskoeffizienten (HTC) zu beobachten. Die Parameter der Untersuchung sind die Anzahl der Zwischenzeilen und die Musterausrichtung der modifizierten benetzbare Oberfläche.

Pool-Boiling Wärmeübertragung Enhancement auf zylindrischen Oberflächen mit Hybrid Benetzbare Patterns

In this study, pool-boiling heat-transfer experiments were performed to investigate the effect of the number of interlines and the orientation of the ...

pool-boiling-heat-transfer-enhancement-on-cylindrical-surfaces-with

Research

JoVE Journal

Engineering

9.0K Aufrufe.  National Taiwan University.  Pool siedenden Wärmeübertragungs Experimente wurden durchgeführt, um die Auswirkungen von Hybrid-Spritzmuster auf dem Wärmeübertragungskoeffizienten (HTC) zu beobachten. Die Parameter der Untersuchung sind die Anzahl der Zwischenzeilen und die Musterausrichtung der modifizierten benetzbare Oberfläche. 

Serie: Pool-Boiling Heat-Transfer Enhancement on Cylindrical Surfaces with Hybrid Wettable Patterns

Visualization of High Speed Liquid Jet Impaction on a Moving Surface

Two apparatuses for examining liquid jet impingement on a high-speed moving surface are described: an air cannon device (for examining surface speeds between 0 and 25 m/sec) and a spinning disk device (for examining surface speeds between 15 and 100 m/sec). The air cannon linear traverse is a pneumatic energy-powered system that is designed to accelerate a metal rail surface mounted on top of a wooden projectile. A pressurized cylinder fitted with a solenoid valve rapidly releases pressurized air into the barrel, forcing the projectile down the cannon barrel. The projectile travels beneath a spray nozzle, which impinges a liquid jet onto its metal upper surface, and the projectile then hits a stopping mechanism. A camera records the jet impingement, and a pressure transducer records the spray nozzle backpressure. The spinning disk set-up consists of a steel disk that reaches speeds of 500 to 3,000 rpm via a variable frequency drive (VFD) motor. A spray system similar to that of the air cannon generates a liquid jet that impinges onto the spinning disc, and cameras placed at several optical access points record the jet impingement. Video recordings of jet impingement processes are recorded and examined to determine whether the outcome of impingement is splash, splatter, or deposition. The apparatuses are the first that involve the high speed impingement of low-Reynolds-number liquid jets on high speed moving surfaces. In addition to its rail industry applications, the described technique may be used for technical and industrial purposes such as steelmaking and may be relevant to high-speed 3D printing.

Two experimental devices for examining liquid jet impingement on a high-speed moving surface are described: an air cannon device and a spinning disk device. The apparatuses are used to determine optimal approaches to the application of liquid friction modifier (LFM) onto rail tracks for top-of-rail friction control.

Visualisierung von High-Speed-Flüssigkeitsstrahl-Impaction auf einer sich bewegenden Oberfläche

Two apparatuses for examining liquid jet impingement on a high-speed moving surface are described: an air cannon device (for examining surface speeds ...

Forschung

Ingenieurwesen

Measurements of Local Instantaneous Convective Heat Transfer in a Pipe - Single and Two-phase Flow

This manuscript provides step by step description of the manufacturing process of a test section designed to measure the local instantaneous heat transfer coefficient as a function of the liquid flow rate in a transparent pipe. With certain amendments, the approach is extended to gas-liquid flows, with a particular emphasis on the effect of a single elongated (Taylor) air bubble on heat transfer enhancement. A non-invasive thermography technique is applied to measure the instantaneous temperature of a thin metal foil heated electrically. The foil is glued to cover a narrow slot cut in the pipe. The thermal inertia of the foil is small enough to detect the variation in the instantaneous foil temperature. The test section can be moved along the pipe and is long enough to cover a considerable part of the growing thermal boundary layer.
At the beginning of each experimental run, a steady state with a constant water flow rate and heat flux to the foil is attained and serves as the reference. The Taylor bubble is then injected into the pipe. The heat transfer coefficient variations due to the passage of a Taylor bubble propagating in a vertical pipe is measured as function of the distance of the measuring point from the bottom of the moving Taylor bubble. Thus, the results represent the local heat transfer coefficients. Multiple independent runs preformed under identical conditions allow accumulating sufficient data to calculate reliable ensemble-averaged results on the transient convective heat transfer. In order to perform this in a frame of reference moving with the bubble, the location of the bubble along the pipe has to be known at all times. Detailed description of measurements of the length and of the translational velocity of the Taylor bubbles by optical probes is presented.

This manuscript describes methods aimed at measuring the local instantaneous convective heat transfer coefficients in a single or two-phase pipe flow. A simple optical method to determine the length and the propagation velocity of an elongated (Taylor) air bubble moving at a constant velocity is also presented.

Messungen der lokalen momentane konvektive Wärmeübertragung in einem Rohr - Einzel- und zwei-Phasen-Strömung

This manuscript provides step by step description of the manufacturing process of a test section designed to measure the local instantaneous heat transfer ...

Uncoupling Coriolis Force and Rotating Buoyancy Effects on Full-Field Heat Transfer Properties of a Rotating Channel

An experimental method for exploring the heat transfer characteristics of an axially rotating channel is proposed. The governing flow parameters that characterize the transport phenomena in a rotating channel are identified via the parametric analysis of the momentum and energy equations referring to a rotating frame of reference. Based on these dimensionless flow equations, an experimental strategy that links the design of the test module, the experimental program and the data analysis is formulated with the attempt to reveal the isolated Coriolis-force and buoyancy effects on heat transfer performances. The effects of Coriolis force and rotating buoyancy are illustrated using the selective results measured from rotating channels with various geometries. While the Coriolis-force and rotating-buoyancy impacts share several common features among the various rotating channels, the unique heat transfer signatures are found in association with the flow direction, the channel shape and the arrangement of heat transfer enhancement devices. Regardless of the flow configurations of the rotating channels, the presented experimental method enables the development of physically consistent heat transfer correlations that permit the evaluation of isolated and interdependent Coriolis-force and rotating-buoyancy effects on the heat transfer properties of rotating channels.

Here, we present an experimental method for decoupling the interdependent Coriolis-force and rotating-buoyancy effects on full-field heat transfer distributions of a rotating channel.

Abkoppeln Corioliskraft und rotierenden Auftrieb Auswirkungen auf Vollfeld Heat Transfer Eigenschaften eines rotierenden Kanals

An experimental method for exploring the heat transfer characteristics of an axially rotating channel is proposed. The governing flow parameters that ...

Analyzing Mixing Inhomogeneity in a Microfluidic Device by Microscale Schlieren Technique

In this paper, we introduce the use of microscale schlieren technique to measure mixing inhomogeneity in a microfluidic device. The microscale schlieren system is constructed from a Hoffman modulation contrast microscope, which provides easy access to the rear focal plane of the objective lens, by removing the slit plate and replacing the modulator with a knife-edge. The working principle of microscale schlieren technique relies on detecting light deflection caused by variation of refractive index1-3. The deflected light either escapes or is obstructed by the knife-edge to produce a bright or a dark band, respectively. If the refractive index of the mixture varies linearly with its composition, the local change in light intensity in the image plane is proportional to the concentration gradient normal to the optical axis. The micro-schlieren image gives a two-dimensional projection of the disturbed light produced by three-dimensional inhomogeneity.
To accomplish quantitative analysis, we describe a calibration procedure that mixes two fluids in a T-microchannel. We carry out a numerical simulation to obtain the concentration gradient in the T-microchannel that correlates closely with the corresponding micro-schlieren image. By comparison, a relationship between the grayscale readouts of the micro-schlieren image and the concentration gradients presented in a microfluidic device is established. Using this relationship, we are able to analyze the mixing inhomogeneity from associate micro-schlieren image and demonstrate the capability of microscale schlieren technique with measurements in a microfluidic oscillator4. For optically transparent fluids, microscale schlieren technique is an attractive diagnostic tool to provide instantaneous full-field information that retains the three-dimensional features of the mixing process.

Herein, we describe a procedure that employs microscale schlieren technique to measure mixing inhomogeneity in a microfluidic device. Through calibration, distribution of concentration gradient can be derived from the micro-schlieren image.

Analyse von Misch Inhomogenität in einer mikrofluidischen Vorrichtung von Microscale Schlieren Technik

In this paper, we introduce the use of microscale schlieren technique to measure mixing inhomogeneity in a microfluidic device. The microscale schlieren ...

Biotechnik

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.

Skalierbare Stempeldruck und Fertigung von Hemiwicking Oberflächen

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. ...

Rendering SiO2/Si Surfaces Omniphobic by Carving Gas-Entrapping Microtextures Comprising Reentrant and Doubly Reentrant Cavities or Pillars

We present microfabrication protocols for rendering intrinsically wetting materials repellent to liquids (omniphobic) by creating gas-entrapping microtextures (GEMs) on them comprising cavities and pillars with reentrant and doubly reentrant features. Specifically, we use SiO2/Si as the model system and share protocols for two-dimensional (2D) designing, photolithography, isotropic/anisotropic etching techniques, thermal oxide growth, piranha cleaning, and storage towards achieving those microtextures. Even though the conventional wisdom indicates that roughening intrinsically wetting surfaces (&#952;o &#60; 90&#176;) renders them even more wetting (&#952;r &#60; &#952;o &#60; 90&#176;), GEMs demonstrate liquid repellence despite the intrinsic wettability of the substrate. For instance, despite the intrinsic wettability of silica &#952;o &#8776; 40&#176; for the water/air system, and &#952;o &#8776; 20&#176; for the hexadecane/air system, GEMs comprising cavities entrap air robustly on immersion in those liquids, and the apparent contact angles for the droplets are &#952;r &#62; 90&#176;. The reentrant and doubly reentrant features in the GEMs stabilize the intruding liquid meniscus thereby trapping the liquid-solid-vapor system in metastable air-filled states (Cassie states) and delaying wetting transitions to the thermodynamically-stable fully-filled state (Wenzel state) by, for instance, hours to months. Similarly, SiO2/Si surfaces with arrays of reentrant and doubly reentrant micropillars demonstrate extremely high contact angles (&#952;r &#8776; 150&#176;&#8211;160&#176;) and low contact angle hysteresis for the probe liquids, thus characterized as superomniphobic. However, on immersion in the same liquids, those surfaces dramatically lose their superomniphobicity and get fully-filled within &#60;1 s. To address this challenge, we present protocols for hybrid designs that comprise arrays of doubly reentrant pillars surrounded by walls with doubly reentrant profiles. Indeed, hybrid microtextures entrap air on immersion in the probe liquids. To summarize, the protocols described here should enable the investigation of GEMs in the context of achieving omniphobicity without chemical coatings, such as perfluorocarbons, which might unlock the scope of inexpensive common materials for applications as omniphobic materials. Silica microtextures could also serve as templates for soft materials.

Rendering SiO2/Si Surfaces Omniphobic by Carving Gas-Entrapping Microtextures Comprising Reentrant and Doubly Reentrant Cavities or Pillars

This work presents microfabrication protocols for achieving cavities and pillars with reentrant and doubly reentrant profiles on SiO2/Si wafers using photolithography and dry etching. Resulting microtextured surfaces demonstrate remarkable liquid repellence, characterized by robust long-term entrapment of air under wetting liquids, despite the intrinsic wettability of silica.

Rendern von SiO2/Si Oberflächen Omniphobic durch Schnitzen von Gas-Entrapping Mikrotexturen bestehend reentrant und doppelt reentrant Hohlräume oder Säulen

We present microfabrication protocols for rendering intrinsically wetting materials repellent to liquids (omniphobic) by creating gas-entrapping ...

Proof-of-Concept for Gas-Entrapping Membranes Derived from Water-Loving SiO2/Si/SiO2 Wafers for Green Desalination

Desalination through direct contact membrane distillation (DCMD) exploits water-repellent membranes to robustly separate counterflowing streams of hot and salty seawater from cold and pure water, thus allowing only pure water vapor to pass through. To achieve this feat, commercial DCMD membranes are derived from or coated with water-repellent perfluorocarbons such as polytetrafluoroethylene (PTFE) and polyvinylidene difluoride (PVDF). However, the use of perfluorocarbons is limiting due to their high cost, non-biodegradability, and vulnerability to harsh operational conditions. Unveiled here is a new class of membranes referred to as gas-entrapping membranes (GEMs) that can robustly entrap air upon immersion in water. GEMs achieve this function by their microstructure rather than their chemical make-up. This work demonstrates a proof-of-concept for GEMs using intrinsically wetting SiO2/Si/SiO2 wafers as the model system; the contact angle of water on SiO2 is &#952;o &#8776; 40&#176;. Silica-GEMs had 300 &#956;m-long cylindrical pores whose diameters at the (2 &#956;m-long) inlet and outlet regions were significantly smaller; this geometrically discontinuous structure, with 90&#176; turns at the inlets and outlets, is known as the &#34;reentrant microtexture&#34;. The microfabrication protocol for silica-GEMs entails designing, photolithography, chrome sputtering, and isotropic and anisotropic etching. Despite the water loving nature of silica, water does not intrude silica-GEMs on submersion. In fact, they robustly entrap air underwater and keep it intact even after six weeks (&#62;106 seconds). On the other hand, silica membranes with simple cylindrical pores spontaneously imbibe water (&#60; 1 s). These findings highlight the potential of the GEMs architecture for separation processes. While the choice of SiO2/Si/SiO2 wafers for GEMs is limited to demonstrating the proof-of-concept, it is expected that the protocols and concepts presented here will advance the rational design of scalable GEMs using inexpensive common materials for desalination and beyond.

Proof-of-Concept for Gas-Entrapping Membranes Derived from Water-Loving SiO2/Si/SiO2 Wafers for Green Desalination

Presented here is a stepwise protocol for realizing gas-entrapping membranes (GEMs) from SiO2/Si wafers using integrated circuit microfabrication technology. When silica-GEMs are immersed in water, the intrusion of water is prevented, despite the water-loving composition of silica.

Proof-of-Concept für Gas-Entrapping Membranen abgeleitet von wasserliebenden SiO2/Si/SiO2 Wafern für grüne Entsalzung

Desalination through direct contact membrane distillation (DCMD) exploits water-repellent membranes to robustly separate counterflowing streams of hot and ...

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.

Präparation von freiflächigen hyperbolischen Wasserwirbeln

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

Testing the Heat Transfer Efficiency of a Finned-tube Heat Exchanger

Source: Michael G. Benton and Kerry M. Dooley, Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA
Heat exchangers transfer heat from one fluid to another fluid. Multiple classes of heat exchangers exist to fill different needs. Some of the most common types are shell and tube exchangers and plate exchangers1. Shell and tube heat exchangers use a system of tubes through which fluid flows1. One set of tubes contains the liquid to be cooled or heated, while the second set contains the liquid that will either absorb heat or transmit it1. Plate heat exchangers use a similar concept, in which plates are closely joined together with a small gap between each for liquid to flow1. The fluid flowing between the plates alternates between hot and cold so that heat will move into or out of the necessary streams1. These exchangers have large surface areas, so they are usually more efficient1.
The goal for this experiment is to test the heat transfer efficiency of a finned-tube heat exchanger (Figure 1) and compare it to the theoretical efficiency of a heat exchanger without fins. The experimental data will be measured for three different flow rates of monoethylene glycol (MEG). Two different water flow rates for each MEG flow rate will be used. Using the Wilson plot method the heat transfer coefficients will be determined from the experimental data. Additionally, the Reynold&#39;s number and the amount of heat transferred will be compared for flow with and without the fins to evaluate heat transfer efficiency.
<img alt="Figure 1" src="/files/ftp_upload/10437/10437fig1.jpg" /> 
Figure 1: Finned-tube Heat Exchanger. 1) MEG outlet temperature 2) water inlet temperature 3) MEG inlet temperature 4) water outlet temperature 5) water meter 6) MEG accumulation sight glass/cylinder.

Heat Transfer Efficiency Test of a Finned-tube Heat Exchanger

Prüfung der Wärmeübertragungseffizienz eines Rippenrohrwärmetauschers

Source: Michael G. Benton and Kerry M. Dooley, Department of Chemical Engineering, Louisiana State University, Baton Rouge, LA
Heat exchangers transfer ...

Lehre

JoVE Science Education

Chemische Verfahrenstechnik

Quenching and Boiling

Source: Alexander S Rattner, Sanjay Adhikari, and Mahdi Nabil; Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, University Park, PA
Controlled heating followed by rapid cooling is an important element of many materials processing applications. This heat-treating procedure can increase material hardness, which is important for cutting tools or surfaces in high wear environments. The rapid cooling stage is called quenching, and is often performed by immersing materials in a fluid bath (often water or oil). Quenching heat transfer can occur due to forced convection - when the action of rapidly moving material through coolant drives the heat transfer process, and due to free convection - when the reduced density of hot fluid near the material surface causes buoyancy-driven circulation and heat transfer. At high material temperatures, the coolant can boil, leading to increased heat transfer effectiveness. However, when extremely hot materials are quenched, they can be blanketed in relatively low thermal conductivity coolant vapor, leading to poor heat transfer.
In this experiment, quenching heat transfer will be measured for a heated copper cylinder, which is representative of small heat-treated parts. The transient sample temperature profile will be measured during quenching and compared with theoretical results for free convection heat transfer. Boiling phenomena will also be investigated qualitatively.

Quenching, Boiling, Convection and Nusselt Number

Abschrecken und Sieden

Source: Alexander S Rattner, Sanjay Adhikari, and Mahdi Nabil; Department of Mechanical and Nuclear Engineering, The Pennsylvania State University, ...

Pool-Boiling Wärmeübertragung Enhancement auf zylindrischen Oberflächen mit Hybrid Benetzbare Patterns

Zusammenfassung

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