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. Preparación de las superficies modificadas <ol><li> Pulir manualmente la pieza de ensayo (cilindro de cobre hueco con una longitud de 40 mm (L), un diámetro exterior de 25 mm (d o), y un diámetro interior de 18 mm (d i)) durante 15 min usando un esmeril # 2000 papel. Limpiar la superficie pulida de un aclarado con acetona seguido de agua DI. </li><li> Colocar la probeta pulida en un horno durante 2 horas a una temperatura constante de 120 ° C. </li><li> Preparar una solución de nanopartículas de SiO 2 superhidrófilo mediante los pasos siguientes. <ol><li> Preparar la solución A mediante la mezcla de 1: 4 relaciones molares de tetraetoxisilano y agua DI. Añadir 2 gotas de 37% de HCl concentrado a la solución A y agitar durante 2 h. </li><li> Hacer la solución B mezclando una proporción de 1: 3 molar de etanol y agua DI. </li><li> Mezclar 1 ml de la solución A a 80 ml de solución B y se agita durante 2 h. </li><li> Añadir 32 g de SiO 2 nanopartículas (diámetro de 40 nm) a la solu preparadosción y se agita durante 1 h. </li></ol></li><li> Sumergir la pieza de ensayo en la solución preparada usando el aparato de recubrimiento por inmersión a una velocidad de 5 mm / min. Mantenga la pieza de ensayo recubierto en una estufa a 120 ° C durante 1 h. </li><li> Preparar 2, 4, y 8 patrones híbridos interlineado con diferentes orientaciones a lo largo de la dirección axial (como se muestra en la Figura 1) utilizando los siguientes pasos. <ol><li> Enmascarar la zona a estar sin recubrir utilizando la cinta de aislamiento de acuerdo con el número requerido de interlíneas con la orientación adecuada (Para la superficie 2-interlínea en una orientación 0 °, ajuste interlíneas en el centro y la zona de superhidrófilo (área a recubrir) en el lado superior. por otro lado, para la orientación 90 °, ajustar uno interlínea en la parte superior y otro en la parte inferior y para la orientación de 180 °, ajuste área superhidrófilo en la parte inferior y las interlíneas en el centro. de manera similar, ajustar el posición de las 4, 8 superficies interlineado con la diferente orientation como se muestra en la Figura 1). </li><li> Sumergir la pieza de ensayo enmascarado en la solución preparada mediante el uso de un aparato de recubrimiento por inmersión, inmersión a una alta velocidad de inmersión y ascenso a una velocidad lenta de 5 mm / min. Mantenga la pieza de ensayo recubierto en una estufa a 120 ° C durante 1 h. </li><li> Retire la cinta de aislamiento de la zona enmascarada para obtener el número requerido de interlíneas con la orientación apropiada. </li></ol></li></ol><img alt="Figura 1" src="/files/ftp_upload/55387/55387fig1.jpg" /> Figura 1. Selección de superficies diferentes interlineado. (a) Esquema de superficies diferentes interlineado con diferentes orientaciones. La relación de área de una superficie de cobre plano y una superficie de superhidrófilo es de 1: 1 en todas las condiciones. criterios de selección (b) la orientación. (c) vista isométrica de la 2 interlínea superficie orientada 0 ° de ángulo. Orientación se selecciona como el ángulo entre la línea de base y revestimientolínea central del primer patrón hidrofílico desde el lado superior y se mide en una dirección hacia la derecha. <a href="http://ecsource.jove.com/files/ftp_upload/55387/55387fig1large.jpg" target="_blank">Haga clic aquí para ver una versión más grande de esta figura.</a> 2. Procedimiento Experimental <ol><li> Uso de la cinta de aislamiento, fijar un tubo de vidrio en cada base circular de la pieza de ensayo revestida. </li><li> Horizontalmente solucionar este conjunto a la cámara de 140- x 140- x 160 mm (como se muestra en la Figura 2) usando pasta de silicona según la posición requerida de interlíneas. </li><li> Colocar un 550-W, diámetro de 18 mm, y el calentador de cartucho de 40 mm de longitud con una película fina de pasta térmica en el área circunferencial en el agujero de la pieza de ensayo. </li><li> Conectar el calentador de cartucho a una unidad de alimentación de corriente continua (DC). </li><li> Place de tipo T termopares en los 8 orificios de 1 mm igualmente espaciados, con profundidades alternas de 5 mm y 7 mm, como se muestra en la figura3 Conéctelas al registrador de datos. </li><li> Insertar y fijar detectores de temperatura de resistencia (RTD), un condensador de reflujo, y un calentador auxiliar en los espacios provistos en la cubierta superior. Fijarlos sobre la cámara de ebullición. </li><li> Llenar 1.400 ml de agua DI en la cámara de piscina punto de ebullición. </li><li> Conectar el condensador de reflujo a una cámara de enfriamiento que se mantiene a 5 ° C. </li><li> Antes del experimento, hervir vigorosamente el agua DI en la cámara de piscina-hirviendo durante 30 min utilizando el calentador auxiliar. </li><li> Mantenga el agua DI a la condición de ebullición saturado utilizando el calentador auxiliar. Posteriormente, encender la fuente de alimentación y dar una corriente inicial de 0,1 A. </li><li> Espere durante 2 minutos con el fin de alcanzar un estado de equilibrio. Entonces, aumentar la corriente eléctrica con incrementos de 0,3 A. </li><li> Registre la temperatura en cada entrada de potencia utilizando el registrador de datos. Continuar el experimento hasta que se alcanza una corriente máxima de 4 A. Mientras tanto, registrar la dinámica de burbujas f<html> o cada entrada de energía mediante el uso de una cámara CCD colocado en frente de la cámara de piscina punto de ebullición, que se centra en la pieza de ensayo. </li></ol><img alt="Figura 2" src="/files/ftp_upload/55387/55387fig2.jpg" /> Figura 2. Esquema de la Cámara Pool-hirviendo. tubos de vidrio están conectados a ambos lados del cilindro de cobre hueco con pasta de silicona. Este se fija a la cámara de piscina de punto de ebullición con pasta de silicona. <a href="http://ecsource.jove.com/files/ftp_upload/55387/55387fig2large.jpg" target="_blank">Haga clic aquí para ver una versión más grande de esta figura.</a> <img alt="figura 3" src="/files/ftp_upload/55387/55387fig3.jpg" /> Figura 3. Termopar de posicionamiento. 8 termopares se colocan dentro de los agujeros de 1 mm de diámetro circunferencialmente en el lugar pieza de ensayo en un diámetro de 20 mm. Las profundidades de orificios de 1 mm de diámetro alternos se fijan a 5 mm y 7 mm, respectivamente./files/ftp_upload/55387/55387fig3large.jpg&quot; target = &#39;_ blank&#39;&gt; Haga clic aquí para ver una versión más grande de esta figura. 3. Reducción de Datos <ol><li> Calcular la entrada de calor (Q) mediante el uso de la siguiente ecuación 19 Q = I V (1) NOTA: I y V son la corriente de entrada en amperios y la tensión en voltios, respectivamente. </li><li> Estimar la pérdida de calor (pérdida Q) de las dos superficies laterales mediante el uso de la fórmula 19: <img alt="La ecuación 2" src="/files/ftp_upload/55387/55387eq2.jpg" /> (2) NOTA: k es la conductividad térmica del cobre; T 7 mm y T 5 mm son los valores medios de la temperatura a una profundidad de 7 mm y 5 mm, respectivamente; ? X (2 mm) es la diferencia entre las profundidades; y <img alt="Ecuación 2B" src="/files/ftp_upload/55387/55387eq2b.jpg" /> es el área de sección transversal de la prueba p<html> IECE. </li><li> Determinar el flujo de calor (q &#39;&#39;) mediante el uso de la siguiente fórmula 19: <img alt="La ecuación 3" src="/files/ftp_upload/55387/55387eq3.jpg" /> (3) NOTA: A = π d o l es el área circunferencial de la pieza de ensayo. </li><li> Calcular el sobrecalentamiento de la pared (usando la siguiente ecuación 19: <img alt="La ecuación 4" src="/files/ftp_upload/55387/55387eq4.jpg" /> (4) NOTA: T m es la media de T 7 mm y T 5 mm, es la longitud de la pieza de ensayo, r O (12,5 mm) radio exterior de la pieza de ensayo, r m (10 mm) radio de la probeta a la la medición de agujeros, y T sAT es la temperatura de saturación del agua DI como se muestra en la Figura 4. </li><li> Calcular la HTC (α) utilizando la siguiente fórmula 19: pload / 55387 / 55387eq5.jpg&quot;/&gt; (5) </li></ol><img alt="Figura 4" src="/files/ftp_upload/55387/55387fig4.jpg" /> Figura 4. Esquema de Análisis temperatura de la pared. temperatura de la pared se calcula utilizando la temperatura media medida y conocido resistencia térmica cilíndrica. <a href="http://ecsource.jove.com/files/ftp_upload/55387/55387fig4large.jpg" target="_blank">Haga clic aquí para ver una versión más grande de esta figura.</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...

Un sistema de alta flujo de calor para mantener la prestación de enfriamiento en el rango de 10-10 5 W / cm2 se requiere en los campos emergentes de la electrónica, defensa, aviónica, y el desarrollo de dispositivos nucleares. de refrigeración convencionales con el aire no es suficiente para estas aplicaciones debido al coeficiente de transferencia de calor bajo (HTC) para ambas condiciones de libre y convección forzada. Las técnicas de enfriamiento a base de cambio de fase, tales como piscina de ebullición y el flujo de ebullición, son lo suficientemente buenos para eliminar flujos de alta temperatura del orden de 10 - 1.000 W / cm 2 1. Dado que el proceso de transferencia de calor de dos fases es isotérmica, la temperatura del dispositivo enfriado es casi constante sobre su superficie. Debido a la variación insignificante de la temperatura a lo largo de la superficie, el choque térmico del dispositivo puede ser eliminada. Sin embargo, el parámetro de limitación importante en ebullición de transferencia de calor es el flujo de calor crítico (CHF), que causa un aumento anormal de temperatura 2 </sup&gt;. En las últimas décadas, la investigación extensa se ha llevado a cabo para mejorar la CHF mediante el uso de modificación de la superficie, nanofluidos, y la superficie de los revestimientos 3, 4, 5, 6, 7, 8, 9, 10, 11. Entre los diversos métodos, revestimientos de superficies se encuentran para ser el mejor método para mejorar la CHF debido al aumento sustancial en el área de la superficie. Recubrimientos de superficie generalmente aumentan la transferencia de calor por la acción de la aleta, efectos de porosidad, y humectabilidad de la superficie 12. humectabilidad de la superficie juega un papel significativo en la temperatura de ebullición de transferencia. Estudios previos muestran que en condiciones de flujo de calor más bajos, la superficie hidrófoba muestra mejor HTC debido a la nucleación temprano. Sin embargo, enmayor flujo de calor, el desprendimiento de las burbujas formadas es lento debido a la baja afinidad de agua hacia la superficie. Esto conduce a la coalescencia de las burbujas y se traduce en una menor CHF 3. Por otro lado, una superficie hidrófila produce una CHF más alto, debido a la separación rápida de las burbujas formadas, pero da una HTC inferior a flujos de calor bajos, debido a la demora en la nucleación de burbujas 13. Las estructuras híbridas muestran una notable mejora en la temperatura de ebullición de transferencia para todos los flujos de calor debido al efecto combinado de la hidrofobicidad y la hidrofilicidad 14, 15, 16. Hsu et al. producido superficie humectable heterogénea mediante el recubrimiento de superhidrófilo Si las nanopartículas sobre una superficie de cobre enmascarado. Alcanzaron diferentes relaciones de humectabilidad mediante la variación del tiempo de recubrimiento. El inicio de la ebullición se produjo antes en las superficies heterogéneas en comparación con el hsuperficie omogeneous, lo que redujo sustancialmente la pared de sobrecalentamiento 17. Jo et al. realizado ebullición nucleada estudios de transferencia de calor en las superficies humectantes hidrófilos, hidrófobos, y heterogéneos. La superficie de humectación heterogénea se compone de puntos estampadas hidrófobos sobre la superficie hidrófila. Consiguieron CTH más altos y el mismo CHF para la superficie heterogénea en comparación con la superficie hidrófila. Una mejora en la temperatura de ebullición de transferencia depende directamente del número de puntos en la superficie y en las condiciones de punto de ebullición 18. En este estudio, los patrones humectables híbridos axiales fueron producidos sobre una superficie de cobre cilíndrico utilizando la técnica de recubrimiento por inmersión. se llevaron a cabo Pool-hirviendo estudios de transferencia de calor para determinar los efectos de la cantidad de interlíneas y de la orientación del patrón humectable híbrido. Ebullición de flujo de calor, HTC, y dinámica de burbujas se analizaron para los sustratos recubiertos y todo nosre en comparación con el sustrato de cobre.

<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.

Experimentos de transferencia de calor de la piscina de punto de ebullición se llevaron a cabo sobre una superficie cilíndrica humectable híbrido utilizando la configuración experimental cuya esquemática se muestra en la Figura 5. El procedimiento experimental de la piscina de ebullición explicó en el paso 2 de la sección de protocolo se llevó a cabo con éxito mientras se investiga el efecto de la cantidad de interlíneas y de la orientación del patrón humect...

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

experimentos de transferencia de calor de la piscina de punto de ebullición se llevaron a cabo para observar los efectos de los patrones de humectables híbridos en el coeficiente de transferencia de calor (HTC). Los parámetros de la investigación son el número de interlíneas y la orientación patrón de la superficie humectable modificado.

Mejora de la piscina de ebullición de transferencia de calor en superficies cilíndricas con los patrones de humectables Híbridos

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

Universidad de Cartagena UDEC

Research

JoVE Journal

Engineering

9.0K vistas.  National Taiwan University.  experimentos de transferencia de calor de la piscina de punto de ebullición se llevaron a cabo para observar los efectos de los patrones de humectables híbridos en el coeficiente de transferencia de calor (HTC). Los parámetros de la investigación son el número de interlíneas y la orientación patrón de la superficie humectable modificado. 

Video: 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.

Visualización de alta velocidad Liquid Jet impactación sobre una superficie móvil

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

Investigación

Ingeniería

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.

Mediciones de transferencia de calor convectivo instantánea Local en una pipa - flujo bifásico y solo

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.

Fuerza de Coriolis desacoplar y rotación efectos de flotabilidad en el calor de campo completo transferencia de propiedades de un canal de rotación

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.

Analizando Mezcla falta de homogeneidad en un dispositivo de microfluidos por Microscale Schlieren Técnica

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

Bioingeniería

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.

Escalable de sello de impresión y fabricación de superficies de Hemiwicking

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.

Renderización de superficies SiO2/Si omnifóbicas por el tallado microtexturas que atrapan el gas que comprende cavidades o pilares reentrantes y doblemente reentrantes

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.

Prueba de Concepto para Membranas Que Atrapa Gas Derivadas de SiO2/Si/SiO2 amante del agua para la desalinización verde

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.

Preparación de vórtices de agua hiperbólicos de superficie libre

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

Prueba de la eficiencia de transferencia de calor de un intercambiador de calor de tubos con aletas

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

Educación

JoVE Science Education

Ingeniería química

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

Enfriamiento y ebullición

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

Mejora de la piscina de ebullición de transferencia de calor en superficies cilíndricas con los patrones de humectables Híbridos

Resumen

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