Name: pool-boiling heat-transfer enhancement on cylindrical surfaces with hybrid wettable patterns
Uploaded: 2017-04-10T14:00:00.000+00:00
Duration: 7 min 32 s
Description: Watch this Scientific Journal Video about Pool-Boiling Heat-Transfer Enhancement on Cylindrical Surfaces with Hybrid Wettable Patterns at JoVE.com

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.改性的表面的制备<ol><li>使用＃2000砂纸手动抛光该试验片（空心铜圆柱体具有40毫米的长度（L），25毫米外直径（d O），和一个18毫米内直径（d i））的15分钟纸。用丙酮，随后去离子水中清洗干净的抛光表面。 </li><li>在放置2小时的烘箱抛光试验片在120℃的恒定温度。 </li><li>使用以下步骤制备超亲水SiO 2的纳米颗粒溶液。 <ol><li>四乙氧基硅烷和去离子水的4摩尔比:通过混合1制备溶液A.添加37％的2滴浓HCl溶液A中，并搅拌2小时。 </li><li>的乙醇和去离子水3摩尔比:通过混合1使溶液B. </li><li>混合1毫升溶液A的80毫升溶液B，并搅拌2小时。 </li><li> 32克的SiO 2纳米颗粒（40纳米的直径）的添加到制备的SOLU重刑和搅拌1个小时。 </li></ol></li><li>通过使用浸涂装置以5mm / min的速度浸入所制备的溶液的试验片。保持在烘箱中涂覆的试验片在120℃下1个小时。 </li><li>制备2,4，和8沿轴向方向使用以下步骤不同的取向（ 如图1所示）隔行混合模式。 <ol><li>掩蔽的区域，以根据所需数量的与正确的方向（对于2行间表面以0°取向联运的使用绝缘带是未涂覆的，调节在所述中心和所述超亲水区域（区域待涂覆）联运顶侧上。在另一方面，对于90°的取向，在顶部和另一个在底部调节一个行间和用于180°取向，调整在底部超亲水区域和在中心处的联运。类似地，调整与不同○4,8隔行表面的位置rientation 如图1）。 </li><li>通过使用浸涂装置，浸涂以高浸渍速度和上升以5mm / min的速度缓慢浸入所制备的溶液中的掩蔽试验片。保持在烘箱中涂覆的试验片在120℃下1个小时。 </li><li>从掩蔽区域​​除去绝缘带，以获得所需数量的联运与正确方向。 </li></ol></li></ol><img alt="图1" src="/files/ftp_upload/55387/55387fig1.jpg" /> 图1.各种隔行曲面的选择。 （a）用不同的取向各种隔行表面的示意图。一个普通的铜表面和超亲水表面的面积比为1:1中的所有条件。 （b）中取向的选择标准。 （c）该2行间0°角取向的表面的等距视图。取向被选择为基线和涂层之间的角度从顶侧的第一亲水图案的中心线并且在顺时针方向上测量的。 <a href="http://ecsource.jove.com/files/ftp_upload/55387/55387fig1large.jpg" target="_blank">请点击此处查看该图的放大版本。</a> 2.实验步骤<ol><li>使用绝缘带，固定一个玻璃管在涂覆试验片的各圆形基部。 </li><li>水平固定该组件到140-X 140-×160毫米室使用根据联运的所需位置硅浆料（如在图2中所示）。 </li><li>放置一个550-W，直径18毫米，并用导热膏的上圆周区到试验片的孔的薄膜40毫米长的筒式加热器。 </li><li>筒式加热器连接到一个直流（DC）电源单元。 </li><li>地方的T型热电偶进8等距1毫米的孔，具有5mm和7mm备用深度如图3把它们连接到数据记录器。 </li><li>在设置在顶盖的空间插入和固定电阻温度检测器（RTD），回流冷凝器，和一个辅助加热器。解决这些问题在沸腾室。 </li><li>填写1400毫升去离子水入池沸腾室。 </li><li>回流冷凝器连接到被保持在5℃的冷却室中。 </li><li>在实验之前，使用辅助加热器剧烈煮沸去离子水在池沸腾室30分钟。 </li><li>通过使用辅助加热器保持去离子水在饱和沸腾条件。接着，接通电源，并给予0.1 A的初始电流</li><li>为了达到稳定状态等待2分钟。然后，增加用0.3 A的增量电流</li><li>通过使用数据记录器记录在每个功率输入的温度。继续实验，直到达到4 A的最大电流。同时，记录泡沫动力学F<html>或通过使用CCD照相机每个功率输入放置在池沸腾室，其被聚焦在试验片的前面。 </li></ol><img alt="图2" src="/files/ftp_upload/55387/55387fig2.jpg" /> 图2.原理池沸腾商会。玻璃管被连接到与硅膏中的空心铜圆柱体的两侧。这被固定在硅膏池沸腾室。 <a href="http://ecsource.jove.com/files/ftp_upload/55387/55387fig2large.jpg" target="_blank">请点击此处查看该图的放大版本。</a> <img alt="图3" src="/files/ftp_upload/55387/55387fig3.jpg" /> 图3.热电偶定位。 8个热电偶沿周向放置在直径1mm的孔的内部在所述试验片发生在一个直径为20毫米。备用直径1mm孔的深度是固定的以5mm和分别为7毫米。/files/ftp_upload/55387/55387fig3large.jpg"目标=‘_空白’&gt;点击此处查看该图的放大版本。 3.数据缩减<ol><li>通过使用以下等式计算19的热输入（Q） Q = I V（1） 注:I和V分别是安培输入电流和以伏特的电压。 </li><li>通过使用公式19来估计距两个侧表面的热损失（Q 损失 ）: <img alt="公式2" src="/files/ftp_upload/55387/55387eq2.jpg" /> （2） 注:k是铜的热导率; Ť7 毫米和T5 毫米是在7毫米和5毫米，分别深度的温度的平均值; ΔX（2 mm）是深度之间的差异;和 <img alt="式2B" src="/files/ftp_upload/55387/55387eq2b.jpg" />是测试p的横截面面积<html> IECE。 </li><li>通过使用下面的公式19确定的热通量（Q&#39;）: <img alt="公式3" src="/files/ftp_upload/55387/55387eq3.jpg" /> （3） 注:A =πD 2 O l是试验片的圆周区域。 </li><li>计算壁过热（使用下面的等式19: <img alt="公式4" src="/files/ftp_upload/55387/55387eq4.jpg" /> （4） 注:T m是Ť7 毫米和T 为5mm平均，是在试验片，R 0（12.5毫米）试验片的外半径，R M（10毫米）试验片的半径处的长度测量孔，且T是坐在 DI水的饱和温度， 如图4。 </li><li>计算使用下面的公式19中的HTC（α）: PLOAD / 55387 / 55387eq5.jpg" /&gt;（5） </li></ol><img alt="图4" src="/files/ftp_upload/55387/55387fig4.jpg" /> 图4.示意图壁温分析。壁温度用测量的平均温度和已知的圆柱形热电阻计算。 <a href="http://ecsource.jove.com/files/ftp_upload/55387/55387fig4large.jpg" target="_blank">请点击此处查看该图的放大版本。</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...

甲提供在10-10 5瓦的范围内的冷却高热通量维持系统cm 2的需要/电子，国防，航空电子设备，和核装置发展的新兴领域。与空气传统冷却不足以用于这些应用由于两个自由和强制对流条件下低传热系数（HTC）。相位基于变更的冷却技术，例如池沸腾和流动沸腾，都不够好，10的顺序上除去高的热通量- 1000 W / cm 2的1。由于两相热传递过程是等温的，在冷却装置温度在其表面上几乎不变。由于沿表面的温度的变化可以忽略不计，该装置的热冲击可以被消除。然而，在沸腾传热的主要限制参数是临界热通量（CHF），这导致温度2的异常上升</sup&gt;。 在过去的几十年中，广泛的研究已经进行了通过使用表面改性，纳米流体，和表面涂层3，4，5，6，7，8，9，10，11，以改善CHF。在各种方法中，表面涂层由于表面积大幅增加发现改善CHF的最佳方法。表面涂层通常增加鳍动作，孔隙率的影响，和表面润湿性12的热传递。表面润湿性起着沸腾传热一个显著的作用。以前的研究表明，在较低热通量的条件下，在疏水性表面显示出较好的HTC由于前期成核。然而，在较高热通量，所形成的气泡的分离是缓慢由于水朝向表面的低亲和力。这导致气泡聚结和导致较低的CHF 3。在另一方面，亲水性表面产生较高的CHF，因为所形成的气泡的快速拆卸的，但它在低的热通量使下部HTC，由于气泡成核13的延迟。 所述混合结构显示在沸腾传热所有热通量一个显着的提高，由于疏水性和亲水性14，15，16的组合效果。 Hsu 等人。通过涂覆超亲水的Si产生的异质可湿性表面纳米颗粒上的掩蔽铜表面上。它们通过改变涂层时间来实现不同的润湿性比。沸腾的发病早期出现异质表面上比在Homogeneous表面，其实质上减少了壁17过热。曹某等人。上的亲水性，疏水性，和异构的润湿表面进行核沸腾热传递的研究。将不均匀的润湿表面是由亲水性表面上的疏水性图案化的点。他们得到了较高的HTC的和非均相表面相比，亲水性表面一样瑞士法郎。在沸腾传热的改进直接取决于在表面上并在沸腾条件18的点的数量。 在这项研究中，使用浸涂技术的圆柱形的铜表面制作轴向混合可湿性图案。池沸腾传热研究，以确定联运的数目和混合可湿性图案的取向的影响。沸腾的热通量，HTC，和气泡动力学分析对于所有涂覆基材和我们与铜相比，衬底再。

<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.

池沸腾传热实验是在使用的实验装置，其示意图示于图5中的混合动力车可湿性圆筒面进行。池沸腾实验程序在协议部分的步骤2中说明成功地进行了当调查联运的数目和在水池沸点性能混合可湿性图案的定向的效果。的热通量相​​对于壁过热和HTC相对于热通量:不同的处理表面的池沸腾的表演在图的条款来表示。 ...

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

池沸腾传热进行实验以观察对传热系数（HTC）混合可湿性图案的影响。调查的参数是联运的数量和改性可湿性表面的图案取向。

在圆柱面池沸腾传热强化与混合可湿性模式

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 次观看.  National Taiwan University. 池沸腾传热进行实验以观察对传热系数（HTC）混合可湿性图案的影响。调查的参数是联运的数量和改性可湿性表面的图案取向。 

视频: 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.

高速喷液嵌塞对移动表面的可视化

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

科研

工程学

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.

管道单、两相流局部瞬时对流换热的测量

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.

解耦科里奥利力和旋转浮力对旋转通道全场传热性能的影响

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.

由微型条纹分析技术在微流控设备混合不均匀

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

生物工程

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.

可缩放邮票印刷及不堪砌面的制作

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.

通过雕刻包含可重入和双重入的腔或柱的气体镶入微纹理来渲染 SiO2/Si 曲面全功能性

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.

气体夹膜的概念验证，源自爱水的SiO 2/Si/SiO2晶圆，用于绿色海水淡化

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.

自由表面双曲水涡的制备

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

测试芬管热交换器的传热效率

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

教育

JoVE Science Education

化学工程

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

淬火和沸腾

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

在圆柱面池沸腾传热强化与混合可湿性模式

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