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).

수정 된 표면의 제조 1 <ol><li> 수동 # 2000 에머리를 사용하여 15 분 동안 시험편 (중공 구리 실린더 40 mm의 길이 (l), 25 mm의 외경 (d 오)로하고, 18 mm의 내경 (d의 Ⅰ)) 연마 종이. DI 물 다음 아세톤으로 세척하여 광택 표면을 청소합니다. </li><li> 120 ℃의 일정 온도에서 2 시간 동안 오븐에서 연마 된 시험편을 놓는다. </li><li> 다음 단계를 사용하여 초 친수성의 SiO2 나노 입자 용액을 준비합니다. <ol><li> 테트라에 톡시 실란 및 DI 워터의 몰비 4 : 1을 혼합하여 용액 A를 준비한다. 37 %의 2 방울을 A 액에 염산을 농축하고, 2 시간 동안 교반 추가. </li><li> 에탄올 및 DI 물의 몰비 3 : 1 혼합하여 용액 B를 만든다. </li><li> 용액 B의 80 mL의 A 액 1 ㎖를 혼합하고 2 시간 동안 교반한다. </li><li> 준비된 SOLU에의 SiO2 나노 입자 (40 나노 미터 직경) 32 g을 넣고1 시간 동안 기 저어. </li></ol></li><li> 5mm / min의 속도로 딥 코팅 장치를 이용하여 제조 한 용액에 시편을 담근다. 1 시간 동안 120 ℃의 오븐에서 코팅 된 시편을 유지. </li><li> 다음 단계를 사용하여 (도 1 참조)의 축 방향을 따라 서로 다른 방향으로 2, 4, 8 환승 할 하이브리드 패턴을 준비한다. <ol><li> 중심과 초 친수성 영역에 도포되는 (영역) 상에 interlines을 조정 영역을 마스크 0 ° 방향에서의 2 인터 표면에 적절한 방향 (함께 interlines 필요한 수에 따른 절연 테이프를 사용하여 코팅되지하도록 상측. 한편, 90 ° 방향에 대해, 아래쪽 상단과 다른 하나 인터을 조정하고 180 ° 방향에 대해, 초 친수성 아래쪽 영역 및 중앙의 interlines을 조정한다. 유사하게, 조정 다른 출력과 4, 8 개면의 위치 환승 할rientation로서도 1에 도시). </li><li> 5mm / 분의 느린 속도에서 높은 핑 속도 및 상승에 침지 코팅 장치, 딥을 이용하여 제조 된 용액에 마스크 시험편을 담근다. 1 시간 동안 120 ℃의 오븐에서 코팅 된 시편을 유지. </li><li> 올바른 방향으로 interlines 필요한 수를 얻기 위해 마스킹 영역에서 절연 테이프를 분리. </li></ol></li></ol><img alt="그림 1" src="/files/ftp_upload/55387/55387fig1.jpg" /> 도 1 다양 환승 할 표면의 선택. 다른 방향으로 다양한 환승 할 표면 (a) 회로도. 모든 조건에서 1 : 일반 구리 표면과 초 친수성 표면의 면적의 비는 1이다. (b) 방향 선택 기준. (c) 2 인터 0 ° 각도로 배향 된 표면의 투시도. 오리엔테이션 기준선과 코팅 사이의 각도로서 선택된다중앙 상부 측으로부터 제 친수성 패턴의 라인과는 시계 방향으로 측정된다. <a href="http://ecsource.jove.com/files/ftp_upload/55387/55387fig1large.jpg" target="_blank">이 그림의 더 큰 버전을 보려면 여기를 클릭하십시오.</a> 2. 실험 절차 <ol><li> 절연 테이프를 사용하여 피복 된 시험편의 각각의 원형베이스에 한 유리관을 고정한다. </li><li> interlines의 필요한 위치에 따른 실리콘 페이스트를 이용하여 (도 2에 도시 된 바와 같이) 가로 140- 140- X X 160 mm 챔버에이 어셈블리를 고정한다. </li><li> 550 W, 18 mm 직경, 및 시험편의 구멍에 둘레 영역 열 페이스트의 박막을 40 mm 길이의 카트리지 히터를 배치했다. </li><li> 직류 (DC) 전원 공급 장치에 카트리지 히터를 연결한다. </li><li> 도 5와 같이 mm, 7 mm의 깊이가 다른 8 개의 등 간격 1 mm 구멍에 배치 T 형 열전대3 데이터 로거에 연결합니다. </li><li> 상부 커버에 형성된 공간에 (RTD), 환류 ​​응축기 및 보조 히터를 삽입하고 저항 온도 검출기를 고정한다. 끓는 실 이상을 수정합니다. </li><li> 풀 비등 챔버로 DI 물 1,400 mL로 채 웁니다. </li><li> 5 ℃에서 유지되는 냉각 실에 환류 응축기를 연결한다. </li><li> 실험 전에 격렬하게 보조 히터를 사용하여 30 분 동안 풀 비등 챔버의 DI 물을 끓인다. </li><li> 상기 보조 히터를 사용하여 포화 비등 상태에서 DI 워터를 유지. 이어서, 전원을 켜고 0.1 A. 초기 전류를 제공 </li><li> 정상 상태에 도달하기 위해 2 분 기다립니다. 이어서, 0.3 A. 단위로 전류를 증가 </li><li> 데이터 로거를 사용하여 각각의 입력 전력에서의 온도를 기록한다. 4 (A)의 최대 전류에 도달 할 때까지 실험을 계속합니다. 한편, 기포의 강약을 기록<html> 또는 CCD 카메라를 이용하여 각각의 전원 입력 시험편에 집중 풀 비등 실의 전방에 배치. </li></ol><img alt="그림 2" src="/files/ftp_upload/55387/55387fig2.jpg" /> 풀 비등 회의소 그림 2. 도식. 유리 튜브는 실리콘 페이스트 중공 구리 실린더의 양측에 접속된다. 이것은 실리콘 페이스트 풀 비등 실에 고정되어있다. <a href="http://ecsource.jove.com/files/ftp_upload/55387/55387fig2large.jpg" target="_blank">이 그림의 더 큰 버전을 보려면 여기를 클릭하십시오.</a> <img alt="그림 3" src="/files/ftp_upload/55387/55387fig3.jpg" /> 3. 열전대 위치를 그림. 8 열전대의 직경이 20mm의 시험편 대신 원주 1 개 mm 직경의 구멍 안에 위치한다. 다른 직경 1mm의 구멍의 깊이가 각각 5mm 7mm로 고정된다./files/ftp_upload/55387/55387fig3large.jpg &quot;target =&quot;_ blank &quot;&gt; 검색이 그림의 더 큰 버전을 보려면 여기를 클릭하십시오. 3. 데이터 감소 <ol><li> 다음 수학 식 19을 이용하여 입 열량 (Q)을 계산 Q = I V (1) 주 : I 및 V는 각각 A의 입력 전류 및 볼트 단위의 전압이다. </li><li> 식 (19)를 사용하여 양측면으로부터 열 손실 (Q 손실)를 추정 : <img alt="수학 식 2" src="/files/ftp_upload/55387/55387eq2.jpg" /> (2) 주 : K 구리의 열전도율이고; T 및 T 7mm 5mm가 7mm 각각 5mm, 깊이에서의 온도의 평균 값이고; ΔX (2 mM)을 깊이 사이의 차이이고; 과 <img alt="수학 식 (b)" src="/files/ftp_upload/55387/55387eq2b.jpg" /> 테스트 (p)의 단면적은<html> IECE. </li><li> 하기 식 (19)을 사용하여 (Q &#39;를&#39;) 열유속를 결정 <img alt="식 (3)" src="/files/ftp_upload/55387/55387eq3.jpg" /> (삼) 주 : A = π (D)의 입출력 L은 시편의 원주 영역이다. </li><li> 다음 식 (19)를 사용하여 벽면 과열을 (계산 : <img alt="수학 식 4" src="/files/ftp_upload/55387/55387eq4.jpg" /> (4) 주 : T의 m은 T 7mm 및 T 5mm의 평균 인 상기의 시험편 (R)의 출력 (12.5 mm) 시험편의 외 반경 (R)의 m (10mm) 시험편의 반경의 길이는 도 4에 도시 된 바와 같이 구멍을 측정하고, T가 앉아서하는 DI 워터의 포화 온도이다. </li><li> 하기 식 (19)를 사용하여 HTC (α)을 계산한다 : PLOAD / 55,387 / 55387eq5.jpg &quot;/&gt; (5) </li></ol><img alt="그림 4" src="/files/ftp_upload/55387/55387fig4.jpg" /> 벽 온도 분석 그림 4. 회로도. 벽 온도는 측정 된 평균 온도 및 공지 원통형 열 저항을 사용하여 계산된다. <a href="http://ecsource.jove.com/files/ftp_upload/55387/55387fig4large.jpg" target="_blank">이 그림의 더 큰 버전을 보려면 여기를 클릭하십시오.</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...

10-10을 5 W의 범위 인 냉각 제공 고열 플럭스 시스템 유지 / cm 2 전자 방위, 항공 및 핵 발전의 새로운 분야에서 요구된다. 종래의 냉각 공기로 인해 자유 - 강제 대류 조건 모두 낮은 열 전달 계수 (HTC) 이러한 애플리케이션에 충분하다. 1000 W / cm 2 - 1과 같은 풀비 같은 상 변화 계 냉각 기술은 끓는 흐름 (10)의 순서로 높은 열유속 제거에 충분하다. 2 상 열전달 과정이 등온 때문에, 냉각 장치의 온도는, 그 표면 위에 거의 일정하다. 인해 표면을 따른 온도의 변화를 무시할 수있는 장치의 열충격이 제거 될 수있다. 그러나, 열전달 끓는 주요 파라미터는 제한 온도에서 2 이상 상승을 일으키는 임계 열유속 (CHF)은 인 </sup&gt;. 지난 수십 년간, 광범위한 연구가 표면 개질, 나노 유체, 및 표면 코팅 3, 4, 5, 6, 7, 8, 9, 10, 11을 사용하여 CHF를 개선하기 위해 수행되었다. 여러 가지 방법 중에서, 표면 코팅으로 인해 표면적의 상당한 증가에 CHF을 개선하는 가장 좋은 방법으로 발견된다. 표면 코팅은 일반적으로 핀 작용 효과 다공성 및 표면 습윤성 (12)에 의한 열 전달을 증가시킨다. 표면의 젖음성은 열 전달 비등에 중요한 역할을한다. 이전의 연구는 낮은 열유속 조건에서, 소수성 표면으로 인해 초기 핵으로 더 HTC 표시되는지 보여준다. 그러나,에높은 열유속은, 형성된 기포의 분리로 인해 표면을 향해 물 낮은 친화력으로 느리다. 이 기포 합체 리드와 하부 CHF 3 초래한다. 한편, 친수성 표면으로 인해 형성된 기포의 고속 박리, 높은 CHF를 생성하지만 인해 기포 핵 (13)의 지연, 낮은 열 플럭스로 하부 HTC를 준다. 하이브리드 구조로 인해 소수성 및 친수성 (14), (15, 16)의 결합 효과에 대한 모든 열 플럭스 열전달 비등 현저한 향상을 보여준다. 슈는 등. 초 친수성 실리콘 코팅하여 제조 된 이종 습윤 표면을 마스크 표면에 구리 나노 입자. 그들은 코팅 시간을 변경하여 다른 젖음성 비율을 달성했다. 비등 개시는 H에 비해 불균일 표면에 발생 이전실질적으로 감소 omogeneous 벽 표면 (17)을 과열. 조 등. 친수성, 소수성, 이종 습윤면에 핵 비등 열전달 연구를 수행 하였다. 균질 습윤 표면은 친수성 표면 소수성 도트 패턴으로 구성 하였다. 그들은 높은 HTCs 및 친수성 표면에 비해 이종의 표면 같은 CHF를 얻었다. 열전달 비등 향상 직접 표면 및 끓는 조건에 따라 18 점의 개수에 의존한다. 본 연구에서는 축 하이브리드 습윤성 패턴은 딥 코팅 기술을 이용하여 원통형의 구리 표면 상에 제작 하였다. 풀 비등 열전달 연구 interlines 수의 하이브리드 습윤성 패턴의 배향의 영향을 결정하기 위해 수행되었다. 끓는 열유속, HTC, 거품 역학은 모두 코팅 기판 우리 분석 하였다구리 기판과 비교 재.

<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.

풀 비등 열전달 실험 개략도,도 5에 도시 된 실험 구성을 사용하여 하이브리드 습윤성 원통면에서 수행 하였다. interlines의 수와 풀 비등 성능 하이브리드 습윤성 패턴의 배향의 영향을 조사하면서 풀 비등 실험 절차는 프로토콜 부분의 2 단계에서 설명을 성공적으로 수행 하였다. 벽 과열 대 열유속 열유속 대 HTC : 다른 처리 표면의 풀 비등 공연 그래프의 관점...

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

풀 비등 열전달 실험 열 전달 계수 (HTC)의 혼합 수화제 패턴의 영향을 관찰하기 위해 수행되었다. 조사의 매개 변수는 interlines 수 및 습윤 표면 개질의 패턴 방향이다.

하이브리드 수화제 패턴과 원통 표면에 풀 비등 열전달 향상

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 조회수.  National Taiwan University.  풀 비등 열전달 실험 열 전달 계수 (HTC)의 혼합 수화제 패턴의 영향을 관찰하기 위해 수행되었다. 조사의 매개 변수는 interlines 수 및 습윤 표면 개질의 패턴 방향이다. 

비디오: 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.

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

연구

공학

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.

파이프-단일 및 2 단계 흐름에에서 로컬 순간 대류 열 전달의 측정

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.

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.

마이크로 스케일 슐 리렌 기술에 의해 미세 유체 소자 믹싱 비균질성 분석

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

생체공학

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.

확장 가능한 우표 인쇄 및 Hemiwicking 표면의 제조

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.

렌더링 SiO2/Si 표면 재진입 및 이중 재진입 구멍 또는 기둥을 포함하는 가스 를 포함하는 미세 질감을 조각하여 전지성

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.

녹색 담수화용 수중 SiO 2/Si/SiO2 웨이퍼에서 파생된 가스 포획 멤브레인에 대한 개념 증명

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.

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

핀 튜브 열교환기의 열전달 효율 테스트

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

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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

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

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