PNNL Enhanced Pool-Boiling Heat Transfer Using Nanostructured Surfaces PDF Download
Are you looking for read ebook online? Search for your book and save it on your Kindle device, PC, phones or tablets. Download PNNL Enhanced Pool-Boiling Heat Transfer Using Nanostructured Surfaces PDF full book. Access full book title PNNL Enhanced Pool-Boiling Heat Transfer Using Nanostructured Surfaces by . Download full books in PDF and EPUB format.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
Get Book Here
Book Description
Close-up video of boiling taking place on a nanostructured surface in a controlled laboratory experiment.
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
Get Book Here
Book Description
Close-up video of boiling taking place on a nanostructured surface in a controlled laboratory experiment.
Author: Changho Choi
Publisher:
ISBN:
Category : Ebullition
Languages : en
Pages : 146
Get Book Here
Book Description
This objective of this study is to investigate the capability of nanostructured surfaces on dissipating heat flux by performing pool boiling and convective flow boiling. The generation of ultra-high heat flux from high performance electric devices has motivated a number of investigations related to advanced heat transfer especially in two-phase boiling performance. It has been reported by a number of researchers that nanostructured surfaces can result in much enhanced boiling performance, compared to the conventional methods by creating desire conditions for heat transfer. In this thesis, various nanostructured surfaces having different morphology were prepared on several engineering relevant substrates and were characterized for their pool boiling performance. Microreactor-assisted-nanomaterial-deposition, MAND [trademark symbol] was used to fabricate a variety of different ZnO nanostructured surfaces by careful adjustment of the processing parameters. ZSM-5 zeolite was synthesized using hydrothermal reaction. ZnO nanostructures in minichannel were also successfully deposited via a flow cell for the application of flow boiling experiment. Scanning electron microscopy (SEM) and Atomic Force Microscopy (AFM) were carried out to characterize the micro- and nanostructures. Contact angle measurement was conducted to evaluate wettability and X-ray Diffraction (XRD) was used to determine the crystalline structures. The most significant enhancement of critical heat flux (CHF) and heat transfer coefficient (HTC) was observed in the flower like ZnO nanostructured surface. We observed pool boiling CHF of 80-82.5 W/cm2 for nanostructured ZnO on Al surfaces versus a CHF of 23.2 W/cm2 on a bare Al surface with a wall superheat reduction of 25-38°C. This new CHF values on nanostructured surfaces corresponds to a boiling heat transfer coefficient as high as ~ 23000 W/m2K. This represents an increase of almost 4X in CHF on nano-textured surfaces, which is the highest enhancement factor reported today.
Author: Sharan Ram Sriraman
Publisher:
ISBN:
Category :
Languages : en
Pages :
Get Book Here
Book Description
The effect of nano-structured surfaces on pool boiling heat transfer is explored in this study. Experiments are conducted in a cubical test chamber containing fluoroinert coolant (PF5060, Manufacturer: 3M Co.) as the working fluid. Pool boiling experiments are conducted for saturation and subcooled conditions. Three different types of ordered nano-structured surfaces are fabricated using Step and flash imprint lithography on silicon substrates followed by Reactive Ion Etching (RIE) or Deep Reactive Ion Etching (DRIE). These nano-structures consist of a square array of cylindrical nanofins with a longitudinal pitch of 1 mm, transverse pitch of 0.9 mm and fixed (uniform) heights ranging from 15 nm - 650 nm for each substrate. The contact angle of de-ionized water on the substrates is measured before and after the boiling experiments. The contact-angle is observed to increase with the height of the nano-fins. Contact angle variation is also observed before and after the pool boiling experiments. The pool boiling curves for the nano-structured silicon surfaces are compared with that of atomically smooth single-crystal silicon (bare) surfaces. Data processing is performed to estimate the heat flux through the projected area (plan area) for the nano-patterned zone as well as the heat flux through the total nano-patterned area, which includes the surface area of the fins. Maximum heat flux (MHF) is enhanced by ~120 % for the nanofin surfaces compared to bare (smooth) surfaces, under saturation condition. The pool boiling heat flux data for the three nano-structured surfaces progressively overlap with each other in the vicinity of the MHF condition. Based on the experimental data several micro/nano-scale transport mechanisms responsible for heat flux enhancements are identified, which include: "microlayer" disruption or enhancement, enhancement of active nucleation site density, enlargement of cold spots and enhancement of contact angle which affects the vapor bubble departure frequency.
Author: Ali Sadaghiani
Publisher: Academic Press
ISBN: 0128169249
Category : Technology & Engineering
Languages : en
Pages : 259
Get Book Here
Book Description
Nanofluid Boiling presents valuable insights into boiling heat transfer mechanisms, offering state-of-the-art techniques for overcoming obstacles against nanofluid applications. In addition, the book points out emerging industrial applications and guides researchers and engineers in their research and design efforts. In addition, recommendations on future research directions and the design of systems involving nanofluids are presented at the end of each chapter. The book's authors comprehensively cover mechanisms, parametric effects and enhancement techniques in the boiling of nanofluids, providing updated, detailed information about recent developments and findings. - Reveals insights into the findings and mechanisms of boiling heat transfer in nanofluids, guiding researchers and engineers in their research and design efforts - Focuses on parametric effects such as nanofluid properties (size, concentration, nanoparticle type), preparation methods on heat transfer and critical heat flux mechanisms, bubble dynamics, flow patterns, and pressure drop - Presents readers with scaling effects (from macro to microscale) relevant to nanofluid boiling
Author: Dong Soo Jung
Publisher:
ISBN:
Category : Heat
Languages : en
Pages : 246
Get Book Here
Book Description
Author: Vijaykumar Sathyamurthi
Publisher:
ISBN:
Category :
Languages : en
Pages :
Get Book Here
Book Description
Subcooled pool boiling on nanotextured surfaces is explored in this study. The experiments are performed in an enclosed viewing chamber. Two silicon wafers are coated with Multiwalled Carbon Nanotubes (MWCNT), 9 microns (Type-A) and 25 microns (Type-B) in height. A third bare silicon wafer is used for control experiments. The test fluid is PF-5060, a fluoroinert with a boiling point of 56°C (Manufacturer: 3M Co.). The apparatus is of the constant heat flux type. Pool boiling experiments in nucleate and film boiling regimes are reported in this study. Experiments are carried out under low subcooling (5 °C and 10 °C) and high subcooling conditions (20°C to ~ 38°C). At approximately 38°C, a non-departing bubble configuration is obtained on a bare silicon wafer. Increase in subcooling is found to enhance the critical heat flux (CHF) and the CHF is found to shift towards higher wall superheats. Presence of MWCNT on the test surface led to an enhancement in heat flux. Potential factors responsible for boiling heat transfer enhancement on heater surfaces coated with MWCNT are identified as follows: a. Enhanced surface area or nano - fin effect b. Higher thermal conductivity of MWCNT than the substrate c. Disruption of vapor-liquid vapor interface in film boiling, and of the "microlayer" region in nucleate boiling d. Enhanced transient heat transfer caused by local quasi-periodic transient liquid-solid contacts due to presence of the "hair like" protrusion of the MWCNT e. Enhancement in the size of cold spots f. Pinning of contact line, leading to enhanced surface area underneath the bubble leading to enhanced heat transfer Presence of MWCNT is found to enhance the phase change heat transfer by approximately 400% in nucleate boiling for conditions of low subcooling. The heat transfer enhancement is found to be independent of the height of MWCNT in nucleate boiling regime in the low subcooling cases. About 75%-120% enhancement in heat transfer is observed for surfaces coated with MWCNT under conditions of high subcooling in the nucleate boiling regime. Surfaces coated with Type-B MWCNT show a 75% enhancement in heat transfer in the film boiling regime under conditions of low subcooling.
Author: Craig Douglas Gerardi
Publisher:
ISBN:
Category :
Languages : en
Pages : 466
Get Book Here
Book Description
(Cont.) Critical heat flux enhancement in nanofluids of up to 100% was experimentally observed. The cause of this enhancement was determined to be the decreased static contact angle of nanofluid boiled surfaces. The increased wettability modified the growth of bubbles prior to CHF and promoted rewetting of hotspots at CHF. In parallel quenching tests, rewetting temperatures and velocities were simultaneously measured for the first time. Surfaces that had been pre-boiled in nanofluids were found to have significantly higher rewetting temperatures and velocities than clean surfaces. Interpretation of the experimental data was conducted with consideration of the governing surface parameters and existing models. It was found that there is significant room for improvement of most pool boiling models, especially with regard to surface effects. The research performed in this thesis help demonstrate the power of the infrared thermography technique and its potential for future improvement of boiling models.
Author: Youngsup Song
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
Get Book Here
Book Description
This thesis provides important insights to understand the role of surface properties and structures on pool boiling heat transfer, thereby providing guidelines for the systematic design of surface structures for enhanced pool boiling heat transfer.
Author: Nanxi Li
Publisher:
ISBN:
Category :
Languages : en
Pages :
Get Book Here
Book Description
Boiling is a very effective way of heat transfer due to the latent heat of vaporization. Large amount of heat can be removed as bubbles form and leave the heated surface. Boiling heat transfer has lots of applications both in our daily lives and in the industry. The performance of boiling can be described with two important parameters, i.e. the heat transfer coefficient (HTC) and the critical heat flux (CHF). Enhancing the performance of boiling will greatly increase the efficiency of thermal systems, decrease the size of heat exchangers, and improve the safety of thermal facilities. Boiling heat transfer is an extremely complex process. After over a century of research, the mechanism for the HTC and CHF enhancement is still elusive. Previous research has demonstrated that fluid properties, system pressures, surface properties, and heater properties etc. have huge impact on the performance of boiling. Numerous methods, both active and passive, have been developed to enhance boiling heat transfer. In this work, the effect of pressure was investigated on a plain copper substrate from atmospheric pressure to 45 psig. Boiling heat transfer performance enhancement was then investigated on Teflon© coated copper surfaces, and graphene oxide coated copper surfaces under various system pressures. It was found that both HTC and CHF increases with the system pressure on all three types of surfaces. Enhancement of HTC on the Teflon© coated copper surface is contributed by the decrease in wettability. It is also hypothesized that the enhancement in both HTC and CHF on the graphene oxide coated surface is due to pinning from micro and nanostructures in the graphene oxide coating or non-homogeneous wettability. Condensation and freezing experiments were conducted on engineered surfaces in order to further characterize the pinning effect of non-homogeneous wettability and micro/nano structure of the surface.
![Ìtan Ìnú Ìwé Mimó. [With illustrations.]. PDF](https://books.google.com/books/content/images/frontcover/vsTVjwEACAAJ?fife=w80-h100)
Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :
Get Book Here
Book Description
