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Author: Jay D. Sircar
Publisher:
ISBN:
Category :
Languages : en
Pages : 63
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Book Description
We investigated the experimental performance of a nanoporous membrane for ultra-high heat flux dissipation from high performance integrated circuits. The biporous evaporation device utilizes thermally-connected, mechanically-supported, high capillarity membranes that maximize thin film evaporation and high permeability liquid supply channels that allow for lower viscous pressure losses. The 600 nm thick membrane was fabricated on a silicon on insulator (SOI) wafer, fusion-bonded to a separate wafer with larger liquid channels. Spreading effects and overall device performance arising from non-uniform heating and evaporation of methanol was captured experimentally. Heat fluxes up to 412 W/cm2, over an area of O.4x 5 mm, and with a temperature rise of 24.1 K from the heated substrate to ambient vapor, were obtained. These results are in good agreement with a high-fidelity, coupled fluid convection and solid conduction compact model, which was necessitated by computational feasibility, which incorporates non-equilibrium and sub-continuum effects at the liquid-vapor interface. This work provides a proof-of-concept demonstration of our biporous evaporation device. Simulations from the validated model, at optimized operating conditions and with improved working fluids, predict heat dissipation in excess of 1 kW/cm2 with a device temperature rise below 30 K, for this scalable cooling approach.
Author: Jay D. Sircar
Publisher:
ISBN:
Category :
Languages : en
Pages : 63
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Book Description
We investigated the experimental performance of a nanoporous membrane for ultra-high heat flux dissipation from high performance integrated circuits. The biporous evaporation device utilizes thermally-connected, mechanically-supported, high capillarity membranes that maximize thin film evaporation and high permeability liquid supply channels that allow for lower viscous pressure losses. The 600 nm thick membrane was fabricated on a silicon on insulator (SOI) wafer, fusion-bonded to a separate wafer with larger liquid channels. Spreading effects and overall device performance arising from non-uniform heating and evaporation of methanol was captured experimentally. Heat fluxes up to 412 W/cm2, over an area of O.4x 5 mm, and with a temperature rise of 24.1 K from the heated substrate to ambient vapor, were obtained. These results are in good agreement with a high-fidelity, coupled fluid convection and solid conduction compact model, which was necessitated by computational feasibility, which incorporates non-equilibrium and sub-continuum effects at the liquid-vapor interface. This work provides a proof-of-concept demonstration of our biporous evaporation device. Simulations from the validated model, at optimized operating conditions and with improved working fluids, predict heat dissipation in excess of 1 kW/cm2 with a device temperature rise below 30 K, for this scalable cooling approach.
Author: Daniel Frank Hanks
Publisher:
ISBN:
Category :
Languages : en
Pages : 123
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Book Description
Heat dissipation is a critical limitation in a range of electronic devices including microprocessors, solar cells, laser diodes and power amplifiers. The most demanding devices require dissipation of heat fluxes in excess of 1 kW/cm2 with heat transfer coefficients more than 30 W/cm 2K. Advanced thermal management solutions using phase change heat transfer are the most promising approach to address these challenges, yet current solutions are limited due to the combination of heat flux, thermal resistance, size and flow stability. This thesis reports the design, fabrication and experimental characterization for an evaporation device with a nanoporous membrane for high heat flux dissipation. Evaporation in the thin film regime is achieved using nanopores with reduced liquid film thicknesses while liquid pumping is enhanced using the capillary pressure of the 120 nm pores. The membrane is mechanically supported by ridges that form liquid supply channels and also serve as a heat conduction path to the evaporating meniscus at the surface of the membrane. The combination of high capillarity pores with high permeability channels facilitates theoretical critical heat fluxes over 2 kW/cm2 and heat transfer coefficients over 100 W/cm2K. Proof-of-concept devices were fabricated using a two-wafer stack consisting of a bonded silicon-on-insulator (SOI) wafer to a silicon wafer. Pores with diameters 110 - 130 nm were defined with interference lithography and etched in the SOI. Liquid supply microchannels were etched on a silicon wafer and the two wafers were fusion bonded together to form a monolithic evaporator. Once bonded, the membrane was released by etching through the backside of the SOI. Finally, platinum heaters and Resistive Temperature Detectors (RTDs) were deposited by e-beam evaporation and liftoff to heat the sample and measure the device temperature during experiments, respectively. Samples were experimentally characterized in a custom environmental chamber for comparison to the model using R245fa, methanol, pentane, water and isopropyl alcohol as working fluids. A comparison of the results with different working fluids demonstrates that transport at the liquid-vapor interface is the dominant thermal resistance in the system, suggesting a figure of merit: ... The highest heat flux recorded was with pentane at ... and the highest heat transfer coefficient recorded was with ... not including the substrate resistance. However, the samples were observed to clog with soluble, nonvolatile contaminants which limited operation to several minutes. The clogging behavior was captured in a mass diffusion model and a new configuration was suggested which is resistant to clogging. Evaporation from nanopores represents a new paradigm in phase change cooling with a figure of merit that favors high volatility, low surface tension fluids rather than water. The models and experimental results validate the functionality and understanding of the proposed approach and provide recommendations for enhancements in performance and understanding as well as strategies for resistance to clogging. This work demonstrates that nanoporous membranes have the potential for ultra-high heat flux dissipation to address next generation thermal management needs.
Author: Madhusudan Iyengar
Publisher: World Scientific
ISBN: 9811279381
Category : Technology & Engineering
Languages : en
Pages : 479
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Book Description
This book is a comprehensive guide on emerging cooling technologies for processors in microelectronics. It covers various topics such as chip-embedded two-phase cooling, monolithic microfluidic cooling, numerical modeling, and advances in materials engineering for conduction-limited direct contact cooling, with a goal to remedy high heat flux issues.The book also discusses the co-design of thermal and electromagnetic properties for the development of light and ultra-high efficiency electric motors. It provides an in-depth analysis of the scaling limits, challenges, and opportunities in embedded cooling, including high power RF amplifiers and self-emissive and liquid crystal displays. Its analysis of emerging cooling technologies provides a roadmap for the future of cooling technology in microelectronics.This book is a good starting point for the electrical and thermal engineers, as well as MS and PhD students, interested in understanding and collaboratively tackling the complex and multidisciplinary field of microelectronics device (embedded) cooling. A basic knowledge of heat conduction and convection is required.
Author: Kyle L. Wilke
Publisher:
ISBN:
Category :
Languages : en
Pages : 64
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Book Description
Cooling demands of advanced electronics are increasing rapidly, often exceeding capabilities of conventional thermal management techniques. Thin film evaporation has emerged as one of the most promising thermal management solutions. High heat transfer rates can be achieved in thin films of liquids due to a small conduction resistance through the film to the evaporating interface. In this thesis, we investigated evaporation from nanoporous membranes. The capillary wicking of the nanopores supplies liquid to the evaporating interface, passively maintaining the thin film. Different evaporation regimes were predicted through modeling and were demonstrated experimentally. Good agreement was shown between the predicted and observed transitions between regimes. Improved heat transfer performance was demonstrated in the pore level evaporation regime over other regimes, with heat transfer rates up to one order of magnitude larger for a given superheat in comparison to the flooding regime. An improved experimental setup for investigating thin film evaporation from nanopores was developed, where a biphilic membrane, i.e., a membrane with two wetting behaviors, was used for enhanced experimental control to allow characterization of the importance of different design parameters. This improved setup was then used to demonstrate the dependence of thin film evaporation on the location of the meniscus within the nanopores. This dependence on meniscus location within the pore was also shown to increase with increasing superheat. We observed a 46% reduction in heat transfer rates at a superheat of 15 °C for an L* of 14.67 compared to an L* of 2, where L* is the ratio of the depth of the meniscus within the pore to the pore radius. This work provides practical insights for the design of devices based on nanoporous evaporation. Heat transfer regimes can be predicted based on fluid supply conditions, evaporative heat flux, and membrane geometry. Furthermore, the biphilic membrane serves as a valuable experimental platform for testing the role of membrane geometry on heat transfer performance in the pore level evaporation regime. Future work will focus on demonstrating the importance of different parameters and using experimental results to either validate existing models for evaporation from nanopores or develop more suitable ones.
Author: Young Jin Kim
Publisher:
ISBN:
Category :
Languages : en
Pages : 105
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Book Description
Nanostructured materials exhibit useful properties that are not found in the same materials in bulk form. (1) Dramatically increase surface and area and roughness of nanostructured materials is advantageous for evaporative cooling, which is one of the main subjects in this dissertating, due to the strong capillary effect and high density of gas-liquid-solid triple junctions. (2) In magnetic materials, when the size of the magnetic material is decreased to submicron or nano size, magnetic coercivity increases since magnetic domains are confined by the size of the material. (3) Also, unique optical properties of materials in nano size can be utilized for thermal managing and energy saving application. In Chapter 2 of this dissertation, I described the demonstration of using nanoporous membranes in evaporative cooling. Nanoporous membranes have been proposed and theoretically shown as a promising candidate for high heat flux evaporative heat transfer. However, the experimentally demonstrated heat flux has so far been significantly lower than the theoretical prediction, which has cast doubt on the feasibility of achieving a high heat flux from nanoporous membranes. Here we carried out evaporative heat transfer experiments using isopropyl alcohol (IPA) through anodized aluminum oxide (AAO) membranes. For membranes with a 200nm average pore size on a 0.5cm2 size area, we demonstrated a high evaporative heat flux of 210W/cm2 based on the overall AAO surface area, or ~400W/cm2 if only the pore area is considered. This heat flux is close to the theoretical value of 572 W/cm^2 (based on the pore area) for IPA evaporation through nanoporous membranes. Using time synchronized high-speed images, it was verified that evaporation was the main heat transfer mode in the high heat flux regime. The demonstration of high heat flux evaporation through nanoporous membranes, close to the theoretical limit and on a relatively large area (0.5cm2), is significant for the future development of high heat flux thermal management technology for electronic devices. In chapter 3, I presented a noble technique to achieve exchange coupling of hard phase magnetic materials and soft phase magnetic materials. Exchange coupled spring magnets have been suggested as a possible replacement of rare earth contained strong magnets. We have chosen LPT-MnBi as hard phase and FeCo as soft phase magnetic material, as many early conducted theoretical modeling suggests. The optimal size of hard phase magnet for the exchange coupling (approximately twice of single magnetic domain size, ~2[mu]m for MnBi) was achieved by conventional ball milling process, and the shell layer of FeCo was deposited by a noble process called sonic agitation assisted physical vapor deposition (SAA-PVD). TEM image and EDX mapping shows uniform coating of FeCo outer shell layer on the MnBi core. The thickness of the shell layer was in the range of 10~35nm which is slightly less than twice of single domain size of FeCo. Magnetic remanence of ball milled MnBi particles was increased from Ms = 36 emu/g to 51 emu/g after SAPVD process while the coercivity was slightly decreased from 1.1T to 1.0T. (BH)max of the particles after the SAA-PVD process was about 2.5MGOe. Smooth demagnetization curve that resembles that of single magnetic materials and high increase of magnetic remanence suggest that exchange coupling was achieved. In chapter 4, a new route to synthesize thermochromic VO2 particles and properties of the film using the particles was presented. A temperature responding fully reversible metal to insulator phase transition (MIT) accompanied by a change of optical properties only found in Vanadium dioxide monoclinic phase (VO2 (M)) has potential for huge energy saving application by controlling the amount of infrared (IR) light enter into buildings. More synthetic routes are still worthy to be explored because of difficulty in mass production of VO2 (M). In this work, we demonstrated a combination of thermal decomposition method subsequent ball milling process to produce pure VO2 (M) particles. The size of the synthesized particles was between 20 and 200nm. IR modulating smart film was fabricated by blade casting mixture of synthesized VO2 (M) particles and PVP on PET film. The thickness of the film was about 300nm and particles were uniformly dispersed in the film. Despite the irregular shape of the particles and the fact that few portion of the synthesized particles exceeding suggested optimal size range, the transmittance of little less than 40% and the IR modulation of about 20% which values are practically useful was achieved.
Author: Zhengmao Lu
Publisher:
ISBN:
Category :
Languages : en
Pages : 87
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Book Description
Evaporation, a commonly found phenomenon in nature, is widely used in thermal management, water purification, and steam generation as it takes advantage of the enthalpy of vaporization. Despite being extensively studied for decades, the fundamental understanding of evaporation, which is necessary for making full use of evaporation, remains limited up to date. It is in general difficult to experimentally characterize the interfacial heat and mass transfer during evaporation. In this thesis, we designed and microfabricated an ultrathin nanoporous membrane as an experimental platform to overcome some critical challenges including: (1) realizing accurate and yet non-invasive interface temperature measurement; (2) decoupling the interfacial transport resistance from the thermofluidic resistance in the liquid phase and the diffusion resistance in the vapor phase; and (3) mitigating the blockage risk of the liquid-vapor interface due to nonevaporative contaminants. Our nano device consisted of an ultrathin free-standing membrane (~200 nm thick) containing an array of nanopores (pore diameter ~100 nm). A gold layer deposited on the membrane served as an electric heater to induce evaporation as well as a resistive temperature detector to closely monitor the interface temperature. This configuration minimizes the thermofluidic resistance in the liquid and mitigates the contamination risk. We characterized evaporation from this nano device in air as well as pure vapor. We demonstrated interfacial heat fluxes of ~~500 W/cm2 for evaporation in air, where we elucidated that the Maxwell- Stefan equation governed the overall transport instead of Fick's law, especially in the high flux regime. In vapor, we achieved kinetically limited evaporation with an interfacial heat transfer coefficient up to 54 kW/cm2 K. We utilized the kinetic theory with the Boltzmann transport equation to model the evaporative transport. With both experiments and modeling, we demonstrated that the kinetic limit of evaporation is determined by the pressure ratio between the vapor in the far field and that generated by the interface. The improved fundamental understanding of evaporation that we gained indicates the significant promise of utilizing an ultrathin nanoporous design to achieve high heat fluxes for evaporation in thermal management, desalination, steam generation, and beyond.
Author:
Publisher: Elsevier
ISBN: 0443295395
Category : Science
Languages : en
Pages : 314
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Book Description
Advances in Heat Transfer, Volume 58 presents the latest in a serial that highlights new advances in the field, with this updated volume presenting interesting chapters written by an international board of authors. Sample chapters in this new release include Nanoscale Thin Film Evaporation and Ice thermal energy storage modeling: A review. - Provides the authority and expertise of leading contributors from an international board of authors - Presents the latest release in Advances in Heat Transfer serials
Author: Jagath B. Yaddlessalage
Publisher:
ISBN:
Category : Evaporative cooling
Languages : en
Pages :
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Book Description
With the current technological advancement, the size of the electronic components is being reduced to smaller and compact sizes. In the meantime, the packaging density and power consumption is ever increasing. To tackle this challenge, an efficient cooling technology is required. Thin-film evaporation is a very efficient cooling technology. A practical application using thin-film evaporation is a spray cooling which is known as the cooling method that can handle very high heat flux. However, a random spray of coolant cannot guarantee a thin coolant film, therefore either local dry-out or flooding may occur, which hampers cooling efficiency significantly. Moreover, bulky spraying system is not suitable for cooling of small electronic devices. As solving the drawbacks of spraying cooling, it has been suggested making thin liquid films by delivering nanoscale liquid drops to the superhydrophilic nanoporous coating (SHNC). As soon as a nanoscale liquid drop arrives to the SHNC on a hotspot, it spontaneously spreads, forms very thin liquid film, and quickly evaporates. Electrowetting on dielectric (EWOD) digital microfluidics (DMF) is properly suited for this purpose, since it handles liquids in the form of droplets by controlling only electric fields without any bulky mechanical pumps or valves. This dissertation reports an experimental study of three essential requirements of the EWOD DMF towards the thin-film evaporative cooling platform: (1) the high accuracy and consistency in volume of coolant nanodrops dispensed from the reservoir, (2) the fast motion of coolant nanodrops to the hotspot to avoid dry-out, and (3) the simultaneous achievement of both small volume and high frequency of nanodrop that arrives to the hotspot. In this investigation, glass-based EWOD DMF and silicon-based EWOD DMF were developed, fabricated and tested. Deionized (DI) water was used as coolant due to its high heat of vaporization. To increase the volume accuracy of nanodrop, various electrode geometries of the reservoir were designed to control drop pinch-off point. A simple force balance was taken into account for the design. The minimum average volume error of 0.083 % for fifty drops of repeatable drop generation was achieved. The experimental results agreed with the numerically simulated results. To increase the speed of drop motion, three major parameters that affect the speed of drop motion were investigated: The effects of electrode size, electrode geometry and surface roughness were tested. Ten times faster speed (400 mm/s) of drop motion was achieved by modifying the electrode geometry. To achieve simultaneously high frequency and small volume of nanodrops that arrive to the hotspot, a new electrode geometry was designed to split a droplet into two while it moves toward the hotspot. Using this method, the droplet arrival frequency to the heated section was increased 4 times while the droplet volume that arrives to the heated section is 4 times smaller than the volume of droplet generated from the reservoir. By combining all of the above results, fully completed and automated EWOD DMF was designed, fabricated and characterized to deliver liquid in small volume (down to 50 nL) with high accuracy (
Author:
Publisher: Springer
ISBN: 9783319266947
Category : Science
Languages : en
Pages : 0
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Book Description
This Handbook provides researchers, faculty, design engineers in industrial R&D, and practicing engineers in the field concise treatments of advanced and more-recently established topics in thermal science and engineering, with an important emphasis on micro- and nanosystems, not covered in earlier references on applied thermal science, heat transfer or relevant aspects of mechanical/chemical engineering. Major sections address new developments in heat transfer, transport phenomena, single- and multiphase flows with energy transfer, thermal-bioengineering, thermal radiation, combined mode heat transfer, coupled heat and mass transfer, and energy systems. Energy transport at the macro-scale and micro/nano-scales is also included. The internationally recognized team of authors adopt a consistent and systematic approach and writing style, including ample cross reference among topics, offering readers a user-friendly knowledgebase greater than the sum of its parts, perfect for frequent consultation. The Handbook of Thermal Science and Engineering is ideal for academic and professional readers in the traditional and emerging areas of mechanical engineering, chemical engineering, aerospace engineering, bioengineering, electronics fabrication, energy, and manufacturing concerned with the influence thermal phenomena.
Author: David Brutin
Publisher: Academic Press
ISBN: 0128008083
Category : Science
Languages : en
Pages : 464
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Book Description
Droplet Wetting and Evaporation provides engineers, students, and researchers with the first comprehensive guide to the theory and applications of droplet wetting and evaporation. Beginning with a relevant theoretical background, the book moves on to consider specific aspects, including heat transfer, flow instabilities, and the drying of complex fluid droplets. Each chapter covers the principles of the subject, addressing corresponding practical issues and problems. The text is ideal for a broad range of domains, from aerospace and materials, to biomedical applications, comprehensively relaying the challenges and approaches from the different communities leading the way in droplet research and development. - Provides a broad, cross-subject coverage of theory and application that is ideal for engineers, students and researchers who need to follow all major developments in this interdisciplinary field - Includes comprehensive discussions of heat transfer, flow instabilities, and the drying of complex fluid droplets - Begins with an accessible summary of fundamental theory before moving on to specific areas such as heat transfer, flow instabilities, and the drying of complex fluid droplets
