High-pressure Pool Boiling and Physical Insight of Engineered Surfaces PDF Download

Author: Nanxi Li
Publisher:
ISBN:
Category :
Languages : en
Pages :

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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.

Author: Smreeti Dahariya
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Boiling has received considerable attention in the technology advancement of electronics cooling for high-performance computing applications. Two-phase cooling has an advantage over a single-phase cooling in the high heat removal rate with a small thermal gradient due to the latent heat of vaporization. Many surface modifications have been done in the past including surface roughness, mixed wettability and, porous wick copper play a crucial role in the liquid-vapor phase change heat transfer. However, the mechanisms of high-pressure pool-boiling heat transfer enhancement due to surface modifications has not been well studied or understood. The properties of water, such as the latent heat of vaporization, surface tension, the difference in specific volume of liquid and vapor, decrease at high-pressure. High-pressure pool-boiling heat transfer enhancement is studied fundamentally on various engineered surfaces. The boiling tests are performed at a maximum pressure of 90 psig (620.5 kPa) and then compared to results at 0 psig (0 kPa). The results indicate that the pressure influences the boiling performance through changes in bubble dynamics. The bubble departure diameter, bubble departure frequency, and the active nucleation sites change with pressure. The pool-boiling heat transfer enhancement of a Teflon© coated surface is also experimentally tested, using water as the working fluid. The boiling results are compared with a plain surface at two different pressures, 30 and 45 psig. The maximum heat transfer enhancement is found at the low heat fluxes. At high heat fluxes, a negligible effect is observed in HTC. The primary reasons for the HTC enhancement at low heat fluxes are active nucleation sites at low wall superheat and bubble departure size. The Teflon© coated surface promotes nucleation because of the lower surface energy requirement. The boiling results are also obtained for wick surfaces. The wick surfaces are fabricated using a sintering process. The boiling results are compared with a plain surface. The reasons for enhancements in the pool-boiling performance are primarily due to increased bubble generation, higher bubble release frequency, reduced thermal-hydraulic length modulation, and enhanced thermal conductivity due to the sintered wick layer. The analysis suggests that the Rayleigh-critical wavelength decreases by 4.67 % of varying pressure, which may cause the bubble pinning between the gaps of sintered particles and avoids the bubble coalescence. Changes in the pitch distance indicate that a liquid-vapor phase separation happens at the solid/liquid interface, which impacts the heat-transfer performance significantly. Similarly, the role of the high-pressure over the wicking layer is further analyzed and studied. It is found that the critical flow length, [lambda]u reduces by three times with 200 [mu]m particles. The results suggest that the porous wick layer provides a capillary-assist to liquid flow effect, and delays the surface dry out. The surface modification and the pressure amplify the boiling heat transfer performance. All these reasons may contribute to the CHF, and HTC enhancement in the wicking layer at high-pressure.

Author:
Publisher: Springer
ISBN: 9783319266947
Category : Science
Languages : en
Pages : 0

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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: Youngsup Song
Publisher:
ISBN:
Category :
Languages : en
Pages : 0

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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: Vijaykumar Sathyamurthi
Publisher:
ISBN:
Category :
Languages : en
Pages :

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The objective of this investigation is to measure and analyze surface temperature fluctuations in pool boiling. The surface temperature fluctuations were recorded on silicon surfaces with and without multi-walled carbon nanotubes (MWCNT). Novel Thin Film Thermocouples (TFT) are micro-fabricated on test substrates to measure surface temperatures. A dielectric liquid refrigerant (PF-5060) is used as test fluid. Both nucleate and lm boiling regimes are investigated for the silicon test substrates. Dynamics of nucleate boiling is investigated on the CNT coated substrates. High frequency temperature fluctuation data is analyzed for the presence of determinism using non-linear time series analysis techniques in TISEAN© software. The impact of subcooling and micro/nano-scale surface texturing using MWCNT coatings on the dynamics of pool boiling is assessed. Dynamic invariants such as correlation dimensions and Lyapunov spectrum are evaluated for the reconstructed attractor. A non-linear noise reduction scheme is employed to reduce the level of noise in the data. Previous investigations in pool boiling chaos, reported in literature were based on temperature measurements underneath the test surface consisting of single or few active nucleation sites. Previous studies have indicated the presence of low-dimensional behavior in nucleate boiling and high-dimensional behavior in CHF and film boiling. Currently, there is no study detailing the effects of multiple nucleation sites, subcooling and surface texturing on pool boiling dynamics. The investigation comprises of four parts: i) in situ micro-machining of Chromelalumel (K-type) TFT, ii) calibration of these sensors, iii) utilizing these sensors in pool boiling experiments iv) analysis of these fluctuations using techniques of nonlinear time series analysis. Ten TFT are fabricated on a rectangular silicon surface within an area of ~ 3.00 cm x 3.00 cm. The sensing junctions of the TFT measure 50 mm in width and 250 nm in depth. Surface temperature fluctuations of the order of i) 0.65-0.93° C are observed near ONB ii) 2.3-6.5° C in FDNB iii) 2.60-5.00° C at CHF and iv) 2.3-3.5° C in film boiling. Investigations show the possible presence of chaotic dynamics near CHF and in film-boiling in saturated and subcooled pool boiling. Fully-developed nucleate boiling (FDNB) is chaotic. No clear assessment of the dynamics could be made in the onset of nucleate boiling (ONB) and partial nucleate boiling (PNB) regimes due to the effects of noise. However, the frequency spectra in these regimes appear to have two independent frequencies and their integral combinations indicating a possible quasiperiodic bifurcation route to chaos. The dimensionality in FDNB, at CHF and in film-boiling is lower in saturated pool boiling as compared to values in corresponding regimes in subcooled pool boiling. Surface temperature fluctuations can damage electronic components and need to be carefully controlled. Understanding the nature of these fluctuations will aid in deciding the modeling approach for surface temperature transients on an electronic chip. Subsequently, the TFT signals can be employed in a suitable feedback control loop to prevent the occurrence of hotspots.

Author: Nicholas Robert Glavin
Publisher:
ISBN:
Category : Electronic apparatus and appliances
Languages : en
Pages : 109

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Book Description
The high cooling requirements from modern day electronic devices have given rise to a need for alternative heat dissipation methods. State of the art liquid to vapor phase change cooling schemes provide a cooling rate orders of magnitude higher than current single phase systems. Boiling studies have long been performed with the goal to enhance critical boiling parameters such as heat transfer coefficient (HTC) and critical heat flux (CHF) by altering surface morphology. More recently, the desire for active control of boiling processes has been realized due to transient and dynamic changes in system cooling requirements. A means of controlling the boiling process by manipulating surface energy through light excitation can provide the necessary adaptive heat transfer properties. In this study, photonically controlled pool boiling studies are conducted on copper, titanium dioxide, and carbon nanotube (CNT) samples. A significant variance in both HTC and CHF upon light excitation is observed in all samples, with different physical and chemical mechanisms for the change in surface energy. Copper boiling samples were induced to a 35% decrease in CHF condition after several minutes using photonic energy via formation of hydrophobic nanoclusters of copper oxide. Photoactive titanium dioxide and CNT experiments showed a 16.8% decrease and 14.5% increase in HTC, respectively, upon light exposure. Small scale contact angle tests, scanning electron microscopy (SEM), and x-ray photoelectron spectroscopy (XPS) on irradiated samples provide an insight into surface changes due to boiling and ultraviolet (UV) light exposure. In addition to photonically enhanced and controlled heat transfer experiments, a new technique for measuring liquid-solid contact during boiling using electrochemical impedance spectroscopy (EIS) is discussed.

Author: Ėduard Mikhaĭlovich Savit︠s︡kiĭ
Publisher:
ISBN:
Category : Aluminum-copper alloys
Languages : en
Pages : 12

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Author: Ragavendra R. Baliga
Publisher: Elsevier Health Sciences
ISBN: 0323987486
Category : Medical
Languages : en
Pages : 217

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Book Description
In this issue of Heart Failure Clinics, guest editors Drs. Ragavendra R Baliga and George A. Mensah bring their considerable expertise to the topic of Translational Research in Cardio-Oncology. Top experts in the field cover key topics such as radiation-induced cardiac dysfunction; training and career development; cardiovascular imaging; CAR-T cell therapy and cardiovascular disease; and more. Contains 12 relevant, practice-oriented topics including cardio-protection of high-risk individuals; myocardial metabolism; amyloidosis; arrhythmic complications associated with cancer therapies; and more. Provides in-depth clinical reviews on translational research in cardio-oncology, offering actionable insights for clinical practice. Presents the latest information on this timely, focused topic under the leadership of experienced editors in the field. Authors synthesize and distill the latest research and practice guidelines to create clinically significant, topic-based reviews.

Author: N. Zuber
Publisher:
ISBN:
Category : Heat
Languages : en
Pages : 216

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Author: Majid Hosseini
Publisher: Springer Nature
ISBN: 303059565X
Category : Technology & Engineering
Languages : en
Pages : 370

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This book aims at identifying novel advanced materials of extreme wetting properties (MEWP) for practical, industrial applications. The state-of-the art superhdyrophobic, superhdyrophilic, superoleophobic, superoleophilic, and superomniphobic materials, that are MEWP, with respect to their technological and emerging industrial applications are discussed in this book. MEWP offer new perspectives providing numerous potential applications. Hence, these advanced MEWP have the potential to lead to a new generation of products and devices with unique properties and functionalities. Despite the large scientific progress on MEWP there are still some obstacles which have to be solved to make these materials available for real life applications. Recent advances on the production strategies, including methods and materials, of MEWP has shown that the durability and sustainability obstacles can be addressed thus offering the possibility for industrial exploitation. MEWP with wettabilities ranging from superhydrophobicity to superhydrophilicity provide promising avenues for several and important applications, which sometimes are crucial for the humankind. This book also discusses a large variety of other potential applications of MEWP, thus providing new ideas to scientists and engineers for further exploitation of these novel materials. Moreover, the whole spectrum of the recent technological developments, current research progress, future outlook, and the modern trends in the applications of MEWP are discussed in a consistent approach.