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Author: Ri Li Publisher: ISBN: Category : Electronic books Languages : en Pages : 0
Book Description
The cooling of a surface can be achieved by the impingement of spray, which is a free surface flow of droplets ejected from a spray nozzle. Spray cooling can provide uniform cooling and handle high heat fluxes in both single phase and two phases. In this chapter, spray cooling is reviewed from two aspects: the entire spray (spray level) and droplets (droplet level). The discussion on the spray level is focused on the spray cooling performance as a function of fluid properties, flow conditions, surface conditions, and nozzle positioning. The advantages and barriers of using spray cooling for engineering applications are summarized. The discussion on the droplet level is focused on the impact of droplet flow on film flow, which is the key flow mechanism in spray cooling. Droplet flow involves single droplet, droplet train (continuously droplets broke up from jet flow), and droplet burst (droplet groups affecting at a constant frequency), and local cooling enhancement due to droplet flow is discussed in details. Future work and unresolved issues in spray cooling are proposed.
Author: Ri Li Publisher: ISBN: Category : Electronic books Languages : en Pages : 0
Book Description
The cooling of a surface can be achieved by the impingement of spray, which is a free surface flow of droplets ejected from a spray nozzle. Spray cooling can provide uniform cooling and handle high heat fluxes in both single phase and two phases. In this chapter, spray cooling is reviewed from two aspects: the entire spray (spray level) and droplets (droplet level). The discussion on the spray level is focused on the spray cooling performance as a function of fluid properties, flow conditions, surface conditions, and nozzle positioning. The advantages and barriers of using spray cooling for engineering applications are summarized. The discussion on the droplet level is focused on the impact of droplet flow on film flow, which is the key flow mechanism in spray cooling. Droplet flow involves single droplet, droplet train (continuously droplets broke up from jet flow), and droplet burst (droplet groups affecting at a constant frequency), and local cooling enhancement due to droplet flow is discussed in details. Future work and unresolved issues in spray cooling are proposed.
Author: S. M. Sohel Murshed Publisher: BoD – Books on Demand ISBN: 1789848385 Category : Science Languages : en Pages : 154
Book Description
Since conventional cooling techniques are increasing falling short of meeting the ever-growing cooling demands of high heat generating devices, thermal systems, and processes, advanced and innovative cooling technologies are of immense importance to deal with such high thermal management. Hence, this book covers a number of key topics related to advanced cooling approaches, their performance, and applications, including: Evaporative air cooling; Spray impingement cooling; Heat pump-based cooling; Modular cooling for photovoltaic plant; Nucleate pool boiling of refrigerants; Transient flashing spray cooling and application; Compressor cooling systems for industry. The book is aimed at a wide variety of people from graduate students and researchers to manufacturers who are involved or interested in the areas of thermal management systems, cooling technologies, and their applications.
Author: Alex M. Tulchinsky Publisher: ISBN: Category : Electronic apparatus and appliances Languages : en Pages : 306
Book Description
Spray impingement cooling has been shown to be a leading candidate for future high heat flux cooling applications. In general, spray cooling curves consist of three heat flux regimes; single-phase, two-phase and critical heat flux (CHF). CHF is considered the design limit for almost all two-phase cooling applications, as a rapid increase in temperature and decrease in heat flux occurs beyond this point. Recent studies have shown that the addition of micro-structures on the impingement surface can enhance heat transfer relative to a smooth surface. In the present study, spray cooling curves are obtained for two micro-structured surfaces and are compared to smooth surface results. Micro-structured surfaces consisted of bio-inspired fractal-like geometries, denoted as grooves and fins, extending in a radial direction from the center to the periphery of a 37.8 mm circular disc. Depending on the location on the surface, dimensions of groove widths and heights varied from 100 to 500 um, and 30 to 60 um, respectively. Fin width and height dimension remained constant throughout the surface at 127 and 60 um, respectively. Heat flux and wall temperature at the impingement surface were calculated from temperature data measured at multiple locations below the impingement surface. Results are presented as heat flux, q" , versus the wall-to-spray temperature difference, deltaT[subscript w], at each of 5 volume flux, Q", conditions ranging from 0.54 to 2.04 x 10−3 m3/m2s. Convection coefficients, h[subscript cv], and spray efficiencies, n, are also presented for each case as a function of q" and deltaT[subscript w] , respectively. Results of the study indicate that at low and high volume fluxes, an improvement in heat transfer occurs in the single-phase regime for the fin geometry. Enhancement in the single-phase regime did not occur at the intermediate volume flux condition of 1.37 x 10−3 m3/m2s. At all volume flux states tested, significant enhancements, as high as 50% in some cases, were observed in the two-phase regime for the fin structure, whereas the groove structure performed identically to the flat surface in the single-phase regime and exhibited a large degradation in the two-phase and critical heat flux regimes (~50%). Critical heat flux for the fin surface compared to the flat surface was slightly lower at low volume flux conditions, equivalent at the intermediate volume flux, and slightly greater at high volume flux conditions. Further investigations into the underlying mechanisms responsible for these results are needed.
Author: Gustavo F. Gutiérrez-Lopez Publisher: Springer Science & Business Media ISBN: 038775430X Category : Technology & Engineering Languages : en Pages : 475
Book Description
This book presents a significant and up-to-date review of various integrated approaches to food engineering. Distinguished food engineers and food scientists from key institutions worldwide have contributed chapters that provide a deep analysis of their particular subjects. Emerging technologies and biotechnology are introduced, and the book discusses predictive microbiology, packing materials for foods, and biodegradable films. This book is mainly directed to academics, and to undergraduate and postgraduate students in food engineering and food science and technology, who will find a selection of topics.
Author: Xin Feng Publisher: ISBN: Category : Electronic dissertations Languages : en Pages :
Book Description
Among the thermal management solutions for power electronics, two-phase jet or spray impingement cooling are two promising candidates. In this study, electrohydrodynamic atomization (EHDA) method is used to generate spray and jet from the same capillary. This approach enables us to compare the heat transfer coefficient and critical heat flux (CHF) in consistent conditions. Two nondimensional parameters are first developed to lay out the various EHDA modes of ethanol. The experimental results show that the EHDA cooling could enhance the heat transfer coefficient in most conditions, while it could not benefit CHF because the electric repulsive force causes a wide spray angle and less impinging mass flux on the surface. Single and multi micro jet impingement cooling (MJIC) are investigated. Based on the experimental observation and analytical works, a semi-theoretical CHF correlation is proposed based on force and energy balance. The experimental data of water and ethanol are predicted very well by the new model. It also shows the potential to explain the unique feature on the CHF curves of saturated HFE7000 and subcooled ethanol. By using multi MJIC, heat transfer coefficient and CHF might be improved, which mainly depend on fluids and testing conditions.
Author: Guillermo Enrique Soriano Publisher: ISBN: Category : Languages : en Pages :
Book Description
Spray cooling is one of the most promising technologies in applications which require large heat removal capacity in very small areas. Previous experimental studies have suggested that one of the main mechanisms of heat removal in spray cooling is forced convection with strong mixing due to droplet impingement. These mechanisms have not been completely understood mainly due to the large number of physical variables, and the inability to modulate and control variables such as droplet frequency and droplet size. Our approach consists of minimizing the number of experimental variables by controlling variables such as droplet direction, velocity and diameter. A study of heat transfer for single and multiple droplet impingements using HFE- 7100 as the cooling fluid under constant heat flux conditions is presented. Monosized single and multiple droplet trains were produced using a piezoelectric droplet generator with the ability to adjust droplet frequency, diameter, velocity, and spacing between adjacent droplets. In this study, heaters consisting of a layer of Indium Tin Oxide (ITO) as heating element, and ZnSe substrates were used. Surface temperature at the liquid-solid interface was measured using Infrared Thermography. Heat transfer behavior was characterized and critical heat flux was measured. Film thickness was measured using a non-invasive optical technique inside the crown formation produced by the impinging droplets. Hydrodynamic phenomena at the droplet impact zone was studied using high speed imaging. Impact regimes of the impinging droplets were identified, and their effect on heat transfer performance were discussed. The results and effects of droplet frequency, droplet diameter, droplet velocity, and fluid flow rate on heat flux behavior, critical heat flux, and film morphology were elucidated. The study showed that forced heat convection is the main heat transfer mechanism inside the crown formation formed by droplet impingement and impact regimes play an important role on heat transfer behavior. In addition, this study found that spacing among adjacent droplets is the most important factor for multiple droplet stream heat transfer behavior. The knowledge generated through the study provides tools and know-how necessary for the design and development of enhanced spray cooling systems.
Author: Pankaj Saha Publisher: Springer ISBN: 9789811364181 Category : Technology & Engineering Languages : en Pages : 847
Book Description
This book comprises select proceedings of the International Conference on Future Learning Aspects of Mechanical Engineering (FLAME 2018). The book gives an overview of recent developments in the field of thermal and fluid engineering, and covers theoretical and experimental fluid dynamics, numerical methods in heat transfer and fluid mechanics, different modes of heat transfer, multiphase transport and phase change, fluid machinery, turbo machinery, and fluid power. The book is primarily intended for researchers and professionals working in the field of fluid dynamics and thermal engineering.
Author: Yen-Po Lin Publisher: ISBN: Category : Languages : en Pages :
Book Description
Spray cooling has proven to be efficient in managing thermal load in high power applications. Reliability of electronic products relies on the thermal management and understanding of heat transfer mechanisms including those related to spray cooling. However, to date, several of the key heat transfer mechanisms are still not well understood. An alternative approach for improving the heat transfer performance is to change the film dynamics through surface modification. The main goal of this study is to understand the effects of nano-scale features on flat heater surfaces subjected to spray cooling and to determine the major factors in droplet impingement cooling to estimate their effects in the spray cooling system. Single droplet stream and simultaneous triple droplet stream with two different stream spacings (500 [mu]m and 2000 [mu]m), experiments have been performed to understand the droplet-surface interactions relevant to spray cooling systems. Experiments have been conducted on nano-structured surfaces as well as on flat (smooth) surfaces. It is observed that nano-structured surfaces result in lower minimum wall temperatures, better heat transfer performance, and more uniform temperature distribution. A new variable, effective thermal diameter (de), was defined based on the radial temperature profiles inside the impact zone to quantify the effects of the nano-structured surface in droplet cooling. Results indicate that larger effective cooling area can be achieved using nano-structured surface in the single droplet stream experiments. In triple stream experiments, nano-structured surface also showed an enhanced heat transfer. In single stream experiments, larger outer ring structures (i.e. larger outer diameters) in the impact crater were observed on the nano-structured surfaces which can be used to explain enhanced heat transfer performance. Smaller stream spacing in triple stream experiments reveal that the outer ring structure is disrupted resulting in lower heat transfer. Lower static contact angle on the nano-structured surface has been observed, which implies that changes in surface properties result in enhanced film dynamics and better heat transfer behavior. The results and conclusions of this study should be useful for understanding the physics of spray cooling and in the design of better spray cooling systems.
Author: Hsin-Min Tsai Publisher: ISBN: Category : Languages : en Pages :
Book Description
Spray cooling is a promising technique which is used to remove large amounts of heat from surfaces. It is characterized by uniform heat removal, low droplet impact velocity and better cooling efficiency when compared to other cooling schemes. It can be used in electronic cooling, and other applications. However, due to the multiple impacts of droplets, the film fluid dynamics and morphology are quite complicated. Moreover, the effect of heat transfer under spray cooling is not well understood due to the large number of interdependent variables such as impact spacing, impact angle, droplet diameter, droplet velocity and droplet frequency to name a few. An experimental approach is proposed and used to minimize and control key independent variables to determine their effects on surface temperature and heat transfer cooling mode. The effects of droplet impact angle and spacing on different heat flux conditions are studied. The film thickness is also obtained to further investigate the relationship between the independent variable and the observed heat transfer mechanism. The study of coherent droplet impingement on an open surface is experimentally characterized using high speed imaging and infrared thermography. Single stream droplet impingent cooling with different impact angle is also studied. Temperature distribution and impact crater morphology are obtained under different heat flux conditions. Film thickness inside droplet impact craters is measured to understand the relationship between minimum surface temperature and film thickness. Next, double streams droplet impingement cooling with different spacings and impact angles are investigated. The optimum spacing is found to reduce the droplet-to-droplet collision and to minimize splashing, resulting in enhanced heat transfer and better use of the cooling fluid. The film thickness is also measured to understand the relationship between the heat transfer results and the controllable independent variables. The results and conclusions of this study are useful in understanding the physics of spray cooling and can be applied to design better spray cooling systems.
Author: Ri Li
Author: Ri Li
Author: Kerry Oliphant
Author: S. M. Sohel Murshed
Author: Alex M. Tulchinsky
Author: Gustavo F. Gutiérrez-Lopez
Author: Xin Feng
Author: Guillermo Enrique Soriano
Author: Pankaj Saha
Author: Yen-Po Lin
Author: Hsin-Min Tsai