The Study of Impingement Cooling Effects Using a Variable Diameter Synthetic Jet PDF Download

Author: Alexander John Zielinski
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Author: Guillermo Enrique Soriano
Publisher:
ISBN:
Category :
Languages : en
Pages :

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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: Jinjun Wang
Publisher: Cambridge University Press
ISBN: 1107161568
Category : Science
Languages : en
Pages : 293

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Master the theory, applications and control mechanisms of flow control techniques.

Author: S.P. Venkateshan
Publisher: Springer Nature
ISBN: 3030736202
Category : Technology & Engineering
Languages : en
Pages : 560

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p="" This book focuses both on the basics and more complex topics in mechanical measurements such as measurement errors & statistical analysis of data, regression analysis, heat flux, measurement of pressure, and radiation properties of surfaces. End of chapter problems, solved illustrations, and exercise problems are presented throughout the book to augment learning. It is a useful reference for students in both undergraduate and postgraduate programs. ^

Author:
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Languages : en
Pages : 0

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The objective of this project was to perform a comprehensive numerical study for the prediction of conjugate heat transfer during jet impingement cooling. Calculations were done primarily for two working fluids: MIL-7808 and ammonia. A number of substrate materials were studied. The investigation considered both free and confined jet configurations using circular and slot nozzles. Fifteen different disk or plate thicknesses ranging from 0 to 12 mm and eleven different nozzle heights from 0.4 mm to 12.5 mm were used. A number of heat source patterns were considered to explore the effects of magnitude and location of heat generation. Both steady state heat transfer and the transient start-up of power were investigated. It was found that the magnitude of local heat transfer coefficient or Nusselt number decreased with time at all locations on the disk. A higher heat transfer coefficient at the impingement location was seen at a smaller thickness, whereas a thicker plate provided a more uniform distribution of heat transfer coefficient. Materials with a higher thermal conductivity provided more uniform distribution of interface temperature as well as the heat transfer coefficient. Both local and average heat transfer coefficient increased with Reynolds number. For a given flow rate, a higher heat transfer coefficient was obtained with smaller nozzle diameter. Compared to MIL-7808 and FC-77, ammonia provided smaller solid-fluid interface temperature and higher heat transfer coefficient.

Author: Khaider Abu Bakar
Publisher:
ISBN:
Category : Heat
Languages : en
Pages : 74

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Cooling system using jet impingement is already widely used in industries nowadays. There were various approaches that have been investigated in order to produce more efficient jet impingement cooling system. This thesis is study about the effect of the nozzle angle on jet impingement in order to identify the relationship in heat transfer. Besides, investigation on spacing distance between nozzle's edge to the impingement surface and Reynolds number at certain angle also identified in this study. Those studies are needed parallel to the current researchers endeavor for future development of cooling system in global industries. The experiment were perform by vary 3 major parameters such as angle of the nozzle (30°, 45°, 60°, and 90°), distance between nozzle's edge to the impinge surface (H/d= 2, 4, 6, and 8) and also Reynolds number (Re= 2300, 1960,930 and 500).The heat source are heated at 100 0C and cooled down by the flow of air from the nozzle. The heat source temperature after cooling are measured and collected. The result discovers about the relationship nozzle angle for jet impingement cooling system which is heat transfer are more efficient when the angle of nozzle approaching to the normal line as the Nusselt Number are more higher at 90° in range 31.5 w/m2K of heat transfer coefficient compare to the lower angles of the nozzle. Furthermore, higher Reynolds number and close range of distance between nozzle's edges to impingement surface will also gives high Nusselt number which means both also effective cooling effects for the systems.

Author: Samrendra Kumar Singh
Publisher:
ISBN:
Category :
Languages : en
Pages : 290

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Author:
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ISBN:
Category :
Languages : en
Pages : 47

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The overall objective of the program is to enhance the effectiveness of turbine cooling by exploiting the presence and structures of vortices. Program A is concerned with jet impingement cooling and addresses the effects of bulk fluid rotation on jets, their vortical structures and cooling. A low-speed rotating water tunnel has been constructed for flow-visualization study of impinging jets in rotation: in addition, a rotating air rig was also constructed. The results show that the Contour of the impinging jet is crucial in determining the jet trajectory and both the favorable and adverse effects of rotation have been identified in the context of impingement cooling. Program B is concerned with convective and film-cooling. It focuses upon the so-called tornado effect, or the corewise transport of heat through the legs of hairpin vortices, which could lead to enhanced cooling in turbulent flows. An explicit confirmation of the effect have been established by ain water and unsteady heat transfer measurements in air. (AN).

Author: Yen-Po Lin
Publisher:
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Category :
Languages : en
Pages :

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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: R.S. Amano
Publisher: WIT Press
ISBN: 1845649060
Category : Science
Languages : en
Pages : 253

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Book Description
Due to the requirement for enhanced cooling technologies on modern gas turbine engines, advanced research and development has had to take place in field of thermal engineering. Among the gas turbine cooling technologies, impingement jet cooling is one of the most effective in terms of cooling effectiveness, manufacturability and cost. The chapters contained in this book describe research on state-of-the-art and advanced cooling technologies that have been developed, or that are being researched, with a variety of approaches from theoretical, experimental, and CFD studies. The authors of the chapters have been selected from some of the most active researchers and scientists on the subject. This is the first to book published on the topics of gas turbines and heat transfer to focus on impingement cooling alone.