Design and construction of a magnetic force microscope

A magnetic force microscope (MFM) is a special type of scanning force microscope which measures the stray field above a ferromagnetic sample with the help of a ferromagnetic cantilever. The aim of this project was to design and build a MFM head and interface it with a commercial scanning probe electronics controller with the help of an appropriate force sensor. The MFM head and the force sensor were to be designed to work at low temperatures (down to 4 K) and in high vacuum. During this work, a magnetic force microscope (MFM) head was designed. Its design is symmetrical and modular. Two dimensional views were prepared to ensure proper geometry and alignment for the various modules. Based on these views, individual parts in the various modules were manufactured and combined for the final assembly of the head. This MFM head has many essential and advanced features which were incorporated during the design process. Our MFM head has an outside diameter of 5 cm and thus has a low thermal mass. The head operates inside a 100 cm long vacuum can which is kept in a cold bath inside a superinsulated dewar. Other features of this MFM head include thermal compensation of the important parts, flexibility to use commercial MFM cantilevers and a large scan range compared to the previous designs. Some of the anticipated system specifications are: 1) room temperature scanning range of 175?? 175 ??m, 2) low temperature scanning range between 35-50 ??m, 3) smallest detectable magnetic force in the range of one pN and 4) smallest detectable magnetic force gradient in the range of 10-3 to 10 -5 N/m. This MFM head was interfaced to a commercial scanning probe electronics apparatus by designing a fiber-optic interferometer as the sensor for the detection of the cantilever deflection. The fiber-optic sensor also has features of its own such as stability, compactness and low susceptibility to noise because of all-fiber construction. With this MFM head, we hope to image many magnetic samples which were previously impossible to image at Texas A&M

Dropwise Condensation on Inclined Textured Surfaces

Dropwise Condensation on Textured Surfaces presents a holistic framework for understanding dropwise condensation through mathematical modeling and meaningful experiments. The book presents a review of the subject required to build up models as well as to design experiments. Emphasis is placed on the effect of physical and chemical texturing and their effect on the bulk transport phenomena. Application of the model to metal vapor condensation is of special interest. The unique behavior of liquid metals, with their low Prandtl number and high surface tension, is also discussed. The model predicts instantaneous drop size distribution for a given level of substrate subcooling and derives local as well as spatio-temporally averaged heat transfer rates and wall shear stress

Thermohydrodynamik von Closed Loop Pulsating Heat Pipes

Thermal management of electronics is a contemporary issue which is increasingly gaining importance in line with the advances in packaging technology. Immediate and consistent multi-disciplinary research is needed to cater to the prevailing trends of net power and flux levels of upcoming microelectronics products. Material science, packaging concepts, fabrication technology and novel cooling strategies are some of the key areas requiring synchronal research for successful thermal management. Focusing on the latter area, this thesis attempts to describe the complex thermo-hydrodynamics of Closed Loop Pulsating Heat Pipes (CLPHPs) which are new entrants in the family of closed passive two-phase heat transfer systems. These apparently simple looking devices are extremely intriguing for theoretical and experimental investigations alike. It is rare to find a combination of such events and mechanisms, like bubble nucleation/collapse and agglomeration, bubble pumping action, pressure/temperature perturbations, flow regime changes, dynamic instabilities, metastable non-equilibrium conditions, flooding/bridging etc., all together contributing towards the thermal performance of a device. The thermal performance objective function is multi-dimensional and embodies major multi-disciplinary two-phase flow physics. To achieve the goal, five different experimental set-ups have been envisioned, fabricated and tested. The set-ups are designed for flow visualization (including videography and infra-red thermography) coupled with standard thermometry. Six major parameters have emerged as the primary influence parameters which affect the system dynamics. These include:  Internal diameter of the CLPHP tube,  Volumetric filling ratio of the working fluid,  Input heat flux,  Total number of turns,  Operational orientation and,  Thermo-physical properties of the working fluid. The thesis provides detailed discussion on the various design parameters. Apart from the multitude of geometrical, physical and operational variables, the performance is also strongly linked with the flow patterns existing inside the device. Subtle aspects of this two-phase flow dynamics and their interactions with the heat transfer characteristics have been highlighted leading to the formulation of primary design rules. Mathematical modeling of the device operation has also been successfully accomplished by applying two approaches which are quite diverse in nature, viz. (a) Semi-empirical modeling with non-dimensional groups, and (b) Modeling by artificial neural networks. The handicaps and problems of conventional modeling by ‘first principles’, e.g Navier-Stokes equation, are also scrutinized. At the end of this study program, although some nuances of the device operation still remain unexplored, it is believed that major advancement in the understanding of the thermo-hydrodynamics of CLPHPs has been accomplished. With the progress achieved so far, the prospects for this exemplary and unprecedented technology seems quite promising.Das Thermalmanagement von Elektronikbauteilen ist ein Thema, welches aufgrund der Fortschritte in der Mikrosystemtechnik zunehmend an Bedeutung gewinnt. Multidisziplinäre Forschung ist notwendig, um dem vorherrschenden Trend zu immer höheren Leistungen und Wärmestromdichten in künftigen Mikroelektronikbauteilen Rechnung zu tragen. Materialforschung, neuartige modulare Konzepte, Herstellungs-technologien und Strategien in der Kühlung sind einige der Schlüsselbereiche, in denen Forschungsbedarf für ein erfolgreiches Thermalmanagement besteht. Im Mittelpunkt dieser Doktorarbeit steht der letztgenannte Bereich, die Beschreibung der komplexen Thermo-hydrodynamik von geschlossenen pulsierenden Wärmerohren (CLPHPs). Sie sind neu zur Familie der geschlossenen passiven 2-Phasen-Wärmeübertragungssysteme hinzugekommen. Diese auf den ersten Blick sehr einfach ausschauenden Bauteile sind sowohl für theoretische als auch für experimentelle Untersuchungen außerordentlich faszinierend. Es ist selten eine solche Kombination verschiedenster Mechanismen zu finden, wie Wachstum/Kollabieren und Agglomerieren von Blasen, Druck- und Temperaturstörungen, Änderungen im Strömungsmuster, dynamische Instabilitäten, metastabile Nichtgleichgewichtszustände, Flooding/Bridging, usw., die alle die thermische Leistungsfähigkeit des Bauteils beeinflussen. Die Zielfunktion der thermischen Leistungsfähigkeit ist mehrdimensional und beinhaltet komplexe Phänomene der 2-Phasen-Thermofluiddynamik. Um dieses Ziel zu erreichen, wurden fünf unterschiedliche Experimente geplant, aufgebaut und getestet. Die experimentellen Aufbauten erlauben eine Visualisierung der Strömungsvorgänge (inklusive Videoaufzeichnungen und Infrarotthermographie) verbunden mit üblicher Temperaturmessung. Sechs Parameter wurden als Haupteinflussgrößen auf die Systemdynamik erkannt. Diese sind:  der Innendurchmesser der CLPHP  der volumetrische Füllgrad des Arbeitsfluids  die eingebrachte Wärmestromdichte  die Anzahl der Windungen  die Ausrichtung der CLPHP im Betrieb sowie  die thermophysikalischen Eigenschaften des Arbeitsfluids Diese Doktorarbeit beinhaltet eine ausführliche Diskussion der zahlreichen Auslegungsparameter. Abgesehen von der Vielzahl von geometrischen, physikalischen und Betriebsvariablen hängt die thermische Leistungsfähigkeit auch stark von den Strömungs-mustern innerhalb der CLPHP ab. Aspekte dieser 2-Phasenströmungsdynamik und ihrer Interaktion mit der Wärmeübergangscharakteristik wurden herausgearbeitet und in grundsätzlichen Auslegungsrichtlinien formuliert. Die mathematische Modellierung der Betriebszustände der CLPHP ist mit zwei unterschiedlichen Ansätzen erfolgreich bewerkstelligt worden. Zum einen mit einer halbempirischen Modellierung mit dimensionslosen Kennziffern und zum anderen mit künstlichen neuronalen Netzen. Die Nachteile und Probleme konventioneller Modellierungs-methoden, die auf grundlegenden Gleichungen (z.B. Navier-Stokes) aufbauen, sind ebenfalls eingehend untersucht worden. Wenngleich einige Teilaspekte des Betriebsverhaltens der CLPHP weiterhin nicht vollständig geklärt sind, so ist doch als Ergebnis dieser Forschungsarbeit ein großer Fortschritt im Verständnis der Thermohydrodynamik von CLPHP erzielt worden. Mit den bisher erzielten Ergebnissen erscheinen die Aussichten für diese einzigartige Technologie sehr vielversprechend

Dropwise condensation on inclined textured surfaces

Dropwise Condensation on Textured Surfaces presents a holistic framework for understanding dropwise condensation through mathematical modeling and meaningful experiments. The book presents a review of the subject required to build up models as well as to design experiments. Emphasis is placed on the effect of physical and chemical texturing and their effect on the bulk transport phenomena. Application of the model to metal vapor condensation is of special interest. The unique behavior of liquid metals, with their low Prandtl number and high surface tension, is also discussed. The model predicts instantaneous drop size distribution for a given level of substrate subcooling and derives local as well as spatio-temporally averaged heat transfer rates and wall shear stress

Nanoscale and microscale phenomena: fundamentals and applications

The book is an outcome of research work in the areas of nanotechnology, interfacial science, nano- and micro-fluidics and manufacturing, soft matter, and transport phenomena at nano- and micro-scales. The contributing authors represent prominent research groups from Indian Institute of Technology Bombay, Indian Institute of Technology Kanpur and Indian Institute of Science, Bangalore. The book has 13 chapters and the entire work presented in the chapters is based on research carried out over past three years. The chapters are designed with number of coloured illustrations, figures and tables. The book will be highly beneficial to academicians as well as industrial professionals working in the mentioned areas

Innovation, incubation and entrepreneurship: case studies from IIT Kanpur

This book focuses on promoting entrepreneurial ecosystems within universities and educational institutes. It especially emphasizes the thriving systems and practices existing within the Indian Institute of Technology Kanpur (IITK). It discusses cases and successes of the SIDBI Incubation and Innovation Centre in the Institute. This edited volume highlights the vision of IITK and describes a few of the major achievements of the past few years. It especially showcases the requirements and challenges of creating, sustaining, and boosting such entrepreneurial ecosystems and incubation centres. The contents of this book will be useful to researchers, administrators, and corporate collaborators working in the area of monetizing technology coming from educational institutions by converting it to successful products and business ideas.

Thermally Induced Oscillating Flow Inside a Single Capillary Tube: A Step towards the Understanding of the PHP Behavior

International audienc

Local heat transfer measurement and thermo-fluid characterization of a pulsating heat pipe

A compact Closed Loop Pulsating Heat Pipe (CLPHP), filled with ethanol (65% v/v), made of four transparent glass tubes forming the adiabatic section and connected with copper U-turns in the evaporator and condenser sections respectively, is designed in order to perform comprehensive thermal-hydraulic performance investigation. Local heat transfer coefficient is estimated by measurement of tube wall and internal fluid temperatures in the evaporator section. Simultaneously, fluid pressure oscillations are recorded together with the corresponding flow patterns. The thermal performances are measured for different heat input levels and global orientation of the device with respect to gravity. One exploratory test is also done with azeotropic mixture of ethanol and water. Results show that a stable device operation is achieved (i.e. evaporator wall temperatures can reach a pseudo-steady-state) only when a circulating flow mode is established superimposed on local pulsating flow. The heat transfer performance strongly depends on the heat input level and the inclination angle, which, in turn, also affect the ensuing flow pattern. The spectral analysis of the pressure signal reveals that even during the stable performance regimes, characteristic fluid oscillation frequencies are not uniquely recognizable. Equivalent thermal conductivities of the order of 10-15 times that of pure copper are achieved. Due to small number of turns horizontal mode operation is not feasible. Preliminary results indicate that filling azeotropic mixture of ethanol and water as working fluid does not alter the thermal performance as compared to pure ethanol case. © 2013 Elsevier Masson SAS. All rights reserved