http://hdl.handle.net/1721.1/7848 2013-05-22T14:24:47Z http://hdl.handle.net/1721.1/78539 Directional solvent extraction desalination Bajpayee, Anurag World water supply is struggling to meet demand. Production of fresh water from the oceans could supply this demand almost indefinitely. As global energy consumption continues to increase, water and energy resources are getting closely intertwined, especially with regards to the water consumption and contamination in the unconventional oil and gas industry. Development of effective, affordable desalination and water treatment technologies is thus vital to meeting future demand, maintaining economic development, enabling continued growth of energy resources, and preventing regional and international conflict. We have developed a new low temperature, membrane-free desalination technology using directional solvents capable of extracting pure water from a contaminated solution without themselves dissolving in the recovered water. This method dissolves the water into a directional solvent by increasing its temperature, rejects salts and other contaminants, then recovers pure water by cooling back to ambient temperature, and re-uses the solvent. The directional solvents used here include soybean oil, hexanoic acid, decanoic acid, and octanoic acid with the last two observed to be the most effective. These fatty acids exhibit the required characteristics by having a hydrophilic carboxylic acid end which bonds to water molecules but the hydrophobic chain prevents the dissolution of water soluble salts as well the dissolution of the solvent in water. Directional solvent extraction may be considered a molecular-level desalination approach. Directional Solvent Extraction circumvents the need for membranes, uses simple, inexpensive machinery, and by operating at low temperatures offers the potential for using waste heat. This technique also lends itself well to treatment of feed waters over a wide range of total dissolved solids (TDS) levels and is one of the very few known techniques to extract water from saturated brines. We demonstrate >95% salt rejection for seawater TDS concentrations (35,000 ppm) as well as for oilfield produced water TDS concentrations (>100,000 ppm) and saturated brines (300,000 ppm) through a benchtop batch process, and recovery ratios as high as 85% for feed TDS of 35,000 ppm through a multi-stage batch process. We have also designed, constructed, and demonstrated a semi-continuous process prototype. The energy and economic analysis suggests that this technique could become an effective, affordable method for seawater desalination and for treatment of produced water from unconventional oil and gas extraction. Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.; "September 2012." Cataloged from PDF version of thesis.; Includes bibliographical references (p. 131-137). 2012-01-01T00:00:00Z http://hdl.handle.net/1721.1/78237 Development of an air-cooled, loop-type heat pipe with multiple condensers Kariya, H. Arthur (Harumichi Arthur) Thermal management challenges are prevalent in various applications ranging from consumer electronics to high performance computing systems. Heat pipes are capillary-pumped devices that take advantage of the latent heat of vaporization of a working fluid to achieve low thermal resistance (~0.1 °C/W), and have been of particular interest to address these thermal management needs for cooling solutions such as air-cooled heat sinks. This thesis reports the design, fabrication, and characterization of a novel loop-type heat pipe with multiple condensers for a high performance air-cooled heat sink. While multiple-condenser heat pipes have been developed in the past, this heat pipe layout is the first to ensure equal operation of the individual condensers. The layout incorporates wicks in both evaporator and condenser; the wick in the evaporator supplies the capillary pressure to drive the circulation and the wick in the condenser uses capillary pressure to separate the vapor and liquid phases for controlled condensation. Additionally, methods of liquid and vapor pressure control are developed to modulate the capillary pressure in the condenser. The heat pipe was first evaluated using an analytical model to determine the required thermophysical properties and geometries of the capillary wicks in the evaporator and condenser. The model results were subsequently used to obtain a detailed evaporator design that is compatible with the multiple-condenser layout. The evaporator was fabricated with a multi-step metal sintering process, characterized, and integrated into both single-condenser and six-condenser prototypes. The prototypes successfully operated in a wide range of angles, with automatic heat pipe startup and with a heat pipe thermal resistance as low as 0.0065 °C/W with equal condenser performance. The air-cooled, six-condenser prototype demonstrated removal of 500 W from a heat source at 75 °C. The heat pipe cycle developed in this study enables the use of multiple condensers in a loop-type heat pipe to achieve a large surface area with little thermal resistance for heat sink applications. Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.; Cataloged from PDF version of thesis.; Includes bibliographical references (p. 169-172). 2012-01-01T00:00:00Z http://hdl.handle.net/1721.1/78236 Ink jet printing of PZT thin films for MEMS Bathurst, Stephen, 1980- Of the readily available piezoelectric engineering materials perovskite phase lead zirconate titanate (PZT) has the strongest mechanical to electrical coupling. PZT based devices have the potential to have the highest performance. Due to the strong piezoelectric response and low operating voltage, many groups have worked to integrate thin film PZT into a wide range of microelectromechanical systems (MEMS) devices including: actuators, energy harvesters, resonators, pressure sensors, pumps, nano-positioning stages, and MEMS switches. However, processing of thin film PZT is not readily compatible with existing MEMS fabrication processes and significant design constraints exist when integrating thin film PZT. In recent years drop-on-demand (DOD) printing has been studied as a robust, flexible, and inexpensive method of material deposition for MEMS. Direct printing enables the designer to deposit a film based on a digital pattern file only eliminating the need for photolithography and subsequent etching steps in the manufacturing process flow. There is a significant cost savings due to a reduction in the material consumption during manufacturing and in chemical waste produced. The result is a manufacturing process that is cleaner and cheaper than other common deposition techniques. The most compelling benefit of direct printing of PZT is that it provides a freedom of geometry that eliminates many of the design constraints currently associated with PZT MEMS. Since high quality thin films can be achieved with deposition control that is not possible with spin coating, novel functionalities can be incorporated into PZT MEMS. Specifically, PZT printing is able to deposit material over and around large out-of-plane features. In addition, the thickness of thin film PZT can vary deterministically across a device or across a wafer. A new manufacturing method for the deposition of PZT thin films based on ink jet printing has been developed and used to fabricate a piezoelectric micromachined ultrasonic transducer. A solvent system and processes parameters were established that enable the deposition of high quality PZT thin films. Substrate temperature and drop spacing for uniform deposition were determined and both multilayer and single layer PZT films were successfully deposited. Alignment within 10[mu]m and a resolution limit of 30[mu]m were demonstrated. The performance of a printed PZT based ultrasonic transducer was fit to established models to determine piezoelectric coupling and dielectric properties. The piezoelectric coupling coefficient, d₃₁, for printed PZT was between -75pC/N and -95pC/N. Impedance data at 1kHz provided the relative permittivity (750-890) and the dielectric loss tangent (2.4%-2.8%). The final printing process enabled the first digital deposition of thin film PZT and the printed PZT based pMUT confirmed the properties of the film are within the range required for a high performance piezoelectric MEMS devices. Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.; Cataloged from PDF version of thesis.; Includes bibliographical references (p. 108-113). 2012-01-01T00:00:00Z http://hdl.handle.net/1721.1/78210 Efficient design of precision medical robotics Hanumara, Nevan Clancy Medical robotics is increasingly demonstrating the potential to improve patient care through more precise interventions. However, taking inspiration from industrial robotics has often resulted in large, sometimes cumbersome designs, which represent high capital and per procedure expenditures, as well as increased procedure times. This thesis proposes and demonstrates an alternative model and method for developing economical, appropriately scaled medical robots that improve care and efficiency, while moderating costs. Key to this approach is a structured design process that actively reduces complexity. A selected medical procedure is decomposed into discrete tasks which are then separated into those that are conducted satisfactorily and those where the clinician encounters limitations, often where robots' strengths would be complimentary. Then by following deterministic principles and with continual user participation, prototyping and testing, a system can be designed that integrates into and assists with current procedures, rather than requiring a completely new protocol. This model is expected to lay the groundwork for increasing the use of hands-on technology in interventional medicine. Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.; This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.; Cataloged from student-submitted PDF version of thesis.; Includes bibliographical references (p. 106-114). 2012-01-01T00:00:00Z