Mechanical design, calibration, and environmental protection of the REXIS DAM

Thesis: S.M., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2013.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 (pages 167-172).The REgolith X-ray Imaging Spectrometer (REXIS) is a joint effort by MIT and Harvard to build the student-collaboration experiment aboard OSIRIS-Rex, an asteroid sample return mission sponsored by the NASA New Frontiers program. OSIRISREx is scheduled to launch to near-Earth asteroid Bennu in 2016. REXIS is a coded-mask imaging X-ray spectrometer that supports the missions scientific goals by globally and spatially mapping the soft X-ray emission spectrum of Bennu. X-rays corresponding to unique elements are fluoresced from the asteroid by incident solar radiation and enter the instrument through a coded-aperture mask composed of a psuedorandom pinhole pattern. The X-rays that pass through the mask strike an array of four charge-coupled devices (CCDs) that detect the incident photon energy and location on the imaging array. A spatial map of selected elemental abundances on Bennu is constructed by cross-correlating the mask pattern with the collected data. The CCDs are integrated into a Detector Assembly Mount (DAM) that serves three critical functions: Mechanical alignment, calibration and protection of the CCDs. In this thesis we outline the overall design of the REXIS DAM with a focus on its three main functions. Chapter 1 provides background on the OSIRIS-REx mission and the REXIS instrument. Chapter 2 discusses the adaptation of the AXAF CCD Imaging Spectrometer (ACIS) focal plane mechanical design and X-ray Imaging Spectrometer (XIS) flexprint electrical design for the REXIS DAM. Chapter 3 outlines the heritage of the DAM internal calibration sources from XIS and the MIT MicroX project. Driving science and engineering considerations for a calibration scheme are described and then used to inform the mechanical design of a novel calibration set for the REXIS DAM. Chapter 4 illustrates the need for protection from the space environment and analyzes the specific risks to the detectors and DAM in space. Special coatings and a one-time deployable radiation shield are used to protect the assembly and ensure integrity of REXIS science data. Chapter 5 describes the test performed to validate the CCD alignment scheme and the dynamic model of the radiation cover. Chapter 6 summarizes the key results of the present work and outlines plans for future work on the DAM.by Harrison L. Bralower.S.M

A study of electrowetting-assisted boiling

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 47).The classical theory of boiling heat transfer based on bubble dynamics is explained and includes a full derivation of the Rohsenow boiling correlation. An alternative, more accurate correlation for determining boiling heat transfer coefficients is then presented. The theory of DC and AC electrowetting is described along with electrolyis and electric breakdown, two common problems in successfully demonstrating electrowetting. Next, the construction of a 1000V DC power supply for electrowetting experiments is outlined along with failed and successful attempts to create surfaces that exhibit electrowetting. The design and construction of an electrowetting-compatible boiling apparatus capable of delivering up to 1000W of power to a 400mm2 sample is also detailed. The power supply, surfaces, and boiler are used to determine that while electrowetting increases surface wettability it also severely decreases heat transfer, disproving the initial hypothesis. Heat transfer per unit superheat, represented by the dimensionless ratio of the Nusselt number to the Jakob number, is found to increase as a double exponential with decay constants 0.23 ± 0.21 and -14.82 ± 49.69 as a function of the dimensionless electrowetting number, a measure of electrical energy to surface energy of a liquid. Likewise, thermal resistance as a function of the electrowetting number is found to increase as a double exponential with rise constants -37.95 ± 214.4 and -0.32 ± 2.23.by Harrison L. Bralower.S.B

Hydrate-phobic surfaces: fundamental studies in clathrate hydrate adhesion reduction

Clathrate hydrate formation and subsequent plugging of deep-sea oil and gas pipelines represent a significant bottleneck for deep-sea oil and gas operations. Current methods for hydrate mitigation are expensive and energy intensive, comprising chemical, thermal, or flow management techniques. In this paper, we present an alternate approach of using functionalized coatings to reduce hydrate adhesion to surfaces, ideally to a low enough level that hydrodynamic shear stresses can detach deposits and prevent plug formation. Systematic and quantitative studies of hydrate adhesion on smooth substrates with varying solid surface energies reveal a linear trend between hydrate adhesion strength and the practical work of adhesion (γ[superscript total][1 + cos θ[subscript rec]]) of a suitable probe liquid, that is, one with similar surface energy properties to those of the hydrate. A reduction in hydrate adhesion strength by more than a factor of four when compared to bare steel is achieved on surfaces characterized by low Lewis acid, Lewis base, and van der Waals contributions to surface free energy such that the practical work of adhesion is minimized. These fundamental studies provide a framework for the development of hydrate-phobic surfaces, and could lead to passive enhancement of flow assurance and prevention of blockages in deep-sea oil and gas operations.Massachusetts Institute of Technology. Energy Initiative (Chevron Corporation)Massachusetts Institute of Technology. Dept. of Mechanical EngineeringNational Research Council (U.S.) (Postdoctoral Fellowship