Design and Evaluation of Fabric Cooling Channels for Twisted Coiled Actuators

Twisted coiled actuators (TCAs) are biomimetic and inexpensive artificial muscles. To enable their integration into soft robotics, a novel cooling apparatus was designed, consisting of a fabric channel to house the TCA and a miniature air pump for forced convection. The channel was designed to be lightweight, flexible, and easy to integrate into a soft wearable robotic device. The effect that the channel dimensions had on TCA performance (cooling time, heating time, and stroke) was investigated by testing combinations of three widths (6, 8, and 10 mm) and three heights (4, 6, and 8 mm). In general, as the channel dimensions increased, the cooling time and heating time decreased, however the stroke was unaffected (provided that the channel height was above 4 mm). The largest channel, 10 mm width and 8 mm height, resulted in the best combination of cooling time, heating time, and stroke, and thus it was used in a secondary experiment to compare the performance of the TCA with and without the cooling apparatus. When compared to passive cooling without a channel, the cooling apparatus resulted in a 42% decrease in cooling time (21.71 ± 1.24 s vs. 12.54 ± 2.31 s), 9% increase in the heating time (3.46 ± 0.71 s vs. 3.76 ± 0.71 s), and a 28% decrease in stroke (5.40 ± 0.44 mm vs. 3.89 ± 0.77 mm). This work demonstrates that fabric cooling channels are a viable option for cooling TCAs. Future work can continue to improve the channel design and investigate alternative means of air flow to further improve the performance of the TCA

Single-phase liquid flow and heat transfer in plain and enhanced silicon microchannels

Microscale heat transfer and microfluidics have become increasingly important to overcome some very complex engineering challenges. The use of very small passages to gain heat transfer enhancement is a well documented method for achieving high heat flux dissipation. However, some interesting experimental results have caused researchers to question if the conventional theories for fluid flow and heat transfer are valid in the microscale passages. However, there is no significant physical basis for the discrepancies with singlephase liquid flows when the passage is scaled to the microscale. The present work identifies the sources of the discrepancies reported in literature and provides a method to correct for them. In the course of this pursuit, a new experimental facility is developed to generate highly accurate experimental data for single-phase flow of water. The new experimental data are used to highlight the sources of discrepancies and illustrate a course of action to correct for them. Finally, a novel method for creating even greater heat transfer enhancement has been realized. Small offset fins have been fabricated in silicon microchannels in order to create a constantly developing flow in the microchannel heat exchanger and thus heat transfer enhancement. A new parameter based upon the heat flux dissipated and the pressure drop required is developed to aid in the comparison between these enhanced silicon microchannels and plain geometry silicon microchannels. The result is an order of magnitude increase in thermal performance with a marginal increase in overall pressure drop

MODELING AND SIMULATIONS FOR OPTIMIZATION OF MICROFLUIDIC MICROCAPACITOR ARRAYS OF BIOMIMETIC ARTIFICIAL MUSCLES FOR QUIET PROPULSION AND EXOSKELETAL LOCOMOTION

The technology that we focused on was the biomimetic actuation of microfluidic microcapacitors, which are electrostatically actuated structures that contract and function like biological muscles. Our thesis aims to find the optimal muscle-to-tendon ratio while expanding both the standard and gap design arrays and to find the respective force-density saturation values so predicted force output can be calculated for muscle fibers of a practical size. We also studied if a 3D virtual object can be a suitable model for the human operators’ examination of the artificial muscle and the optimization of its structure. Our results showed a maximum force density saturation of 8800 Pa and 6700 Pa when simulating the standard and gap array respectively with planar polarity wired artificial muscles. The optimal muscle-to-tendon ratio from the data gathered on the standard array simulations is approximately 9 to 1, meaning 90 percent of the surface area of the XY plane represents microfluidic capacitors and 10 percent is dielectric tendon material. The optimal muscle to tendon ratio from the data gathered on the gap array simulations is approximately 75 to 25, meaning 75 percent of the surface area of the XY plane are microfluidic capacitors, and 25 percent is both the dielectric material and gaps.Office of Naval Research, Arlington, VA, 22203-1995Outstanding ThesisCaptain, United States Marine CorpsCaptain, United States Marine CorpsApproved for public release. Distribution is unlimited

COUPLED EQUIVALENT CIRCUIT MODEL FOR FLUID FLOW AND HEAT TRANSFER IN LARGE CONNECTED MICROCHANNEL NETWORKS

Ph.DDOCTOR OF PHILOSOPH

Reconfigurable Periodic Porous Membranes & Nanoparticle Assemblies

The thesis here will cover two parts of my research. The focus of the first part of the thesis will be using responsive hydrogel materials to manipulate the pattern transformation at microscale (Chapter 3-5), and meanwhile using the finite element method (FEM) to guide new designs of the periodic porous structures that can undergo controlled pattern transformation processes (Chapter 6). In beginning, I design fabrication methods of micro-structures from responsive hydrogel materials via micro-/nano- imprinting. The responsiveness of the hydrogels is introduced by incorporating responsive monomers into the hydrogel precursors. Here, the responsiveness of the hydrogel leads to the tunable swelling ratio of the hydrogel under external stimuli, e.g. pH, temperature, and variation of humidity, so that the imprinted nano-/micro- structures can be dynamically controlled. Later, upon using FEM simulation, we design and experimentally test the deformation and mechanical properties of the periodic porous membranes based on different collapsing modes of kagome lattices. The experiments are performed at macroscopic scale taking advantage of powerful 3D printing prototyping. As the deformation phenomenon is scale independent, the observed phenomenon is applicable to predict the deformation of the micro-structures. In the second part of the thesis, we investigate two colloidal assembly systems. First (Chapter 7-8), we utilize the new form of silica nanoparticles with chain-like morphology to generate sharp nanostructures on the coating surface that minimize the contact between liquid and solid phase, and thus improve dramatically the water repellency on the coating surfaces. The stability test of the superhydrophobicity against hydrodynamic/hydrostatic pressure, low surface tension liquid, and vapor phase condensation, are also investigated for a complete interpretation of the wetting behavior. Secondly (Chapter 9), I design colloidal suspensions matching the inter-particle interactions with those used in theoretical study of colloidal assembly within the confined the space. The beauty of the system is that the colloidal suspension can be cross-linked and lock the assembled structures, so that the assembled structure can be observed under electron microscope and compare to theory and simulation. So far, a good consistence has been observed, indicating a validated design of the systems

Stiffening of deployable space booms: Automated Protein Crystal Growth Facility

Part of the curriculum for the seniors at Vanderbilt University in the Mechanical Engineering Program is to take a design class. The purpose of the class is to expose the students to the open ended problems which working engineers are involved with every day. In the past, the students have been asked to work in a variety of projects developed by the professor. This year Vanderbilt was admitted into the Advanced Design Program (ADP) sponsored by the Universities Space Research Association (USRA) and the National Aeronautics and Space Association (NASA). The grant sponsored undergraduate design and research into new and innovative areas in which NASA is involved. The grant sponsors the Teaching Assistant as well as provides monies for travel and other expenses. The design and research of the seniors of the 1992-1993 school year in association with NASA and USRA is documented

Two Phase Flow, Phase Change and Numerical Modeling

The heat transfer and analysis on laser beam, evaporator coils, shell-and-tube condenser, two phase flow, nanofluids, complex fluids, and on phase change are significant issues in a design of wide range of industrial processes and devices. This book includes 25 advanced and revised contributions, and it covers mainly (1) numerical modeling of heat transfer, (2) two phase flow, (3) nanofluids, and (4) phase change. The first section introduces numerical modeling of heat transfer on particles in binary gas-solid fluidization bed, solidification phenomena, thermal approaches to laser damage, and temperature and velocity distribution. The second section covers density wave instability phenomena, gas and spray-water quenching, spray cooling, wettability effect, liquid film thickness, and thermosyphon loop. The third section includes nanofluids for heat transfer, nanofluids in minichannels, potential and engineering strategies on nanofluids, and heat transfer at nanoscale. The forth section presents time-dependent melting and deformation processes of phase change material (PCM), thermal energy storage tanks using PCM, phase change in deep CO2 injector, and thermal storage device of solar hot water system. The advanced idea and information described here will be fruitful for the readers to find a sustainable solution in an industrialized society

Index to NASA Tech Briefs, 1972

Abstracts of 1972 NASA Tech Briefs are presented. Four indexes are included: subject, personal author, originating center, and Tech Brief number

Experimental study of fluid flow and heat transfer in tortuous microchannels

Tortuous microchannels have attracted increasing interest due to great potential to enhance fluid mixing and heat transfer. While the fluid flow and heat transfer in wavy microchannels have been studied extensively in a numerical fashion, experimental studies are very limited due to the technical difficulties of making accurate measurements in micro-scale flows. This thesis provides insights into thermohydraulics of tortuous microchannels by developing experimental techniques and performing systematic visualisation and heat transfer experiments. The detailed flow patterns (including Dean vortices) and transition behaviours in wavy channels are successfully identified using Micro-Particle Image Velocimetry (micro-PIV) and 3D reconstruction techniques. Conjugate heat transfer simulations are carried out to understand the complex thermal behaviour present in the current experimental design and to validate and compare with experimental results. The impact of tortuous geometry on flow and heat transfer in microchannels is studied systematically. The high quality experimental data provide a new perspective on flow behaviour and heat transfer performance in wavy microchannels. In addition, the stackability of channels on a plate is considered. The zigzag pathways are found to provide the greatest heat transfer intensification based on a plate structure. A significant component of the research in this thesis has been the development of experimental techniques to measure local heat transfer rates in microchannels. A two-dye laser induced fluorescence (LIF) technique using temperature sensitive particles (TSPs) is developed with promising characteristics for local temperature measurement and the capability for simultaneous measurement of temperature and velocity fields in microscale systems. The advanced experimental techniques developed in this thesis provide important tools for the investigation of thermohydraulics of various micro-devices in the field of engineering

Experimental study of fluid flow and heat transfer in tortuous microchannels

Tortuous microchannels have attracted increasing interest due to great potential to enhance fluid mixing and heat transfer. While the fluid flow and heat transfer in wavy microchannels have been studied extensively in a numerical fashion, experimental studies are very limited due to the technical difficulties of making accurate measurements in micro-scale flows. This thesis provides insights into thermohydraulics of tortuous microchannels by developing experimental techniques and performing systematic visualisation and heat transfer experiments. The detailed flow patterns (including Dean vortices) and transition behaviours in wavy channels are successfully identified using Micro-Particle Image Velocimetry (micro-PIV) and 3D reconstruction techniques. Conjugate heat transfer simulations are carried out to understand the complex thermal behaviour present in the current experimental design and to validate and compare with experimental results. The impact of tortuous geometry on flow and heat transfer in microchannels is studied systematically. The high quality experimental data provide a new perspective on flow behaviour and heat transfer performance in wavy microchannels. In addition, the stackability of channels on a plate is considered. The zigzag pathways are found to provide the greatest heat transfer intensification based on a plate structure. A significant component of the research in this thesis has been the development of experimental techniques to measure local heat transfer rates in microchannels. A two-dye laser induced fluorescence (LIF) technique using temperature sensitive particles (TSPs) is developed with promising characteristics for local temperature measurement and the capability for simultaneous measurement of temperature and velocity fields in microscale systems. The advanced experimental techniques developed in this thesis provide important tools for the investigation of thermohydraulics of various micro-devices in the field of engineering