Inertance Tube Pulse Tube Cryocoolers (ITPTC) are a class of rugged and high-endurance refrigeration systems that operate without a moving part at their low temperature end, and are capable of reaching 4 K or lower. ITPTCs are suitable for application in space vehicles, and attempts are underway worldwide to improve their performance and miniaturize their size. The thermo-fluidic processes in ITPTC are complicated, however, and the details of the mechanisms underlying their performance are not well understood. Elucidation of these underlying processes is the objective of this investigation. In this study, the commercial computational fluid dynamic (CFD) package Fluent䵠was utilized for modeling the entire large ITPTC system that includes a compressor, an after cooler, a regenerator that is represented as a porous medium, a pulse tube, cold and warm heat exchangers, an inertance tube, and a reservoir. The simulations represent a fully-coupled system operating in steady periodic mode, without any arbitrary assumptions. The objective was to examine the extent of multi-dimensional flow effects in an inertance tube pulse tube cryocoolers, and their impact on the performance of these cryocoolers. Computer simulations were performed for two complete ITPTC systems that were geometrically similar except for the length-to-diameter ratios of their regenerators and pulse tubes. For each ITPTC system three separate simulations were performed, one with an adiabatic cold-end heat exchanger (CHX), one with a known cooling heat load, and one with a pre-specified CHX temperature. Each simulation would start with an assumed uniform system temperature, and continue until steady periodic conditions were achieved. The results indicate that CFD simulations are capable of elucidating the complex periodic processes in PTCs very well. The simulation results also show that a one-dimensional modeling of PTCs is appropriate only when all the components of the PTC have very large aspect ratios (i.e., L/D >>1). Significant multi-dimensional flow effects occur at the vicinity of component-to-component junctions, and secondary-flow recirculation patterns develop, when one or more components of the PTC system have small aspect ratios. The simulation results, although limited in scope, also suggest that ITPTCs will have a better overall performance if they are made of components with large aspect ratios.

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Nanofluids consist of nanometer-sized particles or fibers in colloidal suspension within a host fluid. They have been studied extensively since their creation due to their often times anomalous and unique thermal transport characteristics. They have also proven to be quite valuable in terms of the scientific knowledge gained from their study and their nearly unlimited industrial and commercial applications. This research has expanded the science of nanofluids into a previously unexplored field, that of cryogenic nanofluids. Cryogenic nanofluids are similar to traditional nanofluids in that they utilize nanometer-sized inclusion particles; however, they use cryogenic fluids as their host liquids. Cryogenic nanofluids are of great interest due to the fact that they combine the extreme temperatures inherent to cryogenics with the customizable thermal transport properties of nanofluids, thus creating the potential for next generation cryogenic fluids with enhanced thermophysical properties. This research demonstrates that by combining liquid oxygen (LOX) with Multi-Walled Carbon Nanotube (MWCNT) inclusion particles, effective thermal conductivity enhancements of greater than 30% are possible with nanoparticle volume fractions below 0.1%. Three distinct cryogenic nanofluids were created for the purposes of this research, each of which varied by inclusion particle type. The MWCNT's used in this research varied in a number of physical characteristics, the most obvious of which are length and diameter. Lengths vary from 0.5 to 90 microns and diameters from 8 to 40 nanometers. The effective thermal conductivity of the various cryogenic nanofluids created for this research were experimentally determined by a custom made Transient Hot Wire (THW) system, and compared to each other and to more traditional nanofluids as they vary by type and particle volume fraction. This work also details the extensive theoretical, experimental, and numerical aspects of this research, including a rather detailed literature review of many of the salient sciences involved in the study of cryogenic nanofluids. Finally, a selection of the leading theories, models, and predictive equations is presented along with a review of some of the potential future work in the newly budding field of cryogenic nanofluids.

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This thesis discusses the effect of cryogenic temperatures on composite materials. The work includes estimating the shear strength of carbon/epoxy and glass/polyester composites at low temperatures and finding the rate of generation of microcracks in composites at cryogenic temperatures by acoustic emission technique. Microcracks increase the permeability of composites. So to study the permeability growth with microcracks, equipment is also designed to measure the permeability of composite to low temperature fluids. With short beam shear testing it was observed that the shear strength of composites increases with decreasing temperatures. Also carbon/epoxy composites were found to be much stronger than glass/polyester composites. Cryogenic temperatures improve the strength of composites but also generate microcracks in the structure due to the thermal expansion mismatch between the matrix and fiber. With acoustic emission testing from room to –150ºC, it was found that the rate of generation of microcracks increases with reducing temperatures. The work is extended to design a permeability equipment.

The development of prescription methods and evaluation of biomechanical performance of bespoke orthoses has been a source of research for the last 40 years. What started as anecdotal and experience–led knowledge has evolved into a more quantifiable paradigm utilising state of the art technologies commonly found in other high-precision industries. The manufacturing challenges associated with such customised products have been driven by the requirement to produce small (often one-off) batches, bespoke for the end user. The introduction of precise scanning equipment and CAD/CAM systems to the podiatry community is enabling the accurate and repeatable manufacture of orthoses that were previously predominantly hand crafted and shaped. Although these traditional production methods are still in use today, the advantages that scanning and CAD/CAM provide mean they are rapidly being adopted. Today, CNC machining and additive manufacture provide state of the art manufacturing methods for bespoke insoles prescribed and modelled in a CAD environment. However, the limitations of both these manufacturing methods relate to the materials that can be processed, which becomes problematic when manufacturing soft or semi-rigid orthoses. Hence an opportunity exists to develop a new and innovative method for processing foamed polymer materials that are typically vacuum formed today. This research explores the prescription and analysis methods attributed to insole design for sporting applications using specific sports shoes. The insole designs encompass material selection to deliver a product that provides control and function whilst also providing a degree of impact attenuation, recognising the dynamic and high-impact nature of the sportsspecific movements. Consideration is also given to the types of activities that function with the device. This research analyses characteristic plantar pressures experienced whilst undertaking sports-specific movements to aid in the prescription of bespoke insoles for the chosen sport. A design methodology encompassing state of the art scanning technologies and anthropometric measurements provides a repeatable and accurate means to produce the required geometry for a bespoke sport and symptom-specific insole. The research also presents the concept of cryogenic machining, a novel manufacturing method for the CNC machining of foamed polymers. The materials are cooled with the use of a liquid cryogen to below their glass transition temperature at which point relative motion at a molecular level is significantly reduced, providing a rigid and machineable form. This, along with a bespoke cryogenic facility encompassing a vertical 3 axis CNC machining centre, a pressurised liquid nitrogen dewar connected to a bespoke-designed fixture by a vacuum jacketed pipe, enables the dual-sided machining of an amorphous material, something which is not possible with conventional processes. The major contributions of this work are the design methodology to prescribe a sport and symptom-specific insole using state of the art scanning and CAM methods, the design and manufacture of a fixture to facilitate the dual-sided machining of a customised insole and the subsequent testing of the designs in a laboratory environment. In addition the research utilises motion analysis, force plate data and pressure measurement to explore the effects of the insoles on the kinetics, kinematics and peak plantar pressures at discrete anatomical regions during sport-specific manoeuvres.

Cryogenic composites find critical application in the manufacture of fuel tanks for reusable launch vehicles due to significant reduction in overall structural weight of the tank. These fuel tanks contain pressurized cryogen such as hydrogen at cryogenic temperatures. Exposure to varying temperatures and mechanical loads resulting from flight cycle, containment of pressurized cryogen causes thermo-mechanical loading of the composite. The thermo-mechanical loading cycles combined with anisotropy of the composite and mismatch in the thermal and mechanical properties of fibers and matrix lead to transverse matrix cracks (TMC) in each ply. TMC in adjacent plies intersect in localized regions at ply interfaces called crack junctions, which open up due to delamination on application of thermo-mechanical load. TMC and crack junctions usually form a network of leakage paths that assists leakage of cryogen through the composite. In this study, the volumetric flow rate of cryogen leaking through a damaged cross-ply composite with five plies is determined by estimating the effective conductance of the leakage paths. For a given damage state and applied load, crack junction and TMC openings are obtained by finite element analysis. A computational fluid dynamics model is first used to estimate the effective conductance of a leakage path to hydrogen leakage and then a simplified analytical model is used to compute the effective conductance from individual conductances of each crack junction and TMC through a series-parallel combination. A single phase flow model is considered for the numerical analysis of hydrogen flow through TMC and crack junctions. The simulations are carried out using a commercial computational fluid dynamics software, FLUENT. Parametric studies are carried out to investigate the dependence of leak rate of hydrogen on the irregularities of the TMC geometry and TMC, crack junction openings. The simplified model predictions of the effective conductance for the five ply composite show good comparison with numerical simulations.

Cryogenic composites find critical application in the manufacture of fuel tanks for reusable launch vehicles due to significant reduction in overall structural weight of the tank. These fuel tanks contain pressurized cryogen such as hydrogen at cryogenic temperatures. Exposure to varying temperatures and mechanical loads resulting from flight cycle, containment of pressurized cryogen causes thermo-mechanical loading of the composite. The thermo-mechanical loading cycles combined with anisotropy of the composite and mismatch in the thermal and mechanical properties of fibers and matrix lead to transverse matrix cracks (TMC) in each ply. TMC in adjacent plies intersect in localized regions at ply interfaces called crack junctions, which open up due to delamination on application of thermo-mechanical load. TMC and crack junctions usually form a network of leakage paths that assists leakage of cryogen through the composite. In this study, the volumetric flow rate of cryogen leaking through a damaged cross-ply composite with five plies is determined by estimating the effective conductance of the leakage paths. For a given damage state and applied load, crack junction and TMC openings are obtained by finite element analysis. A computational fluid dynamics model is first used to estimate the effective conductance of a leakage path to hydrogen leakage and then a simplified analytical model is used to compute the effective conductance from individual conductances of each crack junction and TMC through a series-parallel combination. A single phase flow model is considered for the numerical analysis of hydrogen flow through TMC and crack junctions. The simulations are carried out using a commercial computational fluid dynamics software, FLUENT. Parametric studies are carried out to investigate the dependence of leak rate of hydrogen on the irregularities of the TMC geometry and TMC, crack junction openings. The simplified model predictions of the effective conductance for the five ply composite show good comparison with numerical simulations.

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