Experimental and Numerical Characterization of an Orifice Type Cryogenic Pulse Tube Refrigerator

An orifice type pulse tube refrigerator (OPTR) was designed, built and operated to provide cryogenic cooling. The OTPR is a travelling wave thermoacoustic refrigerator that operates on a modified reverse Stirling cycle. We consider a system that is comprised of a pressure wave generator (a linear motor), an aftercooler heat-exchanger, a regenerator (comprising of a porous structure for energy separation), a pulse tube (in lieu of a displacer piston as found in Stirling refrigerators) with a cold and a warm heat-exchanger at its two ends, a needle-type orifice valve, an inertance tube and a buffer volume. The experimental characterization is done at various values of mean pressure of helium (∼ 0.35 MPa–2.2 MPa), amplitude of pressure oscillations, frequency of operation and size of orifice opening. A detailed time-dependent axisymmetric computational fluid dynamic (CFD) model of the OPTR is simulated to predict the performance of the OPTR. In the CFD model, the continuity, momentum and energy equations are solved for both the refrigerant gas (helium) and the porous media regions (the regenerator and the three heat-exchangers) in the OPTR. An accurate representation of heat transfer in the porous media is achieved by employing a thermal non-equilibrium model to couple the gas and solid (porous media) energy equations. In the future, a validated computational model can be used for system improvement and optimization.

Optimization of Phononic Crystals for the Simultaneous Attenuation of Out-of-Plane and In-Plane Waves

The topological distribution of the material phases inside the unit cell composing a phononic crystal has a significant effect on its dispersion characteristics. This topology can be engineered to produce application-specific requirements. In this paper, a specialized genetic-algorithm-based topology optimization methodology for the design of two-dimensional phononic crystals is presented. Specifically the target is the opening and maximization of band gap size for (i) out-of-plane waves, (ii) in-plane waves and (iii) both out-of-plane and in-plane waves simultaneously. The methodology as well as the resulting designs are presented.

Effect of Nanosized Filler on Matrix Dominated Properties of Fiber Reinforced Epoxy

In this study, a high-intensity ultrasonic liquid processor was used to obtain a homogeneous molecular mixture of epoxy resin and carbon nano fiber. The carbon nano fibers were infused into the part A of SC-15 (diglycidylether of Bisphenol A) through sonic cavitations and then mixed with part B of SC-15 (cycloaliphatic amine hardener) using a high-speed mechanical agitator. The trapped air and reaction volatiles were removed from the mixture using high vacuum. Nanophased epoxy with 2 wt.% CNF was then utilized in a vacuum assisted resin transfer molding (VARTM) set up with carbon fabric to fabricate laminated composites. The effectiveness of CNF addition on matrix dominated properties of composites has been evaluated by compression, open hole compression and inter-laminar shear. The compression strength, open hole compression strength and ILS were improved by 21%, 23% and 15%, respectively as compared to the neat composite.

Influence of Injection Molding Parameters on Mechanical Properties of Low Density Polyethylene Filled With Multiwalled Carbon Nanotubes

In this paper, we investigated the effect of injection molding parameters such as melt temperature, mold temperature, injection speed and holding pressure on the mechanical properties of low density polyethylene reinforced with 2.5 wt% multi-walled carbon nanotubes. The Taguchi methodology with four factors and two levels was used for the design of the injection molding experiments. The mechanical properties were evaluated by tensile tests in the flow direction at room temperature (23 °C) at crosshead speeds of 1 and 5 mm/min. It was found that the mechanical properties can be modified by manipulating the injection molding parameters. The Young’s modulus of the LDPE-MWNTs composite decreased as the melt temperature increased, while mold temperature, injection molding speed and holding pressure have a moderate influence on the Young’s modulus.

Characterization of a Ferritic Stainless Sheet Steel in Simple Shear and Uniaxial Tension at Different Strain Rates

In this study the mechanical properties of ferritic stainless steel EN 1.4521 (AISI 444) were characterized in uniaxial tension and simple shear. The specimen geometries were designed so that tests could be carried out both with a conventional uniaxial materials testing machine and at high strain rates with the Tensile Hopkinson Split Bar method. During the tests, specimen surface deformation was measured using a three dimensional digital image correlation technique based on a two-camera stereovision setup. This technique allowed direct measurement of the specimen gauge section deformation during the test. Test results indicate that the selected approach is suitable for large strain plastic deformation characterization of ductile metals. The stress-strain data obtained from the simple shear tests shows a correlation with the tensile test results according to the von Mises effective stress-strain criterion. Since necking is absent in shear, test data can be obtained at considerably higher plastic strains than in tension. However, the final fracture occurs under a complex loading mode due to the distortion of the specimen geometry and multiaxial loading introduced by the simple shear arrangement. Test results also show that reliable material data can be obtained at high strain rates.

Simulation of Post Failure Response in Fiber Composites

This study focuses on the compressive failure mechanism in the form of kinkband formation in fiber composites. Taking into account the non-linearities of the constituents, a constitutive model for unidirectional layered materials has been developed and incorporated as a user material in a commercially available finite element code to study effects of kinkband inclination angle and micro-geometry on kinkband formation. The localization of deformation into a single kinkband is studied. In the post failure regime a state is reached where deformation in the kinkband gets stabilized and the kinkband broadens under steady-state conditions.

Phase Transitions of Granular Systems: Between Brazilian Nut Effect and its Reversed Mode

Granular particles with diameters 3mm, 6mm and 0.6mm, of the same density 0.9g/cm3 and the same total weight 100g in vertically vibrating systems were studied. The transition processes of granular systems from Reversed Brazilian Nut (RBN) Effect to Brazilian Nut (BN) Effect at varied conditions, including different vibrating frequencies, amplitudes, and particles sizes, together with computer simulations were investigated. We have observed experimentally that BN Effect or RBN Effect was appeared at certain particle parameters and vibrating conditions, and discussed in five aspects: dynamic equilibrium, separation mode, convection modes, mass distribution and resonance frequency. The results indicate that the upsurge of granular convection and resonance behavior during the processes plays an important role in phase transitions.

Evaluating Performance of Composite Materials for MHK Applications

Montana State University (MSU) has a compilation of material systems, environmental chambers, and mechanical testing equipment to determine composite materials performance and failure characteristics. Mechanical characterization of composite systems will provide direct quantification of the materials under consideration for Marine Hydro Kinetic (MHK) designs that were initially developed for the wind turbine industry. The work presented herein represents the testing protocol development and initial results to support investigations on the effect of sea water absorption on material strength. A testing protocol for environmental effects has been developed for the resin infused in-house fabricated laminates. Unidirectional ([0] and [90]) test samples of 2-mm and 6-mm thickness were be submerged for 1000 hours in synthetic sea water at 40°C with the weight recorded at time intervals over the entire period. After 1000 hours of conditioning, coupons were placed in the synthetic sea water at 20°C until testing. Static compressive and tensile strength properties at temperatures of 5°C, 20°C and 40°C were collected. These initial results show trends of reduced tensile and compressive strength with increasing moisture and temperature in the 0° (longitudinal) direction. In the 90° (transverse) direction, compression strength decreases but tensile strength is little affected as temperature and moisture increase. Elastic modulus (E) is little affected in the longitudinal direction but decreases in the transverse direction.

Modeling of Microstructures Actuation by the Knudsen Thermal Force

Heated microscale objects immersed in a gas ambient are subject to thermal Knudsen forces generated by the non-equilibrium energy exchange between gas molecules and solid surfaces. Knudsen forces are significant when the length scale of a temperature gradient is comparable to the gas molecular mean free path. This can occur for very low gas pressures or at extremely small length scales. The overall goal of this work is to study the feasibility of using Knudsen force as an alternative actuation mechanism for N/MEMS. The kinetic solution of Boltzmann equation using the discrete ordinate/finite volume discretization in the high-dimensional phase space is circumventing difficulties associated with traditional stochastic DSMC approach in dealing with the slow bulk motion. The comparison to measurements by (Passian et al, PRL, 2003) shows that Knudsen force is well reproduced by simulations assuming full momentum accommodation for nitrogen and argon gas and an incomplete accommodation for helium. It provides a pathway for design and analysis of devices taking advantage of the benign mechanism of the Knudsen forces, in particular, the absence of high electric fields. The analysis shows that the Knudsen force results in an impact velocity of only 0.9 cm/s whereas electrostatic forces with low voltages below 0.5V result in impact velocity in the range of 6–20 cm/s. We further discuss how Knudsen force can be used for low impact velocity actuation and also to overcome the stiction problem.

The Optimization of Vibration Induced by a V6 Engine Cooling Module

The engine cooling module consists of condenser, radiator and fan (CRFM), which has long been recognized as a main source of sound and vibration in the automotive industry. As the engine becomes increasingly compact and powerful, customers gradually have higher expectations for automobile NVH performance than ever before. Thus the reduction of noise and vibration induced by CRFM becomes critical, which can greatly influence overall NVH performance. Combined with experimental and numerical methods, this paper focuses on the identification and optimization of steering wheel (SW) vibration induced by CRFM for a vehicle with V6 engine while engine idling. The numerical model established in this paper, based on Matlab and taking chassis vibration into account, can predict and optimize the vibration of CRFM under specific working condition with the help of energy decoupling and Newmark-Beta methodology. The optimization design of CRFM mainly involves the stiffness, position and angle of isolators. The numerical simulation results are validated experimentally, which can help further design of CRFM.