In this work, the peroxide-initiated degradation of polypropylene (PP) in co-rotating intermeshing twin-screw extruders (COITSEs) is analyzed by means of numerical simulations. This reactive extrusion (REX) operation is simulated by implementing (i) a one-dimensional and (ii) a three-dimensional (3D) modeling approach. In the case of the 1D modeling, a REX mathematical model previously developed and implemented as a computer code is used for the evaluation of two scale-up rules for COITSEs of various sizes. The first scale-up rule which is proposed in this work is based on the concept of thermal time introduced by Nauman (1977), and the second one is based on specific energy consumption (SEC) requirements. The processing parameters used in testing the previously referred to scale-up approaches are the mass throughput, the screw rotating speed, and the peroxide concentration, whereas the extruder screw configuration and the barrel temperature profiles are kept constant. The results for the simulated operating conditions show that when the REX operation is scaled-up under constant thermal time, very good agreement is obtained between the weight-average molecular weight (Mw) and poly-dispersity index (PDI) from the larger extruders and the values of these parameters corresponding to the reference extruder. For the constant SEC approach, on the other hand, more significant variations are observed for both of the aforementioned parameters. In the case of the implemented constant thermal time procedure, a further analysis of the effect of the mass throughput and screw speed of the reference device on the scaled-up operation is performed. It is observed that when the lower mass throughput is implemented for the smaller extruder keeping a constant screw speed, the predicted residence times of extrusion for the larger extruders are lower, in general terms, than those corresponding to the reference device, and a converse situation occurs for the higher implemented value of the mass throughput. Also, in general terms, the higher increase of the reaction temperature on the scaled-up operation corresponds to the lower mass throughputs and higher screw speeds specified for the reference extruder. For the 3D modeling approach, two different case studies are analyzed by means of a commercial FEM software package. The REX simulations are performed under the assumption of steady-state conditions using the concept of a moving relative system (MRS). To complement the information obtained from the MRS calculations, simulations for selected conditions (for non-reactive cases) are performed considering the more realistic transient-state (TS) flow conditions. The TS flow conditions are associated to the time periodicity of the flow field inside the conveying elements of COITSEs. In the first case study, the peroxide-initiated degradation of PP is simulated in fully-filled screw elements of two different size COITSEs in order to evaluate scale-up implications of the REX operation. In the second case, the reacting flow is simulated for a conventional conveying screw element and a conveying screw element having a special design and corresponding to the same extruder size. For both of the analyzed cases, the effects of the initial peroxide concentration and mass throughput on the final Mw and PDI of the degraded resin are studied. The effect of the processing conditions is discussed in terms of the residence time distribution (RTD), the temperature of reaction, and the distributive mixing capabilities of the REX system. When analyzing the scale-up case, it is found that for the implemented processing conditions, the final Mws and PDIs are very close to each other in both of the analyzed flow geometries when the specified flow is close to that corresponding to the maximum conveying capabilities of the screw elements. For more restrictive flow conditions, the final Mws and PDIs are lower in the case of the screw element of the larger extruder. It is found that the distributive mixing ability of the reactive flow is mainly related to the specified mass throughput and almost independent of the specified peroxide concentration for a particular extruder size. For the analyzed screw elements, the conveying element corresponding to the small size extruder shows a slightly better distributive mixing performance. For this same case study, a further evaluation of the proposed scale-up criterion under constant thermal time confirms the trend of the results observed for the 1D simulations. In the second case study, the special type of screw element consists of screws rotating at different speeds which have different cross sections. In this case, the outer and inner diameters of both the special and the conventional type of screw elements are specified to be the same. As in the previous case study, the distributive mixing capabilities appear to be independent of the specified peroxide concentrations but dependent on the mass flow rate. It is speculated from the simulation results, from both the transient- as well as the steady-state flow conditions, that the screw element with the special design would yield lower final values of the PDI and Mw. Also, this screw element appears to have improved distributive mixing capabilities as well as a wider RTD.

In this study, the seal bushings were designed to allow the lubricant stored in the screw and the nut system. Effect of thread clearance on the life of the screw were investigated. The screw and nut are made of S45C and HBsC3, respectively. Effects of material pairs on friction coefficient were investigated by using the pin on disk tester to simulate the friction condition between the screw and the nut. Result shows that the life of the screw increases with increasing thread clearance. The longest life for the maximum clearance can achieve 6790 cycles. Under the same surface pressure, the friction coefficients of HBsC3 on self-lubricating alloy and HBsC3 on SCM 440 are much smaller than self-lubricating alloy on self-lubricating alloy and self-lubricating alloy on SCM 440 by using nut on screw.

As materials get reduced in size down to the nanoscale it becomes more complex to characterize them. In this regard transmission electron microscopy has been extensively used to better characterize and understand the mechanical behavior of materials at the nanoscale, although there are various contrast mechanisms that can be used in a TEM micrograph. Focusing in particular on diffraction contrast, we know that dislocation lines are interpreted based on how the displacement field of a dislocation in an infinite crystal influences contrast. However, from a practical standpoint most of the samples that are used in microscopy are of a finite size. Thus, it is important to understand the change in contrast of a screw dislocation by taking into account the effect of crystal size. A MATLAB program has been written to simulate contrast in the TEM of a screw dislocation, taking into account the modified displacement fields for finite size crystals. The effect of reducing crystal size and the effect of microscopic parameters, such as the deviation parameter and g.b diffraction conditions have been also analyzed. / text

This thesis presents a thermodynamic model for a screw chiller and cooling tower system for the purpose of developing an optimized control algorithm for the chiller plant. The thermodynamic chiller model is drawn from the thermodynamic models developed by Gordon and Ng (1996). However, the entropy production in the compressor is empirically related to the pressure difference measured across the compressor. The thermodynamic cooling tower model is the Baker & Shryock cooling tower model that is presented in ASHRAE Handbook - HVAC Systems and Equipment (1992). The models are coupled to form a chiller plant model which can be used to determine the optimal performance. Two correlations are then required to optimize the system: a wet-bulb/setpoint correlation and a fan speed/pump speed correlation. Using these correlations, a "quasi-optimal" operation can be achieved which will save 17% of the energy consumed by the chiller plant.

An experimental study of the drying of sand using an induction heated double-screw conveyor (screw shaft radius 0.0381 m, blade radius 0.0883 m, thread pitch 0.0869 m, heated length 1.96 m) is presented. The main aim was to improve the understanding of the operating characteristics of the dryer and obtain data for testing and refining future mathematical models. In the drying tests, power to the induction coils was controlled to obtain uniform screw shaft temperatures between 150 to 250°C. The angular rotation speed of the screws ranged between 2.5 to 15 rpm; and inlet moisture content (mass fraction of water) was varied between 0.1 to 10 %. The sand used had a mean effective diameter of 0.38 mm, particle density of 2743.7 kg/m3, and uncompacted dry bulk density of 1508.2 kg/m3. The results of sand characterization tests, conveying tests without induction heating, and drying tests are presented and discussed.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1970. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

This thesis describes the measurement of high g-forces, in the range of 400-800g's occurring in a spinal construct during the breaking of the set-screw head using a manual torquing instrument. The measurements were validated using a high speed camera. The design torque (11 N-m) required for breaking the set-screw was compared with the torque calculated from the distortion energy theory for material fracture (9.9 N-m) and an actual measurement using a torque wrench (11.3 N-m). A comparison between the manual and powered instruments showed a 27.68% reduction in g-forces and a 36.42% reduction in die-down time while using the powered instrument. 8.52% less energy was felt on the adjoining screw. The consistency in the powered instrument is higher because the standard deviation using the manual instrument is 8.46, compared to the powered instrument which was 8.31. Also 25g's was recorded on the surgeon's wrist and elbow. Based on previous work done, the external work done by the surgeon was about 60-120 KJ. The onset of fatigue was apparent in consecutive break events as illustrated by the change in EMG parameters over time.

G-Protein Coupled Receptors (GPCRs) are a class of membrane-bound receptor proteins capable of relaying a biological signal across a cell membrane through a solely conformational change in their transmembrane domain. Previous work has shown that helical foldamers composed of achiral monomeric units can be used in an analogous manner to relay stereochemical information on the nano-scale through the conformational control of screw-sense preference. While this work has produced some highly successful examples of signal relay, mimicking the function of GPCRs, its reliance on screw-sense responsive NMR probes has restricted further development into membrane environments. This thesis describes the successful development of a pyrene based screw-sense responsive fluorescence probe and its subsequent use in the development of a series of membrane-based GPCR mimics. This thesis has also details the preliminary steps towards the development of light-responsive controllers of screw-sense preference for nano-scale signal relay devices.

Research evaluating the surgical repair of femoral neck fractures in dogs is limited. This study evaluated the in vitro mechanical properties of canine femoral neck fractures stabilized with two medium Orthofix® Partially-threaded Kirschner Wires (Orthofix pins), a 2.7 mm cortical bone screw placed in lag fashion with anti-rotational Kirschner wire (K-wire), and three 1.1 mm divergent K-wires. This study compared the mean compressive pressure, compressive force and area of compression created by the insertion the Orthofix pins and a 2.7 mm cortical bone screw placed in lag fashion. Monotonic testing was used to quantify mechanical strength and pressure sensitive film was used to quantify compression. There was no significant difference in the stiffness or load to failure for the three repair methods evaluated. There was no significant difference in the compressive pressure, compressive force or area of compression in osteotomies stabilized with Orthofix pins and 2.7 mm bone screws.

No description available.