Thermal Design Characterization of Heat Exchangers for 3 Stages Turbo Centrifugal Geared Air Compressor

A single or multi stage turbo centrifugal geared compressor is widely used in various industrial application such as oil & gas, chemical, power, and air separation plants. It is consist of compression part including air scroll, impeller, and diffuser, gear and bearing, cooling, oil, sealing, and control systems. Shell and tube type heat exchanger commonly used to cool down compressed gas or air between stages or after final stages, and supply oil temperature as a cooler. On compressor’s cooling system strongly required to compact (miniaturization) and high heat transfer capability. Increases of heat transfer capability can result reduce compression aero-power and pumping-power, enhance system stability, and compact. Recently, nanofluid, which is a colloidal dispersion of nano-sized particles in basefluid such as water, ethylene-glycol, propylene-glycol and their mixtures etc., exhibit a significant enhancement in their thermal conductivity. Thus, using nanofluida expected to be an advanced coolant material in compressor cooling system. In this study, HTRI Xist used to thermal design of heat exchanger, nanofluid’s thermal conductivity used to coolant material property. The thermal conductivity of the nanofluid increased by 9.3% compared to that of water. The heat exchanger’s tube side overall heat transfer rate is increased by ~7% compared to that of basefluid

Size effects of mechanical response in thin film samples versus bulk-molecular dynamics simulation study

Understanding the mechanical response of nanocrystalline metals is critical for a wide range of applications and a number of them make a use of nanocrystalline materials in thin film (2D) or wire (1D) form. Despite significant progress in the understanding of the mechanical response of nanocrystals, less is known about how grain-size effects are affected the presence of free surfaces. Here, we characterize the mechanical response of nanocrystalline thin films samples with various grain sizes and at two different strain rates, and then we compare with those in bulk sample. Our simulations show the existence of Hall–Petch maxima for both yield and flow stresses and a quantitative analysis of plastic slip reveal that grain boundary slip decreases while intragranular slip increases with grain size. We also find that Hall–Petch maximum in thin film occur at larger grain size than those in the bulk samples. Our detailed slip analysis shows that the origin of this shift is not the increased grain boundary mobility in the slabs but the weaker size effect of intragranular dislocation-based plasticity

Size-dependent hardness of nanoscale metallic contacts from molecular dynamics simulations

We characterize how size and shape affects the hardness of nanoscale metallic contacts using large-scale molecular dynamics (MD) simulations. High-aspect-ratio contacts continue the experimentally observed trend of hardening with decreasing contact size down to the sub-10-nm regime. However, we find that this effect is shape dependent and the rate of hardening with decreasing contact size diminishes as the aspect ratio of the asperities becomes smaller. Interestingly, low-aspect-ratio asperities that can support simple dislocation glide exhibit softening with decreasing size. A detailed analysis of the MD trajectories reveals the dislocation mechanisms that govern these complex size effects

Competition graphs of degree bounded digraphs

If each vertex of an acyclic digraph has indegree at most $i$ and outdegree at most $j$, then it is called an $(i,j)$ digraph, which was introduced by Hefner~{\it et al.}~(1991). Whereas Hefner~{\it et al.} characterized $(i,j)$ digraphs whose competition graphs are interval, characterizing the competition graphs of $(i,j)$ digraphs is not an easy task. In this paper, we introduce the concept of $\langle i,j \rangle$ digraphs, which relax the acyclicity condition of $(i,j)$ digraphs, and study their competition graphs. By doing so, we obtain quite meaningful results. Firstly, we give a necessary and sufficient condition for a loopless graph being an $\langle i,j \rangle$ competition graph for some positive integers $i$ and $j$. Then we study on an $\langle i,j \rangle$ competition graph being chordal and present a forbidden subdigraph characterization. Finally, we study the family of $\langle i,j \rangle$ competition graphs, denoted by $\mathcal{G}_{\langle i,j \rangle}$, and identify the set containment relation on $\{\mathcal{G}_{\langle i,j \rangle}\colon\, i,j \ge 1\}$

New Long End-Associative Polymers for Mist Control in I. Aqueous Solutions and II. Hydrocarbon Solvents

Ultralong linear polymers are well known to be useful in a variety of applications such as mist control, drag reduction, and agricultural spray drift control. However, the application of ultralong linear polymers is limited by shear degradation of the ultralong polymer chains that occurs under strong flow conditions. To overcome the issue of shear degradation, our group previously designed long end-associative polymers that can self-assemble into megasupramolecules (Mw &#62; 2000 kg/mol) in low polarity solvents like jet fuel. The previously developed long end associative polymers had polycyclooctadiene backbones (1,4 polybutadiene) with carboxylic acid or tertiary amine end groups that associated via hydrogen bonding. They were shear degradation resistant and used as mist-control agents that provided fire-protection to jet fuel at concentrations as low as 0.3wt%. Building upon the previous work, this thesis describes efforts toward expanding the applicability of long end-associative polymers. We first describe the design and synthesis of water-soluble long end-associative polymers for agricultural spray mist-control. We synthesized telechelic polyacrylamides using reversible addition fragmentation chain transfer (RAFT) polymerization. We explored two types of associations that can form stable supramolecules in water: host-guest interactions between adamantane and beta-cyclodextrin (Chapter 1), and metal-ligand association between terpyridine and transition metal ions (Chapter 2). Careful optimization of polymerization conditions allowed the synthesis of ultra-high molecular weight telechelic polyacrylamides with narrow polydispersity. We found that the terpyridine functionalized polyacrylamides with Mw 820 kg/mol could assemble into megasupramolecules (Mw &#62; 2000 kg/mol) upon addition of Fe(II) or Ni(II). In Chapters 3 and 4, we return to long end-associative polymers in hydrocarbon solvents. In Chapter 3, we tackle the issue of poor solubility of the previous generation of associative PCODs in a highly nonpolar solvent, PAO. In Chapter 4, we develop a new generation of end groups for improved solubility and ease of synthesis. Finally in Chapter 5, we discuss polyDODT (poly(3,6-dioxa-1,8-octanedithiol)), a polydisulfide that tends to form a mixture of linear and cyclic species. We present new methods to detect the presence of linear species in the mixture, as well as an alternative synthesis route for synthesis of polyDODT.</p

Validating Dose Uncertainty Estimates Produced by AUTODIRECT: An Automated Program to Evaluate Deformable Image Registration Accuracy.

Deformable image registration is a powerful tool for mapping information, such as radiation therapy dose calculations, from one computed tomography image to another. However, deformable image registration is susceptible to mapping errors. Recently, an automated deformable image registration evaluation of confidence tool was proposed to predict voxel-specific deformable image registration dose mapping errors on a patient-by-patient basis. The purpose of this work is to conduct an extensive analysis of automated deformable image registration evaluation of confidence tool to show its effectiveness in estimating dose mapping errors. The proposed format of automated deformable image registration evaluation of confidence tool utilizes 4 simulated patient deformations (3 B-spline-based deformations and 1 rigid transformation) to predict the uncertainty in a deformable image registration algorithm's performance. This workflow is validated for 2 DIR algorithms (B-spline multipass from Velocity and Plastimatch) with 1 physical and 11 virtual phantoms, which have known ground-truth deformations, and with 3 pairs of real patient lung images, which have several hundred identified landmarks. The true dose mapping error distributions closely followed the Student t distributions predicted by automated deformable image registration evaluation of confidence tool for the validation tests: on average, the automated deformable image registration evaluation of confidence tool-produced confidence levels of 50%, 68%, and 95% contained 48.8%, 66.3%, and 93.8% and 50.1%, 67.6%, and 93.8% of the actual errors from Velocity and Plastimatch, respectively. Despite the sparsity of landmark points, the observed error distribution from the 3 lung patient data sets also followed the expected error distribution. The dose error distributions from automated deformable image registration evaluation of confidence tool also demonstrate good resemblance to the true dose error distributions. Automated deformable image registration evaluation of confidence tool was also found to produce accurate confidence intervals for the dose-volume histograms of the deformed dose

Offline-to-Online Knowledge Distillation for Video Instance Segmentation

In this paper, we present offline-to-online knowledge distillation (OOKD) for video instance segmentation (VIS), which transfers a wealth of video knowledge from an offline model to an online model for consistent prediction. Unlike previous methods that having adopting either an online or offline model, our single online model takes advantage of both models by distilling offline knowledge. To transfer knowledge correctly, we propose query filtering and association (QFA), which filters irrelevant queries to exact instances. Our KD with QFA increases the robustness of feature matching by encoding object-centric features from a single frame supplemented by long-range global information. We also propose a simple data augmentation scheme for knowledge distillation in the VIS task that fairly transfers the knowledge of all classes into the online model. Extensive experiments show that our method significantly improves the performance in video instance segmentation, especially for challenging datasets including long, dynamic sequences. Our method also achieves state-of-the-art performance on YTVIS-21, YTVIS-22, and OVIS datasets, with mAP scores of 46.1%, 43.6%, and 31.1%, respectively

Crack Propagation Simulation Tool

In the massively engineered world that exists today, understanding material behavior is of paramount importance in caring for human safety in design. Molecular dynamic simulations on crack propagation through materials allow visualization of material behavior under stress. The tool, developed by the nanoHUB group as a part of the Network for Computational Nanotechnology at Purdue University, makes performing such simulations accessible to undergraduate students, highly qualified researchers, and all those in between. First, the input deck for the simulation parameters was simplified from the complex, language-specific code into a simple, user-friendly Graphic User Interface (GUI). Several interesting example cases were run through using the GUI and developed to help the user understand the functionality of the tool. The output of the GUI was developed to allow the user to have both numerical and visual depictions of what occurred. The resulting tool allows for a step-by-step walkthrough of generating the case in situations where the user may be unfamiliar with the required code. The user can manipulate the parameters to fit their individual needs in regards to size and strain rate for example. The tool can be used as instructional material in classes such as materials science and validation material for the varied clientele that exists. This nanoHUB tool will contribute to educating future engineers and scientists in materials behavior. Furthermore, it provides engineers and scientists a simple process to model and validate their ongoing projects and research

Finger-triggered portable PDMS suction cup for equipment-free microfluidic pumping

This study presents a finger-triggered portable polydimethylsiloxane suction cup that enables equipment-free microfluidic pumping. The key feature of this method is that its operation only involves a “pressing-and-releasing” action for the cup placed at the outlet of a microfluidic device, which transports the fluid at the inlet toward the outlet through a microchannel. This method is simple, but effective and powerful. The cup is portable and can easily be fabricated from a three-dimensional printed mold, used without any pre-treatment, reversibly bonded to microfluidic devices without leakage, and applied to various material-based microfluidic devices. The effect of the suction cup geometry and fabrication conditions on the pumping performance was investigated. Furthermore, we demonstrated the practical applications of the suction cup by conducting an equipment-free pumping of thermoplastic-based microfluidic devices and water-in-oil droplet generation.11Yscopu

Effects of grain size on the martensitic phase transformation of nanocrystalline Ni/Al shape memory alloys

Shape memory alloys (SMAs) owe their distinct properties to a diffusion less martensitic phase transformation from a high temperature, high symmetry phase (austenite) to a low temperature (martensite) phase upon cooling or strain. Their shape memory and pseudoelastic properties make SMAs useful as active components in microdevices, medical implants and for vibrational damping. Despite their widespread application, the miniaturization limit of SMAs is not known. In this study, we use large-scale molecular dynamics simulations (up to ~40 million atoms) to characterize the martensitic transformation in nanocrystalline Ni/Al disordered alloys. We quantify how mechanical constraints affect both the transformation temperature and the resulting martensitic domain structure. We find that decreasing the grain size makes the transformation more difficult, and this results in a reduction of the transformed volume fraction at a given temperature. Interestingly, we find a minimum in the transformed fraction as a function of decreasing grain size, with extremely fine-grained samples showing a greater tendency to transform