bluuebunny/crossref_metadata_2025 huggingface dataset:
Summary on the Results of Two Computational Fluid Dynamic Benchmarks of Tube and Different Channel Geometries
Authors: Kiss Attila , Churkin Andrey , Pilkhwal Darwan S. , Vaidya Abhijeet M. , Ambrosini Walter , Pucciarelli Andrea , Podila Krishna , Rao Yanfei , Leung Laurence , Yuzhou Chen , Anderson Mark , Zhao Meng
Published: October 2017

Two computational fluid dynamic (CFD) benchmarks have been performed to assess the prediction accuracy and sensitivity of CFD codes for heat transfer in different geometries. The first benchmark focused on heat transfer to water in a tube (first benchmark), while the second benchmark covered heat transfer to water in two different channel geometries (second benchmark) at supercritical pressures. In the first round with the experimental data unknown to the participants (i.e., blind calculations), CFD calculations were conducted with initial boundary conditions and simpler CFD models. After assessment against measurements, the calculations were repeated with the refined boundary conditions and material properties in the follow-up calculation phase. Overall, the CFD codes seem to be able to capture the general trend of heat transfer in the tube and the annular channel but further improvements are required in order to enhance the prediction accuracy. Finally, sensitivity analyses on the numerical mesh and the boundary conditions were performed. It was found that the prediction accuracy has not been improved with the introduction of finer meshes and the effect of mass flux on the result is the strongest among various investigated boundary conditions.
Geometric Error Modeling and Sensitivity Analysis of Single-Axis Assembly in Three-Axis Vertical Machine Center Based on Jacobian-Torsor Model
Authors: Zhengchun Du , Jian Wu , Jianguo Yang
Published: October 2017

The influence of component errors on the final error is a key point of error modeling of computer numerical control (CNC) machine tool. Nevertheless, the mechanism by which the errors in mechanical parts accumulate to result in the component errors and then impact the final error of CNC machine tool has not been identified; the identification of this mechanism is highly relevant to precision design of CNC machine. In this study, the error modeling based on the Jacobian-torsor theory is applied to determine how the fundamental errors in mechanical parts influence and accumulate to the comprehensive error of single-axis assembly. First, a brief introduction of the Jacobian-torsor theory is provided. Next, the Jacobian-torsor model is applied to the error modeling of a single-axis assembly in a three-axis machine center. Furthermore, the comprehensive errors of the single-axis assembly are evaluated by Monte Carlo simulation based on the synthesized error model. The accuracy and efficiency of the Jacobian-torsor model are verified through a comparison between the simulation results and the measured data from a batch of similar vertical machine centers. Based on the Jacobian-torsor model, the application of quantitative sensitivity analysis of single-axis assembly is investigated, along with the analysis of key error sources to the synthetical error ranges of the single-axis assembly. This model provides a comprehensive method to identify the key error source of the single-axis assembly and has the potential to enhance the tolerance/error allocation of the single axis and the whole machine tool.
Harnessing Dielectric Breakdown of Dielectric Elastomer to Achieve Large Actuation
Authors: Zhang Hui , Wang Yingxi , Godaba Hareesh , Khoo Boo Cheong , Zhang Zhisheng , Zhu Jian
Published: October 2017

It is an interesting open question how to achieve large actuation of a dielectric elastomer (DE). In many previous works, in order to harness snap-through instability to achieve large deformation, a reservoir was employed to assist the dielectric elastomer actuator (DEA) to optimize its loading condition/path, which makes the whole actuation system bulky and heavy. In this paper, we explore large actuation of a DE balloon with applications to a soft flight system. The balloon consists of two separate DEAs: The inner one is stiffer while the outer one is softer. The whole actuation system has a small volume and a low weight, but can achieve large actuation by harnessing dielectric breakdown of the inner elastomer. The volume induced by dielectric breakdown is more than 20 times the voltage-induced volume change of DEAs. The experiments demonstrate a soft flight system, which can move effectively in air by taking advantage of large actuation of this DE balloon. This project also shows that failure of materials can be harnessed to achieve useful functionalities.
The Effects of Prosthesis Inertial Parameters on Inverse Dynamics: A Probabilistic Analysis
Authors: Gaffney Brecca M. M. , Christiansen Cory L. , Murray Amanda M. , Myers Casey A. , Laz Peter J. , Davidson Bradley S.
Published: October 2017

Joint kinetic measurement is a fundamental tool used to quantify compensatory movement patterns in participants with transtibial amputation (TTA). Joint kinetics are calculated through inverse dynamics (ID) and depend on segment kinematics, external forces, and both segment and prosthetic inertial parameters (PIPS); yet the individual influence of PIPs on ID is unknown. The objective of this investigation was to assess the importance of parameterizing PIPs when calculating ID using a probabilistic analysis. A series of Monte Carlo simulations were performed to assess the influence of uncertainty in PIPs on ID. Multivariate input distributions were generated from experimentally measured PIPs (foot/shank: mass, center of mass (COM), moment of inertia) of ten prostheses and output distributions were hip and knee joint kinetics. Confidence bounds (2.5–97.5%) and sensitivity of outputs to model input parameters were calculated throughout one gait cycle. Results demonstrated that PIPs had a larger influence on joint kinetics during the swing period than the stance period (e.g., maximum hip flexion/extension moment confidence bound size: stance = 5.6 N·m, swing: 11.4 N·m). Joint kinetics were most sensitive to shank mass during both the stance and swing periods. Accurate measurement of prosthesis shank mass is necessary to calculate joint kinetics with ID in participants with TTA with passive prostheses consisting of total contact carbon fiber sockets and dynamic elastic response feet during walking.
Experimental Investigation of Numerically Optimized Wavy Microchannels Created Through Additive Manufacturing
Authors: Kirsch Kathryn L. , Thole Karen A.
Published: October 2017

The increased design space offered by additive manufacturing (AM) can inspire unique ideas and different modeling approaches. One tool for generating complex yet effective designs is found in numerical optimization schemes, but until relatively recently, the capability to physically produce such a design had been limited by manufacturing constraints. In this study, a commercial adjoint optimization solver was used in conjunction with a conventional flow solver to optimize the design of wavy microchannels, the end use of which can be found in gas turbine airfoil skin cooling schemes. Three objective functions were chosen for two baseline wavy channel designs: minimize the pressure drop between channel inlet and outlet, maximize the heat transfer on the channel walls, and maximize the ratio between heat transfer and pressure drop. The optimizer was successful in achieving each objective and generated significant geometric variations from the baseline study. The optimized channels were additively manufactured using direct metal laser sintering (DMLS) and printed reasonably true to the design intent. Experimental results showed that the high surface roughness in the channels prevented the objective to minimize pressure loss from being fulfilled. However, where heat transfer was to be maximized, the optimized channels showed a corresponding increase in Nusselt number.
Fault Diagnosis in Multistation Assembly Systems Using Spatially Correlated Bayesian Learning Algorithm
Authors: Bastani Kaveh , Barazandeh Babak , Kong Zhenyu (James)
Published: October 2017

The problem of fault diagnosis for dimensional integrity in multistation assembly systems is addressed in this paper. Fault diagnosis under this context is to identify the process errors which significantly contribute to the large product dimensional variation based on sensor data. The main challenges to be resolved in this paper include (1) the number of measurements is less than the process errors, which is typical in practice, but results in an ill-posed estimation problem, and (2) there exists spatial correlation among the dimensional variation of process errors, which has not been addressed yet by existing literature. A spatially correlated Bayesian learning (SCBL) algorithm to address these challenges is developed. The SCBL algorithm is based on the relevance vector machine (RVM) by exploiting the spatial correlation of dimensional variation from various process errors, which occurs in some circumstances of assembled parts and is well defined in GD&T standards. The proposed algorithm relies on a parametrized prior including the spatial correlation, and eventually leads sparsity in fault diagnosis; hence, the issues with ill-posedness and structured process errors will be addressed. A number of simulation studies are performed to illustrate the superiority of SCBL algorithm over state-of-the-art algorithms in sparse estimation problems when spatial correlation exists among the nonzero elements. A real autobody assembly process is also used to demonstrate the effectiveness of proposed SCBL algorithm.
Direct Numerical Simulation of the Microscale Fluid Flow and Heat Transfer in the Three-Phase Contact Line Region During Evaporation
Authors: Batzdorf Stefan , Gambaryan-Roisman Tatiana , Stephan Peter
Published: October 2017

The heat and mass transfer close to the apparent three-phase contact line is of tremendous importance in many evaporation processes. Despite the extremely small dimensions of this region referred to as the microregion compared to the macroscopic length scale of a boiling process, a considerable fraction of heat can be transferred in this region. Due to its small characteristic length scale, physical phenomena are relevant in the microregion, which are completely negligible on the macroscopic scale, including the action of adhesion forces and the interfacial heat resistance. In the past, models have been developed taking these effects into account. However, so far these models are based on the assumption of one-dimensional (1D) heat conduction, and the flow within the thin liquid film forming the microregion near the apparent three-phase contact line is modeled utilizing the lubrication approximation. Hence, the application of existing models is restricted to small apparent contact angles. Moreover, the effects of surface structures or roughness are not included in these lubrication models. To overcome these limitations, a direct numerical simulation (DNS) of the liquid flow and heat transfer within the microregion is presented in this paper. The DNS is employed for validation of the existing lubrication model and for investigation of the influence of surface nanostructures on the apparent contact angle and in particular on the heat transfer within the microregion.
Nonlinear Mechanics of Interlocking Cantilevers
Authors: Brown Joseph J. , Mettler Ryan C. , Supekar Omkar D. , Bright Victor M.
Published: October 2017

The use of large-deflection springs, tabs, and other compliant systems to provide integral attachment, joining, and retention is well established and may be found throughout nature and the designed world. Such systems present a challenge for mechanical analysis due to the interaction of contact mechanics with large-deflection analysis. Interlocking structures experience a variable reaction force that depends on the cantilever angle at the contact point. This paper develops the mathematical analysis of interlocking cantilevers and provides verification with finite element analysis and physical measurements. Motivated by new opportunities for nanoscale compliant systems based on ultrathin films and two-dimensional (2D) materials, we created a nondimensional analysis of retention tab systems. This analysis uses iterative and elliptic integral solutions to the moment–curvature elastica of a suspended cantilever and can be scaled to large-deflection cantilevers of any size for which continuum mechanics applies. We find that when a compliant structure is bent backward during loading, overlap increases with load, until a force maximum is reached. In a force-limited scenario, surpassing this maximum would result in snap-through motion. By using angled cantilever restraint systems, the magnitude of insertion force relative to retention force can vary by 50× or more. The mathematical theory developed in this paper provides a basis for fast analysis and design of compliant retention systems, and expands the application of elliptic integrals for nonlinear problems.
Energy and Cost Analysis of a New Packed Bed Pumped Thermal Electricity Storage Unit
Authors: Benato Alberto , Stoppato Anna
Published: October 2017

Renewable energy sources (RES) are quite capable to actively contribute to meet the today's energy demand. However, many of them have a time-dependent nature that constitutes their major disadvantage. To overcome this drawback, energy storage systems (ESS) need to be set up. In this way, the stored energy can be used in the absence of RES or under peak demand hours. High-temperature pumped thermal electricity storage (PTES) using packed bed constitutes an attractive solution but is characterized by high losses and irreversibilities. For this reason, in this paper, a new plant scheme is presented and its mathematical model built up. To predict the packed bed behavior, a one-dimensional two phase model of the hot and cold storages has been included, while the plant feasibility is evaluated using an energy and a cost analysis. Results show that the highest quantity of energy and round-trip efficiency are reached with a packed bed made of magnetite and titanium oxide.
Nanoparticle Optimization for Enhanced Targeted Anticancer Drug Delivery
Authors: Chamseddine Ibrahim M. , Kokkolaras Michael
Published: October 2017

Nanoparticle (NP)-based drug delivery is a promising method to increase the therapeutic index of anticancer agents with low median toxic dose. The delivery efficiency, corresponding to the fraction of the injected NPs that adhere to the tumor site, depends on NP size a and aspect ratio AR. Values for these variables are currently chosen empirically, which may not result in optimal targeted drug delivery. This study applies rigorous optimization to the design of NPs. A preliminary investigation revealed that delivery efficiency increases monotonically with a and AR. However, maximizing a and AR results in nonuniform drug distribution, which impairs tumor regression. Therefore, a multiobjective optimization (MO) problem is formulated to quantify the trade-off between NPs accumulation and distribution. The MO is solved using the derivative-free mesh adaptive direct search algorithm. Theoretically, the Pareto-optimal set consists of an infinite number of mathematically equivalent solutions to the MO problem. However, interesting design solutions can be identified subjectively, e.g., the ellipsoid with a major axis of 720 nm and an aspect ratio of 7.45, as the solution closest to the utopia point. The MO problem formulation is then extended to optimize NP biochemical properties: ligand–receptor binding affinity and ligand density. Optimizing physical and chemical properties simultaneously results in optimal designs with reduced NP sizes and thus enhanced cellular uptake. The presented study provides an insight into NP structures that have potential for producing desirable drug delivery.
Formability Prediction for Tube Hydroforming of Stainless Steel 304 Using Damage Mechanics Model
Authors: Yuenyong J. , Suthon M. , Kingklang S. , Thanakijkasem P. , Mahabunphachai S. , Uthaisangsuk V.
Published: October 2017

Tube hydroforming (THF) is an important manufacturing technology for producing tube components by means of fluid pressure. In comparison to other basic forming processes like deep drawing, forming steps can be reduced and more complex shape is allowed. In this work, it was aimed to establish the forming limit curve (FLC) of stainless steel tube grade 304 for the THF process by using finite element (FE) simulations coupled with the Gurson–Tvergaard–Needleman (GTN) damage model as failure criterion. The parameters of the GTN model were obtained by metallography analysis, tensile test, plane strain test of the examined steel in combination with the direct current potential drop (DCPD) and digital image correlation (DIC) techniques. These parameters were well verified by comparing the predicted FLC of steel sheet with the experimental FLC gathered from the Nakazima test. Then, the FLC of steel tube 304 was established by FE simulations coupled with the damage model of tube bulging tests. During the bulge tests, pressure and axial feed were properly controlled in order to generate the left-hand FLC, while pressure and external force needed to be simultaneously incorporated for the right-hand FLC. Finally, the FLC was applied to evaluate material formability in an industrial THF process of the steel tube.
Strongly Coupled Fluid–Structure Interaction in a Three-Dimensional Model Combustor During Limit Cycle Oscillations
Authors: Shahi Mina , Kok Jim B. W. , Roman Casado J. C. , Pozarlik Artur K.
Published: October 2017

Due to the high temperature of the flue gas flowing at high velocity and pressure, the wall cooling is extremely important for the liner of a gas turbine engine combustor. The liner material is heat-resistant steel with relatively low heat conductivity. To accommodate outside wall forced air cooling, the liner is designed to be thin, which unfortunately facilitates the possibility of high-amplitude wall vibrations (and failure due to fatigue) in case of pressure fluctuations in the combustor. The latter may occur due to a possible occurrence of a feedback loop between the aerodynamics, the combustion, the acoustics, and the structural vibrations. The structural vibrations act as a source of acoustic emitting the acoustic waves to the confined fluid. This leads to amplification in the acoustic filed and hence the magnitude of instability in the system. The aim of this paper is to explore the mechanism of fluid–structure interaction (FSI) on the LIMOUSINE setup which leads to limit cycle of pressure oscillations (LCO). Computational fluid dynamics (CFD) analysis using a RANS approach is performed to obtain the thermal and mechanical loading of the combustor liner, and finite element model (FEM) renders the temperature, stress distribution, and deformation in the liner. Results are compared to other numerical approaches like zero-way interaction and conjugated heat transfer model (CHT). To recognize the advantage/disadvantage of each method, validation is made with the available measured data for the pressure and vibration signals, showing that the thermoacoustic instabilities are well predicted using the CHT and two-way coupled approaches, while the zero-way interaction model prediction gives the largest discrepancy from experimental results.
Pitch Effects of Encapsulated Phase Change Material Tubes on Charging and Discharging of Solar Thermal Collectors
Authors: Su Yan , Ng Tiniao
Published: October 2017

Comparative studies of five cases of solar collectors have been simulated by the Non-Dimensional Lattice Boltzmann Method (NDLBM) to obtain the effects of the encapsulated phase change material tubes. Both charging and discharging procedures have been compared. The transient averaged temperature, PCM porosity, and energy ratio are presented. Five geometry cases of solar collectors with and without encapsulated phase change material tubes have been simulated. Transient isotherms and streamlines with porosity have been shown for both outside and inside PCM tube regions. The performance enhancement because of the PCM tubes has been presented and the effects due to distributions of the PCM tubes are also discussed. The Pitch effects have been compared based on the three cases.
Adsorption and Capillary Condensation in Nanogap With Nanoposts
Authors: Avanessian Tadeh , Hwang Gisuk
Published: October 2017

Adsorption isotherm and adsorption-capillary transition theories have been developed based on homogeneous micro-/nanoporous materials and structures. However, material and structures are often heterogeneous including local surface roughness and defects, where no predictive tool is available so far. In this study, the adsorption isotherm and the adsorption-capillary transition is examined for Ar-filled Pt nanogap (Lz = 5 nm) with nanoposts (one surface only) using Grand Canonical Monte Carlo (GCMC) simulations. Results show that the presence of the nanoposts causes a bimodal capillary transition and reduces the capillary transition pressure compared to the nanogap with both bare surfaces. The pressure difference between the bimodal transitions is pronounced with decreasing the nanopost pitch size. The larger nanopost height also leads to the early capillary transition, but the bimodal transition is pronounced for moderate heights of the nanoposts. A stronger solid-fluid interaction reduces the adsorption-capillary transition pressure at given temperature and increases the transition pressure difference between the nanogaps with or without nanoposts. The obtained results provide new insights of the role of surface nanostructure (nanoposts) into adsorption isotherm and capillary transition.
Integration of Virtual Reality and CFD Techniques for Thermal Fluid Education
Authors: Zhou Peng , Wang Xiuling , Morales Ulises , Yang Xiaoli
Published: October 2017

Engineering courses such as thermodynamics, fluid mechanics and heat transfer always involve many abstract math, physics concepts and equations — which are difficult to teach and understand. As fundamental courses in engineering programs, they are sometimes taught in big class size — where students may not receive adequate attention and assistance from instructors. To improve the teaching and learning efficiency, we proposed to develop virtual reality based interactive modules for learning computational fluid dynamics. In this paper, case-study learning module is demonstrated for conduction heat transfer. The programming languages of C# and Unity3D were used for the software development. Computational fluid dynamics simulation results obtained from ANSYS/FLUENT were incorporated in the program. The program has the integrated modules of mobility, interactivity, and controllability for the 3D modeling and simulations. Each module was developed separately for facilitating the program management, extension, and upgrades in the future. The developed interactive programs, incorporating rich, interactive, and engaging learning contexts, will help students gain and apply knowledge to solve real-world problems in mechanical engineering.
Aluminum Foam-Based Ultrafast Electronucleation of Hydrates
Authors: Acharya Palash V. , Shahriari Arjang , Carpenter Katherine , Bahadur Vaibhav
Published: October 2017

Nucleation of hydrates requires very long induction (wait) times, often ranging from hours to days. Electronucleation, i.e. nucleation stimulated by the presence of an electric field in the precursor solution can reduce the induction time significantly. This work reveals that porous aluminum foams enable near-instantaneous electronucleation at very low voltages. Experiments with tetrahydrofuran hydrate nucleation reveal that open-cell aluminum foam electrodes can trigger nucleation in only tens of seconds. Foam-based electrodes reduce the induction time by as much as 150X, when compared to non-foam electrodes. This work also discusses two mechanisms underlying electronucleation. These include bubble generation (due to electrolysis), and the formation of metal-ion coordination compounds. These mechanisms depend on electrode material and polarity, and affect the induction time to different extents. This work also shows that foams result in more deterministic nucleation (compared to stochastic) when compared with non-foam electrodes. Overall, electronucleation can lead to a new class of technologies for active control of formation of hydrates.
Contact Line Dynamics of Water Droplets Spreading on Nano-Structured Teflon Surfaces in Dropwise Condensation
Authors: Zhao Lei , Cheng Jiangtao
Published: October 2017

In dropwise condensation process, superhydrophobicity is usually achieved by introducing micro/nano-roughness to hydrophobic materials. The analysis of droplets growing and moving and the optimization of the surface structures entails a comprehensive knowledge of the contact line dissipation. However, it in many cases is neglected due to the insufficient understanding, particularly regarding its magnitude and characteristics. In this study, we report a study on the contact line dynamics of water droplets spreading on nano-structured Teflon surfaces. The Teflon surfaces are modeled on Gromacs 5.1.2 and based on the OPLSAA force field. The Teflon model is then validated by examining the glass transition temperature and thermal expansion coefficient. Patterned pillars are created by a confined layer method. The contact line dynamics of water on as-formed surfaces with different solid fraction is then analyzed using the molecular kinetic theory modified by incorporating both viscous damping and solid-liquid retarding. The unit displacement length of contact line is demonstrated to be a constant value of 0.605 nm on both flat and pillar-arrayed surfaces. The contact line friction coefficient is calculated to be on the same order of magnitude with the dynamic viscosity of water, and can be significantly decreased on superhydrophobic surfaces as a result of reduced liquid-solid contact, although contact line experiences stronger resistance on a single pillar.
Monte Carlo Simulation for Radiative Transfer in a High-Pressure Industrial Gas Turbine Combustion Chamber
Authors: Ren Tao , Modest Michael F. , Roy Somesh
Published: October 2017

Radiative heat transfer is studied numerically for reacting swirling flow in an industrial gas turbine burner operating at a pressure of 15 bar. The reacting field characteristics are computed by Reynolds-averaged Navier-Stokes (RANS) equations using the k-ε model with the partially stirred reactor (PaSR) combustion model. The GRI-Mech 2.11 mechanism, which includes nitrogen chemistry, is used to demonstrate the the ability of reducing NOx emissions of the combustion system. A Photon Monte Carlo (PMC) method coupled with a line-by-line spectral model is employed to accurately account for the radiation effects. CO2, H2O and CO are assumed to be the only radiatively participating species and wall radiation is considered as well. Optically thin and PMC-gray models are also employed to show the differences between the simplest radiative calculation models and the most accurate radiative calculation model, i.e., PMC-LBL, for the gas turbine burner. It was found that radiation does not significantly alter the temperature level as well as CO2 and H2O concentrations. However, it has significant impacts on the NOx levels at downstream locations.
Experimental Investigation of an Ammonia-Water Diffusion-Absorption Refrigerator (DAR) at Part Load
Authors: Najjaran Kheirabadi Ahmad , Freeman James , Ramos Cabal Alba , Markides Christos N.
Published: October 2017

Diffusion absorption refrigeration (DAR) cycles enable passive fully thermally-driven refrigeration for off-grid purposes. Typically, DAR units are designed for a given heat supply load and temperature, although real operation inevitably involves unsteady variations in these inputs. In this study, a thermally-driven DAR unit with a nominal cooling capacity of 120 W is connected to an electric heat source. The working fluid is ammonia-water NH3/H2O, with hydrogen (H2) added as an auxiliary gas to keep the system pressure constant and to decrease the partial pressure of the refrigerant (ammonia) in the evaporator. A control unit is used to adjust and measure the input heat-source power applied to the unit. The operating pressure of the system is 20.7 bar, the ambient temperature is 22 °C and the input thermal power is in the range 250 to 700 W. The cooling capacity of the unit and the input heat load are measured simultaneously at different operation conditions. To measure the cooling power, a cold box is constructed around the evaporator, and a second heater is located inside the cold box which sets the cold space temperature equal to that of the ambient. This allows the coefficient of performance (COP) to be evaluated. The COP and cooling capacity of the unit are investigated at part load by varying the heat supply, from which maximum values are obtained (0.28 and 110 W, respectively). Finally, experimental results are compared to the theoretical predictions from a thermodynamic model of a DAR cycle. Once validated, the model is also used to find the properties of the fluid mixture in different states in the DAR cycle.
Heat Transfer During Condensation of a Low-GWP Refrigerant on an Enhanced Cylindrical Surface
Authors: Chen Tailian
Published: October 2017

In this work, heat transfer coefficients during condensation of an environment-friendly refrigerant R-1233zd(e) on the outside surface of two cylindrical tubes are individually measured. The cooling water flows inside the tubes and provides cooling to the vapor refrigerant. One tube is a plain smooth tube (smooth both inside and outside) while the other tube is an enhanced tube, with the inside surface having 2D helical ridges and the outside surface having 3D extruded fins. The tests were conducted at the saturation temperature 36.1 °C, a typical temperature in chiller condensers. The results show the overall heat transfer coefficients of the enhanced tube are approximately 8.4 times higher as a result of the heat transfer enhancement on both sides. The condensation heat transfer degrades with an increase in the degree of subcooling, and the trend of degradation is the nearly the same for both the smooth and the enhanced tube, both is smaller than that in the Nusselt correlation. Compared with condensation on the smooth surface, the condensation heat transfer from the enhanced surface is enhanced approximately 10.8 times higher than that on the smooth surface. In addition to enlarged heat transfer area of the extruded fins, the enhancement in the condensation heat transfer is partly attributed to a better condensate draining mechanism of the 3D-structured fins where surface tension plays an important role. Further analysis reveals that heat transfer during the condensation process on the 3D low-fin surface follows the Nusselt correlation with a multiplier that accounts for the enhancement in heat transfer, which is desirably simple approach to modeling condensation heat transfer on the complex 3D enhanced surfaces. This work can lead to more insights into the physical mechanisms during the complex condensation process.
Effects of Liquid Viscosity on Bubble Growth From Submerged Orifice Plates
Authors: Manoharan Sanjivan , Jog Milind A. , Manglik Raj M.
Published: October 2017

Experimental investigation of bubble growth from orifice plates submerged in pools of viscous liquids has been carried out using high speed videography. Conflicting effects of viscosity on ebullience have been reported in the literature. These are addressed in the present study and their range of applicability has been identified. Furthermore, the effects of chamber volume on bubble dynamics in viscous media are examined. Orifice plates made of Acrylic glass (a hydrophilic surface) with varying orifice diameters from 0.813 mm to 1.500 mm, have been utilized. Additionally, bubble dynamics from a stainless steel capillary nozzle was captured and compared with that from orifice plates. The six different liquid pools were used, viz., pure distilled water, ethylene glycol, propylene glycol, and three different aqueous glycerol solutions. The aqueous glycerol solutions varied in viscosity from 48 cP to 128 cP. The flow rate was regulated such that the isolated bubble regime was encountered. For the smaller orifices, viscosity effects were present at all flow rates and the bubbles in water-glycerol solutions were much larger than those in pure water. However, for the larger orifice sizes, water-glycerol solutions produced bubbles that were larger than those in water only at high air flow rates. For larger orifice sizes, at low flow rates, there was no increase in bubble size in highly viscous water-glycerol solutions compared to pure water. In fact, with 1.5 mm diameter plate orifice, the bubbles for 128 cP water-glycerol solution were smaller than those in pure water at low air flow rates. When chamber effects were present, the bubbles in the more viscous medium differed in shape and size from those in pure water.
The Impact of Base Metal on the Thermal-Hydraulic Performance of Metal Foam Heat Exchanger for Cooling and Dehumidification Applications
Authors: Nawaz Kashif , Jacobi Anthony M.
Published: October 2017

In the wake of utilization of novel materials in various thermal applications open cell metal foams have received attention due to their inherent properties such as large surface area to volume ratio and higher thermal conductivity. Additionally, complex tetradecahedron structure promotes mixing and makes them a good candidate for heat transfer applications. In this paper, a relative comparison has been made between the thermal-hydraulic performance of aluminum and copper metal foam heat exchangers with the same geometry under dry and wet operating conditions. Heat exchanger consisting of round tube with annular layer of metal foam have been considered. Experiments have been conducted using a closed-loop wind tunnel to measure the heat transfer performance and pressure drop. The impact of base metal (aluminum and copper) on the heat transfer rate has been evaluated at varying air flow rates and upstream relative humidity. It has been found that due to similar geometry (flow depth, face area, pore size) both aluminum and copper foam samples have comparable pressure drop under dry conditions. However, the pressure gradient was noticeably different for two samples under wet operating conditions. An obvious difference in heat transfer rate for aluminum and copper metal foam heat exchangers was observed under both dry and wet operating conditions. The findings have been explained in terms of the impact of the thermal conductivity of base metal and condensate retention.
Material Distribution Optimization in a Metal Matrix Heat Sink Using a Constructal-Design Inspired Unit T-Cell
Authors: Kephart Jacob , Jones G. F.
Published: October 2017

Constructal principles are used to investigate the optimization of material utilization in a metal matrix heat sink that maximizes the total heat transfer rate through the base of heat sink. This approach utilizes a two-dimensional geometry to examine spatial heat flow and optimal material distribution in a metal matrix in the plane perpendicular to the coolant flow direction. The matrix is composed of multiple layers of conductive tees built up from the smallest constituent, the unit T-cell. The unit cell consists of a conductive tee-shaped geometry with the two rectangular void regions each making up half of a cooling channel. The horizontal boundaries must match the temperature and heat flux at the boundaries of the neighboring unit cells as this is a conjugate conduction/convection problem. The geometry of the unit cell is characterized by aspect ratios of channel width to height, overall cell width to height, and channel height to cell height. The matrix structure is assembled by stacking unit cells into multiple layers where the number of cells in each layer is an integer multiple of the cells contained in the lower layer. The solution is obtained for optimal T-cell geometric parameters under a set of predetermined constraints including overall volume, solid fill fraction, and number of layers. When a large number of stacked unit cells are considered, the results describe the ideal spatial distribution of porosity and pore sizes for two dimensional functionally graded metal-matrix heat sink. These results will lead to a better understanding of the role played by the porosity distribution in a metal-matrix heat sink and may be applied to the analysis, optimization, and design of more effective heat sinks.
Air-Side Heat Transfer Enhancement With a Novel Self-Agitator
Authors: Li Zheng , Chen Yangyang , Xu Xianchen , Li Kuojiang , Ke Zhaoqing , Zhou Keyu , Chen Hsiu-Hung , Huang Guoliang , Chen Chung-lung , Chen Chien-Hua
Published: October 2017

Plate fin heat exchanger is widely used for air side cooling. To enhance its thermal performance, a novel self-agitator for air-side heat transfer enhancement was developed and validated both numerically and experimentally. Self-Agitator made of 3D printing material connected to well-designed metal beam was placed between the plate fins. It could lose stability and start to oscillate in the channel due to fluid structure interaction. The oscillation enhanced the mixing so that self-agitator can improve the heat transfer in plate fin. Wind tunnel experiment was carried out and self-agitator can save pumping power up to 40% with the same rejected heat. Numerical model was also developed and verified for this fluid-structure interaction process.
Experimental and Numerical Investigation of Temperature and Flow Distribution Inside a Glove Box Enclosure for a High-Accuracy Coordinate Measurement Machine
Authors: Spernjak Dusan , Morgan Robert , Mejia Alvarez Ricardo , Bernardin John , Ney Stephen A.
Published: October 2017

Experiments and simulations were performed to assess the performance of an HVAC system for the cooling of a Leitz Infinity coordinate measurement machine (CMM) enclosed within a glove box (GB). Manufacturer specifications require maintaining very uniform temperatures with spatial and temporal variations not to exceed 0.3 °C/hr, 0.4 °C/day, and 0.1°C/m. Data were collected at 0.17 Hz by 2 thermocouples located outside the glovebox, 10 static thermocouples located inside the glovebox, and up to 28 thermocouples attached to the moving granite table of the CMM. The latter thermocouples are arrayed in a grid in the volume of interest (VOI) which envelopes the motion of the CMM measuring head above the granite table. Data were collected for periods ranging from 1 to 5 days to observe the effects of temperature variations within the enclosing facility.

Simulations were then performed on the enclosed volume of the GB using ANSYS-CFX to better understand the heat loads, and test temperature variation mitigation strategies. These simulations consisted of 18 runs which varied heat input from the CMM motors, inflow gas temperature from the HVAC system into the GB, and non-uniform GB wall temperature boundary conditions. Heat loads from the motors were found to be insignificant influences on the temperature distribution, while fluid entrainment inside the diffuser was discovered to lead to an adverse temperature distribution, and insufficient cooling in the VOI. Velocity distributions were examined by using a TSI VelociCalc 8345 to verify the presence of stagnant regions in the GB. Finally, modifications to the diffuser design were proposed to eliminate entrainment, improve the flow distribution, and enhance temperature uniformity.
Simulation and Experimental Validation of the Thermal Influence on Self-Heating Metal Density Measurements
Authors: Marchi Alexandria Nicole , Morgan Robert Vaughn , Worrest Hannah Elizabeth , Bernardin John David , Freibert Franz Joseph
Published: October 2017

Bulk density measurements of radioactive materials can give significant information about radiation-induced compositional and structural changes. Traditionally, density measurements of solids are performed using hydrostatic immersion techniques based on Archimedes‘ principal, the precision of which is highly dependent on knowing the density profile of the immersion fluid. However, radioactive materials are inherently self-heating, producing thermal gradients within the immersion fluid, which induce convective flow and density gradients around the sample. In this study, COMSOL Multiphysics models were generated to study how the immersion fluid thermo-physical properties, sample size, shape and orientation, and heating power output affect the buoyancy force on the sample and ultimately the precision of the density measurements. A dimensionless equation was developed and will be fit to simulation and experimental data to build a correlation between the thermo-physical properties of the immersion fluid and the variance in the resulting buoyancy force on the samples with varying heat outputs. Thermal models will be validated experimentally by immersing self-heating metal mimics — tungsten samples with embedded surface mount resistors connected to a controllable power source — into various immersion fluid baths. Schlieren and laser-induced fluorescence flow visualization techniques around the self-heating mimics can be used to validate the density profiles predicted by the numerical models. Only the beginning setup of Schlieren experiments will be discussed as they are ongoing. This correlation, along with concurrent chemical compatibility studies not discussed in this publication, will help derive fluid selection parameters to increase the precision of density measurements. The validated numerical models can also be used to improve density measurement setups and understand where data probes, e.g., thermocouples, should be located to realize the density profile in the immersion fluid during sample measurement.
Design, Fabrication and Testing of Cooling Systems for a Particle Accelerator
Authors: Bernardin John D. , Barkley Walter C. , Gioia Jack , Marroquin Pilar
Published: October 2017

This paper discusses the design, analysis, and testing of a Water Cooling System (WCS) for a Drift Tube Linear (DTL) Particle Accelerator structure at the Los Alamos Neutron Science Center (LANSCE). The DTL WCS removes large amounts of dissipated electrical energy in a very controlled manner to maintain a constant temperature of the large structure. First, the design concept and method of water temperature control is discussed. Second, the layout of the water cooling system, including the selection of plumbing components and instrumentation is presented. Next, the development of a numerical nodal network model, used to size the plumbing, pump, control valves, and mixing tank (heat exchanger), is discussed. Finally, empirical pressure, flow rate, and temperature data from a functioning DTL water cooling system are used to assess the water cooling system performance and validate the numerical model.
Theoretical Study on Aggregation of Nuclei-Containing Gas Phase
Authors: Lan Zhong , Xue Quan , Ma Xuehu , Wang Di , Cao Kejian , Zhao Zongchang
Published: October 2017

Haze is a kind of typical heterogeneous nucleation phenomenon in gas phase condensation process. The existence of dust nucleus may induce water molecule aggregation among vapor phase under a certain humidity. In this article, we try to use Density Functional Theory simulation to explore the evolution mechanism of water molecule aggregation influenced by condensation nucleus from the perspective of molecules assembling. We can get the following results: the subcooling degree and physicochemical properties of nucleation center affect the hydrogen bond within the water clusters and the transformation energy barrier of water molecule aggregation tendency. Water vapor begins to heterogeneously condense or forms aggregation humidity in a certain condition based on the center of condensation nuclei. The analysis shows that the effect law of the degree and scale of aggregation or phase transition are influenced by the change of gas phase partial pressure, supersaturated degree along with particle properties. As the energy barrier of nucleation free energy decreases, the formation of water clusters will be easier.
A Unified Three Dimensional Numerical Simulation of the Pool Boiling Curve
Authors: Garg Deepak , Dhir Vijay K.
Published: October 2017

Three dimensional numerical simulations for pool boiling of saturated water at atmospheric pressure conditions are performed on a horizontal surface using finite difference method under the framework of parallel computing. Since heat conduction in the solid phase is not considered, in order to simulate realistic heating surface, dependence of bubble nucleation frequency and nucleation site density on wall superheat and contact angle are obtained from the correlations reported in the literature. Steady state boiling curve for all the three regimes viz. nucleate, transition and film boiling has been obtained with a unified numerical model by incrementing the wall superheat for a static contact angle of 38°. Evaporative heat flux from the microlayer is separately accounted for in the present study by sub grid modeling. Both the phases are considered as incompressible while the interface separating the phases is solved using level set method. The governing equations of mass, momentum and energy for both the liquid and the vapor phase are solved coupled with the jump conditions at the interface employing ghost fluid and cut cell method. Diffusion terms are treated implicitly while convection terms are treated using second order ENO scheme. Spatial and temporal averaged wall heat flux and wall void fraction are plotted and compared against correlations and experimental values previously reported. The nucleate boiling heat flux obtained from the present numerical model is under predicted in comparison to the Stephan and Abdelsalam correlation. Comparison of the computed wall void fraction against experimental values is done for the transition boiling region. At critical heat flux formation of long vapor column was seen while intermittent liquid surface contacts were seen in the transition boiling regime. The computed critical heat flux value is lower than that obtained from the correlation of Maracy and Winterton.
Solar Concentrator Structural Optimization: A Variable Beam Cross Section Design
Authors: Yang Moucun , Zhu Yuezhao , Fu Wei , Pearce Garth , Taylor Robert A.
Published: October 2017

The design and construction of solar concentrators heavily affects their cost, heat utilization and optical efficiency. Current trough concentrators support the reflector with an equivalent uniform beam configured from a metal grid sub-structure. Under gravity and wind loads, the support-structure stress distribution varies as a function of position of the structure and the tracking angle. In the conventional design, there is ample surplus stiffness and strength designed into some beams of the structure, which increases the overall weight and cost of the structure. This paper describes an approach towards structural optimization of trough concentrators (with the Eurotrough design taken as an example, that means that the safety factors and structure is similar with Eurotrough design) using a variable cross section beam. The main improvement of this approach comes from keeping the beams rigid and strong near the two ends (at the torque box structure) while allowing the middle of the structure to be relatively weak. Reducing the cross-sectional area of the central beams not only reduces amount of material needed for the structure but also reduces the deflection of the reflector. The simulated results show that the concentrator’s structural weight (including the torque box, endplates and cantilever arms) and the maximum displacement of the reflector are reduced about 15.3% (about 151.2kg per 12-metre long element) and 15.5%, respectively. This represents a meaningful capital and installation cost savings while at the same time improving the optical efficiency.