bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of Increased Tooth Clearance on the Performance of a Labyrinth Seal With Oil-Rich Bubbly Laminar Flow
Authors: Zhang Min , Childs Dara W. 
Published: July 2021

Abstract
In recent years, multiphase pumps have become more and more popular because of the capability to simplify the process, reduce the footprint, and lower the cost. To compensate for the axial thrust force, an annular seal is normally used as a balance piston seal, and the labyrinth seal is one of the choices. A typical labyrinth seal consists of a surface with teeth and a smooth surface. The teeth are either on the rotor or the stator. To protect the machine, one side (either the teeth or the smooth surface) is made of a material that can be safely sacrificed during a rub. After the rub, the teeth clearance is increased. This paper studies the impact of the increased teeth clearance on the performance of the labyrinth seal under oil-rich bubbly flow conditions. The test fluid is a mixture of silicone oil (PSF-5cSt) and air with inlet gas volume fraction (GVF) up to 9%. Tests are conducted with pressure drop (PD) = 34.5 bars, rotor speed ω = 5 krpm, and radial tooth clearance Cr = 0.102 mm and 0.178 mm. Test results show that, for all test conditions (before and after injecting air bubbles into the oil flow), increasing Cr from 0.102 mm to 0.178 mm increases the mass flow rate by about 40% but barely changes the test seal's rotordynamic coefficients, i.e., the increased tooth clearance would not change the pump vibration performance.
Forced Response Excitation Due to the Stator Vanes of Two and Three Compressor Stages Away
Authors: Miura Toshimasa , Sakai Naoto , Kanazawa Naoki , Nakayama Kentaro 
Published: July 2021

Abstract
State-of-the-art axial compressors of gas turbines employed in power generation plants and aero engines should have both high efficiency and small footprint. Thus, compressors are designed to have thin rotor blades and stator vanes with short axial distances. Recently, problems of high cycle fatigue (HCF) associated with forced response excitation have gradually increased as a result of these trends. Rotor blade fatigue can be caused not only by the wake and potential effect of the adjacent stator vane, but also by the stator vanes of two, three, or four compressor stages away. Thus, accurate prediction and suppression methods are necessary in the design process. In this study, the problem of rotor blade vibration caused by the stator vanes of two and three compressor stages away is studied. In the first part of the study, one-way fluid structure interaction (FSI) simulation is carried out. To validate the accuracy of the simulation, experiments are also conducted using a gas turbine test facility. It is found that one-way FSI simulation can accurately predict the order of the vibration level. In the second part of the study, a method of controlling the blade vibration is investigated by optimizing the clocking of the stator vanes. It is confirmed that the vibration amplitude can be effectively suppressed without reducing the performance. Through this study, ways to evaluate and control the rotor blade vibration are validated.
Carbon Fiber-Based Twisted and Coiled Artificial Muscles (TCAMs) for Powered Ankle-Foot Orthoses
Authors: Kotak Parth , Wilken Jason M. , Anderson Kirsten M. , Lamuta Caterina 
Published: July 2021

Abstract
Ankle foot orthoses (AFOs) control the position and motion of the ankle, compensate for weakness, and correct deformities. AFOs can be classified as passive or powered. Powered AFOs overcome the limitations of passive AFOs by adapting their performance to meet a variety of requirements. However, the actuators currently used to power AFOs are typically heavy, bulky, expensive, or limited to laboratory settings. Thus, there is a strong need for lightweight, inexpensive, and flexible actuators for powering AFOs. In this technical brief, carbon fiber/silicone rubber (CF/SR) twisted and coiled artificial muscles (TCAMs) are proposed as novel actuators for powered AFOs. CF/SR TCAMs can lift to 12,600 times their weight with an input power of only 0.025 W cm−1 and are fabricated from inexpensive materials through a low-cost manufacturing process. Additionally, they can provide a specific work of 758 J kg−1 when an input voltage of 1.64 V cm−1 is applied. Mechanical characterization of CF/SR TCAMs in terms of length/tension, tension/velocity, and active-passive length/tension is presented, and results are compared with the performance of skeletal muscles. A gait analysis demonstrates that CF/SR TCAMs can provide the performance required to supplement lower limb musculature and replicate the gait cycle of a healthy subject. Therefore, the preliminary results provided in this brief are a stepping stone for a dynamic AFO powered by CF/SR TCAMs.
Proposal of an Improved Contactless Measurement Method Using an Advanced Light Emitting Diode Displacement Sensor for Vibration Stress of Piping Systems
Authors: Maekawa Akira , Tsuji Takashi , Takahashi Tsuneo 
Published: July 2021

Abstract
This paper proposes an improved contactless measurement method for vibration stress of piping systems, by which the measurement time is shorter and the measuring works are more simple. The proposed method includes two processes, in which the bending mode shape of piping vibration is identified by a transmission-type light emitting diode (LED) displacement sensor and the vibration stress is calculated based on beam theory using the approximated curve of the bending mode shape. The proposed method uses one advanced LED displacement sensor to measure the vibration stress in contrast to multiple conventional LED sensors, which must be used in the previous method developed by the authors. Therefore, the measuring system could be reduced in size and a light-weight and portable measurement instrument was developed. The measurement accuracy and reliability of the new method were validated by the vibration experiment using a mockup piping system.
Evaluation of the Influence of 1,4-Dioxane and Exhaust Gas Recirculation on the Performance and Emission Values of a Diesel Engine Fuelled With Low Viscous Biofuel Blend
Authors: Samuel Panithasan Mebin , Venkadesan Gnanamoorthi 
Published: July 2021

Abstract
The world greatly relies on the usage of liquid fuels for its energy needs, especially in the transportation sector, which is very high in developing countries. In countries like India, diesel fuel is mainly used for all its transportation requirements (considering its higher efficiency), leading to higher pollution. Many kinds of research works are conducted to find a replacement for diesel fuel. In which biodiesel is considered to be a potential replacement for diesel. However, the challenges like higher viscosity, lower calorific value, higher NOx emission stands as a huge barrier. To overcome this, this study proposes using a low viscous biofuel, which has a higher calorific value close to diesel. To reduce NOx emission, the exhaust gas recirculation (EGR) technique is used in this study. A single-cylinder, constant speed, water-cooled stationary engine setup is used for this study. 20% of pine oil is blended with diesel, and 10ml of 1,4, dioxane additive is added. These blends are tested in the engine for different load conditions (0, 25, 50, 75 and 100%) with and without 10% EGR. The results showed that pine oil usage negatively affected the performance characters but significantly reduced CO, HC, and Smoke emissions (15.94, 17.04 and 2.47% respectively). The 10ml of 1,4, dioxane further enhanced this reduction (32.61, 28.15 and 4.36% respectively). The 10% EGR usage negatively affected both performance and emission characters, but it reduced NOx emissions significantly (11.53%). This study provides an integrated way to overcome the challenges seen in biodiesel usage with a low viscous biofuel and exhaust gas recirculation technique.
Experimental Investigation of Latent Heat Thermal Energy Storage System Enhanced by Annular and Radial Fins
Authors: Tiari Saeed , Hockins Addison , Moretti Samantha 
Published: July 2021

Abstract
In the current study, the thermal characteristics of a latent heat thermal energy storage system enhanced with annular and radial fins are investigated experimentally. Rubitherm RT-55 is used as the phase change material (PCM) and is enclosed within a vertical cylindrical container. Water is used as the heat transfer fluid (HTF) which is circulated in a copper pipe that passes through the center of the container. The hot HTF is circulated through the system until the entire mass of solid PCM inside the container is melted. Twelve k-type thermocouples are inserted into the container at different levels to monitor the PCM temperature during the charging processes. A thermal imaging camera is used to take thermal images of the latent heat thermal energy system as it operates. The effects of different number of annular and radial fins attached to the central pipe on the thermal performance of the latent heat thermal energy storage system during the charging processes have been studied. It was found that the inclusion of 10 and 20 annular fins decreased the charging time by 79.5% and 82.8%, respectively. The two radial fin designs of 4 fins and 8 fins were assessed and found to decrease charging time by 81.9% and 86.6%, respectively.
A Comparative Study of the Influence of Different Wake Models on Wind Farm Layout Optimization
Authors: Yang Puyi , Najafi Hamidreza 
Published: July 2021

Abstract
The accuracy of analytical wake models applied in wind farm layout optimization (WFLO) problems plays a vital role in the present era that the high-fidelity methods such as LES and RANS are still not able to handle an optimization problem for large wind farms. Based on a verity of analytical wake models developed in the past decades, FLOw Redirection and Induction in Steady State (FLORIS) has been published as a tool integrated several widely used wake models and the expansions for them. This paper compares four wake models selected from FLORIS by applying three classical WFLO scenarios. The results illustrate that the Jensen wake model is the fastest one but the defect of underestimation of velocity deficit is obvious. The Multi Zone model needs to be applied additional tunning on the parameters inside the model to fit specific wind turbines. The Gaussian-Curl wake model as an advanced expansion of the Gaussian wake model does not perform an observable improvement in the current study that the yaw control is not included. The default Gaussian wake model is recommended to be used in the WFLO projects which implemented under the FLROIS framework and has similar wind conditions with the present work.
Performance Considerations for Ground Source Heat Pumps in Cold Climates
Authors: Garber-Slaght Robbin 
Published: July 2021

Abstract
Remote, cold climates present challenges to finding safe and affordable space heating options. In Alaska, residential ground source heat pumps (GSHPs) have been gaining in popularity, even though there is little research on their long-term performance or their effect on soil temperatures. The extended heating season and cold soils of Alaska provide a harsh testing ground for GSHPs, even those designed and marketed for colder climates. The large and unbalanced heating load in cold climates creates a challenging environment for GSHPs. In 2013 the Cold Climate Housing Research Center (CCHRC) installed a GSHP at its Research and Testing Facility (RTF) in Fairbanks, Alaska. The heat pump replaced an oil-fired condensing boiler heating an office space via in-floor hydronic radiant piping. The ground heat exchanger (GHE) was installed in moisture-rich silty soils underlain with 0°C permafrost. The intent of the project was to observe and monitor the system over a 10-year period to develop a better understanding of the performance of GSHPs in sites with permafrost and to help inform future design. As of this writing, the heat pump system has been running for eight heating seasons. The efficiency in those eight heating seasons has been variable with ups and downs that have been difficult to explain. This paper seeks to understand the variability in performance as well as make recommendations for GSHP use in other cold climates.
Sensitivity Analysis of Occupant Preferences on Energy Usage in Residential Buildings
Authors: Pattawi Kaleb , Munankarmi Prateek , Blonsky Michael , Maguire Jeff , Balamurugan Sivasathya Pradha , Jin Xin , Lee Hohyun 
Published: July 2021

Abstract
Residential buildings, accounting for 37% of the total electricity consumption in the United States, are suitable for demand response (DR) programs to support effective and economical operation of the power system. A home energy management system (HEMS) enables residential buildings to participate in such programs, but it is also important for HEMS to account for occupant preferences to ensure occupant satisfaction. For example, people who prefer a higher thermal comfort level are likely to consume more energy. In this study, we used foresee™, a HEMS developed by the National Renewable Energy Lab (NREL), to perform a sensitivity analysis of occupant preferences with the following objectives: minimize utility cost, minimize carbon footprint, and maximize thermal comfort. To incorporate the preferences into the HEMS, the SMARTER method was used to derive a set of weighting factors for each objective. We performed week-long building energy simulations using a model of a home in Fort Collins, Colorado, where there is mandatory time-of-use electricity rate structure. The foresee™ HEMS was used to control the home with six different sets of occupant preferences. The study shows that occupant preferences can have a significant impact on energy consumption and is important to consider when modeling residential buildings. Results show that the HEMS could achieve energy reduction ranging from 3% to 21%, cost savings ranging from 5% to 24%, and carbon emission reduction ranging from 3% to 21%, while also maintaining a low thermal discomfort level ranging from 0.78 K-hour to 6.47 K-hour in a one-week period during winter. These outcomes quantify the impact of varying occupant preferences and will be useful in controlling the electrical grid and developing HEMS solutions.
Cost and Technical Profiling of Geothermal District Heating Using GEOPHIRES and Comsof Heat Simulation Software
Authors: Fry Nicholas 
Published: July 2021

Abstract
The heating of commercial and residential buildings in the United States is mostly dependent on fossil fuel sources such as natural gas. GeoVision, a U.S. Department of Energy study from 2019, found a tremendous market potential for geothermal district heating systems (GDHS). To date, most of the GDHS development, conventional or with heat pumps, has taken place in China and Europe. GDHS component manufacturing capacity in North America is not mature and significant increases in construction would likely require importation of European goods. This project attempts to expand market intelligence by simulating the cost for installation of modern European pipe, control, substations, and heat interface units serving a conventional GDHS in Helena, Montana. A shallow, low-temperature (&lt; 75°C) surface manifestation, 2 kilometers from the service area, is the heat source.
Three production simulations with varying wellhead flow rates were made, then projected across a heat network using two simulation tools: GEOthermal energy for Production of Heat and electricity (GEOPHIRES) and Comsof Heat. Correlations between flow rates, heat losses, utilization factors, and costs indicate important variables for developer consideration. A cost profile was made using the average of these simulations. Exploiting a shallow, low-temperature heat source for a GDHS often requires greater investment in the heat network than the wellfield.
This project suggests North American geothermal developers must prepare for interdisciplinary GDHS projects that fall outside of their current business models. European DH operators and manufacturers can provide surface system expertise and materials while North America assesses subsurface exploitation targets. Bringing European DH professionals together with North American geothermal experts may help realize the potential of the GeoVision study, unlocking new business opportunities.
Effects of Vortex Generators on the Impingement Jet Arrays Heat Transfer
Authors: Yang Yue , Mao Junkui , Wang Feilong 
Published: July 2021

Abstract
In the jets array cooling system of the gas turbine, the downstream jets will be deflected by the crossflow and the heat transfer in the downstream will be suppressed. In this paper, the rectangular vortex generators are arranged in the jet arrays to enhance the jet impingement heat transfer. Through the numerical simulations, the configuration of rectangular vortex generators (Common-flow-down CFD and Common-flow-up CFU) and the relative position (l2) between the impingements and the rectangular vortex generators are studied. The results show that both of configurations are beneficial to the suppression of the crossflow and enhance the heat transfer in the downstream. The maximum enhancement of the whole regional average Nusselt numbers in CFD-VGs configuration can reach up to 9.09% with lower than 5% increase of the pressure loss and that in CFU-VGs configuration can reach up to 10.8% with lower than 4.8% increase of the pressure loss. From the perspective of the whole regional average Nusselt numbers and the overall thermal efficiency, the CFD-VGs with l2 = 0 has the best performance. However, from the perspective of the whole regional average Nusselt numbers, the CFU-VGs with l2 = 0 has the best performance, while from the perspective of the overall thermal efficiency, the CFU-VGs with l2 = 3 has the best performance.
Machine Learning for Chaotic Rayleigh Transitions
Authors: Tribelhorn Ben , Dillon H. E. 
Published: July 2021

Abstract
This paper is a preliminary report on work done to explore the use of unsupervised machine learning methods to predict the onset of turbulent transitions in natural convection systems. The Lorenz system was chosen to test the machine learning methods due to the relative simplicity of the dynamic system. We developed a robust numerical solution to the Lorenz equations using a fourth order Runge-Kutta method with a time step of 0.001 seconds. We solved the Lorenz equations for a large range of Raleigh ratios from 1–1000 while keeping the geometry and Prandtl number constant. We calculated the spectral density, various descriptive statistics, and a cluster analysis using unsupervised machine learning. We examined the performance of the machine learning system for different Raleigh ratio ranges.
We found that the automated cluster analysis aligns well with well known key transition regions of the convection system. We determined that considering smaller ranges of Raleigh ratios may improve the performance of the machine learning tools. We also identified possible additional behaviors not shown in z-axis bifurcation plots. This unsupervised learning approach can be leveraged on other systems where numerical analysis is computationally intractable or more difficult.
The results are interesting and provide a foundation for expanding the study for Prandtl number and geometry variations. Future work will focus on applying the methods to more complex natural convection systems, including the development of new methods for Nusselt correlations.
Near Infrared Radiative Properties of Thermal Barrier Coatings
Authors: Wang Yao , Hsu Pei-feng , Wu Yingsang 
Published: July 2021

Abstract
Thermal barrier coatings are widely used in gas turbines to protect the gas turbine metal components against very high combustion product temperature. To improve energy efficiency, higher combustion temperatures are needed. A limiting factor at present is the stability under extreme and prolonged heating of thermal barrier coatings. The coatings are typically made by the air plasma sprayed process in which fine particles of yttria-stabilized zirconia (YSZ) are melted or partially melted and ejected from plasma jet at high speed onto the bond coated substrate metal. With increasing combustion temperature and pressure in the modern gas turbine engines radiative heat transfer is becoming an important portion of the overall heat transfer in the thermal barrier coating. This study has demonstrated that the commonly used Kubelka-Munk method in the radiative property reduction from the measured transmittance and reflectance spectra of YSZ coatings will incur inaccurate result when the coating optical thickness is not sufficiently large. An alternative method — the discrete ordinates method with the asymmetric spherical ring angular quadrature — is used instead. The absorption and scattering coefficients of air plasma sprayed YSZ films are determined over the wavelength range from 1 to 2.6 μm at room temperature. Over this near infrared wavelength range, the scattering coefficient decreases with the increasing wavelength and the absorption coefficient is very small overall. The pore size distributions before and after the 50-hr temperature gradient, thermal cycling are compared. The sintering effect as well as the crack growth will impact the coating radiative properties. These results point to a clear need for better understanding of the radiative heat transfer process, which includes the microstructure-property relationship, progressive changes of the radiative properties with the operation condition and time.
The Effects of Bending on Heat Pipes
Authors: Mahdavi Mahboobe , Faghri Amir 
Published: July 2021

Abstract
A comprehensive three-dimensional numerical model is developed to evaluate the effect of bending on water-copper cylindrical heat pipes. This model distinguishes itself from other models by its ability to uniquely determine the operating pressure of the heat pipe based on the operating and physical conditions. The effects of one 90-degree bend and two 90-degree bends are evaluated on the performance of a heat pipe. Two types of wicks are considered: a screen mesh wick and a sintered powder wick. The obtained results show that bending does affect the vapor pressure drop; however, the changes are not significant when compared to the operating pressure of the heat pipe. If the bending is performed in a manner where the wick is not damaged and the liquid is not blocked from returning to the evaporator, the performance of the heat pipe will not be affected significantly. In addition, if the heat pipe is operating in the horizontal direction, where both evaporator and condenser legs are at the same level, bending does not affect the liquid pressure drop significantly; however, the screen mesh does provide a higher capillary limit. The results also showed that the effects of gravity can be important when bending heat pipes and consideration should be given for this factor. When the bent heat pipe works against gravity, the sintered powder wick heat pipes showed higher capillary limits.