bluuebunny/crossref_metadata_2025 huggingface dataset:
Adolescents' capacity to take action on obesity: A concurrent controlled before‐and‐after study of the European CO‐CREATE project
Authors: Herstad Sondre Haugsbø , Grewal Navnit Kaur , Banik Anna , Klepp Knut‐Inge , Knai Cecile , Luszczynska Aleksandra , Mendes Sofia , Rito Ana , Rutter Harry , Lien Nanna
Published: September 2023

This study evaluated the effect on reported readiness for action and attitudes toward obesity prevention among older adolescents (mean age 17) who took part in a youth‐led participatory action research European initiative (CO‐CREATE Youth Alliances) compared with a comparison group that acted as controls. This was a concurrent before‐and‐after controlled study across five countries and took place between September 2019 and October 2020. Adolescents (n = 159) recruited from schools and youth organizations came together with researchers and formed 15 Youth Alliances. An online questionnaire measuring their readiness for action and attitudes toward obesity prevention was administered. Alliance members (n = 62) who filled in the questionnaire at both baseline and postinitiative, and adolescents from the comparison group (n = 132) who completed the questionnaire twice were included in the main analysis. Two‐level linear mixed models controlling for country‐related variance were fitted. Alliance members scored significantly higher than the comparison group on two factors in each of the readiness for action, responsibility, and drivers of behavior concepts. The findings suggest that involving youth in co‐creating policies to prevent obesity may increase adolescents' readiness for action and promote a shift in adolescents' conceptualization of obesity from an individual perspective to a societal responsibility and drivers of behavior.
Learning from the CO‐CREATE project: A protocol for systems thinking across research (STAR)
Authors: Knai Cécile , Savona Natalie , Finegood Diane , Aguiar Anaely , Blanchard Laurence , Conway‐Moore Kaitlin , Helleve Arnfinn , Klepp Knut‐Inge , Lien Nanna , Luszczynska Aleksandra , Vlad Ioana , Rønnestad Alfred Mestad , Rutter Harry
Published: September 2023

The CO‐CREATE project aimed to work with young people to create, inform, and disseminate obesity‐preventive evidence‐based policies using a complex systems perspective. This paper draws lessons from this experience and proposes a protocol for embedding systems thinking within a research project. We first draw on existing systems thinking frameworks to analyze how systems thinking was translated across CO‐CREATE, including the flow and relationship between the work packages and in the methods used. We then take the lessons from CO‐CREATE and the principles of existing systems thinking frameworks—which focus on various points of intervention planning and delivery but not on research projects as a whole—to formulate a protocol for embedding systems thinking across a research project. Key lessons for future planning and delivery of systems‐oriented research projects include incorporating “boundary critique” by capturing key stakeholder (adolescent) values and concerns; working to avoid social exclusion; ensuring methodological pluralism to allow for reflection and responsiveness (with methods ranging from group model building, Photovoice, and small group engagement); getting policy recipients to shape key questions by understanding their views on the critical drivers of obesity early on in the project; and providing opportunity for intraproject reflection along the way.
Encouraging greater empowerment for adolescents in consent procedures in social science research and policy projects
Authors: Samdal Oddrun , Budin‐Ljøsne Isabelle , Haug Ellen , Helland Trond , Kjostarova‐Unkovska Lina , Bouillon Claire , Bröer Christian , Corell Maria , Cosma Alina , Currie Dorothy , Eriksson Charli , Felder‐Puig Rosemarie , Gaspar Tania , Hagquist Curt , Harbron Janetta , Jåstad Atle , Kelly Colette , Knai Cecile , Kleszczewska Dorota , Kysnes Bjarte Birkeland , Lien Nanna , Luszczynska Aleksandra , Moerman Gerben , Moreno‐Maldonado Concepcion , NicGabhainn Saoirse , Pudule Iveta , Rakic Jelena Gudelj , Rito Ana , Rønnestad Alfred Mestad , Ulstein Madeleine , Rutter Harry , Klepp Knut‐Inge
Published: September 2023

The United Nations Convention on the Rights of the Child emphasizes the importance of allowing children and adolescents to influence decisions that are important to them following their age and maturity. This paper explores the principles, practices, and implications around using parental versus child/adolescent consent when participating in social science research and policy development. Experiences from two studies are presented: The Confronting Obesity: Co‐creating policy with youth (CO‐CREATE) and the Health Behaviour in School‐aged Children (HBSC) study, a World Health Organization (WHO) Collaborative Cross‐National study. Although parental consent may be an important gatekeeper for protecting children and adolescents from potentially harmful research participation, it may also be considered an obstacle to the empowerment of children and adolescents in case they want to share their views and experiences directly. This paper argues that evaluation of possible harm should be left to ethics committees and that, if no harm related to the research participation processes is identified and the project has a clear perspective on collaborating with the target group, adolescents from the age of 12 years should be granted the legal capacity to give consent to participate in the research project. Collaboration with adolescents in the development of the research project is encouraged.
Plant secondary metabolite has dose‐dependent effects on bumblebees
Authors: Jones Patricia L. , Warburton Reed C. , Martin Kyle R.
Published: September 2023

The presence of secondary metabolites in flower nectar can mediate interactions between plants, pollinators, herbivores, and microbes. Milkweeds range in concentrations of cardenolides in flower nectar from ~ 1 to 100 ng μl–1. Using three different behavioral assays with bumblebees Bombus impatiens, we examined the impacts of the commercially available cardenolide ouabain at the range of concentrations at which cardenolides naturally occur in milkweeds. We show that after four days of exposure bees in consumption assays drank more of a nectar solution with a low ouabain concentration of 10 ng μl–1 than the control sucrose nectar, and over the course of the experiment bees consumed less of the 100 ng μl–1 ouabain solution than the control. Bee activity levels in Petri dish arena assays were not impacted by ouabain consumption, even at the highest concentrations; however, in free‐flying choice assays, bees preferentially visited artificial flowers containing 10 ng μl–1 ouabain more than flowers with sucrose control, or flowers with 100 ng μl–1 of ouabain. We therefore conclude that cardenolides may provide plants advantages to pollination at the low end of the naturally occurring range of concentrations for cardenolides, but may be costly to plants at the high end of the range. This research highlights that secondary metabolites in nectar may be under selection to be maintained at low concentrations, and species with high concentrations of secondary metabolites may be under conflicting selection pressures to maintain high circulating levels to deter herbivores at the cost of reduced pollination.
Effect of spinal cord stimulation on quality of life and opioid consumption in patients with failed back surgery syndrome
Authors: Elkholy Mohamed Amgad Elsayed , Nagaty Ahmed , Abdelbar Ahmad Elsayed , Simry Hisham Abdelsalam Mohamed , Raslan Ahmed M.
Published: September 2023

Background

Failed back surgery syndrome (FBSS) is a constellation of conditions occurring after spine surgeries, characterized by the presence of persistent or recurring low back pain that has a significant impact on patients' quality of life. Neuromodulation in the form of Spinal Cord Stimulation (SCS) is considered an indispensable treatment modality in the management of certain chronic pain conditions and it is showing good results for improvement in pain scores and functional capacity of the FBSS patients.

Objectives

To assess the change in pain scores, quality of life, and opioid medication intake as an outcome of neuromodulation procedures performed on patients diagnosed with failed back surgery syndrome, and to detect the post‐procedure complications.

Methods

A prospective observational study was conducted at two university hospitals in Egypt and the U.S.A. during the period from September 2019 to August 2021 for patients who underwent spinal cord stimulation procedures for FBSS with follow‐up period of at least 1 year. Patients who are 18 years old or older diagnosed with FBSS for more than 6 months and treated with spinal cord stimulation with successful trials during this time frame were included in the study.

Results

Thirty‐four patients were included in this study who had successful SCS trials and underwent permanent implantation of SCS devices with post‐procedure follow‐up period of 12 months. Patients showed a median pain numerical rating scale (NRS) of 7/10 at baseline with a median NRS of 4/10 through the follow‐up period. Basic mobility and daily activity scores assessed by activity measure of post‐acute care (AM‐PAC) showed significant improvement from the mean of 16.87 ± 2.74 at baseline to a mean of 19.97 ± 2.93 through follow‐up. In addition, there was a reduction in opioid medication usage. Post‐procedure complications was of low percentage with the most detected were battery dysfunction in 7 patients and pocket pain in 6 patients. Reoperation was needed in 13 patients with 4 needed just revision and 9 patients required a complete removal of the device.

Conclusion

Spinal cord stimulation is an effective modality of treatment for cases of failed back surgery syndrome with a statistically significant reduction in pain scores and a significant improvement in quality of life. Also, it achieves a recognizable reduction in opioid analgesic medications, with a reliable safety profile as detected with the recorded post‐procedure complications. However, randomized controlled trials with more patients and long‐term follow‐up are highly recommended.
Two problems on the distribution of Carmichael's lambda function
Authors: Pollack Paul
Published: September 2023

Let denote the exponent of the multiplicative group modulo n. We show that when q is odd, each coprime residue class modulo q is hit equally often by as n varies. Under the stronger assumption that , we prove that equidistribution persists throughout a Siegel–Walfisz‐type range of uniformity. By similar methods we show that obeys Benford's leading digit law with respect to natural density. Moreover, if we assume Generalized Riemann Hypothesis, then Benford's law holds for the order of a mod n, for any fixed integer .
Stability of polydisc slicing
Authors: Glover Nathaniel , Tkocz Tomasz , Wyczesany Katarzyna
Published: September 2023

We prove a dimension‐free stability result for polydisc slicing due to Oleszkiewicz and Pełczyński. Intriguingly, compared to the real case, there is an additional asymptotic maximizer. In addition to Fourier‐analytic bounds, we crucially rely on a self‐improving feature of polydisc slicing, established via probabilistic arguments.
El espejo de los ausentes
Authors: Ortegón Pérez Germán
Published: September 2023

El espejo de los ausentes es una apuesta narrativa que pone a dialogar a los objetos-sujetos de cada fotografía, con la cámara, conmigo como fotógrafo, con el papel, los pigmentos, el impresor, el marquetero y los espectadores. Las huellas de historias vividas o no vividas, reflejadas en las imágenes, despiertan nuestros sentidos aquí o en cualquier lugar del mundo. La propuesta visual que cruza la geografía de lugares y objetos, producto de los vejámenes de la guerra y el abandono, expone la ausencia de sus dueños, habla de otros que no están y que también nos habitan en diversos planos, hilando historias entre la memoria y el olvido.
Comprehensive Performance Analysis and Correlation Fitting of R744 and Its Mixture Used in Refrigeration and Heat Pump Systems
Authors: Sun Dahan , Liu Zhongyan , Zhang Hao , Zhang Xin
Published: September 2023

In this paper, the performance of R744 and R744/R170 mixed refrigerants in refrigeration and air source heat pump systems is studied by the simulation method. The change trend of coefficient of performance (COP), refrigeration/heat capacity, power consumption with discharge pressure, and the ratio of R744 is analyzed. In addition, optimal parameters of the system are discussed in detail with the change of evaporation temperature, outlet temperature of the gas cooler, and different proportions of R744. The results show that when the discharge pressure is 8–12 MPa, there is a critical ratio of R744. When the ratio of R744 is less than the critical ratio, the optimal pressure of the system increases with the increase of the ratio of R744, and when the ratio of R744 is higher than critical ratio, the optimal pressure of the system decreases with the increase of the ratio of R744. The change trend of COP with the ratio of R744 is first decreasing and then increasing, the optimal discharge temperature of the system increases with the increase of the ratio of R744, and the change trend of optimal discharge pressure with the ratio of R744 is first increasing and then decreasing. In addition, when the evaporation temperature is 233–253 K and the gas cooler outlet temperature is 308–318 K, the average optimal pressure and temperature of R744/R170 (25/75) are 11.64% and 8.06% lower than R744, respectively. And it is the most suitable refrigerant to replace R744. Finally, the optimal performance parameter correlations of R744, R744/R170 (25/75), R744/R170 (50/50), and R744/R170 (77.6/22.4) under the given conditions are fitted through the simulation data.
A Spatio-Temporal Prediction and Planning Framework for Proactive Human–Robot Collaboration
Authors: Flowers Jared , Wiens Gloria
Published: September 2023

A significant challenge in human–robot collaboration (HRC) is coordinating robot and human motions. Discoordination can lead to production delays and human discomfort. Prior works seek coordination by planning robot paths that consider humans or their anticipated occupancy as static obstacles, making them nearsighted and prone to entrapment by human motion. This work presents the spatio-temporal avoidance of predictions-prediction and planning framework (STAP-PPF) to improve robot–human coordination in HRC. STAP-PPF predicts multi-step human motion sequences based on the locations of objects the human manipulates. STAP-PPF then proactively determines time-optimal robot paths considering predicted human motion and robot speed restrictions anticipated according to the ISO15066 speed and separation monitoring (SSM) mode. When executing robot paths, STAP-PPF continuously updates human motion predictions. In real-time, STAP-PPF warps the robot’s path to account for continuously updated human motion predictions and updated SSM effects to mitigate delays and human discomfort. Results show the STAP-PPF generates robot trajectories of shorter duration. STAP-PPF robot trajectories also adapted better to real-time human motion deviation. STAP-PPF robot trajectories also maintain greater robot/human separation throughout tasks requiring close human–robot interaction. Tests with an assembly sequence demonstrate STAP-PPF’s ability to predict multi-step human tasks and plan robot motions for the sequence. STAP-PPF also most accurately estimates robot trajectory durations, within 30% of actual, which can be used to adapt the robot sequencing to minimize disruption.
Experimental Investigation of Transient Flow Phenomena in Rotating Compressor Cavities
Authors: Pernak Mikolaj J. , Nicholas Tom E. W. , Williams Jake T. , Jackson Richard W. , Tang Hui , Lock Gary D. , Scobie James A.
Published: September 2023

The clearance of compressor blade tips during aero-engine accelerations is an important design issue for next-generation engine architectures. The transient clearance depends on the radial expansion of the compressor discs, which is directly coupled to conjugate heat transfer in co-rotating discs governed by unsteady and unstable buoyancy-induced flow. This paper discusses an experimental and modeling study using the Bath Compressor Cavity Rig, which simulates a generic axial compressor at fluid-dynamically scaled conditions. The rig was specifically designed to generate heat transfer of practical interest to the engine designer and validate computational codes. This work presents the first study of the fundamental fluid dynamic and heat transfer phenomena under transient conditions. The rotating flow structure was seen to be characterized by coherent pairs of cyclonic/anticyclonic vortex pairs; the strength, rotational frequency, stability, and number of these unsteady structures changed with changing rotational Reynolds and Grashof numbers during the transients. These structures, measured by unsteady pressure transducers in the rotating frame of reference, were only present when the flow in the rotating cavity was dominated by buoyancy. Experimental correlations of both Nusselt number and radial mass flowrate in the rotating core were correlated against Grashof number. Remarkably, the experiments revealed a consistent correlation for both steady-state and transient conditions over a wide range of Gr. The results have a practical application to thermo-mechanical models for engine design.
Computational Fluid Dynamics Simulations of the Unsteady-State Flow Through a 1.5-Stage High-Work Turbine
Authors: Hansen Thorsten , Munktell Erik , Scheuerer Georg , Zhuang Qingyuan , Zwiener Kim
Published: September 2023

Behr et al. (2007, “Unsteady Flow Physics and Performance of a One-and-1/2-Stage Unshrouded High Work Turbine,” ASME J. Turbomach., 129, pp. 348–359) have experimentally investigated the unsteady-state flow and clocking effects in a 1.5-stage high-work turbine. Their test rig had a first stator row with 36 blades, a 54-bladed rotor at 2700 rpm, and a second stator row with 36 blades. They studied four different stator-clocking positions. The present paper computationally investigates the unsteady-state flow through the 1.5-stage turbine by performing computational fluid dynamics simulations with the simcenter star-ccm + software. The mathematical model of the simulations consisted of the ensemble-averaged unsteady-state mass, momentum, and energy equations complemented by the SST turbulence model. The authors applied a quality assessment procedure to the computational results before comparing them to the experimental data. They reported the numerical accuracy using the Grid Convergence Index (GCI). The results showed an increase in the calculated efficiencies of the unsteady-state over the steady-state results, bringing data and simulations closer. The total pressure contours at the rotor and second stator exit planes also agreed well with the experiments. Finally, the paper includes simulations of the effects of different stator-clocking positions. The results showed a similar response to the change in stator-clocking position as the experiments.
Phase Change Material for Thermal Energy Storage in Buildings Based on Sodium Sulfate Decahydrate and Disodium Hydrogen Phosphate Dodecahydrate
Authors: Turnaoglu Tugba , Kumar Navin , Hirschey Jason , Li Yuzhan , Akamo Damilola O. , LaClair Tim J. , Rios Orlando , Gluesenkamp Kyle R. , Graham Samuel
Published: September 2023

The worldwide increasing energy demand and 2050 net zero carbon target urge the globe to solve the energy challenge. Thermal Energy Storage (TES) has received significant attention in recent years as TES can be integrated into heating, ventilation, and air-conditioning systems where the energy would be stored during low-demand times and dispatched during high-demand times, resulting in controlling the peak load and improving energy savings. Material development is an integral part of TES. Salt hydrates are appealing due to cost-effectiveness, low- to no toxicity, and their high melting enthalpy, where energy is stored as latent heat. However, most salt hydrates are prone to incongruent melting (i.e., phase separation upon melting), which results in poor stability and large supercooling. In this study, we produced a highly stable novel energy storage material at a composition of 32 wt% sodium sulfate decahydrate, 52 wt% sodium phosphate dibasic dodecahydrate, 12 wt% milled expanded graphite, and 4 wt% borax. The material has a melting temperature of 28°C and an energy storage capacity of 167 kJ/kg with a supercooling of less than 3°C. The system showed no loss in energy storage performance after 150 cycles. The findings suggest that the novel energy storage material developed in this might be utilized in building heating and cooling applications.
Occupant Behavior Modeling for Building Performance Simulation: Review of the Recent Advances and Research Trends
Authors: Ahmed Omar , Sezer Nurettin , Ouf Mohamed , Wang Liangzhu (Leon) , Hassan Ibrahim Galal
Published: September 2023

Occupant Behavior (OB) is one of the key determinants in building energy use. To acquire accurate and reliable Building Performance Simulation (BPS) results, significant attention must be focused on the precise representation of OB in BPSs. The simplistic manner in which OB has usually been considered in BPSs, leads to a considerable performance gap between actual and simulated building energy use. Despite the presence of numerous review articles on various elements of OB, there is still a need for a thorough review that combines and evaluates recent studies in one article. In this review, the most recent research studies on different aspects of OB in BPS are aggregated, evaluated, and summarized. Available OB models and their application in BPS tools are outlined. A summary of the data collection methods utilized in OB modeling is provided. Common quantitative OB modeling methodologies in BPS are discussed. The primary uses, benefits, and shortcomings of each modeling methodology are explained. The available literature on the impact of various OB patterns and occupant interaction with building systems is assessed. In summary, this work presents the state-of-the-art OB models in BPS, allowing researchers and practitioners to select and implement appropriate OB models in accessible BPS tools.
Multiphase Modeling in a Parallel Plate Fluidized Bed Receiver for Concentrating Solar Power
Authors: Appaswamy Krutika , Schirck Jason , Punchi Wedikkara Chathusha , Morris Aaron , Ma Zhiwen
Published: September 2023

A novel high temperature particle solar receiver is developed by using a light trapping planar cavity configuration. As particles fall through the cavity, the concentrated solar radiation warms the boundaries of the receiver and in turn heats the particles. Particles flow through the system, forming a packed bed at the lower end, leaving the system from the bottom at a constant flow rate. Air is introduced to the system as the fluidizing medium to improve particle heat transfer and mixing. A laboratory scale cavity receiver is built and a near IR quartz lamp is used to provide flux to the vertical wall of the heat exchanger. The system is modeled using a continuum two-fluid method. The computational model matches the experimental system size and the particle size distribution is assumed monodisperse. A conduction model that accounts for the effects of solid concentration is implemented, and the heat flux boundary condition matches the experimental setup. Radiative heat transfer is estimated using a widely used correlation during the post-processing step to determine an overall heat transfer coefficient. The model is validated against testing data and achieves less than 30% discrepancy and a heat transfer coefficient greater than 1000 W/m2K.
Modeling Tool Development and Validation for Solar Industry Process Heat Using Particle Thermal Energy Storage
Authors: Gifford Jeffrey , Hamilton William , Wang Jing , Ma Zhiwen
Published: September 2023

U.S. industry sectors used 26.2 quadrillion Btu and accounted for 33% of total energy consumption in 2021 according to the Energy Information Agency. Industrial process heat accounts for 70% of industrial energy use with application temperatures ranging from 60°–1100°C. Industry processes, heavily relying on fossil fuels of cheap coal or natural gas, differ widely in operating conditions and load requirements which makes them difficult to standardize and imposes great challenges in decarbonization. Industry processes require reliable energy supply and vary widely in temperature ranges. Storing energy from renewable sources is necessary to improve reliability and to mitigate renewable intermittency when replacing carbon fuel-based heat supplies to achieve energy savings and reduce emissions. To this end, we have developed a particle-based thermal energy storage (TES) technology using low-cost and highly stable silica sand as a storage medium.

The economic and performance-based analysis is key for renewable energy sources to reliably supply industry process heat and ultimately displace fossil fuels for decarbonization. The diversified industrial processes need case-by-case analysis and design. Therefore, an adaptive modeling tool is key for renewable power with energy storage to meet industry demands. Thus, a modeling tool to simulate a solar industry process heat system using the particle TES has been developed using the object-oriented equation-based language Modelica and the commercial platform of Modelon Impact. The Modelica-based software tool provides a general simulation environment for the design of reliable solar energy sources integrated with TES for various industrial process applications at different temperatures for economic competence with fossil fuels such as coal and natural gases. It uses both customized and standard component modeling modules in Modelon libraries for the flexibility to be adapted to a specific energy demand application. The particle TES system establishes a uniform energy supply platform with an efficient heat exchanger and particle thermal energy reservoir integrated with renewable powers. The particle TES system can provide a wide temperature range and can have a large storage temperature difference that increases storage energy density; therefore, it can be an adaptable energy storage system integrated with renewable power to supply 24/7 heat for industry decarbonization.
Development of Electrified Transcritical R744 Heat Pump Systems for Northeastern Winter Markets
Authors: Garraway David , Rob S. M. Abdur , Turbeville Geoffrey , Ramamurthy Prathap , Gonzalez-Cruz Jorge E.
Published: September 2023

The main objective of this work is to develop a commercially feasible R744 HP system for the multi-family building sector for cold climates. The motivation behind this effort is the urgent need to bring into the markets, an efficient, low global warming potential air source heat pump system for cold-climates. It will aid in electrifying space heating, an essential strategy to decarbonize our society. We plan to address the efficiency of space heating for colder climates like the Northeast while being affordable and attractive to customers with existing gas or oil-powered systems. Our strategy aims to focus on optimizing the system using transcritical R744, this primarily means a revamp of various components, particularly the gas cooler. Gas coolers have been a challenge in terms of optimization with lower COPs than that of the more commonly used refrigerants. We have conducted an assessment of the viability of a staggered tubes design which allows for more efficient heat transfer between the R744 and air. This is quite important as the refrigerant operates at a much higher temperature (about 220–250°F) than seen in hydrofluorocarbon systems. Lowering the outlet temperature on the gas cooler side is a major step in providing a suitable design to be used in both residential and commercial buildings.

A Blackbox model has been designed, which allows for the simulation of different design options for optimization of the gas cooler design. A 3.5-ton capacity gas cooler with a COP above 2.5 has been designed to be built for lab testing conditions under simulated outdoor winter conditions.
Stochastic Method for Generating Residential Household Energy Models of Varying Income Level and Climate Zone for Testing Energy Fairness
Authors: Covington Hannah , Woo-Shem Brian , Wang Chenli , Roth Thomas , Nguyen Cuong , Lee Hohyun
Published: September 2023

Interest in residential energy management necessitates fairness testing of energy technology and policy developments. Considering income level is particularly important because increased utility bills put low-income households at higher risk of economic and health issues. This paper proposes a novel method for generating diverse household energy models of varying income level and climate zone, which can be used to test the fairness of residential energy developments. Models are stochastically generated using probability distributions based on data from national surveys. Included in the model are constant and time-variable features. Models capture the randomness inherent in the residential sector while still following realistic patterns in building structure, appliance stock, and occupant behavior. Validation of the model generation technique was done by comparing the energy consumption of simulated households to their counterparts in survey data. Models were validated with correlation analysis and t-tests, with the null hypothesis being that the slope found in correlation analysis was equal to 1. The null hypothesis could not be rejected (P > 0.05), and the data for all validation tests was very highly correlated (0.81 < r2 < 1.00).
Economic Feasibility Analysis of Developing Large-Scale Hybrid Solar-Wind Energy Plants on Farms and Ranches in South Texas
Authors: Giuffrida Jose , Cruz Mariee , Martinez-Gomez Erick , Ludtke Sophia , Li Hua
Published: September 2023

Renewable energy is considered one of the most promising strategies to reduce the use of fossil fuels in society. However, the initial cost is the concern that has been consistently identified as the main obstacle to market penetration of renewable energy systems. The purpose of this research is to evaluate the economic feasibility of the implementation of hybrid solar-wind energy plants on farms and ranches in South Texas. To carry out this study, four farms were selected in four different counties according to a set of criteria: distance to major cities, access to existing infrastructures including transmission lines and roads, available land, and wind and solar energy potentials in the area. One potential farm or ranch was selected from each county, and five different scenarios have been analyzed ranging from 100% wind to 100% solar for each selected farm or ranch. 100 MW was selected as the nameplate capacity of all the scenarios. HOMER Pro software was used to conduct the economic feasibility analysis. Net present cost, annual worth, present worth, return on investment, payback period, and levelized cost of energy were calculated and compared between different scenarios and different counties, which helped identify the best scenario for each county. The results also show the changes in the economic feasibility of developing large-scale hybrid solar-wind energy plants in different counties depending on the resources available in the area.
Status Quo of Heliostat Field Deployment Processes
Authors: Sment Jeremy , Zolan Alexander , Zhu Guangdong
Published: September 2023

Deployment of the solar field of a concentrating solar power plant is one of many factors that are integral to the success of a project. Knowledge transfer from outside the industry is limited due to the unique nature of heliostats, which redirect sunlight to a receiver with high precision while maintaining a high level of reflectivity. Moreover, learning from project to project can be limited due to the site-specific nature of projects, as the market includes several developers, each with their own unique design. In this paper, we discuss the state of the art in heliostat field deployment. We cover all the key aspects of deployment from project assessment to a fully functioning system, which include site selection, layout development, supply chain, assembly, site preparation and construction, calibration, and operations and maintenance.
Energy and Exergy Analysis of a Locally Developed 6W VRE Mobile Solar Charger
Authors: Gothaang Phodiso , Masoso Okatoseng T. , Nwaigwe Kevin N.
Published: September 2023

Following the intensified shift to a mixed-mode teaching and learning approach, a common challenge faced by students at the University of Botswana is a scarcity of charging points. Most charging points are indoors and not adequate for the student population. Even when available, indoor charging stations have no provision for chargers, hence the development of a mobile charging station equipped with all classes of chargers. In this study, an investigation of the energy and exergy performance of the locally developed 6W charging station, designed to improve charging convenience to the University of Botswana community, is undertaken. In carrying out the energy and exergy analysis, measurements of irradiance, wind speed, voltage, and current were undertaken for the existing system at intervals of 30 minutes and the results were analyzed. The solar station analysis indicated maximum and average energy efficiencies of 14.15 % and 11.92 % respectively, an exergy efficiency average of 5.44 %, and an exergy efficiency maximum of 12.16 %. The system achieved a power conversion efficiency of 12.9 % and a 1.24 % increase in the exergy efficiency after it was modified. At high module temperatures, the performance of the module was severely affected as the losses were high. Results achieved from the extensive performance analysis of the developed 6W system will help improve the energy and exergy performance of the system.
Experimental Study on the Effect of Uneven Heat Load on the Airflow Uniformity and Thermal Performance in a Small-Scale Data Center
Authors: Chang Ze-Wen , Wang Chi-Chuan
Published: September 2023

This study focuses the effect of uneven loading on the flow distribution across the data racks subject to a raised flow simulated small data center. A total of 10 data racks having a total thermal power of 50 kW is investigated. Tests are conducted for both semi-enclosed and fully enclosed cold aisle. For the even power case, all the data racks are operated with 5 kW, and for uneven case, one side of the data racks contains 7.5 kW heat generation for each data rack and the other side of data racks is 2.5 kW. The tested flowrates are 2.4 CMS and 3.4 CMS, respectively. Yet both semi-enclosed and fully enclosed cold aisle are tested in this study. It is found that for a higher supply volumetric flowrate of 3.4 or 2.4 CMS, the effect of maldistribution for even power case is rather small for the case of uniform heating load. Conversely, for semi-enclosed cold aisle, load, the difference in air volumetric flowrate on both sides has increased significantly, the hotter racks contain higher flowrate. The flow mal-distribution accounts for 6% at a flowrate of 3.4 CMS, and the difference is amplified to 12% for a smaller air flowrate of 2.4 CMS. For the fully enclosed cold aisle at a higher flowrate of 3.4 CMS subject to uneven heating load, the flow mal-distribution in both sides is insignificant. However, mal-distribution for uneven heating load may occur when the supplied flowrate is reduced to 2.4 CMS for the fully enclosed arrangement.
Effects of Natural Convection Mass Transfer on Drying Aerogels With Supercritical Carbon Dioxide
Authors: Abolorunke Friday N. , Dinh Hy , Karamanis Georgios , Remella Karthik , Hodes Marc
Published: September 2023

In manufacturing silica aerogels, the alcohol solvent is often extracted from a wet gel via supercritical carbon dioxide (SCCO2) drying to avoid, during the majority of the drying process, crossing the liquid-vapor phase boundary and thus prevent capillary forces from collapsing the delicate mesoporous structure. Our understanding of the relevant physics is limited due to the complex phenomena involved in this transport process. Therefore, a rigorous model that captures the underlying physics is essential to understand the transport phenomena for scaling up the drying process and reducing overall manufacturing costs. Several studies that model the SCCO2 drying of aerogel have ignored the effect of natural convection on the extraction rate. Here, we developed a 3D model to capture the natural convective mass transfer due to variation in fluid density as the concentration of carbon dioxide CO2 changes in an ethanol-carbon dioxide mixture. The geometry is an annular gel concentric with an open region where SCCO2 flows. The aerogel is modeled as a porous medium where the flow is modeled using Darcy’s law. We solve the compressible forms of the momentum, continuity, and species equations that govern and couple the transport in the open region and the porous medium. Also, we account for the variation in molecular diffusivity in the species transport equation using a mass-fraction-dependent diffusion coefficient. We show the changes in the mass transfer rates relative to the case where natural convection is ignored to be substantive.
Multimodal Characterization of Steady-State and Transient Boiling Heat Transfer
Authors: Pandey Hari , Dunlap Christy , Williams Amanda , Marsh Jackson , Hu Han
Published: September 2023

Boiling is a high-performance heat dissipation process that is central to electronics cooling and power generation. The past decades have witnessed significantly improved and better-controlled boiling heat transfer using structured surfaces, whereas the physical mechanisms that dominate structure-enhanced boiling remain contested. Experimental characterization of boiling has been challenging due to the high dimensionality, stochasticity, and dynamicity of the boiling process. To tackle these issues, this paper presents a coupled multimodal sensing and data fusion platform to characterize boiling states and heat fluxes and identify the key transport parameters in different boiling stages. Pool boiling tests of water on multi-tier copper structures are performed under both steady-state and transient heat loads, during which multimodal, multidimensional signals are recorded, including temperature profiles, optical imaging, and acoustic signals via contact acoustic emission (AE) sensors, hydrophones immersed in the liquid pool, and condenser microphones outside the boiling chamber. The physics-based analysis is focused on i) extracting dynamic characteristics of boiling from time lags between acoustic-optical-thermal signals, ii) analyzing energy balance between thermal diffusion, bubble growth, and acoustic dissipation, and iii) decoupling the response signals for different physical processes, e.g., low-to-midfrequency range AE induced by thermal expansion of liquids and bubble ebullition. Separate multimodal sensing tests, namely a single-phase liquid test and a single-bubble-dynamics test, are performed to reinforce the analysis, which confirms an AE peak of 1.5 kHz corresponding to bubble ebullition. The data-driven analysis is focused on enabling the early fusion of acoustic and optical signals for improved boiling state and flux predictions. Unlike single-modality analysis or commonly-used late fusion algorithms that concatenate processed signals in dense layers, the current work performs the fusion process in the deep feature domain using a multi-layer perceptron regression model. This early fusion algorithm is shown to lead to more accurate and robust predictions. The coupled multimodal sensing and data fusion platform is promising to enable reliable thermal monitoring and advance the understanding of dominant transport mechanisms during boiling.
Visualization-Aided Experimental Study of Thermal and Hydraulic Characteristics of Subcooled Flow Boiling of R-134A in a Microchannel Evaporator of a Pumped Two-Phase Loop
Authors: Kokate Rohan , Park Chanwoo
Published: September 2023

Conventional liquid cooling systems based on relatively inefficient forced convection are often not capable of handling high heat dissipation rates, especially for high-power electronics. A pumped two-phase loop (P2PL), which is an active two-phase cooling system, uses two-phase heat transfer (boiling and condensation) which is efficient and capable of handling high heat fluxes and is an order of magnitude higher than the forced convection of liquid cooling. In this study, an experimental investigation was performed using P2PL with R-134a for analyzing subcooled flow boiling in a microchannel evaporator. The ranges of mass flux are from 47.9 to 143.8 kg/m2-s, heat flux from 0 to 34 W/cm2, and quality from subcooled to critical heat flux. Flow visualization using a sight glass tube at the outlet of the evaporator was employed to investigate the influence of heat flux and mass flow rate on the two-phase flow patterns. Five two-phase flow regimes — nucleate boiling, bubbly flow, slug flow, stratified flow, annular flow, and misty flow — were identified based on the flow visualization which coincides perfectly with the slope changes of the boiling curve. The results of this study show that for a fixed wall temperature, in the convective boiling dominant region heat flux dissipation increases with mass flux, while it remains independent of mass flux in the nucleate boiling dominant region. A peak heat transfer coefficient was observed at a high exit vapor quality which corresponds to the annular flow regime with thin-film evaporation. The transient responses were used to characterize the single-phase and two-phase flows along with the critical heat flux (CHF) by investigating the dryout propagation in the microchannel. Further, the evaporator pressure drop increased linearly with heat flux in the two-phase regimes with the point of minimum pressure drop occurring at a heat flux beyond the Onset of Nucleate Boiling (ONB).
Phase Change Materials for Absorbing Peak Heat Loads in Aircraft: An Effectiveness-NTU Model for Predicting the Performance of Compact Heat Exchanger
Authors: Frank Julie Y. , Borman Duncan J. , Greiciunas Evaldas , Khan Amirul , Summers Jon
Published: September 2023

Thermal Management Systems (TMS) have been identified as one of the limiting factors in the design of future aircraft. A PCM heat exchanger could be added to TMS to help relieve the heat load on current technologies in aircraft. To date, compact PCM heat exchangers adapted for the use in aerospace have received limited attention in the literature. In this work, an effectiveness-NTU model for a PCM compact heat exchanger is proposed based on a simplified Stefan condition which could be used for the initial sizing of the PCM heat exchanger based on a given thermal loading profile. This approach significantly reduces the computational expense of the model when compared to solving the Stefan condition in an ODE system, while still accounting for the melting/solidification cycle length. As such, it is possible to directly obtain realistic dimensions for the PCM channel for a non-finned case from the model. Results show good energy conservation, which builds confidence in the model, and similar trends are observed to what has previously been described in CFD studies and experimental results.
Flow Interference Between Tandem Cylinder With Forced Convection in Staggered Position
Authors: Sarout Yuvraj , Islam Md. , Fatt Yap , Janajreh Isam
Published: September 2023

Flow-induced vibration of the filleted (rounded corner) oscillating cylinder is numerically investigated at Re = 150 and Pr = 0.7. The upstream cylinder (UC) is static while the downstream cylinder (DC) is elastically mounted which is allowed to vibrate in the transverse direction with a spacing ratio (L/D) = 5 and staggered angle (α) of 45°. Square cylinder is gradually filleted into the circular cylinder by changing r* (filleted radius) = 0 (square cylinder), 0.5, 0.75 and 1 (circular cylinder). Computations were carried out for reduced mass m* = 10 and varying reduced velocity (Ur) = 2, 4, 6, 8 and 10, structural damping constant is set to be zero which gives rise to high vibrational amplitude. Both cylinders were maintained at a constant temperature (T* = 1) while the upcoming flow is set to be at T* = 0. Vibrational characteristics are scrutinized with help of frequency characteristics of vibrating cylinder, vibrational amplitude, drag coefficient, lift coefficient and instantaneous z-vorticity contours. When natural frequency (fn) and vortex shedding frequency (fs) overlap, it causes synchronization or lock-in. The lock-in phenomenon usually occurred at Ur = 6 leading to higher vibrational amplitude for all geometries and dropped at Ur = 8 but persisted at Ur = 8 and 10 for r* = 0. Due to higher vibrational amplitude, the flow structure is more complicated at Ur ≥ 6. The maximum value of average Nusselt number (Nuavg) is at Ur = 6 for circular DC, whereas the minimum lies at Ur = 2 for square upstream cylinder. Generated results envisage results of flow interferences and forced convection of tube arrays in heat exchangers and marine structures. Understanding the mechanisms of flow-induced vibration in staggered cylinders is crucial for designing and optimizing these systems, as well as for ensuring their safe and reliable operation.
An Air Conditioning Cycle Using Lower Critical Solution Temperature Mixtures
Authors: Kocher Jordan D. , Menon Akanksha K. , Yee Shannon K.
Published: September 2023

The refrigerants and electricity consumption of existing air conditioning systems create significant greenhouse gas (GHG) emissions. This work describes a new air conditioning cycle that uses a lower critical solution temperature (LCST) liquid mixture to provide dehumidification and cooling. The cycle uses no refrigerants and is driven by low-grade heat. Upon heating, the LCST mixture phase separates into a water-rich phase and a water-scarce phase. After cooling both phases to ambient temperature, the water-scarce phase absorbs moisture from humid air (providing dehumidification), while the water-rich phase desorbs water to the outdoor air (providing evaporative cooling). In this work, we theoretically develop and experimentally demonstrate this cycle for the first time, using three different LCST mixtures. A ternary mixture of oleic acid, lidocaine, and water showed the best performance by dehumidifying air to ∼86% relative humidity, while the other LCST mixtures we investigated were only able to dehumidify to ∼98% relative humidity. While a relative humidity of 86% is still too high for thermal comfort, this first investigation of a new cycle motivates further investigation into other LCST mixtures. Future discoveries could lead to new mixtures that can reach lower humidities. To this end, we derive the thermodynamic equations that govern LCST liquid mixtures and determine the enthalpy and entropy of mixing that these hypothetical future LCST mixtures would possess.