bluuebunny/crossref_metadata_2025 huggingface dataset:
Two Methods for Studying the Developmental Significance of Family Structure Trajectories
Authors: Johnston Carol A. , Crosnoe Robert , Mernitz Sara E. , Pollitt Amanda M.
Published: December 2019

Objective

The objective of this research note is to use both sequence analysis (SA) and repeated‐measures latent class analysis (LCA) to identify children's family structure trajectories from birth through age 15 and compare how the two sets of trajectories predict alcohol use across the transition from adolescence into young adulthood.

Background

Contemporary family scholars have studied the influence of changes in family structure, often referred to as family structure instability, on child and adolescent development. Typically, this research has focused on either the number or type of transitions children have experienced, but statistical advances are increasing the viability of more complex person‐centered approaches to this issue, such as SA and LCA. The choice to use one approach or the other, however, is often discipline specific and relies on different assumptions and estimation techniques that may produce different results.

Method

The authors used data from the National Longitudinal Study of Youth–Child and Youth Cohort (N = 11,515) to identify clusters (using SA) and classes (using repeated‐measures LCA) that represented children's family structure trajectories from birth through age 15. Using two multiple‐group random slope models, the authors predicted alcohol use across adolescence and young adulthood (ages 16–24) among the clusters (Model 1) and classes (Model 2).

Results

The SA identified five clusters, but the LCA further differentiated the sample with more detail on timing and identified eight classes. The sensitivity to timing in the LCA solution was substantively relevant to alcohol use across the transition to young adulthood.

Conclusion

Overall, the SA is perhaps more suited to research questions requiring exclusive group membership in large, comparative analyses, and the LCA more appropriate when the research questions include timing or focus on transitioning into or out of single‐parent and stepfamily homes.
Call to expand teaching opportunities in rural family medicine
Authors: Walters Lucie , Worley Paul
Published: December 2019

To build and sustain rural medical workforces internationally, the authors of this commentary argue for innovative small group pedagogy tailored to remote and rural family medicine.
5‐Nonyloxytryptamine oxalate–embedded collagen–laminin scaffolds augment functional recovery after spinal cord injury in mice
Authors: Kalotra Shikha , Saini Vedangana , Singh Harpal , Sharma Anuradha , Kaur Gurcharan
Published: December 2019

Polysialic acid (PSA) is crucial for the induction and maintenance of nervous system plasticity and repair after injury. In order to exploit the immense therapeutic potential of PSA, previous studies have focused on the identification and development of peptide‐based or synthetic PSA mimetics. 5‐Nonyloxytryptamine (5‐NOT) has been previously reported as a PSA‐mimicking compound for promoting functional recovery after spinal cord injury in mice. In order to explore the neuroregeneration potential of 5‐NOT, the current study was based on a biomaterial approach using collagen–laminin (C/L) scaffolds. Inin vitrostudies, 5‐NOT was observed to promote neurite outgrowth, migration, and fasciculation in cerebellar neuronal cells, whereas in 3D cell cultures it showed more ramification and complex Sholl profiles. 5‐NOT promoted the survival and neurite length of cortical neurons when cocultured with glutamate‐challenged astrocytes. Inin vivostudies, spinal cord compression injury mice were used with immediate application of C/L hydrogels impregnated with 5‐NOT. C/L + 5‐NOT–treated mice demonstrated ∼75% of motor recovery 14 days after injury. Furthermore, this effect was shown to be dependent on the ERK–MAPK pathway and augmentation of cell survival. Thus, based on a biomaterial approach, our current study provides new insight for 5‐NOT–containing hydrogels as a promising candidate to speed up recovery after central nervous system injuries.
Stem cell‐derived conditioned media from human exfoliated deciduous teeth promote bone regeneration
Authors: Hiraki Tomoka , Kunimatsu Ryo , Nakajima Kengo , Abe Takaharu , Yamada Sakura , Rikitake Kodai , Tanimoto Kotaro
Published: December 2019

Objectives

Cleft lip and palate (CL/P) are common congenital orofacial anomalies. Autogenous iliac bone grafting closes alveolar cleft defects but requires surgical intervention. Mesenchymal stem cell culture supernatant can regenerate tissues via paracrine activity. However, little is known about the bone‐regenerative effects of stem cells from human exfoliated deciduous teeth (SHED) and conditioned media (CM). Our aim was to address this.

Materials and methods

Stem cells were isolated from primary tooth pulp and cultured. Defects were made in calvariae of immunodeficient mice and implanted with stem cell‐ or CM‐containing atelocollagen. Regenerated bone was analysed by microcomputed tomography, haematoxylin–eosin and Masson's trichrome staining. Vascular endothelial growth factor, CD31 and CD34 expression were confirmed by immunohistochemistry, and the presence of several proteins and growth factors was verified in SHED‐CM.

Results

Bone regeneration was enhanced in defects treated with stem cells and CM compared to that in controls 8 weeks after transplantation. Mature bone formation and angiogenesis were confirmed with CM but not with stem cells or in controls. Secretome analysis using multiple cytokine assays revealed that SHED‐CM contained tissue‐regenerating factors with roles in angiogenesis and osteogenesis.

Conclusion

CM non‐invasively regenerate bone and might be effective to reconstruct alveolar clefts in CL/P patients.
Examination and genetic analysis of a yellow‐green leaf mutant a269 of sweetpotato
Authors: Luo Zhongxia , Zhang Xiongjian , Chen Jingyi , Wang Zhangying , Huang Lifei , Zou Hongda , Yao Zhufang , Yang Yiling , Fang Boping
Published: December 2019

The genetic behaviour of a yellow‐green leaf sweetpotato mutant, a269, was analysed to prepare for genetic mapping and cloning of this mutant and to elucidate the regulation of its molecular mechanisms. The phenotypic stability of the mutant was observed under natural conditions, and photosynthetic pigments in mature leaves were measured. GN1323 and a269 were crossed and backcrossed. Genetic behaviour was assessed using phenotypic expression and segregation in F1, BC1 and BC2. The a269 leaves were yellow‐green at all stages after germination. The thylakoid lamellae of a269 were disorganized, had incomplete grana and were fewer compared with GN1323. The direct and reciprocal F1 populations had normal leaf colour, whereas the BC2 populations had yellow‐green leaves. Segregation of plants with normal‐ and yellow‐green leaf colour in the four BC1 populations satisfied the backcross segregation ratio of 11 : 1 for auto‐allohexaploids. The a269 mutant is stable, and its trait is controlled by one recessive nuclear locus.
Impact of sensory impairments on dementia incidence and symptoms among Japanese older adults
Authors: Maruta Michio , Tabira Takayuki , Sagari Akira , Miyata Hironori , Yoshimitsu Koji , Han Gwanghee , Yoshiura Kazuhiro , Matsuo Takashi , Kawagoe Masahiro
Published: December 2019

Background

Dementia and behavioural and psychological symptoms of dementia affect older adults' care‐need levels. With aging comes an increase in the incidence of sensory impairments, which promotes the development of dementia. We investigated the association between sensory impairments – visual impairment (VI), hearing impairment (HI), and dual sensory impairment (DSI), the behavioural and psychological symptoms of dementia, and dementia incidence.

Methods

This was a retrospective study that used Japanese long‐term care insurance certification data from 2010 to 2017 of City A. The 2190 older adults who did not have dementia in 2010 were classified into four impairment categories: VI, HI, DSI, and no sensory impairment. The incidence of dementia was examined using Kaplan–Meier survival analysis and log‐rank testing. Cox proportional hazards analysis was used to investigate the risk of developing dementia associated with sensory impairments, compared to the risk for no sensory impairment. Pearson's χ2 tests were used to compare the prevalence of behavioural and psychological symptoms of dementia among the four groups.

Results

HI and DSI were associated with a higher cumulative dementia incidence compared to no sensory impairment (log‐rank χ2 = 10.42; P  < 0.001, and log‐rank χ2 = 39.92; P  < 0.001, respectively), and DSI showed higher cumulative dementia incidence than HI (log‐rank χ2 = 11.37; P  = 0.001). Cox proportional hazards analysis showed that DSI is the greatest risk factor for developing dementia among sensory impairments (hazard ratio, 1.45; 95% CI, 1.22–1.71; P < 0.001). Older adults with VI had a significantly higher prevalence of day‐night reversal than the other groups.

Conclusions

Our results indicate that older adults with sensory impairments have a high incidence of dementia, with DSI presenting the greatest risk. Older adults with VI were found to be more likely to have day‐night reversal symptoms when dementia occurs.
Exploring the impacts of mindfulness and yoga upon childbirth outcomes and maternal health: an integrative review
Authors: Van der Riet Pamela , Francis Lyn , Rees Angela
Published: December 2019

Background

Foetal development and the long‐term outcomes of the infant are influenced by the intrauterine environment. Strategies to enhance maternal health in pregnancy are needed to improve health outcomes for childbearing women and babies, advancing the well‐being of our general population.

Aim

To synthesise the existing literature to determine the impacts of mindfulness and yoga practice upon birth outcomes and maternal health.

Methods

An integrative literature review using Whittemore and Knafl's framework was undertaken in 2016–2017. Two search strategies included database peer‐reviewed journal articles and ancestry searching, that is exploring the reference list of relevant research articles. After screening and checking the eligibility, a total of 12 articles were included in this review. Data analysis involved coding, visual displays, thematic analysis and comparison, and conclusion drawing.

Results

The results of this review identified a broad theme that mindfulness and yoga practice is associated with improved maternal mental health antenatally and postnatally. Subthemes have been presented under the central theme including the following: increased mindfulness correlates with decreased fear of childbirth; reduced symptoms of anxiety and depression; and supportive group settings found to be beneficial by pregnant women.

Conclusion

The evidence presented in this review suggests that mindfulness and yoga practice are feasible and cost‐effective interventions to enhance maternal mental health, particularly for women experiencing mental health challenges. Mindfulness and yoga practised regularly in the antenatal period can significantly promote the health of pregnant women and potentially their developing babies.
Asymptotic normality of generalized maximum spacing estimators for multivariate observations
Authors: Kuljus Kristi , Ranneby Bo
Published: December 2019

In this paper, the maximum spacing method is considered for multivariate observations. Nearest neighbor balls are used as a multidimensional analogue to univariate spacings. A class of information‐type measures is used to generalize the concept of maximum spacing estimators of model parameters. Asymptotic normality of these generalized maximum spacing estimators is proved when the assigned model class is correct, that is, the true density is a member of the model class.
Organizational Resources and the Gender Gap in Congregational Lay Leadership
Authors: Ferguson Todd W.
Published: December 2019

The purpose of this study is to examine how organizational resources affect the gender gap within lay (volunteer) leadership in religious congregations. Using institutional theory as a framework, this study situates congregations within a larger field of organizations competing for legitimacy. Congregations with higher levels of resources—such as wealthier members, better‐educated members, or larger memberships—are more likely to be connected to the core of the field and therefore more likely to have gender egalitarian practices in order to signal their legitimacy. Therefore, I hypothesize that women in resource‐rich congregations will have greater access to volunteer leadership positions than women in congregations that are resource deficient. I analyze 70,942 individuals in 344 religious congregations from the 2001 U.S. Congregational Life Survey using multilevel modeling. I show that religious congregations with more members, better‐educated attenders, and wealthier attenders have smaller gender gaps in volunteer leadership positions. Congregational resources can mitigate the gender gap in lay leadership, and women within resource‐rich organizations have greater access to positions of authority.
Chronic lymphopenia and neutropenia in a dog with large granular lymphocytic leukemia
Authors: Museux Kristina , Turinelli Vanessa , Rosenberg Dan , Rodriguez Piñeiro Isabel
Published: December 2019

T‐cell large granular lymphocytic leukemia (T‐cell LGLL) is the most common presentation of chronic lymphocytic leukemia (CLL) in dogs. Aleukemic or subleukemic leukemia is a particularly rare variation in both humans and dogs, where bone marrow proliferation is either not or only sparsely translated in the peripheral blood. Neutropenia is a prominent feature in cases of human T‐cell LGLL but is normally absent in canine CLL. This report describes a case of a dog presented with an almost 3‐year history of asymptomatic neutropenia, lymphopenia, and thrombocytopenia (without anemia). A bone marrow examination, the exclusion of infectious diseases, and clonality testing led to the diagnosis of subleukemic LGLL that responded well to therapy (death occurred 2.5 years later due to an unrelated cause).
In vitro antimicrobial efficacy of two medical grade honey formulations against common high‐risk meticillin‐resistant staphylococci and Pseudomonas spp. pathogens
Authors: Cremers Niels , Belas Adriana , Santos Costa Sofia , Couto Isabel , de Rooster Hilde , Pomba Constança
Published: December 2019

Background

Antimicrobial resistance is a problem in human and animal healthcare. Honey may be used for its wound healing properties and antimicrobial effects.

Objective

To investigate the antimicrobial activity of two commercially available medical grade honeys (MGHs) against Staphylococcus spp. and Pseudomonas spp. isolates.

Methods and materials

Two formulations, MGH1 (40% w/v honey) and MGH2 (80% w/v Manuka honey), were tested in vitro for minimal inhibitory concentrations (MIC) and minimal bactericidal concentrations (MBC) against 11 Staphylococcus and 11 Pseudomonas isolates at low [1.5 × 104 colony forming units (cfu)/well] and high (1.5 × 106 cfu/well) concentrations of inoculum, representing systemic and cutaneous bacterial loads during infection, respectively.

Results

MGH2 showed a lower MIC against staphylococci than MGH1, although this was not statistically significant. MGH1 had stronger bactericidal effects against staphylococci than MGH2, although this effect was statistically significant only at the higher bacterial concentration (P < 0.01). For Pseudomonas spp., MGH1 had significantly higher antimicrobial activity (both MIC and MBC) than MGH2 against all isolates tested and at both bacterial concentrations (P < 0.05).

Conclusions and clinical importance

Both MGHs were effective in vitro against common cutaneous pathogens including meticillin‐resistant staphylococci and Pseudomonas species. The higher efficacy of the MGH1 formulation against Pseudomonas and its consistent effects against staphylococci, while containing only half of the amount of honey compared to MGH2, invites further investigation of the mechanisms and clinical applications of MGH1.
Clinical utility, dose determination, and safety of ocular contrast‐enhanced ultrasonography in horses: A pilot study
Authors: Blohm Klaas‐Ole , Tichy Alexander , Nell Barbara
Published: December 2019

Objective

To determine efficacy of contrast‐enhanced ultrasonography (CEUS) using different sulfur hexafluoride (SF6) doses to assess blood flow and perfusion in equine eyes and to evaluate safety of SF6 in horses.

Procedures

Ocular B‐mode and contrast‐enhanced ultrasonography were performed bilaterally in nine sedated university‐owned horses. Intravenous SonoVue® bolus injections of 5, 10, 15, 20, 25, and 30 mL were administered for 2/18, 5/18, 6/18, 3/18, 1/18, and 1/18 eyes, respectively. Doses were increased based on ascending bodyweight. Each eye within one horse was examined utilizing a different dose. Qualitative blood flow and quantitative perfusion were analyzed. Heart and respiratory rates were monitored nonsedated, sedated, and during first and second minutes of CEUS.

Results

Qualitative contrast enhancement (CE) was visible in 7/9 animals. Quantitative CE was measurable bilaterally in four horses, unilaterally in three individuals, and not detected in two animals. In all horses with unilateral CE, the positive eye received the higher dose. Fifteen mL dose resulted in significantly shorter time to peak than 10 mL (P < .05). Peak intensity, maximum signal increase, and corresponding area under the curve were significantly higher for 15 and 20 mL doses compared with 10 mL (P < .05). Uveal and retinal tissues were enhanced frequently. Twenty‐five and 30 mL doses revealed no CE. Only sedation reduced heart rates significantly (P < .05). Clinically relevant changes in respiratory rates or adverse reactions following SF6 application were not observed.

Conclusions

Contrast enhancement was in most instances dose‐dependent. Fifteen mL appeared appropriate to assess equine ocular perfusion. The reliability in horses remains questionable; however, CEUS was well‐tolerated.
On the Nonlinear Snap-Through of Arch-Shaped Clamped–Clamped Bistable Beams
Authors: Zhao Jian , Zhang Jian , Wang K. W. , Cheng Kai , Wang Hongxi , Huang Yu , Liu Pengbo
Published: December 2019

Bistable compliant elements offer excellent advantages in many applications ranging from high precision sensing to energy harvesting. The essential nonlinear mechanics of such elements are strongly coupled with their buckling mode, geometric parameters, and loading conditions. The force–displacement plot of bistable curved beams could contain a displacement limit point, which cannot be well modeled by the commonly used smooth cubic function and would cause operational problems due to incorrect predictions of the bistability. In this technical brief, the nonlinear bistable mechanics of a compliant curved beam with both ends fixed is analyzed based on the large deflection finite element theory. By using the multistep displacement loading method, the deformation behaviors and their transition from symmetric to asymmetric modes are numerically studied, which provides insights into the force–displacement curve and the multiple snapping pathways. Furthermore, the influences of the structure parameters on bistable mechanics are analyzed, and a quality factor for identifying the occurrence of displacement limit points is introduced for different loading conditions. Finally, a method for achieving a single smooth snapping pathway is proposed, providing a theoretical basis to the design and control of the bistable compliant structures.
Numerical Predictions of Flow Structures and Film Cooling Effectiveness Values of a Turbine Vane: Effects of Secondary Holes
Authors: Zhu Rui , Simon Terrence W. , Xie Gongnan
Published: December 2019

In modern gas turbines, film cooling is the most common and efficient way to provide thermal protection for hot components. Secondary holes to a primary film cooling hole are used to improve film cooling performance by creating anti-kidney vortices, a technique that has been well documented using flat plate models. This study aims to evaluate the effects of secondary holes on film cooling effectiveness over an airfoil. The film cooling performance and flow fields of a row of primary holes with secondary holes on the pressure side and suction side of a C3X vane are numerically investigated and compared with the results of a single row of cylindrical holes and two rows of staggered cylindrical holes. Cases with different blowing ratios are analyzed. It is shown from the simulation that film cooling effectiveness of primary holes with secondary holes is much better than with a single row of cylindrical holes, and slightly better than with two rows of staggered holes on both pressure side and suction side, with the same amount of coolant usage and blowing ratio. The enhancement is higher on the pressure side than on the suction side. The results show that adding secondary holes can enhance film cooling effectiveness by creating anti-kidney vortices, which will weaken jet lift-off from the primary holes caused by the kidney vortex pair, especially at higher blowing ratios. In addition, film coverage of primary holes with secondary holes is wider and persists further downstream than for a single row of cylindrical holes.
Electrowetting-Based Coalescence of Droplets During Dropwise Condensation of Humid Air
Authors: Wikramanayake Enakshi , Bahadur Vaibhav
Published: December 2019

Dropwise condensation yields higher heat transfer coefficients by avoiding the thermal resistance of the condensate film, seen during filmwise condensation. This work explores further enhancement of dropwise condensation heat transfer through the use of electrowetting to achieve faster droplet growth via coalescence of the condensed droplets. Electrowetting is a well understood microfluidic technique to actuate and control droplets. This work shows that AC electric fields can significantly enhance droplet growth dynamics. This enhancement is a result of coalescence triggered by various types of droplet motion (translation of droplets, oscillations of three phase line), which in turn depends on the frequency of the applied AC waveform. The applied electric field modifies droplet condensation patterns as well as the roll-off dynamics on the surface. Experiments are conducted to study early-stage droplet growth dynamics, as well as steady state condensation rates under the influence of electric fields. It is noted that this study deals with condensation of humid air, and not pure steam. Results show that increasing the voltage magnitude and frequency increases droplet growth rate and overall condensation rate. Overall, this study reports more than a 30 % enhancement in condensation rate resulting from the applied electric field, which highlights the potential of this concept for condensation heat transfer enhancement.
Effectiveness of Intermittent Personalized Ventilation Assisting Chilled Ceiling in Protecting Occupants Against Active Particles
Authors: Al-Assad Douaa , Ghaddar Nesreen , Ghali Kamel
Published: December 2019

In this work, an intermittent personalized ventilation (PV) system was coupled with a chilled ceiling system in an office space. The ability of this system in protecting occupants from active particulate matter due to an indoor contamination source was investigated. To perform this study, a 3D transient computational fluid dynamics model was used to determine the velocity, thermal, and particle concentration fields in the space. The fluid flow in the space was experimentally validated in previous works in a climatic chamber equipped with a thermal manikin representing an occupant in an office space. The validated model was used to perform a parametric study varying the intermittent PV operating frequency as well as the particle diameter. The results were used to recommend PV operating conditions, which would ensure the protection of occupant against the contaminants present in the macroclimate and deposited on nearby surfaces. It was found that the intermittent PV should operate at an average flow rate of 7.5 L/s and a frequency of 0.73 Hz. These conditions provided acceptable values of intake fraction in the breathing zone and surrounding microclimate and acceptable deposited fractions. Moreover, these conditions provided good thermal comfort levels (0.86: comfortable) and good protection against passive contaminants (εv,BZ = 64 %).
Performance of Intermittent Personalized Ventilation Assisting Mixing Ventilation in the Presence of Indoor Disturbance
Authors: Al-Assad Douaa , Ghali Kamel , Ghaddar Nesreen
Published: December 2019

In this work, an office space is considered, equipped with an intermittent personalized ventilation (PV) system assisting a conventional mixing ventilation system. In ideal offices with no disturbances, it was proven that an intermittent PV average flow rate of 7.5 L/s and frequency of 0.86 Hz could enhance comfort compared to a steady PV and provide protection against contaminants present in the macroclimate. However, office spaces are subject to many disturbances, which could deteriorate the performance of air ventilation systems. In this work, an office door is considered to open disturbing the flow field by establishing pressure gradients. To conduct this study, a 3D computational fluid dynamics model was developed to predict the airflow field variables as well as contaminants’ concentration in the occupant-breathing zone. The model was used to assess the ability of the ventilation systems in maintaining its optimal operating parameters (0.86 Hz) obtained in ideal conditions. Results showed that the optimal PV frequency did not assure the same level of air quality. In fact, ventilation effectiveness decreased by 18% due to the opening door which pulled the PV jet away from the occupant’s breathing zone (BZ). Therefore, in office spaces with high disturbance levels, it is better off to operate the PV under steady state conditions to avoid further disturbance of the jet, or to operate the intermittent PV at low frequencies of 0.3 Hz to 0.5 Hz to minimize turbulence intensities created by the jet fluctuations.
Magnetic Resonance Thermometry: An Emerging Three-Dimensional Temperature Diagnostic Technique
Authors: Benson Michael J. , Cooper Mattias , Van Poppel Bret P. , Elkins Christopher J.
Published: December 2019

Magnetic Resonance Thermometry (MRT) is a developing diagnostic technique that leverages advanced medical technologies to accurately measure the temperature of a fluid flow within and around complex geometries. The full three-dimensional temperature field obtained by MRT can be used to analyze heat transfer characteristics and potentially investigate thermal boundary layers near arbitrarily complex surfaces. This technique requires neither optical nor physical accessibility, thereby enabling a wide range of engineering applications. This paper describes the current state of the art for MRT measurement, detailing turbulent water channel tests, materials selection, scanning parameters, data analysis of time-averaged temperature measurements, and uncertainty estimates.

The purpose of this work was to evaluate and refine the MRT technique to increase the accuracy of temperature measurements and minimize the error in fully turbulent flow measurements. In the present study, a plate with a vertical cylinder extending from both of its sides was placed between two channels, and a diagonal hole was drilled through the cylinder from one side of the plate to the other. This enabled fluid from one channel to mix with the fluid in the other. This experiment studied the mixing of two fluids at different temperatures. The upstream temperatures of each fluid were measured with thermocouples. Both flows were fully turbulent, and the colder temperature channel had a Reynolds number of 11,800. Tests were run with four different fluid temperatures for calibration and to determine any temperature dependence of measurements. Three-dimensional temperature field measurements are reported and details about data processing and procedures to conduct the experiments are provided.

This work resulted in several notable improvements to MRT experimental methods. The test section and water channel were designed to limit the effects of thermal expansion in the stereolithography materials used for manufacturing the complex internal flow geometry. Multiple echo scans were used to minimize the effects of magnetic field drift commonly observed in extended scanning periods in MRI systems. Data analysis techniques were used to quantify expansion effects for both hot and cold flow cases. To quantify measurement uncertainty, the standard deviation of the mean was calculated at each data point across different scan numbers and confidence intervals established using a student t-test. An improved data processing code was used to filter data resulting in increased measurement accuracy and reduced uncertainty to less than 1 °C for most of the domain.

Future work will further refine the experimental techniques to improve scanning procedures, employ high conductivity ceramics and larger geometries with relevant applications, and simplify data processing methods to generate full-field flow temperature data.
A Novel Approach of Designing Aircraft Heat Exchanger for Continuous Working Conditions Using Modified Genetic Algorithm
Authors: Liu Qihang , Zhuang Laihe , Fu Yanchen , Dong Bensi , Wen Jie , Xu Guoqiang
Published: December 2019

A novel approach is proposed to design an aircraft heat exchanger considering multiple working conditions to develop the conventional approach that designs for only one working condition. Calculation results show that the performance of the heat exchangers designed by this novel approach meets the requirement of pressure drop and heat transfer for all working conditions (flight height varies from 0 m to 12,000 m, and Mach number varies from 0 to 1.2). After working conditions discrete and heat exchanger design, the extreme working conditions of pressure drop and heat transfer rate are found not coincided, which have been all considered in design without artificially screening. Therefore, it is not necessary to find a ‘seeming extreme working condition’ before design for this approach. In the optimization design, a deeply optimized structure of heat exchanger is proposed by changing the values of the selected structural parameters to reduce by roughly 30% of the total weight in comparison to common design results. Moreover, the pressure drop and the heat transfer rate of the optimal result can be reasonably distributed at different working conditions. Actually in this novel approach, more other specific criteria required could be also added into the integrate criterion of optimization to control the result. In addition, two detailed optimization methods, sacrifice of secondary objective parameters and ‘the macro-to-micro design method’, have been proposed in optimization design for further optimal structure.
Heat Transfer From a Row of Heated Pipes in Horizontally Layered Porous Media
Authors: Ngo C. C. , Al Edhari A. J.
Published: December 2019

A two-dimensional transient model has been developed using COMSOL Multiphysics modeling software to simulate the heat transfer processes from a row of heated pipes in horizontally layered media consists of two porous sublayers with different permeabilities. The application of the present study is related to thermal energy storage or radiant floor heating system using the embedded piping system as the heat source. The present numerical simulation was first compared and validated using a parallel experimental work. The transient temperature profiles of the layered system obtained from both the experimental and numerical work are in good agreement. Once the numerical code is validated, a parametric numerical study has been performed to investigate the effects of layered system configurations on the heat transfer characteristics. Porous media with different properties were modeled using the subsurface flow (Brinkman’s model formulation) and heat transfer module. Different layered system configurations were simulated by adjusting the sublayer thicknesses and using different permeability ratios for the layered system. For a layered porous system with different permeabilities, the dominant mode of heat transfer changes from heat conduction to heat convection depending on the ratio of the porous layer permeabilities. The interface location of the two media relative to the depth of the embedded heated pipes also plays an important role in the heat transfer results. The numerical results are presented in contour plots to examine the temperature distribution within the layered system (for energy storage application) as well as along the top surface of the system (for radiant floor heating application). The heat transfer results suggest that the layer configuration of the media plays an important role in the performance of radiant floor heating system.
The Effect of Chamber Pressure on the Thermal Performance of New Refrigerant R513a During Spray Cooling
Authors: Abdulrazzaq Nabeel M. , Salman Azzam S. , Anumbe Noble , Tikadar Amitav , K. Oudah Saad , Khan Jamil
Published: December 2019

In this paper, the performance of a new low-GWP refrigerant R513a was experimentally investigated, during spray cooling. A spray cooling system was designed to work as a sub-system within a closed-loop refrigeration system. The influence of chamber pressure on heat flux and heat transfer coefficient were experimentally investigated. A smooth plain copper surface heated by a cartridge heater was cooled by the refrigerant (R513a) while flowing through a nozzle in the spray chamber. The results showed that chamber pressure has a significant impact on the overall thermal performance of the spray cooling operation. It was also determined that higher chamber pressures resulted in higher thermal performance. The highest chamber pressure attained in this study was 0.6 MPa. Furthermore, the surface temperature of the heated surface increased due to the increase of the saturation temperature of the liquid over the surface.
Plasmonic Waveguiding in Subwavelength Particles Suspended in Various Dielectric Media
Authors: Yuksel Anil , Cullinan Michael , Yu Edward T. , Murthy Jayathi
Published: December 2019

Near-field electromagnetic coupling between nanoparticles in dielectric media has led to new advances in next generation technologies such as photonic integrated circuits and photonic sintering. Understanding the light confinement between nanoparticles at subwavelength dimensions is vital in such applications. For instance, the wavelength of the incident light, dielectric medium properties, nanoparticle size, interparticle spacing, and relative orientation between the nanoparticles affect the near-field plasmonic interactions that characterize the thermal energy transport. In this study, we perform a field intensity analysis by looking at the relative orientation of gold (Au) and copper (Cu) nanoparticles which have 25, 50 and 100 nm radius under 532 nm laser irradiation in different surrounding medium to understand the thermal energy transport between the nanoparticles at different relative orientations.
Numerical Simulation of Melting in Metal Foam/Paraffin Composite Phase Change Material Using a Physically More Reasonable Macroscale Model
Authors: Yao Yuanpeng , Wu Huiying
Published: December 2019

In this work, a macroscale model for melting phase change of metal foam/paraffin composite phase change material (MFPC) is developed by employing the enthalpy-porosity method and volume averaging technique. Both cases of varied and unvaried paraffin density during phase change are investigated in the model, and diffusion dominated interstitial heat exchange between paraffin and metal foam is considered along with the convection dominated interstitial heat transfer. The visualization experiments on melting phase change of copper foam/paraffin composite are carried out to validate the developed phase change model. It is found that with consideration of varied density of paraffin, the developed model can effectively solve the real melting problem of MFPC when metal foam is initially filled with solid paraffin. If the Boussinesq approximation is employed (i.e., unvaried paraffin density is considered during phase change), the model is more appropriate for the phase change problem on condition that metal foam can just be filled with liquid paraffin in the end of the melting process. Hence according to different treatments of paraffin density, the application of the phase change model needs to consider the influence of real paraffin filling condition of MFPC. The phase change model considering diffusion dominated interstitial heat transfer between stationary paraffin and metal foam can more accurately capture the solid-liquid phase interface positions as compared with the model only considering the convection dominated interstitial heat transfer. The present study can provide guidance for physically more reasonable simulation of the practical phase change problem of MFPC.
Optimization Strategy for Contradiction Between Intermitting Oxygen Consumption in Converter Steelmaking and Continuous Oxygen Production by Air Separation Unit
Authors: Tong Lige , Liu Yuxin , Hao Yang , Yin Shaowu , Liu Chuanping , Wang Li , Xie Raru
Published: December 2019

In order to solve the problem of overpressure release of oxygen supply network caused by the contradiction between continuous oxygen production by air separation unit (ASU) and intermitting oxygen consumption in converter steelmaking, a pressure balance strategy for pre-adjusting liquid-vapor ratio of ASU was proposed. Used Aspen Plus software, a full-compression model of an ASU in an iron and steel enterprise was established. Before stopping oxygen consumption in the converter steelmaking, method of pre-adjusting liquid-vapor ratio from the low-pressure distillation column to reduce the oxygen production of the air separation unit was calculated. This strategy consists of two steps. First step is pre-adjusting liquid-vapor ratio from the low-pressure distillation column to reduce the oxygen production of ASU, before stopping oxygen consumption in the converter steelmaking. The second step is the reduction of the supply oxygen production pipe network pressure, when stopping oxygen consumption in the converter steelmaking. The pre-adjusting oxygen production and the starting time are the key of the strategy. The energy consumption analysis of the strategy is carried out. The results show that the strategy reduces the pressure of the oxygen supply pipe network by 1.3% and reduces the large amount of oxygen release, while increase of the energy consumption of ASU is neglected.
Effect of Carbon Particle Seeding As Radiant Absorbent for Enhanced Heat Transfer
Authors: Najafabadi Hamed Abedini , Ozalp Nesrin
Published: December 2019

Carbon particles can be used as catalyst in solar reactors where they serve as radiant absorbent and nucleation sites for the heterogeneous decomposition reaction. Unlike commonly used metal catalysts, carbon catalyst does not have durability problem and high cost. However, in order to achieve sustainable catalytic decomposition of feedstock over carbon catalysts at elevated temperatures, the surface area of the carbon particles must be maintained. A subsequent treatment of deactivated carbon samples with CO2 at about 1000°C would increase the surface and would recover the original activity as catalyst. In solar reactor, carbon particles are directly exposed to the high-flux irradiation providing efficient radiation heat transfer directly to the reaction site. Therefore, one of the key parameters to achieve higher conversion efficiencies in solar reactor is the presence and transport of carbon particles. This paper will present impact of carbon use in enhancing the heat transfer inside a solar reactor radiated by a solar simulator. Flux entering the receiver is determined using Monte Carlo ray tracing (MCRT) method which is coupled with energy balance equations to derive numerical model describing dynamic temperature variation in solar receiver. Simulation results indicated that feeding carbon particles results to lower temperatures for the cavity walls and working fluid compare to the case that no carbon is injected. This finding is in accordance with our experimental results obtained from a cylindrical cavity receiver radiated by a 7 kW solar simulator. The results indicated that heat transfer within the system is highly influenced by the particle size. At particle sizes larger than 450 μm, carbon feeding increases the thermal efficiency of the system.
Flowing Electrolyte As Coolant Inside the Microgrooves Embedded in the Electrodes: A Novel Thermal Management of Li-Ion Batteries
Authors: K. Mohammadian Shahabeddin , Zhang Yuwen
Published: December 2019

One way to enhance thermal performance of the Li-ion batteries is embedding microgrooves inside the porous electrodes and flowing the electrolyte through these microgrooves. A 2D thermal Lattice Boltzmann Method (LBM) was employed to predict electrolyte flow, heat transfer, and internal heat generation inside the positive porous electrode. Size and number of the microgrooves were investigated, and it was found that embedding microgrooves inside the porous electrode improved the thermal performance of the Li-ion battery by keeping the electrode in lower temperatures and improving its temperature uniformity. Furthermore, increasing the number of microgrooves (in a constant ratio between total size of the microgrooves to size of the porous electrode) kept the porous electrode in lower temperatures and enhanced temperature uniformity.
The Effect of Net-Type Spacer on the Performance of Direct Contact Membrane Distillation System for Seawater Desalination: Heat and Mass Transfer Analysis
Authors: Alwatban Anas M. , Alshwairekh Ahmed M. , Alqsair Umar F. , Alghafis Abdullah A. , Oztekin Alparslan
Published: December 2019

This work aims to study the effects of the net-type spacer on the performance of direct contact membrane distillation (DCMD) modules. Laminar and k-ω SST turbulence models are used to conduct simulations in three-dimensional modules with and without spacers. The spacers are placed in the middle of the feed and permeate channel. The net type spacers of diameter 0.25h and 0.5h were considered, where h is the height of each channel. The inlet temperature of the feed and the permeate channel set to 353 K and 293 K. The feed Reynolds number is varied (500, 1500) while the permeate Reynolds number is fixed at 330. We revealed that the presence of spacer in the flow channels mitigates both the temperature and the concentration polarization and yields higher vapor permeation. We also showed that the module containing larger size spacers yields better flux performance and lower level of temperature and concentration polarization. Moreover, the modules containing spacers become more efficient as the feed flow rate is increased.
Confined Impinging Slot Jets in Porous Media With Nanofluids
Authors: Buonomo Bernardo , di Pasqua Anna , Manca Oronzio , Sekrani Ghofrane , Poncet Sebastien
Published: December 2019

In this paper a numerical investigation on mixed convection in confined slot jets impinging on a porous media is accomplished. The working fluids are pure water or Al2O3/water based nanofluids and a single-phase model approach has been adopted in order to describe their behavior. A two-dimensional configuration is analized and different Peclet numbers and Rayleigh numbers are considered. The thermal non-equilibrium energy condition is assumed to execute two-dimensional simulations on the system. The examined foams are characterized by distinct values of pores per inch, PPI, equal to 5, 10, 20 and 40. The particle volume concentrations range from 0% to 4% and the particle diameter is equal to 30 nm. The target surface is heated by a constant temperature value, calculated according to the value of Rayleigh number. The distance of the target surface is five times greater than the slot jet width. The aim consists into study the thermal and fluid-dynamic behaviour of the system. Results show increasing values of the convective heat transfer coefficients for increasing values of Peclet number and nanoparticle concentration. Furthermore, the heat transfer coefficient presents a different behavior at varying PPI numbers for different Peclet numbers.
Transient Thermo-Diffuso-Capillary Convection Around a Bubble in a Surfactant Solution: A Numerical Investigation Using the Volume-of-Fluid Technique
Authors: Kalaikadal D. S. , Manglik R. M. , Jog M. A.
Published: December 2019

Marangoni Convection occurs when a surface tension gradient is established at a liquid-gas interface. The variation in surface tension could be driven by an interface temperature gradient, resulting in Thermocapillary Convection, or by an interface concentration gradient, giving rise to Diffuso-Capillary Convection, or a combination of both. Such flows are found to be of interest in microgravity (and otherwise), as they are known to significantly contribute to heat and mass transfer enhancement at the interface. This paper deals with the computational study of bubble induced thermo-diffuso capillary convection in the presence of surfactants and a stratified thermal field.

Bubble induced thermo-capillary convection in a pure liquid has been substantially studied and the effects of various parameters like liquid properties, wettability, bubble size, channel depth, and temperature gradients on the strength of thermo-capillary currents and the associated heat transfer enhancement at the bubble interface are well established.

In this study the physico-chemical properties of an aqueous solution of Sodium-Dodecyl-Sulphate (SDS), a surfactant, were used to introduce the effects of surfactant concentration-induced surface-tension gradients in addition to the temperature induced gradients. Unlike in purely thermo-capillary flows, where the interface sees a near-constant surface-tension gradient from base to apex, the presence of surfactant molecules at the interface results in gradients that vary significantly along the interface with maximum gradients at the bubble base and the apex, resulting in a pair opposing vortices anchored to the bubble interface. The presence of the opposing vortices, results in weaker capillary-flows at higher thermal Marangoni numbers. This is in contrast with purely thermal Marangoni convection, where a larger Marangoni number yields a stronger capillary flow.

It was also observed that while the Marangoni number may provide an accurate estimation of heat-transfer enhancement under steady-state conditions, it may not be possible in the case of a transiently developing Marangoni-flow. The heat transfer enhancement is maximum near the time of bubble introduction and then diminishes to a lower, stable value. Also, the capillary flows and the associated heat transfer is found to significantly vary with the wetting behavior at the liquid-solid-vapor interface, even for the same set of Marangoni numbers.