bluuebunny/crossref_metadata_2025_split huggingface dataset:
Identification of Gas Flow Regimes in Adiabatic Microtubes by means of Wall Temperature Measurements
Authors: Kashiwagi R , Hong C , Asako Y , Morini G L , Faghri M 
Published: September 2020

Abstract
There exists the laminar flow, transitional flow, turbulent flow and choked flow regimes in a microtube gas flow. Development of a non-invasive identification method of the flow regimes within a microdevice is expected. This paper demonstrated how the internal gas flow regimes can be identified by measuring the distribution of the external wall temperature of the microchannel along the flow direction. A series of experiments were conducted by using nitrogen as working fluid through a stainless steel micro-tube with an inner diameter of 523 µm and a fused silica micro-tube having a diameter of 320 µm. The experiments were performed by fixing the back pressure at the exit of the microchannel at the atmospheric value and by varying the inlet pressure in order to modify the gas flow regime. In order to measure the external wall temperature along the microtube, two or three bare type-K thermocouples with a diameter of 50 µm were attached to the micro-tube external surface by using a high conductivity epoxy. In the case of the microtube having a diameter of 523 µm, local pressures were measured at three local pressure ports along the microtube. The pressure ports were placed on the opposite side of the tube wall where three thermocouples were attached. The microtube external wall was thermally insulated with foamed polystyrene to prevent heat gain or loss from the surrounding. The experimental results show that the wall temperature decreases in the laminar flow regime, increases in the transitional flow regime, decreases in the turbulent flow regime and it stays nearly constants in the choked flow regime. The behavior of the average Fanning friction factor and the local Mach number can be explained by identifying the flow regime. It is clarified that the microtube external wall temperature is a reliable indicator of the flow regime.
Numerical analysis of double-layered microchannel heat sinks with different microchannel heights
Authors: Savino S , Nonino C 
Published: September 2020

Abstract
A numerical parametric analysis is carried out to investigate the thermal performance of double-layered microchannel heat sinks for different values of the relative channel height and fixed values of the total pumping power, with the additional constraint that the pressure drop be the same in the two layers in order to allow a much simpler header design, which can only include a single inlet and a single outlet. Single-layered microchannel heat sinks are also considered for additional comparisons. The computed results show that, in the hypothesis of this work (i) the ratio of the heights of the upper and lower microchannels only has a marginal effect on the overall thermal resistance but a significant influence on the temperature uniformity of the bottom (heated) surface and (ii) a better temperature uniformity is achieved when the heights of the upper microchannels are larger than those of the lower ones.
CFD simulation of turbulent flows over wire-wrapped nuclear reactor bundles using immersed boundary method
Authors: Cervone Antonio , Chierici Andrea , Chirco Leonardo , Da Vià Roberto , Giovacchini Valentina , Manservisi Sandro 
Published: September 2020

Abstract
A preliminary study for lead-bismuth eutectic (LBE) turbulent flows over wire-wrapped nuclear reactor bundles is performed. The 19-pin hexagonal bundle geometry, representative of NACIE-UP facility and adopted in the MYRRHA reactor [1, 2], is considered. The presence of the helical wire wrap has a strong effect on flow patterns inside the bundle geometry, with induced secondary flows and enhanced mixing [3]. From a computational point of view, the wire-wrapped geometry model is much more complex to realize than the bare rod configuration and simplified models are often used [4, 5]. In order to overcome the difficulties of the model generation, an hybrid body fitted immersed boundary method is used. A computational grid that fits the presence of bundle pins is generated, as for the case of the bare rod configuration, allowing a better control of mesh resolution in the regions close to wall boundaries. The immersed boundary method is used to model the presence of the helical wire wrap so that its effect on fluid motion can be taken into account.
Design and implementation of a modulating test plant to assess the performance of innovative cross-flow heat recovery units for air conditioning system: preliminary results.
Authors: Bonfiglio C , Bozzoli F , Cattani L , Pagliarini G , Rainieri S. , Vilar França M , Vocale P 
Published: September 2020

Abstract
Nowadays global warming has increased consciousness of the dangers of energy wastefulness: in the last 50 years the temperature of the Earth’s surface rose by approximately 1 °C. The building sector is responsible for a very high percentage of world carbon emissions and with the increasing of the request for comfort, heating, ventilation and air conditioning, buildings energy consumption is rapidly growing. Consequently, it appears fundamental the role played by the improvement of buildings energy performance within global policies of emissions reduction. In this context an increasing attention is given to the energy waste reduction in tertiary sector: bars, offices, restaurants, meetings, shops, school buildings, gyms and in general in the buildings in which the minimization of the energy dissipation is requested. The present study is part of the NANOFANCOIL project (POR-FESR 2014-2020): one of the objectives was the design and implementation of a modulating test plant to assess the performance of innovative cross-flow heat recovery units for air conditioning system. This experimental setup was mainly composed by two climatic chambers that enabled to simulate the environmental conditions of interest. The temperature could vary from -20°C to 0°C and from 10°C to 30°C for the cold and the hot chamber, respectively (i.e. the outdoor and the indoor environment). Moreover, the climatic chamber that simulates the indoor environment could be controlled also in terms of humidity thanks to a steam humidifier that guaranteed 5 kg/h of vapour. Preliminary results about the heat transfer behaviour of a cross-flow heat recovery unit (air-to-air) for controlled mechanical ventilation systems that employs mini-channels in order to increase performance and reduce size and costs are presented here.
Measurements of Spectrally Averaged Absorptivity and Emissivity for a Selective Solar Absorber in High Vacuum Under Direct Solar Illumination
Authors: Alessandro C D’ , De Maio D , De Luca D , Musto M , Di Gennaro E , Rotondo G , Dalena D , Russo R 
Published: September 2020

Abstract
The innovative ultra-high vacuum technology applied to solar thermal flat panels, allows to reach high operating temperatures (up to 200 °C) without concentration, cutting out both convective and conductive thermal losses of the internal gas. The system losses are mainly due to the radiative energy emitted by the absorber. In this paper, a power balance equation has been used to perform the best fit of the data recorded with the absorber first exposed to the Sun illumination (up to the stagnation temperature, typically above 300 °C) and then cooled down by using an opaque shield. In particular, the fitting procedure is useful to evaluate the spectrally averaged absorptivity and the temperature dependent spectrally averaged emissivity of the absorber in a realistic operating condition.
An experimental study on the transient thermal response of an electronic equipment box for UAV remote sensing applications
Authors: Tanda G 
Published: September 2020

Abstract
An experimental study of the transient thermal characteristics of an electronic equipment box is presented. The box is designed to house devices typically used for UAV-based remote sensing applications. Different cooling systems, aimed at maintaining all the components within their allowable temperature limits for the duration (15-20 min) of each UAV flight, have been considered. They include forced convection of external or internal air and use of storage units (cold gel packs) inside the box. Experiments indicated that a mixed active/passive technique consisting in the combination of cold gel packs and internal ventilation, without any air renewal, provides the most suitable cooling condition.
Numerical modelling of a PV-T collector working as evaporator in a solar assisted heat pump
Authors: Zanetti E , Del Col D 
Published: September 2020

Abstract
A numerical study of a PV-T collector working as an evaporator for a solar assisted heat pump is presented. The work has been realized in the framework of the SolairHP project for the study of a reversible dual source heat pump. The main objective is to increase the seasonal coefficient of performance of the heat pump compared to an air source heat pump and reduce the overall electrical consumption by including a solar collector-evaporator. A mathematical steady state model of the solar evaporator device has been realized in Matlab environment: it considers the energy and mass fluxes in three dimensions by working a discretization of the main surfaces of the PV sandwich and of the absorber plate (roll-bond plate). The input of the model are the ambient conditions (irradiance components and air temperature), the thermodynamic conditions of the refrigerant at the inlet (enthalpy and mass flowrate) and the circuitation. The main results of the model are the electric and thermal efficiency, the conditions of the refrigerant all along the channels and the temperature distribution on the PV-T surfaces. The numerical model has been used in the design procedure of the solar evaporators to be coupled to a 8 kW heat pump working with R32. A preliminary seasonal analysis on the PV-T evaporator has been realized in order to evaluate the advantage of the dual source system.
Towards DES/DDES computation of the flow field and heat transfer adopting elliptic relaxation and local correlation based transition approaches
Authors: D’Alessandro V , Giammichele L , Lops C , Ricci R 
Published: September 2020

Abstract
As Large–Eddy Simulation (LES) shall remain too expensive in the following few decades for the ever increasing number of engineering complexities, researches have shifted much of the attention and effort to hybrid formulations incorporating Reynolds–Averaged Navier– Stokes (RANS) equations and LES in a certain ways. The long term goal of this research activity is to develop accurate hybrid RANS/LES methods. These approaches are particularly appealing in massively separated flows since they offer good prediction performance and they can be considered a good trade–off, in terms of computational resources, if compared with standard LES techniques. In particular with this work we want to deeply investigate Detached–Eddy Simulation (DES) based on: (i) elliptic relaxation turbulence model; (ii) Spalart Allmaras local correlation based transition model (LCTM). Specifically, we analyze v2–f DES approach for the convective heat transfer around a sphere at Re = 5000 (with Pr = 0.71) and we compare these results with the so called delayed version of the model. At the same time we also investigate the LCTM version of the SA model, in the DES context.
Numerical Simulations of the flow field within a 1:10 Aspect Ratio duct at intermediate Re
Authors: Vignati Federica , Fustinoni Damiano , Gramazio Pasqualino , Vitali Luigi , Niro Alfonso 
Published: September 2020

Abstract
Numerical simulations are carried on to study the fluid-dynamical features of a smooth duct with aspect ratio of 10. The duct is operated with an incompressible, newtonian fluid, whose Reynolds number, computed over the hydraulic diameter and bulk velocity, ranges from 470 to 14500, encompassing laminar and turbulent flow. To capture the details of all the flow scales, Direct Numerical Simulations are performed, by means of a code developed at Politecnico di Milano. The adopted code is a finite-difference, structured grid solver, that includes a mass flow rate correction. The latter guarantees high accuracy in the calculation of unsteady flows, or during the transition to turbulent regime, and it allows to check the consistency of numerical results.
Both global parameters –including the friction factor and the identification of the laminar-to-turbulent transition and local flow features, e.g., corner vortexes, are investigated and presented in this work. Preliminary analyses agree fairly well with literature data and with experimental results obtained at ThermALab of Politecnico di Milano.
The final goal of this work, including a deep integration between the numerical and the experimental setup, is to carry on detailed investigations of the fluid-dynamical and thermal characteristics of ribbed ducts, in the perspective of heat transfer enhancement and pressure drop reduction.
Increased efficiency of combined heat and power plants by utilizing waste heat for resorption chillers and their combination with hydrocarbon chillers
Authors: Ziegler O , Hesse U , Thomas C 
Published: September 2020

Abstract
The use of waste heat has long been a topic to increase the efficiency of large-scale industrial processes, but it is becoming as well important in the commercial sector and in small and medium-sized industrial plants. For a sustainable and decentralized energy supply it is necessary to utilize all exergy flows much more than before. Particularly in decentralized combined heat and power (CHP) plants, the annual coefficient of performance is low due to seasonal temperature fluctuations, as the generated heat cannot be used or can only be used partly during the summer and transitional months. Interface technologies such as sorption technology can be used to further increase the utilization rate of such CHP plants and provide cooling capacity at the same time. This concept allows the utilization of previously unused waste heat to generate cooling in the temperature range from -6°C to 15°C, without the necessity of significant amounts of electric energy for the operation of additional compression refrigeration systems. In a pilot project funded by the German Federal Ministry of Economic Affairs and Energy, a thermally driven refrigeration plant with a small cooling capacity of maximum 25 kW using the resorption principle was evolved under these aspects and installed in a supermarket. Special focus is given to the flexibility of the plant technology as well as to the potentials of combinations of thermally and electrically driven chillers with natural refrigerants such as hydrocarbons and ammonia and the integration of thermal storage for temporal decoupling or discontinuous availability of heat and cooling load.
Confined Copolymer Structures
Authors: Pezzutti Aldo D. , Hernández Hugo 
Published: September 2020

Abstract
Bulk morphologies of diblock copolymers have been extensively studied in literature both experimentally and theoretically. Depending on the composition of the blocks it is comprised of, the bulk structures correspond to lamellae, gyroids, cylinder hexagonal arrangements and BCC structures of spheres. Recent research has shown that confinement is a powerful tool to break the symmetry of a structure, and obtain new shapes, different from those of the bulk.
The process of forming new morphologies by confinement in nano-droplets, created from a dewetting process, was simulated. The structures obtained showed a great similarity with the experimental results present in the literature.
The developed model captures the fundamental interactions that determine the dynamics of the phase separation process of the confined copolymer system between a rigid substrate and a free surface.
Study of acoustic characteristics of the swirling flow generated in ejector
Authors: Vekteris V , Styra A , Mokshin V , Turla V , Viselga G , Tetsman I 
Published: September 2020

Abstract
The article deals with changes in the density of pulsating water and air flow generated in pulsating flow ejector. Transformation of the fluid motion equation to Lighthill’s equation describing density change and acoustic radiation of the flow is presented. Calculation results demonstrate suitability of the ejector to cause acoustic agglomeration and effectively remove iron particles from potable water.
Methods and tools for teaching programming at university
Authors: Kasyanov Victor N. , Kasyanova Elena V. 
Published: September 2020

Abstract
The paper is devoted to the methods and tools for teaching programming developed in the A.P. Ershov Institute of Informatics Systems. Practical work on programming and an introductory course of programming on the basis of the Zonnon language are considered. The paper also describes the development of an adaptive system for distance learning and a visual cloud system that supports parallel and functional programming.
A Novel Technique for Optimization of Statistical Decisions under Parametric Uncertainty through Invariant Statistical Embedding and Averaging in Terms of Pivotal Quantities
Authors: Nechval N. A. , Berzins G. , Nechval K. N. , Danovics V. 
Published: September 2020

Abstract
In the present paper, a new technique of invariant embedding of sample statistics in a decision criterion (performance index) and averaging this criterion via pivotal quantity is proposed for intelligent constructing efficient (optimal, uniformly non-dominated, unbiased, improved) statistical decisions under parametric uncertainty. The technique of invariant statistical embedding and averaging in terms of pivotal quantities (ISE&APQ) is independent of the choice of priors and represents a novelty in the theory of statistical decisions. It allows one to eliminate unknown parameters from the problem and to find the efficient statistical decision rules, which often have smaller risk than any of the well-known decision rules. To illustrate the proposed technique of ISE&APQ, application examples are given.
ml-experiment: A Python framework for reproducible data science
Authors: Molner Domenech Antonio , Guillén Alberto 
Published: September 2020

Abstract
Nowadays, data science projects are usually developed in an unstructured way, which makes it difficult to reproduce. It is also hard to move from an experimental environment to production. Operational workflows such as containerization, continuous deployment, and cloud orchestration allow data science researchers to move a pipeline from a local environment to the cloud. Being aware of the difficulties of setting those workflows up, this paper presents a framework to ease experiment tracking and operationalizing machine learning by combining existent and well-supported technologies. These technologies include Docker, Mlflow, Ray, among others. The framework provides an opinionated workflow to design and execute experiments either on a local environment or the cloud. ml-experiment includes: an automatic tracking system for the most famous machine learning libraries: Tensorflow, Keras, Fastai, Xgboost and Lightgdm, first-class support for distributed training and hyperparameter optimization, and a Command Line Interface (CLI) for packaging and running projects inside containers.
Evaluation of the effectiveness of the soil-cement with hydrophobized surface for road construction
Authors: Kuyukov S , Testeshev A , Zhigailov A , Shmatok V 
Published: September 2020

Abstract
The paper presents an assessment of the effectiveness of the use soil-cement with hydrophobized surface by conducting a feasibility study. The work performed theoretical studies and the calculation part. The object of study is a soil-cement with hydrophobized surface at the base in road foundation of the road. The subject of the study is the economic efficiency of the use of modified soil-cement. Theoretical studies are based on the choice of methodology for assessing the economic efficiency of the use of this material with its subsequent description. The calculation part includes determining the benefits of road users, current and one-time costs from the use of various constructions of pavement for the billing period. The result of the calculations is a graph of the dependence of the economic efficiency of various structures on traffic intensity. The use of soil-cement with hydrophobized surface will reduce economic costs in the construction of roads, increase the speed and quality of work, increase the overhaul time of roads of federal and regional significance.
Influence of light aggregate on structure formation of lightweight concrete
Authors: Larsen O A , Bulgakov B I , Gafarov R M , Melikhov D O 
Published: September 2020

Abstract
Recycling of glass industry waste is relevant in the world today. It is caused by the increase of environmental problems and devastation of natural resources. One of the option of cullet recycling is production of foamed lightweight glass aggregate. It is energy efficient material with size up to 75 mm, irregular shape and relatively low strength. High specific surface area of aggregate leads to increase the cement consumption to achieve acceptable concrete compaction. This article presents the results of size gradings selection of coarse foamed glass aggregate and its water demand in concrete mix. The determination of structure formation period and water demand of foamed glass aggregate are presented. The influence of particle size distribution of lightweight aggregate on structure formation period of lightweight concrete is established. The density and compressive strength of structural lightweight concrete with foamed lightweight glass aggregate are 1468 kg/m3 and 19 MPa, respectively. The density and strength of insulating lightweight concrete are 1167 kg/m3 and 10 MPa, respectively. The cement consumption of structural and insulating concrete is 260 kg and 254 kg, respectively.
Calculation of shear stresses in the soil of the subgrade using empirical plasticity conditions
Authors: Aleksandrov A , Dolgih G , Kalinin A 
Published: September 2020

Abstract
The aim of the work is to replace the criterion of the original Mohr – Coulomb criterion with an empirical plasticity condition in which the limit state arises at deformation εlim<15 %. As a result of the analysis of experimental data on testing soils by triaxial compression, an empirical plasticity criterion is obtained. The limiting state by the empirical criterion occurs when the sample is deformed by 10–12%. The shear stresses calculated by this plasticity condition exceed the shear stresses calculated by the Mohr – Coulomb criterion. Therefore, the application of the proposed criterion in the calculation of pavement by shear resistance in the soil of the subgrade requires an increase in the thickness of the structural layers, compared with the traditional calculation, which is based on Mohr – Coulomb.