Numerical Simulation of Frost Formation on a Plate-Fin Evaporator

In the present paper, the Eulerian-granular model is adopted, to predict the frost growth on one channel of a plate-fin evaporator. A proper mass transfer model and modified frosting criteria are used to simulate the frost formation process. First, the model is validated with experimental data obtained under various operating conditions. The numerical predictions for the frost thickness and density are in good agreement with available experimental data. Furthermore, a parametric analysis is carried out to study the impact of the geometrical parameters of a three-dimensional plate-fin evaporator. A qualitative comparison shows a good agreement between the numerical data and experimental observations reported in the literature. One interesting outcome emerging from this study is that the distance between refrigerant tubes can play an important role in the frosting time

Gill's problem in a sandwiched porous slab

The classical Gill's stability problem for the stationary and parallel buoyant flow in a vertical porous slab with impermeable and isothermal boundaries kept at different temperatures is reconsidered in a different perspective. A three-layer slab is studied instead of a homogeneous slab as in Gill's problem. The three layers have a symmetric configuration where the two external layers have a high thermal conductivity, while the core layer has a much lower conductivity. A simplified model is set up where the thermal conductivity ratio between the external layers and the internal core is assumed as infinite. It is shown that a flow instability in the sandwiched porous slab may arise with a sufficiently large Rayleigh number. It is also demonstrated that this instability coincides with that predicted in a previous analysis for a homogeneous porous layer with permeable boundaries, by considering the limiting case where the permeability of the external layers is much larger than that of the core layer

Growth and aggregation regulate clusters structural properties and gel time

Silica aerogels’ unique physical and chemical properties make them fascinating materials for a wide variety of applications. In addition to hydrophobization by silylation, aging is very important in the synthesis of silica aerogel by ambient pressure drying. Here we systematically study the effect of aging on the physico-chemical properties of silica aerogel with emphasis on ambient dried materials. Silica gels were aged for different times and at different temperatures in their gelation liquid (without solvent exchange), hydrophobized in hexamethyldisiloxane and subsequently dried either at ambient pressure or from supercritical CO2. Dynamic oscillatory rheological measurements demonstrate that aging reinforces the alcogels, particularly at high strain. The specific surface area decreases with increasing aging time and temperature as a consequence of Ostwald ripening processes during aging. With increasing aging time and temperature, the linear shrinkage and bulk density decrease and the pore size and pore volume increase for the ambient dried gels, but remain nearly constant for supercritically dried gels. Small-Angle X-ray scattering does not detect significant structural changes at length scales smaller than about hundred nanometers, but hints at systematic variations at larger length scales. The findings of this study highlight the importance of aging to increase the ability of the gel particle network to withstand irreversible pore collapse during ambient pressure drying

XERIC climate-control system for energy-efficient electric vehicles: first experimental results and numerical evaluation of the overall performance

The paper reports the main developments and results achieved so far within the EU-funded H2020 XERIC project, which is aimed at developing a new climate control system that is able to increase Battery Electric Vehicles (BEVs) autonomy thanks to its high energy efficiency. The XERIC system combines a traditional Vapor Compression Cycle (VCC) with a Liquid Desiccant Cycle (LDC), by taking advantage of an innovative component, called Three-Fluids Combined Membrane Contactor (3F-CMC). The two experimental setups arranged to test LDC alone and the overall XERIC system are presented. Then, the experimental results obtained in the first test campaign are given and discussed. Finally, the numerical tool developed in the Matlab/Simulink environment for the evaluation of the performance of the overall XERIC system is introduced and a preliminary comparison between numerical results and experimental measurements is provide

Design and testing of a GPS/GSM collar prototype to combat cattle rustling

Rustling is an age-old practice that was widespread in Italy until the first half of the 20th century. Today, incidents of cattle rustling are again being reported. However, the problem is not only found in Italy. It is also becoming a plague for ranchers in the US and is still rampant in East Africa. In Italy, the cattle rustling phenomena have usually been limited through the direct control of the herdsmen. Global positioning system (GPS) and geographic information system (GIS) combined technologies are increasingly applied for tracking and monitoring livestock with greater spatial and temporal resolution. However, so far, no case studies of the use of GPS technology to combat cattle rustling have been reported in the literature. The aim of this research was to develop a GPS/GSM (global system for mobile communication) collar, using commercial hardware and implementing a specific software [ARVAshepherd 1.0; ARVAtec Srl, Rescaldina (MI), Italy] to track animals' movements outside their grazing area and to signal when animals are straying outside virtual perimeters. A phase I study was conducted from January to June 2011 to build the GPS/GSM collar and to assess its performances in terms of GPS accuracy and precision, while a phase II study was conducted in July 2011 to test the GPS collar under real-life operating conditions. The static GPS positioning error achieved a circular error probable (50%) and horizontal 95% accuracy of 1.462 m and 4.501 m, respectively. This is comparable with values obtained by other authors in static tests of a commercial GPS collar for grazing studies. In field tests, the system was able to identify the incorrect position of the cattle and the warning messages were sent promptly to the farmer, continuing until the animals had been repositioned inside the fence, thus highlighting the potential of the GPS/GSM collar as an anti-theft system

3D-CFD analysis of the effect of cooling via minitubes on the performance of a three-fluid combined membrane contactor

Abstract A 3D computational fluid dynamics model was adopted to study the effects of internal cooling on the performance of a three-fluid combined membrane contactor (3F-CMC), in the presence of minitubes in solution and a spacer in the air channel. This compact 3F-CMC is part of a hybrid climate-control system, recently developed for serving in electric vehicles. For the studied operating conditions, results show that the absorption and sensible effectiveness parameters increase up to 77% and 124% by internal cooling, respectively. This study also reports 3D flow effects on the heat and mass transfer enhancement inside the contactor, with implications for further design improvements

An Edge-based Architecture for Phasor Measurements in Smart Grids

This paper investigates the application of Kubernetes and Edge computing technologies to operate IT services in the context of power systems and smart grids. Traditional services for grid monitoring such as Phasor Measurement Units (PMUs) and Phasor Data Concentrators (PDCs) require a centralized architecture and a rigid networking infrastructure in order to properly function, which today is only achieved at the High Voltage (HV) transmission level. Furthermore, manual intervention is often the only option for PMUs/PDCs maintenance. In this work, the traditional PMU/PDC services were deployed as docker-containers in a decentralized Kubernetes cluster, which can represent any kind of geographically dispersed TCP/IP network. By leveraging remote orchestration, several key benefits are achieved: (1) no manual reconfiguration of the PMU-PDC communications upon network reconfiguration, (2) automatic PMU traffic redirection in case of PDC service redeployment in a different location, and (3) reduced data-loss upon PDC failure and enhanced overall system resiliency due to minimized ICT services down-time

Effects of flow direction and thermal short-circuiting on the performance of coaxial ground heat exchangers

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PROTEUS: an immersive tool for exploring the world of cultural heritage across space and time scales

AbstractIn the field of digital humanities, it is increasingly necessary to develop and validate virtual reality tools that are capable of combining various scientific data in a virtualized context providing also access and user friendly consultation of online repositories. This paper reports the main aspects of the implementation of a virtual reality tool integrated with an online repository for storing 3D models, metadata and chemical analyses related to different sectors of digital humanities. The virtual reality software, developed for the Oculus Quest 2 hardware, is called PROTEUS and allows for seamless transition from the macroscopic world of digital humanities to the microscopic world of molecular sciences. The paper illustrates, by means of some case studies, the performances of this innovative tool that permits the researcher to understand and manipulate objects, to test hypotheses and to seek meaningful results, visualising the metadata while changing the parameters of the simulation in a dynamic and interactive way. This represents also a significant step forward in the democratisation of science, thanks to an user-friendly and immersive access to advanced scientific algorithms, which allow the natural perception of structural and topological features of the underlying molecular and supra-molecular systems. Graphical Abstrac