Reducing the Natural Convection Inside an Enclosure Using a Concentric Internal Open Square

This paper presents the results of a numerical simulation for the natural convection inside an enclosure that has an inner open square at its center. The inner square is open at the top and connected to the ceiling of the enclosure. The open inner square distorts the convection patterns, slows down the flow, and provides a compartment to confine the fluid at the core of the enclosure. Ultimately, this lowers the local Nusselt number, Nu, along the hot wall, and reduces the heat flux through the enclosure. The analysis shows the effects of changing the dimensions of the inner square on the heat flux through the enclosure for a range of Ryleigh numbers from 103 to 106. Short-sided inner squares work as flow deflectors while long-sided inner squares provide compartments to accommodate new flow circulation at the core of the enclosure. The inner square is most effective when the length of its sides equals the width of the stagnant core inside the empty enclosure at the same Ryleigh number, and the heat flux at this condition is the lowest. Inner squares made of thermally conducting materials can reduce the heat flux through the enclosure by 70%, while adiabatic inner squares can reduce the heat flux by 90%. Inner squares reduce the external heat load on buildings when fitted inside the holes of hollow bricks used in building facades. The external heat flux can be lowered by 30%-55% depending on the square material and outer side temperature.

Innovative Use of Wireline Tools Enables Successful Re-Entry on Subsea Wells

Re-entry of subsea wells can always hide unforeseen difficulties. Contingency mobilization of coiled tubing (CT) usually gives a wide spread of solutions to overcome most of the possible events. However, when operating on a winterized semisubmersible rig in the remote fields of the Barents Sea, rig-up of CT spread can be costly and complicated. Furthermore, lighter and easily deployable wireline powered mechanical tools have proven to be effective in tackling most of the possible challenges. Possible tubing obstruction issues can be resolved via clean-out/suction, pumping, or milling methods. In this instance, all three were used with different tools to clear the obstruction from the tubing and to clean with precision inside an internal fishing profile of a well head barrier plug to allow for well access. The first challenge encountered when re-entering the tubing in Well-1 was the presence of a 151m long hydrate plug. It was easily removed by an e-line tool capable of applying 10 bar of dynamic underbalance, while maintaining a continuous flow circulation. Such an application is a novel development in the use of existing tools. After removing the hydrate plug, it was discovered that the tubing was plugged by 246m of wax deposits, which were preventing communication with the reservoir. To overcome this problem, a jetting tool was utilized to continuously pump fresh wax solvent inside the landing string. Pumping continuously fresh wax dissolvent provided a unique and effective means to mechanically and chemically remove a significant obstruction. Once the communication with the reservoir was re-established, an additional obstruction of almost 129m (resistant to the wax dissolvent) was encountered. To overcome this challenge an e-line milling tool was utilized, and the resulting debris was bullheaded down into the reservoir. Similarly, when re-entering Well-2 a challenge was encountered to pull a barrier plug due to debris deposits inside the internal fishing profile. Both e-line milling and suction tools were sequentially used to resolve the problem and prepare the plug for retrieval. The tools used were already available on the market for different applications. In this case the tools were used in an alternative way, using their features to solve issues beyond conventional expectations. The result fosters confidence to plan future re-entry without the need for mobilizing a CT spread.

Experimental Study on the Stability and Transient Behavior of a Closed-Loop Two-Phase Thermosyphon (CLTPT) Charged with NOVEC 649

Currently, the growing need for efficient refrigeration resources in the industrial sector has led to an increasing interest in finding technologies with a higher heat removal potential and better cooling performance. Along these lines, two-phase liquid cooling appears to be a very interesting solution, with the CLTPT (closed-loop two-phase thermosyphon) being one of the leading alternatives. Most works in the scientific literature study loop thermosyphons that work in flow boiling conditions in steady state. The present paper analyzes the transient thermal behavior of a pool boiling CLTPT gravitational channel as a passive cooling system using NOVEC 649 as working fluid. The evaporator works with two submerged cylindrical heaters that represent different heat sources located in different positions. The initial transient behavior and consequent instabilities of a laboratory-scale facility were studied, followed by a stability analysis for various power inputs. Parameters such as temperature and pressure along the experimental setup were monitored, and the effects of internal pressure and room conditions were also tested. The results show some instabilities in the process to start the flow circulation and a relative stability and quick adaptation to changes when circulation is reached. The temperature in the evaporator chamber was highly homogeneous during the whole process; however, the temperature changes in the riser and the loop top were delayed with respect to the evaporator zone. The analysis shows several pressure and temperature raises before the vapor flux reaches the condenser. When the flow circulation is established, the system becomes highly stable and thermally homogeneous, decreasing the thermal resistance when increasing the power input. The stability analysis also showed that, when the system reaches the steady state, the changes in the power input produce a transient increase in the pressure and temperature of the fluid, followed by a quick decrease of the previous steady state values. The heat transfer analysis in the evaporator shows a higher heat flux on the upper heater caused by the buoyancy flow that rises from the lower heater. It was also observed that the lower heater reaches the CHF point with a lower heat flux.

Investigation of the Zinc-Copper Catalyst NIAP-06-06 for Steam Conversion of Carbon Monoxide in the Synthesis of Methanol

The possibility to use the zinc-copper catalyst NIAP-06-06 for steam conversion of CO in the synthesis of methanol was explored. The catalyst was characterized by means of TPR H2, XRD and SEM methods and tested in the methanol synthesis in flow and circulation modes at a pressure of 5.0 MPa and gas hourly space velocity of 3000 h–1 over a temperature range of 220–260 °С. The catalyst was shown to be highly active and selective toward the methanol synthesis from a gas with the H2 /СО ratio 3.9, which is obtained by steam conversion of methane. The use of tubular catalytic reactors connected in series in the flow-circulation mode makes it possible to convert more than 70 % of CO and obtain crude methanol with the concentration of 95 %. In the circulation mode, a methanol output of 427.7 kg/(m3 cat·h) was achieved on the catalyst.

Impacting Droplet Can Mitigate Dust from PDMS Micro-Post Array Surfaces

In this paper, the impact mechanisms of a water droplet on hydrophobized micro-post array surfaces are examined and the influence of micro-post arrays spacing on the droplet behavior in terms of spreading, retraction, and rebounding is investigated. Impacting droplet behavior was recorded using a high-speed facility and flow generated in the droplet fluid was simulated in 3D geometry accommodating conditions of the experiments. Micro-post arrays were initially formed lithographically on silicon wafer surfaces and, later, replicated by polydimethylsiloxane (PDMS). The replicated micro-post arrays surfaces were hydrophobized through coating by functionalized nano-silica particles. Hydrophobized surfaces result in a contact angle of 153° ± 3° with a hysteresis of 3° ± 1°. The predictions of the temporal behavior of droplet wetting diameter during spreading agree with the experimental data. Increasing micro-post arrays spacing reduces the maximum spreading diameter on the surface; in this case, droplet fluid penetrated micro-posts spacing creates a pinning effect while lowering droplet kinetic energy during the spreading cycle. Flow circulation results inside the droplet fluid in the edge region of the droplet during the spreading period; however, opposing flow occurs from the outer region towards the droplet center during the retraction cycle. This creates a stagnation zone in the central region of the droplet, which extends towards the droplet surface onset of droplet rebounding. Impacting droplet mitigates dust from hydrophobized micro-post array surfaces, and increasing droplet Weber number increases the area of dust mitigated from micro-post arrays surfaces.

A Simplified Methodology for Optimal Location and Setting of Valves to Improve Equity in Intermittent Water Distribution Systems

In this paper, a simplified methodology to increase the water distribution equity in existing intermittent water distribution systems (WDSs) is presented. The methodology assumes to install valves in the water distribution network with the objective to re-arrange the flow circulation, thus allowing an improved water distribution among the network users. Valve installation in the WDS is based on the use of algorithms of sequential addition (SA). Two optimization schemes based on SA were developed and tested. The first one allows identifying locations of gate valves in order to maximize the global distribution equity of the network, irrespectively of the local impact of the valves on the supply level of the single nodes. Conversely, the second scheme aims to maximize the global equity of the network by optimizing both location and setting (opening degree) of control valves, to include the impact of the new flow circulation on the supply level of each node. The two optimization schemes were applied to a case study network subject to water shortage conditions. The software EPA Storm Water Management Model (SWMM) was used for the simulations in the wake of previous successful applications for the analysis of intermittent water distribution systems. Results of the application of the SA algorithms were also compared with those from the literature and obtained by the use of the multi-objective Non-Dominated Sorted Genetic Algorithm II (NSGA II). The results show the high performance of SA algorithms in identifying optimal position and settings of the valves in the WDS. The comparison pointed out that SA algorithms are able to perform similarly to NSGA II and, at the same time, to reduce significantly the computational effort associated to the optimization process.

Preface to “Understanding volcanic processes through geophysical and volcanological data investigations: some case studies from Italian sites (EGU2019 GMPV5.11 session, COV10 S01.11 session)”

Volcanic dynamics is driven by the complex interplay between fluid flow (circulation of magmatic and/or hydrothermal fluids) and rock structure (volcano conduits, dykes), the comprehension of which requires both multi-parametric monitoring and modelling of relevant physical and chemical processes of the system. Understanding the factors controlling the dynamics of the processes involved in these interactions is necessary to characterize the overall behaviour of a volcano and the eventual transition mechanisms among stationarity, unrest phases and eruptive styles. The starting point in this context is to have high-quality data of several parameters (seismological, geochemical, geodetic, volcanological), acquired both over years of monitoring activity and focused field experiments. Fundamental contributions come from the use of combined multi-parametric datasets and the adoption of innovative analysis techniques and multi-disciplinary approaches. This Special Issue is addressed to those researchers, who focus their investigations in the field of volcano dynamics. Its main purpose is to shed light on the processes occurring in active volcanic systems over different time scales, with relevant implications for the hazards and the modern monitoring, thus promoting future discussions on this topic. The Issue contains this introducing preface, which describes the Volume aims, and 14 papers, reflecting the main themes. The papers are devoted to the study of some Italian sites, but the proposed approaches are general and therefore applicable to any other volcanic/hydrothermal areas.