Modelling and Control of the Moisture in a Test Bench Flow with Time-delay

International audienceMoisture control in systems with time delay is studied in this work to be assessed in a process-control system (Test bench). To further investigate the phenomenon of transport delay in flows, the test bench system has been studied. In this work it is presented the design and validation of a model which describes the dynamics of mass transport phenomena. In order to control the moisture in the test bench, it is design a state-feedback controller such that the closed-loop system is robustly stable has an upper bound for the time delay

Prediction-based control of moisture in a convective flow

International audience— This work studies a convective flow system and presents experimental closed-loop results carried out on a test-bench representative of several industrial processes. This test bench consists of a horizontal column equipped with a mist actuator located at the inlet and fans generating an air flow circulating along the tube. Following our recent theoretical design, we implemented a prediction-based control strategy aiming at stabilizing the mist at the output of the tube actuating on the wind speed. Correspondingly, this setup involves a transport input-dependent delay (between the inlet and the output of the tube). We propose a control-oriented model, in which the transport delay satisfies an integral equation, and compared our prediction-based design with a conventional Proportional-Integral controller. Experimental results underline the relevance of the proposed approach

Adaptive compensation of diffusion-advection actuator dynamics using boundary measurements

International audience— For (potentially unstable) Ordinary Differential Equation (ODE) systems with actuator delay, delay compensation can be obtained with a prediction-based control law. In this paper, we consider another class of PDE-ODE cascade, in which the Partial Differential Equation (PDE) accounts for diffusive effects. We investigate compensation of both convec-tion and diffusion and extend a previously proposed control design to handle both uncertainty in the ODE parameters and boundary measurements. Robustness to small perturbations in the diffusion and convection coefficients is also proved

3D Photocatalytic Air Processor for Dramatic Reduction of Life Support Mass and Complexity

To dramatically reduce the cost and risk of CO2 management systems in future extended missions, we have conducted preliminary studies on the materials and device development for advanced "artificial photosynthesis" reaction systems termed the High Tortuosity PhotoElectroChemical (HTPEC) system. Our Phase I studies have demonstrated that HTPEC operates in much the same way a tree would function, namely directly contacting the cabin air with a photocatalyst in the presence of light and water (as humidity) to immediately conduct the process of CO2 reduction to O2 and useful, "tunable" carbon products. This eliminates many of the inefficiencies associated with current ISS CO2 management systems. We have laid the solid foundation for Phase II work to employ novel and efficient reactor geometries, lighting approaches, 3D manufacturing methods and in-house grown novel catalytic materials.The primary objective of the proposed work is to demonstrate the scientific and engineering foundation for light-activated, compact devices capable of converting CO2 to O2 and mission-relevant carbon compounds. The proposed HTPEC CO2 management system will demonstrate a novel pathway with high efficiency and reliability in a compact, lightweight reactor architecture. The proposed HTPEC air processing concept can be developed in multiple architectures, such as centralized processing as well as "artificial leaves" distributed throughout the cabin that utilize pre-existing cabin ventilation (wind). Additionally, HTPEC can be deployed with spectrally tunable collection channels for selectable product generation. HTPEC employs light as its only energy source to remove and convert waste CO2 using a non-toxic composite catalyst.We have demonstrated in the Phase I studies the production, tunability and robustness of the novel composite catalysts following the preliminary work in the Chen laboratory. Additionally, we have designed, fabricated and tested all components of HTPEC device with active materials, including flow modeling to optimize flow mixing and pressure drop as well as the production of ethylene and other larger hydrocarbons. To best determine how this technology could be implemented, we also performed system integration optimization and trade studies. This includes parameters such as mass, volume, power in relation to selected mission configurations, CO2 delivery methods and light source/delivery approaches

DRAINAGE BEHAVIOR OF AQUEOUS, POLYMERIC, AND OIL-BASED NITROGEN FOAMS: THEORETICAL AND EXPERIMENTAL INVESTIGATION

Foams can be formulated to have a wide range of densities and viscosities. This unique behavior makes foam suitable for underbalanced drilling where pressure exerted on formation is maintained below pore pressure and at the same time, favorable conditions for a good hole-cleaning can be established in the wellbore. Foams are also used as in fracturing, cementing, and, enhanced oil recovery applications. However, the disadvantage of foam is its inherent instability. The stability of aqueous foams in vertical conduits has been extensively investigated. However, in many industrial applications such as underbalanced drilling foam is used in inclined configurations. The stability of foams inclined conduits is not well understood. The effect of geometry is often ignored. In addition, polymer-based and non-aqueous foams with more complex flow and stability behavior are becoming more common. As a result, there is a strong need to investigate foams to better understand the effects of different operational factors (inclination, conduit geometry, base fluid type, and shearing) on their stability. Thus, the main goal of this study is to investigate each of these factors with respect to their impact on foam stability. To achieve this, foam stability experiments were conducted in concentric annulus and straight pipe sections. The pipe section is manufactured from a fully transparent PVC pipe, enabling visual inspection of foam structure and liquid drainage. The annulus is made of stainless steel casing and a rotating inner PTFE (polytetrafluoroethylene) rod. Three types of foams (aqueous, polymeric-based and oil-based foams) were used in the investigation. All tests were performed at 400 KPa and ambient temperature (22 ± 2oC). Foam quality was ranged from 40 - 80%, except for oil-based foam which was limited to 70% due to instability at high qualities. Foam rheology data was obtained from pipe viscometers before conducting stability tests. Two inclination angles (0o and 30o) were considered in this study. For tests conducted in the annulus, the rotation speed of the inner rod was varied (0, 4, and 7 rpm) to examine the impact of shearing on foam stability. Hydrostatic pressure data measured from the annular test section is converted into density profiles, which are used to determine the drained liquid volume as a function of time. In straight pipe sections, the volume of drained liquid was measured using a measuring tape. A digital camera with a microscope was used to capture images of foam in real-time to examine the process of foam decay (i.e. the degree of bubble coarsening and coalescence). Foam stability increased with quality. For a given quality, foam prepared with polymeric fluid was the most stable, while oil-based foam was the least. The wall effects can hinder bubble and drained liquid motion and consequently delay drainage. As a result, foam drained more slowly in the annulus than in pipe. Inclining the test sections resulted in much faster drainage, possibly due to the formation of a liquid layer between foam structure and container walls that flows down due to gravity, effectively avoiding the hydraulic flow resistance of foam structure. The effect of shearing on drainage was minimal for the level of shear rate applied. Channel-dominated model developed in this study is suitable for all foams considered (40-80%). Node-dominated model is not recommended for these wet foams as it tends to over predict liquid volume fractions at early time steps

Experimental analysis of crankcase oil aerosol generation and control

Crankcase ventilation contributes significantly to diesel engine particulate emissions. Future regulations will not only limit the mass of particulate matter, but also the number of particles. Controlling the source of crankcase emissions is critical to meeting the perennial legislation. Deficiency in the understanding of crankcase emissions generation and the contribution of lubricating oil has been addressed in detail by the experimental study presented in this thesis. A plethora of high speed laser optical diagnostics techniques have been employed to deduce the main mechanisms of crankcase oil aerosol generation. Novel images have captured oil atomisation and passive oil distribution around the crankcase of an optically accessed, motored, four cylinder, off highway, heavy duty, diesel engine. Rayleigh type ligament breakup of oil films present on the surface of dynamic components, most notably the crankshaft, camshaft and valve rockers generated oil drops below 10 micrometers. Data illustrated not only crankcase oil aerosol generation at source, but it has provided valuable information on methods to control oil aerosol generation and improve oil circuit efficiency. The feasibility of utilising computational fluid dynamics to predict crankcase oil aerosol generation has been successfully assessed using the experimental data. Particle sampling has characterised the crankcase emissions from both a fired and motored diesel engine crankcase. The evolution of submicron crankcase particles down to 5 nm has been recorded from both engines, including the isolated contribution of engine oil, at a wide range of engine test points. Results have provided constructive insight into the generation and control of this complex emission. The main mechanism of crankcase oil aerosol generation was found to be crankshaft oil atomisation. This atomisation process has been analysed in detail, involving high speed imaging of primary and satellite drop generation and high speed digital particle image velocity of the crankshaft air flow. A promising mechanism of regulating and controlling crankcase oil aerosol emissions at source has been studied experimentally

Thermofluidic Characterization of Carbon Dioxide Near Critical Conditions at Microscale

This work revealed the thermo physical characteristics of near critical and supercritical carbon dioxide at the micro scale. The results include the extension of flow boiling heat transfer correlations, boiling inception, near critical bubble dynamics, thermalization mode shift, Joule Thomson effect and pressure drop evaluation. It was found that extremely low superheat temperatures are required for boiling inception near the critical conditions (i.e., T=31.4 °C, and P=7.37 MPa), and boiling heat transfer correlations were extended up to a reduced pressure of 0.99. The work also revealed a significant enhancement of the heat transfer coefficient as the critical conditions approached, which was partially attributed to a shift of the thermalization mode (i.e., up to x 3 higher compared to lower reduced pressures). For the first time, the thermalization shift in convective micro scale flows was visualized and measured using marker-less technique. Additionally, it was found that near the critical conditions the growth and translation of bubbles slowed down and were driven by thermal diffusion (i.e., asymptotical thermally driven models described the bubble dynamics well). Moreover, the interactions between the bubbles had major influence on the bubbles\u27 growth rate. Subsequently, a micro-orifice was integrated into the microchannel to demonstrate the importance and applicability of the Joule Thomson coefficient (JTh) in the vicinity of the critical point of CO2. In the experiments the fluid\u27s temperature was reduced to -10.8 °C, which is 34 °C below ambient, without complicated thermal insulation due to the sustainable Joule-Thomson effect. Lastly, pressure drop for the micro-orifice were compared with different models (i.e., homogeneous and separated two phase flow, capillary tube, and short tube orifice correlation). The capillary tube model best predicted the measured pressure drop. To conclude, this work presents a major advancement in understanding the thermophysical behavior of carbon dioxide and will lay the foundation to its wider utilization in the future

Computational fluid dynamics modelling of benzene abatement using cryogenic condensation

Eng. D. ThesisThis thesis presents a computational fluid dynamics model of aerosol nucleation and growth using a Eulerian-Lagrangian approach. The research aimed to assess the applicability of cryogenic condensation to controlling benzene emissions from an industrial process operated by the industrial research sponsors. Cryogenic condensation is an attractive option for controlling vent emissions of volatile organic compounds (VOCs). In speciality chemicals industries such as pharmaceuticals, nitrogen is often used to create an inert atmosphere in vessel headspace. Cryogenic condensation can utilise the cooling potential of existing nitrogen infrastructure, making the process energy efficient in comparison to conventional alternatives such as adsorption and thermal oxidation. However, many pollutants freeze or desublimate at the low temperatures (ca. -100°C) used in cryogenic condensation. For these high melting point VOCs, a fine particulate could form under the temperature gradients inside the condenser. Through modelling the process, the research aimed to answer two main questions: will cryogenic condensation control benzene vapour emissions down to the limits set by the environmental regulators; and will it reach this limit without generating a benzene aerosol particulate that becomes entrained in the outlet gas. The research found that the cryogenic condensation alone would not reach the strict emissions limit required by the regulation, and that particle entrainment does make a contribution to this. The model showed roughly 97% of benzene is captured (compared to 99.978% removal that would be required to meet emissions limits) with around 1% escaping as particulate. This information is useful to the industrial sponsors of the research, and other industries considering using cryogenic condensation for benzene abatement. The modelling approach used is a novel contribution to the field with wider potential applications in other areas