Small-scale Rig Research Articles

Harnessing the power of neural networks for the investigation of solar-driven membrane distillation systems under the dynamic operation mode

Accurate modeling of solar-driven direct contact membrane distillation systems (DCMD) can enhance the commercialization of these promising systems. However, the existing dynamic mathematical models for predicting the performance of these systems are complex and computationally expensive. This is due to the intermittent nature of solar energy and complex heat/mass transfer of different components of solar-driven DCMD systems (solar collectors, MD modules and storage tanks). This study applies a machine learning-based approach to model the dynamic nature of a solar-driven DCMD system for the first time. A small-scale rig was designed and fabricated to experimentally assess the performance of the system over 20 days. The predictive capabilities of two neural network models: multilayer perceptron (MLP) and long short-term memory (LSTM) were then comprehensively examined to predict the permeate flux, efficiency and gain-output-ratio (GOR). The results showed that both models can efficiently predict the dynamic performance of solar-driven DCMD systems, where MLP outperformed the LSTM model overall, especially in the prediction of efficiency. Additionally, it was indicated that the accuracy of the models for the prediction of GOR can be significantly improved by increasing the size of the dataset.

DFIG Topologies for DC Networks: A Review on Control and Design Features

The doubly fed induction machine has been traditionally adopted in adjustable-speed ac power generation drives in order to take advantage of the reduced rating for the power electronic interface. Aside this well-established application where the doubly fed induction generator (DFIG) is controlled by a back-to-back converter, recent literature records a growing interest toward un-conventional DFIG drives for dc power generation, combining DFIG high control freedom with simplified power electronic interfaces to achieve an overall cheap and fully controllable system. Despite several concepts have been demonstrated on small-scale rigs, there is a lack of systematic comparison among different topologies and control solutions. This paper bridges this gap by providing a review of recent topologies, their control, design and performance, and operation issues. As major novelties, this paper includes off-spec performance comparison of different torque-ripple mitigation strategies, discussion of sizing requirements for generator and power electronics, fundamental aspects of the behavior under voltage dips, and priorities and challenges for future research on the subject.

Development and Dynamical Analysis of Laboratory Facility Exhibiting Full-Scale Combustion Instability Characteristics

This paper describes a new approach that uses a small-scale rig, high-speed optical diagnostics, and the Krylov-based dynamic mode decomposition data analysis technique to elucidate the mechanisms that drive tangential combustion instabilities in full-scale combustors, e.g., liquid rocket engines. The developed rig uses a single injector to supply gaseous reactants whose mean flow direction is perpendicular to the excited, transverse, acoustic oscillations with frequencies equivalent to those encountered in full-scale engines. The strongly coupled fluid mechanics, combustion dynamics, and acoustic oscillations were studied using synchronized, high-speed (10 kHz) particle image velocimetry; OH-planar laser induced fluorescence; chemiluminescence; and dynamic pressure measurements. Each dataset was analyzed with the dynamic mode decomposition method to determine the approximate, complex frequencies and mode shapes of the system’s least-stable modes. The results of this analysis suggest that the fluid dynamics are heavily influenced by shear layer instabilities and helical vortices, signs of which appear in multiple modes with a similar convective velocity. From the fluorescence data, a 168 Hz mode identified near the observed combustion instability frequency suggests a linkage between the transverse acoustic oscillations and the oscillations of the vortex breakdown bubble. This study also suggested that a better description of the driving mechanism might be obtained in the future by simultaneously analyzing all the measured datasets by the dynamic mode decomposition.

Sensorless Frequency and Voltage Control in the Stand-Alone DFIG-DC System

A sensorless stand-alone control scheme of a doubly fed induction generator (DFIG)-DC system is investigated in this paper. In this layout, the stator voltage is rectified by a diode bridge that is directly connected to a dc bus. The rotor-side voltage source inverter is the only controlled converter required in this system and is directly powered by the same dc bus created by the stator-side rectifier. DC voltage and stator frequency are regulated by two independent proportional-integral regulators that give the references for inner current controllers implementing field-oriented control. As it is capable of creating a stable and regulated dc bus, this system can be conveniently adopted to supply dc loads or to form a dc grid. Due to the constraint imposed by the stator diode bridge, the DFIG has to operate under a constant stator voltage, and the conventional stator field-oriented control implemented in stand-alone ac DFIG must be modified. This paper presents the control structure and the theoretical framework for the controller synthesis. Simulation and experimental validations on a small-scale rig are included.

Small scale boilover and visualization of hot zone

Experimental studies of boilover were conducted in small scale rig at Universiti Teknologi PETRONAS (UTP), Malaysia and Loughborough University, United Kingdom. The study at UTP was aimed to demonstrate the ability of conducting tests at a smaller scale to simulate the boilover phenomenon. At Loughborough University, a novel laboratory scale rig was designed and built in order to obtain visual records of fuels' behaviour in a pool fire. The ultimate objective of these studies is to develop a greater understanding of boilover pertaining to fires involving the contents of storage tanks. Fuel mixtures containing light and heavy components were burnt as to study the feasibility of reproducing hot zone formation and boilover in a smaller scale and a safe environment. Boilover occurred after certain period of burning. It is found that thickness of the hot zone changed with time. It is also found that the time needed to start boilover increased when fuel thickness increased. The visualization of the fuel behaviour during the experiments was obtained to better understand the formation and growth of hot zone, the boiling of water layer and hence the boilover occurrence. Based on the data analysis and the photographs recorded from the experiments, the laboratory scale experimental rig could be used to simulate the hot zone formation mechanism and the boilover event safely and successfully. Such information are important for the understanding towards boilover phenomenon.

Model-based active control of a continuous structure subjected to moving loads

Modelling of a structure is an important preliminary step of structural control. The main objectives of the modelling, which are almost always antagonistic are accuracy and simplicity of the model. The first part of this study focuses on the experimental and theoretical modelling of a structure subjected to the action of one or two decelerating moving carriages modelled as masses. The aim of this part is to obtain a simple but accurate model which will include not only the structure-moving load interaction but also the actuators dynamics. A small scale rig is designed to represent a four-span continuous metallic bridge structure with miniature guiding rails. A series of tests are run subjecting the structure to the action of one or two minicarriages with different loads that were launched along the structure at different initial speeds. The second part is dedicated to model based control design where a feedback controller is designed and tested against the validated model. The study shows that a positive position feedback is able to improve system dynamics but also shows some of the limitations of state- space methods for this type of system.

Turbulent Drag Reduction by Biopolymers in Large Scale Pipes

In this work, we describe drag reduction experiments performed in a large diameter pipe (i.d. 100 mm) using a semirigid biopolymer Xanthan Gum (XG). The objective is to build a self-consistent data base which can be used for validation purposes. To aim this, we ran a series of tests measuring friction factor at different XG concentrations (0.01, 0.05, 0.075, 0.1, and 0.2% w/w XG) and at different values of Reynolds number (from 758 to 297,000). For each concentration, we obtain also the rheological characterization of the test fluid. Our data is in excellent agreement with data collected in a different industrial scale test rig. The data is used to validate design equations available from the literature. Our data compare well with data gathered in small scale rigs and scaled up using empirically based design equations and with data collected for pipes having other than round cross section. Our data confirm the validity of a design equation inferred from direct numerical simulation (DNS) which was recently proposed to predict the friction factor. We show that scaling procedures based on this last equation can assist the design of piping systems in which polymer drag reduction can be exploited in a cost effective way.

Medium-Scale Experiments on Stabilizing Riser-Slug Flow

Summary This is the second of two papers describing control experiments on a medium-scale slug rig. The first paper (Sivertsen et al. 2009) describes experiments performed on a small-scale laboratory rig built at the Norwegian University of Science and Technology (NTNU) Department of Chemical Engineering. These experiments showed that, despite noisy measurements, it is possible, with feedback control, to "stabilize the flow" (i.e., to achieve reasonably smooth flow in the normally riser-induced severe slug-flow region) using only topside measurements. The question to be answered is whether these results also apply for larger riser systems. In the present paper, we look at some results obtained from a 10-m-high, 3-in.-diameter medium-scale test rig located at the Statoil Research Centre in Porsgrunn, Norway. Several cascade control structures are tested and compared, both with each other and with the results obtained from the small-scale NTNU loop. The rig was also modeled and analyzed using a simple three-state dynamic model. The new experiments were successful and confirm the results of Sivertsen et al. (2009) from the small-scale rig. The valve opening with nonslug flow operation could be increased from approximately 12% with no control to almost 24% with control using topside measurements only. This makes it possible to produce with a larger production rate and increase the total recovery from the producing oil field. The valve opening with control could be further increased to approximately 28% using measurements from the bottom of the riser, but such measurements may not be available in many cases.

Small-scale experiments on stabilizing riser slug flow

This paper describes the study and results from a small-scale lab rig, build to test different riser slug control strategies without the huge costs involved in larger scale experiments. Earlier experiments on this small-scale rig have shown that it was possible to stabilize the flow using a PI controller with a pressure measurement located upstream the riser base as measurement (Sivertsen and Skogestad, 2005). During these earlier experiments, the slug flow behaved a bit differently from that observed in larger facilities. Instead of severe slugs where the gas entered the riser, the gas was released as Taylor bubbles. As one Taylor bubble managed to enter the riser, several more would quickly follow as the pressure drop across the riser decreased. To get a slug flow pattern that was closer to severe slugs, the length of the riser and the size of the gas buffer tank were increased. After implementing this new equipment, the slug flow regime resembled more the severe slugs seen in larger rigs. The aim now was to control the flow using only topside measurements and to compare with results found using upstream measurements. A controllability analysis was performed in order to screen the different measurement candidates using a model developed by Storkaas et al. (2003). The analysis showed that it should be possible to control the flow using only topside measurements. The results from this analysis were then used as a background for the experiments performed in the lab. The experimental results were successful. They showed that it was possible to control the flow and the results were actually better than predicted from the analysis. In fact, the results are comparable with the results obtained when using a pressure measurement upstream the riser (subsea measurement).

Heat transport in a three-stage thermal energy system using phase change material slurries

This study investigated the feasibility of creating a phase-change slurry in which a phase-change material is microencapsulated and suspended in a carrier fluid. The heat transportation, pumping power consumption, viscosity, and pressure loss of the flowing slurries were measured in order to determine the most suitable concentration of micro encapsulated phase change material (MCPCM) used in the slurry over the range 5-40%. The effects of repeated use of liquid-solid phase-change particles upon melting and solidifying were studied using a small-scale rig of a closed loop circuit comprised of heating and cooling sections. Results indicated that the use of a MCPCM slurry can improve the performance of a working fluid by up to 52% as compared to a single-phase fluid. However, increasing the concentration of the MCPCM to 40% was found to have little effect on heat transport. MCPCM slurry containing a high concentration of MCPCM had a high apparent viscosity. Use of an ionic surfactant was found to be effective in reducing the viscosity. Results also showed that a 20-30% concentration was the most suitable concentration for the working fluid due to the associated heat capacity and reasonable pressure drop. The use of such a slurry could reduce the power consumption of the pump by 16%. Stratification between the solid particles and the carrier fluid was a major drawback and made it difficult to use a conventional open system. This problem was overcome by combining an open and a closed system into a three-stage (open-closed-open) operation.

Use of Dynamic Probing to Inspect the Beds of Damaged and Reconstructed Buildings

A proximate method, which utilizes dynamic probing with a small-scale rig for inspection of the foundations on clayey soils, is discussed. Concise results are cited for field tests conducted to substantiate the procedure, and an empirical formula is presented for calculations. An example of the practical application of this procedure and the equipment used to inspect the slab foundation of a damaged building in Ufa are cited.

Detection of incipient cavitation in pumps using acoustic emission

This work concerns the detection of incipient cavitation in pumps using acoustic emission (AE). Three activities have been pursued in this context: (a) the construction of a small-scale rig for the investigation of cavitation detection using AE sensors; (b) the acquisition of data on a 75 kW single-stage centrifugal pump in an industrial test loop under normal running and cavitation conditions; (c) the determination of parameters that could be used for the early diagnosis of cavitation within pumps. In the laboratory-scale apparatus water was pumped around a short loop by a 3 kW centrifugal pump. The flow loop contained a section specifically designed to induce cavitation by means of reducing the pressure level to that of the vapour pressure of the fluid. This apparatus was used to produce a variety of well-controlled cavitation conditions which were useful in determining the suitability of AE for the detection of cavitation. The industrial-scale tests consisted of progressively reducing the net positive suction head in a 75 kW pump while recording the AE signals at various points on the test loop and pump. Results are presented from both laboratory and full-scale tests which demonstrate the feasibility of detecting incipient cavitation using AE in the face of background noise from normal running of the pump. The features of AE which are indicative of cavitation are also seen to change continuously as NPSH is decreased. Thus early detection of cavitation is possible, certainly before any indication is seen on the dynamic head.

Experiments of Two-phase Flow Dynamics of Marine Reactor Behavior under Heaving Motion

Two-phase flow dynamics of a marine propulsion reactor—of the steam generator in particular—subjected to heaving acceleration were studied on a small-scale rig simulating the primary and secondary circuits of those of N. S. Mutsu. To impart the heaving acceleration, the rig was mounted on a suspended platform oscillated in vertical direction by hydraulic device. Heaving acceleration applied to this rig proved the responding variations of circulating flow, of evaporator steam void fraction and of downcomer water level to be proportional in amplitude to that of the acceleration. The circulating flow was found to pulsate with phase lag behind the heaving acceleration indicative of a second order lag function. Constriction of flow channel downstream of the evaporator—producing resistance against flow amounting to 1.15 times that of the entire loop—proved to amplify significantly the responding pulsations of circulating flow. The pulsations were conversely appreciably diminished by the insertion of a second channel constriction upstream of evaporator—producing 2.7 times loop resistance. When devoid of heaving acceleration, with insertion of flow constriction downstream of evaporator, circulating flow was indicated to be controlled by density wave oscillation, whereas upon application of heaving acceleration, the flow came to be controlled by the external acceleration.

ADSORPTION HEAT PUMP USING HFC REFRIGERANTS

This work is concerned with the investigation of an adsorption heat pump using hydrofluorocarbon (HFC) refrigerants. A small-scale rig was used to study the performance of several combinations of refrigerant and activated carbon which might be used in an adsorption heat pump. Experimental results are presented here together with conclusions and suggestions for further work. © 1997 by John Wiley & Sons, Ltd.

Experiments of Two-phase Flow Dynamics of Marine Reactor Behavior under Heaving Motion.

Two-phase flow dynamics of a marine propulsion reactor-of the steam generator in particular-subjected to heaving acceleration were studied on a small-scale rig simulating the primary and secondary circuits of those of N. S. Mutsu. To impart the heaving acceleration, the rig was mounted on a suspended platform oscillated in vertical direction by hydraulic device. Heaving acceleration applied to this rig proved the responding variations of circulating flow, of evaporator steam void fraction and of downcomer water level to be proportional in amplitude to that of the acceleration. The circulating flow was found to pulsate with phase lag behind the heaving acceleration indicative of a second order lag function. Constriction of flow channel downstream of the evaporator-producing resistance against flow amounting to 1.15 times that of the entire loop-proved to amplify significantly the responding pulsations of circulating flow. The pulsations were conversely appreciably diminished by the insertion of a second channel constriction upstream of evaporator-producing 2.7 times loop resistance. When devoid of heaving acceleration, with insertion of flow constriction downstream of evaporator, circulating flow was indicated to be controlled by density wave oscillation, whereas upon application of heaving acceleration, the flow came to be controlled by the external acceleration.

Natural convection in the cranked thermosyphon

The paper presents the results of an experimental investigation of the heat transfer characteristics of the cranked, tubular thermosyphon under single phase conditions. Using water in a small scale rig, data have been obtained for 10 5.9 < Ra < 10 7.5, and have been plotted in the usual form of Nu vs Ra. The effect of Rayleigh number on Nusselt number suggests three flow regimes: for Ra ≲ 10 6.5. a laminar, impeded regime is generally indicated; for Ra > 10 7.15, the data suggest a turbulent boundary layer regime; between these regimes is a third which has the characteristics of a short-lived fully-mixed turbulent regime.

The influence of tilt on natural convection in the elbow thermosyphon

The paper presents the results of an experimental study of natural convection in a water-filled, elbow thermosyphon. Data have been obtained with a small-scale rig in which the Rayleigh number was varied in the range 10 5.6 < Ra < 10 7.6 with 1.98 cm inner diameter tubes having heated and cooled lengths ranging from 20 to 80 cm. The main purpose of the study was to determine the effect of tilting an initially-vertical cooled section. The results show that forward, or positive, tilts produce very little effect on the heat transfer rate while backward, or negative, tilts produce a dramatic reduction within the first 20 degrees.

Brush plating of bearing alloys on aluminium alloy shells: Turner, M. Diss. Abstr. Int.52 (Jan 1992) 304 pp

The turbocharging of diesel engines has led to increase in temperature, load and corrosive attack of plain bearings. To meet these requirements, overlay plated aluminium alloys are now preferred. Currently, lead-tin alloys are deposited using a zincate layer and nickel strike, as intermediate stages in the process. The nickel has undesirable seizure characteristics and the zincate can given rise to corrosion problems. Consequently, brush plating allows the possible elimination of these stages and a decrease in process together with greater automation. The effect of mode application, on the formation of zincate films, using film growth weight measurements, potential-time studies, peel adhesion testing and Scanning Electron Microscopy was studied, for both SIC and AS15 aluminium alloys. The direct plating of aluminium was also successfully achieved. The results obtained indicate that generally, although lower adhesion resulted when a brush technique was used, satisfactory adhesion for fatigue testing was achieved. Both lead-tin and tin-cobalt overlays were examined and a study of the parameters governing brush plating were carried out using various electrolytes. An experimentally developed small scale rig, was used to produce overlay plated bearings that were fatigue tested until failure. The bearings were then examined and an analysis of the failure mechanisms undertaken. The results indicated that both alloy systems are of the regular codeposition type. Tin-cobalt overlays were superior to conventional lead-tin overlays and remained in good condition, although the lining (substrate) failed. Brush plated lead-tin was unsatisfactory. Sufficient understanding has now been gained, to enable a larger scale automated plant to be produced. This will allow a further study of the technique to be carried out, on equipment that more closely resembles that of a full scale production process.