Transient Operating Modes Research Articles

WAYS TO MANAGE HEATING INERTIA

Purpose. The research paper proposes to estimate the effect of heat inertia of the water heating system, in transient operation modes, on the temperature condition in the passenger car, as well as to offer technical solutions intended to reduce the heating system inertia effect and to maintain a stable temperature condition in the passenger car premises in transitional modes of the heating system. Methodology. The author developed the method for controlling the heat transfer of heating system pipes with the help of regulating casing. To control the heating system and the heat transfer of heating pipes, two types of temperature control sensors were used in the passenger car: certain sensors interacted with regulatory casings, while the others interacted with high-voltage tubular heating element control devices. To assess the efficiency of heat interchange regulation of heating pipes and the heating system control, with installed regulating casings, the operation of the heating system with regulating casings and two types of sensors was mathematically modelled. Mathematical modelling used the experimental test data. The results of experimental tests and mathematical modelling were compared. Findings. Currently in operated passenger cars, control of heating appliances is not constructively provided. Automatic maintenance of the set temperature in a passenger car is limited to switching on and off of high-voltage tubular heating elements. The use of regulating casings on heating pipes allows reducing the effects of heat inertia and maintaining stable thermal conditions in a passenger car, using the heating system as a heat accumulator, and also provides the opportunity to realize an individual control of air temperature in the compartment. Originality. For the first time, the paper studied the alternative ways of regulating the temperature condition in a passenger car. Using of the heating system as a heat accumulator. Practical value. The regulation of the heat transfers of the heating pipes by regulating casings allows reducing the effect of thermal inertia of the heating system on the temperature condition in a passenger car, implementing individual adjustment of air temperature in a compartment within 40% of the power of the heating pipe section, using the heating system as a heat accumulator.

Energy efficiency of the machine-tractor unit in transient modes

The study of transient modes of operation of the machine-tractor unit (MTU) in order to improve energy efficiency and energy saving is a very important task. The process of starting and accelerating of MTU is the heaviest mode of operation, which is characterized by considerable dynamic loads and which has a significant influence on the most important indicators: productivity, fuel efficiency, as well as slipping of propulsors, abrasion of the soil and tires, loading and lifetime of the elements of the transmission of tractors. One of the effective methods for reducing dynamic loading is the introduction of elastic-damping links in the drive of propulsors of tractors. The study of impact of elastic-damping drive of traction wheels on the parameters of the MTU operation during the acceleration period were carried out in a complex way: theoretically, on the six mass dynamic equivalent model developed by us, which adequately reflects the actual overclocking processes, and experimentally, in the field conditions on full-scale samples. Methods of software mathematical modeling and developed methods of experimental research were used. The complex of the conducted researches has established: due to the decrease in dynamic loads the improvement of all operational parameters of the MTA has been obtained, including: reduction in the slippage of propellers, tire wear and abrasion, a significant increase in energy efficiency: specific fuel consumption in the process of starting and accelerating of MTU with an elastically damping drive on stubble in gears from the third to the sixth decreases by an average of 40% compared to a rigid serial drive. Due to the smoothing of the peaks of the hook load (by 38%) and the torque (by 36%) with the elastic elements, a more smooth and at the same time more intensive acceleration of the unit is obtained (acceleration time is shortened due to the fact that the slippage is reduced and crankshaft speed is reduced in lesser degree).

Feedback on the Surveillance 8 challenge: Vibration-based diagnosis of a Safran aircraft engine

This paper presents the content and outcomes of the Safran contest organized during the International Conference Surveillance 8, October 20–21, 2015, at the Roanne Institute of Technology, France. The contest dealt with the diagnosis of a civil aircraft engine based on vibration data measured in a transient operating mode and provided by Safran. Based on two independent exercises, the contest offered the possibility to benchmark current diagnostic methods on real data supplemented with several challenges. Outcomes of seven competing teams are reported and discussed. The object of the paper is twofold. It first aims at giving a picture of the current state-of-the-art in vibration-based diagnosis of rolling-element bearings in nonstationary operating conditions. Second, it aims at providing the scientific community with a benchmark and some baseline solutions. In this respect, the data used in the contest are made available as supplementary material.

JUSTIFICATION OF RATIONAL KINEMATIC CHARACTERISTICS OF MOLDING VIBRATING TABLE

Purpose. One of the efficient ways to obtain castings of complex shape is lost foam casting (LFC) in the evacuated molds (containers). Upgrading the quality of this casting method requires improvement of molding techniques. The molding process involves layer-by-layer vibratory compaction of sand in the containers. Most of the lines of LFC sections are equipped with vibrating tables with inertia oscillators driven by induction motors, operating at nominal speed. A promising way of improving the molding technique is the rational setting of the following parameters of vibrating table: vibration displacement, velocity and acceleration. These parameters are determined by the elastic-mass characteristics of the system «vibrating table – mold» and perturbing forces created by inertia oscillators. The aim of the study is to determine the rational range of setting the parameters of oscillators at which the qualitative layer-by-layer compaction of the molding sand in the mold takes place. Methodology. The efficiency criterion for setting characteristics of the vibrating table there were taken the values of averaged accelerations of 6.5 – 7.5 m/s2 corresponding to maximum compaction degree of dry molding sand and the range of acceleration values 9 – 9.5 m/s2 for giving the sand «pseudo-yielding». For the study it was developed a mathematical model of oscillations of the movable part of vibrating table with two types of casting containers for steady and transient operation modes. Findings. In the process of research of the mold oscillations it was calculated the natural frequencies of oscillations at different elastic-mass characteristics of the system using a mathematical model. It was constructed the frequency response of displacements and accelerations of the moving part of the table with container filled with molding sand layer-by-layer. Originality. The author proposes a method of determining the range of frequency setting of inertial oscillators of table, which make it possible to obtain qualitative compaction of dry molding sand in the mold. Practical value. In the process of molding using the lost foam casting models the mold mass is increasing due to the layer-by-layer filling of the mold with molding sand. The change of mass characteristics of the mold requires operational change of the kinematic characteristics of the vibrating table – vibration acceleration. The proposed mathematical model allows determining the ranges of setting the frequency parameters of inertial oscillators of molding table at all stages of molding.

Design of a Brushless PM Starter Generator for Low-Cost Manufacture and a High-Aspect-Ratio Mechanical Space Envelope

This paper presents the results of a brushless permanent magnet (PM) starter-generator design, which caters for low-cost manufacture and a highly constrained mechanical space envelope. The starter-generator design addresses the low-cost requirement through the use of aluminium winding conductors and ferrite PM. This presents several challenges which include, but are not limited to, the selection of an appropriate machine topology to realise a high specific output with the lower performance materials, minimizing the power losses associated with the higher resistivity of aluminium, and the enhancement of thermal performance. The problem is further exacerbated by the demanding space envelope, operating requirements, and the necessity of “design for manufacture.” The selection of an appropriate machine topology is paramount in the present application as the limited mechanical space-envelope results in a “pancake” like geometry in which the aspect ratio of the stator outer diameter to the machine active length is high. To provide a solution satisfying all these challenging design requirements, an approach combining the theoretical electromagnetic and thermal analyses together with tests on machine subassemblies has been employed here. Such a method allows for a more informed design process, where the manufacture and assembly nuances affecting the starter-generator's performance are identified and accounted for prior to prototyping of the complete machine assembly. This paper discusses the employed design methodology in detail. A number of machine designs with alternative winding constructions have been considered providing an insight into challenges and limitations for the cost-effective winding construction utilizing aluminium conductors. The results from analysis of the starter generator suggest that the proposed machine design is capable of achieving the design requirements for both continuous and transient operating modes.

Problems and Development of Methods of Dynamic Simulation of Cryogenic Systems

The problems of designing and employing cryogenic systems operating in transient modes over a considerable operating time as well as various methods of simulating transient operation of these systems are discussed. The advantages of application of dynamic simulation of cryogenic systems over classical methods of calculation of steady-state mode are shown. The available information on dynamic simulation of large helium cryogenic systems is reviewed. To validate the dynamic simulation method, the transient mode of operation of a large helium liquefier is analyzed applying universal software tool for dynamic simulation modeling of chemical systems, the results of which are compared with the experimental data.

Localization of the current of commutator traction motors in constant operation modes of electric stock

A problem of evaluating the possibility of a proposed devise to limit motor current when supply voltage is restored after a short period of separation of a pantograph from a contact wire is formulated. An analysis of the transient processes in the circuits of the traction commutator motors under transient operation modes of the electric stocks and the current limiter in the course of voltage recovery on the pantograph after its separation from the contact wire, the assessment of the variants of feeding the excitation winding; calculation of the parameters of the proposed current limiters; development of variants of computer models; and investigation of the transient processes in the traction motor chain at the supply voltage recovery are carried out in the present article. The effect of excitation winding feeding on the additional power source, as well as the area of possible limitation and exclusion of the motor current inrushes I the course of voltage source recovery, are estimated. The variants of the discharge of the storage element on the excitation winding and the relationships between the capacitor parameters depending on the required value of the winding voltage are considered. A method of controlling excitation winding current from an independent source is implemented. The use of the method and the protection device allows one to increase the commutation resistance of the traction motors at the inrushes or the voltage recovery after loss of the contact of the pantograph with the contact wire, to decrease the possible commutation violation, and to reduce the number of failures.

Mathematical modeling and optimization of transiant thermoelectric cooling process

Detailed theoretical and experimental studies of thermoelectric cooling, as well as its optimization carried out mainly for the steady state operation of the cooling modules. The process of transient cooling insufficiently studied. However, deeper cooling than under stationary conditions may occur in transient modes when optimization. Optimization problems of transient thermoelectric cooling are problems of optimal control of objects with distributed parameters. The article suggests a generalized mathematical model of transient cooling. This model takes into account the main physical factors that affect the process. The problem of optimal control of transient mode of operation of the thermoelectric cooler with an arbitrary number of stages is formulated. It is proposed a method of solving it. The method consists in sampling the object and moving the object with lumped parameters, which is used to optimize the Pontryagin maximum principle. The article gives examples of computer modeling of optimal process control functions of transient thermoelectric cooling. These functions can be used in the construction and auto-calibration PI and PID controllers for the automatic process control of transient cooling in the thermoelectric devices for different purposes.

Modeling and Simulation of the Steady-State and Transient Performance of a Three-Way Pressure Reducing Valve

This paper deals with modeling and simulation of a class of three-way pressure reducing valves. The study aims to point out the peculiarities of function and operation of this class of valves in the steady-state and transient modes of operation. A comprehensive nonlinear mathematical model is deduced in order to predict the performance of the studied valve in both modes. The proposed model takes into consideration most nonlinearities of the studied valve. A computer simulation, based on the proposed model, is performed to predict the steady-state and transient performance. During the simulation study, it was found that nonlinearity occurs due to the following factors: the transient change in the valve operating pressures and the change in the throttling areas of the valve restrictions and their discharge coefficients. The transient change in the valve operating pressures causes nonlinear velocity changes of the fluid flow passing through the throttling areas of the valve restrictions. These throttling areas usually have nonlinear mathematical formulas. The discharge coefficients of these throttling areas are assumed constant independent of the flow rates, Reynolds number, and dimensions of these areas. However, these parameters affect the discharge coefficient in a complicated manner. The validity of the proposed model is assessed experimentally in the steady-state and transient modes of operation. The results show good agreement between simulation and experiment in both modes. The study shows that the geometry of the throttling orifice, which connects the upstream port to the downstream port, plays an important role in the studied valve steady-state and transient performance. This result implies the need for further investigation of the effect of the dimensions of the throttling orifices on the steady-state and transient performance of hydraulic control valves.

Novel bifunctional catalysts based on crystalline multi-oxide matrices containing iron ions for CO2 hydrogenation to liquid fuels and chemicals.

Seven solid mono-, bi- and tri-metallic oxide matrices where Fe(2+,3+) ions are distributed in different chemical/spatial environments were synthesized and characterized by XRD, N2-adsorption and EDAX methods. After basification with potassium, all matrices were activated by carburization or reduction-carburization under conditions selected based on the TPC/TPR spectra, tailoring the carburization extent of iron. The performances of the activated Fe-based catalysts with respect to CO2 conversion and C5+ selectivity were measured in a fixed-bed reactor under standard conditions in transient and continuous operation modes in units containing one or three reactors in series with water separations between the reactors. The catalysts were characterized by XRD, N2-adsorption, HRTEM-EELS and XPS before and after steady-state operation in the reactors. It was found that the rate of CO2 conversion is not limited by thermodynamic equilibrium but is strongly restricted by water inhibition and it depends on the nature of the Fe-oxide precursor. The ratio between the FTS and RWGS rates, which determines the C5+ hydrocarbons productivity, is strongly affected by the nature of the Fe-oxide matrix. The catalysts derived from the Fe-Al-O spinel and Fe-Ba-hexaaluminate precursors displayed the best balance of the two functions RFTS/RRWGS = 0.77-0.78. They were followed by magnetite, CuFe-delafossite, K-ferrite, Fe-La-hexaaluminate and LaFe-perovskite with a gradual lowering of RFTS/RRWGS from 0.60 to 0.15 and a gradual decrease in the C5+ productivity. The active sites that enhance the RWGS reaction are located on the surface of the Fe-oxide phases, while the FTS and methanation reactions occur on the surface of the Fe-carbide phases.

Enhanced dynamical response of derivative controlled third order phase locked loops

Dynamical responses of third order phase locked loops with resonant filters are examined by modifying the control signal applied to loop oscillator. Using signals obtained at some internal nodes of loop resonant filter, the control signal is modified. These signals are effectively single or double derivatives of normal control signal. Performances of modified loops are found to improve during transient and tracking modes of loop operation. This is established through analytical, numerical simulation and experimental studies. The dynamics of the loops in unstable self-oscillatory and aperiodic oscillating modes could also be controlled by these additional derivative control signals.

Experimental characterization of the ITER TF structure cooling in HELIOS test facility

During ITER plasma operation, large thermal loads are generated in the stainless steel Toroidal Field (TF) coil casing. To minimize the impact on the temperature of the TF Cable in Conduit Conductor (CICC), these heat loads are intercepted by case cooling channels which are implemented at the interface to the winding pack. One of the design options for the case cooling channels consists of a stainless steel pipe inserted in a rectangular groove which is machined in the casing and filled by a charged resin of high thermal conductivity. A higher number of cooling pipes is arranged at the plasma facing wall of the case, thus providing a better shielding to the TF conductor at high field. To assess the efficiency of the cooling pipes and their thermal coupling with the charged resin, experimental characterizations have been performed. First of all, the thermal resistance vs temperature of some of the individual components of a TF coil has been measured on representative samples in a cryogenic bench. Further characterizations have been performed on an integrated mock-up of the TF cooling scheme at cryogenic temperature in HELIOS test facility at CEA Grenoble. The mock-up consists of a piece of TF casing that can be heated uniformly on its surface, one cooling channel implemented in the groove which is filled with the charged resin, the filler, the ground insulation, the radial plate and one insulated CICC. The cooling pipe and the CICC are cooled by supercritical helium at 4.4 K and 5 bar; the instrumentation consists of temperature, pressure and mass flow sensors. Both stationary and transient operating modes have been investigated to assess the thermal efficiency of the case cooling design. The experimental tests are presented and the first results are discussed and analyzed in this document.

Comparative study of the transient emission profiles of a light-duty vehicle powered by petrodiesel and a light-duty vehicle powered by biodiesel (Jatropha curcas)

Jatropha curcas biodiesel was produced via transesterification in the presence of acid catalysts. The fatty acid compositions of the biodiesel were determined using gas chromatography and mass spectroscopy. The emission features of a light-duty vehicle fuelled with Jatropha curcas methyl ester and a light-duty vehicle fuelled with petrodiesel fuel were compared in transient operating modes. In comparison with petrodiesel, under the standard test cycle, the hydrocarbon emissions, the carbon monoxide emissions and the particulate matter emissions from the vehicle fuelled with Jatropha curcas methyl ester were decreased by 57.5%, 40.8% and 42.7% respectively, owing to the 11% oxygen content in the biodiesel; however, the nitrogen oxide emissions increased by 4.9%. The regularity of the nitrogen oxide emissions in the transient operating mode are characterized by an innovative term, namely the volumetric concentration ratio of nitrogen oxide to carbon dioxide. The correlations of the transient nitrogen oxide emissions with the carbon dioxide emissions, the fuel consumptions and the operating modes are comprehensively analysed. In the constant-speed mode, the nitrogen-oxide-to-carbon-dioxide ratio becomes stabilized at a relatively low level but rises to a peak under transient conditions. This behaviour particularly occurs when the constant-speed mode shifts to an acceleration operation and when a deceleration operation shifts to a constant-speed mode. During the transient shifting stage, the nitrogen-oxide-to-carbon-dioxide ratio of the biodiesel vehicle is greater than that of petrodiesel vehicle; however, the nitrogen-oxide-to-carbon-dioxide ratios are only slightly different in the stable operating mode.

Implementation of a transient exergy analysis for a plate-fin heat exchanger

A 2nd law thermodynamic analysis with exergy analysis can provide a more robust means of accounting for all of the energy flows within and in between subsystems and the work potential. These energy flows may be thermal, chemical, electrical, pneumatic, etc. Some systems such as air or ground vehicles have very transient modes of operation. Energy optimisation of these vehicles through modelling and simulation may be guided by minimisation of exergy destruction. Quantifying the exergy destruction of a transient system is not trivial. For tracking exergy destruction, a novel transient exergy analysis has been implemented into the heat exchanger model. The heat exchanger model is a plate–fin configuration and is capable of handling several different types of fluids. The model is able to track the change of exergy within the control volume of the heat exchanger and fluids within the heat exchanger. This paper demonstrates the implementation of a transient exergy analysis for a heat exchanger.

Influence of Longitudinal Heat Conduction on the Dynamic and Statistical Characteristics of the Plate-Type Heat Exchangers

The numerical methods of the determination of dynamic and static characteristics of the plate-type heat exchangers with the back-stream circuit of the motion of heat carriers have been considered. The numerical method was developed on the basis of implicit difference scheme. The data of multivariant computations of transient processes of the heat exchanger module are given taking into consideration the longitudinal heat conduction of the separation wall made of aluminum and steel. The stationary state of the heat exchanger and its performances are considered as the completion of the transient process. In the range of adopted values of the velocity and temperature of the flows and partition wall thickness the longitudinal heat conduction affects the parameters of the transient modes of heat exchanger operation; for the stationary states this influence is insignificant.

The influence of locomotive diesel engine transient operating modes on energy usage

This paper analyzes the influence of transient operating modes in the Cat 3512B-HD and MTU 4000 R41 locomotive diesel engines on their energy usage. This analysis represents an integral component of the technological research and development performed at Lietuvos Geležinkeliai AB (JSC Lithuanian Railways) with the objective of increasing the efficiency of freight transportation with the upgraded 2M62M and modern ER20CF/2ER20CF diesel locomotives. The influence of transient modes on the operating variables of the locomotive diesel engines was evaluated under operational load-cycling conditions to aid in the selection of appropriate parameters (e.g., the train weight, the diesel locomotive type, and the technical characteristics of the diesel locomotive to be modeled) for freight transportation on Lithuanian railway lines. It was determined that the engine’s electronic control system compensates for the negative effects of transient operations on the engine’s energy usage. As a result, the increase in fuel consumption is less than 3% during transient operation when compared to steady-state operation. Through this research, methodological foundations have been formulated and adapted for the use of the mathematical modeling of the transient modes of locomotive diesel engines to optimize freight transportation, resulting in an expected decrease of 10–15% in fuel consumption.

Numerical Simulation and Investigation of High Frequency Tube Welding Process

Welding processes and installations used nowadays are mainly developed on practical experience and analytical calculations. Nevertheless, high frequency induction tube welding is a very complex three-dimensional dynamic process, where the electromagnetic and thermal characteristics are distributed not only in space but in time as well. A more profound detailed investigation of the induction tube welding process can be only done by numerical modeling. Full and local three-dimensional transient numerical models of induction tube welding process with continuous movement of the welded tube have been developed and tested. Coupled electromagnetic and thermal analyses are carried out at each time step of simulation for correction of temperature dependent material properties. Voltage or current of the induction coil can be individually input into electromagnetic analysis at each time step. This approach allows simulating “quasi” steady-state and transient operation modes.

Analysis of Friction Induced Thermo-Mechanical Stresses on a Heat Exchanger Pile in Isothermal Soil

In most analytical and numerical models of heat exchanger piles, strain incompatibilities between the soil and the pile are neglected, and axial stresses imposed by temperature changes within the pile are attributed to the thermal elongation and shortening of the pile. These models incorporate thermo-hydro-mechanical couplings in the soil and within the pile foundation, but usually neglect thermo-mechanical couplings between the two media. Previous studies assume that the stress changes imposed by temperature variations in a heat exchanger pile are mainly due to the constrained thermal elongation and shortening of the pile. Also, several recent approaches utilize spring models that focus only on the soil-pile interface in modeling temperature-induced stresses in a heat exchanger pile and implicitly ignore the effect of the full displacement field on soil-pile interaction. By contrast, in this paper, interface elements are introduced in a numerical model of a heat exchanger pile, analyzed in axisymmetric and stationary conditions. The pile is subjected to a uniform temperature increase, with free top and fixed top conditions in elastic and elasto-plastic soil profiles. Simulation results show that the constrained vertical elongation is the most detrimental factor for pile foundation performance. However it is worth noticing that while mechanical constraints (e.g., fixed top and/or fixed bottom) impose maximum stress increases at the ends of the pile, interface effects result in maximum stresses around the mid-length of the pile. This preliminary study indicates that soil-pile friction does not increase pile internal stresses to the point where it would be necessary to over-dimension the foundation pile for heat exchanger use. Furthermore, one cannot expect a significant gain in foundation performance due to the improvement of soil-pile frictional resistance as a result of increased lateral stresses at soil-pile contact. Additional numerical analyses are ongoing, in order to investigate the role of the degree of fixity induced by the building on the heat exchanger pile, and to extend these preliminary analyses to transient operational modes and cyclic thermo-mechanical loading of the heat exchanger pile.

Study of Exhaust Emissions Reduction of a Diesel Fuel Operated Heater During Transient Mode of Operation

SHRNUTÍ Naftová nezávislá topení se obecně používají jako nezávislý zdroj tepla kdekoliv, kde je k dispozici zdroj nafty a elektrické energie. Vzhledem k faktu, že účinnost budoucích spalovacích motorů se bude zvyšovat a pro ohřev prostoru pro cestující tak zbude k dispozici ještě méně tzv. odpadního tepla, význam nezávislých zdrojů tepla dál poroste. Současné emisní předpisy pro nezávislá topení nejsou v Evropě natolik přísná, jako emisní předpisy pro spalovací motory. Předpisy se týkají emisí ve výfukových plynech pouze v tzv. ustálených režimech, nikoli v režimech přechodových, jako je studený start a vypnutí topení. A právě ve zmiňovaných dvou přechodových režimech konvenčního typu nezávislého naftového topení dochází k razantnímu nárůstu emisí CO, HC a také kouřivosti (především emisí bílého kouře). Obsahem tohoto článku je studie možných řešení, použitelných pro nezávislá naftová topení s cílem eliminovat zvýšené emise škodlivin a také kouře během studeného startu a vypínání topení.

Modern state of cycle chemistry monitoring systems at thermal power stations according to the experience gained at the moscow power engineering institute and Element research and production center

Information about the development history of cycle chemistry monitoring systems is presented. The first pilot monitoring system at the Ryazan district power station is briefly described including the characteristics of the analyzers used in the system. The main principles for constructing monitoring systems are formulated. The characteristics of the monitoring systems that were designed and put in operation in the period from 2008 to 2011 are given together with a list of instruments and sample preparation devices used in them. The main advantages of modern analyzers used for chemical monitoring purposes are pointed out. Some problems affecting the operation of monitoring system equipment in the startup and transient operating modes of main power-generating equipment are specially mentioned.