Steady-state Method Research Articles

Определение коэффициента теплопроводности деревянных клееных конструкций с учетом макроструктуры и плотности древесины

The paper considers calculated and experimental methods of determining the thermal conductivity coefficient of wooden glued structures. The author shows that when designing the thermal protection of building enclosure structures in the form of CLT-panels or wooden glued laminated timber, one uses reference data on the thermal conductivity coefficient for pine or spruce. In practice, the value of the thermal conductivity coefficient may be less than the reference value; as a consequence, the thickness of the building enclosing structures is overestimated. This is not reasonable in terms of material intensity of construction. When considering wood as an anisotropic material, the peculiarities of the macrostructure and differences in the density of individual layers, as well as the wood species, should be taken into account when determining the parameters of structures. Based on the physical description of the thermal conductivity process and the fundamental laws of heat and mass transfer, the author proposes that it is necessary to adjust the results of calculations to the actual values of the thermal conductivity coefficient of multilayer wooden glued structures. The paper presents the results of experimental determination of the thermal conductivity coefficient of pine and aspen wood using steady-state and unsteady heat flow methods. It is shown that, depending on the density and wood species, experimental values of the thermal conductivity coefficient from 0.102 to 0.115 W·m-1∙K-1 can be obtained.

Dual-stage theoretical model of magnetorheological dampers and experimental verification

The theoretical model for predicting the damping characteristics of magnetorheological dampers (MRDs) not only facilitates the optimization of MRD parameters, but also provides assistance for the theoretical design of MRDs. However, some existing models have limitations in fully characterizing the damping characteristics of MRDs. In this paper, the working stage of MRDs was categorized into yield and pre-yield stages based on whether the internal magnetorheological fluid attains the dynamic shear yield state or not, and the Herschel–Bulkley model with pre-yield viscosity (HBPV) and improved polynomial model (IPOL) were employed to respectively characterize the yield and pre-yield stages of MRDs. Subsequently, the HBPV-IPOL model was proposed to characterize the complete damping characteristics of MRDs in low-frequency vibration conditions, with considering the local loss effect of the fluid in the model. To accurately characterize the magnetic induction intensity in the MRD damping channel, employing the steady-state finite element method for magnetic field analysis; on this basis, dividing the damping channel to investigate the variation trends of the magnetic induction intensity in different regions. Simultaneously, the zero-field region hypothesis was proposed to quantitatively consider the influence of minute magnetic induction intensity in the traditional zero-field regions on the damping characteristics of MRDs. Finally, integrating the impact trends of currents in different regions, and employing the HBPV model to determine the impact magnitude of each region within the damping channel on the damping characteristics of the MRD in the yield stage. In the pre-yield stage, polynomial curves were fitted to experimental damping force–velocity curves, and the obtained polynomials were employed to predict the damping characteristics. Extensive experiments have been conducted on MRD samples to assess the predictive performance of the model on MRD damping characteristics under sinusoidal displacement excitation vibration conditions with different excitation currents, vibration frequencies and vibration amplitudes.

Microstructure and properties of Sn-modified graphite film/Al laminated composites by hot press sintering

Graphite/Al composites have received widespread attention due to high thermal conductivity, low density, and excellent processability. In this study, a new process for preparing graphite/Al composites is proposed, which includes preparing Sn-Ag-Ti modified graphite films and then hot pressing and sintering them with aluminum to form laminated composites. The influence of different process parameters on the microstructure and thermal conductivity of a novel modified graphite film/Al composites was investigated. The results show that at 600 °C/30 min/5 MPa, the composites with 57.2 % graphite volume fraction has the highest heat flux of 2.536 J/s, which is higher than Cu 1.636 J/s, and the tensile strength is 45.72 MPa. The thermal conductivity of the large plate measured by the steady-state method is 677 W/(m·K), which is 92.8 % of the theoretical thermal conductivity.

Studies on Fluorescence Quenching, Decay Rate Parameters, Dipole Moment, Rotational Diffusion of 3-(benzo[d]thiazol-2-yl)-7-(diethylamino)-2H-chromen-2-one Laser Dye in Excited Singlet State: Temperature Effect.

The effect of temperature on the absorption and emission characteristics of 3-(benzo[d]thiazol-2-yl)-7-(diethylamino)-2H-chromen-2-one (3BT7D2H-one) laser dye in glycerol solvent has been studied by the steady-state method. Fluorescence intensity decreases with an increase in temperature and shifts towards a shorter wavelength. Parameters like fluorescence lifetime, rate constants, activation energy, and dipole moment (using the thermochromic method) are determined experimentally. Also, the temperature effect on rotational diffusion of 3BT7D2H-one laser dye is studied and also estimated theoretical and experimental hydrodynamic volumes.

Efficiency assessment of variable speed air source heat pump heating systems: A hybrid data-driven and theoretical approach

The laboratory performance evaluations of variable speed air source heat pumps typically adhere to standard steady-state test methods, which neglect the dynamic characteristics associated with actual operation. The evaluation of energy efficiency influencing factors in the actual installed project is crucial for guiding improvements in energy efficiency. The aim of this paper is to identify any loss of dynamic operation, a hybrid approach combining data-driven and theoretical methodologies for modeling and assessing the efficiency of variable speed air source heat pump heating systems based on operation state decomposition. The innovation of this study lies in the abandonment of the previous method for constructing performance maps based on compressor speeds, and instead adopting the concept of thermodynamic perfectibility is introduced to characterize the steady-state performance, serving as a benchmark for identifying operational losses including unsteady-state operation loss, stand-by loss, and defrosting loss based on the actual operating state of the variable speed air source heat pumps. The findings from six monitoring projects indicate that the failure to consider crucial dynamic characteristics can lead to deviations of 4.7%–36.5% from actual performance. These deviations can be attributed to various factors, including a loss of up to 27.2% due to unsteady operation, a standby loss of up to 7.9%, and an unnecessary defrosting operation resulting in a defrosting loss of up to 8.9%.

Prioritization in the Presence of Self-ordering Opportunities in Omnichannel Services

Motivated by the popularity of mobile-order-and-pay applications, especially in fast-casual food restaurants and coffee shops, we study omnichannel service systems—where customers can employ mobile applications for self-ordering—with respect to sojourn times, throughput, and social welfare. Our models are two-stage queues with two customer classes: Walk-ins and mobiles. We identify Pareto efficient prioritization policies, highlighting trade-offs between each class’s mean sojourn times. We allow customers to make strategic joining decisions based on their anticipated delays under an information structure where walk-ins observe partial queue length information. We draw from a wide array of techniques, including steady-state, transient, busy period, hitting-time analyses, and matrix analytic methods. We showcase the significance of prioritization on the system throughput and social welfare. We demonstrate settings where a traditional service system’s (typically beneficial) transformation to an omnichannel reduces throughput. Our analysis highlights the importance of prioritization policy choice for an efficient transition to an omnichannel service system. The throughput-optimal policy choice highly depends on the operational parameters and customer patience levels; implementing a wrong policy can yield a significant loss in throughput and profitability.

Modulation of the Excited States of Ruthenium(II)-perylene Dyad to Access Near-IR Luminescence, Long-Lived Perylene Triplet State and Singlet Oxygen Photosensitization.

Herein, we present a novel ruthenium(II)-perylene dyad (RuPDI-Py) that combines the photophysical properties of pyrrolidine-substituted perylene diimide (PDI-Py) and the ruthenium(II) polypyridine complex [Ru(phen)3]2+. A comprehensive study of excited-state dynamics was carried out using time-resolved and steady-state methods in a dimethyl sulfoxide solution. The RuPDI-Py dyad demonstrated excitation wavelength-dependent photophysical behavior. Upon photoexcitation above 600 nm, the dyad exclusively exhibits the near-infrared (NIR) fluorescence of the 1PDI-Py state at 785 nm (τfl = 1.50 ns). In contrast, upon photoexcitation between 350 and 450 nm, the dyad also exhibits a photoinduced electron transfer from the {[Ru(phen)3]2+} moiety to PDI-Py, generating the charge-separated intermediate state {Ru(III)-(PDI-Py)•-} (4 μs). This state subsequently decays to the long-lived triplet excited state 3PDI-Py (36 μs), which is able to sensitize singlet oxygen (1O2). Overall, tuning 1O2 photoactivation or NIR fluorescence makes RuPDI-Py a promising candidate for using absorbed light energy to perform the desired functions in theranostic applications.

Effect of Sawdust Addition on Thermal Conductivity of Clay Bricks

This research was conducted to find an alternative to the brick wall constituent material with the lowest thermal conductivity value by adding sawdust. The method of measuring the thermal conductivity value used is the steady-state hot plate method. From the test results obtained the more the addition of sawdust, the value of thermal conductivity obtained is also increasing. With the best conductivity value obtained by the author is in the addition of sawdust as much as 5 grams with a conductivity value of 0.006573945Q W/mK.

A Novel Method for Line Selection for Cross-Line Two-Point Successive Grounding Faults Utilizing Transient and Steady-State Information

In order to improve the performance of an arc suppression coil grounding system in handling cross-line two-point successive grounding faults (CTSGs), the applicability of the transient quantity method and the steady-state quantity method for assessing CTSGs is analyzed. Then, a novel method for line selection for CTSGs was proposed, which comprehensively utilizes transient and steady-state information. Specifically, this method adopts a continuous line selection process, with priority given to the transient quantity method, and a supplementary line selection process, with priority given to the steady-state quantity method. After accurately selecting some faulty lines, such lines are tripped, and then, the process proceeds with continuous line selection again. When the number of cycles exceeds the set value, and the fault line cannot be completely cut off, they are tripped one by one according to the degree to which they are approaching the steady-state method criterion, from large to small. Furthermore, in response to the dramatic increase in computing volume that is caused by the continuous application of the transient method in on-site applications and the impact of current transformer accuracy on the steady-state method, this paper proposes corresponding solutions. PSCAD simulation, full-scale tests, and field recording data tests verify that this paper’s method can accurately detect a CTSG.

Temperature effect on spectral characters and dipole moment in short-lived excited singlet S1 state of 3HBI-7D-2HChromen-2-one laser dye in non-associative and highly viscous glycerol solvent

Steady state method is employed to study the effect of temperature on the absorption and emission characteristics of 3-(1H-benzo[d]imidazol-2-yl)-7-(diethylamino)-2H-chromen-2-one(3HBI-7D-2HChromen-2-one) laser dye in glycerol solvent. Temperature induces thermal effect on maxima absorption, emission wavelength, fluorescence intensity etc. Radiative and non-radiative transition probabilities mechanism, fluorescence lifetime, frequency assisted parameters decay rate constants, and activation energy is estimated. Advance thermochromic shift method is adopted to determine the ground and excited state dipole moments.

The Dynamic Assimilation Technique measures photosynthetic CO2 response curves with similar fidelity to steady-state approaches in half the time.

The net CO2 assimilation (A) response to intercellular CO2 concentration (Ci) is a fundamental measurement in photosynthesis and plant physiology research. The conventional A/Ci protocols rely on steady-state measurements and take 15-40 min per measurement, limiting data resolution or biological replication. Additionally, there are several CO2 protocols employed across the literature, without clear consensus as to the optimal protocol or systematic biases in their estimations. We compared the non-steady-state Dynamic Assimilation Technique (DAT) protocol and the three most used CO2 protocols in steady-state measurements, and tested whether different CO2 protocols lead to systematic differences in estimations of the biochemical limitations to photosynthesis. The DAT protocol reduced the measurement time by almost half without compromising estimation accuracy or precision. The monotonic protocol was the fastest steady-state method. Estimations of biochemical limitations to photosynthesis were very consistent across all CO2 protocols, with slight differences in Rubisco carboxylation limitation. The A/Ci curves were not affected by the direction of the change of CO2 concentration but rather the time spent under triose phosphate utilization (TPU)-limited conditions. Our results suggest that the maximum rate of Rubisco carboxylation (Vcmax), linear electron flow for NADPH supply (J), and TPU measured using different protocols within the literature are comparable, or at least not systematically different based on the measurement protocol used.

Experimental investigation on temperature-dependent effective thermal conductivity of ceramic fiber felt

This paper presents a method to invert the effective thermal conductivity of ceramic fiber felt under high temperatures using experimentally measured specific heat capacity, density, and transient temperature data. The method combines the solution of the heat transfer equation with an inversion method based on real-valued genetic algorithm (GA) optimization, and 11 target parameters can be simultaneously inverted with one experimental dataset. The effective thermal conductivities of ceramic fiber felt were obtained by inversion under ambient pressures of 2 Pa and 100 kPa, compression ratios of 0.8–1.0, and temperature ranges of 295∼1273 K. The results indicates that the effective thermal conductivities of ceramic fiber felt derived from the inversion method are in concurrence with the outcomes of the steady state method. The effective thermal conductivities of the ceramic fiber felt range from 0.069 to 0.321 W m−1 K−1. It is observed that the effective thermal conductivity increases with higher temperature, and decreases with growing compression ratio. The impact of ambient pressure on effective thermal conductivity is linked to the level of compression.

A 1-dimensional-two-layer transient drift-flux model for hydraulic transport pipelines: modelling and experiments of bed layer erosion and density wave amplification

Abstract Hydraulic transport pipelines in the dredging, mining and deep sea mining are designed using steady-state methods. However, these methods cannot predict density wave formation. Density waves form a risk for pipeline blockages, therefore there is a need to understand and preferably be able to model the process. The density waves studied in this research are caused by a stationary sediment deposit in the pipeline. This article explores the development of a new transient design model, based on 1-dimensional-two-layer Driftflux CFD. The two layers model the exchange of sediment between the turbulent suspension, and a stationary bed layer, and can therefore model density wave amplification. An empirical erosion-sedimentation closure relationship is applied to model the sediment exchange between the two layers, and is calibrated using experiments. The final model is also validated against a second experiment, specifically for density wave amplification. The experiments and the model show good agreement on the erosion of a stationary bed layer and the growth rate of a density wave and the amplitude of the density wave.

Reliability analysis and inverse optimization method for floating wind turbines driven by dual meta-models combining transient-steady responses

This study introduces an innovative framework aimed at enhancing the reliability, lifespan, and cost-effectiveness of floating wind turbines. By seamlessly integrating transient and steady-state response surface methods, this approach reduces the dimensionality of high-cost, high-fidelity simulation data for floating wind turbines. It effectively utilizes time-domain stochastic response history samples, addressing two critical aspects in reliability analysis, including statistical properties related to maximum loads relevant for static strength design and the distribution characteristics of vibration amplitudes pertinent to fatigue damage design. The processed data is used to construct a forward 1st metamodel, which is integrated into a multi-objective optimization algorithm. This algorithm determines optimal hyperparameters based on stochastic environmental conditions. Subsequently, an inverse 2nd metamodel is established, working in conjunction with the 1st metamodel, forming a dual structure for reliability analysis. Extensive Monte Carlo simulations and probability density analyses demonstrate the effectiveness of the adaptive flexible controller frequency strategy, obtained using the proposed framework, in reducing vibration-induced blade-tip-tower collision risks and long-term vibration damage, particularly at low to medium wind speeds. This significantly improves turbine stability and safety, enhancing overall performance. The proposed methodology provides valuable insights into the design, manufacturing, and operation of floating wind turbines.

Performance analysis of thermally and non-conductive cement mortar prepared from waste iron scraps and magnetite sand

ABSTRACT The existing thermal conductive pavement exploits heating cables as the heat source commonly. However, the poor thermal conductivity of the upper layer in the pavement structure results in a low energy utilisation efficiency. In order to ensure energy transfer efficiency and reduce energy consumption, this paper investigates the application of waste iron scraps and magnetite sand in cement-based materials. The mechanical properties, electrical conductivity and thermal conductivity of cement mortar were tested by ISO method, two-electrode method and plate steady-state method, and the drying shrinkage condition of the specimens was studied by drying shrinkage test. The results showed that there was a critical value of mechanical property enhancement of mortar by waste iron scraps and magnetite sand, while the electrical and thermal conductivity were positively correlated with their admixtures. The study obtained the optimal ratio of waste iron scraps and magnetite sand in the system that would exhibit excellent thermal and mechanical properties while having low electrical conductivity. It can be concluded that this study provides suggestions for solving the problems of low exploitation rate of solid waste and low heat transfer efficiency of thermal conductive pavement.

Temperature Effect on Fluorescence Intensity and Dipole Moment Using Thermochromic Shift Method of 7DA3MHBI-2HChromen-2-one Laser Dye in Highly Viscous Glycerol Solvent.

The steady-state method is used to study the effect of temperature on the fluorescence characteristics of 7-(diethylamino)-3-(1-methyl-1H-benzo[d]imidazol-2-yl)-2H-chromen-2-one (7DA3MHBI-2HChromen-2-one) laser dye in glycerol solvent for the temperature range 293-343K. Absorption and emission characteristics are affected by varying temperatures due to induced thermal effects. Transition probabilities mechanism of non-radiative and radiative are studied and frequency dependent parameters are estimated. Dipole moments in the ground and excited state are estimated using the thermochromic shift method over general solvatochromic methods.

Net-zero carbon configuration approach for direct air carbon capture based integrated energy system considering dynamic characteristics of CO2 adsorption and desorption

Direct air carbon capture (DAC) is a promising negative carbon technology to balance unavoidable carbon emissions from distributed sources. Deploying DAC into the integrated renewable energy system provides an effective way to achieve regional carbon neutrality. Developing a reasonable configuration approach for the DAC-based integrated energy system (IES) is the premise to ensure the stable, flexible, economic and net-zero carbon operation. However, DAC system captures CO2 from the air through adsorption and desorption with a much lower respond speed than other energy generation, conversion and storage equipment in the IES. Meanwhile, the CO2 adsorption/desorption rate varies significantly with time, making the energy consumption of DAC does not fully correspond to the amount of CO2 being captured. Conventional steady-state IES configuration methods fail to reflect such characteristics of the DAC, which may lead to non-optimal or even infeasible configurations. To this end, this paper develops a configuration-oriented dynamic model for the DAC process to correctly reflect the energy consumption characteristics under given internal operating conditions and the variations of the CO2 adsorption/desorption rate over time. The DAC model is embedded into the configuration framework of the DAC-based IES, formulating a novel configuration approach that optimizes the investment, operation and maintenance, carbon reduction and renewables utilization performance. The optimal capacity of DAC and the corresponding time periods for adsorption, desorption and shutdown operation in typical scenario are determined, revealing the coordinated manner of DAC system with other devices within the IES. Case studies demonstrate the effectiveness of the proposed configuration approach, which can meet the carbon neutral target with the lowest economic cost. Further comparisons also verify the advantages of flexible operation of the DAC system to achieve better coordination with renewable generations and more efficient CO2 capture.

The poor reliability of thermal conductivity data in the aerogel literature: a call to action!

Aerogels are an exciting class of materials with record-breaking properties including, in some cases, ultra-low thermal conductivities. The last decade has seen a veritable explosion in aerogel research and industry R&D, leading to the synthesis of aerogels from a variety of materials for a rapidly expanding range of applications. However, both from the research side, and certainly from a market perspective, thermal insulation remains the dominant application. Unfortunately, continued progress in this area suffers from the proliferation of incorrect thermal conductivity data, with values that often are far outside of what is possible within the physical limitations. This loss of credibility in reported thermal conductivity data poses difficulties in comparing the thermal performance of different types of aerogels and other thermal superinsulators, may set back further scientific progress, and hinder technology transfer to industry and society. Here, we have compiled 519 thermal conductivity results from 87 research papers, encompassing silica, other inorganic, biopolymer and synthetic polymer aerogels, to highlight the extent of the problem. Thermal conductivity data outside of what is physically possible are common, even in high profile journals and from the world’s best universities and institutes. Both steady-state and transient methods can provide accurate thermal conductivity data with proper instrumentation, suitable sample materials and experienced users, but nearly all implausible data derive from transient methods, and hot disk measurements in particular, indicating that under unfavorable circumstances, and in the context of aerogel research, transient methods are more prone to return unreliable data. Guidelines on how to acquire reliable thermal conductivity data are provided. This paper is a call to authors, reviewers, editors and readers to exercise caution and skepticism when they report, publish or interpret thermal conductivity data.Graphical

СРАВНИТЕЛЬНЫЙ АНАЛИЗ АКТИВНОСТИ И СЕЛЕКТИВНОСТИ КАТАЛИЗАТОРА LD-145, РЕГЕНЕРИРОВАННОГО МЕТОДОМ СВЕРХКРИТИЧЕСКОГО ФЛЮИДНОГО ЭКСТРАКЦИОННОГО ПРОЦЕССА С ИСПОЛЬЗОВАНИЕМ В КАЧЕСТВЕ ЭКСТРАГЕНТА СВЕРХКРИТИЧЕСКОЙ ПРОПАН/БУТАНОВОЙ СМЕСИ И СВЕРХКРИТИЧЕСКОГО ДИОКСИДА УГЛЕРОДА

A comparative analysis of activity and selectivity of nickel-molybdenum catalyst LD-14 5samples regenerated by supercritical fluid extraction process using supercritical propane/butane mixture and supercritical carbon dioxide as an extractant was carried out. The activity and selectivity of the catalysts were evaluated by steady-state method in a 200 ml autoclave. The process was carried out in hydrogen medium at a temperature of 573 K and a pressure of 3.0 MPa. The products obtained during the reactions were identified on an Agilent chromatography-mass spectrometer with a quadrupole mass analyzer. The separation was carried out on a capillary column with nonpolar stationary phase (DB&HP-5MS UI). The conversion of dibenzothiophene (DBT) was used to evaluate the activity of the catalysts in hydrodesulfination reactions, and the selectivity of direct desulfurization and hydrogenation was determined. The method of catalytic tests under steady-state conditions used in this work is a comparative method and allows to obtain relative data on the activity and selectivity of catalysts under proper selection of experimental conditions (average conversion at the level of 40-60 %). The results of the analysis show that the samples regenerated using supercritical carbon dioxide exhibit higher activity than those regenerated using supercritical propane/butane mixture. The highest hydrogenation capacity was achieved on the samples regenerated with supercritical carbon dioxide, modified with hexane and ethanol, they have 84% and 82.6% conversion of methylnaphthalene, respectively, and recovered activity in hydrodesulfination reactions (DBT conversion 64.6% and 69.1%). The obtained data are in full agreement with the results of studies carried out earlier on the flow unit. Thus, on the basis of catalytic tests it has been established that regeneration of spent nickel-molybdenum catalyst LD-145 should be carried out by supercritical fluid extraction process using supercritical carbon dioxide modified with hexane or ethanol.

Photodynamics of azaindoles in polar media: the influence of the environment.

We have studied the relaxation dynamics of a family of azaindole (AI) structural isomers, 4-, 5-, 6- and 7-AI, by steady-state and time-resolved methods (fs-transient absorption and fluorescence up-conversion), in solvents of different polarity. The measurements in aprotic solvents show distinctive fluorescence yields and excited state lifetimes among the isomers, which are tuned by the polarity of the medium. Guided by simple TD-DFT calculations and based on the behavior observed in the isolated species, it has been possible to address the influence of the environment polarity on the relaxation route. According to the obtained picture, the energy of the nπ* state, which is strongly dependent on the position of the pyridinic nitrogen, controls the rate of the internal conversion channel that accounts for the distinctive photophysical behavior of the isomers. On the other hand, preliminary measurements in protic media (methanol) show a very different photodynamical behavior, in which the anomalous measured fluorescent patterns are very likely the result of reactive channels (proton transfer) triggered by the electronic excitation.