Heating Schedule Research Articles

Dynamic temperature model of district heating system based on operation data

Abstract The simulation of thermal dynamic characteristics of district heating system is of great significance for heat source optimization and scheduling. However, there are two problems in the real-time simulation of temperature distribution in urban district heating systems. First, the structure of the system is complex and it is difficult to obtain all detailed information to establish an accurate model, and the actual varying operating conditions are also hard to be reflected in the model. Second, the accurate and elaborate model could not meet requirements of real-time calculation and optimization. Therefore, the model must be simplified to reflect the dynamic changes of key parameters and be updated simultaneously by using actual operation data. In this paper, the key parameters of the dynamic temperature model are identified and optimized based on the function method and operation data, and a case is studied to verify the feasibility of the method, which demonstrates that it can calculate the outlet temperature distribution of the district heating system accurately and quickly. Thus, this work lays a model foundation for actual heat source optimal scheduling.

A potential source of undiagnosed Legionellosis: Legionella growth in domestic water heating systems in South Africa

Legionella is a genus of pathogenic bacterial mesophiles that cause a range of diseases collectively referred to as Legionellosis, with immuno-compromised individuals being particularly susceptible. Water heaters, a potential domestic niche for these pathogens, are heavy energy consumers, causing cost-sensitive users to employ energy-saving initiatives, such as scheduling and lower temperature set points. However, lower water temperatures allow Legionella to flourish. This paper uses computational fluid dynamics modelling to show that a horizontal electric water heater provides an environment that is conducive to Legionella growth, although its prevalence is probably higher in the downstream pipes. The presence of Legionella in water heaters is established through water sampled from five in-field water heaters, of which the temperatures and heating schedules are known. Microbiological techniques (PCR and weight-based qRT-PCR) are used to assess the presence of Legionella and L. pneumophila at point-of-use taps. A model is used to determine the potential infection rate from these concentrations, demonstrating that undiagnosed Legionellosis infection is likely. In low- and middle-income countries, like South Africa, misdiagnosis of Legionellosis may be common due to the shadow cast by HIV and TB prevalence.

Crystal Growth and Basic Transport and Magnetic Properties of MnBi <sub>2</sub>Te <sub>4</sub>

We report successful growth of magnetic topological insulator (MTI) MnBi2Te4. Depending, upon the heating schedule the phase formation in terms of various Bi2Te3 + MnTe structures viz. MnBi2Te4, MnBi4Te7, MnBi6Te10 and MnTe are seen in powder X-ray diffraction of crushed resultant crystals. The heating schedule basically deals with growth of the crystal from melt at 9000C and very slow cooling (10C/hr) to around 6000C with 24 hours hold time, followed by cooling to room temperature. Our detailed, PXRD Reitveld analysis showed that the resultant crystal is dominated by MnBi4Te7, MnBi6Te10 phases along with some MnTe content. The transport measurements showed a step like behavior at around 150K followed by cusp like structure in resistivity at around 25K (TP) due reported anti-ferromagnetic ordering of Mn. Both the resistivity transitions are seen clearly in dR/dT measurements at 150K and 20K respectively. The 25Ktransition of the compound is also seen in magnetic susceptibility. Low temperature (5K) magneto-resistance (MR) in applied field of up to 6 Tesla exhibited -ve MR below 3 Tesla and +ve for higher fields. Also, seen are steps in MR below one Tesla. The studied MnBi2Te4 MTI crystal could be a possible candidate for Quantum Anomalous Hall (QAH) effect.

Improved Copper-Molybdenum Composite Material Production Technology

This paper devoted to the perfection of manufacturing technique of the composite material fillets (based on copper matrix and molybdenum filler) for SHF electronics products, based on pressure metal treatment methods. The derivatization of high quality constructional material of Mo-Cu-base composite materials with targeted properties is a complex process. Difficulties for obtaining of the composite materials are arise from the large differences in properties of copper and molybdenum, as also the need to take into account such factors as particle size, uniformity of copper and molybdenum powders particles size distribution, accuracy of control and maintenance of the sintering temperature, adherence of heat schedules, holding and cooling. As the result of the research the following operations had been added to the technology process: disintegration control of each fillet after pressing; control of the absence of “dewetting” of copper, cracks and cleavage of each fillet after sintering; cold second pressing of fillets after sintering, sometimes two-fold with intermediate hydrogen annealing; sampling control of density and the value of electric conductivity of fillets. The introduction of the additional operations in the Mo-Cu composite technology process made it possible to improve characteristics of the produced materials, and to increase the yield up to 85%.

Experimental and numerical study on optimization of heating process for small-sized workpieces in vacuum heat treatment furnace

In this paper, experimental investigation and numerical simulation on heating process of small-sized workpieces in vacuum heat treatment furnace have been conducted. The proportional-integral-derivative (PID) control algorithm was employed for the temperature control of the numerical heat transfer model. Compared with the experimental data, the numerical results were validated. The computational maximum temperature difference of workpieces agreed well with the measured ones. In order to develop a new heating schedule for efficiently and uniformly heating loads, effects of heating rate, preheating rate and preheating temperature on heating performance have been researched. The results show that the maximum temperature difference decreases as the heating rate and preheating rate decrease appropriately. It is also found that decreasing preheating temperature can reduce the temperature difference of first-stage but increase the one of second-stage. Based on the results, an optimum heating process is proposed, through which the temperature difference within the workpiece drops below 50 °C during the whole heating schedule.

Influence of composition and heating schedules on compatibility of FeCrAl alloys with high-temperature steam

FeCrAl alloys are proposed and being intensively investigated as alternative accident tolerant fuel (ATF) cladding for nuclear fission application. Herein, the influence of major alloy elements (Cr and Al), reactive element effect and heating schedules on the oxidation behavior of FeCrAl alloys in steam up to 1500 °C was examined. In case of transient ramp tests, catastrophic oxidation, i.e. rapid and complete consumption of the alloy, occurred during temperature ramp up to above 1200 °C for specific alloys. The maximum compatible temperature of FeCrAl alloys in steam increases with raising Cr and Al content, decreasing heating rates during ramp period and doping of yttrium. Isothermal oxidation resulted in catastrophic oxidation at 1400 °C for all examined alloys. However, formation of a protective alumina scale at 1500 °C was ascertained despite partial melting. The occurrence of catastrophic oxidation seems to be controlled by dynamic competitive mechanisms between mass transfer of Al from the substrate and transport of oxidizing gas through the scale both toward the metal/oxide scale interface.

Transient radiative-conductive heat transfer modeling in constructional semitransparent silica ceramics

The article deals with transient radiative – conductive heat transfer investigation in constructional silica ceramics with 10% of total porosity in 2D slab geometry. An empirical model, the so-called effective thermal conductivity (ETC) approximation, and rigorous radiative heat transfer (RCHT) problem solution are compared. Effective thermal conductivity coefficients were determined by both quasi-stationary and non-stationary sample heating and corresponding conductive heat transfer inverse problem solution. Rigorous RCHT calculations were based on radiative transfer equation solution. Spectral directional-hemispherical reflectances were used for scattering and absorption coefficients determination by an identification technique. Identification was based on direct problem solution by invariant embedding technique and parametric optimization. Mie theory and independent scattering approximation with regard to scatterers (pores) size distribution were used for mean scattering cosine estimation. It was shown that in the case of non-stationary temperature regime with rapid heating and cooling stages ETC models fail to predict through the thickness temperature distribution with absolute error less than 502013100 K. The absolute value of this error is strongly affected by the heating schedule. Moreover, calculations revealed several features of the heat flux through the unheated boundary that could not be taken into considerations by effective thermal conductivity approaches.

Combined kinetic analysis of multistep processes of thermal decomposition of polydimethylsiloxane silicone

In this work, we studied the thermal decomposition of a widely employed silicone elastomer, polydimethylsiloxane, in an inert atmosphere. This silicone elastomer has several applications due to its high thermal stability such as MEMS (microelectromechanical systems) precursors, microfluidic components, adhesives, lubricants, and precursors for non-porous ceramics. Therefore, a reliable description of the thermal decomposition kinetics is important to prevent or control the decomposition in such applications. While the decomposition has been amply reported as a complex process, most kinetic studies published on this system use simplified methods that avoid the fact that the entire process cannot be described by a single kinetic triplet. Here, we have studied the decomposition process by first separating the overall reaction into its three constituent steps which were subsequently analysed independently. The deconvolution was carried out using Fraser-Suzuki function that is capable of fitting an asymmetric peak fitting function. The resulting kinetic parameters proved to be able to reconstruct the original experimental curves but are also capable of producing accurate predictions of curves recorded at heating schedules different from those employed to record the experimental data used in the kinetic analysis. Finally, it was found that the rate limiting step of all stages is the diffusion of the gases released during the polymer decomposition through the transforming polymeric matrix.

Efficiency of the Operation of the Cogeneration Steam Turbine Plants at the Variable Heat and Electric Load Schedules

Efficiency of the Operation of the Cogeneration Steam Turbine Plants at the Variable Heat and Electric Load Schedules

Effect of sintering profile on densification, microstructure and mechanical properties of Al2O3-3YSZ-Ni composite

In the present study, the effect of heating schedules on densification, microstructure and mechanical properties of the Al2O3-3YSZ-Ni composite was investigated. The composites were fabricated by one-step sintering (OSS) at temperatures T for 3 h (T/3 h), and two-step sintering (TSS) starting by preheating to a temperatures T1 for 0.5 h, followed by a drop in temperature to T2 equal to 1600 °C for 3 h (T1/0.5 h, 1600 °C/3 h). The contribution of smaller grain size and the improvement of relative density produced by TSS lead to enhanced hardness and fracture strength of the composite without destroying its fracture toughness. The hardness of composites increased with increasing sintering temperature, where its highest value 14.51 GPa was attained at T1 = 1720 °C for TSS. As well, strength was enhanced and reached 417 MPa. However, the toughness for TSS was decreased slightly with increasing T1 and attained its highest value of 6.21 MPa m½ at T1 = 1650 °C.

Study on electrical and structural properties in SiO2 substituted Li2O-Al2O3-GeO2-P2O5 glass-ceramic systems

Two different LAGP glasses with nominal compositions a) Li1.5Al0.5Ge1.5P2.9Si0.1O12 (LAGP1) b) Li1.5Al0.5Ge1.5P2.5Si0.5O12 (LAGP2) were prepared to see the effect of SiO2 substitution in place of P2O5 on their phase formation and electrical properties. Different heat schedules were applied to see the phase evolution in these glass-ceramics (GC). The electrical conductivity of the glass-ceramics samples was measured using impedance analyzer in the frequency range of 0.1–106 Hz and temperature range of 300–373 K. XRD confirm presence of pure LiGe2(PO4)3 in LAGP1 GC sample whereas LAGP2 shows additional minor phases along with LiGe2(PO4)3. In LAGP2 GC XRD patterns showed a little shift in peak position as compared to LAGP1 GC because of SiO2 substitution. LAGP1 shows ionic conductivity value of around 2.45 ×10−4 S/cm at room temperature (RT) for the sample heat treated at 750 oC whereas the LAGP2 GC sample shows maximum conductivity of 8.95 ×10−6 S/cm for the sample heat treated at 700 °C. The conductivity value increased to nearly one order higher with increase in temperature upto 333 K. The lower conductivity value of LAGP2 sample is due to presence of additional minor insulating phases in the sample. The activation energies for dc conductivity was calculated as 0.43 eV and 0.48 eV for LAGP1 and LAGP2, respectively. Ionic mobility of these samples were determined using the permittivity and loss factor and the mobility value is higher for LAGP1 GC (1.34 ×10−3 cm2/V-s) as compared to LAGP2 GC sample (3.56 ×10−6 cm2/V-s). Microstructure of glass- ceramics samples shows growth of very fine structure of around 100 nm size in LAGP1 GC where as in LAGP2 GC microstructures are looking like small globules of less than 100 nm sizes and are interconnected to form a chain like structure. LAGP1 GC with high ionic conductivity is found to have more potential advantages over LAGP2 GC for use in Li-ion battery.

Numerical Analysis of Flow Fields and Temperature Fields in a Regenerative Heating Furnace for Steel Pipes

In the production process of large-diameter seamless steel pipes, the blank heating quality before roll piercing has an important effect on whether subsequently conforming piping is produced. Obtaining accurate pipe blank heating temperature fields is the basis for establishing and optimizing a seamless pipe heating schedule. In this paper, the thermal process in a regenerative heating furnace was studied using fluent software, and the distribution laws of the flow field in the furnace and of the temperature field around the pipe blanks were obtained and verified experimentally. The heating furnace for pipe blanks was analyzed from multiple perspectives, including overall flow field, flow fields at different cross sections, and overall temperature field. It was found that the changeover process of the regenerative heating furnace caused the temperature in the upper part of the furnace to fluctuate. Under the pipe blanks, the gas flow was relatively thin, and the flow velocity was relatively low, facilitating the formation of a viscous turbulent layer and thereby inhibiting heat exchange around the pipe blanks. The mutual interference between the gas flow from burners and the return gas from the furnace tail flue led to different flow velocity directions at different positions, and such interference was relatively evident in the middle part of the furnace. A temperature “layering” phenomenon occurred between the upper and lower parts of the pipe blanks. The study in this paper has some significant usefulness for in-depth exploration of the characteristics of regenerative heating furnaces for steel pipes.

Influence of different heat treatment methods of titania film on performance of DSSCs

Titania mesoporous film is a key component of dye-sensitized solar cells (DSSCs) as it transfers electrons from dye molecule to external circuit through the transparent conducting oxide (TCO). Interparticle connectivity, porosity and cracks in the titania films play an important role in determining the performance of DSSCs. The heating schedule with respect to the repetitive coating to build up titania film thickness impacts the titania film characteristics. In the present study, experiments were designed to carry out heat treatments with expectation of improving connectivity and healing cracks. Repetitive screen printing was carried out with either heat treatment after each print step (multiple sintering) or the heat treatment was carried out just once after the desired thickness had been attained (single-step sintering). Interconnectivity of the titania particles in the sintered titania film was analyzed by impedance spectroscopy and nanoindentation. Titania films sintered by MS showed better performance in terms of higher efficiency for the corresponding DSSCs than those prepared using titania films sintered by SS.

Combined heat and power scheduling: Utilizing building‐level thermal inertia for short‐term thermal energy storage in district heat system

A major limitation to integrating wind power in electric power system (EPS) is the massive generation capacity of the high‐penetration inflexible combined heat and power (CHP) units in district heating system (DHS). A heat and power optimal dispatch is established in this study to exploit building‐level thermal inertia as a form of short‐term thermal energy storage (TES) to unlock the flexibility of CHP units. This proposed short‐term building TES can provide storage potential by utilizing small variations in indoor temperature under the proposed dispatch control model to control the storage capacity in the dispatch process. A linear optimization operational model is run to integrate energy systems by balancing heat and power demands over multiple time periods with CHP units, wind power, short‐term building TES, and district‐level heating network (DHN) storage capacity. A two‐stage decomposition–coordination iteration algorithm is proposed to solve this optimization program. The simulation results are analyzed to determine the potential benefits of this short‐term TES in terms of economics, wind power integration, and the flexibility of CHP units. © 2018 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Coarsening of AA6013-T6 Precipitates During Sheet Warm Forming Applications

The use of warm forming for AA6xxx-T6 sheet is of interest to improve its formability; however, the effect warm forming may have on the coarsening of precipitates and the mechanical strength of these sheets has not been well studied. In this research, the coarsening behavior of AA6013-T6 precipitates has been explored, in the temperature range of 200-300 °C, and time of 30 s up to 50 h. Additionally, the effect of warm deformation on coarsening behavior was explored using: (1) simulated warm forming tests in a Gleeble thermo-mechanical simulator and (2) bi-axial warm deformation tests. Using a strong obstacle model to describe the yield strength (YS) evolution of the AA6013-T6 material, and a Lifshitz, Slyozov, and Wagner (LSW) particle coarsening law to describe the change in precipitate size with time, the coarsening kinetics were modeled for this alloy. The coarsening kinetics in the range of 220-300 °C followed a trend similar to that previously found for AA6111 for the 180-220 °C range. There was strong evidence that coarsening kinetics were not altered due to warm deformation above 220 °C. For warm forming between 200 and 220 °C, the YS of the AA6013-T6 material increased slightly, which could be attributed to strain hardening during warm deformation. Finally, a non-isothermal coarsening model was used to assess the potential reduction in the YS of AA6013-T6 for practical processing conditions related to auto-body manufacturing. The model calculations showed that 90% of the original AA6013-T6 YS could be maintained, for warm forming temperatures up to 280 °C, if the heating schedule used to get the part to the warm forming temperature was limited to 1 min.

Chemical and kinetic insights into the Thermal Decomposition of an Oxide Layer on Si(111) from Millisecond Photoelectron Spectroscopy

Despite thermal silicon oxide desorption is a basic operation in semiconductor nanotechnology, its detailed chemical analysis has not been yet realized via time-resolved photoemission. Using an advanced acquisition system and synchrotron radiation, heating schedules with velocities as high as 100 K.s−1 were implemented and highly resolved Si 2p spectra in the tens of millisecond range were obtained. Starting from a Si(111)-7 × 7 surface oxidized in O2 at room temperature (1.4 monolayer of oxygen), changes in the Si 2p spectral shape enabled a detailed chemical analysis of the oxygen redistribution at the surface and of the nucleation, growth and reconstruction of the clean silicon areas. As desorption is an inhomogeneous surface process, the Avrami formalism was adapted to oxide desorption via an original mathematical analysis. The extracted kinetic parameters (the Avrami exponent equal to ~2, the activation energy of ~4.1 eV and a characteristic frequency) were found remarkably stable within a wide (~110 K) desorption temperature window, showing that the Avrami analysis is robust. Both the chemical and kinetic information collected from this experiment can find useful applications when desorption of the oxide layer is a fundamental step in nanofabrication processes on silicon surfaces.

Production of transparent yttrium oxide ceramics by the combination of low temperature spark plasma sintering and zinc cation-doping

1mol% Zn2+-doped Y2O3 powder was consolidated utilizing spark plasma sintering (SPS) by systematically varying the heating schedule, sintering temperature, heating rate, holding time at the sintering temperature, and loading stress. Transparent, Zn2+-doped Y2O3 polycrystals were successfully produced at the heating rate of 2°C/min, sintering temperature of 890°C, holding time of 30min, and loading stress of 150 or 170MPa. The highest transmittance in the Zn2+-Y2O3 bodies at a wavelength of longer than 600nm was comparable to those in the undoped SPSed Y2O3 in the literature. Employing a sintering temperature and loading stress higher than the optimum values led to coarsened pore and grain sizes, resulting in a decreased transparency. Low heating rate at temperatures above 700°C was desirable for the attainment of high transparency. The grain boundary segregation of Zn2+ cations effectively contributed to the reduction of the sintering temperature required for attainment of transparency in the Y2O3 by SPS.

Coordination of heat and power scheduling in micro-grid considering inter-zonal power exchanges

This paper addresses optimal day-ahead scheduling of Combined Heat and Power (CHP) units of an Active Distribution Network (ADN) with Electric Storage Systems (ESS) and Thermal Storage Systems (TSS) considering Industrial Customers (ICs) inter-zonal power exchanges. The ADN operator may use CHP units to supply its ICs and based on smart grid conceptual model, it can transact electricity with upward wholesale electricity market and its downward ICs' systems; meanwhile its ICs can transact energy with each other through the ADN main grid. Basically, the optimal scheduling of CHP units problem is a Mixed Integer Non Linear Programing (MINLP) problem with many stochastic and deterministic variables. However, the electricity transactions between the ADN and its ICs in normal and contingency scenarios may highly complicate this problem. In this paper, linearization techniques are adopted to linearize equations and a two-stage Stochastic Mixed-Integer Linear Programming (SMILP) model is utilized to solve the problem. The first stage models behavior of operation parameters and minimizes the operation costs; check the feasibility of the ICs' requested firm and non-firm power exchanges, and the second stage considers the system's stochastic contingency scenarios. The competitiveness of ADN in the deregulated market can be improved by adjustment of the proposed decision variables in the two stage optimization procedure. The proposed method is applied to 18-bus, 33-bus IEEE test systems. The effectiveness of the proposed algorithm has been investigated.

Hybrid PSO-SQP for solving combined heat and power dynamic economic emission dispatch problem with non-smooth cost function

In this paper we propose a hybrid particle swarm optimization (PSO) and sequential quadratic programming (SQP) for solving the combined heat and power dynamic economic emission dispatch (CHPDEED) problem. The primary objective of CHPDEED is to determine the optimal heat and power generation schedule of the online generating units over a fixed interval by simultaneously minimizing the generation cost and emission level and satisfying the dynamic constraints and other constraints. Taking into account the valve point effects, CHPDEED is considered as a multi-objective optimization problem with non-smooth characteristics. In the hybrid method, PSO is used as a global search to find near global optimal solution and this solution is used as initial for the SQP to find the global optimal solution at the end. The proposed method is verified using a test system consisting of eleven units and considering transmission line losses and valve point effects. The numerical results show the effectiveness and the superiority of the introduced method over other published methods.

Analysis of thermal energy performance in continuous annealing furnace

In this paper, the effects of several parameters such as the strip width and thickness, strip velocity and also heating power produced by radiant tubes and its distribution on the overall efficiency of continuous annealing furnace were analyzed. A mathematical model was developed to compute the total heat absorbed by the strip. Then, the overall efficiency was calculated. It was recognized that the strip with lower thickness and width may reduce the thermal performance of continuous annealing line. According to this study, both of strip velocity and heating power should be carefully adjusted in each heating schedule. One of the greatest benefits of this work rather than other previous studies is that both strip velocity and heat power are simultaneously considered such that the operator can make a better sense of setting parameters among tangible choices for a predetermined schedule. The results showed despite more heat provided at the entry of the furnace, the effect of adjusting the heating power at the exit of furnace on overall efficiency was remarkably more.