High-temperature Heater Research Articles

APPLICATION OF CARBON-CARBON COMPOSITE MATERIALS FOR THE MANUFACTURE OF HIGH-TEMPERATURE HEATERS OF HEAT EXCHANGERS WITH AUTOMATIC TEMPERATURE CONTROL


 The article justifies the use of high-temperature heaters made of carbon-carbon composite material (CCCM) for the thermal unit of a silicon single crystal growth chamber. The conducted analysis confirms that the electrical properties of composite materials, specifically their specific resistance, allow for the creation of heating elements for high-temperature vacuum furnaces or furnaces operating in inert atmospheres at temperatures up to 2200°C.
 The use of heaters made from carbon-carbon composite material eliminates the main drawback of graphite heaters - uncontrolled energy dissipation during resistive heating due to the presence of transient electrical resistance at the junctions of graphite plates, and ensures a more uniform temperature field throughout the chamber volume. The capabilities in terms of the maximum permissible temperature of such a CCCM heater exceed the working temperature by more than two times, which also positively affects the service life.
 The modes of thermal processes occurring during crystal growth are determined by the technological process depending on the composition of the raw material and require high uniformity of heating in the working zone, high precision, and stability of the heater's temperature control. For precise temperature regulation, it is proposed to additionally measure the integral temperature in the chamber indirectly, which is based on measuring the electrical current passing through the heater, which is in thermodynamic equilibrium with the object. Thus, the heater is considered as a system susceptible to various thermal influences that determine the heat transfer process and the temperature change within the chamber and in the zone of the thermal unit's bricks.
 An improved structural diagram of a step-type extremal control system is proposed for automatic temperature control of a high-temperature heater using modern power electronics, sensors, microprocessors. To ensure speed and accuracy in temperature control, the pulse-phase control method implemented with modern specialized thermoregulator with PID-regulation was applied.
 Experimental tests conducted on the «Redmet-30» installation under factory conditions confirm the energy efficiency of using high-temperature heaters made of CCCM.

Dynamic compensation by coupled triple-thermocouples for temperature measurement error of high-temperature gas flow

The gas flow temperature signal simulation system (ATSSS) plays a crucial role in the hardware-in-the-loop simulation of hypersonic aircraft. The accuracy of gas flow temperature measurements is of paramount importance for the ATSSS. This system comprises a high-temperature plasma heater, a gas flow mixing chamber, and thermocouples. The ATSSS exhibits specific characteristics such as high temperatures, rapid temperature changes, and fast flow rates. However, due to the large measurement time constant of high-temperature thermocouples, significant dynamic errors are introduced into the measurement results. To address this issue and enhance the dynamic measurement accuracy of gas flow temperature, this study establishes a thermocouple heat transfer model for the ATSSS. It also analyzes the mechanism behind the generation of dynamic errors in the ATSSS and proposes a three-thermocouple coupled temperature measurement dynamic compensation method (TTCTMDC). This method compensates for errors caused by thermal convection, thermal radiation, and thermal conduction under high-temperature conditions. Simulation results demonstrate that the proposed method can reduce errors by 50% to 80%. In addition, an experimental platform for the ATSSS is constructed, and the TTCTMDC method is employed to compensate for measurement errors. The results indicate that the dynamic measurement error can be reduced to 1/4 to 1/2 of the original value using the TTCTMDC method. This research lays a foundation for the successful development of the ATSSS and provides a novel approach to dynamically measuring high-temperature gas flow, thereby advancing scientific research in the field of measurement.

Two-step thermal treatment of electrochemical graphene oxide films for high-performance electrical heating and electromagnetic interference shielding

Electric heaters have attracted growing interest due to their wide applications in healthcare, smart wear, and aerospace. Contrarily, conventional heaters fail to meet the expectations of flexibility, high temperature, and efficiency. The current protocol focus on the fabrication of a flexible, high-temperature, and high-performance heater through a multi-step strategy. The modified two-step electrochemical exfoliation approach facilitated the formation of electrochemical graphene oxide (EGO). The simple two-step thermal treatment of EGO produced graphene film. The EGO structure exhibits excellent flexibility, good electrical conductivity, and thermal stability after thermal treatment. Consequently, graphene film showed good flexibility and efficient electric heating performance. It only required 13 s to reach 401.2 °C at 3.5 V. Additionally, graphene film displays sufficient heating reliability, stability, and repeatability under heating cycles and prolonged heating. Moreover, it demonstrates electromagnetic interference shielding effectiveness of up to 30383.6 dB cm2/g. Therefore, graphene film has emerged as a promising alternative for developing intelligent clothes, wearable devices, and healthcare devices.

Effect of the annealing temperature on the structural properties of hafnium nanofilms by magnetron sputtering

In this work investigated the effect of the annealing temperature on hafnium nanofilms obtained by DC magnetron sputtering on Si substrates. The nanofilms annealed through 100°C to 700°C by a High-Temperature Strip Heater Chambers (HTK-16N) on an X-ray Diffractometer (XRD). The microstructure and morphology of the films at different temperatures were investigated by XRD, Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and Raman Microspectrometer (RS). It was found that annealing affects changes in the lattice strains, texture, grain size, and roughness of Hf nanofilms. According to XRD data, the structure of the thin films showed amorphous from room temperature to 100°C and starting from a temperature of 200°C were changed crystallization. At 500°C a monoclinic structure corresponding to hafnium dioxide HfO2was formed in hafnium nanofilms.

Robust nanotransfer printing by imidization-induced interlocking

The importance of the nanotransfer technique has been increased owing to its possibility in nanoscale mass-production, enabled by cost-effective and simply fabricable features. In this study, we developed a novel method for robust nanotransfer printing based on imidization-induced mechanical interlocking. The proposed imidization-induced nanotransfer printing (InTP) method enables various metal nanostructures to be easily transferred onto a polyimide substrate based on the mechanical interlocking force by using a controlled imidization process. The designed functional nanopatterns are transferred with high robustness. In addition, using a partial imidization process, we apply an additional adhesion force at the pattern-substrate interface to transfer materials with poor intrinsic adhesion, such as nickel, successfully. Owing to the exceptional robustness of the method, various 3D nanostructures, such as asymmetric sidewalls, suspended nanowires, and dual-layer line patterns, can be successfully transferred. Moreover, the InTP method was used to fabricate a uniform and high-temperature film heater and an asymmetric blind film.

Exergy analysis of supercritical CO2 coal-fired circulating fluidized bed boiler system based on the combustion process

A process simulation on a 600 MW supercritical CO2 (S–CO2) coal-fired circulating fluidized bed (CFB) boiler system was established with the detailed combustion reaction and heat exchange being involved, based on which the detailed exergy distributions of the boiler, as well as its dependence on the varying operating conditions were comprehensively studied. The results showed that the boiler accounting for the largest exergy loss has the exergy efficiency of about 57.7%, which is higher than that of pulverized coal boilers with steam cycle or S–CO2 cycle by 3–5% points. As the excess air coefficient increases, the exergy efficiency of the boiler increases first and then decreases, and the better performance is obtained under 1.1–1.3 of excess air coefficient. When the load decreases, the heat proportion of the cooling wall increases significantly while that of the high-temperature heater accordingly decreases. The exergy efficiency of the boiler decreases with decreasing load especially under the load of 80%∼60%. Additionally, the combustion simulation also effectively predicted the decreases in the SO2, NO and CO emissions with the increasing excess air, and the sharp decrease in SO2 emission as the load is below 80%.

An Appraisal of an Artificial Neural Network Model to Predict Improvement of Generating Capacity of a Coal Thermal Power Plant

Base load of the South Africa electricity supply utility (Eskom) is primarily generated from the coal thermal power plant. A scheduled routine maintenance is crucial in ensuring that each unit of the power plant continues to operate according to the manufacturer’s specifications. The research focused on the analyses of “before and after” outage data obtained from the unit cards and power meters in one of the Eskom’s “once-through” 600 MW coal boiler, with a mechanical conversion efficiency of 35%. The data set collected from the metering cards and also the power meters installed in the designated unit of the coal thermal power plant were divided into training, validation and testing data set of inputs; which included average air heater temperature, average main stream super heater temperature, average high pressure and temperature heater temperature, the total mass of coal burnt, average of the cold and hot condenser well pressure and temperature and auxiliary power consumption) and the targets (power generated) both “before and after outage” scenarios. An artificial neural network model was developed to predict the desired output using the training data set. Furthermore, the model was validated and tested by the validation and test data set. The train neural network showed that the overall correlation coefficient of the outputs and targets for “before and after outage” was 0.979 and 0.992, respectively.

Mathematical modeling of complex heat transfer in a closed internal volume of a high-temperature radiant heater

Mathematical modeling of complex heat transfer in a closed internal volume of a high-temperature radiant heater

Soot abatement from biomass boilers by means of open-cell foams filters

Abstract Currently, fossil fuels such as oil, coal and natural gas represent the main energy sources in the world, but it is well known that these sources of energy will deplete within the next years. So, due to increasing environmental concerns especially related with the use of these fossil fuels, new solutions to limit the greenhouse gas effect are continuously sought. Among the available alternative energy sources, including hydro, solar, wind etc. to mitigate greenhouse emissions, biomass is the only carbon-based sustainable option. However despite an environmentally friendly use of renewable energies, incomplete combustion of biomass can lead to the emission of environmental pollutants as well as substances which are hazardous to health. In comparison to gaseous and liquid fossil fuels, the emissions of particulate matter (PM, or soot) are higher, leading to concerns about the availability of cost-effective techniques to reduce emissions in biomass combustion plants: so filtration devices are mandatory. Actually different filtration systems are available; some have reached a technological maturity and a consequent wide diffusion while others, though promising, have not yet demonstrated adequate features to be considered competitive. In the first class there are electrostatic precipitators, sleeve filters and wet scrubbers, which are standard solutions in medium to large plants. In the second class there are ceramic filters which in principle can be applied both in new equipment and in retrofit of existing boilers, and may be easily scaled according to the size of the boiler. In our previous works we studied the use of catalytic ceramic wall flow filters as soot emission control devices of biomass-fired boilers and stoves. Starting from those results, in this work we investigated the use of a different kind of filters, the open-cell ceramic foams, characterized by a different porosity if compared to wall flow filters. The prepared filters were tested in a customised sampling line at the exhaust of a 30 kW pellets boiler, and regeneration was specifically obtained by a high-temperature electrical heater. PM concentration in the flue gas was monitored by means of a real-time continuous detector and a cascade impactor. The tests evidenced that the higher average pores diameter of the foams, compared to ceramic wall-flow filters, resulted in two main consequences, (i) lower pressure drop, and (ii) a filtration efficiency higher than 50%. These results are very important, in particular because the pressure drop never reached a critical value for the normal biomass boiler functioning: in this way this solution could be a feasible device for soot emissions control. Further studies are still running to investigate the deposition of a catalyst on the foams.

The effect of false-twist texturing parameters on the structure and crimp properties of polyester yarn

In this paper, the effect of false-twist texturing parameters (texturing speed, heater temperature, draw ratio and disc-to-yarn speed ratio (D/Y ratio)) on the structure and crimp properties of polyester yarn has been studied using a high temperature heater and high texturing speeds. Textured yarn was analyzed and characterized in terms of the degree of crystallinity, degree of orientation and crimp properties (crimp contraction, crimp module and crimp stability). The most important parameters, significantly affecting yarn temperature and its uniformity and thus textured yarn structure and crimp properties, are texturing speed and heater temperature. Depending on these texturing parameters, the degree of crystallinity and orientation varied in the range of 24.48 to 36.66% and 0.371 to 0.595, respectively. The crimp characteristics increase with the increase in heater temperature, and decrease with the increase in texturing speed. The effect of draw ratio and D/Y ratio on the textured yarn structure and properties is less pronounced. Obtained results show that partially oriented polyester yarn used in this study can be textured at significantly higher texturing speed (up to 1100 m/min) than the standard texturing speed (up to 700 m/min) used for the yarn count examined.

Self-excited pressure pulsations in ethanol under heater subcooling

This paper presents experimental results of investigation of high-intensity cooling of high-temperature metal heater by subcooled ethanol flow. The experiments have proved the presence of self-excited pressure pulsations with amplitude of 1.15 MPa, arising in ethanol. Expanding real signals of the sensors by the Hilbert−Huang transform has resulted in the intrinsic mode functions. Analysis of these functions and the high-speed video shooting results allows identifying the basic frequencies and mechanisms of pressure oscillations. Comparison of the results with the data of film cooling and bubble boiling on the cooled heater has shown that maximum values of non-stationary heat-transfer coefficients for the self-excited oscillations and for the bubble boiling are the same.

Mg<sub>2</sub>Si<sub>2</sub>O<sub>6</sub>-CaMgSi<sub>2</sub>O<sub>6</sub> 系相平衡と Mg<sub>2</sub>Si<sub>2</sub>O<sub>6</sub>-Fe<sub>2</sub>Si<sub>2</sub>O<sub>6</sub>系の1気圧における相平衡

New phase diagrams in Mg2Si2O6-CaMgSi2O6 system and Mg2Si2O6-Fe2Si2O6 system and stability field of high-temperature orthopyroxene in these systems are proposed. The enthalpy and volume change of the phase transition between low- and high-temperature orthopyroxenes with composition (Ca0.06Mg1.94)Si2O6 at atmospheric pressure were obtained to be 6.2 kJ/mol and 10.25 Å3/unit cell, respectively, and the slope was calculated to be 0.0056 GPa/°C at transition temperature, 1170 °C. From these values, the phase boundary of these phases was defined as P(GPa) = 0.0056T(°C)-6.55. Using this relationships and data of synthetic experiments in previous studies, the phase diagrams and the stability fields of high-temperature orthopyroxene in Mg2Si2O6-CaMgSi2O6 system from atmospheric pressure to 1.0 GPa were determined. The transitions between low- and high-temperature orthopyroxenes with the compositions in Mg2Si2O6-Fe2Si2O6 system were observed at about 1000-1200 °C by using high-temperature in-situ X-ray powder diffraction experiments with a multiple-detector system and a high-temperature strip heater chamber in an atmosphere of Ar plus 1% H2. The stability field of high-temperature orthopyroxene was above 1200 °C and new phase diagram in Mg2Si2O6-CaMgSi2O6 system at atmospheric pressure was proposed.

Supercritical CO2 Rankine cycles for waste heat recovery from gas turbine

A supercritical carbon dioxide (S-CO2) Rankine cycle for waste heat recovery (WHR) from a gas turbine can achieve high efficiency despite its simplicity and compactness in comparison to a steam/water cycle. With respect to WHR, it is very important to maximize the net output power by incorporating the utilization efficiency of the waste heat in conjunction with the cycle thermal efficiency. A simple S-CO2 Rankine cycle used for a high-temperature source cannot fully utilize the waste heat because the working fluid is preheated by the recuperator to a high temperature to achieve a high cycle efficiency. To recover the remaining waste heat from a simple cycle, a cascade cycle with a low-temperature (LT) loop can be added to the high-temperature (HT) loop, or a split cycle—in which the flow after the pump is split and preheated by the recuperator and LT heater separately, before the HT heater can be used. This study presents a comparison of three cycles in terms of energy and exergy analyses of their systems. The results show that a split cycle can produce the highest power of the threes systems considered over a wide range of operating conditions. The reasons for this are explained in detail.

고온 공기 가열기 개발 현황 조사 및 고찰

극초음속 공기 흡입 추진기관의 지상 시험 시 추진기관의 고속 비행 조건을 모의하기 위해 고온 공기를 공급할 수 있는 고온 공기 가열기가 필요하다. 본 논문에서는 다양한 고온 가열기들을 조사하여 유형별로 정리하고, 장단점을 비교하였다. 가열기는 크게 유동장 내 연소 가열기, 아크 가열기, 축열식 가열기, 열교환식 가열기 4종류로 분류할 수 있었으며, 각각의 장단점이 다양하므로 목적에 맞게 가열기를 선정하여야 한다. A high temperature heater is required to supply high temperature air to the hypersonic propulsion system in order to simulate high velocity flying condition during the ground test. Various high temperature heaters were reviewed, categorized, and analyzed in this paper. Heaters were categorized in 4 groups; in-stream combustion heater, electric arc heater, storage heater, and heat exchange heater. Each group has its own advantages and disadvantages, so the heater should be selected considering its purpose.

Phase transitions between high- and low-temperature orthopyroxene in the Mg2Si2O6-Fe2Si2O6system

We observed isosymmetric phase transitions of orthopyroxene in the Mg 2 Si 2 O 6 -Fe 2 Si 2 O 6 system during high-temperature in situ X-ray powder diffraction experiments with a multiple-detector system and a high-temperature strip heater chamber in an atmosphere of Ar plus 1% H 2 . The transition temperatures we determined for natural orthopyroxenes were 1113–1147, 1120–1139, and around 1200 °C for Fs 10 , Fs 14 , and Fs 37 , respectively, and those for synthetic orthopyroxenes were 1048–1075, 961–1048, and 1037–1148 °C for Fs 20 , Fs 30 , and Fs 46 , respectively. Our experiments showed that the transition from low- to high-temperature orthopyroxene in the Mg 2 Si 2 O 6 -Fe 2 Si 2 O 6 system occurred at about 1000–1200 °C. We concluded that the stability field of low-temperature orthopyroxene was below 1000 °C and that of high-temperature orthopyroxene was above 1200 °C.

Focus on test, measurement, and materials

Focus on test, measurement, and materials

Towards MEMS Pellistor Spectrometers

We report on an innovative use of high-temperature MEMS heater platforms as micro pellistor spectrometers. MEMS heater elements, initially designed for use as thermal infrared emitters, were fitted with thin-film noble metal layers to enable catalytic combustion processes on the hotplate surface. The modified heater platforms were operated in a range of combustible gas ambients while applying saw-tooth-like heater waveforms. Measurements of this kind revealed the heat of reaction vs. hotplate temperature profiles for each individual gas. We find that different families of gases yield distinctly different heat of reaction vs. temperature profiles and that these profiles allow the different families, and members inside some of these families, to be distinguished.

Effects of Heat Transfer in Closed Cavity with Different Arrange Forms of Heater

By using the method of finite element, a numerical simulation of heat transfer of the compressed air in a closed square cavity with high temperature heater. Analyze the effects of heat transfer performance, temperature and flow field in closed cavity with different arrangement of heater. Provide a basis for optimizing heater arranged location. The transfer area of heater is the same. And the structure form of the heater includes quadrilateral centered, cross centered and piecewise evenly arranged. Heating efficiency is highest when the heater quadrilateral centered and when heater cross centered, the temperature of the cavity is best in the horizontal direction

CO2 laser debonding of a ceramic bracket bonded with orthodontic adhesive containing thermal expansion microcapsules

We have been studying an easy bracket debonding method using heating of an orthodontic adhesive containing thermal expansion microcapsules. However, heating with a high-temperature heater brings obvious risks of burns around the oral cavity. Thus, we examined safer and more effective bracket debonding methods. The purpose of this in vitro study was to examine the reduction in debonding strength and the time taken using a bracket bonded with an orthodontic adhesive containing thermal expansion microcapsules and a CO2 laser as the heating method while maintaining safety. Ceramic brackets were bonded to bovine permanent mandibular incisors using bonding materials containing various microcapsule contents (0, 30, and 40wt%), and the bond strengths were measured after laser irradiation for 4, 5, and 6s and compared with nonlaser-treated groups. Subsequently, the temperature in the pulp chamber during laser irradiation was measured. After laser irradiation for 5 or 6s, the bond strengths of the adhesive containing 40wt% microcapsules were significantly decreased to ∼0.40 - 0.48-fold (4.6-5.5MPa) compared with the nonlaser groups. The mean temperature rise of the pulp chamber was 4.3°C with laser irradiation for 6s, which was less than that required to induce pulp damage. Based on these results, we conclude that the combined use of a CO2 laser and an orthodontic adhesive containing thermal expansion microcapsules can be effective and safe for debonding ceramic brackets with less enamel damage or tooth pain.

Thermal-fluidic characteristics of a high temperature heater in an experimental helium loop for VHTR simulations

A medium-scale helium loop for simulating a VHTR (Very High Temperature Reactor) is now under construction in KAERI (Korea Atomic Energy Research Institute). Two electric heaters of the test helium loop heat the helium fluid up to 950°C at a pressure of 1–9MPa. To optimize the design specifications of the experimental helium loop, conjugate heat transfer in the high-temperature helium heater was analyzed using CFD (Computational Fluid Dynamics) simulations. The main factors tested in this CFD analysis were the effects of turbulence, radiation, gravity, and geometrical configuration of the heater. From the analysis results, the optimum design configuration was selected confirming that the thermal characteristics of the heater meet the design requirements well. In this study, the interrelated effects of buoyancy forces and radiation heat transfer on the geometrical configuration were closely investigated. It was concluded that the buoyancy effects on the helium flows of the heater would be suppressed by the radiation heat transfer inside the heating channel. Various emissivity values of the reflector materials were also tested. Gravity had greater effect on the temperature distribution for a lower emissivity, but the maximum temperature variations due to the emissivity changes from 0.1 to 0.9 were limited to within a few tens of degrees. Finally, more detailed analyses on the HTH (high temperature heater) of the medium scale helium loop including the spacers were performed, and it was confirmed that the thermal-fluidic characteristics of the HTH satisfied the design requirements.