Heating Wire Research Articles

Numerical study on natural convection heat transfer of supercritical CO2 in an infinite space

A numerical study of natural convection heat transfer from horizontal heating wire to supercritical carbon dioxide (sCO2) in an infinite space was performed. The qw ∼ ∆T curves of sCO2 natural convection heat transfer were calculated in a wide range of parameters, where initial bulk temperature (Tib) and operating pressure (P) varied in the range: 275 K < Tib < 345 K and 7.5 MPa < P < 11 MPa, respectively. Then, we reported from the viewpoint of pseudo-phase transition for supercritical fluids, the characteristics and mechanism of sCO2 natural convection heat transfer were revealed through comparing with qw ∼ ∆T curve of subcritical pool boiling. The similarity between film-like heat transfer at Tw > Tpc for supercritical pressure and film boiling at Tw > Tsat for subcritical pressure was demonstrated. The influence of operating parameters such as Tw, Tib, and P on sCO2 heat transfer was also discussed. For supercritical film-like heat transfer, thermal resistance of film-like which reflects the effect of gas-like film thickness and its thermal conductivity on heat transfer was proposed. Expectedly, the variation of thermal resistance explained successfully the difference of sCO2 heat transfer under different operating parameters. The investigation is of paramount importance in comprehension of sCO2 heat transfer mechanism for designing heat exchanger component in the advanced sCO2 application.

P‐62: Fast Response LCD under Low Temperature Environments Using In‐cell Heater Wires

One of the challenges inherent in automotive LCD relates to the response characteristics displayed in low‐temperature environments. In this study, we devised a panel by incorporating heater wires into the Thin‐Film Transistor (TFT) substrate of the LCD, which was optimized through thermal simulations. Additionally, we validated the enhanced response time in low‐temperature environments by utilizing the optimized heater wires within the LCD cell for automotive applications.

Research on the Strength Characteristics of Thermally-Stabilized Loess by Microwave and Resistance Wire Heating

Research on the Strength Characteristics of Thermally-Stabilized Loess by Microwave and Resistance Wire Heating

Experimental and theoretical research on the temperature evolution law of overcurrent fault wires

AbstractTo investigate the problems of overload and excessive thermal insulation associated with building electrical fires caused by wires, a theoretical model of wire heat transfer is established, and the pyrolysis and combustion phenomena of the insulation layer are analyzed. The results showed that the temperature evolution of the wire underwent three stages: constant temperature, insulation heating, and high‐temperature pyrolysis. The insulation layer experiences bulging, exhausting, carbonization, dripping, and burning in sequence, and insulation layer dripping requires at least 160 A of current. As the current increases, the temperature increase rate of the wire increases gradually, and the fusing time of the wire gradually decreases. Under the same current, 160°C is the turning point at which the temperature increases. The temperature increase rate of the copper wire is greater than that of the aluminum alloy wire, and the temperature increase rate of the bare wire is greater than that of the insulated wire. The fusing time of an aluminum alloy wire is less than that of a copper wire, and the fusing time of a bare wire is less than that of an insulated wire. The research results provide theoretical guidance for the prevention and investigation of building electrical fires.

Discrete element analysis of heat transfer characteristics of concrete pavement under electrical heating for snow melting and deicing

The carbon fiber electrothermal method is an efficient approach for snow melting and deicing of pavements in the cold winter. The heat transfer mechanism needs to be explored for the carbon fiber electrothermal system design, especially how the microstructure affects the thermal behavior of pavement. To do so, a discrete element method (DEM) based heat transfer model considering the pavement microstructure has been established in the current study. The shape and content of coarse-grained aggregates have been represented by using the irregular polygonal aggregate method. The accuracy and feasibility of the proposed model were verified by comparing the numerical results with the measured data. On this basis, the heat transfer characteristics of pavements during snow melting and deicing using the carbon fiber electrothermal method have been investigated. The results show that the ambient temperature and the carbon fiber heating wire (CFHW) temperature are the two primary factors affecting the heating efficiency and the maximum temperature on the pavement surface. The spacing and buried depth of the CFHW also play a crucial role in determining the temperature rise rate and the uniformity of temperature distribution of the road surface layer. Furthermore, the effect of the aggregate content on the overall heating rate is not as significant as that of the specific heat capacity ratio of the aggregate to the mortar, suggesting modifying the thermal conductivity of aggregates to enhance deicing efficiency rather than changing the aggregate contents. The effects of the CFHW design parameters on the temperature distribution of the pavement surface are also investigated. The maximum and minimum temperatures of the pavement layer decrease gradually with the increase of the laying spacing and burial depth of the CFHW, but the temperature difference increases with the increase of the laying spacing of the CFHW and decreases with the increase of the burial depth. The research results can provide a reference for the optimization design of snow melting and deicing of pavements by the CFHW heating method.

Heat transfer error analysis of high-temperature wall temperature measurement using thermocouple

Thermocouples are widely employed as the temperature measuring element for an aero-engine. However, due to the unique characteristics of the aero-engine test environment, there exist significant temperature measurement errors of the thermocouple. The steady-state heat transfer error of the thermocouple can be attributed to convection heat transfer error, wire heat transfer error, and radiation heat transfer error. The flow and heat transfer process of wall temperature measurements using armored K-type thermocouples were simulated numerically by Fluent software at the Mach number of 0.1–0.5 and the temperature of 700∼1200 K. The results indicate that convective error accounts for more than 55 % of the total transfer error. To reduce excessive temperature measurement errors, a novel airflow stagnation cover structure around the thermocouple was presented. When the diameter of the stagnation cover is 2 mm, the error of the thermocouple is reduced to less than 1 %.

Simultaneous measurement of thermal conductivity and emissivity of micro/nanomaterials

Although thermal conductivity of micro/nano scale material has been readily measured, the high specific surface area leads to non-negligible radiative heat transfer. Here, a method for simultaneous measurement of intrinsic thermal conductivity and emissivity of micro/nano materials was developed and verified. The physical model of this measurement principle consisted of two parallel platinum wires, which serve as both heaters and heat flux meters. Thermal conductivity and emissivity can be derived by comparing the changes in the average temperature rise of the heater and sensor platinum wires before and after attaching the test sample. The thermal conductivity and emissivity of an individual platinum wire were determined to 71.7 W/(m·K) and 0.14, which are consistent with the reference values. Subsequently, the thermal conductivity and emissivity of the polymer composite fiber were measured to be 1.45 W/(m·K), 0.73 and 1.87 W/(m·K), 0.8 at different composite filler concentrations. In principle, this method is applicable for accurately measuring the thermal transport properties of any micro/nano wires using appropriate sensors.

Isoprenoid emissions from Schima superba and Cunninghamia lanceolata: Their responses to elevated temperature by two warming facilities

Isoprenoids (including isoprene (ISO) and monoterpenes (MTs)) are the majority of biogenic volatile organic compounds (BVOCs) which are important carbon-containing secondary metabolites biosynthesized by organisms, especially plant in terrestrial ecosystem. Results of the warming effects on isoprenoid emissions vary within species and warming facilities, and thus conclusions remain controversial. In this study, two typical subtropical tree species seedlings of Schima superba and Cunninghamia lanceolata were cultivated under three conditions, namely no warming (CK) and two warming facilities (with infrared radiators (IR) and heating wires (HW)) in open top chamber (OTC), and the isoprenoid emissions were measured with preconcentor-GC–MS system after warming for one, two and four months. The results showed that the isoprenoid emissions from S. superba and C. lanceolata exhibited uniformity in response to two warming facilities. IR and HW both stimulated isoprenoid emissions in two plants after one month of treatment, with increased ratios of 16.3 % and 72.5 % for S. superba, and 2.47 and 5.96 times for C. lanceolata. However, the emissions were suppressed after four months, with more pronounced effect for HW. The variation in isoprenoid emissions was primarily associated with the levels of Pn, Tr, monoterpene synthase (MTPS) activity. C. lanceolata predominantly released MTs (mainly α-pinene, α-terpene, γ-terpene, and limonene), with 39.7 % to 99.6 % of the total isoprenoid but ISO was only a very minor constituent. For S. superba, MTs constituted 24.7 % to 96.1 % of total isoprenoid. It is noteworthy that HW generated a greater disturbance to physiology activity in plants. Our study provided more comprehensive and more convincing support for integrating temperature-elevation experiments of different ecosystems and assessing response and adaptation of forest carbon cycle to global warming.

Entire mechanical analysis of prestressed CFRP strengthened RC beams under different prestressed introduced methods

In order to clarify the effect of mechanical tensioning and SMA wire heating recovery on introducing prestress into CFRP sheet strengthened reinforced concrete (RC) beams, an experimental research on the bending performance of prestressed CFRP sheet strengthened RC beams was conducted. Based on the test results, a bending carrying capacity model for RC beams externally strengthened with prestressed CFRP sheets was proposed. The model provides calculation methods for the decompression moment, cracking moment, yielding moment, and ultimate moment, corresponding to different failure modes of the RC beams strengthened with externally bonded prestressed CFRP sheets. Four experimental beams were designed to verify the accuracy of the model with the prestresses of 100 MPa and 200 MPa. The results show that during the yield stage and strengthening stage, the loading-unloading stress-strain relationship curves of SMA wire under different prestrains are basically consistent. When the prestrain of SMA wire is 10%, the maximum recovery stress reaches 448.5 MPa. Under the same prestrain conditions, the maximum recovery stress of CFRP sheets was reduced by 37.8–39.5% when the prestress was introduced through heating recovery of SMA wires. The failure mode of mechanically tensioned prestressed CFRP sheet strengthened beams is the CFRP sheet debonding caused by mid-span bending cracks, while the failure mode of strengthened beams with prestressed CFRP sheet by SMA wire heating recovery is the CFRP sheet end debonding. The cracking moment and yield moment of the strengthened beams are significantly increased by two methods of introducing prestressing. The stiffness improvement of mechanically tensioned prestressed CFRP sheet strengthened beam is relatively large. While, the prestressed CFRP sheet strengthened beam by SMA wire heating recovery gradually experience end peeling failure of the CFRP sheet, and the prestressing effect does not effectively limit the development of cracks, resulting in limited stiffness improvement. The calculation results are in good agreement with the experimental results, proving that the proposed method for analyzing the entire bending process can be used to predict the bending mechanical properties of the prestressed CFRP sheet strengthened beams.

Design of an electric activation system for the smart hybrid tendons crack-closure system in concrete beams.

This work presents the design of a smart activation system for the crack-closure technology of the Hybrid Tendons. Previous research has demonstrated the effectiveness of this technology in providing a self-repairing mechanism for concrete elements. The Hybrid Tendons are made combining a pre-stressed Kevlar inner core restrained by a Shape Memory Polymer sleeve. To trigger the crack-closing action, the Shape memory potential of the outer sleeve needs to be activated via heating. The work focuses on the design and testing of an electric activation system for the Hybrid Tendons using a system of heating wires. Kanthal wires are chosen for this application and integrated in the manufacturing process of the Hybrid Tendons: the wires are wrapped around each tendon and connected to a power supply. An experimental campaign is conducted to assess the system's capability to activate the Hybrid Tendons and deliver the crack-closing action in concrete beams under constant load. Additionally a numerical model is also developed to offer a sound interpretation of the experimental results. The system is ultimately proven successful in activating the Hybrid Tendons embedded in the concrete, effectively delivering the crack-closing action and boosting the flexural response of the structural element.

Effects of nano-metal oxide additives on ignition and combustion properties of MICs-boron rich fuels

Boron has been considered a promising powdered metal fuel for enhancing composite propellants' energy output due to its high energy density. However, the high ignition temperature and low combustion efficiency limit the application of boron powder due to the high boiling point of the boron oxide layer. Much research is ongoing to overcome these shortcomings, and one potential approach is to introduce a small quantity of metal oxide additives to promote the reaction of boron. This study prepared boron-rich fuels with 10 wt% of eight nano-metal oxide additives by mechanical ball milling. The effect of metal oxides on the thermo-oxidation, ignition, and combustion properties of boron powder was comprehensively studied by the thermogravimetric analysis (TG), the electrically heated filament setup (T-jump), and the laser-induced combustion experiments. TG experiments at 5 K/min found that Bi2O3, MoO3, TiO2, Fe2O3, and CuO can promote thermo-oxidation of boron. Compared to pure boron, Tonset can be reduced from 569 °C to a minimum of 449 °C (B/Bi2O3). Infrared temperature measurement in T-jump tests showed that when heated by an electric heating wire at rates from 1000 K/s to 25000 K/s, the ignition temperatures of B/Bi2O3 are the lowest, even lower than the melting point of boron oxide. Ignition images and SEM for the products further showed that the high heating rate is beneficial to the rapid reaction of boron powder in the single-particle combustion state. Fuels (B/Bi2O3, B/MoO3, and B/CuO) were mixed with the oxidant AP and ignited by laser to study the combustion performance. The results showed that B/CuO/AP has the largest flame area, the highest BO2 characteristic spectral intensity, and the largest burn rate for powder lines. To combine the advantages of CuO and Bi2O3, binary metal oxide (CBO, mass ratio of 3:1) was prepared and the test results showed that CBO can very well improve both ignition and combustion properties of boron. Especially B/CBO/AP has the highest burn rate compared with all fuels containing other additives. It was found that multi-component metal-oxide additive can more synergistically improve the reaction characteristics of boron powder than unary additive. These findings contribute to the development of boron-rich fuels and their application in propellants.

Discrete element analysis of heating transfer characteristics of airport pavements by using electro thermal method for snow melting and deicing

This study presents a discrete element investigation on the internal temperature change characteristic and heat transfer efficiency in airport concrete pavement by using the carbon fiber electrothermal method for snow melting and deicing. A discrete element model for snow melting and deicing of airport concrete pavement by using the carbon fiber electrothermal method was generated. The temperature evolution on the surface of the pavement was captured and compared with the indoor experimental results. The numerical simulation results were in good agreement with the experimental results, which verified the applicability of the numerical model. On this basis, the effects of the heating temperature and heating paths on the internal heat conduction and temperature field distribution were investigated. The results showed that the temperature of the pavement surface and the temperature rise gradient are linearly related to the temperature of the carbon fiber heating wire. The initial heating time has little influence on the temperature rise path of the road surface layer after stopping heating and reheating. The temperature of the road surface layer rises slowly after the heating is stopped, and then decreases linearly at a rate of 0.4 °C/h not corresponding to the initial heating time.

Fabrication of Titanium Aluminide Alloys by Twin-Wire Tungsten Inert Gas Welding Applied with High-Frequency Induction Heating Wire Technology: Processing, Microstructure, and Properties

Fabrication of Titanium Aluminide Alloys by Twin-Wire Tungsten Inert Gas Welding Applied with High-Frequency Induction Heating Wire Technology: Processing, Microstructure, and Properties

Numerical investigation of heat transfer in wire and tube-based phase change material heat exchanger

The utilization of latent heat storage units with their high energy density and isothermal heat transfer behavior can enhance the performance of thermal energy systems. This study aims to investigate the effect of fin placement on the melting time of a wire and tube-based Phase Change Material (PCM) heat exchanger using numerical simulations. The study introduces a new complex geometry for the heat exchanger, and numerical analysis of heat transfer was conducted in Ansys Fluent software using an established solidification and melting model. The numerical results were validated against experimental data, and it was found that the position of the tubes and fins had a significant impact on heat transfer within the PCM. The model was able to predict temperature data with a maximum discrepancy of 3%.

Dependence of Radiance of Burning Coal Bed on Ash Formation and Dew Condensation

Abstract In this study, coal samples with different moisture contents were prepared using a drying and humidification system. Coal samples were placed in a crucible and ignited using a heating wire, to which power was applied during coal combustion. The combustion radiance of coal samples with three moisture contents (0, 20, and 50%) was measured using a narrow-angle radiometer at three temperatures (10, 25, and 50 °C). A numerical simulation model was developed to predict the unsteady radiation characteristics of a coal layer burning on one-dimensional planar plates. The unsteady energy balance equation and radiative transfer equation were solved using the semi-implicit Runge–Kutta method and discrete ordinates method. In addition, the effect of dew condensation on the radiance was investigated. The greatest reduction in radiance was observed during the burning of the high-moisture coal. Furthermore, the effect of ash (converted from coal) on radiance was examined. The results demonstrated that certain changes in the optical properties during the burning of coal to ash can alter the absorption as well as anisotropic scattering, and thereby the radiance, as combustion proceeds.

Effect of heating wires with electric potential on pool-boiling heat transfer under an electric field

In this study, we investigated the influence of heating wires with electric potential on a pool-boiling system under an electric field. We employed a numerical method that combines the pseudopotential lattice Boltzmann model, leaky dielectric model, and finite-difference model. Heating wires with different positions and electric potentials above a horizontal heater were explored. A detailed analysis of the boiling process occurring on the heater was performed at various electric-field intensities and for different boiling regimes, both with and without wires. For the pool-boiling system without heating wires, the results revealed that the critical heat flux (CHF) increased with the electric-field intensity, and the superheat required for the system to attain film boiling increased with electric field intensity. Placing heating wires on the heater surface resulted in the deterioration of heat transfer in the system without an electric field. However, the optimal distance between the heating wires and the heater remarkably promoted heat transfer during the film-boiling regime. The introduction of heating wires with electric potential into the system disrupted the original electric-field distribution, consequently impacting the boiling process and heat transfer. Compared with the system without both heating wires and an electric field, the system without heating wires exhibited a 7.9 % increase in the largest CHF at a low electric-field intensity of CaE = 0.2. However, at the same electric-field intensity, the largest CHF increased by up to 39.4 % when heating wires with an electric potential were employed. These findings provide a theoretical foundation for the practical application of effectively employing wires with electric potential to enhance boiling heat transfer.

On-Site Application of End-Grain Bonded Timber Under Low Curing Temperatures

The end-grain bonding of timber components using the Timber Structures 3.0 technology (TS3) is an advancing construction method in timber engineering. This technology allows the realisation of any plate size by bonding plates on-site where low temperatures influence the performance. Therefore, investigations are underway to evaluate the influence of the low temperatures on the curing process. Additionally, research is in progress to discover techniques to reduce any adverse effects of low curing temperatures on the mechanical properties of the bond. The implementation of particular measures, such as the inclusion of milled heating wires into the joint and the pre-heating of the joint with a hot air blower, has been identified as advancing the potential for grouting even in the face of low external temperatures, as recent research has indicated.

Experimental study on influence of temperature on breakdown in a waveguide cavity

Radio frequency (RF) breakdown is one of the crucial factors limiting the power capacity of high-power microwave (HPM) generators. In this paper, a waveguide cavity has been designed to study quantitatively the influence of temperature on high-gradient RF breakdown. The two planes of the waveguide cavity are divided into a strong-field side and a weak-field side with the feeding of microwave signals. The temperature of the strong-field side of the waveguide cavity can be adjusted from ambient temperature (25 °C) to 435 °C by loading a resistive wire heater. The breakdown threshold of the waveguide cavity decreases apparently with the increase in the temperature. The breakdown threshold at 408 °C is 751 kV/cm, which is about 150 kV/cm lower than that at ambient temperature. In addition, the higher the temperature, the more pronounced the pulse shortening. Under the same microwave power injection, the averaged pulse width of HPM after passing through the waveguide cavity at 408 °C is equal to 17.6 ns, shortened by about 1/3 compared to that at ambient temperature. The quantitative study of the influence of temperature on the RF breakdown provides a new guideline for exploring breakdown suppression methods in HPM generators.

Determination of flow velocities using fiber-optic temperature measurements

A new flow measuring technique is introduced to measure liquid flow velocities under harsh circumstances in environments with dirt, high pressures and elevated temperatures as in boreholes within the earth’s crust. A glass fiber embedded in a cable with heating wires measures the temperature within the heated cable with fiber-optic temperature sensing. Similar to hot-wire anemometry (HWA), the velocity dependence of convective heat transfer is exploited to measure the velocity around the cable as a cylinder in crossflow. In the first experiment, a borehole-mimicking test rig and a realistic prototype of a borehole probe were built and the flow along the borehole axis was investigated. The concept of this new measurement technique was proven, since the expected Nusselt-Reynolds characteristic of a cylinder in crossflow has been successfully measured. Furthermore, a temperature profile model across the cables cross section has been developed to account for the unexpectedly low ranges of Nusselt number. The model accuracy has been addressed with a second experiment, where a straight segment of a custom-built heated cylinder was placed in a water channel perpendicular to the flow direction. The upstream flow speed during this set of measurements was recorded using particle image velocimetry (PIV), while multiple temperature sensors in the channel, on the probe’s sheath and within the probe delivered the information for the heat transfer model.

High performance microheater-based catalytic hydrogen sensors fabricated on porous anodic alumina substrates

Catalytic combustion-type gas sensors are widely used in industry and everyday life for detecting flammable gases. However, high power consumption is one of the main drawbacks of the catalytic sensors. Replacing the platinum wire heating element with a thin-film microheater can significantly reduce power consumption, but maintaining high sensitivity and long-term stability of such devices is a challenge. Here we developed microheater-type catalytic hydrogen sensors based on porous anodic aluminium oxide served simultaneously as a substrate for platinum microheater and as a carrier for a catalyst. The fabricated sensors have a high sensitivity of 76 mV/vol% hydrogen. The deviation of the sensor response during continuous operation for 14 days is less than 4%. The relative humidity of the ambient atmosphere does not affect the sensor response. The fast sensor response time (0.4 s) makes it possible to use the pulsed power supply mode to reduce the power consumption to 3.2 mW without sacrificing the measurement accuracy. The performance of the developed catalytic hydrogen sensors promotes the high competitiveness in the market and the prospects for industrial applications.