Temperature Heating Element Research Articles

Determining the absolute number density of a thermal vapor via photon correlations

We propose a technique to determine the absolute number density N of an alkali-metal vapor confined within a nanocell. This method is based on near-resonant driving of the vapor's constituent atoms and determining the mean interparticle distance (or equivalently the temperature) from the power spectrum associated with the offset photon intensity-intensity correlation function g(2)(τ)−1. In our investigation, we treat the atoms as an average of interacting and radiating dipole pairs randomly positioned within the nanocell. We observe that the power spectrum of the emitted light has a central dip for interparticle distances corresponding to ∼λ/5 and that this result is robust to variations in the driving Rabi frequency and the average detuning. With our proposed method, we can overcome the limitations in defining the absolute number density N, which is currently typically deduced from the temperature of heating elements applied externally to the cell. Published by the American Physical Society 2024

Enhanced comprehension of the cross-scale forming mechanism in CF/PEEK resistance welding: Analysis of temperature gradients and meso–microscopic phase transitions

Resistance welding technology is an effective solution for connecting thermoplastic composites. However, limited research on non-uniform distribution of interfacial temperature and complex evolution mechanism of phase-change molding hinders its application. This reliance on traditional experimental and trial-and-error methods severely impedes its development. Therefore, this study employed a novel cross-scale numerical simulation method, being applied for the first time in the field of resistance welding for elucidating the underlying mechanism of joint formation through multi-component phase transformation. The constructed model accurately represented the transient heat transfer of a realistic wire mesh structure in three dimensions, while incorporating complex gradient effects arising from both spatial and temporal variations in heating element temperature due to air interference. Further, melting, flow, and consolidation behavior of the resin matrix in resistance welding of carbon fiber/polyetheretherketone (CF/PEEK) thermoplastic composite was investigated herein at a mesoscopic scale. To accomplish this objective, a three-phase flow spatial forming and evolution model for resistance welding was developed at the mesoscopic scale by integrating principles from fluid dynamics. Interestingly, introduction of an air phase reinstated the spatial voids formation and flow in resistance welding, providing robust evidence for the initiation mechanism of internal defects. Moreover, this study revealed variations in the melting mode of PEEK resin across different regions within the weld and highlighted distinct distributions of voids resulting from uneven heat transfer. The interfacial phenomenon and flow diffusion mechanism between components in resistance welding tests were further verified and discussed through analyzing scanning electron microscopy and energy dispersive spectroscopy results. Temporal and spatial correlation in void distribution within the welding zone was observed, which was found to be consistent with simulation results. Specifically, with the progress of the welding process, air near the wire mesh gradually dispersed into the laminate, with significantly more voids at weld seam edges than in central regions. This research methodology based on stepwise scale reduction offers a promising avenue for investigating resistance welding and other connection forming applications, in particular, within the context of engineering underlying logical behavior.

Optimization of Hot Gas Welding of Hybrid Thermoplastic-Thermoset Composites Using Taguchi Method

In this study, the influence of four different process parameters on hot gas welding of CF/epoxy fiber composites functionalized with a PA6 thermoplastic film is investigated. Additional experiments are carried out on specimens adorned with triangular beads of coupling material that are printed onto the plates, ensuring extra material within the joining zone. This approach offers a great advantage for compensating geometric tolerances. The parameters considered are common process parameters for regular two-step processes: Heating element temperature (THE), heating time (HT), welding force (F) and welding time (HTF). The design of experiments (DoE) is planned according to the Taguchi method. An orthogonal array is used to set up the experimental plan. Three factor levels of each welding parameter are considered. The test series are carried out with two sample variants. In the second sample variant, additional thermoplastic material is placed in the joining zone. The strength of the welded joints is investigated by tensile shear tests according to DIN EN 1465. The results show that the welding force has the greatest influence on the welding strength. Heating times of 20 s were found to be optimal. Within the first sample variant, a saturation behavior of the welding force can be observed at 500 N. Higher heating element temperatures (500 °C) and welding forces (1165 N) are advantageous using additional material. High welding temperatures result in a negative effect on the interdiffusivity of the polymer chains.

Modelling of a Heated Gas-solid Fluidised Bed using Eulerian Based Models

ABSTRACT An Eulerian-Eulerian granular model was used to simulate the flow and heat transfer through a heatedgassolid fluidised bed. The primary objective of the study was to determine whether the Eulerian-Eulerian granular model adequately predicts the chamber pressure drop, temperature, and bed expansion through the bed. The model predictions were assessed and validated for various flow-regimes, namely the fixed-bed, smooth, bubbling fluidisation, and the maximum fluidisation regimes. This was done on an experimental scale heated gas-solid fluidised bed. However, the results are generalisable for heated gas-solid fluidised beds when the flow is laminar. Numerical models were created using Computational Fluid Dynamics (CFD). The CFD-model predictions were investigated, analysed, and compared to experimental results. Basic experiments were carried out to obtain varying hydrodynamic characteristics. The results showed a slight overprediction of pressure drop and bed expansion, however, the results were still in close agreement with the experiment. In contrast, underprediction of chamber temperatures were obtained. Based on the results of this study, it is recommended that the Eulerian model be used to predict dynamic flow behaviour. Before minimum fluidisation, when in a fixed bed regime, pressure drop in the chamber increases with no increase in bed height. No visible bubbles were present in the fixed bed regime. When fluidisation has been reached, the bed height rises whereas the pressure drop tends to a constant value. Bubble size increases with chamber height and increased superficial velocities. Bubble speed increased with increased chamber height. With increased superficial velocity, the chamber temperatures increase to a maximum temperature of326.65 K with an initial heating element temperature of373.15 K. However, when excessive heat is present in the gas-solid fluidised bed, other methods that sufficiently incorporate particle-particle interactions and bubble-bubble interactions, are recommended. An investigation should be lent to bubble-bubble interactions in the fluidised beds with relation to heat transfer. Additional keywords: Heated fluidised bed, computational fluid dynamics, CFD, Eulerian, granular, fluidisation, gas-solid

Deicing Concrete Pavements and Roads with Carbon Nanotubes (CNTs) as Heating Elements.

Existing deicing technologies involving chloride and heating wires have limitations such as reduced durability of roads and surrounding structures, and high labor requirements and maintenance costs. Hence, in this study, we performed indoor experiments, numerical analyses, and field tests to examine the efficiency of deicing using carbon nanotubes (CNTs) to overcome these limitations. For indoor experiments, a CNT was inserted into the center of a concrete sample and then heated to 60 °C while maintaining the ambient and internal temperatures of the sample at −10 °C using a refrigeration chamber. Numerical analysis considering thermal conductivity was performed based on the indoor experimental results. Using the calculation results, field tests were conducted, and the thermal conduction performance of the heating element was examined. Results showed that the surface temperature between the heating elements exceeded 0 °C. Moreover, we found that the effective heating distance of the heating elements should be 20–30 cm for effective thermal overlap through the indoor experiments. Additionally, the numerical analysis results indicated that the effective heating distance increased to 100 cm when the heating element temperature and experiment time were increased. Field test results showed that 62 cm-deep snow melted between the heating elements (100 cm), thus, verifying the possibility of deicing.

Dissolved gas analysis of thermal faults in transformer liquids simulated using immersed heating method

Dissolved gas analysis (DGA) is considered as one of the most effective techniques to diagnose transformer incipient faults. With the increasing applications of alternative liquids in transformers, fault gas generation characteristics of the liquids were investigated in laboratory under simulated faults. Immersed heating method has been widely used to simulate thermal faults, of which the complete fault temperature range was hardly achieved. In this paper, pool boiling theory was introduced to explain the underlying reason that why the complete fault temperature range cannot be achieved using immersed heating method. There are three stages in pool boiling including natural convection region, nucleate boiling region and film boiling region. The Nukiyama temperature of a mineral oil was found to be 330°C. This is the highest stable temperature achieved by the immersed heating method in T2 region, beyond which the heating element temperature is unstable and hence temperature measurement is unreliable. The Nukiyama temperature of an ester liquid was found to be 390°C, which is higher than that of the mineral oil due to its higher boiling point. The findings imply that the previously published T2 DGA results obtained using immersed heating method at reported temperatures beyond the Nukiyama temperature have likely been in T3 region near to the melting temperature of the heating element (normally higher than 1000°C).

THE AUTOMOBILE TIRES VULCANIZATION METHOD REPAIR PROCESS EXPERIMENTAL INVESTIGATION

In the article local repair automobile tires expediency by vulcanization means in mechanical damage carcass case is shown. It has been established that analytical and experimental data on determining the required temperature of the heating element have a significant discrepancy. It was found that on the vulcanization degree among all factors temperature and pressure on the welding surfaces are the most influential. After processing the experimental data and using the static methods, mathematical dependence of the temperature on the welding surface from the heating element temperature and on the welding surfaces as a second-degree polynomial is obtained. In order to verify the research results reliability, the control welding of the automobile tires with cord lateral rupture was conducted, which gave positive results.

Research on three‐phase four‐leg matrix converter based more electric aircraft wing ice protection system

In this study, a new three-phase four-leg matrix converter (TFMC) topology is proposed, and the three-dimensional space vector modulation (3DSVM) strategy is used to realise the output with the three-phase unbalanced load. Aiming at the situation that the icing area of the more electric aircraft on the wing is larger than the icing area in the belly, wing ice protection system is constructed by using the TFMC. Through the real-time detection of the heating element temperature and icing condition by the sensor installed in the wing and belly position, working temperature and three-phase output power of TFMC can be set reasonably. In order to save fuel consumption and reduce operating costs, the key point is to reduce the power transmission in belly position. Finally, simulation and experiment verify the correctness of the proposed 3DSVM strategy and realise the TFMC output with unbalanced three-phase load.

Constructive and technological aspects of the heat flow imitator based on diamond-like films

The paper describes features of the design and manufacturing technology of a volumetric detachable heat flow imitator designed for the study of thermal characteristics and for carrying out thermal tests of heat pipes of cooling systems for electronic equipment. The authors use thin alumina ceramic plates with deposited with diamond-like films as heating elements of the imitator. Experimental results are presented on the surface temperature of heating elements and the temperature drop between the heating elements and the heat pipe in the region of the input heat flux values from 5 to 25 W. The use of the proposed heat flow imitator allows speeding up the process of research and testing of heat pipes.

Measurements of the evaporation rate upon evaporation of thin layer at different heating modes

Technique for measurements of the evaporation rate of a heated liquid layer is presented. The local minimum is observed which is associated with the point of equilibrium of the liquid–gas interface. It is shown when no heat is applied to the heating element temperature in gas phase is larger than in liquid, and evaporation occurs with the rate of 0.014–0.018 μl/s. Then evaporation rate is decreasing with increasing the heater temperature until the equilibrium point is reached at the liquid–gas interface. Further increasing of the heater temperature leads to increasing of the evaporation rate.

Effect of Zr Content on the Morphology and Emissivity of Surface Oxide Scales on FeCrAlY Alloys

The investigation aims at obtaining a life time extension of FeCrAlY heating elements by increasing the emissivity of the alumina surface scales. This approach will allow the use of a lower heating element temperature without decreasing the usable heat output. For this purpose, the oxidation mechanisms of Zr‐doped FeCrAlY model alloys were investigated. For thick specimens a high Zr addition is accompanied by an undesired rapid increase of the oxidation rate adversely affecting the life time of the component. However, for thin foil heating elements (typically 50–200 μm thickness) an optimized high Zr content might be a suitable concept for obtaining a high emissivity, because apparently, a dark appearing, high emissivity oxide may be obtained without occurrence of dramatic internal oxidation.

Direct in situ thermometry: Variations in reciprocal-lattice vectors and challenges with the Debye–Waller effect

Conventional in situ transmission electron microscopy (TEM) enables the atomic-scale study of dynamic materials processes on millisecond time scales. Specimen holders capable of being heated to over 1000°C have provided insight into myriad processes, including nanoscale thermal transport, structural phase transitions, and catalytic reactions. In order for such studies to be accurate and precise, direct determination of the specimen temperature – rather than the heating-element temperature – is critical. Further, such methods should be versatile in that any temperature across a wide range may be measured, irrespective of single-indicator properties specific to the specimen (e.g., first-order phase transition, melting point, etc.). Here, we describe a rigorous approach to direct, in situ thermometry of TEM specimens that exploits lattice thermal expansion and the resultant decrease in diffraction-vector magnitude in reciprocal space. Via sub-pixel measurement of reciprocal-lattice-vector magnitudes, picometer increases in lattice parameters are measured over a continuous temperature range and compared to those expected from the coefficient of thermal expansion. Statistical treatment of several experimental trials conducted on nanostructured aluminum thin films shows excellent agreement with both theory and (indirect) measurement of the in situ heating holder. Additionally, we illustrate how uncontrolled, thermally-induced variation in single-crystal orientation leads to modulation of the excitation error and, therefore, the Bragg-spot intensities resulting in a convolution of heating and tilting effects, thus complicating temperature determination via the Debye–Waller effect.

Thermal and sanitary performance of domestic hot water cylinders: Conflicting requirements

In order to understand the sanitary implications around the demand side management of domestic hot water cylinders, microbial samples were taken from the bottom of 10 UK domestic electric hot water tanks whose heating elements are connected to a controlled off-peak supply. The results indicated high concentrations of bacteria in the water and biofilm. Microbial concentrations remained high in spite of the application of seven hours of heating during off-peak hours. Further numerical and experimental work shows that this problem arises due to the differing modes of heat transfer that prevail above and below the immersion element. The results from thermal and bacterial growth models suggest that it is impossible to achieve sanitary conditions throughout standard domestic hot water tanks without significantly increasing the heating element temperature or lowering the heating element from its current position. Raising the immersion thermostat temperature results in additional heat losses whilst lowering the immersion position compromises thermal stratification leading to uneconomical operation. Guidelines around storing hot water at temperatures that are sufficient for the purposes of sterilizing human pathogens such as Legionella, fail to take account of the conflict between thermal and sanitary performance. By better understanding the distribution of temperatures and bacteria within hot water tanks along with the associated risks, improved design and control strategies may be adopted to facilitate effective demand side management of hot water systems whilst meeting sanitary requirements.

SIMULASI KARAKTERISTIK ALIRAN DAN SUHU FLUIDA PENDINGIN (H2O) PADA TERAS REAKTOR NUKLIR SMR (SMALL MODULAR REACTOR)

Safety is an issue that is of considerable concern in the design, operation and development of a nuclear reactor. Therefore, the method of analysis used in all these activities should be thorough and reliable so as to predict a wide range of operating conditions of the reactor, both under normal operating conditions and in the event of an accident. Performance of heat transfer to the cooling of nuclear fuel, reactor safety is key. Poor heat removal performance would threaten the integrity of the fuel cladding which could further impact on the release of radioactive substances into the environment in an uncontrolled manner to endanger the safety of the reactor workers, the general public, and the environment. This study has the objective is to know is profile contour of fluid flow and the temperature distribution pattern of the cooling fluid is water (H2O) in convection in to SMR reactor with fuel sub reed arrangement of hexagonal in forced convection. In this study will be conducted simulations on the SMR reactor core used sub channel hexagonal using CFD (Computational Fluid Dynamics) code. And the results of this simulation look more upward (vector of fluid flow) fluid temperature will be warm because the heat moves from the wall to the fluid heater. Axial direction and also looks more fluid away from the heating element temperature will be lower.

Composition modifications and heat treatment procedures for increasing the emissivity of alumina surface scales on FeCrAl alloys

The oxidation limited lifetime of thin-walled FeCrAlY heating elements is governed by the depletion of the aluminium reservoir from the bulk alloy as a result of scale growth, whereby the lifetime is known to strongly decrease with increasing temperature. The present investigation aims at obtaining a heating element lifetime extension by increasing the emissivity of the growing alumina scales because this would allow using a lower heating element temperature without decreasing the usable heat output. For this purpose, the oxidation mechanisms of a Zr doped FeCrAlY alloy as function of time, temperature, composition and component thickness were investigated using a combination of experimental techniques such as thermogravimetry, optical microscopy, scanning electron microscopy, transmission electron microscopy, focused ion beam technique, sputtered neutrals mass spectrometry and glow discharge optical emission spectroscopy. The emissivity of the oxide scales was determined by measuring the reflectivity of oxidised specimens as a function of wavelength and correlated with the oxide scale morphologies as a function of initial alloy composition and pretreatment procedure. The results showed that an increased emissivity of the alumina scales as a result of a change in oxide morphology (i.e. wavy scaleyalloy interface and incorporation of the Zr-oxide precipitates across the oxide scale) can be obtained by suitable Zr-doping of the alloy. The emissivity value during long term exposure at high temperatures is, however, adversely affected by depletion of Zr in the bulk alloy, especially in thin components. Pretreatment of the alloys in a H2–H2O containing atmosphere (low pO2) resulted in an increased emissivity, probably due to an increased Fe (and Cr) content in the outer part of the alumina scale.

The influence of heating element temperature on productivity

A study to determine the most optimal heating element for any given processing configuration yields a surprisingly simple log-linear dependence of the productivity on the heating-element temperature. Aluminum, iron, and aluminum-oxide processing efficiencies are studied for conditions that span heat treating to melting. The authors note that, in general, the highest element temperature that may effectively be used for a given heating process is the high-productivity solution.

NATURAL CONVECTION IN A SQUARE ENCLOSURE HEATED PERIODICALLY FROM PART OF THE BOTTOM WALL

Transient heat transfer by laminar natural convection in a square cavity partially heated from below is studied numerically using a finite difference procedure. The temperature of the heating element is uniform, but its magnitude varies sinusoidally with time, oscillating about a fixed mean value. The opposite cold wall is maintained at a constant temperature, while the rest of the bottom wall and the vertical walls are adiabatic. The transient solutions obtained are all periodic in time (0.02 ≤ τ ≤ ∞). Parameters of the problem are the enclosure aspect ratio (A = 1), dimensionless length of the heating element (0.125 ≤ B ≤ 0.5), position of the heating element (0 ≤ a ≤ 0.25), dimensionless amplitude of the heating element temperature (0 ≤ a ≤ 0.4), Prandtl number (Pr = 0.72), and Raykigh number (10 5 ≤ Ra ≤ 2 × 106). Heat transfer and effects of various parameters on the flow and temperature fields are studied.

Natural Convective Heat Transfer on a Vertical Plate with Discontinuous Surface Temperature : Effect of Heat Conduction in the Plate

Natural convective heat transfer from a vertical plate having separated heating elements has been studied by numerical computation and experiment. IT has been found that convective heat transfer from the plate and the temperature distribution of unheated elements vary depending upon the ratio of thermal conductivity of convective fluid to that of the material of unheated elements, the ratio of thickness to length of unheated elements, and the length and surface temperature of heating elements. The heat transfer data are correlated by using a parameter S=B.Rλ/GrL1/4, presented in this paper through the vectorial dimensional analysis, and by an observation of convective behavior visualized by Mach-Zehnder interferometer and computational results. An empirical formula has been presented to predict heat transfer coefficients of discontinuously heated plates based on the new parameter S.