Evaluation of heat transfer coefficient of tungsten filaments at low pressures and high temperatures

Chondrakis, N.G.; Topalis, Frangiskos V.

doi:10.1016/j.applthermaleng.2010.09.005

Cited by 4 publications

(4 citation statements)

References 19 publications

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“…Hence, it is difficult to configure a closed-loop control considering the directly measured temperature value. To solve this problem, the temperature of the tungsten filament was derived as indicated in Equation (11), considering the change in resistivity based on the tungsten filament temperatures listed in Table 1 [20]. The temperature of the current filament is indirectly estimated in Equation ( 11) by substituting the electrical resistivity value calculated in the digital signal processor (DSP) [21].…”

Section: Proposed Methodsmentioning

confidence: 99%

Filament X-ray Tube Current Control Method Using Indirect Filament Temperature Estimation

2021

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The recent increase in ailments has increased the demand for diagnosis and surgery based on X-rays. An X-ray system using a filament-type tube heats the filament for operation, and the electrons emitted by the thermal energy during this process produce X-rays. Conventionally, current control-based methods are used to regulate heating. However, these methods do not control the temperature of the filament, resulting in lower or higher output than the desired dose rate. Therefore, we propose a filament temperature control method that enables constant temperature control, which cannot be achieved using the existing heating method for X-ray systems with filament tubes. Additionally, we developed an indirect temperature estimation algorithm for the tungsten filament to incorporate the proposed method. To validate the tube current control through temperature control, we performed experiments to compare the existing current-controlled heating and temperature control methods in terms of the filament temperature. As the tube current is proportional to the dose rate, it was measured through a comparative analysis of the change in the output of dose rate over time. The obtained results validate that the proposed method can maintain both the filament temperature and tube current at the desired level.

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Section: Proposed Methodsmentioning

confidence: 99%

Filament X-ray Tube Current Control Method Using Indirect Filament Temperature Estimation

2021

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“…One final point here is that the Joule heating of the surface of the tungsten carbide tip can be estimated by a similar calculation. Tungsten has a resistivity of 5.427×10 −8 Ω m [51,52], specific heat capacity of 131.29 J kg −1 K −1 [52] and a density of 19.25×10 3 kg m −3 [52]. With these values it is found that the rate of Joule heating of the surface of a tungsten electrode is about seven orders of magnitude slower than the rate of Joule heating of the adjacent saline, which is due to the resistivity of tungsten being about 10 7 times smaller than the resistivity of saline.…”

Section: A Simple Model Of Prebreakdown Vapour Formationmentioning

confidence: 99%

Fast framing imaging and modelling of vapour formation and discharge initiation in electrolyte solutions

Asimakoulas

Graham

Krčma

et al. 2020

Plasma Sources Sci. Technol.

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The formation of vapour and initiation of electrical discharges in normal saline and other NaCl solutions has been observed and modelled. Millisecond pulses of -160 to -300 V were applied to a sharp tungsten carbide electrode immersed in the liquid. A fast framing camera was used to observe vapour layer growth around the electrode by shadowgraphy. Images were also taken without backlighting to observe emission accompanying breakdown. The conductivity of the vapour layer has been estimated by comparison of experimentally measured impedances with impedances calculated by finite element modelling of the liquid and vapour around the electrode observed by shadowgraphy. The conductivity of the vapour layer is estimated to vary between ∼ 1 and 10 −3 S/m, which are orders of magnitude higher than expected for water vapour. The reason for the high conductivity is not clear, but may be due to injection of charge carriers into the vapour by corona discharge at the sharp tip and/or the presence of cluster ions in the vapour. Alternatively, the vapour layer may be a foam mixture of high conductivity liquid and low conductivity vapour bubbles. Discharge formation does not occur primarily at the sharp tip of the electrode, but rather at the side. Finite element models of the vapour layer show that the highest electric fields are found close to the sharp tip of the electrode but that the field strength drops rapidly moving away from the tip. By contrast slightly lower, but consistently high, electric fields are often observed between the side of the electrode and the liquid vapour boundary where plasma emission is mostly observed due to the shape of the vapour liquid boundary. The electron number density in the discharge is estimated to be ∼ 10 21 m −3 . There is evidence from the shadowgraphy for different boiling mechanisms; nucleate boiling at lower voltages and film boiling at higher voltages. A rule of thumb based on a simplistic model is suggested to predict the time to discharge based on electrode area, initial current, and electrolyte temperature, density, conductivity and heat capacity.

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“…Tal relação é dada pela equação (1), onde T H e R H são respectivamente a temperatura e a resistência do filamento durante o pré-aquecimento (a quente -hot), dados em Kelvin [K] e ohm [ ]. T C e R C são os mesmos parâmetros medidos antes do pré-aquecimento (a frio -cold) [7].…”

Section: A Pré-aquecimentounclassified

“…Da equação (1), considerando T C à temperatura ambiente, i.e., T C =25 °C (298 K), tem-se que para uma temperatura T H de 700 °C (973 K), a razão R H /R C , ou simplesmente R HC , é aproximadamente 4,28 e para uma temperatura de 1.000 °C (1.273 K), R HC está em torno de 5,95. Na literatura, estes valores são estabelecidos e aproximados para 4,25 e 6,25 [6][7][8].…”

Section: A Pré-aquecimentounclassified

Modelagem Estática e Dinâmica de Lâmpada Fluorescente UV e Aplicação para fins de Purificação de Água

Matheus¹,

Brito²,

Canesin³

2013

Eletrônica de Potência

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Resumo-A partir de ensaios realizados com uma lâmpada fluorescente UV comercial, caracteriza-se o comportamento da resistência dos filamentos e desenvolve-se um modelo estático capaz de representar a característica resistiva da coluna de gás em regime permanente. O modelo desenvolvido está baseado numa equação polinomial de quinta ordem, sendo aplicável tanto para simulação quanto para projeto dos reatores. Ainda, uma importante contribuição é a determinação da característica R HC dos filamentos da lâmpada, a qual é utilizada para o dimensionamento do circuito de controle capaz de realizar um adequado pré-aquecimento da lâmpada, considerando a aplicação de purificação de água.

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Evaluation of heat transfer coefficient of tungsten filaments at low pressures and high temperatures

Cited by 4 publications

References 19 publications

Filament X-ray Tube Current Control Method Using Indirect Filament Temperature Estimation

Filament X-ray Tube Current Control Method Using Indirect Filament Temperature Estimation

Fast framing imaging and modelling of vapour formation and discharge initiation in electrolyte solutions

Modelagem Estática e Dinâmica de Lâmpada Fluorescente UV e Aplicação para fins de Purificação de Água

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