The Experts below are selected from a list of 140886 Experts worldwide ranked by ideXlab platform
John R. Thome - One of the best experts on this subject based on the ideXlab platform.
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an updated three zone Heat Transfer Model for slug flow boiling in microchannels
International Journal of Multiphase Flow, 2017Co-Authors: Mirco Magnini, John R. ThomeAbstract:Abstract This work proposes a novel physics-based Model for the fluid mechanics and Heat Transfer associated with slug flow boiling in horizontal circular microchannels to update the widely used three-zone Model of Thome et al. (2004). The Heat Transfer Model has a convective boiling nature and predicts the time-dependent variation of the local Heat Transfer coefficient during the cyclic passage of a liquid slug, an evaporating elongated bubble and a vapor plug. The capillary flow theory, extended to incorporate evaporation effects, is applied to estimate the bubble velocity along the channel. A liquid film thickness prediction method also considering bubble proximity effects, which may limit the radial extension of the film, is included. The minimum liquid film thickness at dryout is set to the channel wall roughness. Theoretical Heat Transfer Models accounting for the thermal inertia of the liquid film and for the recirculating flow within the liquid slug are utilized. The Heat Transfer Model is compared to experimental data taken from three independent studies. The 833 slug flow boiling data points cover the fluids R134a, R245fa and R236fa, and channel diameters below 1 mm. The proposed evaporation Model predicts more than 80% of the database to within ±30%. It demonstrates a stronger contribution to Heat Transfer by the liquid slugs and correspondingly less by the thin film evaporation process compared to the original three-zone Model. This Model represents a new step towards a complete physics-based Modelling of the bubble dynamics and Heat Transfer within microchannels under evaporating flow conditions.
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new prediction methods for co2 evaporation inside tubes part ii an updated general flow boiling Heat Transfer Model based on flow patterns
International Journal of Heat and Mass Transfer, 2008Co-Authors: Lixin Cheng, Gherhardt Ribatski, John R. ThomeAbstract:Corresponding to the updated flow pattern map presented in Part I of this study, an updated general flow pattern based flow boiling Heat Transfer Model was developed for CO2 using the Cheng–Ribatski–Wojtan–Thome [L. Cheng, G. Ribatski, L. Wojtan, J.R. Thome, New flow boiling Heat Transfer Model and flow pattern map for carbon dioxide evaporating inside horizontal tubes, Int. J. Heat Mass Transfer 49 (2006) 4082–4094; L. Cheng, G. Ribatski, L. Wojtan, J.R. Thome, Erratum to: “New flow boiling Heat Transfer Model and flow pattern map for carbon dioxide evaporating inside tubes” [Heat Mass Transfer 49 (21–22) (2006) 4082–4094], Int. J. Heat Mass Transfer 50 (2007) 391] flow boiling Heat Transfer Model as the starting basis. The flow boiling Heat Transfer correlation in the dryout region was updated. In addition, a new mist flow Heat Transfer correlation for CO2 was developed based on the CO2 data and a Heat Transfer method for bubbly flow was proposed for completeness sake. The updated general flow boiling Heat Transfer Model for CO2 covers all flow regimes and is applicable to a wider range of conditions for horizontal tubes: tube diameters from 0.6 to 10 mm, mass velocities from 50 to 1500 kg/m2 s, Heat fluxes from 1.8 to 46 kW/m2 and saturation temperatures from −28 to 25 °C (reduced pressures from 0.21 to 0.87). The updated general flow boiling Heat Transfer Model was compared to a new experimental database which contains 1124 data points (790 more than that in the previous Model [Cheng et al., 2006, 2007]) in this study. Good agreement between the predicted and experimental data was found in general with 71.4% of the entire database and 83.2% of the database without the dryout and mist flow data predicted within ±30%. However, the predictions for the dryout and mist flow regions were less satisfactory due to the limited number of data points, the higher inaccuracy in such data, scatter in some data sets ranging up to 40%, significant discrepancies from one experimental study to another and the difficulties associated with predicting the inception and completion of dryout around the perimeter of the horizontal tubes.
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new flow boiling Heat Transfer Model and flow pattern map for carbon dioxide evaporating inside horizontal tubes
International Journal of Heat and Mass Transfer, 2006Co-Authors: Leszek Wojtan, Lixin Cheng, Gherhardt Ribatski, John R. ThomeAbstract:Keywords: Flow Boiling ; Heat Transfer Model ; Flow Map ; Flow Patterns ; Flow Regimes ; Co2 Reference LTCM-ARTICLE-2006-014doi:10.1016/j.ijHeatmassTransfer.2006.04.003View record in Web of Science Record created on 2006-09-28, modified on 2017-05-10
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Investigation of flow boiling in horizontal tubes: Part II—Development of a new Heat Transfer Model for stratified-wavy, dryout and mist flow regimes
International Journal of Heat and Mass Transfer, 2005Co-Authors: Leszek Wojtan, Thierry Ursenbacher, John R. ThomeAbstract:Abstract The new version of the flow pattern map presented in Part I of this paper has been used to modify the dry angle in the Heat Transfer Model of Kattan–Thome–Favrat [J. Heat Transfer, 120 (1) (1998) 156]. This significantly improves the Heat Transfer prediction in stratified-wavy flow. Moreover, a new Heat Transfer prediction method has been developed for the dryout and mist flow regimes, which extends the applicability of the Heat Transfer Model to these flow regimes. An extensive flow boiling Heat Transfer database has been acquired for R-22 and R-410A to develop and validate the new Heat Transfer prediction methods. The new Model also shows good agreement with the independent Heat Transfer data of Lallemand et al. [M. Lallemand, C. Branescu, P. Haberschill, Local Heat Transfer coefficients during boiling of R-22 and R-407C in horizontal smooth and microfin tubes, Int. J. Refrigeration, 24 (2001) 57–72].
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Heat Transfer Model for evaporation in microchannels part i presentation of the Model
International Journal of Heat and Mass Transfer, 2004Co-Authors: John R. Thome, Vincent Dupont, Anthony M JacobiAbstract:A three-zone flow boiling Model is proposed to describe evaporation of elongated bubbles in microchannels. The Heat Transfer Model describes the transient variation in local Heat Transfer coefficient during the sequential and cyclic passage of (i) a liquid slug, (ii) an evaporating elongated bubble and (iii) a vapor slug. A time-averaged local Heat Transfer coefficient is thus obtained. The new Model illustrates the importance of the strong cyclic variation in the Heat Transfer coefficient and the strong dependency of Heat Transfer on the bubble frequency, the minimum liquid film thickness at dryout and the liquid film formation thickness.
Marom Bikson - One of the best experts on this subject based on the ideXlab platform.
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bio Heat Transfer Model of deep brain stimulation induced temperature changes
Journal of Neural Engineering, 2006Co-Authors: Maged Elwassif, Qingjun Kong, Maribel Vazquez, Marom BiksonAbstract:There is a growing interest in the use of chronic deep brain stimulation (DBS) for the treatment of medically refractory movement disorders and other neurological and psychiatric conditions. Fundamental questions remain about the physiologic effects of DBS. Previous basic research studies have focused on the direct polarization of neuronal membranes by electrical stimulation. The goal of this paper is to provide information on the thermal effects of DBS using finite element Models to investigate the magnitude and spatial distribution of DBS-induced temperature changes. The parameters investigated include stimulation waveform, lead selection, brain tissue electrical and thermal conductivities, blood perfusion, metabolic Heat generation during the stimulation and lead thermal conductivity/Heat dissipation through the electrode. Our results show that clinical DBS protocols will increase the temperature of surrounding tissue by up to 0.8 °C depending on stimulation/tissue parameters.
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bio Heat Transfer Model of deep brain stimulation induced temperature changes
International Conference of the IEEE Engineering in Medicine and Biology Society, 2006Co-Authors: Maged Elwassif, Qingjun Kong, Maribel Vazquez, Marom BiksonAbstract:There is a growing interest in the use of chronic deep brain stimulation (DBS) for the treatment of medically refractory movement disorders and other neurological and psychiatric conditions. Fundamental questions remain about the physiologic effects and safety of DBS. Previous basic research studies have focused on the direct polarization of neuronal membranes by electrical stimulation. The goal of this paper is to provide information on the thermal effects of DBS using finite element Models to investigate the magnitude and spatial distribution of DBS induced temperature changes. The parameters investigated include: stimulation waveform, lead selection, brain tissue electrical and thermal conductivity, blood perfusion, metabolic Heat generation during the stimulation. Our results show that clinical deep brain stimulation protocols will increase the temperature of surrounding tissue by up to 0.8 deg C depending on stimulation/tissue parameters.
Tim Ameel - One of the best experts on this subject based on the ideXlab platform.
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experimental validation of a three dimensional Heat Transfer Model within the scala tympani with application to magnetic cochlear implant surgery
IEEE Transactions on Biomedical Engineering, 2021Co-Authors: Fateme Esmailie, Mathieu Francoeur, Tim AmeelAbstract:Magnetic guidance of cochlear implants is a promising technique to reduce the risk of physical trauma during surgery. In this approach, a magnet attached to the tip of the implant electrode array is guided within the scala tympani using a magnetic field. After surgery, the magnet must be detached from the implant electrode array via localized Heating, which may cause thermal trauma, and removed from the scala tympani. Objectives The objective of this work is to experimentally validate a three-dimensional (3D) Heat Transfer Model of the scala tympani which will enable accurate predictions of the maximum safe input power to avoid localized hyperthermia when detaching the magnet from the implant electrode array. Methods Experiments are designed using a rigorous scale analysis and performed by measuring transient temperatures in a 3D-printed scala tympani phantom subjected to a sudden change in its isothermal environment and localized Heating via a small Heat source. Results The measured and predicted temperatures are in good agreement with an error less than 6% (p=~0.84). For the most conservative case where all boundaries of the Model except the insertion opening are adiabatic, the power required to release the magnet attached to the implant electrode array by 1 mm3 of paraffin is approximately half of the predicted maximum safe input power. Conclusions A 3D Heat Transfer Model of the scala tympani is successfully validated and enables predicting the maximum safe input power required to detach the magnet from the implant electrode array. Significance This work will enable the design of a thermally safe magnetic cochlear implant surgery procedure.
John E Bowers - One of the best experts on this subject based on the ideXlab platform.
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a compact Heat Transfer Model based on an enhanced fourier law for analysis of frequency domain thermoreflectance experiments
Applied Physics Letters, 2015Co-Authors: Ashok T Ramu, John E BowersAbstract:A recently developed enhanced Fourier law is applied to the problem of extracting thermal properties of materials from frequency-domain thermoreflectance (FDTR) experiments. The Heat Transfer Model comprises contributions from two phonon channels: one a high-Heat-capacity diffuse channel consisting of phonons of mean free path (MFP) less than a threshold value, and the other a low-Heat-capacity channel consisting of phonons with MFP higher than this value that travel quasi-ballistically over length scales of interest. The diffuse channel is treated using the Fourier law, while the quasi-ballistic channel is analyzed using a second-order spherical harmonic expansion of the phonon distribution function. A recent analysis of FDTR experimental data suggested the use of FDTR in deriving large portions of the MFP accumulation function; however, it is shown here that the data can adequately be explained using our minimum-parameter Model, thus highlighting an important limitation of FDTR experiments in exploring ...
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a compact Heat Transfer Model based on an enhanced fourier law for analysis of frequency domain thermoreflectance experiments
arXiv: Mesoscale and Nanoscale Physics, 2015Co-Authors: Ashok T Ramu, John E BowersAbstract:A recently developed enhanced Fourier law is applied to the problem of extracting thermal properties of materials from frequency-domain thermoreflectance (FDTR) experiments. The Heat Transfer Model comprises contributions from two phonon channels; one a high-Heat-capacity diffuse channel consisting of phonons of mean free path (MFP) less than a threshold value, and the other a low-Heat-capacity channel consisting of phonons with MFP higher than this value that travel quasi-ballistically over length scales of interest. The diffuse channel is treated using the Fourier law, while the quasi-ballistic channel is analyzed using a second-order spherical harmonic expansion of the phonon distribution function. A recent analysis of FDTR experimental data suggested the use of FDTR in deriving large portions of the MFP accumulation function; however, it is shown here that the data can adequately be explained using our minimum-parameter Model, thus highlighting an important limitation of FDTR experiments in exploring the accumulation function of bulk matter.
Xinhua Xu - One of the best experts on this subject based on the ideXlab platform.
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development of a simplified Heat Transfer Model of hollow blocks by using finite element method in frequency domain
Energy and Buildings, 2016Co-Authors: Anbang Li, Xinhua XuAbstract:Abstract Hollow blocks or bricks are widely used due to the good thermal insulation, lightweight, acoustic insulation, etc. This paper presents the development of a simplified Heat Transfer Model of hollow block for simple and efficient Heat flow calculation. This Model is developed based on parameter identification in frequency domain by using finite element method in frequency domain. Firstly, the frequency domain finite element Model (FDFEM) of the hollow block is developed by using finite element method in frequency domain to obtain the theoretical frequency characteristics of this structure. Then, the Heat Transfer function Model in the form of s-polynomial (i.e., the s-polynomial Heat Transfer function Model) is identified by using a parameter identification procedure based on the calculated theoretical frequency thermal characteristics. Finally, the simplified Heat Transfer Model, i.e., the Conduction Transfer Function (CTF) coefficients, of this hollow block are derived from the identified s-polynomial Heat Transfer function Model. A case study is presented for the prediction of the dynamic Heat Transfer of this hollow block by using the simplified Heat Transfer Model. The predicted dynamic Heat Transfer of this block is validated by experimental data.
