Pub Date : 2020-06-22DOI: 10.1080/15567265.2021.2002484
Luke Yates, Zhe Cheng, T. Bai, K. Hobart, M. Tadjer, T. Feygelson, B. Pate, M. Goorsky, S. Graham
ABSTRACT As wide bandgap electronic devices have continued to advance in both size reduction and power handling capabilities, heat dissipation has become a significant concern. To mitigate this, chemical vapor deposited (CVD) diamond has been demonstrated as an effective solution for thermal management of these devices by directly growing onto the transistor substrate. A key aspect of power and radio frequency (RF) electronic devices involves transient switching behavior, which highlights the importance of understanding the temperature dependence of a material’s heat capacity and thermal conductivity when modeling and predicting a devices electro-thermal response. Due to the complicated microstructure near the interface between CVD diamond and electronic material, it is difficult to measure both properties simultaneously. In this work, we use time-domain thermoreflectance (TDTR) to simultaneously measure the in-plane thermal conductivity and heat capacity of a 1-µm-thick CVD diamond film via multi-frequency analysis. We obtain temperature dependent thermal properties by using the pump beam to heat the sample according to increasing power. This mitigates the need for a more complicated setup using a thermal stage but has limited upper temperature boundaries based on the sample geometry and thermal properties. The results show that the in-plane thermal conductivity varied slightly with an average of 103 W/m-K over a temperature range of 302–327 K, while the specific heat capacity has a strong temperature dependence over the same range and compares well with heat capacity data of natural diamond in literature.
{"title":"Simultaneous Evaluation of Heat Capacity and In-plane Thermal Conductivity of Nanocrystalline Diamond Thin Films","authors":"Luke Yates, Zhe Cheng, T. Bai, K. Hobart, M. Tadjer, T. Feygelson, B. Pate, M. Goorsky, S. Graham","doi":"10.1080/15567265.2021.2002484","DOIUrl":"https://doi.org/10.1080/15567265.2021.2002484","url":null,"abstract":"ABSTRACT As wide bandgap electronic devices have continued to advance in both size reduction and power handling capabilities, heat dissipation has become a significant concern. To mitigate this, chemical vapor deposited (CVD) diamond has been demonstrated as an effective solution for thermal management of these devices by directly growing onto the transistor substrate. A key aspect of power and radio frequency (RF) electronic devices involves transient switching behavior, which highlights the importance of understanding the temperature dependence of a material’s heat capacity and thermal conductivity when modeling and predicting a devices electro-thermal response. Due to the complicated microstructure near the interface between CVD diamond and electronic material, it is difficult to measure both properties simultaneously. In this work, we use time-domain thermoreflectance (TDTR) to simultaneously measure the in-plane thermal conductivity and heat capacity of a 1-µm-thick CVD diamond film via multi-frequency analysis. We obtain temperature dependent thermal properties by using the pump beam to heat the sample according to increasing power. This mitigates the need for a more complicated setup using a thermal stage but has limited upper temperature boundaries based on the sample geometry and thermal properties. The results show that the in-plane thermal conductivity varied slightly with an average of 103 W/m-K over a temperature range of 302–327 K, while the specific heat capacity has a strong temperature dependence over the same range and compares well with heat capacity data of natural diamond in literature.","PeriodicalId":49784,"journal":{"name":"Nanoscale and Microscale Thermophysical Engineering","volume":"25 1","pages":"166 - 178"},"PeriodicalIF":4.1,"publicationDate":"2020-06-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45983292","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-04-16DOI: 10.1080/15567265.2020.1853290
Mohammad Rezaeimoghaddam, Z. Dursunkaya
ABSTRACT Heat transfer via phase change is a major contributor to heat removal in numerous engineering applications. Thin films of liquid result in increased heat transfer due to a reduction of conduction resistance, in addition the pressure jump at the liquid-vapor interface also affects the rate and direction of the rate of phase change. Because of these effects the morphology of the substrate surface is expected to affect the film shape, hence heat transfer, especially in thin films. In this study, the influence of surface characteristics on the rate of phase change from micron- and submicron-sized 2D droplets – i.e. films extending to infinity – forming on a substrate are modeled. Surface film profiles are generated on both flat and nonflat surfaces, triangular or wavy in nature, and a kinetic model for quasi-equilibrium phase change is applied. In the case of wavy surfaces, the surface is assumed to be a harmonic wave with an amplitude equal to the surface roughness and a wavelength corresponding to values commonly encountered in applications. Due to the presence of intermolecular forces at the contact line, which renders the solution of the augmented Young-Laplace equation stiff, an implicit scheme is employed for the numerical integration. To verify the method, the predictions of a molecular dynamics (MD) simulation of a nano-sized droplet present on a V-grooved surface are compared to the continuum model. The augmented Young-Laplace equation is solved numerically along with a phase change model originating from kinetic theory to calculate the shape of the two-phase interface forming the droplet and study the effect of various parameters on the rate of phase change. Results are obtained for droplets with liquid pressures higher and lower than that of vapor, resulting in opposite contribution to phase change due to the pressure jump at the interface. The results show that the heat-transfer rate can be substantially altered due primarily to the combined effects of surface morphology and disjoining pressure. It is also concluded that wavy surfaces with short amplitudes are preferable to ones with longer amplitudes for enhancing the rate of evaporation or condensation.
{"title":"The effect of surface morphology on the rate of phase change of micron and sub-micron sized 2-D droplets","authors":"Mohammad Rezaeimoghaddam, Z. Dursunkaya","doi":"10.1080/15567265.2020.1853290","DOIUrl":"https://doi.org/10.1080/15567265.2020.1853290","url":null,"abstract":"ABSTRACT Heat transfer via phase change is a major contributor to heat removal in numerous engineering applications. Thin films of liquid result in increased heat transfer due to a reduction of conduction resistance, in addition the pressure jump at the liquid-vapor interface also affects the rate and direction of the rate of phase change. Because of these effects the morphology of the substrate surface is expected to affect the film shape, hence heat transfer, especially in thin films. In this study, the influence of surface characteristics on the rate of phase change from micron- and submicron-sized 2D droplets – i.e. films extending to infinity – forming on a substrate are modeled. Surface film profiles are generated on both flat and nonflat surfaces, triangular or wavy in nature, and a kinetic model for quasi-equilibrium phase change is applied. In the case of wavy surfaces, the surface is assumed to be a harmonic wave with an amplitude equal to the surface roughness and a wavelength corresponding to values commonly encountered in applications. Due to the presence of intermolecular forces at the contact line, which renders the solution of the augmented Young-Laplace equation stiff, an implicit scheme is employed for the numerical integration. To verify the method, the predictions of a molecular dynamics (MD) simulation of a nano-sized droplet present on a V-grooved surface are compared to the continuum model. The augmented Young-Laplace equation is solved numerically along with a phase change model originating from kinetic theory to calculate the shape of the two-phase interface forming the droplet and study the effect of various parameters on the rate of phase change. Results are obtained for droplets with liquid pressures higher and lower than that of vapor, resulting in opposite contribution to phase change due to the pressure jump at the interface. The results show that the heat-transfer rate can be substantially altered due primarily to the combined effects of surface morphology and disjoining pressure. It is also concluded that wavy surfaces with short amplitudes are preferable to ones with longer amplitudes for enhancing the rate of evaporation or condensation.","PeriodicalId":49784,"journal":{"name":"Nanoscale and Microscale Thermophysical Engineering","volume":"24 1","pages":"184 - 200"},"PeriodicalIF":4.1,"publicationDate":"2020-04-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/15567265.2020.1853290","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41915700","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-04-02DOI: 10.1080/15567265.2020.1744776
F. Hai, Wei Zhu, S. Liang, Xiaoyi Yang, Yuan Deng
ABSTRACT The pool boiling performance plays a key role in the development of high heat flux dissipating applications. The high critical heat flux and low wall superheat are two of the critical factors that affect the long-term life of devices. In this paper, enhanced pool boiling performance can be achieved by well-designed microchannels in copper surfaces using a precision diamond dicing method. The microchannel patterned surface with the channel length of 0.4 mm obtains a critical heat flux of 169.8 W/cm2, which has a 193% enhancement compared to the plain surface. Besides, the extremely low wall superheat of 3 K has been achieved, and thus the heat transfer coefficient reaches 51.8 W/cm2·K, about 738% larger than that of the plain surface. Herein, the microcavity has increased the nucleation site, the surface can promote the bubbles escape, and then the channel can continuously supply the liquid. Hence, the extremely low wall superheat at high heat flux occurs due to the rapid bubble departure and enhanced capillary feeding of liquid replenishment to active nucleation sites on the surface. The above results provide an effective way for the realization of high-performance two-phase microchannel patterned heat sinks via optimizing the microstructure geometry.
{"title":"Enhanced Pool Boiling Performance of Microchannel Patterned Surface with Extremely Low Wall Superheat through Capillary Feeding of Liquid","authors":"F. Hai, Wei Zhu, S. Liang, Xiaoyi Yang, Yuan Deng","doi":"10.1080/15567265.2020.1744776","DOIUrl":"https://doi.org/10.1080/15567265.2020.1744776","url":null,"abstract":"ABSTRACT The pool boiling performance plays a key role in the development of high heat flux dissipating applications. The high critical heat flux and low wall superheat are two of the critical factors that affect the long-term life of devices. In this paper, enhanced pool boiling performance can be achieved by well-designed microchannels in copper surfaces using a precision diamond dicing method. The microchannel patterned surface with the channel length of 0.4 mm obtains a critical heat flux of 169.8 W/cm2, which has a 193% enhancement compared to the plain surface. Besides, the extremely low wall superheat of 3 K has been achieved, and thus the heat transfer coefficient reaches 51.8 W/cm2·K, about 738% larger than that of the plain surface. Herein, the microcavity has increased the nucleation site, the surface can promote the bubbles escape, and then the channel can continuously supply the liquid. Hence, the extremely low wall superheat at high heat flux occurs due to the rapid bubble departure and enhanced capillary feeding of liquid replenishment to active nucleation sites on the surface. The above results provide an effective way for the realization of high-performance two-phase microchannel patterned heat sinks via optimizing the microstructure geometry.","PeriodicalId":49784,"journal":{"name":"Nanoscale and Microscale Thermophysical Engineering","volume":"24 1","pages":"66 - 79"},"PeriodicalIF":4.1,"publicationDate":"2020-04-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/15567265.2020.1744776","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43081800","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-04-02DOI: 10.1080/15567265.2020.1744777
Ilke Albar, Nazli Donmezer
ABSTRACT Understanding the mean free path distribution of the dominant heat carriers is very important in determining the ballistic to diffusive heat transport transition in nanoscale devices. This is true for the high electron mobility transistors made from GaN where both the thickness of the buffer layer and localized heating causing ballistic-diffusive heat transfer may complicate the transport properties needed to describe the device thermal response. In this work, we obtain the mean free path–thermal conductivity relation of phonons in bulk wurtzite GaN crystals using two different, ab-initio-based calculations. While the Vienna Ab-initio Simulation Package (VASP) is used in both approaches at the initial stage, the first method does not calculate the third-order force constants (FCs) and approximates the anharmonicity with a single fitting parameter in determination of discrete phonon properties thermal conductivity and relaxation time, while the second method uses third-order force constants directly. Results show that the third-order FCs are important in modeling the contribution of high-frequency optical phonons with relatively short MFPs, to the thermal conductivity of the material. Yet these effects are more significant at high temperatures and at samples without crystallographic disorders, and they can be omitted while modeling the real samples at low temperatures.
{"title":"Mean Free Path–Thermal Conductivity Accumulation Calculations for Wurtzite Gallium Nitride: Two Approaches","authors":"Ilke Albar, Nazli Donmezer","doi":"10.1080/15567265.2020.1744777","DOIUrl":"https://doi.org/10.1080/15567265.2020.1744777","url":null,"abstract":"ABSTRACT Understanding the mean free path distribution of the dominant heat carriers is very important in determining the ballistic to diffusive heat transport transition in nanoscale devices. This is true for the high electron mobility transistors made from GaN where both the thickness of the buffer layer and localized heating causing ballistic-diffusive heat transfer may complicate the transport properties needed to describe the device thermal response. In this work, we obtain the mean free path–thermal conductivity relation of phonons in bulk wurtzite GaN crystals using two different, ab-initio-based calculations. While the Vienna Ab-initio Simulation Package (VASP) is used in both approaches at the initial stage, the first method does not calculate the third-order force constants (FCs) and approximates the anharmonicity with a single fitting parameter in determination of discrete phonon properties thermal conductivity and relaxation time, while the second method uses third-order force constants directly. Results show that the third-order FCs are important in modeling the contribution of high-frequency optical phonons with relatively short MFPs, to the thermal conductivity of the material. Yet these effects are more significant at high temperatures and at samples without crystallographic disorders, and they can be omitted while modeling the real samples at low temperatures.","PeriodicalId":49784,"journal":{"name":"Nanoscale and Microscale Thermophysical Engineering","volume":"24 1","pages":"80 - 93"},"PeriodicalIF":4.1,"publicationDate":"2020-04-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/15567265.2020.1744777","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46412349","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-04-02DOI: 10.1080/15567265.2020.1765912
S. Uchida, K. Fujiwara, M. Shibahara
ABSTRACT In this study, non-equilibrium molecular dynamics simulations were conducted for a coexistence system of water and ice on a wall surface with a single nanoparticle to reveal the effects of water solidification on the nanoparticle in the vicinity of a wall surface. We further investigated the effect of the presence and size of particles on the density profile of water in the vicinity of the wall surface and the force acting on particles from water molecules, when the solidification interface contacted the wall and the particles. The results revealed that a strong mutual influence exists between the solidification interface and the nanoparticle on the wall’s surface; the nanoparticle on the wall prevents water solidification in proximity to the wall. Moreover, the force acting on the nanoparticle from water molecules changes as the solidification interface approaches; the cooling temperature is shown to affect the direction of this force. It indicates that the solidification process is a key influential factor which affects nanoparticle movements on a wall surface at molecular scales.
{"title":"Molecular Dynamics Study of Interactions between the Water/ice Interface and a Nanoparticle in the Vicinity of a Solid Surface","authors":"S. Uchida, K. Fujiwara, M. Shibahara","doi":"10.1080/15567265.2020.1765912","DOIUrl":"https://doi.org/10.1080/15567265.2020.1765912","url":null,"abstract":"ABSTRACT In this study, non-equilibrium molecular dynamics simulations were conducted for a coexistence system of water and ice on a wall surface with a single nanoparticle to reveal the effects of water solidification on the nanoparticle in the vicinity of a wall surface. We further investigated the effect of the presence and size of particles on the density profile of water in the vicinity of the wall surface and the force acting on particles from water molecules, when the solidification interface contacted the wall and the particles. The results revealed that a strong mutual influence exists between the solidification interface and the nanoparticle on the wall’s surface; the nanoparticle on the wall prevents water solidification in proximity to the wall. Moreover, the force acting on the nanoparticle from water molecules changes as the solidification interface approaches; the cooling temperature is shown to affect the direction of this force. It indicates that the solidification process is a key influential factor which affects nanoparticle movements on a wall surface at molecular scales.","PeriodicalId":49784,"journal":{"name":"Nanoscale and Microscale Thermophysical Engineering","volume":"24 1","pages":"53 - 65"},"PeriodicalIF":4.1,"publicationDate":"2020-04-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/15567265.2020.1765912","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49655177","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-04-02DOI: 10.1080/15567265.2020.1755399
Ben-Dian Nie, B. Cao
ABSTRACT Thermal wave, namely wavelike behavior of heat propagation in transient heat conduction, enjoys much attention due to the recent investigations into phonon hydrodynamics in low-dimensional materials. In this paper, an improved phonon Monte Carlo (MC) simulation algorithm is developed based on the Callaway’s dual relaxation time approximation model, which can deal with the coupling of normal and resistance scattering processes. Via the method, more thermal wave evidences are observed from the microscopic view of phonons, including overshooting and diffraction. Furthermore, the ballistic and hydrodynamic thermal waves are deeply studied. Two kinds of dissipation are found to exist in thermal waves, namely spatial dissipation and resistance dissipation. The former keeps the conservation of phonon momentum, but it lengthens the wavelength and decreases the peak temperature. The latter destroys the phonon momentum and keeps the original profile, lowering the peak temperature. Finally, phonon transport phenomena in Ziman hydrodynamic regime and diffusive regime are investigated, by introducing the scattering probability. The propagation tendency of thermal energy is found to decrease with the increasing scattering probability. The investigations into phonon hydrodynamics help to understand the heat transport characteristics and improve thermal management in low-dimensional materials.
{"title":"Thermal Wave in Phonon Hydrodynamic Regime by Phonon Monte Carlo Simulations","authors":"Ben-Dian Nie, B. Cao","doi":"10.1080/15567265.2020.1755399","DOIUrl":"https://doi.org/10.1080/15567265.2020.1755399","url":null,"abstract":"ABSTRACT Thermal wave, namely wavelike behavior of heat propagation in transient heat conduction, enjoys much attention due to the recent investigations into phonon hydrodynamics in low-dimensional materials. In this paper, an improved phonon Monte Carlo (MC) simulation algorithm is developed based on the Callaway’s dual relaxation time approximation model, which can deal with the coupling of normal and resistance scattering processes. Via the method, more thermal wave evidences are observed from the microscopic view of phonons, including overshooting and diffraction. Furthermore, the ballistic and hydrodynamic thermal waves are deeply studied. Two kinds of dissipation are found to exist in thermal waves, namely spatial dissipation and resistance dissipation. The former keeps the conservation of phonon momentum, but it lengthens the wavelength and decreases the peak temperature. The latter destroys the phonon momentum and keeps the original profile, lowering the peak temperature. Finally, phonon transport phenomena in Ziman hydrodynamic regime and diffusive regime are investigated, by introducing the scattering probability. The propagation tendency of thermal energy is found to decrease with the increasing scattering probability. The investigations into phonon hydrodynamics help to understand the heat transport characteristics and improve thermal management in low-dimensional materials.","PeriodicalId":49784,"journal":{"name":"Nanoscale and Microscale Thermophysical Engineering","volume":"24 1","pages":"122 - 94"},"PeriodicalIF":4.1,"publicationDate":"2020-04-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/15567265.2020.1755399","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46185567","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-02-17DOI: 10.1080/15567265.2020.1861139
Yigit Akkus, Akif Turker Gurer, K. Bellur
ABSTRACT A fundamental understanding of the evaporation/condensation phenomena is vital to many fields of science and engineering, yet there is many discrepancies in the usage of phase-change models and associated coefficients. First, a brief review of the kinetic theory of phase change is provided, and the mass accommodation coefficient (MAC, ) and its inconsistent definitions are discussed. The discussion focuses on the departure from equilibrium; represented as a macroscopic “drift” velocity. Then, a continuous flow, phase change driven molecular-dynamics setup is used to investigate steady-state condensation at a flat liquid-vapor interface of argon at various phase-change rates and temperatures to elucidate the effect of equilibrium departure. MAC is computed directly from the kinetic theory-based Hertz–Knudsen (H-K) and Schrage (exact and approximate) expressions without the need for a priori physical definitions, ad-hoc particle injection/removal, or particle counting. MAC values determined from the approximate and exact Schrage expressions ( and ) are between 0.8 and 0.9, while MAC values from the H-K expression ( ) are above unity for all cases tested. yield value closest to the results from transition state theory [J Chem Phys, 118, 1392–1399 (2003)]. The departure from equilibrium does not affect the value of but causes to vary drastically emphasizing the importance of a drift velocity correction. Additionally, equilibrium departure causes a nonuniform distribution in vapor properties. At the condensing interface, a local rise in vapor temperature and a drop in vapor density is observed when compared with the corresponding bulk values. When the deviation from bulk values are taken into account, all values of MAC including show a small yet noticeable difference that is both temperature and phase-change rate dependent. Graphical abstract
{"title":"Drifting mass accommodation coefficients: in situ measurements from a steady state molecular dynamics setup","authors":"Yigit Akkus, Akif Turker Gurer, K. Bellur","doi":"10.1080/15567265.2020.1861139","DOIUrl":"https://doi.org/10.1080/15567265.2020.1861139","url":null,"abstract":"ABSTRACT A fundamental understanding of the evaporation/condensation phenomena is vital to many fields of science and engineering, yet there is many discrepancies in the usage of phase-change models and associated coefficients. First, a brief review of the kinetic theory of phase change is provided, and the mass accommodation coefficient (MAC, ) and its inconsistent definitions are discussed. The discussion focuses on the departure from equilibrium; represented as a macroscopic “drift” velocity. Then, a continuous flow, phase change driven molecular-dynamics setup is used to investigate steady-state condensation at a flat liquid-vapor interface of argon at various phase-change rates and temperatures to elucidate the effect of equilibrium departure. MAC is computed directly from the kinetic theory-based Hertz–Knudsen (H-K) and Schrage (exact and approximate) expressions without the need for a priori physical definitions, ad-hoc particle injection/removal, or particle counting. MAC values determined from the approximate and exact Schrage expressions ( and ) are between 0.8 and 0.9, while MAC values from the H-K expression ( ) are above unity for all cases tested. yield value closest to the results from transition state theory [J Chem Phys, 118, 1392–1399 (2003)]. The departure from equilibrium does not affect the value of but causes to vary drastically emphasizing the importance of a drift velocity correction. Additionally, equilibrium departure causes a nonuniform distribution in vapor properties. At the condensing interface, a local rise in vapor temperature and a drop in vapor density is observed when compared with the corresponding bulk values. When the deviation from bulk values are taken into account, all values of MAC including show a small yet noticeable difference that is both temperature and phase-change rate dependent. Graphical abstract","PeriodicalId":49784,"journal":{"name":"Nanoscale and Microscale Thermophysical Engineering","volume":"25 1","pages":"25 - 45"},"PeriodicalIF":4.1,"publicationDate":"2020-02-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/15567265.2020.1861139","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43310970","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-01-02DOI: 10.1080/15567265.2019.1683106
Dudong Feng, Eric J. Tervo, S. Yee, Zhuomin M. Zhang
ABSTRACT The output power of thermophotovoltaic (TPV) cells may be greatly increased when the gap between the emitter and cell is reduced to submicron distances (near-field regime), at which photon tunneling due to evanescent waves becomes important. Accurate modeling of TPV cells in these conditions is crucial for the design and optimization of near-field TPV systems. The conventional or standard modeling method uses the summation of the dark current and the short-circuit current, while the direct method applies the photon chemical potential. It has been shown that the two methods are linked through a modification of the direct method using Wien’s approximation. By contrasting different modeling approaches, we quantitatively analyze the effects of evanescent waves on the TPV cell performance parameters, especially the dark current, for different emitter and cell materials in the near-field regime. Our results show that the saturation current by radiative recombination is strongly affected by evanescent waves and the bandgap energy. The current-voltage characteristics calculated by different modeling methods are displayed to demonstrate that a constant saturation current typically used in the standard method could cause substantial error in the near-field regime. For a TPV system with an emitter operating at relatively low temperatures, we show that it is necessary to include the photon chemical potential in the computation of the net radiative heat transfer between the emitter and receiver.
{"title":"Effect of Evanescent Waves on the Dark Current of Thermophotovoltaic Cells","authors":"Dudong Feng, Eric J. Tervo, S. Yee, Zhuomin M. Zhang","doi":"10.1080/15567265.2019.1683106","DOIUrl":"https://doi.org/10.1080/15567265.2019.1683106","url":null,"abstract":"ABSTRACT The output power of thermophotovoltaic (TPV) cells may be greatly increased when the gap between the emitter and cell is reduced to submicron distances (near-field regime), at which photon tunneling due to evanescent waves becomes important. Accurate modeling of TPV cells in these conditions is crucial for the design and optimization of near-field TPV systems. The conventional or standard modeling method uses the summation of the dark current and the short-circuit current, while the direct method applies the photon chemical potential. It has been shown that the two methods are linked through a modification of the direct method using Wien’s approximation. By contrasting different modeling approaches, we quantitatively analyze the effects of evanescent waves on the TPV cell performance parameters, especially the dark current, for different emitter and cell materials in the near-field regime. Our results show that the saturation current by radiative recombination is strongly affected by evanescent waves and the bandgap energy. The current-voltage characteristics calculated by different modeling methods are displayed to demonstrate that a constant saturation current typically used in the standard method could cause substantial error in the near-field regime. For a TPV system with an emitter operating at relatively low temperatures, we show that it is necessary to include the photon chemical potential in the computation of the net radiative heat transfer between the emitter and receiver.","PeriodicalId":49784,"journal":{"name":"Nanoscale and Microscale Thermophysical Engineering","volume":"24 1","pages":"1 - 19"},"PeriodicalIF":4.1,"publicationDate":"2020-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/15567265.2019.1683106","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42171311","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-01-02DOI: 10.1080/15567265.2019.1689590
Peter Zakšek, M. Zupančič, P. Gregorčič, I. Golobič
ABSTRACT Nucleate pool boiling experiments were performed on plain and five laser-textured stainless-steel foils using saturated pure water, 100% ethanol, 0.4% and 4.2% mole fraction ethanol – water mixtures. All laser-textured samples contained untreated, smooth 0.5 mm wide regions and intermediate textured surfaces, that differ in the width of the laser patterned regions (from 0.5 mm to 2.5 mm). For smooth surfaces, we measured significant decreases in average heat transfer coefficients (HTC) and increases in bubble activation temperatures in comparison with the laser-textured surfaces for all the tested working fluids. Significant enhancement in HTC (280%) on a textured heating surface with 2.5-mm-wide laser pattern was recorded using pure water. For pure ethanol, the highest enhancement of 268% was achieved on a heating surface with 1.5-mm-wide laser pattern. The highest enhancement of HTC for the tested binary mixtures was obtained using 2.0-mm wide-laser-textured regions (HTC improved by 235% and 279% for the 0.4% and 4.2% mixtures, respectively). Our results indicate that laser texturing can significantly improve boiling performance when the intervals of the laser-textured patterns are close to the capillary lengths of the tested fluids.
{"title":"Investigation of Nucleate Pool Boiling of Saturated Pure Liquids and Ethanol-Water Mixtures on Smooth and Laser-Textured Surfaces","authors":"Peter Zakšek, M. Zupančič, P. Gregorčič, I. Golobič","doi":"10.1080/15567265.2019.1689590","DOIUrl":"https://doi.org/10.1080/15567265.2019.1689590","url":null,"abstract":"ABSTRACT Nucleate pool boiling experiments were performed on plain and five laser-textured stainless-steel foils using saturated pure water, 100% ethanol, 0.4% and 4.2% mole fraction ethanol – water mixtures. All laser-textured samples contained untreated, smooth 0.5 mm wide regions and intermediate textured surfaces, that differ in the width of the laser patterned regions (from 0.5 mm to 2.5 mm). For smooth surfaces, we measured significant decreases in average heat transfer coefficients (HTC) and increases in bubble activation temperatures in comparison with the laser-textured surfaces for all the tested working fluids. Significant enhancement in HTC (280%) on a textured heating surface with 2.5-mm-wide laser pattern was recorded using pure water. For pure ethanol, the highest enhancement of 268% was achieved on a heating surface with 1.5-mm-wide laser pattern. The highest enhancement of HTC for the tested binary mixtures was obtained using 2.0-mm wide-laser-textured regions (HTC improved by 235% and 279% for the 0.4% and 4.2% mixtures, respectively). Our results indicate that laser texturing can significantly improve boiling performance when the intervals of the laser-textured patterns are close to the capillary lengths of the tested fluids.","PeriodicalId":49784,"journal":{"name":"Nanoscale and Microscale Thermophysical Engineering","volume":"24 1","pages":"29 - 42"},"PeriodicalIF":4.1,"publicationDate":"2020-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/15567265.2019.1689590","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41807920","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-01-02DOI: 10.1080/15567265.2019.1689589
N. Usov, O. N. Serebryakova, E. M. Gubanova
ABSTRACT The specific absorption rate of magnetic nanoparticles in a rotating magnetic field has been calculated taking into account both thermal fluctuations of the particle magnetic moments and strong magneto-dipole interactions in nanoparticle clusters with various filling factors. For an assembly of interacting superparamagnetic nanoparticles, the maximal values of the specific absorption rate in a rotating magnetic field are found to be 30–40% greater than that in alternating magnetic field. In addition, for the given filling factor and magnetic field amplitude in rotating magnetic field the nanoparticles in a wider range of diameters can effectively contribute to the energy absorption process. Therefore, the use of rotating magnetic field seems preferable in magnetic nanoparticle hyperthermia.
{"title":"The heating of magnetic nanoparticles in a rotating magnetic field","authors":"N. Usov, O. N. Serebryakova, E. M. Gubanova","doi":"10.1080/15567265.2019.1689589","DOIUrl":"https://doi.org/10.1080/15567265.2019.1689589","url":null,"abstract":"ABSTRACT The specific absorption rate of magnetic nanoparticles in a rotating magnetic field has been calculated taking into account both thermal fluctuations of the particle magnetic moments and strong magneto-dipole interactions in nanoparticle clusters with various filling factors. For an assembly of interacting superparamagnetic nanoparticles, the maximal values of the specific absorption rate in a rotating magnetic field are found to be 30–40% greater than that in alternating magnetic field. In addition, for the given filling factor and magnetic field amplitude in rotating magnetic field the nanoparticles in a wider range of diameters can effectively contribute to the energy absorption process. Therefore, the use of rotating magnetic field seems preferable in magnetic nanoparticle hyperthermia.","PeriodicalId":49784,"journal":{"name":"Nanoscale and Microscale Thermophysical Engineering","volume":"24 1","pages":"20 - 28"},"PeriodicalIF":4.1,"publicationDate":"2020-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/15567265.2019.1689589","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41642005","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：