Pub Date : 2018-11-14DOI: 10.1080/15567265.2018.1520762
M. Markov, M. Zebarjadi
ABSTRACT In early 90s, Hicks and Dresselhaus proposed that low dimensional materials are advantages for thermoelectric applications due to the sharp features in their density-of-states, resulting in a high Seebeck coefficient and, potentially, in a high thermoelectric power factor. Two-dimensional (2D) materials are the latest class of low dimensional materials studied for thermoelectric applications. The experimental exfoliation of graphene, a single-layer of carbon atoms in 2004, triggered an avalanche of studies devoted to 2D materials in view of electronic, thermal, and optical applications. One can mix and match and stack 2D layers to form van der Waals hetero-structures. Such structures have extreme anisotropic transport properties. Both in-plane and cross-plane thermoelectric transport in these structures are of interest. In this short review article, we first review the progress achieved so far in the study of thermoelectric transport properties of graphene, the most widely studied 2D material, as a representative of interesting in-plane thermoelectric properties. Then, we turn our attention to the layered materials, in their cross-plane direction, highlighting their role as potential structures for solid-state thermionic power generators and coolers.
{"title":"Thermoelectric transport in graphene and 2D layered materials","authors":"M. Markov, M. Zebarjadi","doi":"10.1080/15567265.2018.1520762","DOIUrl":"https://doi.org/10.1080/15567265.2018.1520762","url":null,"abstract":"ABSTRACT In early 90s, Hicks and Dresselhaus proposed that low dimensional materials are advantages for thermoelectric applications due to the sharp features in their density-of-states, resulting in a high Seebeck coefficient and, potentially, in a high thermoelectric power factor. Two-dimensional (2D) materials are the latest class of low dimensional materials studied for thermoelectric applications. The experimental exfoliation of graphene, a single-layer of carbon atoms in 2004, triggered an avalanche of studies devoted to 2D materials in view of electronic, thermal, and optical applications. One can mix and match and stack 2D layers to form van der Waals hetero-structures. Such structures have extreme anisotropic transport properties. Both in-plane and cross-plane thermoelectric transport in these structures are of interest. In this short review article, we first review the progress achieved so far in the study of thermoelectric transport properties of graphene, the most widely studied 2D material, as a representative of interesting in-plane thermoelectric properties. Then, we turn our attention to the layered materials, in their cross-plane direction, highlighting their role as potential structures for solid-state thermionic power generators and coolers.","PeriodicalId":49784,"journal":{"name":"Nanoscale and Microscale Thermophysical Engineering","volume":"23 1","pages":"117 - 127"},"PeriodicalIF":4.1,"publicationDate":"2018-11-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/15567265.2018.1520762","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47139854","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 : 2018-09-25DOI: 10.1080/15567265.2018.1520763
Han-Ling Li, B. Cao
ABSTRACT Heat conduction in radius direction is of great importance to the use of two-dimensional materials and experiments. In this paper, radial ballistic-diffusive heat conduction in nanoscale is investigated by the phonon Monte Carlo (MC) method and phonon Boltzmann transport equation. We find that owing to the two-dimensional nature, the radial heat transport is dominated by two parameters, including the Knudsen number (Kn) and the radius ratio of the two concentric boundaries, the former of which is defined as the ratio of the phonon mean-free-path to the distance of the two boundaries. Compared with the one-dimensional cases, radial ballistic transport not only leads to boundary temperature jumps and the size effect of the effective thermal conductivity, but also results in a nonlinear temperature profile in logarithm radius coordinate, a difference of the inner and outer boundary temperature jumps, a stronger size effect, and a nonuniform local thermal conductivity within the system. When the value of Kn is far less than one, diffusive transport predominates and the effect of the radius ratio is negligible. Whereas, when Kn is comparable to or larger than one, the intensity of ballistic transport compared to diffusive transport will be increased significantly as the radius ratio decreases. In addition, the models for the temperature profile and the effective thermal conductivity are derived by an interpolation of the limit solutions and modification of the previous model, respectively. The good agreements with the phonon MC simulations demonstrate their validity.
{"title":"Radial ballistic-diffusive heat conduction in nanoscale","authors":"Han-Ling Li, B. Cao","doi":"10.1080/15567265.2018.1520763","DOIUrl":"https://doi.org/10.1080/15567265.2018.1520763","url":null,"abstract":"ABSTRACT Heat conduction in radius direction is of great importance to the use of two-dimensional materials and experiments. In this paper, radial ballistic-diffusive heat conduction in nanoscale is investigated by the phonon Monte Carlo (MC) method and phonon Boltzmann transport equation. We find that owing to the two-dimensional nature, the radial heat transport is dominated by two parameters, including the Knudsen number (Kn) and the radius ratio of the two concentric boundaries, the former of which is defined as the ratio of the phonon mean-free-path to the distance of the two boundaries. Compared with the one-dimensional cases, radial ballistic transport not only leads to boundary temperature jumps and the size effect of the effective thermal conductivity, but also results in a nonlinear temperature profile in logarithm radius coordinate, a difference of the inner and outer boundary temperature jumps, a stronger size effect, and a nonuniform local thermal conductivity within the system. When the value of Kn is far less than one, diffusive transport predominates and the effect of the radius ratio is negligible. Whereas, when Kn is comparable to or larger than one, the intensity of ballistic transport compared to diffusive transport will be increased significantly as the radius ratio decreases. In addition, the models for the temperature profile and the effective thermal conductivity are derived by an interpolation of the limit solutions and modification of the previous model, respectively. The good agreements with the phonon MC simulations demonstrate their validity.","PeriodicalId":49784,"journal":{"name":"Nanoscale and Microscale Thermophysical Engineering","volume":"23 1","pages":"10 - 24"},"PeriodicalIF":4.1,"publicationDate":"2018-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/15567265.2018.1520763","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46528506","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 : 2018-09-07DOI: 10.1080/15567265.2018.1497110
W. Ji, P. Zhao, Chuang-Yao Zhao, Jing Ding, W. Tao
ABSTRACT In order to investigate the effect of surface wettability on the pool boiling heat transfer, nucleate pool boiling experiments were conducted with deionized water and silica based nanofluid. A higher surface roughness value in the range of 3.9 ~ 6.0μm was tested. The contact angle was from 4.7° to 153°, and heat flux was from 30kW/m2 to 300kW/m2. Experimental results showed that hydrophilicity diminish the boiling heat transfer of silica nanofluid on the surfaces with higher roughness. As the increment of nanofluid mass concentration from 0.025% to 0.1%, a further reduction of heat transfer coefficient was observed. For the super hydrophobic surface with higher roughness (contact angle 153.0°), boiling heat transfer was enhanced at heat flux less than 93 kW/m2, and then the heat transfer degraded at higher heat flux.
{"title":"Pool boiling heat transfer of water and nanofluid outside the surface with higher roughness and different wettability","authors":"W. Ji, P. Zhao, Chuang-Yao Zhao, Jing Ding, W. Tao","doi":"10.1080/15567265.2018.1497110","DOIUrl":"https://doi.org/10.1080/15567265.2018.1497110","url":null,"abstract":"ABSTRACT In order to investigate the effect of surface wettability on the pool boiling heat transfer, nucleate pool boiling experiments were conducted with deionized water and silica based nanofluid. A higher surface roughness value in the range of 3.9 ~ 6.0μm was tested. The contact angle was from 4.7° to 153°, and heat flux was from 30kW/m2 to 300kW/m2. Experimental results showed that hydrophilicity diminish the boiling heat transfer of silica nanofluid on the surfaces with higher roughness. As the increment of nanofluid mass concentration from 0.025% to 0.1%, a further reduction of heat transfer coefficient was observed. For the super hydrophobic surface with higher roughness (contact angle 153.0°), boiling heat transfer was enhanced at heat flux less than 93 kW/m2, and then the heat transfer degraded at higher heat flux.","PeriodicalId":49784,"journal":{"name":"Nanoscale and Microscale Thermophysical Engineering","volume":"22 1","pages":"296 - 323"},"PeriodicalIF":4.1,"publicationDate":"2018-09-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/15567265.2018.1497110","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41925546","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 : 2018-08-30DOI: 10.1080/15567265.2018.1490938
Lin Liu, Hongyu Huang, Zhaohong He, Shijie Li, Jun Li, Jie Chen, Lisheng Deng, Y. Osaka, N. Kobayashi
ABSTRACT A series of experimental investigations had been performed to analyze the heat and mass transfer performance for two novel types of silica-based consolidated composite adsorbents developed by the freeze-drying method. The first type of adsorbent is silica gel consolidated with carboxymethyl cellulose (CMC) (SC), while the other is silica gel consolidated with CMC and carbon fiber powder (SCC). Results indicate that the thermal conductivity of consolidated composite adsorbents increases with the mass proportion of carbon fiber powder, while it decreases with the increasing moisture content in the preparation process of the adsorbents. When the mass ratio of silica gel, CMC, and carbon fiber powder is 4:1:4, the highest thermal conductivity of consolidated composite adsorbent obtained from experiments reaches 1.66 W m−1 K−1, which is 13.4 times greater than that of pure silica gel. Furthermore, the results of macroporous properties analysis of typical samples including SC20 and SCC20 (where the 20 means that the undried samples have a water content of 20% by mass during the preparation process) show that heat transfer additives effectively improve the macroporous porosity and permeability of the consolidated composite adsorbents. The study on adsorption dynamic performance indicates that the freeze-drying method helps to improve the adsorption performance including adsorption rate and equilibrium water uptake. The experimental results also show that the mass transfer coefficient K of the two typical samples are approximately stable at 5 × 10−3 s−1 when the adsorption temperature is ranged between 30 and 40°C, which are almost twice the corresponding values of the samples developed by heating–drying method. Therefore, the proposed approach which is the consolidation with heat transfer additives combined with freeze-drying method is effective for simultaneously enhancing the heat and mass transfer performance of the silica gel adsorbents.
采用冻干方法制备了两种新型硅基固结复合吸附剂，对其传热传质性能进行了实验研究。第一类吸附剂是与羧甲基纤维素(CMC) (SC)固结的硅胶，另一类是与羧甲基纤维素(CMC)和碳纤维粉(SCC)固结的硅胶。结果表明，固结复合吸附剂的导热系数随碳纤维粉质量比例的增加而增加，而随吸附剂制备过程中含水量的增加而降低。当硅胶、CMC和碳纤维粉的质量比为4:1:4时，实验得到的固结复合吸附剂的最高导热系数达到1.66 W m−1 K−1，是纯硅胶的13.4倍。此外，对SC20和SCC20等典型样品的大孔性能分析结果(其中20表示制备过程中未干燥样品的质量含水量为20%)表明，传热添加剂有效提高了固结复合吸附剂的大孔孔隙度和渗透率。吸附动态性能的研究表明，冷冻干燥方法有助于提高吸附性能，包括吸附速率和平衡吸水量。实验结果还表明，当吸附温度在30 ~ 40℃范围内时，两种典型样品的传质系数K在5 × 10−3 s−1处近似稳定，几乎是加热干燥法样品的两倍。因此，采用导热添加剂固结与冷冻干燥相结合的方法可以有效地同时提高硅胶吸附剂的传热传质性能。
{"title":"The heat and mass transfer performance of facile synthesized silica gel/carbon-fiber based consolidated composite adsorbents developed by freeze-drying method","authors":"Lin Liu, Hongyu Huang, Zhaohong He, Shijie Li, Jun Li, Jie Chen, Lisheng Deng, Y. Osaka, N. Kobayashi","doi":"10.1080/15567265.2018.1490938","DOIUrl":"https://doi.org/10.1080/15567265.2018.1490938","url":null,"abstract":"ABSTRACT A series of experimental investigations had been performed to analyze the heat and mass transfer performance for two novel types of silica-based consolidated composite adsorbents developed by the freeze-drying method. The first type of adsorbent is silica gel consolidated with carboxymethyl cellulose (CMC) (SC), while the other is silica gel consolidated with CMC and carbon fiber powder (SCC). Results indicate that the thermal conductivity of consolidated composite adsorbents increases with the mass proportion of carbon fiber powder, while it decreases with the increasing moisture content in the preparation process of the adsorbents. When the mass ratio of silica gel, CMC, and carbon fiber powder is 4:1:4, the highest thermal conductivity of consolidated composite adsorbent obtained from experiments reaches 1.66 W m−1 K−1, which is 13.4 times greater than that of pure silica gel. Furthermore, the results of macroporous properties analysis of typical samples including SC20 and SCC20 (where the 20 means that the undried samples have a water content of 20% by mass during the preparation process) show that heat transfer additives effectively improve the macroporous porosity and permeability of the consolidated composite adsorbents. The study on adsorption dynamic performance indicates that the freeze-drying method helps to improve the adsorption performance including adsorption rate and equilibrium water uptake. The experimental results also show that the mass transfer coefficient K of the two typical samples are approximately stable at 5 × 10−3 s−1 when the adsorption temperature is ranged between 30 and 40°C, which are almost twice the corresponding values of the samples developed by heating–drying method. Therefore, the proposed approach which is the consolidation with heat transfer additives combined with freeze-drying method is effective for simultaneously enhancing the heat and mass transfer performance of the silica gel adsorbents.","PeriodicalId":49784,"journal":{"name":"Nanoscale and Microscale Thermophysical Engineering","volume":"22 1","pages":"255 - 269"},"PeriodicalIF":4.1,"publicationDate":"2018-08-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/15567265.2018.1490938","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47903311","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 : 2018-08-20DOI: 10.1080/15567265.2018.1497111
Yiming Rong, Pengfei Ji, M. He, Yuwen Zhang, Yong Tang
ABSTRACT Megahertz is the highest femtosecond laser repetition rate that the state-of-the art technology can achieve. In this article, a single femtosecond laser pulse is burst into multiple femtosecond laser pulses to process aluminum. The temporal gap between two consecutive burst pulses is 2 picoseconds, which is much shorter than the temporal gap between two consecutive pulses at the repetition rate of megahertz. By taking the thermophysical scenarios of femtosecond laser induced of electron thermalization, electron heat conduction, electron–phonon-coupled heat transfer and atomic motion into account, a multiscale framework integrating ab initio quantum mechanical calculation, molecular dynamics and two-temperature model are constructed. The effect of femtosecond laser pulse number on the incubation phenomenon is studied. Comparing with the single pulse-processing aluminum film, the femtosecond laser in burst mode leads to smaller thermal stress, which is favorable to reduce the thermal mechanical damage of the material beneath the laser-irradiated surface. Appreciable differences among the simulation results by using electron thermophysical parameters from ab initio quantum mechanical calculation and those from experimental measurement, empirical estimation and calculation are found, indicating the essentials to precisely model the electron thermal response subject to femtosecond laser excitation.
{"title":"Multiscale Investigation of Femtosecond Laser Pulses Processing Aluminum in Burst Mode","authors":"Yiming Rong, Pengfei Ji, M. He, Yuwen Zhang, Yong Tang","doi":"10.1080/15567265.2018.1497111","DOIUrl":"https://doi.org/10.1080/15567265.2018.1497111","url":null,"abstract":"ABSTRACT Megahertz is the highest femtosecond laser repetition rate that the state-of-the art technology can achieve. In this article, a single femtosecond laser pulse is burst into multiple femtosecond laser pulses to process aluminum. The temporal gap between two consecutive burst pulses is 2 picoseconds, which is much shorter than the temporal gap between two consecutive pulses at the repetition rate of megahertz. By taking the thermophysical scenarios of femtosecond laser induced of electron thermalization, electron heat conduction, electron–phonon-coupled heat transfer and atomic motion into account, a multiscale framework integrating ab initio quantum mechanical calculation, molecular dynamics and two-temperature model are constructed. The effect of femtosecond laser pulse number on the incubation phenomenon is studied. Comparing with the single pulse-processing aluminum film, the femtosecond laser in burst mode leads to smaller thermal stress, which is favorable to reduce the thermal mechanical damage of the material beneath the laser-irradiated surface. Appreciable differences among the simulation results by using electron thermophysical parameters from ab initio quantum mechanical calculation and those from experimental measurement, empirical estimation and calculation are found, indicating the essentials to precisely model the electron thermal response subject to femtosecond laser excitation.","PeriodicalId":49784,"journal":{"name":"Nanoscale and Microscale Thermophysical Engineering","volume":"22 1","pages":"324 - 347"},"PeriodicalIF":4.1,"publicationDate":"2018-08-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/15567265.2018.1497111","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49210680","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 : 2018-08-15DOI: 10.1080/15567265.2019.1580807
Jihoon Jeong, Xianghai Meng, A. Rockwell, S. Bank, W. Hsieh, Jung‐Fu Lin, Yaguo Wang
ABSTRACT We developed a picosecond transient thermoreflectance (ps-TTR) system for thermal property characterization, using a low-repetition-rate picosecond pulsed laser (1064 nm) as the heating source and a 532 nm CW laser as the probe. Low-repetition-rate pump eliminates the complication from thermal accumulation effect. Without the need of a mechanical delay stage, this ps-TTR system can measure the thermal decay curve from 500 ps up to 1 ms. Three groups of samples are tested: bulk crystals (glass, Si, GaAs, and sapphire); MoS2 thin films (157 ~ 900 nm thickness); InGaAs random alloy and GaAs/InAs digital alloy (short period superlattices). Analysis of the thermoreflectance signals shows that this ps-TTR system is able to measure both thermal conductivity and interface conductance in nanostructures. The measured thermal conductivity values in bulk crystals, MoS2 thin films, and InGaAs random alloy are all consistent with literature values. Cross-plane thermal conductivity in MoS2 thin films does not show obvious thickness dependence. Thermal conductivities of GaAs/InAs digital alloys are smaller than InGaAs random alloy, due to the efficient scattering at interfaces. We also discuss the advantages and disadvantages of this newly developed ps-TTR system comparing with the popular time-domain thermoreflectance system.
{"title":"Picosecond transient thermoreflectance for thermal conductivity characterization","authors":"Jihoon Jeong, Xianghai Meng, A. Rockwell, S. Bank, W. Hsieh, Jung‐Fu Lin, Yaguo Wang","doi":"10.1080/15567265.2019.1580807","DOIUrl":"https://doi.org/10.1080/15567265.2019.1580807","url":null,"abstract":"ABSTRACT We developed a picosecond transient thermoreflectance (ps-TTR) system for thermal property characterization, using a low-repetition-rate picosecond pulsed laser (1064 nm) as the heating source and a 532 nm CW laser as the probe. Low-repetition-rate pump eliminates the complication from thermal accumulation effect. Without the need of a mechanical delay stage, this ps-TTR system can measure the thermal decay curve from 500 ps up to 1 ms. Three groups of samples are tested: bulk crystals (glass, Si, GaAs, and sapphire); MoS2 thin films (157 ~ 900 nm thickness); InGaAs random alloy and GaAs/InAs digital alloy (short period superlattices). Analysis of the thermoreflectance signals shows that this ps-TTR system is able to measure both thermal conductivity and interface conductance in nanostructures. The measured thermal conductivity values in bulk crystals, MoS2 thin films, and InGaAs random alloy are all consistent with literature values. Cross-plane thermal conductivity in MoS2 thin films does not show obvious thickness dependence. Thermal conductivities of GaAs/InAs digital alloys are smaller than InGaAs random alloy, due to the efficient scattering at interfaces. We also discuss the advantages and disadvantages of this newly developed ps-TTR system comparing with the popular time-domain thermoreflectance system.","PeriodicalId":49784,"journal":{"name":"Nanoscale and Microscale Thermophysical Engineering","volume":"23 1","pages":"211 - 221"},"PeriodicalIF":4.1,"publicationDate":"2018-08-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/15567265.2019.1580807","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45236656","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 : 2018-07-31DOI: 10.1080/15567265.2018.1495282
M. R. Haque, C. Qu, E. Kinzel, A. Betz
ABSTRACT The Gibbs free energy barrier for heterogeneous nucleation of a condensed droplet on a rough surface changes significantly with changes of humidity content in the condensing environment. The influence of environmental factors (ambient temperature and relative humidity) and substrate characteristics (topology, surface chemistry, and substrate temperature) on atmospheric condensation phenomenon is very important to elucidate the condensed droplet wetting state and condensate harvesting applications. Condensation from the humid air has been reported for plain silicon and fabricated nanopillar surfaces to facilitate condensate harvesting. Droplet growth and size distributions were recorded for 90 min. Spherical droplets condensed on the silicon surfaces and irregular-shaped droplets were observed on the nanopillar surfaces due to the pinning effect of the pillars. The effect of droplet pinning on coalescence events has been described based on the energy balance for the condensed droplets. A mathematical model reveals that certain dimensional combinations (pillar pitch, pillar diameter, and pillar height) of the nanopillar geometry are required to exhibit the pinning mechanism for condensed droplets. Regeneration of droplets was observed at void spaces generated from coalescence events. The growth of individual droplets was tracked over multiple time and length scales, starting from nucleation to get further insight into the direct growth and coalescence mechanisms. Abbreviation: ESEM: Environmental Scanning Electron Microscope; HCP: Hexagonal Closed-Packed; MPL: Microsphere Photolithography; RH: Relative Humidity
{"title":"Droplet Growth Dynamics during Atmospheric Condensation on Nanopillar Surfaces","authors":"M. R. Haque, C. Qu, E. Kinzel, A. Betz","doi":"10.1080/15567265.2018.1495282","DOIUrl":"https://doi.org/10.1080/15567265.2018.1495282","url":null,"abstract":"ABSTRACT The Gibbs free energy barrier for heterogeneous nucleation of a condensed droplet on a rough surface changes significantly with changes of humidity content in the condensing environment. The influence of environmental factors (ambient temperature and relative humidity) and substrate characteristics (topology, surface chemistry, and substrate temperature) on atmospheric condensation phenomenon is very important to elucidate the condensed droplet wetting state and condensate harvesting applications. Condensation from the humid air has been reported for plain silicon and fabricated nanopillar surfaces to facilitate condensate harvesting. Droplet growth and size distributions were recorded for 90 min. Spherical droplets condensed on the silicon surfaces and irregular-shaped droplets were observed on the nanopillar surfaces due to the pinning effect of the pillars. The effect of droplet pinning on coalescence events has been described based on the energy balance for the condensed droplets. A mathematical model reveals that certain dimensional combinations (pillar pitch, pillar diameter, and pillar height) of the nanopillar geometry are required to exhibit the pinning mechanism for condensed droplets. Regeneration of droplets was observed at void spaces generated from coalescence events. The growth of individual droplets was tracked over multiple time and length scales, starting from nucleation to get further insight into the direct growth and coalescence mechanisms. Abbreviation: ESEM: Environmental Scanning Electron Microscope; HCP: Hexagonal Closed-Packed; MPL: Microsphere Photolithography; RH: Relative Humidity","PeriodicalId":49784,"journal":{"name":"Nanoscale and Microscale Thermophysical Engineering","volume":"22 1","pages":"270 - 295"},"PeriodicalIF":4.1,"publicationDate":"2018-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/15567265.2018.1495282","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44862347","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 : 2018-07-03DOI: 10.1080/15567265.2018.1486929
K. Kothari, M. Maldovan
ABSTRACT Controlling thermal transport in optoelectronic devices is a fundamental determinant of optimum performance. We study in-plane thermal transport mechanisms in GaAs/AlAs and their alloy-based superlattices while rigorously accounting for phonon interlayer coupling and interface scattering. We provide an extensive microscopic analysis of phonon transport to enable rational thermal material design. We also predict the thermal conductivity of realistic finite-sized GaAs/AlAs superlattices for efficient heat control in III–V superlattice-based optoelectronic devices.
{"title":"Analysis of in-plane thermal phonon transport in III–V compound semiconductor superlattices","authors":"K. Kothari, M. Maldovan","doi":"10.1080/15567265.2018.1486929","DOIUrl":"https://doi.org/10.1080/15567265.2018.1486929","url":null,"abstract":"ABSTRACT Controlling thermal transport in optoelectronic devices is a fundamental determinant of optimum performance. We study in-plane thermal transport mechanisms in GaAs/AlAs and their alloy-based superlattices while rigorously accounting for phonon interlayer coupling and interface scattering. We provide an extensive microscopic analysis of phonon transport to enable rational thermal material design. We also predict the thermal conductivity of realistic finite-sized GaAs/AlAs superlattices for efficient heat control in III–V superlattice-based optoelectronic devices.","PeriodicalId":49784,"journal":{"name":"Nanoscale and Microscale Thermophysical Engineering","volume":"22 1","pages":"239 - 253"},"PeriodicalIF":4.1,"publicationDate":"2018-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/15567265.2018.1486929","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48414818","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 : 2018-07-03DOI: 10.1080/15567265.2018.1475526
Yujie Chen, Yu Zou, Bo Yu, Dongliang Sun, Xue-Jiao Chen
ABSTRACT Molecular dynamics simulation is conducted to study the effects of surface wettability on rapid boiling and bubble nucleation over smooth surface. The simple L-J liquid is heated by smooth metal surface with different conditions of wettability in cuboid simulation box. The results show that surface wettability has significant impact on phase transition of liquid film. When the heating temperature is 200 K, the rapid boiling occurs above strongly hydrophilic and weakly hydrophilic surfaces; however, only slow evaporation phenomenon occurs above weakly hydrophobic surface within 2.5-ns simulation time. The reason is that the interaction between argon and platinum atoms is stronger over hydrophilic surface, which has higher efficiency in heat transfer. Furthermore, based on the difference of surface wettability in heat transfer efficiency, the surface with nonuniform wettability is constructed, and the central region is more hydrophilic than surrounding region. The growing process of bubble nucleus can be completely observed above the more hydrophilic region.
{"title":"Effects of Surface Wettability on Rapid Boiling and Bubble Nucleation: A Molecular Dynamics Study","authors":"Yujie Chen, Yu Zou, Bo Yu, Dongliang Sun, Xue-Jiao Chen","doi":"10.1080/15567265.2018.1475526","DOIUrl":"https://doi.org/10.1080/15567265.2018.1475526","url":null,"abstract":"ABSTRACT Molecular dynamics simulation is conducted to study the effects of surface wettability on rapid boiling and bubble nucleation over smooth surface. The simple L-J liquid is heated by smooth metal surface with different conditions of wettability in cuboid simulation box. The results show that surface wettability has significant impact on phase transition of liquid film. When the heating temperature is 200 K, the rapid boiling occurs above strongly hydrophilic and weakly hydrophilic surfaces; however, only slow evaporation phenomenon occurs above weakly hydrophobic surface within 2.5-ns simulation time. The reason is that the interaction between argon and platinum atoms is stronger over hydrophilic surface, which has higher efficiency in heat transfer. Furthermore, based on the difference of surface wettability in heat transfer efficiency, the surface with nonuniform wettability is constructed, and the central region is more hydrophilic than surrounding region. The growing process of bubble nucleus can be completely observed above the more hydrophilic region.","PeriodicalId":49784,"journal":{"name":"Nanoscale and Microscale Thermophysical Engineering","volume":"22 1","pages":"198 - 212"},"PeriodicalIF":4.1,"publicationDate":"2018-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/15567265.2018.1475526","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46830230","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}
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