Pub Date : 2023-08-29DOI: 10.1080/15567265.2023.2252884
Bei Zhang, Shidong Zhang, Gang Zhang
ABSTRACT Rational design and adjustment of flexible thermoelectric devices are key points for sustainable and effective thermoelectric conversion, which remains a fundamental challenge due to inherent high thermal conductivity and uncontrolled carrier concentration induced by non-uniform dispersion. Under ingenious combination of weakly-coupled hollow interface and nanotube structure, thermoelectric performance of a dumbbell-like molecular junction comprised of a phenyl-terminated polyyne as central molecule and two semi-infinite 1D single-walled carbon nanotube (SWCNT) as electrodes has been investigated at certain twisted angles (θ). The results indicate that molecule twisting can be reviewed as an effective thermoelectric switch to coordinatingly control electronic and phononic transmission properties simultaneously. Resonance of molecular discrete state and electrode continuous state leads to low thermal conductance, which is sensitively affected by twist angle. Meanwhile, cyclic transformation between p-type and n-type flexible thermoelectrics can be realized by manipulating twist angle in a certain period of rotation. Thermoelectric performance of such a molecular junction can be further improved by boron atom doping at head-to-tail positions, and an excellent figure of merit (ZT = 1.75) is observed near Fermi level under 25° twisted angle. This result inspires an effective strategy to modulate and control thermoelectric conversion, which will greatly broaden applications in thermoelectric twistronics.
{"title":"Effective Thermoelectric Switch of Hollow Weakly-Coupled Molecular Junction Based on Twist Angle Effect with Boron-Doping","authors":"Bei Zhang, Shidong Zhang, Gang Zhang","doi":"10.1080/15567265.2023.2252884","DOIUrl":"https://doi.org/10.1080/15567265.2023.2252884","url":null,"abstract":"ABSTRACT Rational design and adjustment of flexible thermoelectric devices are key points for sustainable and effective thermoelectric conversion, which remains a fundamental challenge due to inherent high thermal conductivity and uncontrolled carrier concentration induced by non-uniform dispersion. Under ingenious combination of weakly-coupled hollow interface and nanotube structure, thermoelectric performance of a dumbbell-like molecular junction comprised of a phenyl-terminated polyyne as central molecule and two semi-infinite 1D single-walled carbon nanotube (SWCNT) as electrodes has been investigated at certain twisted angles (θ). The results indicate that molecule twisting can be reviewed as an effective thermoelectric switch to coordinatingly control electronic and phononic transmission properties simultaneously. Resonance of molecular discrete state and electrode continuous state leads to low thermal conductance, which is sensitively affected by twist angle. Meanwhile, cyclic transformation between p-type and n-type flexible thermoelectrics can be realized by manipulating twist angle in a certain period of rotation. Thermoelectric performance of such a molecular junction can be further improved by boron atom doping at head-to-tail positions, and an excellent figure of merit (ZT = 1.75) is observed near Fermi level under 25° twisted angle. This result inspires an effective strategy to modulate and control thermoelectric conversion, which will greatly broaden applications in thermoelectric twistronics.","PeriodicalId":49784,"journal":{"name":"Nanoscale and Microscale Thermophysical Engineering","volume":"27 1","pages":"168 - 181"},"PeriodicalIF":4.1,"publicationDate":"2023-08-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46565909","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 : 2023-07-31DOI: 10.1080/15567265.2023.2240877
Jie Lin, Mei-Jiau Huang
ABSTRACT The roughness and film thickness effects on the interfacial thermal resistance (ITR) are explored at two deliberately selected temperatures in use of Monte-Carlo simulation method. Particular methods are proposed to define properly the phonon emitting temperature based on the one-way deviational heat flux, and to define correctly the phonon equilibrium temperature by considering the different properties and residence times of incident, transmitted, and reflected phonons near an interface. A mixed mismatch model which allows polarization conversion is constructed and employed. The so-obtained traditional ITRs, defined based on the emitting temperature difference, and the revised ITRs, defined based on the equilibrium temperature difference, are compared with model predictions in the literature. Simulation results show that at high temperature the revised ITR decreases monotonically with increasing film thickness and at low temperature it possesses a local minimum against the interface roughness. The latter is explained by the monotonically increasing traditional ITR and monotonically decreasing ratio of the equilibrium temperature difference to emitting temperature difference with increasing roughness. Among all the studied models, only the newly proposed one can well predict the ITR for different interface roughness at low temperature. None of the models captures the monotonic decrease of ITR with film thickness at high temperature however.
{"title":"An Investigation into the Roughness and Film Thickness Effects on the Interfacial Thermal Resistance","authors":"Jie Lin, Mei-Jiau Huang","doi":"10.1080/15567265.2023.2240877","DOIUrl":"https://doi.org/10.1080/15567265.2023.2240877","url":null,"abstract":"ABSTRACT The roughness and film thickness effects on the interfacial thermal resistance (ITR) are explored at two deliberately selected temperatures in use of Monte-Carlo simulation method. Particular methods are proposed to define properly the phonon emitting temperature based on the one-way deviational heat flux, and to define correctly the phonon equilibrium temperature by considering the different properties and residence times of incident, transmitted, and reflected phonons near an interface. A mixed mismatch model which allows polarization conversion is constructed and employed. The so-obtained traditional ITRs, defined based on the emitting temperature difference, and the revised ITRs, defined based on the equilibrium temperature difference, are compared with model predictions in the literature. Simulation results show that at high temperature the revised ITR decreases monotonically with increasing film thickness and at low temperature it possesses a local minimum against the interface roughness. The latter is explained by the monotonically increasing traditional ITR and monotonically decreasing ratio of the equilibrium temperature difference to emitting temperature difference with increasing roughness. Among all the studied models, only the newly proposed one can well predict the ITR for different interface roughness at low temperature. None of the models captures the monotonic decrease of ITR with film thickness at high temperature however.","PeriodicalId":49784,"journal":{"name":"Nanoscale and Microscale Thermophysical Engineering","volume":"27 1","pages":"149 - 167"},"PeriodicalIF":4.1,"publicationDate":"2023-07-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47635030","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 : 2023-06-04DOI: 10.1080/15567265.2023.2220769
Donghyuk Kim, Hyunju Kim
ABSTRACT Recently, the incidence of skin cancer has been increasing owing to the development of science and technology and the increase in outdoor activities. Research on photothermal therapy as a treatment technique for similar skin cancer is in progress. Photothermal therapy is a treatment technique that removes tumor tissue by increasing the temperature. It has the advantage of rapid recovery and a low risk of secondary infection. In this study, a numerical investigation of photothermal therapy based on heat transfer is conducted on squamous cell carcinoma present inside the skin layer. Analysis is performed by varying the number of injections of gold nanoparticles, volume fraction of gold nanoparticles in the tumor, and laser intensity. In addition, conditions for maximizing expression of apoptosis in the tumor and minimizing amount of thermal damage to surrounding normal tissues are identified through the variable which is apoptosis retention ratio, thermal hazard value and effective apoptosis retention ratio. It was confirmed that the optimal therapeutic effect was shown when the volume fraction of injected GNPs was 10−3, the number of injections was 6 times, and the irradiated laser intensity was 140 mW for the tumor presented in this study. Ultimately, these results are expected to accelerate the commercialization of photothermal therapy.
{"title":"Study on Apoptosis of Squamous Cell Carcinoma Using Photothermal Therapy with Partial Injection of Gold Nanoparticles","authors":"Donghyuk Kim, Hyunju Kim","doi":"10.1080/15567265.2023.2220769","DOIUrl":"https://doi.org/10.1080/15567265.2023.2220769","url":null,"abstract":"ABSTRACT Recently, the incidence of skin cancer has been increasing owing to the development of science and technology and the increase in outdoor activities. Research on photothermal therapy as a treatment technique for similar skin cancer is in progress. Photothermal therapy is a treatment technique that removes tumor tissue by increasing the temperature. It has the advantage of rapid recovery and a low risk of secondary infection. In this study, a numerical investigation of photothermal therapy based on heat transfer is conducted on squamous cell carcinoma present inside the skin layer. Analysis is performed by varying the number of injections of gold nanoparticles, volume fraction of gold nanoparticles in the tumor, and laser intensity. In addition, conditions for maximizing expression of apoptosis in the tumor and minimizing amount of thermal damage to surrounding normal tissues are identified through the variable which is apoptosis retention ratio, thermal hazard value and effective apoptosis retention ratio. It was confirmed that the optimal therapeutic effect was shown when the volume fraction of injected GNPs was 10−3, the number of injections was 6 times, and the irradiated laser intensity was 140 mW for the tumor presented in this study. Ultimately, these results are expected to accelerate the commercialization of photothermal therapy.","PeriodicalId":49784,"journal":{"name":"Nanoscale and Microscale Thermophysical Engineering","volume":"27 1","pages":"135 - 148"},"PeriodicalIF":4.1,"publicationDate":"2023-06-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45806628","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 : 2023-04-21DOI: 10.1080/15567265.2023.2202699
Xin-Bo Zhang, Cheng-Long Zhou, Feng Gu, Xiao-Ping Luo, Yong Zhang, H. Yi
ABSTRACT The energy conversion performance of thermophotovoltaic (TPV) systems can be improved when the vacuum gap between the emitter and the TPV cell is at the near-field owing to the photon tunneling of evanescent waves. Among them, the back-gapped-reflector TPV systems have gained interest as a method of improving their conversion efficiency by optimizing the spectral absorption of TPV cells. In this work, we introduce an alternative concept for the back-gapped-reflector TPV systems, namely the medium-bridge near-field TPV system, by building a medium bridge between the metal reflector and the TPV cell using SU8 nanofilm. The SU8 medium-bridge achieves a noticeable improvement in output performance by increasing the spectral absorption of the InAs cell and reducing parasitic absorption losses of the Au substrate. The results indicate that, as a consequence of the improved effect of the medium-bridge, the output power density and efficiency of this system exceed those of the conventional TPV system (which lacks a medium-bridge) by 26.4% and 36.5%, respectively. Moreover, we systematically analyze the modulation of medium-bridge thicknesses and cell thickness on output performance and clarify how both affect energy losses of this near-field TPV system. Our work offers a strategy to improve the energy conversion performance of the near-field TPV system, opening new opportunities for developing near-field energy conversion.
{"title":"Medium-Bridge Near-Field Thermophotovoltaic System","authors":"Xin-Bo Zhang, Cheng-Long Zhou, Feng Gu, Xiao-Ping Luo, Yong Zhang, H. Yi","doi":"10.1080/15567265.2023.2202699","DOIUrl":"https://doi.org/10.1080/15567265.2023.2202699","url":null,"abstract":"ABSTRACT The energy conversion performance of thermophotovoltaic (TPV) systems can be improved when the vacuum gap between the emitter and the TPV cell is at the near-field owing to the photon tunneling of evanescent waves. Among them, the back-gapped-reflector TPV systems have gained interest as a method of improving their conversion efficiency by optimizing the spectral absorption of TPV cells. In this work, we introduce an alternative concept for the back-gapped-reflector TPV systems, namely the medium-bridge near-field TPV system, by building a medium bridge between the metal reflector and the TPV cell using SU8 nanofilm. The SU8 medium-bridge achieves a noticeable improvement in output performance by increasing the spectral absorption of the InAs cell and reducing parasitic absorption losses of the Au substrate. The results indicate that, as a consequence of the improved effect of the medium-bridge, the output power density and efficiency of this system exceed those of the conventional TPV system (which lacks a medium-bridge) by 26.4% and 36.5%, respectively. Moreover, we systematically analyze the modulation of medium-bridge thicknesses and cell thickness on output performance and clarify how both affect energy losses of this near-field TPV system. Our work offers a strategy to improve the energy conversion performance of the near-field TPV system, opening new opportunities for developing near-field energy conversion.","PeriodicalId":49784,"journal":{"name":"Nanoscale and Microscale Thermophysical Engineering","volume":"27 1","pages":"195 - 207"},"PeriodicalIF":4.1,"publicationDate":"2023-04-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44244514","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 : 2023-04-03DOI: 10.1080/15567265.2023.2197026
Hao Hong, Mei-Jiau Huang
ABSTRACT The thermal conductivity of tortuous silicon nanowires with constant cross section at room temperature was investigated in use of full-spectrum Monte-Carlo simulations. Various geometric features that can be possibly used to describe the tortuosity of the nanowires were studied and their relationships with the thermal conductivity were explored. Comparison of simulation results with experimental data shows similar magnitudes and variation trend of the thermal conductivity against the nanowire hydraulic diameter. The more tortuous, the smaller the thermal conductivity is. Among all, data collapse is best when shown against the surface-to-volume ratio and the correlation length of the surface roughness does not affect the thermal conductivity at all. By taking the surface-to-volume ratio into account for the boundary scattering rate, which also depends on the phonon frequency indirectly through the phonon group velocity, we are able to obtain satisfactory predictions based on a linear spectral model, not only about the thermal conductivity but also about the spectral heat flux density distribution. The model also shows that the relative reduction caused by tortuosity decreases with increasing frequency. For highly tortuous nanowires of diameter 22 nm, simply increasing the tortuosity is sufficient to obtain simulated thermal conductivities that are smaller than the experimentally measured value.
{"title":"The Tortuosity Effect on the Thermal Conductivity of Si Nanowires","authors":"Hao Hong, Mei-Jiau Huang","doi":"10.1080/15567265.2023.2197026","DOIUrl":"https://doi.org/10.1080/15567265.2023.2197026","url":null,"abstract":"ABSTRACT The thermal conductivity of tortuous silicon nanowires with constant cross section at room temperature was investigated in use of full-spectrum Monte-Carlo simulations. Various geometric features that can be possibly used to describe the tortuosity of the nanowires were studied and their relationships with the thermal conductivity were explored. Comparison of simulation results with experimental data shows similar magnitudes and variation trend of the thermal conductivity against the nanowire hydraulic diameter. The more tortuous, the smaller the thermal conductivity is. Among all, data collapse is best when shown against the surface-to-volume ratio and the correlation length of the surface roughness does not affect the thermal conductivity at all. By taking the surface-to-volume ratio into account for the boundary scattering rate, which also depends on the phonon frequency indirectly through the phonon group velocity, we are able to obtain satisfactory predictions based on a linear spectral model, not only about the thermal conductivity but also about the spectral heat flux density distribution. The model also shows that the relative reduction caused by tortuosity decreases with increasing frequency. For highly tortuous nanowires of diameter 22 nm, simply increasing the tortuosity is sufficient to obtain simulated thermal conductivities that are smaller than the experimentally measured value.","PeriodicalId":49784,"journal":{"name":"Nanoscale and Microscale Thermophysical Engineering","volume":"27 1","pages":"110 - 124"},"PeriodicalIF":4.1,"publicationDate":"2023-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42054386","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 : 2023-04-03DOI: 10.1080/15567265.2023.2198581
M. Dorokhin, Y. Kuznetsov, P. Demina, I. Erofeeva, A. Zavrazhnov, M. Boldin, E. A. Lantsev, A. Popov, A. Boryakov, A. Zdoroveyshchev, M. Ved, D. Zdoroveyshchev, M.G. Korotkova
ABSTRACT A spark plasma sintering technology has already become rather common for the fabrication of GexSi1-x nanostructured thermoelectric solid solutions. Such trend is related with a number of opportunities and technological tools that enable precise properties manipulation. The present paper is devoted to discussing the modulation of GexSi1-x spark plasma sintering technique that consists in the use of silicon phosphide as a source of n-type doping within the process of sintering. The composition of the sintered powder is investigated. The synthesis of a solid solution was carried out in the process of sintering. The SiP is a chemically stable non-toxic compound that can replace toxic phosphorus in thermoelectric technology thus reducing the safety requirements of the corresponding technology process. The paper investigates the effect of SiP concentration on thermoelectric characteristics. The impurity distribution is analyzed, and the association of phosphorus atoms into clusters at a very high doping level is shown. The distribution of impurity elements was controlled by EMF analysis in a scanning electron microscope. It was shown that sintering of Ge-Si-SiP powder mixture allowed obtaining the phosphorus doped GexSi1-x material with high electron concentration that demonstrate high level of thermoelectric properties. The obtained thermoelectric characteristics are compared with the world's best nanostructured materials
{"title":"High-Efficiency Spark Plasma Sintered Ge0.3Si0.7:P Thermoelectric Energy Converters with Silicone Phosphide as a Source of Phosphorus Doping","authors":"M. Dorokhin, Y. Kuznetsov, P. Demina, I. Erofeeva, A. Zavrazhnov, M. Boldin, E. A. Lantsev, A. Popov, A. Boryakov, A. Zdoroveyshchev, M. Ved, D. Zdoroveyshchev, M.G. Korotkova","doi":"10.1080/15567265.2023.2198581","DOIUrl":"https://doi.org/10.1080/15567265.2023.2198581","url":null,"abstract":"ABSTRACT A spark plasma sintering technology has already become rather common for the fabrication of GexSi1-x nanostructured thermoelectric solid solutions. Such trend is related with a number of opportunities and technological tools that enable precise properties manipulation. The present paper is devoted to discussing the modulation of GexSi1-x spark plasma sintering technique that consists in the use of silicon phosphide as a source of n-type doping within the process of sintering. The composition of the sintered powder is investigated. The synthesis of a solid solution was carried out in the process of sintering. The SiP is a chemically stable non-toxic compound that can replace toxic phosphorus in thermoelectric technology thus reducing the safety requirements of the corresponding technology process. The paper investigates the effect of SiP concentration on thermoelectric characteristics. The impurity distribution is analyzed, and the association of phosphorus atoms into clusters at a very high doping level is shown. The distribution of impurity elements was controlled by EMF analysis in a scanning electron microscope. It was shown that sintering of Ge-Si-SiP powder mixture allowed obtaining the phosphorus doped GexSi1-x material with high electron concentration that demonstrate high level of thermoelectric properties. The obtained thermoelectric characteristics are compared with the world's best nanostructured materials","PeriodicalId":49784,"journal":{"name":"Nanoscale and Microscale Thermophysical Engineering","volume":"27 1","pages":"125 - 134"},"PeriodicalIF":4.1,"publicationDate":"2023-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47404074","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 : 2023-03-19DOI: 10.1080/15567265.2023.2190449
R. Esquivel-Sirvent, A. Gusso, F. Sánchez Ochoa
ABSTRACT We present a theoretical study of the near-field radiative heat transfer (NFRHT) between two -GeSe monolayers, each at a different temperature. (This is a relevant 2D material with superior electron transport and optical properties compared to black-phosphorus monolayers). The required optical conductivity of the monolayer is calculated using density functional theory including spin-orbit coupling, and using the Perdew-Burke-Erzenhof parametrization. Both the intra and interband transitions are taken into account, as well as the contribution of the optical phonons. This allows us to obtain more realistic predictions of the NFRHT between two monolayers of GeSe. The role of the electron doping concentration and the plasma relaxation frequency is investigated, showing a non-monotonic dependence on the radiative heat transfer with increasing doping, and having an optimal doping where the heat flux is maximize. A strong optical anisotropy in the electric conductivity is obtained from the contribution of both electrons and ions This anisotropy is explored, showing that the relative rotation of two monolayers results in modulation of the NFRHT much larger than previously found for similar 2D materials, like -GeSe. As the angle of rotation between the monolayers increases the total heat transfer decreases. Our analysis demonstrates the relevance of properly taking into account the materialelectronic and ionic contributions.
{"title":"Near-Field Radiative Heat Transfer between $beta-$GeSe monolayers: An ab initio study","authors":"R. Esquivel-Sirvent, A. Gusso, F. Sánchez Ochoa","doi":"10.1080/15567265.2023.2190449","DOIUrl":"https://doi.org/10.1080/15567265.2023.2190449","url":null,"abstract":"ABSTRACT We present a theoretical study of the near-field radiative heat transfer (NFRHT) between two -GeSe monolayers, each at a different temperature. (This is a relevant 2D material with superior electron transport and optical properties compared to black-phosphorus monolayers). The required optical conductivity of the monolayer is calculated using density functional theory including spin-orbit coupling, and using the Perdew-Burke-Erzenhof parametrization. Both the intra and interband transitions are taken into account, as well as the contribution of the optical phonons. This allows us to obtain more realistic predictions of the NFRHT between two monolayers of GeSe. The role of the electron doping concentration and the plasma relaxation frequency is investigated, showing a non-monotonic dependence on the radiative heat transfer with increasing doping, and having an optimal doping where the heat flux is maximize. A strong optical anisotropy in the electric conductivity is obtained from the contribution of both electrons and ions This anisotropy is explored, showing that the relative rotation of two monolayers results in modulation of the NFRHT much larger than previously found for similar 2D materials, like -GeSe. As the angle of rotation between the monolayers increases the total heat transfer decreases. Our analysis demonstrates the relevance of properly taking into account the materialelectronic and ionic contributions.","PeriodicalId":49784,"journal":{"name":"Nanoscale and Microscale Thermophysical Engineering","volume":"27 1","pages":"95 - 109"},"PeriodicalIF":4.1,"publicationDate":"2023-03-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46751884","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}
ABSTRACT Silica aerogel is an excellent thermal insulator for high-speed aircraft, but there is little research on it in a high-temperature and complex-pressure environment. This research aims to evaluate the thermal insulation performance of silica aerogel monoliths with different porosities under large temperature differences and pressure gradients. We established an experimental system to measure and analyze the hot surface temperature response by fixing the heat flux and the cold surface temperature at transient pressure conditions. An unsteady-state heat transfer model considering gas flow is developed. The effective thermal conductivity of silica aerogels with 79.55 ~ 90.91% porosity is measured at different temperature differences between cold and hot surfaces (127 ~ 512 K), near-vacuum (<10 Pa), and transient pressure conditions. The results demonstrated that silica aerogel with 90.91% porosity showed the best thermal insulation performance when the temperature differences were over 500 K, while the aerogel with 79.55% porosity became the best when the temperature differences were less than 500 K. In addition, both the temperature and pressure difference affect the thermal insulation performance: the energy transport caused by gas flow affects the dynamic temperature response when gas permeability is of the order of 10−15 m2; the thermal insulation performance is improved by increasing gas permeability and pressure difference when gas flow and heat transfer directions are opposite.
{"title":"Thermal Insulation Performance of Monolithic Silica Aerogel with Gas Permeation Effect at Pressure Gradients and Large Temperature Differences","authors":"Hao-Qiang Pang, Shengping Zhang, Tingmei Fan, Xu Zhang, Tianlin Liu, Yan-Feng Gao","doi":"10.1080/15567265.2023.2189441","DOIUrl":"https://doi.org/10.1080/15567265.2023.2189441","url":null,"abstract":"ABSTRACT Silica aerogel is an excellent thermal insulator for high-speed aircraft, but there is little research on it in a high-temperature and complex-pressure environment. This research aims to evaluate the thermal insulation performance of silica aerogel monoliths with different porosities under large temperature differences and pressure gradients. We established an experimental system to measure and analyze the hot surface temperature response by fixing the heat flux and the cold surface temperature at transient pressure conditions. An unsteady-state heat transfer model considering gas flow is developed. The effective thermal conductivity of silica aerogels with 79.55 ~ 90.91% porosity is measured at different temperature differences between cold and hot surfaces (127 ~ 512 K), near-vacuum (<10 Pa), and transient pressure conditions. The results demonstrated that silica aerogel with 90.91% porosity showed the best thermal insulation performance when the temperature differences were over 500 K, while the aerogel with 79.55% porosity became the best when the temperature differences were less than 500 K. In addition, both the temperature and pressure difference affect the thermal insulation performance: the energy transport caused by gas flow affects the dynamic temperature response when gas permeability is of the order of 10−15 m2; the thermal insulation performance is improved by increasing gas permeability and pressure difference when gas flow and heat transfer directions are opposite.","PeriodicalId":49784,"journal":{"name":"Nanoscale and Microscale Thermophysical Engineering","volume":"27 1","pages":"75 - 94"},"PeriodicalIF":4.1,"publicationDate":"2023-03-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45631465","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 : 2023-01-02DOI: 10.1080/15567265.2023.2180458
P. Henadeera, N. Samaraweera, Chathura Ranasinghe, A. Wijewardane
ABSTRACT The superior thermal insulating properties of nanostructured semiconductor materials over their bulk counterparts, make them promising candidates for Thermo-Electric (TE) applications. In this study, the superior thermal insulating properties of a new class of one-dimensional nanostructures made by sintering linearly placed nanoparticles, called Nano Particle Chains (NPC) are analyzed for a variety of surface and constriction modifications. The NPC structure which has been shown to be capable of achieving a one-order reduction in thermal conductivity over comparably sized nanowires is revealed to house a new phonon suppression mechanism in addition to commonly discussed phonon boundary scattering and quantum confinement effects. In the current work, this quantum confinement based thermal conductivity reduction mechanism is revealed to be a variation in the phonon Density of States (DoS) along the longitudinal/transport direction of the structure due to the presence of the nanoscale constrictions. Subsequently, the phonons are forced to change the distribution of modes while traveling across the structure, thus resulting in lower thermal conductivity. Additionally, the effects of common phonon suppression techniques such as superlattice, shell alloy, and surface atom removal, used in semiconductor nanostructures are also evaluated on NPC configurations to fully determine the phonon transport characteristics within different classes of the material.
{"title":"Surface and Constriction Engineering of Nanoparticle Based Structures Towards Ultra-Low Thermal Conductivity as Prospective Thermoelectric Materials","authors":"P. Henadeera, N. Samaraweera, Chathura Ranasinghe, A. Wijewardane","doi":"10.1080/15567265.2023.2180458","DOIUrl":"https://doi.org/10.1080/15567265.2023.2180458","url":null,"abstract":"ABSTRACT The superior thermal insulating properties of nanostructured semiconductor materials over their bulk counterparts, make them promising candidates for Thermo-Electric (TE) applications. In this study, the superior thermal insulating properties of a new class of one-dimensional nanostructures made by sintering linearly placed nanoparticles, called Nano Particle Chains (NPC) are analyzed for a variety of surface and constriction modifications. The NPC structure which has been shown to be capable of achieving a one-order reduction in thermal conductivity over comparably sized nanowires is revealed to house a new phonon suppression mechanism in addition to commonly discussed phonon boundary scattering and quantum confinement effects. In the current work, this quantum confinement based thermal conductivity reduction mechanism is revealed to be a variation in the phonon Density of States (DoS) along the longitudinal/transport direction of the structure due to the presence of the nanoscale constrictions. Subsequently, the phonons are forced to change the distribution of modes while traveling across the structure, thus resulting in lower thermal conductivity. Additionally, the effects of common phonon suppression techniques such as superlattice, shell alloy, and surface atom removal, used in semiconductor nanostructures are also evaluated on NPC configurations to fully determine the phonon transport characteristics within different classes of the material.","PeriodicalId":49784,"journal":{"name":"Nanoscale and Microscale Thermophysical Engineering","volume":"27 1","pages":"25 - 41"},"PeriodicalIF":4.1,"publicationDate":"2023-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44878702","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 : 2023-01-02DOI: 10.1080/15567265.2023.2173108
Amrendra Kumar, N. Manna, Sreyash Sarkar, N. Biswas
ABSTRACT In micro-scale sensitive medicinal and biochemical systems, improving mixing efficiency with small velocity limitations is critical. This work examines the influencing key parameters and their implications on mixing efficiency in a new two-dimensional electroosmotic micromixer (EM) with nonaligned input and outlet microchannels. The micromixer uses electroosmosis force generated by microelectrodes mounted on the walls of a square split and recombine (SSAR) mixing chamber to blend fluids of various concentrations, which enter into an intake microchannel from different inlets. The governing equations along with the specified boundary conditions are solved by the finite element-based solver. Thorough investigations are executed to explore how the mixing performance of the new microchannel mixer is affected by both flow (inlet velocity) and electric field (electrode potential arrangement, voltage magnitude, AC frequency, and phase difference) parameters. The results revealed that only adding electrode pairs always doesn’t increase the mixing efficiency of SSAR-EM, rather electrode polarity configuration along with an increase in electrode pair optimizes fluid mixing. Also, according to the present observations, the mixing performance of SSAR-EM is strongly sensitive to the input fluid velocity, the phase difference applied to the micro-electrodes, the AC frequency, and the amplitude of the alternating voltage. Corresponding to optimal parameters (i.e. velocity of 50 µm/s, AC-frequency of 8 Hz, voltage of 100 mV, and phase difference of 7π/36-radian), the mixing efficiency of SSAR-EM becomes 98.26%.
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