arXiv subjects

Nuo Yang

Publications and source records attributed to Nuo Yang.

At least 37 records · Page 2Linked to original sources

arXiv2021

Improving the mass transfer rate and energy efficiency of solar still by enhancing the inner air circulation

Solar still is an eco-friendly and convenient desalination system that can provide fresh water for remote areas and emergencies. The energy efficiency and productivity of conventional solar still are unsatisfying and need improvement, which requires a deep understanding of the heat and mass transfer process in solar still. In this work, the effect of the inner air circulation on the system's heat and mass transfer performance and energy efficiency are studied theoretically and experimentally. The theoretical results reveal that a weak acceleration of the air circulation inside the SS will significantly increase its performance, due to the improved mass transfer process. By enhancing the inner air circulation, the evaporation and condensation in the solar still can reach up to the limit, and the theoretical energy efficiency reaches up to 87%, 91.5%, and 94.5%, for the input power density at 300 W/m2, 500 W/m2, and 700 W/m2, respectively. Besides, lower ambient temperature and higher ambient convective heat transfer coefficient will decrease the energy efficiency. Given the heat loss, the experimental energy efficiencies are only 3% to 6% lower than the theoretical results, which indicates that the great performance predicted by the theory can be realized in practical application. This work provides a new understanding and strategy for improving the performance of the solar still.

physics.app-ph↗

arXiv2021

Violation of Fourier's law in homogeneous systems

Hotspot is a ubiquitous phenomenon in microdevices/chips. In homogeneous nanoscale graphene disk with a hotspot, a graded thermal conductivity is observed previously even when the system size is fixed. However, the underlying physical mechanism is not clear. In this work, the hotspots in homogeneous 2D disk/3D ball and graphene disk are studied based on phonon Boltzmann transport equation. The mechanisms of phonon scattering are analyzed. It is found that for a system with fixed size, the graded thermal conductivity is predictable as long as there is not sufficient phonon scattering, which is independent on material properties, dimensions or system size. This work may shed light on both theoretical and experimental studies on heat dissipation of microelectronics.

cond-mat.mes-hall↗

arXiv2021

Thermal Conductivities and Mechanical Properties of Epoxy Resin as a Function of the Degree of Cross-linking

Epoxy resins are widely used polymer matrices for numerous applications. Despite substantial advances, the molecular-level knowledge-base required to exploit these materials to their full potential remains limited. A deeper comprehension of structure/property relationships in epoxy resins at the molecular level is critical to progressing these efforts. It can be laborious, if not impractical, to elucidate these relationships based on experiments alone. Here, molecular dynamics simulations are used to calculate and compare thermal conductivities and mechanical properties of an exemplar epoxy resin, Bisphenol F cross-linked with Diethyl Toluene Diamine, revealing these inter-relationships. Both elastic modulus and thermal transport of the epoxy resin show an increase with greater cross-linking. Specifically, decomposition of the thermal conductivity into different force contributions suggests that the bonded term contributes to an increase in the heat flux. These outcomes provide a foundation for designing and fabricating customized epoxy resins with desirable thermal and mechanical attributes.

cond-mat.mtrl-sci↗

arXiv2021

Optimizing Thermal Transport in Graphene Nanoribbon Based on Phonon Resonance Hybridization

As a critical way to modulate thermal transport in nanostructures, phonon resonance hybridization has become an issue of great concern in the field of phonon engineering. In this work, we optimized phonon transport across graphene nanoribbon and obtained minimized thermal conductance by means of designing pillared nanostructures based on resonance hybridization. Specifically, the optimization of thermal conductance was performed by the combination of atomic Green` s function and Bayesian optimization. Interestingly, it is found that thermal conductance decreases non-monotonically with the increasing of number for pillared structure, which is severed as resonator and blocks phonon transport. Further mode-analysis and atomic Green` s function calculations revealed that the anomalous tendency originates from decreased phonon transmission in a wide frequency range. Additionally, nonequilibrium molecular dynamics simulations are performed to verify the results with the consideration of high-order phonon scattering. This finding provides novel insights into the control of phonon transport in nanostructures.

cond-mat.mes-hall↗

arXiv2021

A compact flat solar still with high performance

Solar still is a convenient off-grid device for desalination, which can provide fresh water for families, ships, islands and so on. The conventional inclined solar still (ISS) suffers from low efficiency and low productivity. To improve the performance of solar still, a flat solar still (FSS) is proposed, which has a working principle similar to the solar cell. The condensate water in FSS is collected by the capillary grid attached under the ultra-hydrophilic glass cover, instead of by gravity. Therefore, FSS avoids the inclined structure and is much more compact than ISS. The daily productivity of FSS reaches up to 4.3 kg/m2. Theoretical analysis shows that the enhanced mass transfer in FSS by the compact structure is an important factor for high performance. More interestingly, FSS can also be easily extended to more stage for latent heat recovery. The results show that the daily productivity of a double-stage FSS reaches up to 7 kg/m2, which is much higher than the conventional solar still. FSS paves a new way in designing and optimizing of solar still.

physics.app-ph↗

arXiv2020

Thermal conductivity of one-dimensional carbon-boron nitride van der Waals heterostructure: A molecular dynamics study

Investigating thermal transport in van der Waals heterostructure is of scientific interest and practical importance for their applications in a broad range. In this work, thermal conductivity of one-dimensional heterostructure consisting of carbon and boron nitride nanotubes is systematically investigated via molecular dynamics simulations. Thermal conductivity is found to have strong dependences on temperature, length and diameter. In addition, the axial strain and intensity of van der Waals interaction are demonstrated to be able to modulate thermal conductivity up to about 43% and 37%, respectively. Moreover, the dependence of thermal conductivity on the chirality of componential nanotubes is studied. These results are explained based on lattice dynamics insights. This work not only provides feasible strategies to modulate thermal conductivity, but also enhances the understanding of the fundamental physics of phonon transport in one-dimensional heterostructure.

cond-mat.mes-hall↗

arXiv2020

Electric-field-induced modulation of thermal conductivity in poly(vinylidene fluoride)

Phonon engineering focuses on heat transport modulation on atomic-scale. Different from reported methods, it is shown that electric field can also modulate heat transport in ferroelectric polymers, poly(vinylidene fluoride), by both simulation and measurement. Interestingly, thermal conductivities of poly(vinylidene fluoride) array can be enhanced by a factor of 3.25 along the polarization direction by simulation. The semi-crystalline poly(vinylidene fluoride) film can be also enhanced by a factor of 1.5 which is found by both simulation and measurement. The morphology and phonon property analysis reveal that the enhancement arises from the higher inter-chain lattice order, stronger inter-chain interaction, higher phonon group velocity and suppressed phonon scattering. This study offers a new modulation strategy with quick response and without fillers.

cond-mat.mes-hall↗

arXiv2020

Maximization and Minimization of Interfacial Thermal Conductance by Modulating the Mass Distribution of Interlayer

Tuning interfacial thermal conductance has been a key task for the thermal management of nanoelectronic devices. Here, it is studied how the interfacial thermal conductance is great influenced by modulating the mass distribution of the interlayer of one-dimensional atomic chain. By nonequilibrium Green's function and machine learning algorithm, the maximum/minimum value of thermal conductance and its corresponding mass distribution are calculated. Interestingly, the mass distribution corresponding to the maximum thermal conductance is not a simple function, such as linear and exponential distribution predicted in previous works, it is similar to a sinusoidal curve around linear distribution for larger thickness interlayer. Further, the mechanism of the abnormal results is explained by analyzing the phonon transmission spectra and density of states. The work provides deep insight into optimizing and designing interfacial thermal conductance by modulating mass distribution of interlayer atoms.

cond-mat.mtrl-sci↗

arXiv2020

Reduction of interfacial thermal resistance of overlapped graphene by bonding carbon chains

Exploring the mechanism of interfacial thermal transport and reducing the interfacial thermal resistance is of great importance for thermal management and modulation. Herein, the interfacial thermal resistance between overlapped graphene nanoribbons is largely reduced by adding bonded carbon chains by performing molecular dynamics simulations. And the analytical model (cross-interface model, CIM) is utilized to analyze and explain the two-dimensional thermal transport mechanism at cross-interface. An order of magnitude reduction in interfacial thermal resistance is found as the graphene nanoribbons are bonded by just one carbon chain. Interestingly, the decreasing rate of interfacial thermal resistance slows down gradually with the increasing of the number of carbon chains, which can be explained by the proposed theoretical relationship based on CIM. Moreover, by the comparison of CIM and traditional simplified model, the accuracy of CIM is verified and demonstrated in overlapped graphene nanoribbons. This work provides a new way to improve the interfacial thermal transport and reveal the essential mechanism for low-dimensional materials applied in thermal management.

cond-mat.mes-hall↗

arXiv2020

Prediction of tubular solar still performance by machine learning integrated with Bayesian optimization algorithm

Presented is a new generation prediction model of a tubular solar still (TSS) productivity utilizing two machine learning (ML) techniques, namely:Random forest (RF) and Artificial neural network (ANN). Prediction models were conducted based on experimental data recorded under Egyptian climate. Meteorological and operational thermal parameters were utilized as input layers. Moreover, Bayesian optimization algorithm (BOA) was used to obtain the optimal performance of RF and ANN models. In addition, these models results were compared to those of a multilinear regression (MLR) model. As resulted, experimentally, the average value accumulated productivity was 4.3 L/(m2day). For models results, RF was less sensitive to hyper parameters than ANN as ANN performance could be significantly improved by BOA more than RF. In addition, RF achieved better prediction performance of TSS on the current dataset. The determination coefficients (R2) of RF and ANN were 0.9964 and 0.9977, respectively, which were much higher than MLR models, 0.9431. Based on the robustness performance and high accuracy, RF is recommended as a stable method for predicting the productivity of TSS.

physics.app-ph↗

arXiv2019

Phonon Transport within Periodic Porous Structures -- From Classical Phonon Size Effects to Wave Effects

Tailoring thermal properties with nanostructured materials can be of vital importance for many applications. Generally classical phonon size effects are employed to reduce the thermal conductivity, where strong phonon scattering by nanostructured interfaces or boundaries can dramatically supress the heat conduction. When these boundaries or interfaces are arranged in a periodic pattern, coherent phonons may have interference and modify the phonon dispersion, leading to dramatically reduced thermal conductivity. Such coherent phonon transport has been widely studied for superlattice films and recently emphasized for periodic nanoporous patterns. Although the wave effects have been proposed for reducing the thermal conductivity, more recent experimental evidence shows that such effects can only be critical at an ultralow temperature, i.e., around 10 K or below. At room temperature, the impacted phonons are mostly restricted to hypersonic modes that contribute little to the thermal conductivity. In this review, the theoretical and experimental studies of periodic porous structures are summarized and compared. The general applications of periodic nanostructured materials are further discussed.

physics.app-ph↗

arXiv2019

Cross interface model for the thermal transport across interface between overlapped boron nitride nanoribbons

The application of low-dimensional materials for heat dissipation requires a comprehensive understanding of the thermal transport at the cross interface, which widely exists in various composite materials and electronic devices. In this work, we proposed an analytical model, named as cross interface model (CIM), to accurately reveal the essential mechanism of the two-dimensional thermal transport at the cross interface. The applicability of CIM is validated through the comparison of the analytical results with molecular dynamics simulations for a typical cross interface of two overlapped boron nitride nanoribbons. Besides, it is figured out that the factor (η) has important influence on the thermal transport besides the thermal resistance inside and between the materials, which is found to be determined by two dimensionless parameters from its expression. Our investigations deepen the understanding of the thermal transport at the cross interface and also facilitate to guide the applications of low-dimensional materials in thermal management.

cond-mat.mes-hall↗

arXiv2019

Ultralow Thermal Conductance of the van der Waals Interface between Organic Nanoribbons

Understanding thermal transport through nanoscale van der Waals interfaces is vital for addressing thermal management challenges in nanoelectronic devices. In this work, the interfacial thermal conductance (GCA) between copper phthalocyanine (CuPc) nanoribbons is reported to be on the order of 10^5 Wm-2K-1 at 300 K, which is over two orders of magnitude lower than the value predicted by molecular dynamics (MD) simulations for a perfectly smooth interface between two parallelly aligned CuPc nanoribbons. Further MD simulations and contact mechanics analysis reveal that surface roughness can significantly reduce the adhesion energy and effective contact area between CuPc nanoribbons, and thus result in an ultralow GCA. In addition, the adhesion energy at the interface also depends on the stacking configuration of two CuPc nanoribbons, which may also contribute to the observed ultralow GCA.

physics.app-ph↗

arXiv2019

Micro/nanomaterials for improving solar still and solar evaporation -- A review

In last decades, solar stills, as one of the solar desalination technologies, have been well studied in terms of their productivity, efficiency and economics. Recently, to overcome the bottleneck of traditional solar still, improving solar still by optimizing the solar evaporation process based on micro/nanomaterials have been proposed as a promising strategy. In this review, the recent development for achieving high-performance of solar still and solar evaporation are discussed, including materials as well as system configurations. Meanwhile, machine learning was used to analyze the importance of different factors on solar evaporation, where thermal design was founded to be the most significant parameter that contributes in high-efficiency solar evaporation. Moreover, several important points for the further investigations of solar still and solar evaporation were also discussed, including the temperature of the air-water interface, salt rejecting and durability, the effect of solid-liquid interaction on water phase change.

physics.app-ph↗

arXiv2019

Thermal conductivity of molybdenum disulfide nanotube from molecular dynamics simulations

Single layer molybdenum disulfide (SLMoS2), a semiconductor possesses intrinsic bandgap and high electron mobility, has attracted great attention due to its unique electronic, optical, mechanical and thermal properties. Although thermal conductivity of SLMoS2 has been widely investigated recently, less studies focus on molybdenum disulfide nanotube (MoS2NT). Here, the comprehensive temperature, size and strain effect on thermal conductivity of MoS2NT are investigated. A chirality-dependent strain effect is identified in thermal conductivity of zigzag nanotube, in which the phonon group velocity can be significantly reduced by strain. Besides, results show that thermal conductivity has a ~T-1 and a ~L\b{eta} relation with temperature from 200 to 400 K and length from 10 to 320 nm, respectively. This work not only provides feasible strategies to modulate the thermal conductivity of MoS2NT, but also offers useful insights into the fundamental mechanisms that govern the thermal conductivity, which can be used for the thermal management of low dimensional materials in optical, electronic and thermoelectrical devices. Introduction.

cond-mat.mes-hall↗

arXiv2019

Thermal characterization of convective heat transfer in microwires based on modified steady state "hot wire" method

The convection plays a very important role in heat transfer when MEMS work under air environment. However, traditional measurements of convection heat transfer coefficient require the knowledge of thermal conductivity, which makes measurements complex. In this work, a modified steady state "hot wire" (MSSHW) method is proposed, which can measure the heat transfer coefficient of microwires' convection without the knowledge of thermal conductivity. To verify MSSHW method, the convection heat transfer coefficient of platinum microwires was measured in the atmosphere, whose value is in good agreement with values by both traditional measurement methods and empirical equations. Then, the convection heat transfer coefficient of microwires with different materials and diameters were measured by MSSHW. It is found that the convection heat transfer coefficient of microwire is not sensitive on materials, while it increases from 86 W/(m$^2$K) to 427 W/(m$^2$K) with the diameter of microwires decreasing from 120 $μ$m to 20 $μ$m. Without knowing thermal conductivity of microwires, the MSSHW method provides a more convenient way to measure the convective effect.

physics.app-ph↗

arXiv2019

Materials discovery and properties prediction in thermal transport via materials informatics: a mini-review

There has been an increasing demand for materials with special thermal properties, whereas experimental discovery is high-cost and time-consuming. The emerging discipline `Materials Informatics' is an effective approach that can accelerate materials development by combining material science and big data technique. Recently materials informatics has been applied to the design of novel materials such as thermal interface materials for heat-dissipation, and thermoelectric materials for power generation. This mini-review summarized the research progress on the applications of materials informatics for the thermal transport properties prediction and discovery of materials with special thermal properties, including optimal thermal conductivity, interfacial thermal conductance and thermoelectricity efficiency. In addition, some perspectives are given for the outlook of materials informatics in the field of thermal transport.

cond-mat.mtrl-sci↗

arXiv2019

Efficiency enhancement on the solar steam generation by wick materials with wrapped graphene nanoparticles

Solar steam generation technology can utilize abundant and renewable solar energy for many applications. In this work, we proposed a solar steam generator using wick material with wrapped graphene nanoparticles, and the energy efficiency can reaches up to 80%. Instead of traditional smearing method, the chemical wrapping method was used to better adhere the graphene nanoparticles on the wick materials. Through the SEM morphological results, the graphene nanoparticles are shown to be evenly wrapped across the fibres of the wick material, which have better dispersity and stability. The evaporation rate, instantaneous energy efficiency and the absorptivity of three wick materials with/without nanoparticles under different conditions were compared and analyzed. Among the three different wick materials, the flannel cloth with dense fine hairs can provide three-dimensional contact area for wrapping graphene nanoparticles and thus contribute to better evaporation. Additionally, the influence of two different reduction methods and different concentrations of graphene oxide solution on the energy efficiency was also discussed. Our work offers a simple and effective way of using nanotechnology in practical application for solar steam generation.

physics.app-ph↗