55,252 research outputs found
Applicability of Phase-Function Normalization Techniques for Radiation Transfer Computation
No full textThe applicability of recently-developed four phase-function (PF) normalization techniques for modeling radiation transfer in strongly anisotropic scattering media is intensively examined using the discrete-ordinate method. The three simple techniques via normalization of only the forward- and/or backward-scattering directions were shown to reduce normalization complexity whilst retaining diffuse radiation computation accuracy for Henyey-Greenstein (HG) PFs. For Legendre PFs, however, such simple techniques are found to result in unphysical negative PF value at one or few correction direction in some cases. Additionally, negative PF values can occur for these simple techniques for ballistic radiation transfer for both HG and Legendre PF types. If negative-intensity correction is applied, however, radiative heat transfer calculation can still converge regardless of the appearance of negative PF values. The relatively complex Hunter and Guo 2012 technique, in which normalization is realized through a correction matrix covering all discrete directions, is shown to be applicable for diffuse and ballistic radiation for both PF types.Peer reviewed
High thermal conductance across c-BN/diamond interface
No full textHigh thermal conductivity electronic components with low interfacial thermal resistance are of technological importance and fundamental interest of research. Diamond, a superhard material with ultrahigh thermal conductivity at room temperature, is desirable for microelectronics thermal management. Cubic polymorph of boron nitride (c-BN) is a promising material due to wide bandgap and diamond like structure and properties. To understand the nature in thermal transport of diamond, c-BN and the most commonly used silicon (Si) semiconductor, ab initio phonon Boltzmann transport equations are employed to investigate lattice vibrational properties of these three materials. At 300 K, the predicted thermal conductivity of Si, diamond and c-BN reached 142, 2112, and 736 W/(m·K), respectively. What's more, heat transport phenomena across the interfaces of Si/diamond, c-BN/diamond and Si/c-BN are unfolded. In comparison, the interfacial thermal conductance of c-BN/diamond is ten-fold of Si/diamond; besides, the thermal conductance across Si/c-BN interface is 20.2% larger than that of Si/diamond at 300 K and 18.9% larger at 340 K. These findings provide us new vision and potential solution to heat dissipation of high-local-power density devices, shedding light on future thermal management of c-BN and diamond related electronics.Peer reviewe
First-principles investigation on thermal properties and infrared spectra of imperfect graphene
No full textIn this study we used first-principles density functional theory to investigate the thermal and optical properties of graphene. Graphene phonon properties were first calculated by the density-functional perturbation theory and then used to acquire thermal properties such as the specific heat, free and total energy, and entropy, as well as the infrared and Raman spectra. Results show that the peaks of phonon density of states at about 40 and 45.5 THz in the perfect graphene (G) were shifted to 40.5 and 46 THz in the imperfect graphene (G-D), respectively. There are peaks at 16.5, 19, 25, and 43.5 THz in the G-D curve, while there is no obvious peak at same frequencies in that of the G. The specific heat and entropy are lower for the G-D than for the G at temperature > 280 K, but the tendency is slightly reversed at temperature 1300 K, but lower at temperature below 1250 K than for the G. In the infrared (IR) spectrum, no absorption peak exists for perfect graphene, but strong absorption is found at about 233, 830 and 1392 cm-1 for the G-D. The character peak of sp2 carbon atom in-plane vibration in the Raman spectrum is shifted from 1589 cm-1 for the G to 1530 cm-1 for the G-D. The defects in the G-D caused the peaks and splits in the IR and Raman spectra.Peer reviewe
On-chip, dynamic, cryogenic temperature monitoring via PDMS micro-bead coatings
No full textPolydimethylsiloxane (PDMS) microshells/beads coated onto an electrical current-carrying wire are demonstrated for on-chip, dynamic, cryogenic temperature measurement via monitoring optical whispering-gallery mode (WGM) frequency shifts. PDMS is found to be capable of supporting WGM resonance at cryogenic temperatures down to 95 K, limited by the present lab-built cryogenic working environment. The effect of the polymeric sensor diameter on temperature sensitivity is explored and discussed. The sensors are tested for their real-time temperature monitoring capabilities and accuracy in the cryogenic temperature regime of 95–140 K, and a comparison to a theoretical model, where the electrical resistivity of nichrome wire at cryogenic temperature is also experimentally determined, is examinedPeer reviewe
Flow and heat transfer inside a new diversion-type gas heating device
No full textThe present paper characterizes ethylene glycol flow and heat transfer inside a new diversion-type gas heating device. A 2-D natural convection heat transfer model was built and solved by the finite volume method with unstructured body-fitted grids. The numerical model was first validated through temperature comparison with experimental measurements in a conventional device structure. Then analyses and comparisons of the flow fields and temperature distributions with use of different guide plate structures were carried out. The numerical results show that using the guide plate structures can form better organized flow patterns that augment heat transfer. The heat required for heating up the gas passing through the heating device can be reduced by 3% via installing two guide plates.Peer reviewed
Reborn Translated: Xiaolu Guo as a World Author
No full textThis paper introduces the concept of “world author,” taking as its exemplar the Chinese British writer and filmmaker Xiaolu Guo. It investigates how Guo utilizes her bilingualism to construct and negotiate her creative agency, especially when dealing with the political and commercial forces imposed on diasporic authors. Through engaging with Rebecca Walkowitz’s idea of world literature as being “born translated,” I point out that the translational should not be limited to the thematic and representational arrangements internal to a given text. Instead, translation as movements between linguistic systems and media forms can generate multipleversions of a text, to the point that such translational multiplicity fundamentally challenges its supposed singularity. This argument is demonstrated with Guo’s self-translation of the stories of Fenfang and her filmic adaptation of the novel UFO in Her Eyes. Through these examples of what I call “translational rebirths,” I demonstrate the importance of paratextual details and intertextual connections between clusters of an author’s creative output for the interpretation and appreciation of l’oeuvre d’un auteur instead of une oeuvre d’art. This case study also shows the need for the academic debates on world literature to go beyond the singularity of texts and evaluative criteria of worldliness based on this assumption, so that the discipline can realize its full potential in accommodating multilingual transnational authors like Guo
Kinematic Simulation and Structure Analysis of a Morphing Flap
No full textThis thesis presents a study on the design and analysis of a morphing flap
structure integrated with actuation mechanism for potential application to large
aircraft. Unlike the conventional rigid flap mounted on the wing trailing edge,
the morphing flap is designed as a unitized structural system integrated with
three primary components: the upper and lower flexible skins reinforced by
stringers, an eccentric beam actuation mechanism (EBAM) with discs fixed on it,
and the connection of the discs with the stringers. Based on the EBAM concept
proposed by Dr Guo in previous research [1], the current study has been
focused on the EBAM design and optimization, kinematic simulation and
structural modelling of the morphing flap.
Although a lot of efforts have been made to develop the morphing flap in
previous research, it is lack of detailed design of the disc-skin linkage and clear
view on the mechanism optimization in relation to the shape requirement. The
main objective of this research is to meet the morphing shape requirements and
calculate the actuation torque for a specified morphing flap. Firstly effort was
made to design and optimize the disc shape and locations in the EBAM for the
best matching of the specified morphing shape with minimum actuation torque
demand. It is found that minimum three discs are required and their locations
have little effect on the actuation torque. Secondly attention was focused on
designs of the disc and a C-linkage with the stringers. To ensure that the C-
linkage works in practice, a twisted stringer flange design was proposed. Thirdly
the actuation mechanism was integrated with the stiffened skin to play the role
of an active rib in the flap structure. Based on the design, FE modelling and
analysis of the morphing flap structure was carried out. The behaviour of the
morphing flap under the internal actuation and external aerodynamic load was
applied for stress analysis and detailed design of the structures. Finally the
kinematics of the integrated morphing flap was simulated by using CATIA to
demonstrate the feasibility and the effectiveness of the improved design
3-D simulation of gases transport under condition of inert gas injection into goaf
No full textTo prevent coal spontaneous combustion in mines, it is paramount to understand O2 gas distribution under condition of inert gas injection into goaf. In this study, the goaf was modeled as a 3-D porous medium based on stress distribution. The variation of O2 distribution influenced by CO2 or N2 injection was simulated based on the multi-component gases transport and the Navier-Stokes equations using Fluent. The numerical results without inert gas injection were compared with field measurements to validate the simulation model. Simulations with inert gas injection show that CO2 gas mainly accumulates at the goaf floor level; however, a notable portion of N2 gas moves upward. The evolution of the spontaneous combustion risky zone with continuous inert gas injection can be classified into three phases: slow inerting phase, rapid accelerating inerting phase, and stable inerting phase. The asphyxia zone with CO2 injection is about 1.25~2.4 times larger than that with N2 injection. The efficacy of preventing and putting out mine fires is strongly related with the inert gas injecting position. Ideal injections are located in the oxidation zone or the transitional zone between oxidation zone and heat dissipation zone.Peer reviewed
Heat Transfer and Thermodynamic Processes in Coal-Bearing Strata Under Spontaneous Combustion Condition
No full textSimulations and experiments have been carried out to investigate heat transfer and thermodynamic processes in coal-bearing strata in order to quantitatively understand the development of underground coal fires under spontaneous combustion condition. With controlled temperature and under lean oxygen conditions, the thermodynamic parameters for coal oxidation at different stages are experimentally determined in combination with simultaneous thermal analysis. A combined heat transfer model of conduction, convection and radiation with finite reactions is developed for the porous coal and rocks. The temperature distributions in the coal and roof strata at different times are simulated based on the single- and two-stage kinetic models, respectively, and compared with field geophysical prospecting. Effects of oxidation kinetic properties due to coal metamorphism on propagation of coal fires are examined. It reveals that a significant step change exists during the thermal process of coal fire caused by two-stage oxidation, and the coal rank of occurrence directly determines the spontaneous combustion period of underground coal fire.Peer reviewe
Spectral investigation of solar energy absorption and light transmittance in a water-filled prismatic glass louver
No full textWater-filled prismatic glass louver was proposed to save energy consumptions in buildings because such innovative louvers can harvest solar energy as well as improve daylighting quality rather than “block” sunlight like traditional louvers. To enable this technology the effectiveness of ultraviolet (UV) and infrared (IR) energy harvest and visible (VIS) light transmittance was investigated via Monte Carlo simulations in this case study. The 7-band spectral model for glass and water was evaluated and adopted for several cases of solar spectra of different air mass (AM) coefficients with both direct and diffuse irradiation. Absorption and transmittance in different band regimes as well as in water and glass respectively were differentiated and compared. Practical solar data in Phoenix, Flagstaff, and Golden were utilized to demonstrate the performance of the proposed louver under different locations and realistic conditions. Results show that the device facing normally to direct sunlight can harvest around 51-54% of the total solar energy and transmit 74-76% VIS for daylighting in the range of AM1 to AM3. In particular for AM1.5, VIS transmittance reaches 76% for both direct and diffuse irradiation; UV absorption achieves 80% and 85% and IR absorption reaches 64% and 82% for diffuse and collimated irradiation, respectively. In all the three places tested, the device absorbs about 81% IR and 87% UV, and transmits about 76% VIS.Peer reviewe
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