Effects of anisotropic composite skin on electrothermal anti-icing system

To study the effects of anisotropic thermal conductivity of composite aircraft skin on the heat transfer characteristics of electrothermal anti-icing system, the differential equation of anisotropic heat conduction was established using coordinate transformation of principal anisotropy axis. In addition, it was coupled with the heat and mass transfer model of the runback water film on the anti-icing surface to perform numerical simulation of the electrothermal anti-icing system. The temperature results of the vertical and cylindrical orthotropic thermal conduction in the rectangular and semi-cylindrical composite skin were consistent with those obtained by the traditional orthotropic model, which verified the anisotropic heat conduction model. The temperature distribution of anti-icing surface agreed well with the literature data, which validated the coupled heat and mass model of the runback water flow and the anisotropic skin. The anisotropic thermal conductivity of composite skin would make temperature change more gradual, and the effect was more significant where the curvature of the temperature curve was greater. However, the anti-icing surface of the electrothermal anti-icing system was slightly affected by the anisotropic heat conduction of the multilayered composite skin

Evaporation/boiling heat transfer characteristics in an artery porous structure

Nucleate boiling is one of the most efficient and effective heat transfer modes, but is limited by the critical heat flux (CHF). An innovative artery porous structure was proposed in this work to enhance the CHF based on the concept of "phase separation and modulation" by forming individual flow paths for liquid supply and vapor venting while keeping the liquid/vapor interface located in the porous structure. In the experiment, the porous structure was made of sintered copper microparticles, multiple arteries were machined directly on the heated surface, and water was employed as the working fluid. The experimental results were compared with those on a flat surface, and a unique evaporation/boiling curve for the artery porous structure was revealed. The experiment validated the principle proposed here for CHF enhancement, and a maximum heat flux of 416 W/cm2 on a heating area of 0.78 cm2 was achieved without the occurrence of any dryout. Further increase of heat flux was limited only by the design temperature of the electrical heater, and a much higher CHF can be expected. In addition, the effects of pore size, artery depth and contact condition on the evaporation/boiling heat transfer performance in the artery porous structure were also experimentally investigated, which can guide further design optimizations of this novel structure

Numerical simulation of aircraft thermal anti-icing system based on a tight-coupling method

Considering the influence of surface temperature distribution on air convective heat transfer coefficient, the robust tight-coupling method is firstly developed for aircraft thermal anti-icing simulations under icing conditions. To include the effects of the impinging water droplets on the conjugate heat transfer of thermal anti-icing systems, the Messinger thermodynamic model of runback water film is modified and added to the tightly coupled calculation of the external air flow and the internal solid skin heat conduction. Numerical simulations are carried out on an electro-thermal anti-icing system under both dry air and icing conditions, and the main conclusions below can be drawn. First, convective heat transfer coefficient changes slightly with surface temperature near the leading edge, but is obviously affected by temperature distribution in the downstream area. Second, the anti-icing temperature deviations between the predicted value and the experiment date are acceptable and comparable to the calculation results in the literature, verifying the feasibility and effectiveness of the tight-coupling method. Third, compared with the traditional decoupled loose-coupling method, the robust tight-coupling anti-icing method successfully captures the effect of surface temperature on convective heat transfer coefficient, and predicts higher temperature with lower drop rate on the downstream surfaces

Unsteady simulation of aircraft electro-thermal deicing process with temperature-based method

Considering the mass and energy sources carried by the accumulated ice layer, an unsteady heat and mass transfer model of the runback water film on the deicing surface is established to simulate aircraft electro-thermal deicing process. With the extension of the freezing coefficient to the transient calculation, the coupled heat transfer of the runback water and the solid skin is solved at each time step by a temperature-based method. Unsteady numerical simulation is carried out for the electro-thermal deicing system of a NACA 0012 airfoil. The temperature variations with time are in acceptable agreement with the literature data, and the unsteady temperature-based deicing model is verified. The calculation results of temperature, runback water flux and ice thickness on the deicing surface are analyzed at different time points, and it is shown that the unsteady electro-thermal deicing model can capture the main features of the icing, ice melting and re-freezing processes in the transient deicing simulations

Improved Charge Separation and Photovoltaic Performance of BiI3 Absorber Layers by Use of an In Situ Formed BiSI Interlayer

Stable and nontoxic bismuth iodide (BiI3) is emerging as a promising absorber material for solar cell applications as it possesses favorable optical properties such as a narrow bandgap (1.7 eV) and a high absorption coefficient (105 cm–1) in the visible region. Despite these promising features, solar cells employing this material have only achieved power conversion efficiencies in the region of 1% as of yet, which is distant from the theoretical efficiency limit of 28%. It is reasonable to suppose that the relatively low performance of BiI3-based solar cells may originate from very short carrier lifetimes (180–240 ps) in BiI3, which makes efficient separation of mobile charges a crucial factor for the improvement of the photovoltaic performance of this material. Herein, transient optical spectroscopy is employed to show that the use of a bismuth sulfide iodide interlayer between the electron transport layer (ETL) and the bismuth iodide absorber promotes efficient charge separation. On the basis of this knowledge, we report BiI3 solar cells with a power conversion efficiency of 1.21% using a solar cell architecture comprised of ITO/SnO2/BiSI/BiI3/organic HTM/Au

Distributed fault estimation with randomly occurring uncertainties over sensor networks

This paper is concerned with the distributed fault estimation problem for a class of uncertain stochastic systems over sensor networks. The norm-bounded uncertainty enters into the system in a random way governed by a set of Bernoulli distributed white sequence. The purpose of the addressed problem is to design distributed fault estimators, via available output measurements from not only the individual sensor, but also its neighbouring sensors, such that the fault estimation error converges to zero exponentially in the mean square while the disturbance rejection attenuation is constrained to a give level by means of the H∞ performance index. Intensive stochastic analysis is carried out to obtain sufficient conditions for ensuring the exponential stability as well as prescribed H∞ performance for the overall estimation error dynamics. Simulation results are provided to demonstrate the effectiveness of the proposed fault estimation technique in this paper.This work was supported in part by the National Natural Science Foundation of China [ grant number 61329301], [grant number 61422301], [grant number 61374127]; the Outstanding Youth Science Foundation of Heilongjiang Province [grant number JC2015016]; the Alexander von Humboldt Foundation of Germany

Experimental study on the supercritical startup of cryogenic loop heat pipes with redundancy design

Cryogenic loop heat pipe (CLHP) is one of the key components in the future space infrared exploration system, which enables effective and efficient cryogenic heat transport over a long distance with a flexible thermal link. To realize reliable and long life operation, a CLHP-based thermal control system with redundancy design was proposed in this work, where two nitrogen-charged CLHPs were employed to provide cryocooling at 80–100 K. This study focused on the supercritical startup of the CLHPs with redundancy design, and an extensive experimental study under four possible working modes was conducted. Experimental results showed that with 2.5 W applied to the secondary evaporator, each CLHP could realize the supercritical startup successfully in the normal working mode; however, the required time differed a lot because the difference in the transport line diameter significantly affected the cryocooling capacity to the primary evaporator. In the backup conversion mode, instant switch of the two primary evaporators may cause an operation failure, and an auxiliary operation of the secondary evaporator in advance was necessary to make the primary liquid line filled with liquid. In the malfunction conversion mode, the simulated infrared detector had to be first shut down, but the time needed for the backup CLHP to realize the supercritical startup became obviously shorter than that in the normal working mode, because the primary evaporator of the backup CLHP was always in a cryogenic state. In the dual operation mode, the two CLHPs could realize the supercritical startup simultaneously, but a temperature oscillation phenomenon was observed, which can be eliminated by increasing the heat load applied to the secondary evaporator

Exciton entanglement in two coupled semiconductor microcrystallites

Entanglement of the excitonic states in the system of two coupled semiconductor microcrystallites, whose sizes are much larger than the Bohr radius of exciton in bulk semiconductor but smaller than the relevant optical wavelength, is quantified in terms of the entropy of entanglement. It is observed that the nonlinear interaction between excitons increases the maximum values of the entropy of the entanglement more than that of the linear coupling model. Therefore, a system of two coupled microcrystallites can be used as a good source of entanglement with fixed exciton number. The relationship between the entropy of the entanglement and the population imbalance of two microcrystallites is numerically shown and the uppermost envelope function for them is estimated by applying the Jaynes principle.Comment: 16 pages, 6 figure

A Numerical Study of Fluid Flow and Heat Transfer in Carbon Dioxide Enclosures on Mars

In order to support the future thermal control and energy conservation design for the Mars rover, numerical studies on natural convection in CO₂ enclosures on Mars’ surface were conducted for both horizontal and vertical enclosures. The parameters are as follows: the atmospheric pressure was 1000 Pa, the gravitational acceleration was 3.62 m/s², and the Prandtl number was 0.77. The heat flux, temperature, and velocity fields of the CO₂ enclosures were obtained with the aspect ratio ranging from 5.56 to 200 and the Grashof number ranging from 430 to 2.6 × 10⁴. It was found that natural convection formed more easily in the horizontal enclosures than that in the vertical enclosures when the enclosures had same thickness. With the increasing thickness of the enclosures, Rayleigh–Bénard convections formed in the horizontal enclosures, while only single-cell convections formed in the vertical enclosures. The heat flux through the horizontal enclosures was greater than that through the vertical enclosures with the same thickness when natural convection formed. The maximum difference between them reached 35.26%, which was illustrated by the field synergy principle. A hysteresis phenomenon of the natural convection dominating the heat transfer was found in the vertical enclosure on Mars’ surface. New values for the critical Grashof number and correlations for the average Nusselt number for both the horizontal and vertical CO₂ enclosures on Mars’ surface were also develope

Predicting biomedical relationships using the knowledge and graph embedding cascade model

Advances in machine learning and deep learning methods, together with the increasing availability of large-scale pharmacological, genomic, and chemical datasets, have created opportunities for identifying potentially useful relationships within biochemical networks. Knowledge embedding models have been found to have value in detecting knowledge-based correlations among entities, but little effort has been made to apply them to networks of biochemical entities. This is because such networks tend to be unbalanced and sparse, and knowledge embedding models do not work well on them. However, to some extent, the shortcomings of knowledge embedding models can be compensated for if they are used in association with graph embedding. In this paper, we combine knowledge embedding and graph embedding to represent biochemical entities and their relations as dense and low-dimensional vectors. We build a cascade learning framework which incorporates semantic features from the knowledge embedding model, and graph features from the graph embedding model, to score the probability of linking. The proposed method performs noticeably better than the models with which it is compared. It predicted links and entities with an accuracy of 93%, and its average hits@10 score has an average of 8.6% absolute improvement compared with original knowledge embedding model, 1.1% to 9.7% absolute improvement compared with other knowledge and graph embedding algorithm. In addition, we designed a meta-path algorithm to detect path relations in the biomedical network. Case studies further verify the value of the proposed model in finding potential relationships between diseases, drugs, genes, treatments, etc. Amongst the findings of the proposed model are the suggestion that VDR (vitamin D receptor) may be linked to prostate cancer. This is backed by evidence from medical databases and published research, supporting the suggestion that our proposed model could be of value to biomedical researchers