A high performance polybenzoxazine derived from bio-based furfurylamine was synthesized in an efficient and straightforward way. For comparison, its petroleum-based analogue was also prepared from 4, ...4-diaminodiphenylmethane (DDM). The chemical structures of the precursors were confirmed by Nuclear Magnetic Resonance Spectroscopy (1H-NMR and 13C-NMR) and Fourier Transform Infrared Spectroscopy (FT-IR). After the curing reaction was investigated by Differential Scanning Calorimetry (DSC) and FT-IR in detail, the thermal and mechanical properties of the cured resins were studied by Dynamic Mechanical Analysis (DMA) and Thermogravimetric Analysis (TGA). Results demonstrated that the polybenzoxazine based on furfurylamine (BZ-F) possessed higher glass transition temperature (270 °C) and better thermal stability associated with higher charring ability when compared with the one (BZ-DDM) derived from DDM, which might be attributed to the stronger hydrogen bonding interaction in the BZ-F system and the post-curing reaction on furan ring above 280 °C. In this paper, the hydrogen bonding effect on the properties of polybenzoxazine has been especially studied, which might give us a guidance to design and synthesize the polybenzoxazine with high performance.
Display omitted
•Benzoxazine (BZ-F) with high purity was synthesized from bio-based furfurylamine.•Oxygen atom in furan ring led to more hydrogen bond in pBZ-F system.•pBZ-F system demonstrated higher performance.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
•The tight-coupling method is firstly developed for aircraft thermal anti-icing simulations under icing conditions.•A modified heat and mass transfer model of the runback water is established for the ...tight-coupling simulations.•The predicted anti-icing temperatures are in acceptable agreement with the experiment data, verifying the tight-coupling method.•Convective heat transfer coefficient is affected by surface temperature distribution, and the tight-coupling method can model this effect and predict more reasonable results.
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.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
•Cylindrical evaporator-CC coupling structure was visually analyzed at three tilt angles.•The performances of the vapour-liquid interface in the coupling structure was studied.•The bubble generation ...and its movement in the coupling structure were observed and studied.•Temperature fluctuations of the LHP were related to the oscillations of vapour-liquid interface.•The conclusions are helpful for the heat transfer mechanism of the LHP in gravity applications.
To visually analyze the flow and heat transfer characteristics of the working fluid in a loop heat pipe (LHP), the evaporator-compensation chamber (CC) was designed as a half-sectioned cylindrical structure sealed with a glass window. Using acetone as the working fluid, visualization experiments were performed under different heat loads and tilt angles. The vapour-liquid distribution in the evaporator-CC coupling structure and the temperature variation characteristics of the LHP system were investigated at three tilt angles of the evaporator-CC coupling structure. According to the experimental results including the startup and steady-state operation, some important conclusions have been drawn as summarized below: (1) with the subcooled liquid outflow from the bayonet tube, the vapour-liquid interface in the evaporator-CC coupling structure rises when the heat load is applied to the evaporator; (2) the bubble generation inside the porous wick becomes more intense with an increased heat load, and there are various bubble movement patterns at different tilt angles; (3) the temperature fluctuation of the LHP system is closely related to the oscillation of the vapour-liquid interface in the evaporator core.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In this paper, we aim to improve the tracking performance of the manipulator joint system by establishing accurate friction model based on the Stribeck model and the cubic polynomial method. ...Meanwhile, in view of the established system model, an adaptive Radial Basis Function Neural Network (RBFNN) compensation computed-torque controller is designed for the manipulator joint system. Firstly, we consider the friction modeling process at low- and high- velocity regions to advance the model accuracy, and identify the parameters in the friction model equation offline via the particle swarm optimization (PSO) algorithm. Secondly, an adaptive RBFNN algorithm is developed to analyze the unmodeled dynamics online and introduce it to the computed-torque controller design. After that, we further conduct the stability analysis for the proposed controller based on the Lyapunov stability criterion. Finally, the self-developed manipulator joint platform introduction, the simulation experiment and the contradistinctive experiments are given to illustrate the effectiveness of designed controller.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Epoxy resins with high thermal and mechanical performance as well as good resistance to fire are difficult to synthesize. In this work, a high-performance intrinsically flame-retardant epoxy resin ...(diglycidyl ether of daidzein (DGED)) was synthesized from renewable daidzein using an efficient one-step process, without the addition of additional flame retardants. The structure of DGED was confirmed by Fourier transform infrared (FTIR), 1H NMR, and 13C NMR before it was cured with 4,4′-diaminodiphenylmethane (DDM). A commercial diglycidyl ether of bisphenol A (DGEBA) was cured with the same curing agent. Results indicated that the cured DGED/DDM system possessed glass transition temperature (T g) of up to 205 °C (172 °C for DGEBA/DDM), and tensile strength, tensile modulus, flexural strength, and flexural modulus of 83, 2972, 131, and 2980 MPa, respectively, all much higher than those of cured DGEBA/DDM. The cured DGED/DDM system demonstrated excellent flame-retardant properties, showing a residual char of 42.9% at 800 °C, limiting oxygen index (LOI) of 31.6%, and flammability rating of V-0 in UL94 test. This work provides us an efficient method to prepare high-performance epoxy resin from renewable resource.
Full text
Available for:
IJS, KILJ, NUK, PNG, UL, UM
In this study, visualization treatment was applied to the flat disk-shaped evaporator of a loop heat pipe. By observing the liquid/vapor behavior inside the evaporator and compensation chamber, the ...effects of orientation on the performances during startup and during a step-increase in heat load were investigated. With water as the working fluid, the loop heat pipe was tested under three typical orientations of φ = −90°, φ = 0°, and φ = +90°. The startup time was the shortest for the φ = −90° orientation but there could be a slight temperature overshoot, resulting in an unsmoothed startup process. The startup speeds under the φ = 0° and φ = +90° orientations were similar, both without any significant temperature overshoot. The orientation could significantly change the heat leak and, therefore, the operating temperature and the heat-transfer limit. For the φ = +90° and φ = −90° orientations, the heat-transfer limits were about 71% and 157% of the value at the φ = 0° orientation, respectively. Based on visual observations, for the loop heat pipe operating in gravity-driven mode, there could be two different paths for the working fluid to return to the evaporator, namely, along the vapor line for low heat loads and along the condenser and liquid lines for relatively large heat loads, respectively.
Full text
Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Flat-plate loop heat pipe (FLHP) is a passive two-phase heat transfer device. Comparing with traditional LHP with a cylindrical evaporator, it can be directly connected to a flat heat source without ...the employment of a saddle, which can effectively reduce the system thermal resistance and enhance the temperature uniformity. In this work, a stainless steel-ammonia FLHP was developed, and extensive experiments have been conducted to investigate its startup characteristics with the evaporator in the horizontal and vertical positions. Experimental results show that the FLHP exhibits excellent startup performance. It can successfully start up at a small heat load as low as 2 W with no obvious temperature overshoot. In a wide power range of 5–35 W, the FLHP generally starts up in only one situation, much simpler than the startup of a LHP with a cylindrical evaporator. For this rectangular evaporator, the heat leak from the evaporator to the compensation chamber (CC) becomes very small. As a result, the vapor can easily exit the condenser in most cases in the power range of 5–35 W, leading to a 100% utilization efficiency of the condenser and the resultant satisfactory thermal performance of the FLHP. In addition, the startup performance and the system thermal resistance of the FLHP are insensitive to the evaporator orientation, promising great application potential in future electronics cooling.
Full text
Available for:
EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Return-Oriented Programming (ROP) is a new technique that helps the attacker construct malicious code mounted on x86/SPARC executables without any function call at all. Such technique makes the ROP ...malicious code contain no instruction, which is different from existing attacks. Moreover, it hides the malicious code in benign code. Thus, it circumvents the approaches that prevent control flow diversion outside legitimate regions (such as W ⊕ X ) and most malicious code scanning techniques (such as anti-virus scanners). However, ROP has its own intrinsic feature which is different from normal program design: (1) uses short instruction sequence ending in “ret”, which is called gadget, and (2) executes the gadgets contiguously in specific memory space, such as standard GNU libc. Based on the features of the ROP malicious code, in this paper, we present a tool DROP, which is focused on dynamically detecting ROP malicious code. Preliminary experimental results show that DROP can efficiently detect ROP malicious code, and have no false positives and negatives.
PDF
