Advanced Materials Research Vol. 711

Abstract: In order to transfer heat as much as possible through a unit area in unit time, this paper introduces three enhanced heat transfer structures, namely microchannel, open-celled metal foam and open-celled sintered porous metal. From two aspects of the heat transfer performance and the flow resistance, this paper reviews their research progress. Among three kinds of enhanced heat transfer structures, open-celled sintered porous metal has the best heat transfer performance, followed by open-celled metal foam and micro-channel. While, the sequence of the pressure drop of three kinds of enhanced heat transfer structures is in the reverse order. Thus, Enhanced heat transfer Structures with good heat transfer performance and small pressure drop are the future research direction.

Abstract: This study investigates the effects of increasing the evaporating area of wick in a loop heat pipe (LHP). This work attempts to improve the performance of the loop heat pipe by increasing the number of grooves and thereby the surface area of the wick. The number of grooves is increased from eight to twelve. Experimental results show that increasing the number of grooves not only increases the surface area of the wick but also enhances LHP performance. When the evaporating surface area increases by 50%, which corresponds to increasing the number of grooves from eight to twelve, the heat transfer capacity increases from 310W to 470W and the thermal resistance is reduced from 0.21°C/W to 0.17°C/W. According to preliminary measurements, increasing the number of grooves in the loop heat pipe is highly promising for improving the heat transfer performance.

Abstract: As to traditional single electrode free welding arc, changes about energy density of the ionizing region in the center of arc column is not obvious with current increases due to structural limitations. In this paper, we developed parallel multi-electrode arc discharge torch which is based on the mechanism of self-magnetic contraction effect in welding arc, the torch effectively improve energy density of ionization region in non-melting inert gas arc, which is proved by experiments, and we discussed, effect of the pulse input energy and pulse frequency to energy density of the arc with parallel multi-electrode torch. This study demonstrated the approach of improving the energy density of arc ionizing region by self-magnetic pinch effect is feasible.

Abstract: A series of biomass moulded coal were preparation by cow dung and brown coal as raw material. The effect of Na₂CO₃ NaHCO₃ NaOH and KOH were studied on Ignition loss rate and Iodine adsorption value in the process of carbonization for biomass moulded coal. The result showed that the effect of Na₂CO₃ and NaHCO₃ were obvious than NaOH and KOH in the ignition loss rate, but the effect of NaOH and KOH were obvious than Na₂CO₃ and NaHCO₃ in the Iodine adsorption value.

Abstract: The quality of the hole produced during the drilling of composite materials is one of the controlling factors for the resulting joint strength and integrity of the structural component. Quality of the hole depends on the condition of the cutting tool. Continuous cutting tool condition monitoring method is vital to accomplish the desired hole quality. To address this concern, an online tool condition monitoring technique using a simple audio microphone as a sensor is developed and Recurrence Quantification Analysis (RQA) methodology was used as a signal analysis tool to predict the tool condition in terms of flank wear. A series of experimental drilling operation was carried out on uni-directional carbon fiber reinforced plastic (CFRP) composite. It was found that the amplitude of the microphone signal decreases with the increase of the tool flank wear. In addition, from the selected eight RQA output variables, six of them show an increasing trend with the increase of the measured flank wear, whereas, two of them show a decreasing trend with the increase of tool wear. The same trend has been observed in both set of experiments. These results demonstrate that, this novel approach is an effective and economical online tool condition monitoring method.

Abstract: The integral top cover for nuclear reactor pressure vessel is an important force component in the pressure vessel. It works under the HPHT and radiation long time, which increases forging difficultly and needs extremely high quality. Due to the effect of bi-directional tensile stress in spherical part during the shape forming stage of the integral top cover, it is easy to make holes and other defects of the blank extend. Then, it is necessary to study the behavior of the inner hole defect of integral top cover. This paper, by numerical simulation technology, concrete analyses the volume of the hole defect, the size of the hole defect and variation of the hole edges in the stress-strain fields during the shape forming stage of the integral top cover. It researches the control scope of the original size of blank holes when the integral top cover forging meet the requirements of the flaw detection. Research results show that, according to the requirements of volume and maximum size permissible value, the diameter of holes in the integral top cover blank should be respectively less than 1.8 mm, 1.5 mm.

Abstract: In the precision hot plate for wafer processing, the temperature uniformity of upper plate surface is one of the key factors affecting the quality of wafers. Precision hot plates require temperature variations less than ±1.5% during heating to 120°C. In this study, we have manufactured the flat plate heat pipe hot chuck of circle type (300mm) and investigated the operating characteristics of flat plate heat pipe hot chuck experimentally. Various screen mesh (40, 80, 120) were used as the structure and chamber was changed.

Abstract: The low molecular syringaldehyde was found to be a preferred natural mediator for pulp delignification in the electrochemically mediated delignification system (EMD-system). Electrochemical treatment of poplar kraft pulp with syringaldehyde results in the reduction of kappa number of about 28%, but the loss of viscosity is only 6.6%. During the process of electrochemically mediated delignification , the delignification efficiency is dependent on the voltage, the dosage of syringaldehyde , reaction temperature , pH value, reaction time and the composition of electrolyte solution. The optimum operating parameters of electrochemical delignification with syringaldehyde are obtained as follows: syringaldehyde 1mmol/l, voltage 1.8v, temperature 45°C, reaction time 4.5h, the pH-value in the range from 4.0 to 5.0, sodium sulfate 0.05mol/l.

Abstract: This paper focused on the Cu alloy elements macro segregation of large squeeze casting wheel hub, analysed element segregation on the wheel axle, wheel arm and wheel rim. Three positions on the hardness and mechanical properties were tested, researched the influence of element segregation on the hardness and mechanical properties.

Abstract: In this paper, a type of Si₃N₄/TiC micro-nanocomposite ceramic tool materials were fabricated via hot pressing technique by adding Si₃N₄ and TiC nanoparticles. Cutting forces, temperature and wear behavior in dry machining of nodular cast iron with Si₃N₄/TiC micro-nanocomposite ceramic tool were investigated, in comparison with a commercial Sialon ceramic tool. Turning experiments were carried out at three different cutting speeds, which were 110, 175, and 220 m/min. Feed rate ( f ) and depth of cut (a_p) were kept fixed at 0.1 mm/rev and 0.5 mm. The results show that the radial thrust force (F_y) become the largest among the three cutting force components (F_x , F_y and F_z), and F_y is the most sensitive to the changes of feed rate and depth of cut. In dry cutting of nodular cast iron, the cutting tool temperature rise rapidly with increase in cutting speed. The cutting temperature reach nearly 1000°C at the cutting speed of 220 m/min. The two types of ceramic tools have similar cutting performance, while the Si₃N₄/TiC micro-nanocomposite tool exhibits a better cutting performance than that of the Sialon tool. The wear rate of Si₃N₄/TiC micro-nanocomposite ceramic cutting tool is mainly dominated by the abrasion, while the wear rate of Sialon ceramic cutting tool is dominated by the abrasive action, and pullout of grains.