جستجوی مقالات مرتبط با کلیدواژه « carbon nano tube » در نشریات گروه « مکانیک »

In this research, semi-solid powder processing was used to fabricate Al7075-CNT nanocomposite. The effect of process variables including compression time, semi-solid temperature and the CNT percent on the sample’s hardness and microstructure was investigated. The 1%-CNT nanocomposite is observed to be superior in hardness compared to the base alloy, but the 2%-CNT sample’s hardness was between the base alloy and 1%-CNT sample. It was observed that the compression time and semi-solid temperature do not have a significant effect on the sample’s hardness. Compression for 10 minutes and forming temperature of 620 °C were selected as the suitable variables. Microstructural examination showed that in 1%-CNT alloy, the reinforcing phase is completely penetrated in the aluminum matrix and there is no CNT accumulation on the sample’s surface unlike the 2%-CNT sample. Quantitative analysis showed that a proper percentage of CNT had the greatest effect on the hardness. Increasing the temperature from 600 to 620 °C by 10% and increasing the compression time from 5 to 15 minutes by 2% increased the hardness of 1%-CNT samples compared to the base alloy.

Electrical discharge machining is a non-traditional machining process, which is widely used for machining high-strength metals and alloys with low machinability. Due to the thermoelectric nature of this process, the poor surface integrity of the parts produced by this method is one of its weaknesses. In this research, the electric discharge machining method has been used for the machining of Ti-6Al-4V alloy using carbon nanotubes added to the dielectric. In this study, input variables include discharge current intensity, pulse duration, and dielectric; the effect of their changes on the shape of the output pulses, material removal rate, tool wear ratio, surface rouhness and heat affected layer has been investigated. The results show that the addition of carbon nanotubes to the dielectric reduces the harmful pulses and increases the effective pulses in machining, reduces the matrial removal rate and decrease the tool wear rate. The presence of carbon nano tubes significantly improves the surface quality and reduces the heat-affected layer.

In this study, aluminum sheets reinforced by carbon nanotubes were fabricated using the Accumulative Roll Bonding (ARB) method. The ARB process was chosen among the severe plastic deformation methods to strengthen metal sheets using carbon nanotubes owing to the enhanced microstructure and mechanical properties of final products. In order to evaluate the mechanical properties of the specimens, tensile tests were carried out and the strength of sheets made by ARB method was compared to single-layer pure aluminum and reinforced composite sheets. Microstructural changes of composite sheets were studied by optical microscopy after each cycle of rolling process. The results showed that spreading of (0. 5 to 1.5) wt% of CNTs increased the ultimate strength of the composite sheets while by aggregating the CNTs more than 1.5 wt% a decreasing trend of the ultimate strength was observed. Furthermore, the composites fabricated from 7 cycle of rolling process had a homogeneous distribution of particles and strong bonding between particles and matrix without having any porosity. Also it was found that the tensile strength of composite sheets also increased as the number of cycles increased.

In this paper, the thermal analysis of a solar wall equipped to nano phase change material is carried out, numerically. The governing equation of transient heat conduction is solved by a finite difference technique based on enthalpy method. The validation of numerical results of present study is carried out with the experimental data. There is a fair agreement between numerical results and experimental data. In parametric studies the volume fraction effect of carbon nano tubes and alumina nano particles and the thickness of phase change material is investigated. Present study results showed that suitable improvement in solar wall thermal performance is obtained due to the addition of carbon nano tubes and alumina nano particles to base phase change material. However, carbon nano tubes yield better performance. Performance improvement reasons include the increase of heat transfer speed due to the increase of thermal conductivity and the completion of melting and solidification process. Occurrences resultant leads to a 9% increase in the thermal efficiency of solar wall for 3% volume fraction of carbon nano tubes. Generally, the results of present study give the possibility of the design of a solar wall equipped to phase change material with about 40% of thermal efficiency.

Nanofluids as new groups of the heat transfer environments with unique and special properties have attracted particular attention in recent decades. Knowing the characteristics of the nanofluid is the first step in the nanofluid study, which is very important in describing its behavior. Although many attempts have been made to modeling the thermodynamic properties of nanofluids, a comprehensive model for predicting these properties has not yet been provided. In this work has been studied the dynamic viscosity of water-single wall carbon nanotube nanofluid and the effect of volume fraction and size of nanoparticles and nanofluid temperature on it in ranging from 〖25〗^°C to 〖65〗^°C with an interval of 10 °C and 0.125% to 0.734% (0.125%, 0.25%, 0.5%, 0.734%) respectively. After the full explanation of the interaction between base fluid and nanoparticle atoms and analyzing the shear stress autocorrelation function, the results show that the presence of nanoparticles in the base fluid and the addition of its, reducing the temperature, as well as reducing the size and diameter of the carbon nanotubes, increase the dynamic viscosity of nanofluids. Finally, the interpretation and conclusion of the results is discussed.

In the present research the effect of adding multi wall Carbon nano tubes (with 10-15 nano meter diameter) on the heat transfer coefficient of a heat exchanger is investigated. This work is performed by a co current flexible double pipe heat exchanger made of PVDF. To this end, the viscosity and thermal conductivity of nano fluids is measured experimentally for various temperatures and concentrations. The nano fluid temperature is set at 35°C, 40°C, 45°C and 50°C. The flow rate of nano fluid inside the inner tube was adjusted at 100 , 200 , 300 while, the cold water flow rate of the outer tube is 100 The results shows that heat transfer coefficient of the heat exchanger improves with increasing the fluid temperature, concentration and flow rate. The most effective factor on the heat transfer coefficient is flowrate. Obtained results indicate that using this nano fluid enhances heat transfer coefficient 75%.