مجله مهندسی مکانیک امیرکبیر
سال پنجاه و پنجم شماره 5 (امرداد 1402)

This research has analyzed the drilling process in the human femur bone in order to determine the heat transfer coefficient and investigate the occurrence or non-occurrence of thermal necrosis. 3D drilling simulation have carried out in natural with air and force convection with normal-saline and the analysis performed for three feed rates of 50, 100 and 150mm/min at rotational speeds of 500, 1000 and 2000 rpm. The results show that in the natural cooling state, the highest generated heat is equal to 4J at 50mm/min and 500rpm while the lowest value of generated heat is 1.65J at 150mm/min and 2000rpm. The maximum difference of the average heat transfer coefficient with the experimental results is %12.5, which represents a good accuracy of the present results. The results in this state also show that the average heat transfer coefficient at 100 and 150mm/min is %55 and %29.1 more, respectively, and it is %5 less at 50mm/min rate, compared to the constant value of 20w/m2.k which is considered in the previous researches. Thermal necrosis occurs under all conditions of the natural cooling. In the force cooling, the highest average heat transfer coefficient with normal_saline is 150mm/min at a rotational speed of 2000rpm, which is equal to 3650w/m2.k and in all conditions, the bone temperature has not exceeded the temperature limit of thermal necrosis

The present research deals with the experimental investigation and comparison of microchannel and vane-tube condenser in a refrigeration cycle. This research investigate the effect of the type of condenser on the efficiency of the duct-split with a cooling capacity of 2.5 tons of refrigeration using experimental tests. For this purpose, two microchannel and fin-tube condensers have been used in a refrigeration cycle that has R407c refrigerant. Except for the condenser, the rest of the components of the refrigeration cycle, such as the fan, compressor, expansion valve, and evaporator are the same in both refrigeration cycles. The effect of the type of condenser on the performance coefficient of the refrigeration cycle has been evaluated at three different speeds of the condenser fan. Also, compressor power, evaporator cooling power, condenser thermal power, and temperature-entropy diagram (T-s) were extracted. Six different experiments have been conducted, and each experiment has been repeated three times to ensure the results. The results show that the use of the microchannel condenser in the same conditions and with 700 g less refrigerant charge in the entire refrigeration cycle, increases the performance factor by about 4% compared to the system that has fin-tube condenser.

Today, the use of nanofluids in microchannels is widely used for cooling microelectronic components. In this study, the flow and heat transfer of nanofluid in a converging and diverging microchannel has been investigated. The governing equations are solved by finite element method and two-phase mixture model in Comsol Multiphysics software. The results of this simulation were obtained for Reynolds numbers (100-700) and different concentrations of nanoparticles (0-0.02) for diverging and converging microchannels with different slopes (0-0.05). Also, the effect of two different nanofluids water-copper and ethylene-glycol-copper has been considered in the simulations. Nanoparticles diameter is 50 nm and the average height of the microchannels is 50 microns. The results include Nusselt number and performance coefficient for different situations. For water-copper nanofluid with a volume fraction of 1% in a converging microchannel with a slope of 3% and Reynolds 100, it increases by about 1.6 times for a converging microchannel and 1.1 times for a diverging microchannel compared to a flat microchannel. In this case, the performance coefficient for convergent and divergent microchannel is 1.37 and 1.74, respectively. In the same conditions, for ethylene glycol-copper nanofluid, the Nusselt number for converging microchannel becomes 1.22 times compared to flat microchannel and 1.13 times for divergent microchannel. In this case, the performance coefficient for convergent and divergent microchannel is 1.17 and 1.4 respectively.

Due to the vast and diverse applications of electrospray in various aspects of human life, this subject has always been of interest to researchers. This article discusses the experimental investigation of the electrospray process for the ethanol-water mixture with three different concentrations of 70%, 96%, and 99.9%. In this article, first, different electrospray modes for 70% ethanol, based on high-speed images, are defined and explained. For three concentrations of 70%, 96%, and 99.9% of the ethanol-water mixture, the Taylor cone angle and the jet diameter at the onset and end of the stable electrospray region have been calculated. For this purpose, high-speed imaging and processing of the resulting images have been utilized. The cone angle and the diameter of the jet exiting from the cone for the three fluids have been calculated for all onset and end points of the stable electrospray region for flow rates ranging from 0.1 to 1 mL/h. The average jet diameter for all points of the stable region for 70%, 96%, and 99.9% ethanol fluids is equal to 34.43, 33.78, and 31.70 microns, respectively. Additionally, the average cone angle for all points of the stable region is 87.26°, 85.80°, and 84.13° for ethanol fluids, 70%, 96%, and 99.9%, respectively. Therefore, the highest cone angle and jet diameter values correspond to 70% ethanol, and the lowest values correspond to 99.9% ethanol.

One of the main goals in the field of lab-on-a-chip is the manipulation of microparticles and cells on microfluidic chips. Methods based on magnetic forces, with remote controllability over particle movement, are considered one of the most appealing techniques toward this goal. Recently, inspired by electronic circuits and to transport particles in a controlled fashion in a tri-axial magnetic field, magnetophoretic circuits based on TI-shaped magnetic thin films are introduced. However, to date, capacitors are not used in order to store transported particles in these circuits. Here, TI magnetophoretic capacitors are introduced and characterized. The capability of the capacitor for storing particles of different sizes at various rotating magnetic field frequencies is studied. Towards this goal, finite element methods are used to simulate the magnetic potential energy distribution created by the magnetic thin films. Also, the trajectory of the magnetic particles, considering the drag forces, based on semi-analytical analysis and stochastic numerical analysis, are investigated. The simulation results are validated experimentally. At the operating frequency of 0.1 Hz loading efficiency of 98% was achieved. Adding this circuit element to the magnetophoretic circuits results in a complete chip, with important applications in lab-on-a-chip systems, single-cell biology, and drug screening.

Carbon dioxide (CO2) is the primary greenhouse gas and its capturing by calcium looping process is considered as one of the most promising technologies to reduce the negative effects on climate changes. Since the calcium looping process is carried out at temperature higher than 700 oC, it is not always possible to perform experimental investigations of the reactions taking place in industrial scales at real conditions. Therefore, in this research, two kinetic models including random pore and fractal-like models were used for the modeling of carbonation and sulfation reactions. The results showed that due to the importance of the diffusion stage in the product layer, the difference between the experimental data and the ones predicted by random pore model increased by passing time, and this difference was more increased under higher concentrations of sulfur dioxide. On the contrary, the fractal-like model with considering variable diffusion coefficients during the reaction time, presented a better accuracy. The fractal-like model was used to predict the carbonation and sulfation reactions conversions at cycles 5, 15, and 30, showing 60, 37, and 27% carbonation conversion, and 1.6, 1.3, and 1.1% sulfation conversion, respectively. In addition, the conversions were decreased during the consecutive cycles due to the decrease of capture capacity and specific surface area of the adsorbent.