نشریه مهندسی مکانیک مدرس
سال بیست و دوم شماره 4 (فروردین 1401)

An experimental study on the effects of methane-oxygen partially-premixed input flow characteristics in a mesoscale reactor with constant length and geometry was investigated in the present work. For this research, two partially-premixed ratios of 25% and 50% are considered. The reactor is mounted horizontally, made from quartz material and its geometric characteristics are internal diameter: 5 mm, wall thickness: 1 mm, and length: 10 cm. In this research, we have tried to determine the factors affecting flame regimes. The range of flame regimes, flame dynamics, the outer wall temperature distribution of the reactor, frequency, and oscillation of oscillating flames, along with the intensity of the Repetitive Extinction and ReIgnition (RERI) extinguishing sound, were analyzed and reported. This flame's dynamics are more affected by changes in mixing ratio, oxygen volume flow rate, and fuel volume flow rate, causing changes in inlet flow velocity and equivalence ratio, respectively. Examination of the results of acoustic oscillations indicates an increase in oscillating flame velocity with increasing volumetric flow and mixing ratio. Loud extinguishing sound of flames when quenching is caused by converting a portion of the thermal energy of the flame into sound in the flame arrestor and the acoustic vibration waves resulting from the extinguishing of the flame and the difference in gas velocity.

Concerning the limitations and environmental problems of fossil fuels, the use of renewable energy systems is necessary and inevitable, but the development of the use of these systems due to their unsustainable nature requires energy storage systems. Compressed air energy storage systems and pumped hydroelectric have a high potential for applying renewable energy systems in terms of power and storage time, but both have environmental and site limitations. The hybrid system of compressed air energy storage and pumped hydroelectric with the advantages of both systems is suitable for wide application. So far, less research has been done to analyze this hybrid system, and therefore the relationship between system parameters and system efficiency required further investigation. Also, the combined systems presented in previous research have two problems; Water evaporation and limitations in system operating pressure. In this paper, a new hybrid system is presented in which the rate of water evaporation is minimized by modifying the structure of the previous systems, and also the limitation of the operating pressure is determined by the existing compression technology. The present study showed that the ratio of air volume to high-pressure tank volume has the greatest effect on system efficiency and is a determining parameter. The amount of energy saved in the current research system is significant compared to previous researches and a roundtrip efficiency of 90% can be obtained. The energy analysis of the present paper determined the parameterchr('39')s interaction and their limitations in order to pave the way for design and feasibility.

The laser cladding of industrial parts to improve their mechanical properties by metal alloys and composites has been a challenge for scientists and experts. The quality and properties of the cladding layer are determined by many factors such as cladding geometry, microstructure, dilution ratio, defects, distortion, surface smoothness, metallurgical changes in the substrate and process efficiency. In this study, the effect of important parameters of the cladding process on the geometric shape, hardness and dilution ratio of the cladding layers of martensitic stainless steel (17-4 PH ) on the substrate of plain carbon steel by solid-state continuous laser with maximum power 2 kW and the method of direct deposition of metal powder are discussed. Variable parameters of laser cladding including powder feed rate, laser scanning speed and laser power have been studied. The parameters of surface quality, geometric shape and absence of porosity have been evaluated and compared. The minimum dilution about 9% was obtained at a 10 mm/s scanning speed, 10 g/min powder feed rate and 330 watts laser power. The results have been showed, appropriate incorporation and uniform distribution of cladding powder has created a cladding surface without any crack and porosity. By studying the hardness of the samples, it has been concluded that the hardness of the substrate surface has increased after cladding.

In this paper, a new model for estimation of the electrical conductivity of polymer carbon nanotube (CNT) nanocomposites based on the conventional power-law model and Halpin-Tsai formulation has been proposed. Halpin-Tsai model was originally presented to calculate the tensile modulus of composites, which can be modified for estimation of the electrical conductivity by replacing the electrical parameters. The nature of “b” exponent in power-law model is defined according to CNT dimensions, CNT electrical conductivity and the interphase thickness and also the impacts of these parameters on the “b” and the electrical conductivity of nanocomposite are taken into consideration. The developed model interprets that the electrical conductivity of polymer-CNT nanocomposite increases as the concentration, length and electrical conductivity of CNT and the interphase thickness increase. Furthermore, reduction in CNT diameter and waviness results in growth of nanocomposite electrical conductivity. In order to validate the developed model, nanocomposite samples with different volume fractions were produced by solid-state technique of the melt-blending method. The results of calculations and experimental procedure show good agreement.

In this paper, the dynamic response of steel plates under repeated blast loading using a ballistic pendulum system were investigated. In this regard, experiments were performed on three different configurations: unwelded, welded with single and double welding lines. To apply the dynamic load in a wide range, the plastic explosive charge (C4) in different masses of 25, 35, 45, and 50 g were used. Besides, to investigate the behavior of the structure under repeated loading, experiments were tested on up to 3 loads. Experimental observations demonstrate that with increasing charge mass, the large inelastic deformation with necking and tensile tearing around of the boundary were observed in higher charge masses and loading repetitions in higher numbers. For the unwelded plate, at the 3rd load with a charge mass of 25g, a change in the failure mode was observed (large inelastic deformation with necking around part of the boundary), however, for the welded plate with a single weld line, the same deformation mode occurred at the 3rd blast load by the charge mass of 35g. For the welded plate with two weld lines, the same failure mode was observed at the 3rd blast load by the charge mass of 45g. These observations indicate the effect of the weld line and its numbers on the variation of failure modes. The obtained result is one of the main objectives of the present study to show how using welding lines and their arrangements affect the deformation mode and the failure mechanism of steel plates.

In this paper, a simple and low weight gadget, without the need for a nurse, is designed in a low cost, taking into safety, flexibility and mobility for the user. This paper presents a new system that the controller system is designed and implemented based on the combination of acceleration sensor data and image processing system with the aim of controlling the movement of the smart wheelchair. This design, the user can take control of the smart wheelchair without using hands. This gadget can be a good solution for disabled people to make their life easy.The results of the smart wheelchair control testing with hybrid controller indicate that the accuracy and speed of the wheelchair response high. The experimental tests suggest that the proposed design of controller gadget is efficient and low cost as well as allowing disabled people to more easily control their wheelchairs and to lead independent lives.