Iranian Journal of Mechanical Engineering Transactions of ISME
Volume:24 Issue: 1, Mar 2023

Rotameters for gas flow-rate measurements are calibrated and scaled by air or oxygen at standard atmospheric pressure and temperature in the fabrication plants. To utilize these rotameters for gas flow rate measurements at different conditions, they have to be recalibrated again. This is not an easy task in the labs environment and should be carried out with so much care to obtain accurate measurements at the specified operating conditions. A novel straightforward and reliable procedure for calibrating rotameters under specific lab conditions is introduced in this paper which enables researchers to practice it with usual limitations of time and budgets. The practice involves producing proper calibration curves based on the theoretical formulations. As an example, the principle of action and characteristics of an air calibrated rotameter is investigated, when it is going to measure oxygen flow rate at different pressure and temperature.  It is shown that a linear function can be derived to estimate the true flow rates of gases based on the indicated flow rate readings on the rotameter scale and the corrected flow rate mentioned in the literature.

The present study investigates the surface roughness of the Bronze element on heat transfer in pool boiling process. The experiments were carried out with a solution of deionezed water (50%) and isopropanol (50%) in a specified container containing a hollow cylinder of bronze metal. The results indicated that the roughness index had a significant effect on the bubble dynamic. Increasing the surface roughness led to promote the bubble generation points and bubble departure diameter subsequently heat transfer enhancement through fluctuations in the solution. In addition, artificial neural network (ANN) and genetic algorithm (GA) were applied for developing the bubble departure diameter that the roughness index was one of the independent variables. Although the ANN was more capable than GA in data prediction, the GA could be employed as a more efficient and easy available approach. Therefore, the both models were powerful with acceptable errors (R2ANN=0.9982, R2GA =0.9929). Finally, the processed models were compared to Cole, Van Stralen, Lee and Stephane models. The results depicted that the ANN and GA methods had superior agreement with the experimental data than other models.

The analytical method is developed to examine the fracture behavior of a functionally graded piezoelectric rectangular plane (FGPRP) with finite geometry under impact loads. The material properties of the FGPRP vary continuously in the transverse direction. Two different types of boundary conditions are examined and discussed in the analyses. The finite Fourier cosine and Laplace transforms are employed to obtain stress and electric displacement fields in the finite plane containing electro-elastic screw dislocation. Based on the distributed dislocation technique, a set of integral equations for the finite plane is weakened by multiple parallel cracks under electromechanical impact loads. By solving numerically, the resulting singular integral equation, the dynamic stress intensity factor (DSIF) is obtained for the electrically impermeable case. The new results are provided to show the applicability of the proposed solution. The effects of the geometric parameters including plate length, width, crack position, crack length, loading parameter, and FG exponent on the dynamic stress intensity factors are shown graphically and discusseThe analytical method is developed to examine the fracture behavior of a functionally graded piezoelectric rectangular plane (FGPRP) with finite geometry under impact loads. The material properties of the FGPRP vary continuously in the transverse direction. Two different types of boundary conditions are examined and discussed in the analyses. The finite Fourier cosine and Laplace transforms are employed to obtain stress and electric displacement fields in the finite plane containing electro-elastic screw dislocation. Based on the distributed dislocation technique, a set of integral equations for the finite plane is weakened by multiple parallel cracks under electromechanical impact loads. By solving numerically, the resulting singular integral equation, the dynamic stress intensity factor (DSIF) is obtained for the electrically impermeable case. The new results are provided to show the applicability of the proposed solution. The effects of the geometric parameters including plate length, width, crack position, crack length, loading parameter, and FG exponent on the dynamic stress intensity factors are shown graphically and discussed.

In this paper, new optimizations of the two-layer microbeams based on the classical and non-classical theory are presented. In the first step, the natural frequency is obtained based on the modified couple stress theories. Afterwards, three important functions of the microbeams which are used as microsensors, sensitivity, quality factor, and maximum stress are defined. In the subsequent stage, two and three objective optimizations are carried out by using the genetic algorithm. At the two-objective optimization, sensitivity and quality factor are selected as objective functions. At the three objective optimizations, the maximum stress adds to the objective functions. The geometric parameters are design variables and there are some constraints and limits for those. The results are presented based on the classical and non-classical theory and optimal points are obtained for each optimization by using MATLAB.

The utilization of ultrasonic waves is a method to reduce frictional drag. Available hypotheses state that ultrasonic vibrations reduce frictional drag by creating cavitation, forming a fluid vapor layer surrounding the surface, and reducing its contact surface. This paper examines the hypothesis by performing experimental tests to eliminate the cavitation effect via increasing the pressure and investigates other factors affecting the frictional drag reduction. Experimental tests showed that by applying ultrasonic vibrations, frictional drag is reduced by an average of about 9%. Besides, by eliminating the cavitation effect, the frictional drag reduction is nearly 6%. It reveals that about 3% of frictional drag reduction was related to cavitation. The shear stress relation shows that the effect of variation of shear surface and distance in the presence of ultrasonic vibrations are negligible, and therefore the only factor that affects the drag force reduction is viscosity. It can be hypothesized that ultrasonic vibrations reduce viscosity by mechanisms such as increasing both local temperature and the distance between molecules. The tests showed that the viscosity was reduced by 6% by using ultrasonic waves.

This paper is dealing with the Elastoplastic analysis of rotating disks of variable thickness made of functionally graded materials based on Tresca's yield criterion. To do so, the governing equations of rotating annular disks are established based on the elasticity theory. Then, using Tresca's yield criterion and the elastic-perfectly plastic flow law, the displacement equations and stresses are obtained in the plastic region. In order to find the effects of the shape of the disk profile on its stress distribution, the thickness of the disk cross-section is supposed to vary as an exponential function of the radius. In addition, considering different places at which the yielding starts, the process of expanding the plastic flow is investigated. The obtained results are validated against those reported for homogeneous as well as constant thickness FGM disks, showing good agreement. The findings also demonstrate that taking the variable thickness for the disk cross-section into account has a significant effect on the stress distribution and prediction of the place where the yielding initiate.

This paper presents a new model to study the friction between rough surfaces with random distribution of the asperities, taking into account the contact mechanics. The results obtained show that as the surface separation decreases, the normal and friction forces increase and the coefficient of friction decreases. This model predicts higher friction forces and coefficient of friction than the model based on the Hertzian contact model. The sensitivity of the coefficient of friction to material properties is investigated using two sets of material properties. Assuming that the standard deviation and the radius of the asperities are constant, the first set investigates the variation of the adhesion energy, length of Burgers vectors, and elastic modulus parameters for the base material silicon. In the second set, real materials such as silicon, Fe, Cu, Au, and Ag are studied in contact with a silicon substrate. The results show that the friction coefficient decreases with the increase of the adhesion energy and increases with the increase of the length of Burgers vectors and elastic modulus.