مهندس محمود نوروزی

Nowadays, the utilization of smart materials is experiencing rapid growth across a wide range of industrial systems. Magnetorheological elastomers are a class of smart materials and possess two unique features, i.e. adjustable hardness and damping capabilities. These characteristics make them widely used in various industrial applications. Hence, understanding their behavior in different systems is necessary. The focus of this work is to study the dynamic behavior of magnetorheological elastomers under different static pre-strains in tension-compression mode. In this study, three isotropic samples were fabricated and the force-deflection features of them were acquired under harmonic excitation with various strain amplitudes, static pre-strains, frequencies, and magnetic flux densities. Assess the effect of static pre-strain on the dynamic response of the magnetorheological elastomers, studying the effects of other parameters like strains, frequencies, and magnetic flux densities on the dynamic modulus of magnetorheological elastomers, and proposing a novel phenomenological-based model to predict the viscoelastic behavior of magnetorheological elastomers are the innovative aspects of this study. The results showed that the dynamic modulus of magnetorheological elastomers will increase by superimposing the static pre-strain. Furthermore, the relative MR effect decreases when the static pre-strain is applied. The maximum relative MR effect of 288.3158% have been achieved at a strain of 4%, a frequency of 7 Hz, and a static pre-strain of 0%.

One of the unique features of viscoelastic fluids in unsteady flows is the damping oscillatory behavior without using oscillation and external force, the cause of this is the elastic feature of these fluids. In this essay, the power-law preconditioning method of local stress sensors is used for the first time, to solve the numerical solutions of unsteady flows of viscoelastic fluid while passing through two fixed parallel planes. The Maxwell's equations have been used for this simulation. In this method, by adding a false time derivative to the governing equations, the formation of equations become hyperbola (artificial compressibility). By acquiring the preconditioning matrix of these equations that are corrected from the relationship between stress fields, solving unsteady incompressible flow equations as artificial compressible, is possible when using a dual-time algorithm that contains inner and external cordon. For convergence of inner cordon , Vossougi Far’s four-step numerical method is used. For discretization of equations, the first-order finite difference and second-order finite difference are used. The calculations of unsteady flows of viscoelastic fluid for Reynolds numbers, Weissenberg numbers and various passive viscosity ratio, are presented. These results are similar to numerical results. The convergence rate results show that the power-law preconditioned method of local stress sensor for a viscosity ratio of less than 0.5 for high stability, increase the convergence speed and reduce the cost of calculations.

In this paper, using experimental studies, the effect of volumetric filling ratio and evaporator and condenser length ratio on the performance of the pulsating heat pipe has been investigated using the response surface methodology. The surface methodology is a response to a set of statistical techniques and applied mathematics to construct experimental models with the aim of reducing experiments. In order to improve the performance of the pulsating heat pipe, the present study studies the minimum thermal resistance under the influence of two parameters. The pulsating heat pipe with general dimensions of 3 × 210 × 200 mm consists of four rounds of copper pipe with internal and external diameters of 2.4 and 3 mm, respectively. Experimental results show that the changes in thermal resistance in terms of the parameters of the volume filling ratio and the ratio of the length of the evaporator to the condenser, has a turning point before which the relationship between thermal resistance and each of the parameters will be inverted and then direct.

This study is aims to perform three-dimensional simulation gas turbine internal cooling system for stationary and rotating mode at the middle region of four-pass smooth channels to assess fluid flow and turbulent heat transfer. The geometry of bend has been changed to U-shape turn and the guide vane in the bending region is Installed in order to enhance higher overall performance the cooling channel. The results of the governing equations are obtained using the Reynolds stress turbulence model. cooling channels are simulated in three different Reynolds numbers ranges from 20,000 to 60,000 and the rotation number of 0/13. The effect of the guide vanes on the U-shaped bend region, in addition to reducing the separation bubble area and circulation fluid in the upstream bend flow, it causes more uniform flow structure in the bend region and subsequent passage. So that the correction of bend and the use of flow guide vane to the base geometry in the case stationary of pressure drop and the coefficient of thermal performance decreases by about 13.4% and increases by 22.5%, respectively. The effect of the guide van on the amount of heat transfer in the rotating state is not noticeable, but due to the reduction of pressure drop, it increases the coefficient of thermal performance up to 9.4%.

In this paper, the crown formation and temporal propagation due to the oblique impact of a plane two-dimensional drop onto preexisting film in the non-Newtonian viscoelastic fluid are analyzed numerically. The finite volume method is applied to solve the governing equations and the volume of fluid technique is used to track the free surface of liquid phases. Here, the well-known Oldroyd-B model is used as the constitutive equation for the viscoelastic phase. However, the formation and temporal evolution of the crown’s shape is emphasized and the effects of elastic and surface tension forces on the crown’s dynamic are considered in detail. The results show that the increase in Weissenberg number, viscosity ratio, and Weber number leads to an increase in both the dimensionless crown height (Z*) and spread factor (S*), while impact angle has a major effect on the control of the crown’s height, on the other hand, this parameter has a negligible effect on spread factor in viscoelastic fluid. Moreover, by thickening of fluid film, the crown’s height increase, and the crown’s radius decrease. As the main finding of the present study, the fluid’s elasticity in the presence of surface tension force can enhance the rate of the crown propagation in the impact of an oblique drop onto liquid film.

Magneto-rheological fluids are one of the intelligent fluids which have been extensively used in engineering application including magneto-rheological dampers. Having yield stress in a magnetic field and ability to control and increase their viscosity are their most important characteristics. After three different carbonyl iron powders were subjected to analysis, five different magneto-rheological fluids were synthesized and were tested for stability and the optimized fluid obtained. The results obtained from the optimized magneto-rheological fluid with 85% (weight %) iron powder was similar to that of LORD oil. Also, a modified non-Newtonian rheological model was developed to predict the behavior of the optimized magneto-rheological fluid which is more accurate than Bingham and Herschel-Bulkley models and could be implemented in computational fluid dynamic modelling. The modelling of the damper was conducted by implementing modified non-Newtonian and Bingham models using analytical quasi-static, unsteady and computational fluid dynamicmethods and the results were validated with experimental data. The results show that neglecting factors including fluid shear thinning, wall shear stress and inertia term effects and effect of magnetic field on plastic viscosity in conventional modelling methods results in considerable error that will increase as magnetic field, Reynolds number and gap are increasing.

Injection of foam into oil reservoir, is a new method for enhanced oil recovery (EOR). One of the advantages of using foam is the stable displacement of porous submersible oil due to its relative low mobility. The challenge for foam application in the oil recovery is to maintain its stability when it comes to contact with the oil phase. Therefore, before using foam in the EOR process, its properties and interactions with the oil must be characterized. in this research, by creating two different laboratory setups at the bubble and bulk scale, the foam stability contributing factors and the viscosity of different types of foam were measured. Changes of different type of foam’s height in the vertical column were studied at the bulk scale. Ate the bubble scale, by building a transparent hele-shaw cell that is equipped with pressure sensors, the evolution of the foam were examined quantitatively and qualitatively. The Results showed that the surfactant type had a significant effect on the stability of foam bubbles; so that the combination of 1:1 SDS and CAPB with the highest stability, increased foam half life time by 124% at the bubble scale and by %33 at the bulk scale. in the presence of the oil phase its destructive effect on foam stability, increased with the reduction of the viscosity and the density of the oil agent. Also, the results showed that the foam quality would directly affect the viscosity of the foam, while its flow rate had an inverse effect.

Two phases flows particularly motion droplets into a second fluid have variety of application in different industries including oil and gas industry, medicine and pharmaceutical, extraction of metals, power plants as well as heat exchangers. In this paper, dynamic of a Newtonian drop falling in laminar regime is studied. A fluid which its viscosity is 340 cP is used in order to produce an inertia flow. In experimental section, de-ionized water and glycerin solutions with volume concentrations of 21:79 and 17:83 are used for drop phase. By increasing the volume of drop that leads to rising the inertia force, the drop shape is changed from spherically and a dimple at the rear of drop is appeared. Inertial forces, surface tension and hydrodynamic tension play a significant role on drop shape. Increasing the drop volume causes expanding the dimple consequently drag force is enhanced and terminal velocity of drop is decreased as well. According to the experimental observations, variations of viscosity ratio does not have a profound effect on drop deformation. Moreover, increasing the Reynolds number leads to reduction of pressure coefficient. It is shown that the experimental observations have an appropriate agreement with analytical results.

This paper presents an analytical solution for heat transfer in heterogeneous composite conical shells with temperature dependent conduction coefficients for the first time. The geometry of the shell is completely conical shaped and the fibers are winded around the laminate in the desired direction. In order to achieve the most general solution, the general boundary condition is considered at the basis of shell and the effect of heat convection resulted from flow motion around the body and different kinds of non-axisymmetric radiative heat flux at outer side of shell is modeled. Heterogeneous effect in this case is the results of the dependency in conduction heat transfer coefficient on temperature. Therefore, the heat transfer equation should first be transformed using the Kirchhoff transform to a solvable equation using integral transformation, then, the partial differential equation becomes an ordinary differential equation Fourier transformation. Finally, the transformed differential equation can be solved Green's functions. In the end, the reversal integral transformation and reversal Kirchhoff conversion are applied to obtain heterogeneous temperature distribution. Validation of the this analytical solution is performed by comparing the analytical results with the solution of second order finite different method and some applied cases are considered to investigate the capability of current solution for solving the industrial problems in the production of composite conical pressure vessels.

Magnetorheological damper, as one of the most widely used equipment in the various industries, was firstly studied and optimized using a molecular properties analysis of operating magnetic fluid in it utilizing dissipative particle dynamics as molecular modeling method. By use of modified Bouc-wen model, hysteresis and damping force level has been calculated in order to provide the required 10 N power requirement in micro-machines and After validation with experimental results presented in papers, the effect of molecular properties of magnetic fluid operating on it has been investigated. Results of molecular modeling by dissipative particle dynamics method show that by increasing mass and diameter of magnetic particles, damping force increases, while by increasing number density of these particles and increasing mass of carrier fluid particles, damping force firstly increases and then decreases, therefore It is necessary to set optimal values. It is also observed that by decreasing thickness of surfactant layer at the surface of the magnetic particles, damping force increases. Finally, according to the obtained results, the optimal values of each studied parameters were determined to provide 10 N damping force with the least amount of energy consumed by damper and selected from commercial magnetic fluids 132-DG fluid as suitable magnetorheological fluid.

In the present study, the sensitivity of the behavior of an Upper-Convected-Maxwell polymer and an Oldroyd-B fluid are compared to a Newtonian fluid. The governing equations are the Navier - Stokes equations and viscoelastic fluid equations. These equations are non-dimensionalized and it is found that Reynolds and Mach numbers are only the dimensionless parameters that exists in all three mentioned fluids. The viscosity of fluids as a friction factor causes that Reynolds number and its changes play an important role in the oscillations and also the attenuation of the fluid transient during Fluid hammer phenomenon. The numerical method used is a two-step variant of the Lax-Friedrichs (LxF) method. The results show that the viscoelastic properties of fluids, such as the non-linear relationship of stress and strain, relaxation time and …, reduce their variability compared to Newtonian fluid. Finally, the maximum sensitivity to Reynolds variations in Newtonian fluid and the minimum amount is observed in the Upper-Convected-Maxwell polymer that there are strong viscoelastic properties in its equations.

In this study, the viscous fingering instability in miscible displacement of Newtonian fluid by viscoelastic fluid in an anisotropic porous media is investigated for the first time. The Oldroyd-B model has been used as the constitutive equation. The roll of velocitydependent transverse and longitudinal dispersions on the fingering instability is investigated through linear stability analysis and nonlinear simulations. The results of linear stability analysis show that the growth rate of instability is decreased by increasing the rate of transverse to longitudinal dispersions and the flow becomes more stable. The nonlinear simulations are performed by use of spectral method and Hartly transformation and the results are included concentration contours, transversely averaged concentration profiles, mixing length and sweep efficiency. The results show that the flow becomes more unstable by increasing the rate of longitudinal to transverse dispersions.

In this paper, the inertial and non-isothermal flow of viscoelastic fluid inside thesymmetric planar sudden expansion channel with an expansion ratio of 1:3 has been numericallyinvestigated in the range of Brinkman numbers (0.01≤Br≤20). The rheological and nonlinear model ofPhan Thien-Tanner (PTT) is used for modeling viscoelastic fluid behavior. The finite volume method(FVM) is employed to discretize the governing equations and the PISO algorithm is used to solve theseequations simultaneously. Due to the significant effect of temperature changes on the viscoelastic fluidproperties, these properties are considered as temperature-dependent and the viscous dissipations termis considered in the energy equation. The main purpose of this study is to investigate the effects ofBrinkman numbers on the heat generation by viscous dissipations term used in the energy equation.Therefore, the streamlines, the length of vortices, the isothermal lines, the distributions of velocity andtemperature and local Nusselt numbers have been examined in the channel expanded part. The resultsshow that for the hydrodynamic and thermally developing zone, the maximum value of the local Nusseltnumbers on the walls of the channel expanded part is located at the end of the first and second vortices.

In this study, the inertial and non-isothermal flow of viscoelastic fluid has been simulated inside the symmetric planar channel with 1:3 sudden expansion. The non-linear form of Phan Thien-Tanner (PTT) has been used for modeling the rheological and complex behavior of the viscoelastic fluid. For creating the non-isothermal flow, temperature values are constant and different at the inlet and on the walls of the channel. To simulate the non-isothermal flow, the PISO algorithm is used and the governing equations are linearized by finite volume method (FVM). Also, fluid properties are a function of temperature and viscous dissipation term has been applied in the energy equation. The main purpose of this study is to investigate the effects of elastic property, inertial force and viscous dissipation on the flow pattern, pressure changes, pressure drop coefficient and loss coefficient for inertial and nonisothermal flow in the expanded part of the planar channel. The results of this study show that increasing the Reynolds number in the range of laminar flow creates an asymmetric flow pattern in the expanded part of the planar channel (unlike the sudden expansion pipe) which plays a major role on the distribution and drop of pressure in this part.

Magneto-rheological damper is one of the most widely used mechanical equipment, which absorbs mechanical shocks by use of magnetic fluid and electrical coil in its structure. In this paper, for the first time, dissipative particle dynamics as a mesoscopic scale modeling method was used to simulate a magneto-rheological damper and its magnetic fluid. Data from 3 categories including magnetic fluids with brand names 122-EG, 132-DJ, and 140-CG have been used and effect of their physical properties on power of damping force have been investigated. Results of modeling show that by increasing shear rate of fluid, shear stress is first increased and, then, it is applied to a constant value, which results in a greater shear stress by applying a stronger magnetic field. It is also observed that, with increasing both maximum piston velocity and strength of magnetic field, maximum power of damping force increased, which in 140-CG is higher than the other fluids. Results of sensitivity analysis show that weight of magnetic particles and strength of dissipative forces have the greatest effect on damping force, in such a way that by increasing weight of magnetic particles and decreasing the dissipative force of particles, accumulation of magnetic particles decrease, so, increasing quality of damping. It was also found that 122-EG is more suitable than other types of magnetic fluids in forming standard magnetic particle chains, and provides a more favorable viscosity distribution for damping.

In the present paper the forced convection heat transfer of non-Newtonian Power-law fluid through an isothermal tube is studied analytically. Exact solutions for thermally developing and fully developed Power-law flows are presented. In the case of thermally developing flow, the energy equation is solved by applying the Separation Method resulting in a homogeneous system of differential equations including Sturm-Liouville equation. Temperature distribution of Power law flow through tube is presented for two states of shear thinning n=0.2 and Newtonian n=1in closed form solutions. The diagram resulted of plotting the local Nusselt number versus the dimensionless tube length for both of two considered states, represents this fact that increasing of the Power law index the Nusselt number is decreased. For the fully developed Power law flow after solving the energy equation finally an ordinary second order differential equation is derived in which the flow temperature distribution is determined by Modal analysis. For different values of Power-law indices firstly, the Nussselt number is determined by wall thermal boundary condition and then the flow temperature distribution is presented by Frobenius method. The results show that the Nusselt number and maximum temperature are decreased by increasing the Power-law index meaning a decrease in the tube heat transfer.

In this study, the fingering instability in displacement of Newtonian fluid by viscoelastic fluid through heterogeneous media is investigated using spectral method and Hartley transforms. The White- Metzner model has been used as the constitutive equation. This model can be presented the shear- thinning and elastic behaviors of viscoelastic fluid very well. The heterogeneity of the media is considered in two different types. In the first case, the permeability of medium exponentially decreases in the transversely section. This case is named decreasing heterogeneity. In the second case, the permeability of the medium will initially be increasing and it reaches to its maximum at the middle of the cross-section and then decreases. This type of heterogeneity is called parabolic heterogeneity. The results are included concentration contours, mixing length and sweep efficiency. It can be seen that in the first case, the degree of heterogeneity has little effect on the structure of fingers. However, increasing in this parameter leads to decrease in mixing length and increase in sweep efficiency. But, in the latter case, with the change in the degree of heterogeneity, the finger structure will be strongly affected. In addition, in this case, increasing the degree of heterogeneity will increase the mixing length and reduce the sweep efficiency. Also, in both cases, the flow becomes more unstable by the shear thinning property of viscoelastic fluid. Although it seems this effect is less in medium with parabolic heterogeneity.

“Water hammer” is one of the phenomena that causes damage in the pipe system and reduces their useful life. Various numerical methods have been used to analyze this problem. In all numerical methods, for calculating the variables that are the velocity and pressure values due to the sudden discontinuity of the flow and motion of the pressure wave along the pipe, the continuum environment of the problem must be discretized in some way. With calculating these aberrations before designing of the structures accurately, appropriate measures can be taken to reduce tensions caused by the water-hammer phenomenon. Background and objectives: The conventional method to numerically solve the differential equations that describe this phenomenon is the method of characteristic lines. In general, in conventional methods where have been developed correctly, such as finite element, finite volume and finite difference, discretization of the spatial domain of the problem is done by gridding. Despite the useful use of these methods in many scientific fields, gridding is a costly and troublesome process, especially on problems with complex boundaries. That is the main motive for the creation of meshless methods. In these methods, the spatial domain of the problem is simply discretized by a number of points. In the present study, for modeling classical water-hammer in a system including valve, pipe and reservoir, a collocated discrete least squares method is used. In the proposed approach implicit Crank-Nicolson method for time discretization is used to provide conditions for problem solving stability. In this method, the velocity and pressure values on the x-t plane are calculated directly from the previous time step simultaneously. This method is quite matrix and the solution process is accomplished including several simple algebraic operations on matrices. In this study, at first this numerical method is described generally then governing equations are calculated and several experiments on water hammer in the form of the problem have been modeled by this method, also the hydraulic analysis of problems and calculation steps for calculating accurate answers are fully described and the results are verified with exact answers and other numerical methods such as MOC method and numerical method used by “Zielk” and the computational average error was estimated to be less than 5% by total squared error criterion. So this method can be considered as a precise, simple, and low-cost numerical method for modeling of water-hammer phenomena. Important properties of the Meshless numerical method included no need to integrate, complete mathematical math operations and meshless space makes it one of the most accurate methods for numerical solution of water hammer phenomenon in the pipe system.