Showing 14 results for Fluid Flow
Mousa Rezaee, Vahid Arab Maleki,
Volume 12, Issue 1 (4-2012)
Abstract
In this paper, the effect of the crack on the vibration behavior of a thick-walled cracked pipe conveying fluid is investigated. The presence of a crack on the pipe introduces considerable local flexibility at the crack location. This flexibility is modeled by the fracture mechanics approach. The accuracy of the model is validated through the experimental data reported in the literature. Then, by using the mentioned model, the vibration analysis of the cracked pipe conveying fluid has been accomplished. Moreover, in order to solve the equation governing the vibration of the cracked pipe conveying fluid, a new analytical technique based on the power series method is proposed. Then, by applying the boundary conditions and the compatibility conditions at the crack location, the frequency equation is obtained. The results are presented by appropriate curves showing the variation of the natural frequency of the cracked pipe conveying fluid in terms of the crack depth and the fluid flow velocity. Also, the results show that for a cracked pipe with a given depth and location for the crack, by increasing the fluid flow velocity, the natural frequencies of the pipe decrease. Also, as the fluid velocity approaches to a certain value, the fundamental natural frequency approaches zero and instability occurs.
Pouyan Adibi, Mohamadreza Ansari,
Volume 14, Issue 3 (6-2014)
Abstract
Abstract- In this paper, the effect of gas and liquid inlet velocities and for the first time the effect of liquid hold up on slug initiation position are studied experimentally. Empirical correlations are also presented based on the obtained results. The tests are conducted for three liquid hold ups (0.25, 0.50 and 0.75) in a long horizontal channel made of Plexiglas with dimensions of 510 cm2 and 36m length in Multiphase Flow Lab. of Tarbiat Modares University. The superficial liquid and air velocities rated as to 0.11-0.56 m/s and 1.88-13 m/s, respectively. The obtained results show that as αl=0.25, slug initiation position is increasing monotonically with Usl and Usg. During αl=0.50, slug initiation position is increasing with Usl and Usg but the slope is smoother than αl=0.25. For αl=0.75, slug initiation position is decreasing monotonically with Usl and Usg. In the case of equal void fraction of phases, slugs are generated weakly (low pressure). However, for the unequal void fraction of phases strong slugs (high pressure) are formed.
Amad Sanei, Alireza Basohbat Novinzadeh,
Volume 14, Issue 6 (9-2014)
Abstract
Abstract: In the papers published on compressible fluid using Pseudo Bond Graph approach, isentropic flow is assumed. However in a converging- diverging nozzle, for a specific pressure ratio, the assumption of isentropic flow is invalid. For the purpose of considering normal shock effects, this paper introduces a new field (NIKE-field) to the pseudo bond graph. The output of the new field can be also used to determine normal shock position and to extract momentum equation as well. In the following, the methodology developed in this paper has been applied a simple pedagogic example. Simulation result is validated by comparison with the analytical result. As the new field can be modeled non-isentropic flow, it can be used to for modeling rockets motors and thrusters in transient state. One of another advantage of new field (NIKE-field) is that it can be easily used in many software applications like MS1, SYMBOLS2000 and 20SIM®; therefore, With regard to the systematic derivation of a mathematical model from a bond graph in these softwares, there is no need to derive any state equations and their solutions.
Mostafa Sefidgar, Hossein Bazmara, Majid Bazargan, S. Mojtaba Mousavi Naeenian, Madjid Soltani,
Volume 14, Issue 9 (12-2014)
Abstract
Nowadays, solid tumor modeling and simulation results are used to predict how therapeutic drugs are transported to tumor cells by blood flow through capillaries and fluid flow in tissues. This model involves processes such as fluid diffusion, convective transport in extracellular matrix, and extravasation from blood vessels. In this paper, a complete model of interstitial fluid flow in tumor and normal tissue is presented with considering multi scale of solution such as blood flow through a capillary (as the smallest scale) to interstitial flow (as the biggest scale). The advanced mathematical model is used to generate a capillary network induce by tumor with two parent vessel around the tumor for the first time. In the following, the blood flow is modeled through the network with considering the non-continuous behavior of blood rheology and adaptability of capillary diameter to hemodynamics and metabolic stimuli. This flow is simultaneously simulated with interstitial flow which is coupled to blood flow through capillary with extravascular flow. The results predict elevated interstitial pressure in tumor region and heterogeneous capillary network which are introduced as barriers to drug delivery.
Masoud Ziaei-Rad, Farzaneh Amani,
Volume 15, Issue 8 (10-2015)
Abstract
In this paper, the heat transfer enhancement by the nanoparticles in the film condensation of nanofluid over a cooled plate is studied numerically. Shooting method and modified-Euler scheme are employed to solve the condensation boundary layer equations. The effect of changes in the plate angle, nanofluid type, volume fraction of nanoparticles and Jacob number, on the velocity and temperature profiles and Nusselt number are investigated. Resulting graphs are compared and validated with the available theoretical results for the base fluid and nanofluid. The results show that the presence of nanoparticles in the liquid film of condensation increases the heat transfer from it. As the plate distances from the vertical position, the temperature change across the boundary layer is close to linear and thus, the heat transfer descends. Also it can be found that the average Nusselt number is almost constant up to the angle of 20o, and then reduces in a gradual manner, so that for instant, for water-TiO2nanofluid, by increasing the angle up to 60o, the temperature gradient is reduced by about 20 percent. Furthermore, it is seen that the relationship between the ratio of nanofluid to pure water Nusselt number and the nanoparticles volume fraction is linear, while the slope of the line for water-Cu and water-Ag is more than other studied nanofluids, i.e., these two nanofluids are more effective in heat transfer enhancement. The obtained results also confirm the fact that the Nusselt theory is only applicable in low Jacob numbers.
Abbas Ehsani, Amir Nejat,
Volume 16, Issue 12 (2-2017)
Abstract
In the present work, a novel electromagnetic actuation flexible-valve micropump using the fluctuating elastic wall is proposed, based on one-way lymph transfer mechanism. A time dependent magnetic field is used for actuating the magnetorheological elastomer (contractible) wall. Two flexible valves are located in two terminals of microchannel in order to filter bidirectional flow and generate one-way fluid flow. Water properties are used for simulation and the maximum Reynolds number is not exceeded from 30, Womersly number is lower than 1 in all cases. Knudsen number is much less than unity, therefore no-slip condition is valid at walls. A fully coupled magneto-fluid-solid interaction approach using time dependent study of two-dimensional incompressible fluid flow is performed. All solid parts follow Hook’s law and simulation is carried out using finite element approach by COMSOL Multiphysics software. A parametric study is conducted and the effect of key geometrical, structural and magnetical parameters have been examined on the net pumped volume. Present micropump is able to generate unidirectional flow and propel net volume of fluid left to right, and the net pumped volume of fluid is affected by design parameters. The proposed design can serve in a wide range of microfluidic applications for example, flow rate and total mass transfer are completely controllable. At the end of the study, an optimum geometrical design based on initial model is proposed. The final design is capable to transmit nearly two times of net volume compare to initial model and more than three times of the previous design.
Fereidoun Sabetghadam, Abdullah Shajari-Ghasemkheily,
Volume 17, Issue 10 (1-2018)
Abstract
A new method is proposed for implementing the no-slip/no-penetration conditions on the irregular immersed boundaries in the vorticity-streamfunction formulation of the incompressible viscous fluid flow. Time integration is performed using a semi-implicit method such that in each time step the vorticity-streamfunction equations are changed to a Helmholtz and a Poisson’s equation. Some singular source terms are added to the right hand sides of these equations, in the solid region, such that the desired boundary conditions can be satisfied. The singular source terms are found, using the inverse problems method, such that the desired boundary conditions of the vorticity-streamfunction equations be satisfied. Since the fast Poisson’s solvers are used, the method is high performance, with the computational effort of O(NlogN); and it is also flexible because it can be applied easily to the complex geometries. The method is applied in simulation of the fluid flow around a square solid obstacle, placed in a channel, and the agreement of the results with the other benchmark results are shown.
Ghassem Heidarinejad, Amir Yousefi,
Volume 18, Issue 4 (8-2018)
Abstract
With the development of computers, the application of numerical methods in solving engineering problems has increased considerably. Methods such as Finite Element Method, Finite Volume Method and Finite Difference Method can be mentioned as some. In this research a Boundary Element Method is applied for numerical simulation. The main difference among the Boundary Element method and other numerical methods is the governing mathematics. At first In this method the governing equation is integrated. This leads to a decrease in the dimensions of the problem and then the simulation is performed. In this research, by a change of variable, the Navier Stokes equation is transformed to Navier equation in Elastostatics at first. Subsequently the methods proposed for solving the problems in Elastostatics is utilized to solve the viscous fluid flow. In fact, the applied fundamental solution is the main difference among the proposed method and other Boundary Element Methods. In the proposed method, in contrast to previously proposed methods, the fundamental solution of the Navier equation is utilized for simulation. At last, by considering the governing mathematics a computer code is developed for viscous flow simulation. The code is applied to two different geometries, a lid-driven-cavity and a backward facing step. Convergent solutions is achieved up to Reynolsds numbers equal with 600 and 100 respectively.
Abazar Abadeh, , Mohammad Javad Maghrebi,
Volume 18, Issue 4 (8-2018)
Abstract
Heat transfer enhancement is widely applicable in various industries, specifically in heat exchangers. Optimizing of heat transfer in the absence of increased pumping energy will result in increased of total efficiency in different systems. In this paper, forced convection heat transfer and fluid flow of fully developed laminar regime in a horizontal tube under uniform and non-uniform step heat fluxes is investigated experimentally. The effect of uniform, non-uniform increasing and decreasing applied heat fluxes on heat transfer and fluid flow are investigated. The effect of various parameters on heat transfer and fluid flow characteristics in these models are reported. Uncertainty analysis is performed and acceptable maximum of 1.8 percent is acquired. The primary results compared to well-known Shah and London equation for validation and maximum error of 8.5 percent is reported. In the present paper, Energy and exergy are two approach of analyzing. Convection heat transfer coefficient enhancement of 19.3 and 22.3 percent compared with model 1 are reported for model 2 and 3 respectively, in energy analysis. Furthermore, in this paper, exergy analysis is done and irreversibility values of 0.0887, 0.0803 and 0.1037 are reported for model 1, model 2 and model 3 respectively. Finally, it is concluded that the model number 3 is the best way to enhance heat transfer because of the maximum averaged Nusselt number and the minimum entropy generation values
Ramin Amini, Mohammad Akbarmakoui, Seyed Mojtaba Mosavi Nezhad,
Volume 18, Issue 8 (12-2018)
Abstract
In this study first the meshless local Petrov-Galerkin (MLPG) method by Radial Basis Function (RBF) has been explained entirely. In this way the governing channel flow expression that is based on the Laplace equation is expanded. In MLPG method, the problem domain is represented by a set of arbitrarily distributed nodes and Quadrature radial basis function is used for field function approximation and local integration is used to calculate the integrals. In the following, MLPG method is verified by exact solution in a numerical example. The Results show that MLPG method presented high accuracy and capability for solving the governing equation of the problem. Finally the velocity field is approximated in middle of nodes by RBF (MatLab code was adopted) in the uniform flow in a sloped channel problem. The MLPG results are compared with the isogeometric analysis (IA) method in the tutorial numerical example of Fluid flow modeling in channel, the velocity contours is detected, and their accuracy is demonstrated by means of several examples. The results showed good conformity compared to available analytical solution. The obtain results explain that Application of meshless method in Fluid flow modeling in channel show the applicability and efficiency of the meshless local Petrov-Galerkin method by Radial Basis Function method.
M. Mohammadi, M. Sefidgar,
Volume 19, Issue 12 (12-2019)
Abstract
Today, mathematical models and numerical methods are highly regarded according to their ability to predict and understand the cancer treatment process. In this research, the drug delivery to the solid tumor with considering its normal surrounding tissue has been studied by stimulating the blood flow in the dynamic capillary network and interstitial flow and adding the solute transport equation to the fluid flow equations. In the present study for the first time, drug delivery has been studied by a multi-scale comprehensive model with considering two parent vessels with different branches and different input and output pressures. In this paper, the intravascular flow was simultaneously simulated with the interstitial fluid flow. The distribution of drug concentration has been investigated at different times. The results show the dependence of the drug delivery to the interstitial fluid pressure, the pressure of the parent vessel and in fact, the blood pressure of each patient, and the capillary network structure. In addition, an increase of about 20% of the average drug concentration in the tumor site in the present study compared to the previous study with a parent vessel is evidence of the key role of the capillary network and its dependent parameters.
Volume 20, Issue 1 (4-2020)
Abstract
Undoubtedly, fluid flow modeling plays an important role in underground structures studies. In many cases, the main system for fluid flow in rock mass is the fractures network. Because of that the measurement of the geometric properties of the discontinuities is a time-consuming process and for some properties like persistence is impossible, the use of stochastic modeling for rock mass is suggested. Uncertainty about the geometric properties of discontinuities has led to use of statistical analysis for more accurately define geometric features. Because of intrinsic statistical nature of the geometric features of discontinuities, a more precise model can be obtained from the development of stochastic three-dimensional geometric models of discontinuities. The most important step in rock mass modeling is the exact definition of the discontinuity network. This makes it possible to provide a better starting point for numerical modeling in mechanical and hydraulic analysis. The Gardaneh-Rokh tunnel with a length of 1300 meters and a maximum volume of 200 meters is located in Chaharmahal Bakhtiary province. The purpose of this study was to investigate the water leakage from joints and fractures in the tunnel and the effect of surface water in the amount of water leakage into the tunnel using analytical and numerical methods. This modeling has been done to increase the understanding of the hydraulic behavior of the massive discontinuity system. In this study, the fractures connected to each other as the main paths of water flow into the tunnel and the control of the hydraulic behavior of the mass are assumed, and the roughness of the joints is neglected To this paper, joint sets in Gagrdaneh Rokh tunnel was modeled using the 3D-DFN code written in the Mathemtica software, after validation of the surveyed and modeled values, it was observed that the percentage of conformance is above 85%. This has led to the use of model outputs with confidence in the hydraulic modeling of the tunnel. This paper is designed with the aim of two-dimensional hydraulic modeling in the UDEC software environment. The modeling fluid is considered as monophasic, and discontinuities are modeled as two-dimensional. Hydraulic modeling is done by calling the joints from the 3D-DFN program output. Comparison of the obtained results shows good matching between the flow rate in the model with the actual flow rate. The resulting total flow rate is estimated to be 362 liters per minute, which is actually set at 375 liters per minute, which is a good match. Also, the sensitivity analysis of fluid flow has been investigated with respect to the maximum and minimum values of apertures, continuity (trace length) and Fisher numbers. With an opening of 5 mm, the water rate to the tunnel will reach 530 liters per minute. This rate is reduced to 172 liters per minute at opening of 1.2mm. The flow rate arrives in continuity of 27 meters to 523 liters per minute, in a trace length of 22 meters to 488 liters per minute and in trace length of 10 meters to 354 liters per minute. The flow rate in Fisher's number is reduced to 410 liters per minute and in Fisher's number 25 to 290 liters per minute.
M.m. Fakhari, H.r. Bokaei, B. Shahriari,
Volume 20, Issue 2 (1-2020)
Abstract
In this paper, the effect of nozzle divergent section geometry on fluid flow and heat transfer within the convergent-divergent nozzle numerically and experimentally is investigated. Axisymmetric supersonic flow simulation for the converging-diverging nozzle is conducted. The flow field is a steady turbulent two-dimensional flow. The working fluid is a combustion product and is considered as a compressible ideal gas. The flow field is simulated using the commercial code FLUENT. The equations are discretized implicitly with the second order of accuracy. In this study, two convergent-divergent nozzles have been analyzed that the divergent part of one is a cone-shaped and the other is bell-shaped. The calculated parameters in the simulation have been compared with the experimental results. Based on the simulation results and the values obtained in the experimental test, the error is less than 4% that is acceptable and appropriate. According to the results, flow simulation accuracy is appropriate.
Fatemeh Pourrezakhader, Roozbeh Abedini-Nassab,
Volume 24, Issue 10 (9-2024)
Abstract
In recent years, paper-based microfluidic devices have attracted significant attention. However, the inability to precisely control multiple fluids simultaneously has remained a major challenge for paper-based microfluidic chips. Here, inspired by electrical circuits, a transistor component has been designed and fabricated for operation in paper-based microfluidic chips. This component, upon receiving an electrical command, regulates the flow of fluid within a paper-based microfluidic channel. The primary advantage of this transistor lies in its bi-stable operation (capability to open and close the channel) despite its simple structure. Its operation is based on the controlled movement of wax, driven by the heat generated from the electrical current applied to the transistor's gate, within the cross-section of the paper. To characterize this transistor, the parameters affecting its operation were analyzed. Experimental results indicated that in a channel with length of 25 mm, with widths of 2 mm and 3 mm, and hydrophobic section lengths of 2 mm and 3 mm, a fluid volume of 30 to 40 microliters could be controlled by applying a gate electrical current of about 1300 milliamperes for less than 35 seconds. Additionally, as a practical demonstration of this transistor's functionality, a sensor circuit was designed and fabricated to detect acidic and basic environments. The proposed transistor, by enhancing fluid controllability in microfluidic chips, plays a key role in advancing this technology. Paper-based microfluidic chips equipped with the transistor presented in this study hold promising potential for applications in medical diagnostics, performing complex multi-step tests, biosensors and chemical sensors
