فهرست مطالب ashkan ghafouri

In this study, the effect of limited inclination angle on two-phase flow in a vertical pipe was investigated, focusing on the formation of liquid film thickness using image recording and processing techniques. To generate annular flow patterns, non-homogeneous air-water flow was utilized in three transparent pipes with diameters ranging from 25 to 75 millimeters. After analyzing the flow pattern results for various superficial gas and liquid velocities, Reynolds numbers, and different pipe diameters, both the maximum and minimum liquid film thicknesses were calculated and presented, along with their ratios. Additionally, the dimensionless equivalent liquid film thicknesses for inclined pipes were provided concerning the uniform film thickness in the fully vertical condition. The results indicated an increase in the ratio of maximum to minimum film thickness with a change in inclination angle from 90 to 85 degrees. Furthermore, the dimensionless equivalent liquid film thickness decreased with inclination angle, consistent with prior research findings. The uncertainty analysis revealed a maximum uncertainty of 4.9 percent in the experimental assessment of the liquid film thickness, which falls within an acceptable range.

An experimental study was carried out in order to find out the effects of ZnO Nano fluid with a mean diameter of 30nm on heat transfer, pressure drop and termal performance of a double tube heat exchanger, where the volume fraction of nanoparticles in the base fluid is less than 1% (low concentration). Ethylene glycol and Nano fluid with particle volume fraction of 0.5%, 0.7% and 1% are used as working fluid. The experiments are carried out in the fully developed turbulent regime. The results indicate that addition of low value of nanoparticles to the base fluid motivates the heat transfer to increase remarkably. The Nano fluid also show that the pressure drop of Nano fluid is slightly higher than that of the base fluid and does not increase with increasing the nanoparticles volume fraction. In this paper, experimental results have been compared with the existing correlations for Nano fluid convective heat transfer coefficient in turbulent regime. Also Nusselt number and friction factor were considered in definition of thermal performance factor for all cases are greater than unity which indicate that this Nano fluid enhances the heat transfer without huge penalty in pumping power. Thermal performance factor maximum is obtained 1.32% by 1% volume fraction and between 1.03%~1.20% by 0.5% volume fraction. Also, for Reynolds about 6300, nusselt number have increased by 0.7% volume fraction, about 19.8 percent. Hence, applying the methods studied here could be considered as a good choice in particle application.

In this study, the effect of using louvered strip inserts in heat exchangers on flow and transfer characteristics is numerically investigated. The continuity, momentum, and energy equations have been solved using a finite volume method. The wall of the tube is heated with a uniform heat flux boundary condition. This paper uses a louvered strip insert arrangement (forward) with a Reynolds number of 10,000. The effects of louvered strip slant angle of  and pitch of 50 mm were used for Al2O3 nanoparticles with different volume fractions in the range of 1% to 4% and different nanoparticle diameters in the range of 20 nm to 50 nm, mixed in a base fluid (water) is used. The comparison of numerical analysis results with existing equations has shown a good convergence. The numerical results reveal that the Nusselt number has increased with decreasing the nanoparticle diameter. The results indicate a slight change in the skin friction coefficient when nanoparticle diameters of Al2O3 nanofluid are varied. The Nusselt number increases with increasing nanoparticle volume fraction of Al2O3 /water nanofluid, while it is found that pure water has the lowest Nusselt number value. Also, the nanofluid has reduced the wall's temperature more than the base fluids (water), which indicates the advantage of using nanofluids in improving the system's thermal performance.

In this experimental study, the effect of using a heat exchanger with louvered strip inserts louvered strip inserts on flow and heat transfer utilizing various types of nanofluids is studied numerically. The continuity, momentum and energy equations are solved by means of a finite volume method (FVM). The top and the bottom walls of the pipe are heated with a uniform heat flux boundary condition. Two different louvered strip insert arrangements (forward and backward) are used in this study with a Reynolds number range of 10,000, 15,000, 20,000, 25,000, 30,000. The effects of various louvered strip slant angles and pitches are also investigated. Three different types of nanoparticles, Al2O3, CuO and ZnO with different volume fractions in the range of 1% to 4% and different nanoparticle diameters in the range of 20 nm to 50 nm, dispersed in a base fluid (water) are used. The numerical results indicate that the forward louvered strip arrangement can promote the heat transfer by approximately 77 % at the lowest slant angle of α=10° and largest pitch of S=50 mm. The maximal skin friction coefficient of the enhanced tube is around 5.7 times than that of the smooth tube and the value of performance evaluation criterion (PEC) lies in the range of 1.34–1.57. It is found that Al2O3 nanofluid has the highest Nusselt number value, followed by ZnO, and CuO while pure water has the lowest Nusselt number. The results show that the Nusselt number increases with decreasing the nanoparticle diameter and it increases slightly with increasing the volume fraction of nanoparticles. The results reveal that there is a slight change in the skin friction coefficient when nanoparticle diameters of Al2O3 nanofluid are varied.

Statistical methods are used in the analysis of all types of data. In this paper, using multivariate analysis of variance and multivariate regression, the data related to the thermal conductivity of nanofluids have been analyzed and the results of the two methods have been compared. A two-step method was used to prepare ethylene glycol-magnesium oxide nanofluid. In order to prepare the nanofluid by suspending the nanoparticles in the base fluid, an ultrasonic homogenizer was used. For this purpose, nanoparticles with diameters of 20, 50, and 100 nm in volume fractions of 0.25, 0.5, 0.75, 1, and 1.25% have been used at temperatures of 25, 30, 35, 40, 45, and 50 degrees Celsius. Transient hot wire method was used to measure thermal conductivity in different volume fractions. Then the obtained experimental values were analyzed using SPSS.26 software. The coefficient of determination and the graphs of the errors obtained in the two methods showed that when the independent variables are defined as grouped, the use of multivariate analysis of variance can better describe the dispersion of the thermal conductivity.

Currently, with the growth and development of new heat transfer technologies, it has been used to reduce the time of heat transfer, reduce the size of heating equipment and finally increase the thermal efficiency. In this research, the validity of the organizations of alumina water and titania water converter with separator, shape and middle fin is done in this field. An international solidwork design has been done and a grid has been made in the Ansys network. The input for this purpose is from the input external union and to get out of the external pressure compliance. Out of compliance in software. In the following, taking into account the volume ratio and diameter of nano particles, a continuity equation and an incompressible Navier-Stokes equation for a coordinate system corresponding to the object have been solved using the control volume method. The results indicate the reduction of the friction coefficient with the increase of the Reynolds number. By comparing the heat transfer coefficient between water-alumina nanofluid and water-titanium dioxide nanofluid, it can be seen that the average value of this coefficient is 14% higher for water-alumina nanofluid. On the other hand, the transformation of the heat transfer coefficient of waterdioxatnium nanofluid compared to water-Al nanofluid is more intense than the changes of Reynolds number. Also, with the increase in diameter from 40 to 60 mm in the range of Reynolds number from 3000 to 8000, an increase in Nusselt number was observed. By examining the performance index, it is evaluated that with the increase in the average diameter, a 19.3% increase in the performance index is observed.

In the experimental study, the formation of the annular flow pattern in a vertical pipe with the counter-current two-phase flow has been investigated with the help of image recording and processing techniques. After separating the created two-phase flow regime, the range of superficial velocity of air (upward) and water (downward) is 3.66-20.94 m/s and 0.06-0.31m/s for annular flow, respectively. The interfacial friction factor (liquid and gas phase) has been evaluated according to the hydrodynamic parameters of the flow. Comparing the average deviation of the results obtained from the current research with the previous research shows that the results are in good agreement. Also, the interfacial shear stress has been calculated and evaluated for two test pipes in the center-current two-phase flow pattern in the annular flow regime. In this research, the interfacial friction factor (liquid and gas phase) is also presented as a new correlation depending on the Reynolds number of the gas flow and the Reynolds number of the liquid flow with a coefficient of determination of R2=0.98.

Due to the application of heat exchange equipment such as converters in various industries, improving heat transfer in this equipment is very important. Various methods are used to improve heat transfer. In this paper, the effect of nanofluid and quadruple barrier type barrier on heat transfer coefficient has been investigated numerically with Ansis Fluent software. The nanofluidused is considered as a homogeneous fluid and the effect of increasing the nanoparticle is applied as an effect on the properties of the nanofluid. The heat transfer coefficient for pure and nanofluid water and barriers in different states was obtained and the amount of heat transfer improvement was obtained. The flow inside the pipe was turbulent and The Reynolds number was considered in the range of 5600 to 12000. Simulation for simple tube mode with pure water, simple tube with nanofluid with volume fraction of 0.5%, tube with barrier with 3, 4 and 5 mm offerings with nanofluid with volume fraction of 0.5% The results showed that with the introduction of nanoparticles, the heat transfer coefficient increased by 52.87%. It also showed that the highest value of Nusseltnumber was obtained in 4 mm width of torsional strips. In this case, the increase in Nusselt number compared to the unobstructed mode in Reynolds 12000 increased by 64.58%. The value of the coefficient of friction was evaluated to determine the pressure drop. At the 3 mm width of the barrier, the maximum coefficient of friction was obtained. In this case, the coefficient of friction increased by 14.26% compared to the unobstructed mode.

In the present study, the hydraulic-thermal design and optimization of a gasketed-plate heat exchanger (GPHE) with an objective function of heat exchanger performance index (the amount of transferred heat exchange to pumping power ratio) is carried out. This process is made by considering 6 design parameters (the port diameter, plate thickness, the enlargement factor, the compressed plate pack length, the horizontal port distance, and the vertical port distance) and through the Bees Algorithm (BA). The present study achieved three solution sets for the design parameters by investigating the sensitivity of the design parameters heeded in the optimization of the GPHE. The design parameters in these three optimal solution sets were opted for in such a way that heat transfer increased by 41.6%, 34.55%, and 20.7%, and pressure drop decreased by 11.89%, 27%, and 83%, respectively.

The present paper, heat transfer and flow of shear-thinning non-Newtonian fluids in a circular tube under constant heat flux with a modified twisted tape, have been numerically studied in a laminar, steady-state and three-dimensional regime. The finite volume method was used to numerically solve the governing equations, modified power-law model be used to describe the dependence between the stresses and shear rates. The physical model is a circular tube with a standard twisted tape with decreasing its width, also a hollow tape in circular tube with an increase in the central cavity of the tape. The heat transfer and the overall performance are unfavorable by cutting off the tape edge. Instead, a decrease in tape width ratio, hollow tape with different removal ratios was used to improve thermal efficiency. the numerical results show that the removal ratio (hollow width of the tape divided by the initial width) equal to 0.3 in the fluids with behavioral indexes 0.86, 0.55 and 0.41 can cause 17.95%, 18.49% and 19.69% increase in thermal performance compared to the best thermal performance mode, respectively. Therefore, the hollow twisted tape is a promising technique for laminar convective heat transfer enhancement.

Drilling mud is one of the most important and basic requirements for drilling oil and gas wells. Optimization of drilling fluid properties leads to reduce drilling time and costs. Water-based drilling mud is one type of drilling fluid that is mainly used in drilling wells due to its environmental compatibility. In this research, in order to increase the efficiency of this type of drilling fluid, graphene and silicon oxide nanoparticles in equal weight ratio in water-based drilling mud have been used. This study investigates the effect of different concentrations (0.25, 0.5, 0.75 and 1% volume fraction) of these nanoparticles on different properties of drilling fluid such as plastic viscosity, yield point, gel strength of 10 minutes and 10 seconds, circulation loss of the samples and the coefficient of thermal conductivity are discussed. All rheological properties tests are performed according to the standard (API RP 13B). The transient hot wire method has been used to determine the thermal conductivity of the fluid. The results show that the increase of nanoparticles has a significant effect on the rheological and thermo-physical properties of water-based drilling mud and reduces plastic viscosity (15%), decreases circulation loss of the samples (25%) and gel strength and also increases the thermal conductivity by 16% in the volume fraction of 1%.

The present paper aimed to conduct an experimental study on the hydro-thermodynamic performance of the double-tube heat exchanger using the water-magnesium oxide nanofluid and double twisted tape with three different steps (3.5,5and7 cm).The experiments were performed in the turbulent flow for the Reynolds numbers from 4400 to 16000 and the nanofluid volume fractions of 0.7%and 1.0%.The results were obtained at different flow rates with or without the use of twisted tape and nanofluid designed and manufactured in the experimental setup to calculate the convection heat transfer coefficient.Also the effect of using double twisted tapes at three steps along with the magnesium oxide nanofluid was greater in the higher Reynolds numbers.In the Reynolds numbers 4400,the convection heat transfer coefficient increased about17%for the volume fraction of0.7%and about 29% for the volume fraction of 1%.Also in the Reynolds number of 16000,it increased about48%for the volume fraction of 0.7% and about53% for the volume fraction of 1%.The simultaneous use of magnesium oxide nanofluid and double twisted tapes with the step of 3.5 cm in the Reynolds number 6400 was more effective than deionized water compared to other results.The performance evaluation criteria were examined in all cases and in case of using nanofluid and twisted tape with the step size of 3.5 cm, the highest value of the performance evaluation criterion is obtained with80% increase compared to the base state.

In the present study, the combination of lattice Boltzmann and immersed boundary methods is used to simulate the motion and deformation of a flexible body. Deformation of the body is studied in microchannel with stenosis and the effect of the flexibility changes on its deformation is investigated. The obtained results in the present manuscript show that by increasing the elasticity modulus, the deformation of the body and its speed decrease. In this case, the flow pressure around the body increase. When the body is initially located outside the microchannel center, tank-treading motion occurs due to the difference in velocity of the shear layers. In addition, with a decrease in the size of microchannel stenosis, the body is less deformed and goes faster and reaches to the end of the microchannel in less time. The faster or slower movement of the biological membranes than the normal state causes the proper exchange of materials between the membrane wall and the surrounding flow and that disturbs its most important duty i.e. the exchange of materials with tissues. The analysis in this study shows that the results of the simulation are in good agreement with the available results and demonstrates the efficiency of the combination of lattice Boltzmann and immersed boundary methods to simulate the dynamic behavior of biological membranes, red blood cells and deformable particles inside the flow.

To increase the numerical accuracy in solving engineering problems, either conventional methods on a fine grid or methods with a high order of accuracy on a coarse grid can be used. In the present research, the second approach is utilized and the arbitrary high order Discontinues Galerkin Arbitrary DERivative (DG-ADER) method is applied to analyze the transient isothermal flow of natural gas through pipelines. The problem is investigated one dimensionally and the effect of friction force between the pipe wall and fluid flow is considered as a source term on the right-hand side of the momentum equation. Therefore, the governing equations have a hyperbolic nature. Two real problems with available field data are simulated using this method. The results show that using DG-ADER method, high accurate results can be obtained even on a coarse grid. Furthermore, the conventional small-amplitude oscillations of DG-ADER scheme do not appear in the transient natural gas flow problems, due to the smoothness of flow field properties.