آرش کریمی پور

The target of this research is to investigate the amount of entropy production during natural convection inside a 2D chamber containing a non-Newtonian nanofluid using the lattice Boltzmann method. The chamber is exposed to uniform heat absorption/production and uniform and non-uniform magnetic field at different angles. The feature of the present work is to evaluate the effect of thermal radiation and the shape of the cavity cold wall in three shapes: smooth, curved and diagonal on the flow characteristics. Application in the design of electronic coolers and solar collectors is one of the practical cases of this numerical research. Acceptable agreement of the obtained results with previous related studies confirmed the validity of the presented results. Based on the results, the presence of radiation parameter leads to the improvement of heat transfer, which is more evident due to the increase of fluid power-law index. In addition to reducing the Nusselt value for enhancing the fluid power-law index, the effectiveness of the presence of the magnetic field in reducing the entropy and heat transfer rate enhances as the fluid power-law index decreases. It is feasible to attain the flow strength and the Nusselt value up to 40% and 61% more, respectively, by applying a vertical and non-uniform magnetic field. Although for heat production mode, there will be the lowest value of thermal performance index and the Nusselt value, the greatest influence of the magnetic field is observed in the heat production mode. By designing the wall in a smooth shape, in addition to increase the thermal performance coefficient, it is possible to decline the Bejan value.

Optimization and economization of processes and structures have been considered from time immemorial and many things have been done to achieve this goal. Protecting the environment and reducing the amount of waste material in nature is very important. Today, the problem of using recycled materials resulting from the destruction of buildings and the reuse of these materials in the construction of concrete has been considered. In this research, the shear behaviour of concrete beams manufactured with recycled coarse aggregate was studied. 9 concrete beams with a cross-section 150 mm wide and 200 mm high and a length of 1500 mm manufactured and tested. Recycled aggregate from building demolition was used at 0%, 50% and 100% mass replacement of natural aggregate. Specimens underwent a four-point bending test. In this test, the shear capacity, maximum deflection at the mid-span of the specimens and tension strain were measured. The determination of the shear behaviour of recycled aggregates concrete beams according to transverse reinforcement spacing was the aim of this study. The results were also compared with ACI, CSA and Eurocode 2 requirements. According to the test results, it was found that there is a significant difference in the shear behaviour of recycled and natural aggregate concrete beams

In this research, the effect of adding 0\% and 2\% volumetric percents of steel fibers in beams containing three patches (43 cm, 34 cm, and 26 cm in length) and recycled aggregate 0 and 100\% on the cracking and expansion path. The cracks were examined under static loading. The purpose of this study is to reduce the minimum crack width for adding steel fibers to reinforced concrete beams made of recycled aggregates and tensile reinforcement patches. Hence, twelve specimens of the beam were made at 150, 200, 1500 mm lengths with a length of different tensile adherence rates and different percentages of steel and recycled aggregates. The experiments were performed as a quadrilateral bend. In experiments, the load-displacement curve in the middle of the span of the specimens, the trajectory expansion along the beam and at the maximum flexural anchor, the width of cracking, and the effect of adding steel fibers on the compression and elongation of the specimens were indirectly investigated. In addition, the results were compared with those presented in the ACI, CSA, NS, CEB FIP, and EuroCode2 regulations. The results of the experiments showed that the addition of steel fibers reduced the slip of the tensile reinforcement in the patched area and decreased the crack-cracking width. Also, with addition of steel fibers in beams made of 2\% recycled aggregate, the patch length can be reduced by 40\%.

Considering the importance of controlling the behavior of structures against lateral loads such as earthquakes, the use of dampers in structures is needed to control and improve the structural responses. In this study, the effect of rotational, viscous, and TADAS frictional damper on the behavior and responses of the 8-story steel frame structure with residential use in Mashhad was investigated. These structures were compared in two cases equipped with a damper and without a damper. Seismic earthquake history was used to apply earthquake force. The history of the earthquakes used was obtained by squared squares method and was matched with the soil type 3 soil. Then each of the structures was studied under the analysis of nonlinear time history in SAP2000 software. In this study, the maximum story displacement, the basic shear and the hysteresis curve of each floor were evaluated to determine the effect of dampers on the behavior of the structures. The results of the investigations show that in the study of the structure equipped with the damper, the specifications of the dampers should be based on the behavior of each floor and the adjustment of the damper according to the overall behavior of the structure is inappropriate.

In this research, the effect of recycled aggregates obtained from the demolition of the old building on the preparation of concrete mixtures has been studied. The purpose of this study was to determine flexural behavior, flexural strength in reinforced concrete beams made of recycled aggregate. In the production of samples, recycled aggregates are used with 0%, 50% and 100% natural aggregates, respectively. The samples were tested for static quadrilateral bending and tested after 28 days of experiment. Therefore, by examining the results of laboratory studies, the flexural behavior of RC beams with the expansion of the recycling has been investigated. In addition, the results are compared with the relationships provided by ACI318, CSA and EuroCode2. The results obtained from this review show that by adding the ratio to the recycled aggregate substitute, the amount of net bending size at the criterial level increases and, with the expansion of the crack extending to the place of loading, the load is released flexibly. In addition, the use of 100% recycled aggregate increases the shape and flexural strength of RC concrete beams.

In this research, the effect of steel fibers on flexural cracking of fiber reinforced concrete beams with lap-spliced bars under static and loading/unloading cycles was investigated. Ten specimens of laboratory beam with the section width of 150mm, height of 200mm and length of 2300mm and with different splice lengths of tension rebars and different percentages of steel fibers were manufactured and tested. Four specimens were subjected to static loads and six specimens were subjected to loading/unloading cycles. Among the specimens, one was selected as the control specimen without having lap-spliced bars and steel fibers. Other 9 specimens were made using steel fibers with different volumetric percentages of 0, 1 and 2. The specimens were conducted under four-point bending tests. It was shown that the flexural crack width in beams decreases with increasing the volume percentage of steel fiber, significantly. Steel fibers in specimens subjected to static loading and loading/unloading cycles increased the energy dissipation.

This paper numerically examines the laminar forced convection of a water–Al2O3 nanofluid flowing through a horizontal rib-microchannel. The middle section of the down wall microchannel is Affected by cold temperatures with a constant and uniform tempreture Tc. The middle section is also influenced by a transverse rib array. The effects of height rib in a two dimensional rib-microchannel on flow and heat transfer parameters of laminar water-Al2O3 nanofluid are investigated. The characteristics of this research are numerically investigated by the commercial software Fluent 6.3 in a Reynolds number as Re=10 and Re=100. Four different states of hight rib are analyzed. Higher conventional internal ribs or increasing the turbulators can significantly improve the performances of the convective heat transfer within a microchannel. It is seen that larger height rib and volume fraction of nanoparticles corresponds more heat transfer rate; however the added high ribs can cause a larger friction factor than that in the corresponding microchannel by constant height rib. At present article the effect of height rib on the fluid flow parameters are also studied for all different states of it. The results show that the microchannel performs better heat transfers at higher values of the Reynolds numbers. For all values of the Reynolds numbers and volume fraction of nanoparticles considered in this study, the average Nusselt number on the middle section surface of the microchannel increases as the solid volume fraction increases.

This work presents a model for calculating the effective ýthermal conductivity of nanofluids. The proposed model ýincludes the effects of nanoparticles and thermal conductivity ýbase fluid.We will focus on experimental of the volume ýconcentration parameter and temperature on thermal ýconductivity, nano-fluid combination and Multi-Walled ýCarbon nanotubes-Oxide / Copper-paid deionized Water. This ýwater-based nanofluids, For two-step volume fractions of the ýý0.1, 0.2, 0.6 Percentage produced And then, Effective thermal ýconductivity is measured precisely. In order to measure the ýthermal conductivity of nanofluids. To measure the thermal ýconductivity coefficient in THW method, KD2-pro and KS1 ýprobe was used, also with the fluid significantly enhancement ýshows in thermal conductivity coefficient. Also with the fluid ýsignificantly enhancement shows in thermal conductivity ýcoefficient. In lower volume fractions we observed ýsignificantly increase in thermal conductivity and receive high ýdegree thermal. Due to the lack of similar studies Due to the ýlack of similar studies to comprehensively and inefficient of ýclassical thermal conductivity, In order to estimate the thermal ýconductivity of nanofluids An empirical model that estimates ýthe thermal conductivity of nanofluids model with deviation ýmargin is very lowþþ.

At present study the flow and heat transfer of Non-Newtonian nanofluid, aqueous solution of carboxymethyl cellulose-Aluminum oxide with different volume fractions of nano particles in a two dimensional microtube is simulated for the first time. Slip velocity and temperature jump boundary conditions are also considered along the microtube walls. The achieved results accuracy is investigated by comparison with those of previous data. The results are presented as isothermal contours, Nusselt number and the profiles of temperature and velocity at different cross sections of the microtube. It is observed that Nusselt number increases with slip velocity coefficient and volume fraction of nano particles; while its rate is more sensitive at higher values of Reynolds number.

Given the need to increase the efficiency of heat transfer in thermal systems, especially systems using nanofluids in microscale and nanoscale heat transfer equipment ideas to improve their performance is very good.In present study, the flow and heat transfer of Water-Cu nanofluid in micro-tube with slip regime with constant wall heat flux numerically simulated with low Reynolds numbers. Slip velocity and temperature jump boundary conditions are also considered along the microtube walls, for first time. The results are presented as the profiles of temperature and velocity. Nusselt number and pressure drop coefficient calculated in interance and full developed region. The effect of slip and using nano particle considerd.
It is observed that Nusselt number increases with slip velocity coefficient and pressure drop coefficient decreases; att intrance region the Raynolds of flow has effect on Nusselt and pressure drop coefficient,too.
Likewise observed nano particle adding to water has low effect to increases Nusselt number and pressure drop coefficientt.

This research is experimental study of emperature and volume fraction effects and provide a new model for nanofluid viscosity of Multi Wall Carbon Nano Tubes-Ethylene glycol. Multi Wall Carbon Nano Tubes viscosity with 1 to 2 nm diameter in Ethylene glycol is calculated at 30° C to 60° C and in the volume fractions of 0.025 to 0.3 using by viscometer. Type of viscometer is Brookfield and model is DV-I Prime. It is observed that the viscosity decreases while temperature is increasing and at high volume fractions the nanofluids, shows non-Newtonian properties. Because there has not been done studies on the nanofluids, new equation for the first time of viscosity is obtained and Einstein and Bachelor models are compared with empirical relationships and In addition to observing the similarities, a separate formula for the Newtonian offered. It should be noted that non-Newtonian case study in this paper is not considered.

In this research, effect of nanoparticles dimeter on free convection of aluminum oxide-water was investigated in a cavity by single phase and two phase models. The range of Rayleigh number is considered 105-107 in volume fractions of 0.01 to 0.03 for nanoparticles with various diameters (25, 33, 50 and 100 nm). Given that the two phase nature of nanofluids, necessity of modeling by this method is increasing. Single phase approach (in contrary of two phase) for nanofluids is based on that the behaviors of each two solid phase (nanoparticles) and liquid phase (base fluid) are completely similar. In this study, Eulerian-Eulerian approach and mixture model was used given that Brownian motion and thermophoresis effects. Brownian motion and thermophoresis creates under influences of volume fraction gradient and temperature gradient, respectively that cause to creating slip between nanoparticles and base fluid; thus, kind of non-uniformity creates on behavior between nanoparticles and base fluid. This non-uniformity leads to significant effects on results of two phase modeling that creates better agreement to single phase modeling with experimental results. Results indicate that heat transfer decreases with increasing diameter and volume fraction of nanoparticles. Also, effect of nanoparticle diameter on flow and heat transfer is tangible.

Due to the increasing demand for using polyethylene pipes in gas distribution networks and regarding the technical specifications of transmission and suitable service condition as well as ease of implementation and installation, these materials are considered as ideal substitutes for metal pipes. Regarding the safety and economic aspects in PE (polyethylene) pipe networks before and during the operations, technical inspection is highly required. Examinations have a significant role in the safety and proper function of gas distribution PE pipes tests, because of the damage of the products and excessive costs and time are not usually affordable. Consequently, the mentioned tests are nowadays being replaced by non-destructive types and admissibility of various industries gas company in these methods is increasing. Electrofusion is a proper and fundamental technique for connecting PE pipes. In this research, the mechanism of electrofusion tapping saddle polyethylene welding has thoroughly been studied and simulated using ABAQUS software. Thermal equation of electrofusion is investigated and the results of simulation as compared with experimental results have been evaluated based on which the best qualified methods for connection have been determined and presented.

Mixed convection of free and force convection heat transfer in an inclined lid driven two dimensional enclosure is studied by using Lattice Boltzmann method (LBM) in different values of inclination angle، Richardson (Ri) and Prandtl numbers (Pr). At present case، the velocity components will be affected by inclination angle، force and free convection movements. To do this، using LBM equations are modified. Comparing present results with those of other available ones implies appropriate accuracy. Results are shown as velocity، temperature and Nusselt number profiles and contours of isotherms and streamlines. It is seen that more Pr corresponds to more heat transfer rate especially at higher values of inclination angle and Ri. As a result، to estimate the averaged Nusselt number، a correlation based on Pr، Ri and inclination angle is presented. Moreover، it is seen that the averaged Nusselt number at the upper limit of the considered range of inclination angle، Richardson and Prandtl numbers variability increases by a factor of 7.

A numerical investigation of laminar mixed convection heat transfer in a shallow two-sided lid driven rectangular enclosure of aspect ratio 5, (AR=5) is executed. The natural convection effect is sustained by subjecting the bottom wall to a higher temperature than its top counterpart. In addition, the two horizontal walls of the enclosure are moving in different directions and the two vertical walls of the enclosure are kept insulate. Discretization of the governing equations is achieved through a finite volume scheme. Fluid flow and heat transfer characteristics are examined in the domain of the Richardson number and Grashof number as and while the bottom side of enclosure is moving in two different horizontal directions. The working fluid is assigned a Prandtl number of 0.7, 10 and 100 throughout this investigation. Temporal variations of streamlines, isotherms, and Nusselt number are presented in this investigation for various pertinent dimensionless groups

A numerical investigation of unsteady laminar mixed convection heat transfer in a lid driven cavity of aspect ratio of 5 is performed. The forced convective flow inside the cavity is attained by a mechanically induced sliding lid, which is set to oscillate horizontally. The natural convection effect is sustained by subjecting the bottom wall to a higher temperature than its top counterpart. In addition, the two vertical walls are kept insulated. Discretization of the governing equations is achieved through a finite volume method. Fluid flow and heat transfer characteristics are examined in the domain at Richardson number, Grashof number and dimensionless lid oscillation frequency of:, , and S=0.001, 0.01, respectively the working fluid is assigned a Prandtl number of 0.7 throughout this investigation. Temporal variations of streamlines, isotherms, and Nusselt number are presented for various dimensionless groups. The results show that with decreasing the value of oscillation frequency, while Ri<1, the amplitude and the period of the rate of heat transfer oscillations increase.