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Developing the high performance electrical devices requires high capacity heat transfer manners, which could be the pulsating heat pipes (PHPs). PHPs have a better performance in compare with conventional heat pipes (HPs), besides, they can be used to improve cooling systems for electrical devices, in future. There are some other applications for PHPs in other industries as heat transfer converters, either. The effect of the evaporator’s length on the PHPs’ performance is investigated experimentally by hiring a five turns PHPs and ferrofluid as set-up and working nanofluid, respectively. The results show that PHPs’ performance is enhanced by increasing the evaporator’s length.

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In this research crack size and location in pipes under fluid pressure will be detected using pipe’s natural frequencies by neural network. Neural network used in this research is multi-layer perceptron. Comparing different inputs, appropriate inputs are selected. Pipes contain water. Steel and aluminum pipes were used in this research. Pressure condition of the pipes is: 1) without water 2) water with zero pressure 3) water with 0.498 MPa 4) water with 0.981 MPa. Crack size range from 0.19043 to 0.6346. Crack location range from 0.199 to 0.403. Many researches have been done about crack detection based on natural frequencies of structures by neural network. However, as far as authors know, no work has been done for crack detection in pipes containing pressurized water. Also in this paper two structures with different materials have been used for neural network training and testing which is another innovation of this research. Comparison of the results of this method with analytic methods shows that the proposed method is always more accurate in detecting crack size but is not always better in estimating crack location.

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This paper investigates the vibration behavior of fluid conveying viscoelastic pipe rested on non-uniform elastic Winkler foundation. The Kelvin-Voigt model is employed to consider the viscoelastic behavior of the pipe. Using the Galerkin’s method, the eigenvalue problem for the simply supported fluid conveying viscoelastic pipe is extracted. The effects of the fluid velocity, the viscoelastic constants and the foundation parameters on the complex eigenvalues and the divergence and the flutter instability of the fluid conveying viscoelastic pipe are studied and discussed. It is found that including the viscoelastic behavior to the pipe material alters the trend of the instability of the fluid conveying pipe, i.e., the first and the second modes divergence and the coupled mode flutter for the elastic pipe change to the first mode divergence, the second mode flutter and the second mode divergence for the viscoelastic pipe, respectively. The structural damping causes the velocity of the divergence instability at the higher modes to be increased. Also, because the viscoelasticity of the pipe affects the different vibration modes in different manner, therefore, the pipe dose not exhibit a coupled-mode flutter. Moreover, the non-uniformity of the foundation stiffness alters the first divergence velocity. The results are verified through comparing them with those reported in the literature.

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In the present study, flow regimes of co-current, air-water two-phase flow in a vertical tube with 70 mm internal diameter were investigated. Simulation accomplished by open source software, OpenFOAM, and One Fluid model has been used to simulate two-phase flow, which in this model, the interface of two-phase flow has been followed by Volume of the Fluid model. Hitherto, most of the researchers conducted experimentally and the researchers in many of numerical studies just investigated the small tubes. The simulation had investigated according to boundary conditions of the vertical tube. Air and water superficial velocities in inlet and pressure in outlet were constant. Moreover, a no-slip condition in the internal tube walls has been considered. The main purpose of this study is to identify the flow regimes based on the superficial velocities of air and water in the inlet. Moreover, the diagrams of density distributions of phases were obtained, with respect to the behavior of each two-phase flow pattern which can be identified. Superficial velocity of air and water were in the range of 0.01-15 m/s and 0.1-1.5 m/s, respectively. By analysis of results, bubbly, slug, churn and annular regimes; furthermore, semi-annular and Cap-Bubbly sub-regimes were observed.

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Accurate prediction of the sediment load is one of the important issues to water engineering. Due to complexity of sedimentation phenomenon and influence of various parameters on estimation of sediment transport rate, determining the governing equations are difficult, and classical mathematical models are not sufficiently accurate in this regard. In the present study the applicability of Gene-Expression Programming (GEP) for modeling bed load discharge in sewer pipes with different boundary conditions was assessed (i.e. fixed and movable beds). Therefore different input models based on theoretical concepts were defined for each boundary condition. In order to develop the models, under two scenarios, different input combinations were considered, first scenario (Scenario1) which uses only hydraulic characteristics and second scenario (Scenario2) which uses both hydraulic and sediment characteristics as inputs for modeling bedload discharge. The sewer pipes experimental data available in the literature were applied for training and testing the employed GEP. For evaluating the efficiency of the models three statistical indexes which called: Determination Coefficient (DC), Correlation Coefficient (R) and Root Mean Square Errors (RSME) were used. Then the accuracy and capability of several available bed load formulas such as Ackers, Neilsen, May, Mayerle and Laursen were investigated and compared with GEP- best modes in each boundary. Also with considering this point that may there is no information about bed boundary condition and for evaluating the applicability of applied technique for a wide range of data; all data series of sediment transport were combined. Then, for predicting Cv, as the dependent variable, several models of Scenarioa 2 analyzed for the combined data. The obtained results confirmed the efficiency of Gene-Expression Programming method for estimation sediment discharge in sewage pipes, and proved this method superior to the semi- theoretical relationships. According to the results it was found that in scenario 1, for all of the cases, model (IV) with input parameters of Fr and y0/D presented better performance than the others models, however it was observed that Scenario 2, which took advantage of both hydraulic and sediment parameters as inputs for modeling sediment discharge in sewer pipes performed more successful than Scenario1 which used only combinations of hydraulic parameters as input variables for models. Comparison between the results of separate data sets and combined data set revealed that analyzing data sets separately led to more accurate outcome. According to the results from fixed beds, it was found that adding Frm and d50/y as an input parameter increased the accuracy of the models. For both smooth and rough beds, the model with input parameters λs, Frm, Dgr, d50/y presented better results from the RMSE, R, and DC viewpoints (i.e. highest R and DC and lowest RMSE). For movable beds condition in the two cases of separate dunes and continuous loos bedform, the model with input parameters of ys/D, Frm, Wb/y0 showed more accuracy. This model showed the influence of flow depth and width and depth of movable bed in estimating of bedload transport in sewer pipes. For loose beds Frm has dominant role than other parameters.

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Welding residual stresses decrease designing stress in natural gas transmission pipes with large diameter under high internal pressure. The outside diameter and wall thickness of API X70 steel in this research are 1423 and 19.8 millimeter. Hole drilling is the most common technique in order to measure residual stresses. Because of large diameter of this pipe, its transportation to conduct hole drilling test is a big problem so cutting a finite sample is desired. In this study standard dimension of this sample plate is analyzed and simulation of welding process is done from which and residual stresses in different directions are obtained. Residual stresses in the thickness direction is presented for the first time. The results showed separating a finite sample with the size of 320×440 millimeter is appropriate to do hole drilling test. The location and amount of the maximum residual stress is evaluated and compared for both simulation and experimental samples. Variation in hoop and longitudinal residual stresses on both internal and external surfaces of pipe samples are investigated. Also validation of simulation results with the experimental results of the same pipe is perfomed. Maximum residual stress (460MPa) is measured on inner surface of the pipe (96 percent of yield stress) which is reduced to 200MPa (42 percent of yield stress) after hydrostatic test. Because residual stress after hydrostatic test is lower than half of yield stress, hole drilling technique is validated after hydrostatic test.