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The encounter between bubble pairs can be happened in the bubble flows and may result in coalescence, which is one of the most important elementary physical processes occurring in liquid columns. Sufficient knowledge of the coalescence process of two bubbles can lead to a better description of the bubbly flow’s behavior. Effects of uniform magnetic fields on the interactions and coalescence of dielectric bubbles were not studied up to now; therefore in this research, interactions and coalescence of two bubbles in a viscous stagnant liquid has been simulated numerically. Considered bubbles are spherical and fluids are stagnant, initially. Both liquid and gas phases considered being incompressible and dielectric where applied magnetic field is uniform. In the numerical simulation of the problem, the Finite Volume method was applied using the SIMPLE algorithm to discretizing the governing equations while the finite difference method was used for discretizing of the magnetic field equation. For simulating the interface of two phases, the level set method has been incorporated. The results outlined in the present study well agree with the existing experimental and numerical results. Obtained results show that applied uniform magnetic field affects shape, dynamics and also interactions and coalescence of bubble pairs. Applied magnetic field enhances coalescence between in-line rising bubbles. Therefore, the external uniform magnetic field could be used for contactless control of the coalescence process between bubbles.

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In this study, forced convective heat transfer characteristics of /water nanofluid flowing through a double pipe heat exchanger with plain twisted tape and cut twisted tape inserts is investigated experimentally to reveal the effect of cut twisted tape and nanofluid concentration on heat transfer. Experiments are conducted in a turbulent flow regime with Re number ranging from 4000-34000 and in the particle volume concentration range of 0<φ<0.1%.The results of thermal studies showed enhancement of convective heat transfer with nanofluids compared with flow of water. Also it was found that in higher Reynolds numbers the nanofluid has better heat transfer capability. The effects of twisted tape with and without cuts on edges on heat transfer coefficient and rate were investigated. It was found that the twisted tape with cut edges could enhance heat transfer rate better than twisted tape without cut edges. The pressure drop was investigated for flow of nanofluid and water. The results showed that there is a little difference between pressure drops in these cases. Friction factor and pressure drop in tube with plain twisted tape and cut twisted tape inserts are increased due to increasing flow resistance and contact surface between fluid and flow passage.

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This paper examines the design, manufacture, and analysis a Gamma-type Stirling engine using the solar parabolic collector. The calculation base for designing is so that the size of the solar parabolic collector needed to start the engine is not too large. After finishing the design and manufacturing of the parts, the assembled Stirling engine was initially initiated by a 550W electric heater tested in two non-insulated and insulated conditions for different input power. In the non-insulated state, the Stirling engine has a maximum power of about 68.69W with an output of 12.66%; and insulated mode of Stirling engine maximum watts with an output of 15.72% was obtained. Then we constructed a solar parabolic collector based on the power of the heater used. Designing the collector is such that it has the ability to reflect around 550W. Thus, the diameter of the collector is 1m and its depth is 12cm. This solar parabolic collector provides the power needed by the engine to work during the day. The maximum output power of the solar Stirling engine is about 30W.