In this paper, heat transfer and magnetic fields in a vacuum induction melting furnace have been studied numerically. To solve the coupled equations of thermal and magnetic induction heating, the finite element method has been used. An induction furnace model is simulated using an industrial geometry. The studies indicate that the effect of the geometry of the crucible and the coil on the melting time has not been thoroughly investigated and requires more in-depth studies. It is attempted to improve the shape of the induction furnace, so that in less time aluminum is melted in a small scale furnace. The effect of the diameter-to-height ratio of the crucible on the duration of melting has been investigated. By decreasing the diameter-to-height ratio, the temperature reaches melting temperature in a shorter time. The results show that for the diameter-to-height ratio of less than 0.4, there will not be a significant change at the average temperature. 10% reduction in the distance between the coils leads to an increase in the average temperature of the working material inside the furnace. With considering the constant density of the coil current and the constant induced current in the heated material, the effects of the number of coil turns on the temperature distribution and magnetic flux are investigated. In this way, the accuracy of the model is also checked by induction heating concepts. The effect of frequency on temperature has been investigated in different coil lengths. The results show that an increase of 4 times in the frequency caused an increase of 1.7 times in the average temperature.

Magneto-rheological damper is one of the most widely used mechanical equipment, which absorbs mechanical shocks by use of magnetic fluid and electrical coil in its structure. In this paper, for the first time, dissipative particle dynamics as a mesoscopic scale modeling method was used to simulate a magneto-rheological damper and its magnetic fluid. Data from 3 categories including magnetic fluids with brand names 122-EG, 132-DJ, and 140-CG have been used and effect of their physical properties on power of damping force have been investigated. Results of modeling show that by increasing shear rate of fluid, shear stress is first increased and, then, it is applied to a constant value, which results in a greater shear stress by applying a stronger magnetic field. It is also observed that, with increasing both maximum piston velocity and strength of magnetic field, maximum power of damping force increased, which in 140-CG is higher than the other fluids. Results of sensitivity analysis show that weight of magnetic particles and strength of dissipative forces have the greatest effect on damping force, in such a way that by increasing weight of magnetic particles and decreasing the dissipative force of particles, accumulation of magnetic particles decrease, so, increasing quality of damping. It was also found that 122-EG is more suitable than other types of magnetic fluids in forming standard magnetic particle chains, and provides a more favorable viscosity distribution for damping.

Prior to entering to the throttling valve of the City Gate Stations (CGS), high-pressure natural gas flow in pipelines is transmitted through Water Bath Indirect Heaters (WBIH), which is increasing its temperature to compensate for the temperature drop caused by the Joule-Thomson effect and preventing the occurrence of the hydration phenomenon, gas freezing, and subsequent blockage of the gas flow path. Because of feeding of processed gas of the network on a large scale, optimizing the WBIHs has a lot of significance. In the present study, each WBIH is simulated by a type of thermodynamic machine, consisting of two distinct thermal systems. According to the problem geometry and governing equations, the thermodynamic analysis of these two systems results in the formulation of a relationship between their thermal efficiencies together and the definition of a parameter was defined as the Thermodynamic Similarity Coefficient (TSC). Then, the results showed that always, a constant logarithmic relationship exists between of the Number of Heat Transfer Units (NTU) values difference of the fire tube and heat coil of the WBIHs with their TSC as well as a constant power relationship between their NTU values ratio with this coefficient too. Finally, by solving the equation system obtained from these two relations, it was possible to determine the optimal values of NTU for the fire tube and heat coil as functions of TSC of the WBIH and to achieve the relationship between their optimum geometric dimensions together in the most ideal heat transfer state with a maximum relative error of about 13%.

The subcooled flow boiling happens when the bulk flow temperature and the interface temperature are lower and higher, respectively than the saturated temperature corresponding to the flow pressure. One way to increase the heat transfer mechanism is to use high porosity metal foams in the ducts, which have a high surface area to volume ratio that increases the heat transfer surface area and the heat transfer coefficient of the duct. In the current study, an experimental apparatus was constructed, and subcooled flow boiling in an annulus tube was investigated. The annulus tube is in the vertical direction, and the internal and external diameters are 50.7 and 70.6mm, respectively. The operating pressure was 1atm, and the working fluid was water. The metal foam used is nickel with 10ppi and a porosity of 95%. In this investigation, heat flux and mass flow rate effectiveness on the heat transfer coefficient are considered. The experiments were performed in the mass flow rate range of 0.012kg/s to 0.0286kg/s in which the flow consists of both forced convection and flow boiling. The mass flow reduction causes the heat transfer coefficient increment to 30% in subcooled boiling regions. The use of porous media also increases the subcooled flow boiling heat transfer coefficient up to 30%.