The purpose of this study is the 3D CFD numerical modeling of a coaxial borehole heat exchanger. The operating fluid inlet velocity, the groundwater seepage velocity, the soil porosity, and the use of nanofluids instead of pure water are investigated. Ansys Fluent software is used for numerical simulation and the k-ε turbulence model is employed for turbulent flow modeling. The results show that they significantly increase the operating fluid temperature. The presence of groundwater seepage decreases the temperature of the working fluid which is related to the groundwater flow velocity. High soil and backfill porosity affect the thermal performance of CBHE, and increase thermal resistance, and decrease thermal conductivity. The nanofluids utilization with a higher thermal conductivity than pure water increases the temperature growth rate along the outer pipe. Kriging optimization method suggested that the best operating conditions for the system are inlet water velocity 0.03 m/s, groundwater velocity 5 m/d, soil porosity 0.28, backfill thermal conductivity 3.3 (W/m.K) and CuO/water nanofluid. By considering the mentioned operating conditions, the working fluid temperature increases by about 6% at the depth of 60 m.

Proton-exchange membrane fuel cells consume hydrogen and air and have high efficiency and power density. The present study three-dimensionally investigates the performance of PEMFCs with different geometries under different operating conditions. The computational fluid dynamics approach was adopted to solve the governing equations. In CFD, the finite volume method is employed to discretize and solve equations. A serpentine gas injection channel and a parallel gas injection channel of the same size were examined. The proposed approach was validated by simulating the base model at 0.6 V and three reference current densities. The present work primarily sought to improve the performance of PEMFCs. Also, the concentration diagram indicated that the water concentration rose on the cathodic side, implying reasonable water transfer management was reasonable. Moreover, the oxygen concentration declined on the cathodic side. The serpentine model was found to have a higher current density and output power than the parallel model. Liquid water production was lower in the serpentine model than in the parallel model. This prevented immersion and fuel cell interruption. Water accumulation in the middle of the PEMFC with the parallel channel hindered uniform temperature and current density distributions. The parallel model underwent a lower pressure drop than the serpentine model. Therefore, lower power was required to pump the gases through the parallel channel. A rise in the reference current density reduced liquid water production and overpotential and improved the current density distribution and temperature distribution in both serpentine and parallel models.

An Eulerian–Eulerian-based two-dimensional mathematical modeling approach for bubbling fluidized bed gasifier using FLUENT has been proposed to transfer energy, momentum, and mass between two phases namely solid and gas together with the application of the kinetic theory of solid particle flow. The modeling equation involves eight homogeneous and five heterogeneous reactions kinetics. The eddy dissipation model of FLUENT has been used to incorporate homogeneous reaction kinetics and a user-defined code has been developed that describes the kinetics of heterogeneous reactions. The simulation result shows that the exit syngas composition is in line with the experimental one and has a maximum error of around 4.05% for CO and 2.68% for hydrogen. This model has been used to study the variation in hydrogen concentration in the syngas to maximize hydrogen production based on different operating and design parameters.

Today, with the development of technology, heat transfer, reducing the time of heat transfer, reducing the size of heat exchangers, and increasing the efficiency are considered. Heat exchangers have many applications in the industry. Therefore, increasing the efficiency of heat exchangers will increase the overall efficiency of a system and optimize energy consumption by a system. In the present study, the main goal is the study the effects of the gradual changes in the inner tube geometrical configuration on the thermal performance of the double-pipe heat exchanger on the thermal performance using Computational Fluid Dynamics (CFD) methods based on the finite volume method. For validation, the results are compared with the valid results previously presented in the published papers, and there is a very good agreement between them. In addition to the basic model, six different geometrical designs are used for the inner tube, in the form of a flat tube and a nozzle-like tube. After the numerical simulation, the increase in heat transfer and the Nusselt number of flow, pressure drop, thermal efficiency and the performance index were calculated for each model and compared with the base model and other models. The results show that the nozzle-like inner tube model has a lower performance than the base model. The model with a flat inner tube, and especially case 4 (The case with the flat inner tube with the aspect ratio of 0.3), has a very impressive performance compared to the base case at Reynolds numbers below 6000. But at higher Reynolds numbers, the basic model will have better overall conditions.