نشریه مهندسی مکانیک تبدیل انرژی
سال هشتم شماره 2 (پیاپی 27، تابستان 1400)

In the present study, the steady-state natural convection heat transfer from a vertical array of a pair of horizontal cam cross-sectional tubes under constant heat flux submerged in water is experimentally investigated. The experiment is carried out for the modified Rayleigh number range of to, and a dimensionless tube spacing range of 1.5, 2.0, and 2.5. The effects of the modified Rayleigh number, cam tube orientation, and dimensionless spacing on the heat transfer rate from the individual tube and the vertical tube array are studied. Based on the results obtained, the effect of thermal plume on the heat transfer rate from the upper cam tube in the vertical array is strongly dependent on the dimensionless spacing. Under fixed conditions, the mean convection coefficient of the single horizontal cam tube with the downward orientation is higher than that of the other orientations for all the modified Rayleigh numbers considered.

In this study, we analyzed the energy, exergy of a multiple energy production system based on geothermal energy. The system under study consists of geothermal subsystems, Rankin organic cycle and PEM electrolyzer and thermoelectric application. The organic fluid used in the Rankin organic cycle contains refrigerant R123. The products of this system produce multiple energy, including electricity and hydrogen. Thermodynamic software for solving engineering equations (EES) was used to model the studied system and also to obtain the results of system analysis. The results were calculated and evaluated using the ambient temperature of Bandar Abbas for the hottest day. According to the studies of the parameters affecting the system outputs, we can name the turbine efficiency, inlet temperature to the evaporator, thermoelectric suitability criterion, pump efficiency and mass flow inlet to the evaporator. The results also showed that the current work geothermal system in a year compared to the ambient temperature of Bandar Abbas can produce 352816.2 kWh of power per year and as a result this system can meet the electricity needs of about 12 Iranian families during the year.

The purpose of this paper is to experimentally investigate the heat transfer of a mixture (free-forced) on a vertical plate under a uniform heat flux with both assisting currents and opposing currents. Heat flux applied to the plate (inversed test design) using number simulation and optimization of thermal element capacities behind the plate has been done. By determining the temperature degree reached to stable temperature degrees and uniform heat fluxes from the plate, heat transfer coefficients we measure by calculation. By performing the relevant experiments and determining dimensionless numbers, Rayleigh, Reynolds and the Grashof show that the results are within the allowable range and the heat transfer flow is mixed convection. Important parameters in flow properties are displayed and analyzed

In this paper, a designate of a small scale solar-wind power plant, integrated with battery storage was performed in order to supply the energy demand of a suburb region of Ahvaz, Iran. The aim of this work was to minimize the expenses by help of Homer software with consideration of the amount of the consumed electricity, solar irradiation and wind velocity for the considered region. To optimize the system, Particle Swarm Optimization (PSO) method was used. The simulation results indicates that in the proposed plan, almost 45% of the costs are spent for purchasing, maintaining and replacing the batteries, while, the portion of solar and wind equipment are 15% and 20%, respectively.

In the present study, the nucleate and film boiling heat transfer of alumina-deionized water and silica-deionized water nanofluids in the presence of microchannel surface has been investigated experimentally. For this purpose, both types of nanofluids with volumetric concentrations of 0.1%, 0.3% and 0.5% were prepared using two-step method. Pure deionized water boiling experiments on polished and microchannel copper surfaces and nanofluid boiling experiments on microchannel copper surface were performed. The results showed that the combination of the presence of nanofluid and microchannel in the boiling process significantly increased the critical heat flux and the minimum heat flux. In the boiling of nanofluids on microchannel surface, the volumetric concentration of 0.5% had the best performance, so that the maximum values of critical heat flux and minimum heat flux for alumina-deionized water nanofluid increased by 93.02% and 105.32%, and for silica-deionized water nanofluid increased by 90.82% and 97.15%, respectively, compared to pure deionized water boiling on the polished surface. In addition, it was observed that with the deposition of nanoparticles on the microchannel surface, the surface wettability increased and the nucleate boiling heat transfer coefficient of nanofluids decreased compared to pure deionized water. But in film boiling, the effects of improving the thermal properties of nanofluids have overcome the destructive effects of nanoparticles deposition on the surface.

A major part of the flow field has no complicated behavior in many laminar & turbulent flows which can use large mesh and simplified governing equation for numerical simulation. In order to reduce memory and CPU time, the flow field was decomposed to several blocks with different size and dimension in each block. A two dimensional backward facing step was considered in this research that used three different type of blocking in numerical modeling. Computer memory and CPU time consumption in addition to numerical result of main fluid parameters. Consideration showed that, suitable combination of used blocks led to the results with the same accuracy as model was employed only one block and experimental results, in addition to the reduction of memory and CPU time consumption.