حسین احمدی کیا

The water consumption of steam power plants is one of the big challenges in the world. One of the suggested methods for reducing water in these power plants is the utilization of forced dry cooling tower. However, these types of cooling towers are dependent on weather conditions and reduced power plant efficiency. One way to solve this problem is to downfall water on it during hot hours. In this article, the forced dry and cooling towers are studied analytically. Then, with the consideration of characteristics of a power plant, the size and characteristics of dry and wet cooling towers are computed according to design temperature. These results are compared with experimental data and wet cooling towers of a power plant, and their accuracy has been verified. Only at temperatures higher than the design temperature is water falling on the tubes and fins of cooling tower. Using data from the weather station of power plant location, the numbers of hours when the ambient temperature has been higher than the design temperature are calculated and water consumption is computed. Calculations show that for a power plant of 320 MW at design temperature of 30°C, ninety seven percent (97%) of the water consumption can be saved. The loss of power output due to the use of dry cooling tower electric fans and pumps is 3.93 percent of output power.

cryosurgery is a minimally invasive treatment that uses low temperature and freezing for ablation the disease tissue from healthy tissues. Due to the addition of nanofluid in disease tissue, It significantly improve freezing efficiency of a conventional cryosurgical procedure. In this study, the effect of different nanofluid and volume fraction of them in heat transfer will be shown. The difference between the Fourier and non-Fourier temperature equation will be shown and for evaluation the effect of nanofluid on the solidification, used the non-Fourier equation. The enthalpy method applied for phase change temperature equations. The results show that with the addition of nanofluid into the tissue due to the increase in the thermal conductivity, its increase in cooling progress and at the same time, the temperature at each point has a smaller value in compared to non-nanofluid. Nanofluid also led to increased in cooling rate (an increase of more than 40 percent by injecting nano-Ag) and thereby further damage to the tumor. It also will be shown that if the thermal conductivity of nanoparticles or nanoparticle concentration increase in the tissue the heat transfer rate increases and therefore make lower temperature tissue and this will lead to further damage to the treated tumor.

Wet cooling towers have a high cooling capacity. However, owing to consumption of large water quantities in wet cooling towers, using them in arid regions facing water resource crisis might cause operational problems. In this research, changing the wet cooling tower of unit 5 of Isfahan Islamabad power plant into a hybrid cooling tower, using parallel path wet/dry configuration is studied. The hybrid cooling tower with the recommended configuration causes minimal changes in the other power plant facilities and has a low construction cost. Two different airflow control systems are investigated for the wet and hybrid cooling towers. In the first system, the amount of airflow rate in the cooling tower is adjusted by means of switching tower ID fans on or off. In the second system, an optimum airflow control mechanism with high-tech fans is devised. The results reveal that the optimum airflow control system is more suitable than the other system, due to less water consumption, preventing the sudden fluctuations of airflow and consequently water consumption rates and less fan power consumption. Experimental data and results obtained by the HTFS software are used for validating the simulated results of the wet cooling tower and air-cooled heat exchangers, respectively. The results demonstrate that the annual amount of water conservation due to changing the wet cooling tower into hybrid tower is approximately 343830 and 348718 cubic meters for fan switching and optimum airflow control systems, respectively.

Using of dry cooling towers or hybridized dry-wet towers is one of the well-known solutions for this purpose. In this paper, dry Heller cooling tower was combined appropriately with existing wet cooling tower to reduce the water consumption. Simulation of dry Heller cooling tower of Shahid Montazery power plant and wet forced counter flow cooling tower of Isfahan power plant was performed. Two cases of parallel and series for combination of dry and wet cooling towers was considered. The results of simulation and analysis of executive methods show that parallel use of Heller tower with wet tower is not reasonable. But series case in various ambient temperatures in two situations of changing pump system and without changing it was recognized appropriate. It was shown that there was no need for changing the pump systems and condenser works in continuous desirable condition. Water saving is full for ambient temperature below 20oC, but in more ambient temperature water saving trend is decreasing.

In this study، classical and generalized dual phase lag bioheat transfer models are applied for investigate thermal damage to skin tissue exposed to the transient heat flux. The analytical bioheat transfer analysis with transient heat flux on skin tissue has only been studied by Pennes and thermal wave models. This paper، for the first time، provides the analytical solution of the dual phase lag model in skin tissue under transient surface heating using Laplace transform method and inversion theorem. Since the dual phase lag model under certain circumstances reduces to the Pennes and thermal wave models، comparisons of the temperature responses and thermal damages between the these three models are carried out. The influence of porosity factor and coupling factor between blood and tissue on the thermal damage of tissue is investigated and the results demonstrate that increases in these factors respectively leads to the higher and lower tissue thermal damage and the effects of these factors on the thermal damage in the depth of tissue is lower than near the surface.

In this study، convergent nozzle ejector in the PEM fuel cell system is analyzed. This method can reduce the parasitic power of the fuel cell، recycle the unconsumed hydrogen to the fuel cell to increase the fuel usage efficiency، utilize the pressure potential energy of hydrogen and regulate the anode humidity with the recycle gas. For this purpose، continuity، momentum، energy and state equations are solved by numerical methods and effects of pressure drop (through the channel towards the anode)، operating pressure and temperature of the fuel cell and also nozzle diameter on the ejector performance was analyzed. With decreasing of pressure drop، even in primary lower pressure، increasing of performance pressure the performance of ejector will improved. The temperature increase has no effect on the performance of the ejector itself، but has enormous effect on the fuel cell. Increasing the diameter ratio of the constant diameter zone to the nozzle diameter leads to increasing of recirculation anode line of the fuel in higher pressure.

In this paper the shaped charge and its analysis methods are introduced and explosion process, liner collapse and jet formation are simulated using LSDYNA960 software. After making sure about the correction of the simulation process and its results, the effects of the main parameters of the shaped charge on the jet properties are investigated. The results of this study show that decreasing the liner apex angle and increasing the detonation velocity of the charge increase the jet velocity. Also decreasing the thickness of the liner near the apex leads to an increase in the jet velocity. Using an appropriate case for the shaped charge also increases the jet velocity about 10%. The results of the simulations are in good agreement both with analytical results and the results of the simulations done by other researchers.

Unsteady laminar and turbulent supersonic flow of discharged projectile from tube has been numerically simulated. The equations of axisymmetric viscous and compressible flow has been numerically solved by van leer flux vector splitting method, with time and space second order accuracy by using moving boundary. When projectile is discharged from tube the complicated flow in front and back of projectile is created. This flow includes types of expansion and shock waves. Complicated intractions between these waves make analysis of this flow difficult. The numerically simulation could predict expansion wave, bow shock wave in front of projectile, barrel shock wave, mach disk, vortex ring, shear layer well. Results show that, there isn’t difference between both laminar and turbulent flow arrangment, but the aerodynamic forces in both of them (laminar and turbulence) is different. The variation of acceleration and aerodynamic forces, when projectile is discharging from tube, due to more intractions between expansion and shock waves, was very much and caused the vibration of projectile and if it is lightweight, this vibration will change its path. While projectile starts to discharge from tube, the acceleration will be maximum but when the entire of projectile discharges from tube, the resistant force is increased and the acceleration is decreased.

This paper reports the numerical study of the flow field arised form impinging of a supersonic moving jet on a solid wall. The flow properties, such as surface pressure distribution are compared with the experimental data for a quasi-static case. The results show that when the distance of the nozzle from the wall is not too small, the quasi-static result is very close to that obtained from an unsteady solution. Also a new combined algebraic turbulence model is proposed for the calculation of eddy viscosity near the solid wall and the shear layer. The new combined model can suitably predict the flow structures, such as the separation region behind the nozzle, the expansion waves at the nozzle exit, the recirculating flow region near the wall, the vortices near the nozzle lateral face, and the transition of regular reflection to a Mach disk at the symmetry axis. For quantities such as the position of Mach disk, the height of the stagnation bubble, and the pressure peak on the surface, the results of the combined model is also in a better agreement with experiment than those obtained from the two-or one-equation models.