نشریه علوم کاربردی و محاسباتی در مکانیک
سال سی و سوم شماره 1 (بهار و تابستان 1400)

Geothermal sources are one of the renewable heat sources. In the present study, at first, the feasibility of using a superheated Kalina cycle to generate power by geothermal sources in Iran has been investigated. Using thermodynamic and thermoeconomic analyses, the effect of operating parameters including turbine pressure and water-ammonia concentration on the performance of the superheated Kalina cycle at a heat source temperature of 170˚C has been investigated. The results show that at a heat source temperature of 170˚C and a concentration of 65%, the highest net power of cycle occurs at turbine pressure of 28.33 bar and the lowest exergy cost of power generation happens at the pressure of 19.44bar. Also, at a constant pressure of 22 bar, the maximum net power and minimum exergy cost of power generation occur at the concentration of 66% and 70.33%, respectively. Finally, minimizing the exergy cost of power generation was selected as the objective function and the values of turbine pressure and water-ammonia concentration were optimized simultaneously using a genetic algorithm. Eventually, in order to achieve maximum performance, for different temperatures of geothermal sources in Iran optimal values of pressure and concentration were introduced in a table.

This paper investigates and studies the vanes of radiometric pumps. An example of a radiometric pump is the Crooks radiometer, which consists of an airtight glass bulb containing a partial vacuum, with a set of vanes mounted on a spindle inside. One side of the vane is white, and the other side is black. In this study, for the first time, a mechanism to measure the temperature directly from hot and cold blades is considered. It is observed that the measured force is proportional to the temperature difference between the two blade ends, and this proportionality is linear. But this relationship is only valid up to the maximum temperature difference. The angular velocity of the blades was also measured by a laser tachometer. The measured velocity is used to calculate the force. This study has been performed in three parts. Part 1 (Laboratory): Designing and constructing a radiometer with different types of vanes. Part II includes the study and review of radiometric flow analysis and theories related to radiometric force. In the third part, a comparison of laboratory results and theories is reported. The tests were performed at four working pressures of 30 pa, 6 pa, 0.6pa, and 0.06 pa. These pressures represent the Knudsen numbers of 0.05, 0.1, 1 and 10 and different flow regimes, respectively. Maximum forces were observed at a pressure of 6 pa and maximum velocity at 0.6 pa, which is in a cooperative agreement with the theoretical data.

Employing large windows in the modern buildings is one the most popular approach among architects and buildings designers but the increase of energy consumption of the building due to down draught effects caused by large windows is one of the challenges against this type of design. Also, preventing of utilizing traditional heating system adjacent to the window is another concern of the approach. In this study, the use of forced convection heating system to mitigate the down-draught effects is simulated by computational fluid dynamic method for three different configurations of the warm air registers mounted (a) under the window; (b) alongside walls and (c) in mixed form under and above the window. The results were investigated by comparing air temperature and velocity distribution in the space and also the thermal comfort conditions were analyzed through Fenger model. The results showed that the third configuration of the inlet registers which they are installed beneath and above the window, is in satisfactory concord to ASHRAE standards and ISO 7730 such that at ankle and breathing height of sitting and standing position, the comfort condition indexes are in regular range of the standards.

In this paper, the problem of perforation of the human cranial bone surface in the shape of a hemisphere using a water jet is numerically simulated in three dimensions. The simulation involves both the flow and heat transfer of the impinging water jet, and surface perforation process. The volume of fluid method was used to model the jet two-phase flow, and Johnson-Cook equation in finite element method was applied for perforating the bone surface. The obtained results show that the pressure and friction coefficients on the surface depend on the nozzle distance from the surface, and the pressure at the stagnation point increases as the nozzle distance decreases. Also, by increasing the nozzle distance, local Nusselt number along the hemisphere radius as well as maximum Nusselt decreases at the stagnation point. The effect of nozzle diameter on pressure and friction coefficients was also investigated and found that the pressure at stagnation point is increased by the nozzle diameter. The change in the jet velocity also showed that a 20% change in velocity has no significant effect on the pressure and friction coefficients, while increases the Nusselt number. In modeling the perforation process, actual properties and coefficients of bone material, such as Poisson's coefficient and Young's modulus were used. Comparison of on-site stress distribution based on Tresca and von Mises criteria showed that according to the proposed parameters, the perforation is performed properly.

Today, the Dual-throat Nozzles are known as one of the most effective approaches for fluidic thrust vectoring. The present study investigates the performance of a dual throat fluidic thrust-vectoring nozzle. The impacts of fuel secondary injection on performance parameters including discharge coefficient, system thrust ratio, pitch thrust-vector angle, pitch thrust-vectoring efficiency, thrust-to-mass-flow ratio and thrust-loss percentage are presented. Injection of seven different fuels including methane, ethane, propane, octane, diesel fuel, kerosene and gasoil have been investigated. Both reacting and non-reaction conditions have been studied. The results show that heavier fuels provide higher discharge coefficients. On the other hand, light fuels have higher thrust ratios. In the non-reacting conditions, diesel fuel and octane have the largest thrust-vector angle,. In general, light fuels offer a better performance in terms of thrust ratio, thrust-vectoring efficiency and thrust-to-mass-flow ratio, whereas heavy fuels have a better performance in terms of discharge coefficient, thrust-vector angle and thrust-loss percentage.

In the present study, the cooling of a pack of lithium-ion batteries in micro-channel heatsink with wavy microtubes was investigated in the presence of silver/water-ethylene glycol (50:50) nanofluid. ANSYS FLUENT software and SIMPLE method are used to solve the equations and coupling of velocity and pressure fields. The results show that this system can maintain the lithium-ion temperature between 295 and 305 K. At all studied concentrations, the maximum temperature difference at the surface is 5 and 7 K, respectively. It is also found that increasing the nanofluid concentration provides a more uniform temperature. At higher Reynolds numbers, although the temperature distribution is more uniform, increasing the nanofluid concentration has no significant effect. For example, at Re = 300, the improvement of surface temperature uniformity is 4.5% with increasing the concentration from zero to 1%. On the other hand, an increment in the Reynolds number has a negative effect on the pumping power of the coolant. Also, the rate of thermal and frictional entropy generation decreases with the volume fraction of nanoparticles, so that at a concentration of 1%, the rate of reduction of frictional entropy relative to pure fluid is 9%.