mohammad eftekhari yazdi

Considering the importance and necessity of energy saving in Iran, different methods have been introduced and examined in order to achieve this goal in the building section. simultaneous use of photovoltaic panels, green roofs, phase-change materials and double-skin facades, can lead to almost 70% Energy saving. considering this fact, it is important to optimize the use of the above technologies, with analyzing their economic and environmental aspects.

In this research, the optimization of PCM types and PCM location in external wall and green roof layers, with the objective of cooling and heating load reduction, for the first time in a building equipped with the aforementioned technologies, was carried out using the genetic algorithm. Three climate condition of Iran consist of Hot arid (steppe-dry mid-latitude and Desert biome-dry tropical) and mild-humid climate was selected. The study was conducted using Design Builder software version 6.1.5.2.

As a result, 9, 9 and 6 optimal solutions were calculated for Tehran with steppe-dry mid-latitude climate, Yazd with Desert biome-dry tropical climates, and Amol with mild-humid climate respectively. The highest amount of energy saving of 70.9% has been achieved for mild-humid climate.

Considering the economic analysis and environmental effects, two following solutions are suggested 1- using RT31 PCM between brick and plaster layers of external wall of the building located in steppe-dry mid-latitude climate 2- using, RT26 Between brick and plaster layers of external wall of the building in desert biome-dry tropical climate.

The purpose of this work is to investigate a different geometry in the parabolic collector in order to increase the thermal efficiency through simultaneous surface and volume absorption in a combined condition. Recently, it has been observed that if the inlet temperature is above 250 °C, Direct absorption collectors can increase efficiency up to 10% Considering that there is a direct relationship between the concentration of nanofluid and the diameter of the transparent tube carrying the fluid with the absorption coefficient, On the other hand, as the concentration of nanofluid increases, fluid sedimentation and system maintenance problems occur. In this research, the amount of nanocarbon used as a suspension of 0.02 gr/l in oil base fluid is considered. According to experimental data, this amount of nano carbon concentration completely absorbs light rays at a depth of 24 (mm) and this absorption coefficient has been used for this specific geometry of the collector. The results show that the rest of the radiation is absorbed on the surface using the central tube, so that the thermal efficiency is up to 6% compared to the usual copper absorption collector, which is about 19 degrees Kelvin.

There are various industries, each of which is somehow involved in the issue of heat transfer, and in many cases, the goal is to increase the rate of heat transfer. In this study, one, two or four injection jets were used together for cooling and the results were compared in terms of the average Nusselt number. Then, by placing the twisted tape at different angles of 180°, 360° and 720° in the injection jet, the average Nusselt number and the minimum and maximum temperature were checked. The results showed that the diameter of the fluid outflow from the nozzle increases by moving away from the jet opening and approaching the hot plate due to the pressure distribution, and when two jets are used in close proximity, the exit from each vortex is created in this place. When using four jets, the outflow from the jet hits the hot plate and creates vortices. With the increase in the number of jets, the Nusselt number and the maximum temperature on the hot surface also increase. The results showed that the average Nusselt number with the angle of the twisted tape, which is placed inside the rotating jet tube, increases at an angle of 180 degrees and decreases at angles of 270 and 360 degrees. In all cases, using twisted strips, the maximum temperature as well as the minimum temperature of the hot surface are higher than when the non-rotating jet is injected on the hot plate. As the distance of the jet from the plane increases, the Nusselt number decreases.

Nowadays different kind of active and passive methods used in order to reduce energy consumption and air pollution in buildings. Simultaneous use of phase-change material (PCM) and green roofs with triple-skin facades (TSF) and triple glazed windows (TGW) in residential buildings equipped with Building-integrated photovoltaics (BIPV) can lead to 70% annual energy saving. On the other hand, PCM type and applying methods in different climate conditions impacts energy saving in these conditions. So for the first time, in this research Multi objective optimization of a residential buildings equipped with above technologies was done by the help of genetic algorithm. Reduction of required heating and cooling loads was chosen as optimization’s objectives and three climate conditions of Iran was selected. Results indicate that maximum energy saving is 73.3%. Maximum Cooling load reduction is 92.2% which is happened in biome-dry tropical climate conditions. In addition, Maximum reduce in Co2 emission is 60.6% for Tehran.

Investigating the effective factors in controlling and increasing stability due to weakening of the balance parts of the body in the elderly with osteoporosis, in order to prevent falling is of particular importance, so in this study, the effect of anti-slip flooring in the stimulation of the somatosensory part of the sole of the foot to improve postural stability and gait balance has been evaluated in the elderly with osteoporosis.

22 elderlies participated (11 elderly women with severe osteoporosis,11 healthy elderly women) in this study in two static and dynamic condition on three different surfaces including sponge non-slippery flooring (FL), PVC patterned non-slippery flooring (SF) and control surface (CO). In the static part, each participant was standing on the force plate for 30 seconds with eyes open and eyes closed. The values of the length, sway and average velocity of the anterior-posterior and internal-external center of pressure of the foot were measured. In the dynamic part, each participant walked at a selected speed on different surfaces and the values of the normalized step and stride length, step width, step and stride time, and average step and stride velocity were measured.

PVC non-slippery flooring (SF) and control surface (CO) reduced all postural stability and gait variables (P < 0.05) in osteoporosis and healthy elderly than soft Sponge Surface (SF). Moreover, all postural stability variable and spatial and temporal gait parameters were significantly more in the osteoporosis elderly than in healthy elderlies (P < 0.05). Moreover, anterior-posterior mean velocity in open-eyed state significantly reduced in both elderly groups than close-eyed state (P < 0.05).

Stiff and patterned surfaces are more effective than soft spongy surfaces in stimulating the somatosensory part of the foot sole to improve stability in both osteoporotic and healthy elderly groups. The results of this study may be helpful to understand the characteristics of the elderly while walking and standing on non-slippery flooring in different environments and the ergonomic design of the environment in order to reduce slips and falls and as a result possible fracture in the elderly with severe osteoporosis. In addition, observation of instability between the elderly with osteoporosis and healthy suggests the need for further investigation and the use of auxiliary exercises to correct and improve stability.

The methods used for maximum exploitation of wind farms’ potentials can be classified into two categories: turbines layout optimization and utilization of turbines with different hub heights. The layout optimizations are generally performed by optimization algorithms. A drawback of these algorithms is their inability to render a single result as the optimized result. In the present study, by using an analytical model for 3D wind velocity distribution in the wake and including wake interactions, a model has been presented for estimation of the generated power of turbines implemented in wind farms. By coupling this model with the cost model of turbines' implementation, a function for the optimized layout has been presented. By calculating this function for different layouts of turbines in farms, the optimized layout can be obtained. In the present study, the calculations of turbines' layout optimization were carried out using a MATLAB-implemented code. By dividing the solution domain into grids and taking into account the minimum optimized distance of turbines from one another from the economical and power output aspects, the value of the layout optimization function has been calculated for different possible layouts. Finally, the layout of kilowatt-scaled turbines located among megawatt-scale ones for Horns Rev offshore farm has been modeled to obtain the maximum power output. From the results obtained for the optimized and maximum number of kilowatt-scaled turbines, it is inferred that the power of the farm has been increased by 7% (3.226 MW) by 35.7% efficiency and 9.35% (4.712 MW) by 34.06% efficiency,respectively.

In the present article, performance of a glazed photovoltaic thermal system integrated with phase change materials (GPVT/PCM) is numerically examined based on both energy and exergy viewpoints. The effect of PCM volumetric fraction and environmental temperature on thermal and electrical characteristics of the system is evaluated. A three-dimensional model of the system is simulated transiently in the ANSYS Fluent 18.2 using pressure-based finite volume method and SIMPLE algorithm selected for coupling pressure and velocity components. Validity of the numerical results is confirmed based on available data. The results indicate that PCM melting is more likely far from the riser tube and absorption of thermal energy be the PCM is mostly effective for filling the PCM container by around 2/3 of the volume. Increase of the PCM volumetric fraction reduces the module temperature and enhances the electrical performance of the system in terms of both energy and exergy efficiencies, while it decreases the thermal efficiency. An opposite trend is experienced by increase of the environmental temperature in which the thermal efficiency enhances and the electrical efficiency declines.

The purpose of this study is to evaluate the impact of moving the condenser of a household refrigerator within the body on the refrigerator's performance and energy consumption. The effects of the internal and external condensers on energy consumption and cooling capacity in a household refrigerator are next explored. This study was conducted experimentally and in a laboratory setting, and all terms and conditions were in accordance with the international electrotechnical commission 62552-2015 for cooling system testing. The studies were conducted in a 5-foot refrigerator. On this refrigerator, both internal and external condenser models were installed. In the first situation, the internal condenser was inserted into the cooling cycle and the associated tests and calculations were performed. In the other situation, the internal condenser was removed from the cooling cycle and the external condenser was replaced by changing the valve status. In this case, the relevant diagrams and calculations were obtained and analyzed. Based on the findings of this study, it can be stated that using the internal condenser reduces energy consumption and, as a result, has a higher energy grade than using the external condenser. The internal condenser in the heat transfer process work better than the external condenser, based on the temperatures obtained. An internal condenser is also a preferable solution for a household refrigerator in terms of installation and cost.

In this study, the aerodynamic performance of a high-speed train against a turbulent air flow is examined numerically from two approaches. First, using computational fluid dynamics, the parameters of aerodynamics and fluid flow are analyzed and then, using Multi-Layer Feed-Forward Neural Network (MLFFNN) Algorithm, a prediction and comparison with the obtained values from the CFD analysis are presented. To achieve this, using Reynolds-Averaged Navier-Stokes (RANS) method with 𝑘-𝜔 (SST) turbulence model, an incompressible turbulent air flow around a high-speed train model by OpenFOAM CFD Software is simulated. In this research, some of the significant and key parameters of fluid flow and aerodynamics as velocity, pressure, streamlines, flow structure, pressure coefficients, drag, lift and side forces for some yaw angles of wind movement and velocity changes are analyzed and compared. In the following, the Multi-Layer Feed-Forward Neural Network which is modified with various data is applied for prediction of the output of the problem. Accordingly, the aerodynamic drag, lift and side forces for the yaw angles of wind movement and velocity changes by this algorithm method are obtained and compared with the obtained results from CFD analysis. The comparisons indicate an appropriate similarity between the CFD data and the used MLFFNN one.

One of the best and most important types of concentrating solar power plants is the linear Fresnel collector. The thermal performance and application of absorber in a solar power plant can be enhanced using direct steam generation technology. A particular discrepancy between the present study and others lies in our attempt at applying a new method for calculating critical heat flux based on Look-up Table. In the current study, effects of nanofluid on the length of the critical heat flux and convection heat transfer coefficient were investigated. The nanoparticles considered in this study were aluminum, silver, nickel, and titanium dioxide at concentrations of 0.01, 0.1, 0.3, 0.5, 1 and 2 %. Modeling results revealed that the heat transfer coefficient increased upon enhancing the volumetric concentration of nanoparticles, thereby improving this coefficient at 2 vol. % nickel nanoparticles, which was 10.6 % above the value of pure water. On the other hand, thermal efficiency was enhanced when nickel nanoparticles were dispersed in pure water such that increase rates of thermal efficiency equaled 11.2, 10.8 and 11.3 % in the months of June, July, and August, respectively, when the volume concentration of nanoparticles was 0.5 %.

The airflow around a simplified train model is investigated using a three-dimensional $gamma-widetilde{Re}_{theta t}$ transitional approach. Four different yaw angles ($theta = 10^{circ}, 20^{circ}, 30^{circ}$, and $40^{circ}$) perpendicular to the body of the simplified train model are considered which the magnitude of front air-flow is constant, and the magnitude of crosswind determines by yaw angle. The main aim of the research is to investigate the influences of the yaw angle and roughness on the time-averaged flow structure, turbulent quantities such as turbulent kinetic energy, dissipation rate, and the aerodynamic forces such as skin friction and pressure coefficients. The findings show that the yaw angle has a pronounced influence on the three-dimensional flow structure around the high-speed train. As the yaw angle augments, the aerodynamic forces like skin friction and pressure coefficients increase. Furthermore, the roughness has a negligible effect on the pressure coefficient. Also, the skin friction coefficient locally increases in the rough train body.

This study intends to semi-analytically investigate the steady 3D boundary layer flow of a SiC-TiO2/DO hybrid nanofluid over a porous spinning disk subject to a constant vertical magnetic field. Here, the novel attitude to single-phase hybrid nanofluid model corresponds to considering nanoparticles and base fluid masses to compute solid equivalent volume fraction, solid equivalent density, and also solid equivalent specific heat at constant pressure. The basic PDEs are transformed into dimensionless ODEs using Von Kármán similarity transformations, which are then solved numerically using bvp4c function. Results indicate that mass suction and magnetic field effects diminish all hydrodynamic and thermal boundary layer thicknesses. Finally, a significant report is presented to investigate quantities of engineering interest due to governing parameters’ effects.

Neural networks can be used in various subjects, such as the discovery of relationships, identification, system modelling, optimization and nonlinear pattern recognition. One of the interesting applications of this algorithm is heat transfer estimation between contacting surfaces. In the current investigation, a comparison study is done for temperature transfer function estimation between contacting surfaces using Group Method of Data Handling (GMDH) neural networks and ANFIS (Adaptive Neuro Fuzzy Inference System) algorithm. Different algorithms are trained and tested by means of input–output data set taken from the experimental study and the inverse solution using the Conjugate Gradient Method (CGM) with the adjoint problem. Eventually, the optimal model has been chosen based on the common error criteria of root mean square error. According to the obtained results among different models, ANFIS with gaussmf membership function has the best algorithm for identification of TCC between two contacting surfaces with 0.1283 error. Also, the inverse method has the lowest error for thermal contact conductance estimation between fixed contacting surfaces with root mean square error of 0.211.

In this paper, an experimental study has been conducted on the rheological behavior of Water (80%) and Ethylene-glycol (20%) in presence of Al2O3-MWCNTs hybrid nanomaterials. For this purpose, nanofluid samples were prepared by suspending the nanomaterials in a mixture of water and EG with solid volume fractions of 0.0625%, 0.125%, 0.25% and 0.5% Viscosity measurements were performed at various shear rates and in the temperatures range of 25 to 50⁰C. Experimental data showed that all hybrid nanofluid samples had Newtonian behavior. also Results showed that nanofluid viscosity decreased with increasing temperature and augmented with increasing the volume fraction. Eventually, a new accurate correlation was developed to assist the calculation of the viscosity of the Al2O3-MWCNTs/water-EG at different temperatures and volume fractions.

The CFD simulation has been undertaken concerning natural convection heat transfer of a nanofluid in vertical square enclosure, whose dimension, width height length (mm), is 40 40 90, respectively. The nanofluid used in the present study is -water with various volumetric fractions of the alumina nanoparticles ranging from 0-3%. The Rayleigh number is . Fluent v6.3 is used to simulate nanofluid considering it as a single phase. The effect of Brownian motion on the heat transfer is examined. A comparison between the two studies of with and without the Brownian motion, shows that when the Brownian motion is considered, the solid volume fraction of nanoparticles has dissimilar effects on the heat transfer. The numerical results show a decrease in heat transfer with increase in particle volume fraction considering Brownian motion effects. Moreover, computed result demonstrates an increase of Nusselt number with Rayleigh number as depicted by experimental results.

The phenomena of formation and detachment of droplets are one of fundamental issues in studying two-phase flows and have been seen in lots of natural phenomenon and processes, such as spraying processes, ink jet printing, emulsion, etc. Between different numerical methods, the lattice Boltzmann method (LBM) has been developed in to an alternative and promising numerical scheme for simulating multi-component fluid flows. In this project, formation and detachment of droplets were simulated, using LBM and particularly index function model. Results were validated using two-phase flows methods. After code validation,the formation and detachment of droplets in a cross-junction micro channel and under the electric field effects were studied. To survey different effects on this phenomenon, dimensionless numbers were studied. Finally, the effect of variation of permittivity, conductivity and capillary number for droplets were studied under different situations. Results show that the electric force have a positive effect in expedition of droplet formation, and also index function model proved its very useful abilities. We have smaller drops with high frequency which shows that we can control the droplet formation.

Emulsion consists of drops of one liquid dispersed into another immiscible liquid, and is a novel technique for producing monodisperse droplets. The aim of this research is to use the Lattice Boltzmann Method (LBM) to simulate two-phase flows in micro-channels to access the emulsification process. For this approach, the Index-Function Model proposed by He is used to simulate drop formation in emulsification process in a co-flowing micro-channel with a complex geometry and three inlets. The simulation is performed to investigate the mechanism of drop generation due to dripping and jetting modes and the mode between them. Index function model, which is a new reliable model to evaluate two-phase flows is applied to track the motion and deformation of the interface between the two immiscible fluids. Accuracy of our results is examined by two well-known basic analytical models including Relaxation of a rectangular drop and Coalescence of two static droplets. Our results indicate good agreement with the analytical data. The dimensionless numbers such as Capillary and Velocity ratio were used. The Capillary number is one of the most important dimensionless numbers in determination of fluid flow characteristics in micro-channels. The simulations reproduce dripping, widening jetting and narrowing jetting simultaneously in a co-flowing microchannel in agreement with the experimental ones. This indicates that index function LBM model has good accuracy and high stability to simulate this kind of flow.