مرتضی خیاط

The development of microchannel manufacturing technology has led to a growing interest in using them as heat exchangers. Microchannels are used to control the temperature of equipment and components that generate a high amount of heat flux. Heat transfer can be further increased by dispersing particles (nano-sized particles) with a low volume fraction into the base fluid (nanofluid). A nanofluid can change the thermophysical properties of a base fluid and improve its thermal performance. The purpose of this study was to examine the heat transfer characteristics of oil-based nanofluid within wavy microchannels in series and parallel arrangements of microchannels. In order to examine the performance of each microchannel separately and to make it easier to draw their diagrams, they are named 1 and 2. Experiments were performed on TiO2 and SiO2 oil-based nanofluids in volume fractions of 0.05 and 0.1, flow rates of 0.5, 1.0, and 1.5 lit/min, and inlet temperatures of 40°C, 45°C, 50°C, 55°C. The results show an increase in the Nusselt number of the base fluid up to 41.8% in the series arrangement and also a decrease in the surface temperature in the series arrangement compared to the parallel arrangement. Also, TiO2 and SiO2 nanofluids with a volume fraction of 0.1 caused the highest increase in heat transfer, up to 56% and 52.7% in parallel arrangement and up to 45.8% and 42% in series arrangement compared to the base fluid, respectively. The pressure drop of the test section in series arrangement was up to 82.1% higher than parallel.

Due to the importance of pipelines as vital arteries for fuel and energy supply in the world, maintenance, stability, continuity of transmission, supply of refinery feeds and fuel supply to various industries is very important and necessary. The present study was conducted to analyze the performance of pigs and to investigate the effect of factors affecting pigging operation in oil pipelines. In this research, by performing experiments in real and operational conditions, the results of pigging operation in product pipelines in different diameters and lengths have been investigated, so that the effect of fouling of the inner wall of the pipeline on the flow rate, pump required power in pump house and pressure drop in different products with different physical conditions as well as calculation and evaluation of pigging speed in each operation and the effect of pig weight on pigging speed and power required in pump houses are presented. The results of this study show that pigging in a 14-inch oil pipeline with a length of 109 km and a flow rate of 360 cubic meters per hour, equivalent to 54,330 barrels per day, which has 0.4 cm of fouling, prevents a reduction in volumetric flow rate of 23 cubic meters per hour, equivalent to 3460 barrels per day, increases the required power of the pump in the pump house by 35.79 kW and increases the pressure drop by 8.9%. Also, by examining the effect of pipeline slope on the pressure behind the pig, knowing that the pump power in the pump house does not change and the pig speed is the same along the route, it is determined that increasing the height of the pipeline causes the static pressure head converted to a height head, and if the pig enters downhill areas, it will cause the height head converted to pressure behind the pig.

In this experimental research, the performance of the close single turn pulsating heat pipe (CPHP) with distilled water as base fluid and distilled water including microparticles (micro-coppers) have been investigated. To evaluate the effect of different parameters on the CPHP performance, several characters like input powers, filling ratio and concentrations of micro-coppers were studied. Findings from experiments indicate that the multiphase flow regime inside the pipe was slug-plug in low powers but it approached to an annular flow in higher value of heat inputs. Furthermore, it is required to mention that the thermal resistance of the device with micro-coppers has decreased with enhancing in the concentration of micro-coppers and input powers and it has the minimum value (0.61degC/W) at filling ratio of 60%, at input power of 60W. Finally, according to any errors of each parameters and by using Holman methods, the maximum uncertainty of experiments was calculated about 8%.

Due to the reduced dimensions of electronic equipment and the need for thermal management of these equipments, In order to increase efficiency and longevity of component, heat sinks with micro aspects are very important. In this study, heat transfer of micro heat pipe has been studied experimentally. For this purpose, firstly the micro heat pipe that is suitable for industrial conditions and restrictions for the production of very small size triangular section was designed and built. According to the very small size of the primary copper tube, the manufacturing process requires precision and advanced technology. In such a way, at first the samples of fine copper tube available in the market was provided and during the process of heat and tension was brought, at the same time, to the desired thickness and diameter and then by using provided wedge the appropriate cross section is achieved. To apply thermal load, a set of various thermal flux was applied to the evaporator and temperature distribution achieved via five thermocouples which were installed on the body in accordance with the set-up and heat resistance was measured. Water and different solution mixture of water and ethanol were used to investigate effect of the electric double layer heat transfer. It was noticed that the electric double layer of ionized fluid has caused reduction of heat transfer.

Due to the growing need of industries to improve heat transfer methods, the nucleate boiling region is of special interest to researchers because fluid boiling makes it possible to achieve higher heat fluxes than processes that are based only on non-boiling convection heat transfer. In addition, the change of working fluid in boiling heat transfer systems from pure fluid to nanofluid improves the heat transfer characteristics and thus allows the transfer of higher heat flux at lower temperatures. At the critical heat flux point, where the heat flux is maximum, it is important to secure the boiling surface and protect it from overheating. The purpose of this study is to numerically simulate the pool boiling of a water-based hybrid nanofluid containing 30% multi-walled carbon nanotubes and 70% titanium oxide with a volumetric concentration of 0.5% on a polished copper circular surface and to investigate the heat transfer characteristics, especially the critical heat flux point. For this purpose, the boiling process of pure deionized water was first simulated by ANSYS-Fluent software and the results were compared with experimental data. According to the observed acceptable agreement, the mentioned water-based hybrid nanofluid, as boiling working fluid is numerically simulated by changing the density of nucleation sites and its heat transfer and heat flux characteristics are obtained. The results show that the critical heat flux for pure deionized water was occurred at 24.4 °C and is about 1.1 MW per square meter, while the critical heat flux for the hybrid nanofluid was occurred at 13 °C and is about 1 MW per square meter.

The main cause of failure and significant reduction in battery performance is a rise in temperature, so battery thermal control systems (BTMS) are built to monitor and optimize the thermal status of batteries. In this paper, two series and parallel arrangements for placing battery packs in electric vehicles with the same number of 17,280, 18650 battery cells are proposed and compared to select the best position for placing the battery packs. With the help of the Comsol program, the temperature change of the battery pack in the laminar fluid flow regime and the heat flux changes in the first 700 seconds of discharging the battery cells from the full charge mode and selecting the best design of the battery pack placement are compared. The maximum closed surface temperature of batteries is measured from the initial temperature of 27 degrees in series and parallel arrangement, respectively. The maximum temperature difference in the series of batteries is 10% different from the parallel arrangement. Also, by comparing the total heat flux, the better performance of the parallel arrangement compared to the arrangement of the battery series, makes this type of design a practical and more cost-effective priority than other designs.

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.

Land vehicles are among the blunt body objects. When a vehicle moves forward, the movement of air around it produces a pressure gradient that varies along the body. This can lead to separation and appearance of a turbulent wake region in the rear of the vehicle. The present study numerically investigates the aerodynamic effects of vortex generators and their arrangement in different positions of 6 and 15 numbers, each with linear, rectangular and triangular arrangements on the back of a car model. Reynolds-Averaged Navier-Stokes (RANS) equations and turbulent models have been used to analyze the changes in drag and lift coefficients obtained from different arrangements of the vortex generators. The results show that the best case for reducing the drag force is related to 6 numbers of vortex generators with linear and triangular arrangement, which reduces the drag coefficient by 2% compared to the car model without vortex generators. In addition, the best case to improve the downforce; in order to increase the stability of the car, is the arrangement of 15 vortex generators with a rectangular alignment, which reduces the lift coefficient by 23.1% compared to the car model without the vortex generator. Also, with increasing the number of vortex generators from 6 to 15, the drag coefficients generally increase.

Numerical simulation of biomass gasification in a fluidized bed has been performed using a hybrid approach, in which the governing equations of the gas phase are solved in Eulerian framework and solid particles are modeled based on Multi Phase Particle-In-Cell (MP-PIC) using mixed Eulerian-Langerian method with closed-loop stochastic approach and the effect of operating factors such as gas velocity inlet to fluidized bed, particle density ratio and and particle size in fluidized bed on mixing quality have been investigated. The results show that the mixing quality reaches 0.97 by increasing the inlet velocity to eight times faster than the minimum fluidization velocity and 0.85 for the four times faster than the minimum fluidization velocity. Also by increasing the density ratio of biomass particles to fixed bed particles from 0.2 to 0.65, the mixing quality increases from 0.86 to 0.96. Furthermore, by reducing the diameter of biomass particles and fixed bed particles from 11 mm to 8 mm and 0.9 mm to 0.6 mm, respectively, the mixing quality increases from 0.8 to 0.95.

Multiphase flows, such as pool boiling, are complex multi-physical -multi-scale problems that require a multitude of numerical techniques to solve different physics combined for a specific set of flow parameters and different regimes. For this reason, a well-established numerical solution for well-validated predictive simulations has not yet been clearly defined. The main purpose of this study is to summarize the methods and basic principles of numerical simulation of pool boiling and explain all the steps of its implementation in ANSYS Fluent software in a clear and transparent manner. In this research, the details of numerical models and the results obtained for the nucleate boiling regime are presented to analyze the single bubble dynamics and calculate the critical heat flux. Heat flux is also included. The results of this study show that numerical simulations have a relatively good agreement with laboratory and experimental data.

These days With respect to the high importance of energy concept, limitation of natural resources, regulation of environmental issues, and global warming, heat transfer systemschr('39') applications get more attention. In the present paper, the experimental effect of Nano-fluid and turbulator on the heat transfer and pressure drop is investigated. AL2O3-SN300 base oil as nanofluid with weight percentage of 0.05, 0.1, 0.3, and 0.5 are used. To investigate the effect of heat transfer, a steel rotational turbulator was inserted inside the heat exchanger. The experiments were conducted under a constant heat flow rate of 3950 W/m2 and 5280 W/m2 and temperatures of 30, 40, 50, and 60 C. The whole process has been repeated for eight different mass flow rates under the laminar flow condition. The results show a higher heat transfer coefficient of Nano-fluid than the base fluid. Increasing the weight percentage of Nano-fluid caused enhancement of pressure drop in the system. The heat transfer coefficient directly relates to the mass flow rate and increases by raising the Reynolds number. The results reveal that using a turbulator enhances the heat transfer significantly. The experimental results are in reasonable agreement with theory by less than 10 percent mean error.

This study aims to investigate the effect of nanoparticle deposition on the boiling surface in the presence of microchannel on the characteristics of boiling heat transfer. In this experimental study, the copper boiling surfaces including polished circular surface, rectangular and trapezoidal microchannels were used. The microchannels include feeding sub-channels perpendicular to the main channel, which increases the boiling surface and separates the downward cool fluid flow and upward hot bubbles. Nuclear boiling experiments on microchannel surfaces in the presence of a hybrid water-based nanofluid containing 70% titanium oxide and 30% OH-based multi-wall carbon nanotubes in volumetric concentrations of 0.1% and 0.5% have been conducted. The results of nanofluid boiling experiments on both microchannel surfaces show that with increasing concentrations, critical heat flux and heat transfer coefficient increases and the highest increase in critical heat flux and heat transfer coefficient is related to the hybrid nanofluid with 0.5 % volumetric concentration on the surface with trapezoidal microchannel and their values are 64.64% and 344.76%, respectively, compared to pure water boiling on the polished copper surface. Also, in boiling of pure water on the deposited surfaces with nanoparticles, the greatest increase in critical heat flux and heat transfer coefficient is related to the surface with trapezoidal microchannels with 0.1% volumetric concentration  and 0.5% and volumetric concentration  and  their values are 120.16% and 149.4% respectively, compared to pure water boiling on the polished copper surface.

Shan-Chen model is the most common model for simulation of multiphase flows using lattice Boltzmann method. The entire multiphase Lattice Boltzman models are limited to regimes, where the temperature dynamics are either negligible or their effects on the flow are unimportant. The entire multiphase LBE models are limited to regimes where the temperature dynamics are either negligible or their effects on the flow are unimportant. The multiphase isothermal lattice Boltzmann equation (LBE) model and single phase thermal LBE (TLBE) model were described. In this research, by combining these two models, the thermal two-phase LBE model was proposed. The coupling of the two models is through a suitably defined body force term. Due to the external nature of this coupling, the new model will have the same stability as the isothermal two-phase model. For this purpose, the scalar thermal model was initially neutral and, then, the Shan-Chen model was expressed in homogeneous state. Also, droplet falling on a heated solid surface and positioning droplet on heated solid surface in different Rayleigh and Reynolds number and different diameter size of droplet were considered. Results show that the temperature in the multiphase flow, as a barrier, delays achieving a stable state, and the fake speed created at the interface area in the temperature field also affects.

Pool boiling has the ability to remove large heat flux at low difference temperature of wall and this can be further enhanced by using surface modification methods. This article investigates pool boiling heat transfer on 4 levels with different orientations. For this purpose, a laboratory device was designed and built. The main goal of providing a simple and cost-effective manner with high durability in industrial applications, to having the highest amount of critical heat flux at the lowest level of super-heated temperature difference. The results show that surface roughness factor causing a delay in connecting the bubbles and heat flux increased slightly. In addition to roughness factor, two factors separating bubbles from the fluid in the heat dissipation and more power nucleation sites and micro-bubble layer can be more important than the surface roughness. The surface polished in one direction with lower roughness has higher critical heat flux than circular rough surface. Ultimately to combine bubble separation and more feed the micro layer with made micro channel. With this method it could be increased 131% critical heat flux and 211% heat transfer coefficient.

In this paper, the effect of adding a hydrophobic micro porous layer (MPL) at the cathode side of a PEM fuel cell on the cell performance is investigated. For this purpose, a three dimensional two-phase non-isothermal simulation of cathode side layers of a PEM fuel cell which includes gas channel, gas diffusion layer (GDL), hydrophobic micro porous layer (MPL) and catalyst layer (CL) has been performed. The governing equations of fluid flow in the fuel cell are solved with a multiphase mixture model via developing a code and distribution of velocity, pressure, temperature, species concentration and liquid water saturation at the various layers of the cathode side of fuel cell are obtained. Furthermore, the effect of physical and wetting properties of MPL including thickness, porosity, contact angle and permeability on saturation level and performance of the fuel cell are studied. The results show that by adding an extra micro porous layer between GDL and catalyst layer because of differencing in the wetting properties of the layers, a discontinuity appears in the liquid saturation and species concentration at the contact surface of them. In addition, according to the obtained results, increasing the MPL porosity cause to decreasing liquid water saturation and improving the cell performance. While increasing the MPL thickness decreases the cell performance. In order to validate the results, the performance curves calculated by single and two-phase simulating were compared with experimental results and a good agreement was found between them.

For the experimental study of fluidized bed`s hydrodynamics and investigating of several effective parameters on this hydrodynamics, a fluidized bed is designed and manufactured. This bed is a cylindrical transparent column with internal diameter as 14 cm. Bed particles are silica sand in the size ranged from 200 to 750 micrometers. In this study, first the Minimum fluidization velocity ("Umf") of Different sieve particles is determined and the effect of particle size and bed height on this velocity is investigated. Then, influence of particle size and bed height on the bed pressure drop is studied. Then experimental results are compared with calculated values from current prediction correlations to determine the deviations of the prediction values from experimental data. As a result, by increasing the particle size in the equal bed height, Minimum fluidization velocity is increased but the pressure drop does not significantly change. Also, by increasing bed height, the Minimum fluidization velocity and pressure drop increased. But for Minimum fluidization velocity, this increase is insignificant and it can be ignored. Also bed pressure drop changed linearly with bed height.

In this work, three-dimensional turbulent forced convection flow through a flattened pipe, partially and completely filled with a porous material, was investigated numerically. Here, the effects of permeability and thickness of the porous layer on the rate of heat transfer and pressure drop were investigated. For this purpose, porous material was inserted in two geometrical arrangements: central and boundary. Also, the pipe had constant-temperature condition. The results for central arrangement show that the rate of heat transfer first increases and then decreases with increasing the thickness of the porous layer, while the pressure drop is monotonically increasing. While for the porous medium boundary arrangement, the rate of heat transfer first decreases and then increases with increasing the thickness of the porous layer. Also the maximum of Nusselt number is occurred for the fully porous pipe configuration.