|
|
| |
 |
Defense of Ph.D. thesis: |
 |
|
| | Post date: 2024/12/17 | |
|
  New: Defense of Ph.D. thesis:
The thesis defense by Mr. Sajad Jabari Neek a Ph.D. candidate in mechanical engineering, entitled " Droplet Drying of Complex Fluids- Oleaster Extract", will be held on 2024-Dec-18 at 16:00 (Tehran time) at the School of Mechanical Engineering of Iranian University of Science and Technology (IUST). The members of the Space Propulsion Research Laboratory (SPRL) invite all interested parties in this field and the other relevant areas to participate in this defense.
Abstract
The challenge of drying droplets of complex fluids often involves unique solutions due to the diverse issues associated with different fluids. Low-fiber oleaster extract is a colloidal pharmaceutical-nutritional substance, under investigation by pharmacists as a potential replacement for the currently available commercial oleaster powder, aiming to minimize the side effects of consuming the fibrous material of the fruit in the human body. The high water-to-solids ratio in this exract—resulting from the aqueous extraction method—leads to chemical spoilage, processing issues, and interest in spray drying. Given the lack of prior studies on this emerging extract, this thesis conducts various thermophysical investigations on this fluid under different temperature and concentration conditions, providing a detailed picture of its properties. The results indicate that due to the simultaneous presence of solid, liquid, and gas phases, this extract qualifies as a complex fluid.
Experimental analysis of the drying kinetics of single droplets of the extract under various drying chamber temperatures and initial droplet concentrations reveals that, after losing water during evaporation, the extract forms an impermeable shell upon reaching a critical concentration. The formation of this shell is attributed to the presence of insoluble hydrophilic compounds and the delayed crystallization of soluble materials on the droplet surface. This shell swells and deflates continuously as water vapor escapes, eventually leading to the formation of a particle with a dry and sticky shell, approximately the same size as the initial droplet, and in some cases, with a moist center. Increasing the drying chamber temperature to 200°C resolves the issue of a moist center, though the shell remains highly sticky.
Further investigations into vacuum drying revealed that the extract does not stabilize into a solid state under vacuum conditions. After dehydration in its most concentrated form, it retains a viscous fluid structure similar to honey. Based on these findings, it was concluded that oleaster extract is not suitable for spray drying. Differential scanning calorimetry (DSC) analysis showed that the low glass transition temperature of the extract (35°C) causes its stickiness. Consequently, maltodextrin (DE5), a permitted additive with a high glass transition temperature (approximately 200°C), was employed to improve the extract, and new formulations were created with more suitable glass transition temperatures. The results showed a significant reduction in the stickiness of the dried material, with no stickiness observed in the MS2 and MS3 formulations, and the particles were properly dried.
Considering the drying kinetics of low-fiber oleaster extract observed in the experiments, it seems feasible to model its behavior using a semi-empirical model based on evaporation theory and machine learning of the drying curve data. The proposed model can predict not only the effects of independent drying variables, such as chamber temperature, concentration, and initial droplet size, on the drying kinetics of the extract but also the conditions that lead to the formation of swollen particles—larger than the initial droplet size.
Keywords
Complex fluids, Low-fibrous extract, Oleaster extract, Single droplet drying, Drying kinetic
|
|
|
|
|
|
| |
|
|
|
Defense of M.Sc.Β thesis: |
|
|
| | Post date: 2024/10/7 | |
|
 New: Defense of M.Sc. thesis:
The thesis defense by Mr. Erfan Dabbaghchian a M.Sc. student in aerospace, entitled " Simulation of flow leakage in impulse turbines' blade tip", will be held on 2024-September-03 at 14:00 (Tehran time) at the School of Mechanical Engineering of Iranian University of Science and Technology (IUST). The members of the Space Propulsion Research Laboratory (SPRL) invite all interested parties in this field and the other relevant areas to participate in this defense.
Abstract
A supersonic turbine is one of the main components of a turbopump, which serves as the power source for a liquid propulsion engine. When the flow rate is low, a high specific work is required for the turbine's operation. Due to the low flow rate, the blade height and consequently the aspect ratio will also be small. To reduce the losses associated with a low aspect ratio, partial admission turbines are used in turbopumps. In this approach, the gas flow only impacts a portion of the rotor blades. At the blade tips, a clearance is considered to prevent contact between the blade and the casing, which results in tip leakage flow.
The focus of this study is to investigate the behavior of tip leakage flow in the space above the blades of a supersonic partial admission impulse turbine. This leakage flow is controlled by cavities specifically designed at the blade tips for this purpose. The study's approach involves numerical simulation and the use of artificial intelligence algorithms to predict the flow behavior within the turbine. To validate the numerical results, the performance of an existing partial admission turbine is simulated, and the obtained results are validated against its experimental data. Subsequently, the same turbine is simulated with modifications to the upper blade profile using several defined geometric parameters, including angle, setback, and cavity depth.
Further steps in this research include analyzing the results of these modifications, creating a database to utilize artificial intelligence algorithms to replace simulations, and predict the turbine's performance. It is worth mentioning that in the end, the optimal blade tip cavity profile is provided by the artificial intelligence algorithm with a negligible error margin (less than 1%).
Keywords: Supersonic impulse turbine, blade tip leakage, neural network, simulation |
|
|
|
|
|
| |
|
|
|
Defense of Ph.D. thesis: |
|
|
| | Post date: 2024/06/27 | |
|
New: Defense of Ph.D. thesis:
The thesis defense by Mr. Masoud Sahami a Ph.D. candidate in mechanical engineering, entitled "Modeling the condensation of multi-component gases in high-speed flows", will be held on 2024-July-02 at 14:00 (Tehran time) at the School of Mechanical Engineering of Iranian University of Science and Technology (IUST). The members of the Space Propulsion Research Laboratory (SPRL) invite all interested parties in this field and the other relevant areas to participate in this defense.
Abstract
The homogeneous condensation phenomenon occurs in high-speed expanding flows in many industrial equipment, such as the last stages of steam turbines, supersonic separators, and thrusters. As a result of temperature and pressure drop in the nozzles of these equipment, the conditions for the condensation and the formation of liquid droplets in high-speed flows are provided. Due to the complexity of droplet formation and growth kinetics, modeling this phenomenon in multi-component high-speed flows is a complex and practical issue. Many previous studies have been limited to ideal gas assumption and equilibrium condensation, which do not match the thermodynamic conditions governing this phenomenon. Therefore, it is necessary to study the effect of this phenomenon on the target parameters to improve the nozzle performance in the different applications, while removing the above assumptions. Determining the location of condensation in the flow and studying the droplet growth physics based on the geometrical and thermodynamic conditions of the nozzle inlet is of particular importance. During the occurrence of non-equilibrium condensation shock, due to the release of latent heat resulting from the phase change, the temperature and pressure increase, affecting the flow thermodynamics and the performance of the nozzles. In this thesis, the effects of non-equilibrium condensation in expanding flows on the performance of converging-diverging nozzles are studied, focusing on improving the propulsion and separation performance of nozzles. For this purpose, the 1D coupled equations of gas dynamics, models of nucleation, and growth of droplets in single-component expanding flows are introduced first. Then, by generalizing the governing equations to binary component gas flow, the condensation phenomenon in a flow composed of hydrogen peroxide propellant decomposition products is modeled based on the numerical method. To increase the model accuracy, especially for high inlet pressure cases, real gas equations of state are used to determine the properties of gas mixtures. The results show that passing through the saturation line of the condensable component and forming droplets during the expansion of the flow in the divergent section of the nozzle improves the propulsion parameters, such as the thrust coefficient, by about 6% compared to the dry state. Due to the small growth of droplets during the free molecular regime, non-equilibrium condensation continues to the thruster nozzle exit. Increasing the length of the nozzle leads to larger nano-droplets, the formation of a higher liquid mass fraction up to 4%, and the transfer of the Wilson point to the upstream parts of the nozzle. Next, generalizing the droplet growth model to a new multi-diameter and multi-component flow, the condensation phenomenon in the combustion products of expanding flue gas has been studied. In this problem, it has been shown that enriching the flow by hydrogen can overcome the limitation of the liquefaction efficiency of separators by increasing the thermal capacity of the carrier gas to absorb latent heat during droplet growth and increase the exit droplet size and liquefaction efficiency. In a particular case, this increase has been estimated to be about 1.3 and 1.5, respectively.
Keywords
Multi-component flow, Condensation shock, Nucleation, Droplet growth, Thrust coefficient, CO2 supersonic sparators
|
|
|
|
|
|
| |
|
|
|
Defence of M.Sc. thesis |
|
|
| | Post date: 2024/06/8 | |
|
 New: Defense of M.Sc. thesis:
The thesis defense by Mr. Vahid Asadi, a M.Sc. candidate in aerospace engineering, entitled " Simulation of a specific gas generator", will be held on 2024-July-08 at 16:00 (Tehran time) at school of mechanical engineering of Iranian University of Science and Technology (IUST). The members of the Space Propulsion Research Laboratory (SPRL) invite all interested parties in this field and the other relevant areas to participate in this defense.
AbstractThe feeding system of liquid propellants has two main tasks. Increasing the pressure of the propellants and feeding them to one or more thrust chambers. The energy required for these tasks is obtained through high-pressure gas, centrifugal pumps, or their combination. In this research, a sample gas generator whose propellant is liquid hydrogen peroxide was first designed using zero-dimensional relations, and then it was modeled in three-dimensional form with the help of computational fluid dynamics using the Fluent solver. The flow inside the gas generator was investigated and analyzed under different working conditions. It is worth noting that the type of solver used is basic pressure and by applying the k-ω-like turbulence model, the liquid phase solution is done with Lagrangian Ruiker. Comparing the results obtained with the help of the numerical simulation, with the results obtained from the CEA software, indicated the agreement of the data of the numerical method with zero-dimensional relationships. This matching of data makes the included numerical method to be considered as a reliable method for estimating and predicting the behavior of the flow inside the gasifier chamber. The behavior curves of the gasifier chamber were obtained for different hydrogen peroxide inlet temperatures and different chamber pressures. It should be noted that the thermal decomposition of hydrogen peroxide was investigated, therefore, using high-temperature nitrogen gas, hydrogen peroxide reached the decomposition temperature, and its behavior was investigated under different conditions.
Keywords
Gas generator, Turbulence ring, Uniform gas, DPM, Thermal decomposition of hydrogen peroxide.
|
|
|
|
|
|
| |
|
|
|
enlightenedNew: Defense of M.Sc. thesis: |
|
|
| | Post date: 2023/08/15 | |
|
 The thesis defense by Mr. Seied Davood Musavian, a Ph.D. candidate in aerospace engineering, entitled " Experimental explanation of the interaction of heterogeneous collision jets", will be held on 2023-Augost-10 at 10:00 (Tehran time) at the Iranian University of Science and Technology (IUST) Mechanical Faculty. The members of the Space Propulsion Research Laboratory (SPRL) invite all interested parties in this field and the other relevant areas to participate in this defense.
AbstractAtomization is the process of breaking down a liquid volume into a spray of small droplets. This process includes the break up of the liquid jet or the liquid sheet that comes out of the injector. In this study, we attempted to compare the behavior of a liquid nitrogen jet, a liquid nitrogen jet impingement, and a liquid nitrogen/methanol semi-cryogenic jet to that of a water jet and a water jet impingement. In addition, the behavior of water jet impingement at various speeds has been studied. Photography was utilized to study the various patterns created during this interaction. The speed of liquid nitrogen jets was increased from 12 to 34 m/s, and the Reynolds number was increased from 50,000 to 136,000. A water jet with a speed of 4-8 m/s has a Rayleigh breakup model, a speed of 8-20 m/s has a first wind-induced breakup model, and speeds over 20 m/s have a multiple peels model. By qualitatively comparing the photos taken of the water jet impingement, the range of velocity and Reynolds number of closed rims, periodic droplets, open rims, and fully developed models were determined. The results revealed a significant insight: when Reynolds numbers exceed 30000, the average droplet diameter measures approximately 80 µm. The study's initial phase employed the liquid nitrogen subcooling technique by holding it at low pressureΩ so that the liquid nitrogen jet exiting the injector into the high-pressure test chamber became a subcooled liquid. The subsequent stages involved exploring the atomization of the jet and the impact of liquid nitrogen jet impingement. Within the range of speeds examined, the breakup model of sub-cooled liquid nitrogen jet impingement in the test chamber is a fully developed model and The impinging jet's surface took on an entirely undulating character. The comparison of liquid nitrogen jet impingement with water jet impingement at equivalent speeds indicated that the former exhibited a quicker breakup due to its lower viscosity and surface tension. Also, due to lower surface tension, heat transfer, and evaporation, the diameter of droplets and ligaments resulting from the impinging of two liquid nitrogen jets is smaller than water. In the impinging of liquid nitrogen/methanol jets, the formation of the vapor phase at the impinging point of the two jets caused the formation of instabilities in the liquid sheet and caused the accelerated breakup. Notably, the vapor phase disrupted the formation of the regular concentric sectors that typically appear in water sheets.
Keywords:
Atomization; Cryogenic jet impingement; Unlike jet impingement; Liquid nitrogen / methanol jet impingement
|
|
|
|
|
|
| |
|
|
|
