حجت قاسمی

At the outlet of a converging nozzle connected to a high-pressure gas source, based on its input pressure, an under-expanded and ultrasonic flow is created, accompanied by a shock wave. A simple design of the Hartmann-Sprenger resonance tube device is made by placing a closed-end tube in front of this converging nozzle. The impact of the shock wave and nozzle outflow jet on the tube causes intense heating in the trapped gas inside the tube. This research investigated the functional cycle of the resonance tube and the fluctuating nature of the flow inside it. The main parameters of the problem in the form of the inlet pressure to the nozzle and the distance between the tube and the nozzle, the determination and the effect of changing their value on the fluctuating performance of the flow inside the tube, and the fluctuations of the pressure at the end of the tube were shown. The dominant frequencies of these oscillations were determined and shown that in the range of input pressure from one to ten bar, the range of dominant frequencies is between 600 and 933 Hz, which are slightly different from the resonant frequency of the tube. The intensification of oscillations and dominant frequencies can only be seen in a certain number of values of the main parameters, and the intended heating is created only in these conditions.

The aim of the present research is to obtain the ability to use the cryogenic propellant engines on a laboratory scale. In this regard, it is necessary to build some experimental motors and investigate the their performance parameters. The liquid oxygen as a common oxidizer and ethanol as a green fuel have been selected as propellant components. The engine is designed to produce 400 kgf force at the nominal condition. The pintle type injector has been chosen in which liquid oxygen and fuel are flowed in the axial and radial directions, respectively. The combustion chamber has been protected against overheating by applying the regenerative cooling. However, the laboratory feature of the engine design has provided the using of water instead the cooling propellant. All main components of the engine such as injector, igniter, and flow controllers, are examined by the cold tests. A comprehensive test facility is designed and set up for hot fire tests in which the performance of almost all parameters can be evaluated. Fifteen fire tests have been performed. Maximum obtained pressure and evaluated combustion efficiency were about 75% of design values.

One of the problems in the experiment of breakup cryogenic liquid jet is the state of discharged cryogenic liquid jet from injector. In some applications, it is necessary jet to be in the sub-cooled condition. However, at atmospheric condition, the discharged cryogenic liquid jet becomes two-phase. In the present article, the methods for sub-cooling of the liquid nitrogen jet are investigated and a simple method to achieve this goal is used. With this method, which is based on holding at low pressure, a sub-cooled liquid nitrogen jet with a temperature of about 7 K lower than the saturation temperature was obtained. Then, the behavior of the liquid nitrogen jet at high pressure and atmospheric pressure is evaluated. High speed camera was used to observe the behavior of the jet. The speed of liquid jet is changed from 12 m/s to 34 m/s according to the Reynolds number from 90000 to 260000. When the liquid nitrogen jet is discharged into the environment under standard conditions, the jet becomes two-phase and expands. The larger the injector pressure difference, the greater the expansion of the jet; So that in the pressure difference of 6 and 13 bar, the diameter of the jet is 1.5 and 3.3 times the diameter of the injector, respectively. In the test speed range, under the conditions provided for the liquid and the environment, the breakup of the sub-cooled liquid jet leads to the production of very small droplets that are consistent with the expectation of such a liquid.

The purpose of this paper is to present experimental data for merging two outlet fluid skirts in a dual pressure-swirl coaxial injector. In this study, a dual pressure-swirl external mixing injector was designed, fabricated. Operational characteristics including discharge coefficient and breakup length with injection pressures difference for internal and external injectors were expressed. Utilizing fast shooting, based on backlighting method, the interaction between the two outlet skirts were investigated and the merge performance map was extracted. The merge performance map results indicated, when the pressure difference of the external injector increases from 0.3 bar to 0.95 bar, the pressure difference of the internal injector for the merge to occur increases. Because the effect of the internal injector injection pressure for merge in this area is greater than the external injector injection pressure, the external injector skirt is pulled toward the internal injector skirt. For injection pressures difference of more than 0.95 bar in the external injector, because the effect of the external injector injection pressure for merge is greater than the internal injector injection pressure, the internal injector injection pressure difference is reduced for the merge to occur and the internal injector skirt is pulled toward the external injector skirt.

Transient evaporation of a bi-component droplet at high temperature and pressure condition has been modeled numerically. In the gas phase, the equations of species, momentum, and energy, and in the liquid phase, the equations of species and energy by assuming fugacity equilibrium, and Peng-Robinson equation of state using the finite volume method have been solved. The droplet is assumed to be spherical, the solubility of the gas in the liquid and effect of gravity have been neglected. The results of the proposed model for heptane-hexadecane droplet in various temperatures and pressures have been validated against the available experimental data. Results were in good agreement. The effect of pressure on the evaporation showed that at a constant temperature, by increasing pressure up to 2 MPa the droplet lifetime increases but further increase in pressure (up to 2.5 MPa) reduces droplet lifetime. Evaporation behavior does not change with different compositions. The role of different equations of state on the prediction of binary droplet lifetime was studied, and finally the effect of ambient temperature and pressure on the surface temperature of the droplet was investigated. It was observed that at high enough pressure and temperature, the droplet surface could reach the critical condition.

In this paper, air gasification of Tehran’s refinery Mazut is investigated. First, Mazut gasification is modeled by the equilibrium method and then, the thermal operating of an entrained flow gasifier is studied experimentally. An entrained flow gasifier is designed and manufactured for 7 kg/h flow rate of heavy fuel oil. The physical/chemical properties of this heavy fuel oil are determined via standard laboratory experiments. In Aspen plus, a parametric study is conducted by the equilibrium model in order to investigate the effects of equivalence ratio on syngas composition, gasification temperature, and higher heating value for the steady-state condition. Temperature distribution along the gasifier and the solid carbon consumption are effective parameters on syngas composition and gasification performance. In an experiment, the gasification temperature is measured at different locations of a gasifier. The modeling results show that the values of H2, CO, and HHV have a maximum which is accompanied with complete consumption of solid carbon at equivalence ratio 0.39. By increasing equivalence ratio, gasification temperature increases which are supported by experimental results. The comparison of modeling and experimental result shows that difference between model and experimental temperature increases by increasing equivalence ratio. Also, after a short distance from the injector, the temperature is decreased along the gasifier with a constant rate. Finally, in order to provide the optimum gasification operation, the proportion between an appropriate gasifier length and operating equivalence ratio is presented based on one of the gasification reaction.

This paper deals with utilization of the network method to fast analysis of the gas turbine combustors. In this method, a combustor is divided into several independent flows by some nodes and interconnecting elements. The fundamental equations which should be satisfied in the network method are conservation equations of mass and energy at each node and the pressure drop-flow rate correlation for each element. These equations constitute a system of equations of flow rate and pressure drop. Solving this system using a set of initial value gives pressure, flow rate, and density at each node that finally leads to a converging solution. The conventional relations for pipes and orifices are used for flow modeling. In order to combustion modeling, equilibrium assumption is applied in the primary and secondary combustion zones. The dilution effect is considered by entering the air from dilution holes into the flow of combustion products. The liner temperature is calculated by considering the effects of convection and radiation in the combustor. By the network method in a can type combustor, at the first step a cold flow analysis is performed and the flow rate and the pressure drop in each element are obtained. In the next step by including the combustion of kerosene and heat transfer, the distribution of flow rates, pressure, temperature, and species concentration of combustion products are calculated. The computation results are compared with the existing experimental data and an excellent agreement is seen. The quality of results and the solution procedure of the problem show that the network method is able to present a costly and accurate analysis to help the combustor designers

The aim of present article is investigation of evaporation of single- and multi-component fuels droplet and study the effect of unsteadiness term on it. Two approaches are used; a fully transient and quasi-steady approaches. The species, momentum, and energy equations for gas phase and species and energy equations for liquid phase are solve numerically by assuming variable properties with respect to temperature. The results obtained from the fully transient approach show an acceptable compliance with experimental data at atmospheric pressure in a wide range of fuel volatility and ambient temperature for the single- and multi-component fuels. Heptane, decane, and hexadecane are used in order to investigate the effects of fuel volatility on evaporation.The steadiness of processes in the gas phase has been checked by using two measures of unsteadiness related to the mass and heat diffusion of fuel vapor on the droplet surface. The deviations of the results of the quasi-steady approach from the fully transient have been justified by the unsteadiness measures. The results show that fuel and ambient temperature have significant effects on the unsteadiness. For heavier fuels and higher ambient temperature, the diviation of quasi- steady approach from fully transient increases. Also the diviation becomes higher when the differences between volatility of component increase. Therefore, it is concluded that the quasi-steady approach presents reasonable results for lighter fuels in the case of single component and whenever the volatilities of components are very close.

This paper introduces a new type of flame holder. Flow field is investigated, using PIV measurements in cold flow regime. The experiments on two types of V-shape flame holder: one with smooth edges and the other with wavy edges. The instantaneous velocity fields, Strouhal number, average velocity, vorticity, and recirculation zone length were among the parameters affected by the flame holder geometry. In this work, we examined the influence of these characteristics. Complex structure and unsteadiness of the flow was obtained with high accuracy. The results indicate an increase in length and width of the recirculation zone when using the wavy edges instead of smooth edges. For both geometries, a symmetrical flow structure was observed behind the flame holder. Also, higher static pressure drop was detected behind the flame holder for geometry with wavy edges.

In this study evaporation of biodiesel droplet under different operating conditions is investigated. The model is a common droplet vaporization model for multicomponent fuels. In this model, gas phase quasi-steady equations are solved analytically and energy and species transport equation in liquid phase are solved numerically. The sub-models are modified to consider high pressure effects. Peng-Robinson equation of state is used for gas phase and phase equilibrium is determined using fugacity. Effects of pressure on the thermophysical and transport properties of gas phase are considered. Five biodiesel with different composition are studied. These biodiesel have different composition of methyl esters. Biodiesel composition has little effects on droplet lifetime and maximum difference is about 20%. It is observed that increasing ambient temperature leads to decrease in droplet lifetime and increases temperature gradient inside droplet. Ambient pressure has different effects on droplet vaporization behavior at different ambient temperature. At lower temperature environment, increasing of pressure increases the droplet lifetime while at higher temperatures droplet lifetime first increases and then decreases with pressure. Increasing initial velocity of droplet reduces the droplet lifetime. Results show that at high pressures, droplet temperature reach to values near to critical temperature and accuracy of quasi-steady approximation decreases. Radius of vapor influenced sphere increases with temperature and decreases with pressure.

This article investigates experimental study of the flow field on a blunt airfoil. For this purpose, PIV technique based on instantaneous flow structures is used in order to view and two dimensional investigation of flow field around unmodified and blunt airfoil and at different times. This study is performed on flows at very low Reynolds number(Reynolds number lower than 4500). This flow regime is very similar to dominant condition on micro air vehicles (MAVs). In order to validate the method used in this study, flow field around cylinder is considered and in continue, instantaneous and mean velocities fields, streamlines and mean vortices field around unmodified and blunt airfoils are obtained. The results show that there are prominent differences on the structure of wake around airfoils and sizes of separation region for blunt and simple airfoils. Meanwhile separation of the flow for both blunt and simple airfoils at this very low Reynolds number, is occurred at angle of attack 5 (at low angle of attack). Also generation of vortex at wake region and their position and circulation at different times, are discussed.

Atomization is a process by which a volume of liquid is converted spray. This process includes the breakup of the liquid jet or the liquid sheet exiting the injector. This paper has experimentally investigated the models and mechanisms for the breakup of the liquid jet and the liquid sheet formed by the jets impingement in a still environment and in an environment with counter flow, coflow, and cross flow. Also, the effects of the impingement angle, injector diameter, and jet length before impingement on the formation of the liquid sheet have been explored. Imaging has been employed to investigate different patterns formed by these interactions. To produce water jets, injectors with 0.4 and 0.9 mm diameters at a velocity range of 1-33 m/s and in accordance with Reynolds numbers between 3,000 and 30,000 have been used. It was found that in the low flow speed range, the water jet breaks up by the Riley's breakup model. While in high speed range, the breakup model is the firstwind - induced breakup model. The measured breakup length has a very good agreement with the result of Sallam’s equation. In investigating the breakup of liquid jets in cross flow, six breakup models were observed, including Rayleigh-like, turbulent, column, bag, multimode and shear breakup models. Also, in paper, an equation has been presented for the penetration of water jet into an air counter flow. Through a qualitative comparison of the images taken from the impingement of two water jets, velocity and Reynolds number ranges of the closed rim, alternating drops, open rim, and fully-developed models were determined. It was observed that, by increasing pre- impingement length of a jet, the instabilities on the liquid sheet increase.

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 paper، the effects of size and density on mixing of solid particles in a fluidized bed have been studied experimentally. For this purpose، a bed consisting of silica sands has been used. The mixing of particles in a two-layer bed has been studied. The lower layer consists of silica sands، while in the upper layer tracer sand particles with different shape، size، density، and color have been used. All events occurring on the bed surface are recorded by a camera above the bed and tracer particles are being tracked، using image processing technique. Particles being mixed in the bed are studied by studying the variation of the tracer particles concentration index with time. First، the mechanism of particle mixing in a two-layer fluidized bed was investigated. Then، the effect of the characteristics of mixing particles on mixing process was studied. The results show that increasing the tracer particle density (approaching the bed sands density)، enhances the penetration of tracer in the bed and reduces the tracer presence on the bed surface. Also، the size of sand particles has significant effect on mixing quality; it makes it possible to find a proper sand size to mix the particles with different densities.

In order to determine accurate solid propellant burning rate by ultrasonic method، pressure dependency relationship of sample`s sound speed should be applied on thickness algorithm. This article presents comprehensive background in ultrasonic method and its application in burning rate measurement. Also pressure dependency of sound speed for several composite propellants based on HTPB had been investigated. Experimental samples with 30 mm length and 30 mm diameter had been tested under different pressure. The sound speed values were determined in each pressure by measuring the flight time of omitted ultrasonic waves and its returned echoes. The pressure varied from zero to 100 bar and the experiments were done for both pressurization and depressurization conditions. The results show that the samples sound speed depends slightly on pressure. Furthermore this relationship is linear. For instance it has been showed that pressure dependent for the speed of sound of HTPB sample had varied over 40 m/s for 1640 m/s average value. Other cases reviewed in this study were to evaluate the effect of pressure on sound speed for variety composition of HTPB with AL and AP particles. At the end some relevant experiments were done for uncertainty analysis of sound speed measurement. 3% uncertainty which is obtained for the sound speed measurements for HTPB is acceptable in comparison with other scientists` experimental results.

he application of the hydrogen peroxide as the oxidizer of a HTPB-based prototype ybrid motor is investigated in this paper. First of all, by studying the thermochemical haracteristics of the propellant,operation range of different compositions is defined. A rototype hybrid motor is then designed and manufactured, which is able to produce 10 kg propellant thrust. Conducting a special procedure available stabilized commercial hydrogen peroxide is processed and converted to a 90% density propellant which has less than 15 ppm tainting. A catalytic igniter is used in order to fire the motor. It was observed that the approach of employing the oxidizer to the catalyst bed is highly effective on the quality of the system performance. So, the injection quality of the oxidizer was investigated for different mass flow rates. The performance of the hybrid motor by HTTPB fuel is studied in a successful experimental test. The results of the test including the pressure and characteristic velocity are compared with the predicted theoretical simulations. Moreover, the performance specifications of the motor like the regression rate are determined and compared with the similar researches.

Instantaneous grain geometry is one of the most affecting parameters on the performance of the solid rocket motors (SRMs). This paper presents the simulation of geometrically complicated solid propellant grain burnback using the level set method. The initial form of the grain is assumed in this method. Propagation of the grain boundaries in a velocity field is described using the Hamilton-Jacobi type equation. The solution of this equation in successive time steps gives the new burning boundaries of the grain. For this purpose, the initial geometry of grain is modeled in any CAD software. Then, the initial burning surfaces of grain are implicitly defined by the sign distance function and are used as the initial conditions of the level set equation. The geometrical characteristics of grain, such as burning surface area, port area, burning perimeter, and port volume are determined by Heaviside and Delta Dirac functions. The result of simulation is validated by an analytically predictable case, which shows excellent agreement. Burnback analysis is done for some practical grains including two cases that the test data were available. Using an unsteady zero dimension interior ballistic analysis, the resulting motor pressure curves are compared with the experimental data showing good agreement. The capability of the approach to handle the analyzing of problems, including non uniform burning velocity and arbitrary burnout configurations of grain are shown in examples.

This paper is dealing with the development of a new version of an existing burning model for predicting the burning rate of different pyrotechnic mixtures of magnesium and sodium nitrate. Modifying some parts of the model including burning time of magnesium particles, thermophysical properties of combustion products, and the mixture density, the burning rate has been predicted for different values of mixture composition and combustion pressure. Comparison of the predicted and available experimental values of the burning rates shows good agreements, especially in pressure dependency.

Iqala (cancelling of the contract) is a legal act that is formed by side's satisfactory contract and makes it breakup. Imami, Hanbali and Shafei Jurists revocate the Iqala. Hanafi Jurists account Iqala revocation into sides of contract, but a new transaction into outsiders. From the Maleki jurists viewpoint, Iqala is a new transaction, but civil code accounts the Iqala Tafasokh (breaking up by sides of contract). It seems that by reason of satisfaction, which is principal element and nature of the contract, Iqala is an indeterminate contract. Unlike the views of maleki and hanafi jurists, Imami, Hanbali and Shafei Jurists believe that Iqala doesn’t make shofaa. According to some jurists, on the base of being a new contract of the Iqala, it is possible to increase or decrease of the saman (recompense of the transaction). On the base of being a transaction of Iqala, it is not possible to breakup (Iqala). On the base of being a new contract of Iqala, perishing of the Avazein (price and its subject) or one of them, suppresses to breakup (Iqala) the contract. Maleki and Hanafi jurists allow the Iqala and making an option in that; but Imami, shafei and Hanbali jurists believe otherwise.