Application of the DSMC Method for Design of a Coaxial Microthruster Nozzle

The Direct Simulation Monte Carlo (DSMC) method is used to numerically simulate and design a micronozzle with improved performance. Thrust calculations using the DSMC method demonstrate that the coaxial micronozzles can achieve milli-Newton thrust levels with specific impulses on the order of 45 s using argon in a cold gas expansion. Improved micronozzle designs of coaxial microthrusters are also proposed. Coaxial micronozzles utilizing center-body geometries to exploit pressure thrust show about 140% increase in specific impulse at low Reynolds numbers compared to a traditional converging nozzle

Effect of molecular models on viscosity and thermal conductivity calculations

The effect of molecular models on viscosity and thermal conductivity calculations is investigated. The Direct Simulation Monte Carlo (DSMC) method for rarefied gas flows is used to simulateCouette and Fourier flows as a means of obtaining the transport coefficients. Experimentalmeasurements for argon (Ar) provide a baseline for comparison over a wide temperature range of 100–1,500 K. The variable hard sphere (VHS), variable soft sphere (VSS), and Lennard-Jones (L-J) molecular models have been implemented into a parallel version of Bird’s one-dimensional DSMC code, DSMC1, and the model parameters have been recalibrated to the current experimental data set. While the VHS and VSS models only consider the short-range, repulsive forces, the L-J model also includes constributions from the long-range, dispersion forces. Theoretical results for viscosity and thermal conductivity indicate the L-J model is more accurate than the VSS model; with maximum errors of 1.4% and 3.0% in the range 300–1,500 K for L-J and VSS models, respectively. The range of validity of the VSS model is extended to 1,650 K through appropriate choices for the model parameters

Gain and Stability Models for HBT Grid Amplifiers

A 16-element heterojunction bipolar transistor (HBT) grid amplifier has been fabricated with a peak gain of 11 dB at 9.9 GHz with a 3-dB bandwidth of 350 MHz. We report a gain analysis model for the grid and give a comparison of the measurement and theory. The measured patterns show the evidence of a common-mode oscillation. A stability model for the common-mode oscillation is developed. Based on the stability model, a lumped capacitor gives suitable phase shift of the circular function, thus stabilizing the grid. A second 18-element grid was fabricated, using this theory, with improved stability

Plasma-Neutral Heat Transfer in Coaxial RF Argon Discharges

Particle-in-cell/Monte Carlo Collision (PIC/MCC) algorithms comprise a numerical model to assess the discharge characteristics of an RF plasma microthruster concept that exploits an RF capacitively coupled discharge (RFCCD) to heat a propellant. The effects of heat transfer between the discharge and the neutral species on microthruster performance are discussed. Heat transfer within the plasma discharge has been shown to greatly affect the discharge characteristics and thruster performance. Increasing the neutral temperature reduces the amount of power transmitted into the fluid through a reduction of the neutral density, and thus reduces effectiveness of the discharge. The PIC/MCC modeling showed that the power transmitted into the fluid increases faster than linear with respect to an increase in applied potential, but the total power absorbed increases on the order of a linear trend. The power transmission efficiency is found to be directly proportional to the applied potential, making the discharge more efficient at higher voltages. The theoretical specific impulse also increases as the applied potential or discharge pressure is increased

RFCCD Microthruster Performance via Numerical Simulation

Particle-in-cell/Monte Carlo (PIC/MCC) and Direct Simulation Monte Carlo (DSMC) algorithms comprise a numerical model to assess the propulsive capability of a RF plasma microthruster concept. This thruster concept is an electrothermal device and exploits RF capacitively coupled discharge (RFCCD) to heat a propellant. This RF plasma microthruster has potential to alleviate some severe constraints on microsatellite propulsion systems such as power, mass, volume and lifetime. The discharge characteristics are investigated by permuting electrode geometry (0.5 - 10 mm) and applied voltage (10 - 500 V) at a constant RF frequency of 200 MHz and a pressure of 3 Torr. PIC/MCC simulations determine the overall trends in plasma characteristics within this parameter space. The PIC/MCC modeling showed that increases in applied potential and inner radius transmit more power to the fluid. A gas heat transfer model enhanced the original PIC/MCC code to reflect effects of neutral gas temperature in the plasma

Performance Modeling of an RF Coaxial Plasma Thruster

The RF plasma thruster has considerable potential to ease the impact of severe constraints on power, mass, volume and lifetime of microsatellite propulsion systems. This concept is classified as an electrothermal propulsion system and exploits RF capacitively coupled discharge (RFCCD) for heating of a propellant. The plasma is characterized as a low-power discharge possessing a low-current density with high uniformity and propagating through low-pressure gas. To assess computationally the thruster’s propulsive capabilities as a function of mass flow rate, electrode separation, RF frequency and power input, a numerical model comprises particle-in-cell/Monte Carlo (PIC/MCC) and Direct Simulation Monte Carlo (DSMC) algorithms. Thruster performance is investigated by permuting electrode geometry (0.5 - 2 cm), chamber pressure (0.05 - 50 Torr), applied voltage (100 - 500 V), and frequency (10 - 1000 MHz). For this parameter space, PIC/MCC determines overall trends in plasma characteristics. One selected case (3 Torr, 500 V, 200 MHz) and its set of conditions (plasma density, plasma heating, gas temperature, etc.) form the basis for an in-depth flow field and thrust performance analysis with DSMC. Assuming adiabatic wall conditions, the RF plasma thruster achieves a specific impulse of 104.4 s with Argon at the throat Reynolds number of 25. The RF heating increases the specific impulse by 125 %. This study shows that propulsive capability of the RF plasma thruster can be enhanced by increasing the discharge chamber length, redesigning the nozzle contour, and using propellants with lower molecular weights

Проектирование электрической части ТЭЦ установленной мощностью 127 МВт

Объектом исследования является электрическая часть теплоэлектроцентрали. Целью работы является проектирование электрической части теплоэлектроцентрали, выбор основное силовое оборудование, выполнения расчет режима работы трансформатора, исследование вставки постоянного тока. Актуальность проектирования теплоэлектроцентрали заключается в том, что их мощность обычно такова, что может обеспечить электроэнергией город. Так же имеется возможно обеспечить город теплоснабжением.The object of the study is the electrical part of the co-generation plant. The aim of the work is the design of the electrical part of the co-generation plant, the selection of the main power equipment, the calculation of the operating mode of the transformer, the study of the high-voltage direct current link. The actuality of designing a co-generation plant is that their power is usually such that it can provide electricity to the city. It is also possible to provide the city with heat

Experimental and Computational Investigation of a RF Plasma Micro-Thruster

A prototype RF plasma micro-thruster has been investigated numerically and experimentally. The experimental results were obtained on a thrust stand capable of micro-Newton resolution. Thrust and mass flow (hence specific impulse) were measured for an argon propellant at mass flows ranging from 0.4 to 5.5 mg/s. An increase over the cold gas thrust of up to 20% was observed for a discharge frequency of 100 MHz and an input power of 77 W. Propulsive efficiency was seen to increase both experimentally and numerically for increasing mass flow and decreasing discharge frequency