The Helium compressor has the inherent characteristics of a lower single-stage pressure ratio and a higher number of stages than an air compressor. The highly loaded design method effectively addressed the compressibility issue of the Helium compressor. However, the compressor designed with this technique has narrow passages, short blades, and a large bending angle, making the end-wall secondary flow more intense than a conventional compressor. In this paper, numerical simulation and experimental validation has been conducted to identify the effectiveness of the axial slot close to the blade root in improving end-wall secondary flow in a high-load Helium compressor cascade, and to provide data and experimental support for the engineering application of high-load Helium compressors. The analytical results show that slotting can utilize the self-pressure difference to generate gap leakage vortices, and the axial momentum generated by the leakage vortices blows away the vortices formed due to the separation of corner area. The airflow flows close to the suction surface of the blade and breaks away at the trailing edge of the blade, merges with the main flow and forms a new vortex. As the height of the channel increases, the blowing away of the vortices in the corner region becomes more pronounced and the cascade improvement performance is better. The test results show that the total pressure loss coefficient at the design operating point is reduced by 6.167% when a slot height of 8.53 mm is positioned at 65% Ca (axial chord length). The improvement effect becomes 16.469% better at a 4° attack angle.

Primary nozzle is one of the most important factors which has a large influence on the performance of thermo-compressors. Most of studies carried out until now, have been performed on single-nozzle thermo-compressors. In this paper, an actual industrial thermo-compressor is considered and the purpose is to study the effect of increasing primary nozzle number on the performance of this thermo-compressor. For this purpose, a triple-nozzle thermo-compressor is simulated numerically and its performance is compared with single-nozzle thermo-compressor. Ideal gas thermodynamic properties are considered to simulate the compressible flow within the thermo-compressor and numerical result is validated using the experimental result. In addition, the effects of variation in mixing chamber convergence angle and position of nozzles at the radial direction in triple-nozzle thermo-compressor are investigated. The numerical results show that at the same condition, a triple-nozzle thermo-compressor is able to provide superior critical back pressure and entrainment ratio than single-nozzle thermo-compressor. The proximity of nozzles (with 34% changes in radial distance) increases the critical back pressure about 8% and decreases the entrainment ratio about 5%. By increasing mixing chamber convergence angle about 66%, the value of critical back pressure decreases about 29% and the value of entrainment ratio decreases about 16% in single nozzle-thermo-compressor and 10% in triple-nozzle thermo-compressor. Also, by 8% reduction of mixing chamber convergence angle, the critical back pressure decreases 6% but entrainment ratio decreases about 2% in single-nozzle thermo-compressor and increases about 3% in triple-nozzle thermo-compressor.

Optically pumped Helium magnetometers are important instruments which have many applications in military, mass spectroscopy and space applications. In this paper, the working principles of Helium magnetometers have been explained. There is also an introduction of a new method for finding the resonant frequency, which has advantages to the typical method such as more sample rate possibility and realizing with cheaper prices.

This article describes an accurate subPico flowmeter bifurcatedin to liquid and gas flowrates less than 1mol/s for both MEMS/NEMS and cryogenic technology applications. The MEMS/NEMS are described as either two Gauges (instrument), or quartz fluctuating forks, even if the liquid or gas flows through an element, as well as cryogenic technology consisting of arrays of either parallel photonic crystal micelles or parallel rectangular nano-channels by using the lithography and anodic bonding techniques on silicon micelles. The behavior of gas or liquid Helium at high pressure was found to differ from the prediction of the conventional Heigen Equation. A hydro-dynamic model showed a gas or liquid properties namely molar flow rate, input and output pressure, two pressure gauges or quartz fluctuating (Todd Helmenstine) forksand the temperature. The measurements with fluid Helium demonstrated that the flow cells could span the flow range from 10-15 to 10-12 mol/s. This paper had focused on a versatile method of creating wide area defect free crystals based on interference lithography (MEMS/NEMS and cryostat). This technique involves splitting a monochromatic plane wave from a laser into multiple beams and recombining them inside a photoresist (fluid compressibility).

The unstable flow with rotating-stall-like (RS) effects in a rotor-cascade of an axial compressor was numerically investigated. The RS was captured with the reduction in mass flow rate and increasing of exit static pressure with respect to design operating condition of the single rotor. The oscillatory velocity traces during the stall propagation showed that the RS vortices repeat periodically, and the mass flow rate was highly affected by the blockage areas made by stall vortices. The results also showed that large scale vortices highly affects on the generation and growth of the new vortices. An unsteady two-dimensional finite-volume solver was employed for the numerical study which was developed based on Van Leer’s flux splitting algorithm in conjunction with TVD limiters and the κ-ε turbulence model was also employed. The good agreement of the computed mass flow rate with the experimental results validates the numerical study.

An analytical treatment of the electron screening effect within an active electron model is given for positronium formation from Helium atoms. A first order distorted wave approximation with correct boundary conditions is applied to evaluate the transition amplitude. In the range of impact energy for which the introduced perturbative approach is valid, both the total and differential cross sections are calculated and the results for total cross sections are compared with the other calculations and with the available experimental data.