Effect of natural convection on oscillating flow in a pipe with cryogenic temperature difference across the ends

The effect of natural convection on the oscillatory flow in an open-ended pipe driven by a timewise sinusoidally varying pressure at one end and subjected to an ambient-to-cryogenic temperature difference across the ends, is numerically studied. Conjugate effects arising out of the interaction of oscillatory flow with heat conduction in the pipe wall are taken into account by considering a finite thickness wall with an insulated exterior surface. Two cases, namely, one with natural convection acting downwards and the other, with natural convection acting upwards, are considered. The full set of compressible flow equations with axissymmetry are solved using a pressure correction algorithm. Parametric studies are conducted with frequencies in the range 5–15 Hz for an end-to-end temperature difference of 200 and 50 K. Results are obtained for the variation of velocity, temperature, Nusselt number and the phase relationship between mass flow rate and temperature. It is found that the Rayleigh number has a minimal effect on the time averaged Nusselt number and phase angle. However, it does influence the local variation of velocity and Nusselt number over one cycle. The natural convection and pressure amplitude have influence on the energy flow through the gas and solid

CFD analysis of high frequency miniature pulse tube refrigerators for space applications with thermal non-equilibrium model

High frequency, miniature, pulse tube cryocoolers are extensively used in space applications because of their simplicity. Parametric studies of inertance type pulse tube cooler are performed with different length-to-diameter ratios of the pulse tube with the help of the FLUENT® package. The local thermal non-equilibrium of the gas and the matrix is taken into account for the modeling of porous zones, in addition to the wall thickness of the components. Dynamic characteristics and the actual mechanism of energy transfer in pulse are examined with the help of the pulse tube wall time constant. The heat interaction between pulse tube wall and the oscillating gas, leading to surface heat pumping, is quantified. The axial heat conduction is found to reduce the performance of the pulse tube refrigerator. The thermal non-equilibrium predicts a higher cold heat exchanger temperature compared to thermal equilibrium. The pressure drop through the porous medium has a strong non-linear effect due to the dominating influence of Forchheimer term over that of the linear Darcy term at high operating frequencies. The phase angle relationships among the pressure, temperature and the mass flow rate in the porous zones are also important in determining the performance of pulse tube refrigerator

Production of Intermediate or Medium Carbon Ferro Chrome at FACOR

FACOR has foreseen the need to develop the intermediate carbon ferro chrome alloy to meet the demands of alloy and stainless steel manufacturers.The paper describes the decarbonisation of liquid high carbon ferro chrome in. an AOD convertor with respect to : (a) Theoretical aspects and fundamentals, (b) Plant and equipment, (c) Process of making intermediate carbon ferro chromium., (d) Advantages of the processto improve the quality with respect to titanium, silicon, hydrogen and nitrogen in intermediate carbon ferro chromium

Reinvestigation of the second negative (A<SUP>2</SUP>&#928;<SUB>u</SUB>-X<SUP>2</SUP>&#928;<SUB>g</SUB>) band system of O<SUB>2</SUB><SUP>+</SUP>

The A2&#928;u state of O2+ was earlier established as an inverted state contrary to previous assumptions. The rotational analysis of a few more bands of the A-X system of O2+ has now been completed. These studies show that the spin-orbit coupling constant A in the A2&#928;u state gradually varies with the vibrational quantum number &#957; and is found to be positive for &#957;&#8805;6. It has also been observed that the spia-rotation interaction is not negligible in the A 2 &#928;u state. The spin splitting constant &#947; is reported for various vibrational levels of this electronic state

Mass Attenuation Coefficient Measurements of Some Nanocarbon Allotropes: A New Hope for Better Low Cost Less-Cumbersome Radiation Shielding Over A Wide Energy Range

The mass attenuation coefficients of graphene, MWNTs and, SWNTs have been measured for gamma energy range 356 to 1332 keV from the radioactive sources 60Co, 133Ba and 137Cs using a well calibrated gamma ray spectrometer consisting of a 3 ́ ́x 3 ́ ́ NaI(Tl) scintillation detector coupled to a PC based 8K nuclear Multi Channel Analyser (MCA). In an interesting way results showed that MWNTs had the highest values of mass attenuation coefficients indicating their potential use as the best shielding material

Open and endovascular repair of the nontraumatic isolated aortic arch aneurysm

ObjectiveRepair of isolated aortic arch aneurysms (nontraumatic) by either open (OAR) or endovascular (TEVAR) methods is associated with need for hypothermic circulatory arrest, complex debranching procedures, or use of marginal proximal landing zones. This study evaluates outcomes for treatment of this cohort.MethodsOf 2153 patients undergoing arch repair (1993-2013), 137 (mean age, 60 years) were treated with isolated arch resection for nontraumatic aneurysms. Treatment was by open (n = 93), hybrid (n = 11), or TEVAR (n = 33) methods, with the last two approaches reserved for poor OAR candidates. Treatment was predominantly for saccular (n = 53) or fusiform (n = 30) aneurysms or dissection (n = 15). Rupture was present in 15%. Prior aortic repair was performed in the ascending (n = 30), arch (n = 40), descending (n = 24), or abdominal (n = 9) aorta. Propensity score adjustment was performed for multivariable analysis to account for baseline differences in patient groups as well as treatment selection bias.ResultsEarly mortality was seen in nine patients (7%). Morbidity included stroke (n = 9), paraplegia (n = 1), and need for dialysis (n = 5) or tracheostomy (n = 10). A composite outcome of death and stroke was independently predicted by advancing age (P = .055) and performance of a hybrid procedure (P = .012). The 15-year survival was 59%, with late mortality predicted by increasing age, presence of peripheral vascular disease, and perioperative stroke (all P < .05). The 10-year freedom from aortic rupture or reintervention was 75% and was higher after OAR (2-year OAR, 94% vs TEVAR or hybrid, 78%; P = .018). After propensity-adjusted Cox regression analysis, both prior abdominal aortic aneurysmectomy (P = .017) and an endovascular or hybrid procedure (P = .001) independently predicted late aortic rupture or need for reintervention.ConclusionsIsolated arch repair remains a high-risk procedure occurring frequently in the reoperative setting. Despite being performed in a higher risk group, endovascular strategies yielded similar outcomes but with an increased risk for aorta-related complications. These data support ongoing efforts to develop branched endografts specifically tailored for arch disease to potentially reduce morbidity related to currently available approaches

The Effectiveness of TAG or Guard-Gates in SET Suppression Using Delay and Dual-Rail Configurations at 0.35 microns

Design options for decreasing the susceptibility of integrated circuits to Single Event Upset (SEU) fall into two categories: (1) increasing the critical charge to cause an upset at a particular node, and (2) employing redundancy to mask or correct errors. With decreasing device sizes on an Integrated Circuit (IC), the amount of charge required to represent a logic state has steadily reduced. Critical charge methods such as increasing drive strength or increasing the time required to change state as in capacitive or resistive hardening or delay based approaches extract a steadily increasing penalty as a percentage of device resources and performance. Dual redundancy is commonly assumed only to provide error detection with Triple Modular Redundancy (TMR) required for correction, but less well known methods employ dual redundancy to achieve full error correction by voting two inputs with a prior state to resolve ambiguity. This requires special circuits such as the Whitaker latch [1], or the guard-gate [2] which some of us have called a Transition AND Gate (TAG) [3]. A 2-input guard gate is shown in Figure 1. It is similar to a Muller Completion Element [4] and relies on capacitance at node "out" to retain the prior state when inputs disagree, while eliminating any output buffer which would be susceptible to radiation strikes. This paper experimentally compares delay based and dual rail flip-flop designs wherein both types of circuits employ guard-gates to optimize layout and performance, and draws conclusions about design criteria and suitability of each option. In both cases a design goal is protection against Single Event Transients (SET) in combinational logic as well as SEU in the storage elements. For the delay based design, it is also a goal to allow asynchronous clear or preset inputs on the storage elements, which are often not available in radiation tolerant designs

Electrical conductivity studies in K<SUB>2</SUB>SO<SUB>4</SUB>-ZnSO<SUB>4</SUB> glasses

The d.c. conductivities of K2SO4-ZnS04 glasses have been measured over a wide range of temperature. It has been found that two different subglassy activation energies are present which may be associated with K+ and Zn++ ions. Also a conductivity maximum occurs as a function of composition. These features have been discussed in the light of the random close packed model of sulphate glasses