Minimum Pressure Values Research Articles

Measurement and modeling of pulsatile flow in microchannel

An experimental study of pulsatile flow in microchannel is reported in this paper. Such a study is important because time-varying flows are frequently encountered in microdevices. The hydraulic diameter of the microchannel is 144 μm and deionized water is the working fluid. The pressure drop across the microchannel as a function of time is recorded, from which the average and r.m.s. pressure drops are obtained. The experiments have been performed in the quasi-steady flow regime for a wide range of flow rate, frequency of pulsations, and duty cycle. The results suggest that the pressure with pulsations lies between the minimum and maximum steady state pressure values. The average pressure drop with pulsation is approximately linear with respect to the flow rate. The theoretical expression for pressure has also been derived wherever possible and the experimental data is found to lie below the corresponding theoretical values. The difference with respect to the theoretical value increases with an increase in frequency and a decrease in flow rate, with a maximum difference of 32.7%. This is attributed to the small size of the microchannel. An increase in frequency of square waveform leads to a larger reduction in pressure drop as compared to rectangular waveform, irrespective of the duty cycle. The results can be interpreted with the help of a first-order model proposed here; the model results are found to compare well against the experimental results. A correlation for friction factor in terms of the other non-dimensional governing parameters is also proposed. Experimental study of mass-driven pulsatile flow in microchannel is being conducted for the first time at these scales and the results are of both fundamental and practical importance.

LES of the Slipstream of a Rotating Train

The slipstream of a high-speed train was investigated using large-eddy simulation (LES). The subgrid stresses were modeled using the standard Smagorinsky model. The train model consisted of a four-coach of a 1/25 scale of the ICE2 train. The model was attached to a 3.61 m diameter rotating rig. The LES was made at two Reynolds numbers of 77,000 and 94,000 based on the height of the train and its speed. Three different computational meshes were used in the simulations: course, medium and fine. The coarse, medium, and fine meshes consisted of 6×106, 10×106, and 15×106 nodes, respectively. The results of the fine mesh are in fairly agreement with the experimental data. Different flow regions were obtained using the LES: upstream region, nose region, boundary layer region, intercarriage gap region, tail region, and wake region. Localized velocity peak was obtained near the nose of the train. The maximum and minimum pressure values are also noticed near to the nose tip. Coherent structures were born at the nose and roof of the train. These structures were swept by the radial component of the velocity toward the outer side of the train. These structures extended for a long distance behind the train in the far wake flow. The intercarriage gaps and the underbody complexities, in the form of supporting cylinders, were shown to have large influences on the slipstream velocity. The results showed that the slipstream velocity is linearly proportional to the speed of the train in the range of our moderate Reynolds numbers.

Acoustics impact on steam dryer induced by main steam line break in a boiling water reactor

In boiling water reactor (BWR) design, significant acoustic pressure loads impact the steam dryer hood as a result of the main steam line break outside containment (MSLB) event. When a main steam line breaks, it is assumed that the pipe instantaneously breaks completely open to the ambient environment (double-ended guillotine break). Due to the huge pressure difference between the inside of the reactor pressure vessel (RPV) and surrounding ambient environment, a shock wave will form at the break point and burst into the surrounding environment. At the same time, an expansion wave will travel upstream through the main steam line to the RPV, which results in a pressure reduction on the outside of the steam dryer hood. This expansion wave will create a substantial pressure difference between the two sides of the steam dryer hood with a resultant high stress on the hood. This differential pressure load is the acoustic load used in the structure design evaluations for this event. A key design basis requirement for the steam dryer is to maintain structural integrity during transient, and accident conditions. Demonstration that the steam dryers meet this design basis requires a calculation of the magnitude of the acoustic load on the steam dryer during a MSLB. In this study, computational fluid dynamics (CFD) is used as an alternate calculation method to investigate the phenomenon of MSLB. Transient simulations with fine time steps were carried out. The results show that CFD is a useful tool to provide additional information on the acoustic load as compared to the traditional methods. From the CFD results, the minimum pressure value and its distribution area at different flow times was identified. Through the modeling, an understanding of the detailed transient flow field, particularly the acoustic pressure field near the dryer hood during the MSLB was achieved.

Optimization of recompression S-CO 2 power cycle with reheating

In the present study, optimization of compressor pressure ratio and intermediate pressure between HP and LP turbines leading to maximum thermal efficiency is implemented for a supercritical CO 2 recompression cycle with reheating applicable to next generation nuclear reactors. Effects of various operating conditions and component performances on the optimal values and cycle efficiency are studied as well. Finally, a comparison between supercritical CO 2 recompression cycles with and without reheating is presented. The optimization of recompression mass fraction shows that the present cycle configuration yields maximum thermal efficiency for nearly equal heat capacity values of both fluids in LTR. The effect of maximum cycle temperature on the optimum pressure ratio is negligible for lower values of minimum cycle temperature and maximum pressure, and the effect becomes significant with an increase in these parameters. Results show that the thermal efficiency improves with a decrease in minimum cycle temperature and with increase in maximum cycle temperature and pressure. The optimum intermediate pressure is exhibited to be higher than the geometric mean value between minimum and maximum pressure and a simple empirical correlation useful for optimum design is presented. The maximum efficiency improvement using reheating is calculated as 3.5% at optimum conditions.

Effects of Rarefaction on Cavity Flow in the Slip Regime

The Navier-Stokes-Fourier equations, with boundary conditions that account for the effects of velocity-slip and temperature-jump, are compared to the direct simulation Monte Carlo method for the case of a lid-driven micro-cavity. Results are presented for Knudsen numbers within the slip-flow regime where the onset of nonequilibrium effects are usually observed. Good agreement is found in predicting the general features of the velocity field and the recirculating flow. However, although the steady-state pressure distributions along the walls of the driven cavity are generally in good agreement with the Monte Carlo data, there is some indication that the results are starting to show noticeable differences, particularly at the separation and reattachment points. The modified Navier-Stokes-Fourier equations consistently overpredict the maximum and minimum pressure values throughout the slip regime. This highlights the need for alternative boundary formulations or modeling techniques that can provide accurate and computationally economic solutions over a wider range of Knudsen numbers.

Catalytic filter elements for combined particle separation and nitrogen oxides removal from gas streams

The development of a catalytically active ceramic filter element for the combined removal of particles and nitrogen oxides from gas streams is presented. A special catalyst support layer with a high BET surface followed by optimized catalytic activation was developed to reach the required nitrogen oxides (NO x) emission levels. The catalytic properties of the developed filter element were studied in detail in a small test rig using cylindrical filter segments. The catalytic filter elements were tested under different operating conditions, such as filtration velocity, operating temperature, and nitrogen oxide (NO) inlet concentrations. Moreover, the filtration properties of the filter elements were determined. As result of these studies, the optimum operating conditions for the catalytic filter element are determined with respect to a minimum differential pressure value in combination with a high catalytic activity towards NO x removal. The advantages and possibilities of the newly developed filter elements are shown and discussed.

The Effects of Splitter Plates on the Vortex Structure behind a Long Flat Plate with a Blunt Trailing Edge

An experimental investigation has been made on the vortex structure behind a long flat plate with a blunt trailing edge. The flow was controlled by an additional splitter plate attached to the trailing edge along the wake center line. The length of the splitter plate, l, was varied from a half to five times the trailing edge thickness, h. Measurements of vortex shedding frequency and of fluctuating velocity and pressure distributions were made in the vortex formation region under the freestream zero pressure gradient. Without splitter plate (l/h=0), the remarkable difference of Strouhal number, S, between for the long flat plate and for the short flat plate, has arisen. A maximum value of the Strouhal number was achieved at the splitter plate length of l/h=1.5, which is the same size for the short flat plate, attached to the long flat plate. The vortex strength expressed by the minimum pressure value on the wake center line, showed a tendency for vortex formation to be suppressed with the splitter plate of l/h≥1, which gave the same trend for the base pressure distribution. The vortex formation length, shear layer thickness, and the reattachment length have been discussed in connection with the vortex shedding.

Performance Evaluation Method for Drainage Piping Systems with Food Disposers in Actual High-Rise Apartment Houses

Regarding drainage piping systems with food disposers in actual super high-rise apartment houses with a height 100m, results were acquired from the experiments for the initial performance evaluation before habitation as well as the running performance evaluation by drainage load prediction after habitation. The knowledge, which contributed to a performance test, was also acquired. Before habitation, the maximum number of 6 simultaneous units of garbage wastewater, bowl flushing water, etc. was loaded. The maximum and minimum air pressure values in pipes were checked in line with the performance criteria of SHASE-S, and the safety of the initial performance was also verified. After habitation, the maximum number of simultaneous drainages was predicted and it was found that the figure recorded at the time of the initial performance verification was satisfactory. Moreover, the running pressure values in 99% of the occurrence probability were acquired, and the safety of running performance was also verified. Furthermore, the relation between the house drain′s water level as a drainage load index and the pressure was determined, and as a result of comparison of pre-habitation and post-habitation, it was confirmed that there was no significant performance deterioration caused by long-term use.

Tongue pressure on loop of transpalatal arch during deglutition

The purpose of this study was to measure tongue pressure exerted on the loop of the transpalatal arch (TPA) during deglutition and to consider the influence of the distance of the loop of the TPA from the palatal mucosa and the anteroposterior position of the loop. Tongue pressures of 4 subjects with normal occlusion were measured with subminiature pressure sensors fixed on the TPA. The distances from the palatal mucosa to the surface of the pressure sensor were set at 2, 4, and 6 mm. The loop of the TPA was placed at the level of the middle of the maxillary second premolars (P), first molars (M1), or second molars (M2). Nine types of TPA devices were measured for each subject. The maximum recorded tongue pressure was taken from each act of deglutition. The minimum pressure value was exerted at position P when the distance from the palatal mucosa to the surface of the pressure sensor was 2 mm. The maximum value was obtained at position M2 and a distance of 6 mm from the palatal mucosa. When distances of 2, 4, and 6 mm were compared, significant differences between 2 and 4 mm, and between 2 and 6 mm were found. Significant differences were observed in comparisons between the positions P and M1, M1 and M2, and P and M2. (Am J Orthod Dentofacial Orthop 2003;123:29-34)

Glibenclamide improves postischemic recovery of myocardial contractile function in trained and sedentary rats

In this study, we sought to determine whether there was any evidence for the idea that cardiac ATP-sensitive K+ (K(ATP)) channels play a role in the training-induced increase in the resistance of the heart to ischemia-reperfusion (I/R) injury. To do so, the effects of training and an K(ATP) channel blocker, glibenclamide (Glib), on the recovery of left ventricular (LV) contractile function after 45 min of ischemia and 45 min of reperfusion were examined. Female Sprague-Dawley rats were sedentary (Sed; n = 18) or were trained (Tr; n = 17) for >20 wk by treadmill running, and the hearts from these animals used in a Langendorff-perfused isovolumic LV preparation to assess contractile function. A significant increase in the amount of 72-kDa class of heat shock protein was observed in hearts isolated from Tr rats. The I/R protocol elicited significant and substantial decrements in LV developed pressure (LVDP), minimum pressure (MP), rate of pressure development, and rate of pressure decline and elevations in myocardial Ca(2+) content in both Sed and Tr hearts. In addition, I/R elicited a significant increase in LV diastolic stiffness in Sed, but not Tr, hearts. When administered in the perfusate, Glib (1 microM) elicited a normalization of all indexes of LV contractile function and reductions in myocardial Ca(2+) content in both Sed and Tr hearts. Training increased the functional sensitivity of the heart to Glib because LVDP and MP values normalized more quickly with Glib treatment in the Tr than the Sed group. The increased sensitivity of Tr hearts to Glib is a novel finding that may implicate a role for cardiac K(ATP) channels in the training-induced protection of the heart from I/R injury.

A Climatology of Transition Season Colorado Cyclones: 1961–1990

Abstract Frequency, track, and intensity characteristics of transition season Colorado cyclones are investigated for the period 1961–90. Monthly cyclone totals are examined for evidence of seasonal frequency variations during the study period. Cyclone track maps for the months of April, May, October, and November are produced and analyzed for variations in azimuth and movement rates. In addition, the monthly distributions of minimum central pressure values are discussed. Transition season Colorado cyclone annual frequencies declined significantly during the period 1961–90, although the decline occurred primarily during the spring months. April has the most Colorado cyclone occurrences of the months examined. Spring and fall Colorado cyclone tracks are shown to be similar in trajectory and 48 h azimuth, though slightly variant in movement rates. Cyclones developing in months closer to the strong Northern Hemisphere winter circulation (April and November) regime tend to be more vigorous in terms of central ...

Pressure deflagration limit of solid rocket propellants: Experimental results

The burning of solid rocket propellants at pressures above and below the pressure deflagration limit (PDL) has been studied experimentally to obtain more details about the propellant combustion behavior in this critical pressure range. This work essentially is devoted to devising an experimental procedure to measure the PDL value with good reproducibility and to check its dependence on the operating conditions and propellant nature. Comparisons between different go/no-go techniques are presented, showing the chosen procedures to yield different results. Several solid rocket propellants have been tested (metalized and nonmetalized composite propellants, catalyzed double-base propellant). The results show a strong decrease of PDL for increasing cross-sectional area of the propellant sample and the trend, for higher sections, evinces an asymptotic PDL value depending only on the propellant nature as its intrinsic property. The external energy addition tends to decrease the PDL, but a minimum pressure value below which burning regime is not possible was still found. The experimental evidence shows that any operating conditions or physical-chemical propellant properties which increas the propellant burning stability yield a lower PDL. Comparisons with results obtained by other researchers validate this trend.

Kinetics of particle formation in the sputtering and reactive ion etching of silicon

Particle formation from a Si substrate in an Ar sputtering plasma and a reactive ion etching plasma of 10% CCl2F2 in Ar has been investigated by laser light scattering. The kinetics of particle growth are studied as a function of rf power and chamber pressure. Threshold behavior for particle generation has been observed in that minimum values of both rf power and pressure are necessary for particles to appear. In both reactive ion etching and sputtering, the smallest particles detected on the wafer are ∼0.2 μm in size. In sputtering most particles are spherical and must have been deposited onto the substrate from the plasma. On the other hand, in reactive ion etching most particles are hemispherical or conical and seem to have grown on the substrate itself. Particle formation is correlated with significant redeposition in sputtering and with deposition of a surface film in reactive ion etching. Si atoms removed from the substrate are probably responsible for the nucleation of particles in both types of plasmas because particle formation is much slower, yet the etch rate is much higher, in reactive ion etching compared to sputtering.

Tracheal tube cuff pressure

Seventy-one adult patients (31 male, 40 female) who presented for surgery underwent orotracheal intubation with Portex Blue Line standard cuff disposable tubes (9-mm for males, 8-mm for females). The tracheal tube cuff was inflated by a trained assistant using a syringe and the initial cuff pressure measured; the minimum cuff pressure required to prevent respiratory gas leakage was also measured and the cuff pressure maintained above this pressure throughout the operation by means of the Cardiff Cuff Controller. Initial cuff pressure values averaged 11.9 kPa for males and 13.5 kPa for females compared with minimum cuff pressure values of 5.2 and 1.2 kPa, respectively. The differences between initial and minimum pressures were statistically highly significant (p much less than 0.001). It is concluded that the present method of inflation may lead to gross overinflation of tracheal tube cuffs and that cuff pressure monitoring may be performed simply by means of an electropneumatic controller. The difference in minimum cuff pressure between males and females suggests that the difference in tracheal size between the sexes is greater than the 9-mm to 8-mm difference in tracheal tube size.

Navier-Stokes simulations of rotor/stator interaction using patched and overlaid grids

An accurate numerical analysis of the flows associated with rotor/stator configurations in turbomachinery can be very helpful in optimizing performance. In this study, the unsteady, thin-layer, Navier-Stokes equations are solved using a system of patched and overlaid grids for a rotor/stator configuration of an axial turbine. The equations necessary for an accurate transfer of information between the several grids are briefly described within the framework of an iterative, implicit algorithm. Results in the form of Mach number contours, time-averaged pressures, unsteady pressures, amplitudes, and phase are presented. The numerical results are also compared with experimental data and the agreement is found to be good. HE aerodynamic processes associated with the flow of fluid through turbomachines pose one of the toughest challenges to the computational fluid dynamicist. The un- steady nature of the flow, the complex geometries involved, the motion of some parts of the system relative to others, and the periodic transition of the flow from laminar to tur- bulent are some of the factors that contribute to the com- plexity of the problem. A clear understanding of these types of flows is essential for the optimization of the performance of turbomachiner y. In this study, an attempt is made to analyze two-dimensional flow past the rotor/stator con- figuration of an axial turbine using state-of-the-art computa- tional tools and computing facilities. The two-dimensional analysis of stator airfoils in isolation or rotor airfoils in isolation is a relatively straightforward task. Such an analysis is valid when the two rows of blades are set far enough apart so that the interaction effects are minimal. However, the desire to minimize engine length re- quires the stator and rotor airfoils to be closely spaced. Clearly, the interaction effects will become more important as the axial gap between the rows is reduced. In fact, the flow becomes periodically unsteady for small values of the axial gap. The experimental results of Ref. 1 show that the temporal pressure fluctuation (the difference between the minimum and maximum pressure values) near the leading edge of the rotor can be as much as 12% of the exit dynamic pressure when the axial gap is reduced to 15% of the chord length (for the operating conditions and geometry chosen). Hence, it is important that the rotor and stator airfoils be treated as a single system when the interaction effects become predominant. A computational tool that provides the design engineer with the necessary aerodynamic data can be used to great advantage in redesigning rotor and stator airfoils to enhance performance. Such a tool has to accurately simulate the unsteady flow associated with rotor/stator con- figurations exhibiting a strong interaction. A finite-differe nce solution to the Navier-Stokes equations requires the generation of a computational grid for the

Anchored Sheet Pile Bulkheads: Design Practice

The state of the art of sheet pile bulkheads design and investigation is reviewed. Using some examples of relatively recent large scale model tests and full scale investigations it is shown that the Coulomb Theory of earth lateral pressure against retaining structures with some empirical modifications could be used in design of anchored sheet pile bulkheads. However, in some cases of full scale investigations of anchored bulkheads it was found that the value of lateral soil pressure exceeded the value of minimum active pressure, as determined by Coulomb Theory, and it was close to “at rest” pressure. This phenomenon is explained by the soil “heredity” effect.

長野県における農村婦人の肥満に関する研究

Qualitative changes in the health hazards are at issue as the rural communities have been transformed in recent years. One such sign is the obesity of women in the rural communities. There is a need to make an epidemiological study on what effects obesity has brought about on their health.We have conducted a fact-finding survey on the distribution of obesity among rural women, changes in the rate of obesity by age, relations among obesity, abnormal findings in various examinations and morbidity, relations between annual changes in body weight and changes in the test values as well as relations between obesity and factors associated with the living environment for an analysis.The survey covered persons who underwent a mass health screening we carried out in Nagano Prefecture. In checking relations between changes in the rate of obesity and factors associated with the living environment, inhabitants of the village of Yachiho in South Saku County of Nagano Prefecture were covered, Findings: The rate of obesity has become higher among rural women in their middle and high age brackets. Particularly, there were marked signs of obesity between 1950 and 1970. By occupation, the rate was high among women who were not engaged in farm work, but by area, the rate was high among women living in the mountain areas. By crop, there were signs of a rise in the rate in areas where vegetables constituted the main produce. There were also signs of a rise among women whose gross income and non-agricultural income were high. In relation to health hazards, the morbidityassociated with the circulatory, endocrine, muscular and skeletal systems was high. In terms of test values, the higher the obesity, the higher the maximum and minimum blood pressure values, ischemic changes ECG, arteriosclerotic changes in the fundus, GOT, GPT, blood glucose, uric acid and total cholesterol. In the dietary pattern, there were signs that the intakes of calory, protein, fat and sugar were higher among women with obesity, whereas the intake of calcium, iron and vitamin C was rather low. By type of food, the intake of sugar, oil and drinks was high among women with obesity, but that of beans, fishes and shellfishes, milk and greens was low. Though the calory was high, signs of an unbalanced nutrition intake, which could be described as low in nutrition, could be observed.

AN OPTIMIZATION METHOD TO DESIGN HYDRAULIC NETWORKS

Nonlinear programming is applied to the solution of hydraulic network problems. The significant differences between the proposed optimization method and other conventional methods are that this method can solve problems with mixed unknowns (e.g. pipe sizes, discharges and pressures), it can optimize solutions involving unknowns defined by inequalities (e.g. specifled minimum discharge and pressure values), it can handle network control problems such as required valve adjustments or in-line booster pump needs, and it may solve problems of networks with continuous discharge distribution along the pipes.