Revised; Originally Published: 2006 / 7 pp.

<p>The accuracy and precision of measurements of pulsating flow obtained with phase contrast magnetic resonance imaging (PC MRI) was studied. Measurements were carried out using known flow rates through a phantom connected to a pump that created pulsation in the flow. Repeated measurements were made in both the negative and positive encoding direction, using both breath-hold and non breath hold sequences. The obtained data was analyzed using code written in MATLAB and also using the FLOW software that is offered by the manufacturer of the MRI system.</p><p>A range of different flow velocities was scanned, and results show that the overall accuracy of the measurements is relatively good, with an average error of between 1.2% to 5.7% using the clinically employed flow calculation software. There is however indication of a systematic phase offset in the data that influences the measurements. The effect of the offset on the results depends on the direction of flow and the sequence used. The results also show the importance of properly selecting the area over which the flow rate is calculated.</p>

A new closed-loop frequency-domain model is developed to incorporate the water hammer effect with pump rotordynamics, in order to investigate the sub-synchronous instability problem observed in a field pump. Seal flow-rate perturbations due to eccentricity are calculated from Soulas and San Andres's seal code. A complete transfer function matrix between rotor motion and reaction force due to pressure perturbation is developed in detail. Stability analysis with transfer-function'add-in' modules is conducted in XLTRC2. Seal clearances and the reaction force angle are found to be important in shifting natural frequencies and damping. The sub-synchronous instability observed in field is duplicated successfully with double-clearance seals.

The accuracy and precision of measurements of pulsating flow obtained with phase contrast magnetic resonance imaging (PC MRI) was studied. Measurements were carried out using known flow rates through a phantom connected to a pump that created pulsation in the flow. Repeated measurements were made in both the negative and positive encoding direction, using both breath-hold and non breath hold sequences. The obtained data was analyzed using code written in MATLAB and also using the FLOW software that is offered by the manufacturer of the MRI system. A range of different flow velocities was scanned, and results show that the overall accuracy of the measurements is relatively good, with an average error of between 1.2% to 5.7% using the clinically employed flow calculation software. There is however indication of a systematic phase offset in the data that influences the measurements. The effect of the offset on the results depends on the direction of flow and the sequence used. The results also show the importance of properly selecting the area over which the flow rate is calculated.

Abstract This study proposes a model to predict the effect of lubricant starvation on EHL behavior of line contact, including the boundaries among the starved, fully flooded, and over-flooded lubrications. A pre-inlet region is analyzed to overcome the discontinuous phenomenon of film thickness at the position of the meniscus presented in the previous model under the starvation. The relationship between the film thickness of the supply region and the position of the meniscus is established. The prediction formulas for the minimum film thickness required to achieve the fully flooded condition is expressed in terms of the load and the speed. This formula can be used to predict the fully flooded/starved boundary under certain of flow rate in the supply end. In the analysis of the pre-inlet region, the surface speed, the pressure and the mass flow rate are assumed to be continuous with the supply region and the pressure region, so that its film thickness can be calculated by the mass flow rate equation. However, when the backflow occurs in the boundary between the pre-inlet and pressure region, only part of the film thickness flows into the pressure region, and the rest film only performs recirculation. When no backflow is observed at this boundary, the film thickness in the pre-inlet region easily rises and continuously connects to the pressure region. If the film thickness in the supply end is increased, the surface speed gradually decreases at the inlet end of the pre-inlet region. When the film thickness in the supply end increases to twice as high as the minimum film thickness that required to achieve the fully flooded condition, the surface speed at the inlet end of the pre-inlet region becomes stationary. Hence, when the film thickness in the supply end continues to increase to more than twice, the backflow occurs at the supply region, and this behavior is called the over-flooded lubrication.

Excess lubricant can be found as reservoirs on the sides of the rolling tracks when the oil flows through the Hertzian contact and the side leakage. Uniform lubricant layers adhered to both rolling surfaces can flow into the supply region by the action of surface tension. Uniform lubricant layers are separated by air so that they move with the surfaces the surface tension of the liquid-air interface and the velocity of the roller. Hence, it can be considered as the fixed flow rate conditions. Under the lubricant starvation and the fixed flow rate conditions, the meniscus in the film inlet is formed due to the action of the surface tension of the oil-air interface, where the fluid pressure in the oil layer is smaller than the ambient pressure. An empirical formula to predict the thickness of the oil layer is derived based on the theoretical analysis and the experimental results of Cann et al. [10]. Results show that this thickness increases the amount of oil in the track and the surface tension of the liquid-air interface, but it decreases with the surface velocity and the oil viscosity. Moreover, the starved, fully flooded, over-flooded regimes are established based on the theoretical analysis. Under the lubricant starvation and the fixed flow rate conditions, the central film thickness in the pressure region increases with increasing the supply flow rate, so that the location of the meniscus moves to upstream. When the supply flow rate is more than 98% flow rate of fully flooded condition, the central film thickness achieves a saturated value. Hence, when the supply flow rate is between 98% and 100% flow rate of fully flooded condition, it is called the fully flooded regime. When the supply flow rate is more than the flow rate of fully flooded condition, the central film thickness remains constant, and the excess oil accumulates in the inlet region, so that the film thickness in the inlet region increases with time. When the supply flow rate is larger than the flow rate of fully flooded condition, it is called the over-flooded region.

Via the viewpoint of fuel and oxidant supply in this study, we compare heterogeneous carbon fiber bipolar plates with graphite bipolar plates that apply to fuel cell. In operating condition with different gas inlet pressure and compressing pressure, we study the penetrability of reactant gases that come into the carbon cloth under the rib of a bipolar plate. Eventually the output voltage and power density are measured to prove the advantages of the new bipolar plate. The experimental results show that carbon fiber bipolar bunch in low compressing pressure 2bar already display high gas penetrability. Its dimensionless flow rate is about quadruple of graphite bipolar plates. The reactant gas can enter the carbon cloth either from the side or from the top of the penetrating carbon fiber bipolar bunch. In addition, carbon fiber bipolar plates are affected slightly by compressing pressure. Further, the total electrical resistant of carbon fiber bipolar plates with carbon cloth already decreases to 18.5mΩ*cm&#x00B2; in low compressing pressure 2bar. Therefore, by appling the new bipolar plate, the fuel cell in compressing pressure 2bar and inlet fuel pressure 1.15bar(absolute pressure) can developed a power rate 180mW/cm&#x00B2;. Concerning graphite bipolar plates, we can find that compressing pressure increase from 1bar to 4bar due to the reduction in total resistance so the output voltage and power density can increase to maximum value 113mW/cm2. However, while we augment more compressing pressure, the influence in reducing total resistance is much smaller than that in reducing the porosity of carbon cloth. Therefore, the output power density decreases. Also, output voltage of carbon fiber bipolar plates at 0.5mA/cm2 is 0.38 V and is higher than that of graphite bipolar plate 0.2 V.

A new closed-loop frequency-domain model is developed to incorporate the water hammer effect with pump rotordynamics, in order to investigate the sub-synchronous instability problem observed in a field pump. Seal flow-rate perturbations due to eccentricity are calculated from Soulas and San Andres's seal code. A complete transfer function matrix between rotor motion and reaction force due to pressure perturbation is developed in detail. Stability analysis with transfer-function'add-in' modules is conducted in XLTRC2. Seal clearances and the reaction force angle are found to be important in shifting natural frequencies and damping. The sub-synchronous instability observed in field is duplicated successfully with double-clearance seals.

Investors should seriously assess and consider investment objects when they are proceeding domestically newly-issued equity funds investment. According to this study, the returns of domestically newly-issued equity funds are negative whether they are invested locally or overseas. If we take excess returns into account, the returns rate will be lower. General excess returns¡]systematic risk BETA¡^¡Bnet flow rate ¡]Flow¡^¡Bequity funds turnover rate¡]Turn¡^¡Baverage investment amount per person¡]AVG¡^etc. four factors are listed in this study. The past ten-year excess returns of domestically newly-issued equity funds are researched the correlationship of these variables. The empirical results show:there is a positively significant relationship risk, the higher the systematic risk is, the better the funds¡¦ performance is. Funds excess returns are positively significantly related with equity funds turnover rate; the situation represents: the more active this month investment objects are the better this month performance is. The relationship between equity funds excess returns and net flow rate is statistically insignificant; no matter what the net buying amount of this month is higher or lower than last month funds assets scale, the performance of the funds is not affected. The relationship between funds excess returns and investment amount is statistically insignificant. As far as domestically newly-issued international equity funds are concerned, funds excess returns are statistically insignificant with systematic risk, net flow rate and funds turnover rate, that is, the performance of international equity funds is not affected by domestical systematic risk, net flow rate and fund turnover rate. Funds excess return rate is negatively significantly related with the investment amount per person, that is, the bigger the net funds assets scale or the smaller the beneficiaries of the funds is, the worse the performance of the funds is. In other words, when topical news¡]for example BDI index fluctuations¡B the rise of BRICs¡B the large scale epidmic¡^ferment,the international equity funds commodity which is enjoying busy trading will result in loss in the first year-end after investing, it verifies the proverb¡XDon¡¦t go to the place where many persons gatter.

The ability of surface-treated silica nanoparticles to stabilize oil/water emulsions presents us with many interesting avenues of study. The goal of this research is to assess the ability of a dispersion of specially surface-treated nanoparticles to stabilize an oil/water emulsion of prescribed internal structure created by flow within a fracture. We hypothesize that for a set of conditions (nanoparticle concentration, salinity, aqueous to organic phase ratio) a critical shear rate exists. That is, for flow rates that exceed this critical shear rate, an emulsion can be created. Flow experiments were conducted within fractured Boise sandstone and cement cylinders. The Boise sandstone core (D = 1 in and L = 12 in) was cut down its length and propped open to a specific aperture with beads. The fracture was saturated with dodecane then displaced with nanoparticle dispersion, and vice versa while pressure drop across the fracture was recorded. Class H cement cylinders (D = 1 in and L = 3 in) were allowed to set, then failed in compression to create a rough-walled fracture along their length. These fractured cement cylinders were then sealed and encased in epoxy to isolate the fractures. CT scans of the encased fractures were used to determine the aperture width, which is utilized when calculating the shear rate inside of the fracture maintained during an experiment. A dispersion of surface-modified silica nanoparticles and decane were coinjected into both the Boise sandstone and cement fractures and the pressure drop was measured across the fractures at a variety of shear rates. The effluent of each experiment was collected in sample tubes. Observation of the effluent and pressure drop data both support our hypothesis of emulsion generation being possible once a critical shear rate has been reached. Alteration of the injected phase ratio and increased residence time of the two phases inside of a fracture both affect the amount of emulsification occurring within the fractures. Increasing the residence time of both phases within a fracture allows for more opportunities for emulsification to occur, resulting in a greater amount of emulsion to be generated. Injection of high or low volumetric ratios of nanoparticle dispersion to organic phase results in little amounts of emulsion generation; however, between the nanoparticle dispersion to organic phase ratios of 0.25:1 and 2:1 significant amounts of emulsion are generated. / text