5,455 research outputs found
Circumferential pressure distributions in a model labyrinth seal
A research program to isolate and study leakage flow through labyrinth glands was initiated. Circumferential pressure distributions were measured in the labyrinth glands with geometry appropriate to the high pressure labyrinths in large steam turbines. Knowledge of this pressure distribution is essential as it is this unequal pressure field that results in the destabilizing force. Parameters that are likely to affect the pressure distributions are incorporated into the test rig. Some preliminary pressure profiles are presented
Experimental investigation of lateral forces induced by flow through model labyrinth glands
The lateral forces induced by flow through model labyrinth glands were investigated. Circumferential pressure distributions, lateral forces and stiffness coefficients data obtained are discussed. The force system is represented as a negative spring and a tangential force orthogonal to eccentricity. The magnitude of these forces are dependent on eccentricity, entry swirl, rotor peripheral velocity and seal size. A pressure equalization chamber at midgland tests should in significantly reduced forces and stiffness coefficients
Empirical load-line capacitance models for HEMT
Models for describing the gate-source and gate-drain capacitances' variation along a resistive load line have been proposed. They are charge conservative and consistent with the small-signal model at bias points along the load line. The extraction procedure for the models' parameters is fast and intuitive. The models can be implemented easily in most circuit simulator programs
Full W-band MMIC medium power amplifier
A full W-band, MMIC amplifier has been tested on-wafer. The chip delivers 25-43 mW with 6.2Ā±1.2 dB associated large-signal gain across 75-110 GHz when input power is held constant at 8 mW. This is the widest bandwidth MMIC amplifier ever published that delivers at least 25 mW over the entire W-band
Novel technique of phase velocity equalization for microstrip coupled-line phase shifters
By properly selecting the characteristic impedance and electrical length of the linking line between the coupled lines, phase velocity compensation for microstrip coupled-line phase shifters can be achieved. This technique does not introduce extra element or modification to the coupling in the main coupled lines. It is simple to implement and it has the potential to be used at mm-wave frequencies
Sand production: A smart control framework for risk mitigation
Due to the current global oil price, the sand production is considered undesirable product and the control of sand production is considered as one of the main concerns of production engineers. It can damage downhole, subsea equipments and surface production facilities, also increasing the risk of catastrophic failure. As a result of that it costs the producers multiple millions of dollars each year. Therefore, there are many different approaches of sand control designed for different reservoir conditions. Selecting an appropriate technique for preventing formation sand production depends on different reservoir parameters. Therefore, choosing the best sand control method is the result of systematic study. In this paper the sand production factors and their effects are presented where the emphasis is given towards the sand prediction to determine the probability of producing sand from the reservoir, followed by the correct prevention implementation of sand control method. The combination of these two is presented as a smart control framework that can be applied for sand production management
Testing Alternative Theories of the Property Price-Trading Volume Correlation
This article examines the correlation between the real housing price and trading volume. Contrary to the predictions of standard rational expectation models, a robust positive correlation between the two variables is identified. While no clear lead-lag relationship is found in the raw data, which is more consistent with the downpayment effect model, the medium-run component of the trading volume tends to lead (and Granger cause) the corresponding component of the property price, which is more consistent with the search theoretic model. An explanation for this difference in behavior is suggested and several future research directions are provided.
Physically-Realizable Uniform Temperature Boundary Condition Specification on a Wall of an Enclosure: Part II ā Problem Solution
Temperature measurements along one side of the rectangular plate showed severe temperature non-uniformity along one side of a wall of a cubical experimental apparatus where the uniform temperature was physically desired. Despite proper planning and analyses, this non-uniformity was high enough that a benchmark study could not be carried out to the desired accuracy of about one percent error. This paper presents and extends analyses made previously based on the modifications to the original design of the apparatus to reduce the temperature non-uniformity on the wall by adding an auxiliary heater around a wall where the uniform temperature was desired. A detailed mathematical analysis shows significant reduction in temperature non-uniformity from about four percent (based on the initial design) to less than one percent (for the modified design). By examining the temperature difference between two locations on the plate, the predicted temperature difference obtained through mathematical analyses show excellent agreement with the measured temperature difference. The temperature non-uniformity along the boundary of a wall was reduced to less than one percent of the overall temperature difference
Physically-Realizable Uniform Temperature Boundary Condition Specification on a Wall of an Enclosure: Part I ā Problem Investigation
Designing an experimental apparatus requires considerable amount of planning. Despite proper planning, one can easily overlook a design such as the standard uniform temperature boundary condition applied to all or portion of a wall of an experimental apparatus. Although this boundary condition is mathematically simple and precise, achieving it physically may not be that simple. This paper addresses one such three-dimensional natural convection heat transfer apparatus that was designed to measure benchmark Nusselt numbers at various Rayleigh numbers with uniform temperatures specified at two walls of the enclosure. It was found that the effect of thermal spreading/constriction resistance on one wall where this uniform temperature condition was prescribed was significant, and as a result, the uniform temperature profile based on the initial design was not physically achieved. In support of this non-uniform temperature observation, this paper presents a thermal resistance model of a plate (which is a portion of this overall heat transfer apparatus) to explain the observed temperature non-uniformity. The results obtained from the current model are validated with measured data, and in terms of a temperature difference between two locations on the plate, the approximate analytical solution is well within the experimental error of 0.03K
Quick-Mixing Studies Under Reacting Conditions
The low-NO(x) emitting potential of rich-burn/quick-mix/lean-burn )RQL) combustion makes it an attractive option for engines of future stratospheric aircraft. Because NO(x) formation is exponentially dependent on temperature, the success of the RQL combustor depends on minimizing high temperature stoichiometric pocket formation in the quick-mixing section. An experiment was designed and built, and tests were performed to characterize reaction and mixing properties of jets issuing from round orifices into a hot, fuel-rich crossflow confined in a cylindrical duct. The reactor operates on propane and presents a uniform, non-swirling mixture to the mixing modules. Modules consisting of round orifice configurations of 8, 9, 10, 12, 14, and 18 holes were evaluated at a momentum-flux ratio of 57 and jet-to-mainstream mass-flaw ratio of 2.5. Temperatures and concentrations of O2, CO2, CO, HC, and NO(x) were obtained upstream, down-stream, and within the orifice plane to determine jet penetration as well as reaction processes. Jet penetration was a function of the number of orifices and affected the mixing in the reacting system. Of the six configurations tested, the 14-hole module produced jet penetration close to the module half-radius and yielded the best mixing and most complete combustion at a plane one duct diameter from the orifice leading edge. The results reveal that substantial reaction and heat release occur in the jet mixing zone when the entering effluent is hot and rich, and that the experiment as designed will serve to explore satisfactorily jet mixing behavior under realistic reacting conditions in future studies
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