Diffuser (thermodynamics)

About: Diffuser (thermodynamics) is a research topic. Over the lifetime, 6731 publications have been published within this topic receiving 54738 citations.

Fragrance diffuser having stepped power levels

Abstract: A fragrance diffuser (100) comprises a housing defining a chamber (116) for holding a fragrance-emitting block (110), a heating element (112) located within the housing, a timing and indicating circuit board (114) to signal when the predicted life of the fragrance emitting block has expired, a power supply connection plug (134) for providing electrical power to the heating element and the timing and indicating board, and a keying system (234, 236, 238) incorporated in the chamber (116) and on the fragrance-emitting blocks (110). The blocks are encoded or keyed to indicate that they possess particular predefined characteristics, such that only blocks having those characteristics may be inserted. The diffuser is constructed with a downwardly-projecting housing extension (132) for the power supply connection to allow the use of an adjacent electric power outlet when the diffuser is properly installed. The diffuser also includes an indicator LED (156) to indicate when a timing interval, corresponding to the life of a fragrance block inserted therein, has expired, wherein the timing interval is reset by a switch (182) only at the request of a user. Various circuit embodiments are disclosed for increasing the power applied to the heating element over time, since the aroma strength of a fragrance block decreases over time.

PIV Measurements and CFD Computations of Secondary Flow in a Centrifugal Pump Impeller

Abstract: Two-dimensional particle image velocimetry measurements and three-dimensional computational fluid dynamics (CFD) analyses have been performed on the steady velocity field inside the shrouded impeller of a low specific-speed centrifugal pump operating with a vaneless diffuser. Flow rates ranging from 80% to 120% of the design flow rate are considered in detail. It is observed from the velocity measurements that secondary flows occur. These flows result in the formation of regions of low velocity near the intersection of blade suction side and shroud. The extent of this jet-wake structure decreases with increasing flow rate. Velocity fields have also been computed from Reynolds-averaged Navier–Stokes equations with the Spalart–Allmaras turbulence model using a commercial CFD code. For the considered flow rates, the qualitative agreement between measured and computed velocity profiles is very good. Overall, the average relative difference between these velocity profiles is around 5%. Additional CFD computations have been performed to assess the influence of Reynolds number and the shape of the inlet velocity profile on the computed velocity fields. It is found that the influence of Reynolds number is mild. The shape of the inlet profile has only a weak effect at the shroud.

Hover and wind-tunnel testing of shrouded rotors for improved micro air vehicle design

Abstract: : The shrouded-rotor configuration has emerged as the most popular choice for rotary-wing Micro Air Vehicles (MAVs), because of the inherent safety of the design and the potential for significant performance improvements However, traditional design philosophies based on experience with large-scale ducted propellers may not apply to the low-Reynolds-number (20,000) regime in which MAVs operate An experimental investigation of the effects of varying the shroud profile shape on the performance of MAV-scale shrouded rotors has therefore been conducted Hover tests were performed on seventeen models with a nominal rotor diameter of 16 cm (63 in) and various values of diffuser expansion angle, diffuser length, inlet lip radius and blade tip clearance, at various rotor collective angles Compared to the baseline open rotor, the shrouded rotors showed increases in thrust by up to 94%, at the same power consumption, or reductions in power by up to 62% at the same thrust These improvements surpass those predicted by momentum theory, due to the additional effect of the shrouds in reducing the non-ideal power losses of the rotor Increasing the lip radius and decreasing the blade tip clearance caused performance to improve while optimal values of diffuser angle and length were found to be 10 and 50% of the shroud throat diameter, respectively With the exception of the lip radius, the effects of changing any of the shrouded-rotor parameters on performance became more pronounced as the values of the other parameters were changed to degrade performance Measurements were also made of the wake velocity profiles and the shroud surface pressure distributions The uniformity of the wake was improved by the presence of the shrouds and by decreasing the blade tip clearance, resulting in lower induced power losses For high net shroud thrust, a favorable pressure distribution over the inlet was seen to be more important than in the diffuser