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First Law Analysis of Control Volumes
Published in V. Babu, Fundamentals of Engineering Thermodynamics, 2019
Diffusers (Fig. 7.2) are quite extensively used in the intake of engines for aircrafts and missiles that fly at supersonic speeds. The function of the diffuser is to decelerate the air that enters the engine and convert the KE of the incoming air stream into enthalpy (or equivalently, the momentum of the air into a pressure rise). The diffuser acts like a nozzle in reverse, in that, the air is forced to flow through the device by its momentum and the diverging passage causes it to decelerate resulting in a pressure increase. At supersonic flight speeds, a substantial amount of compression can be accomplished in this manner. Consequently, the work required for further compression (if any) can be minimized or eliminated altogether. However, diffusion (as a result of deceleration) is quite difficult to accomplish in practice in a stable manner owing to the adverse pressure gradient.
Automated shape optimisation of a plane asymmetric diffuser using combined Computational Fluid Dynamic simulations and multi-objective Bayesian methodology
Published in International Journal of Computational Fluid Dynamics, 2019
S. J. Daniels, A. A. M. Rahat, G. R. Tabor, J. E. Fieldsend, R. M. Everson
The primary function of a diffuser device is to reduce the flow velocity, so as to increase the static pressure passing through the system. Thus the physics of a diffuser is an integral part of many flow systems, such as to evenly distribute the air around a room in a Heating, Ventilation and Air Conditioning (HVAC) application, or to reduce drag for the underside of a car. An improperly designed diffuser may lead to excessive consumption of pumping power or may produce flow maldistribution downstream – a particularly undesirable feature in its application to the automotive industry. The design and performance of plane diffusers have been extensively investigated in the literature. Due to their simplicity, straight walls are commonly used for the diffuser's expanding section, and many studies have been carried out to highlight the parameters that affect the performance of this type of planar diffuser, e.g. length, area ratios and divergence angle. Such analysis has been conducted for both the laminar (e.g. Durst, Melling, and Whitelaw 1974; Nabavi 2010; Suzuki, Colonius, and Pirozzoli 2004; Tsui and Wang 1995) and turbulent regimes (Fox and Kline 1962; Kline, Abbott, and Fox 1959; Reneau, Johnston, and Kline 1967; Waitman, Reneau, and Kline 1961). Indeed, turbulent flows through geometric expansions are of interest for numerous engineering applications, such as the design of turbomachines, combustion engines, heat-exchangers, vehicles, power plants and wind tunnels (e.g. Göttlich 2011; Klein 1995; Lan, Armaly, and Drallmeier 2009; Mehta and Bradshaw 1968).
Downcomer modification in the Jameson cell and its effects on coarse particle flotation
Published in Particulate Science and Technology, 2019
Oktay Şahbaz, Ali Uçar, Bahri Öteyaka
To decrease the turbulence, it is necessary to decrease the velocity of pulp by the increase of outlet diameter of the downcomer without changing the upper part of the downcomer. Therefore, the general compact design of the downcomer that provides better collection remains the same, and the end of the downcomer can be changed as diffuser as seen in Figure 1. Diffuser is an expansion or area increase intended to reduce velocity (White 2005). Therefore, the velocity of pulp can be decreased, and the turbulence may decrease as well. In addition to this design, there will not be any recovery loss due to the same structure for the top of the downcomer.