Diffuser (thermodynamics)

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

A Theory for Stability and Buzz Pulsation Amplitude in Ram Jets and an Experimental Investigation Including Scale Effects

Abstract: From a theory developed on a quasi-one-dimensional-flow basis, it is found that the stability of the ram jet is dependent upon the instantaneous values of mass flow and total pressure recovery of the supersonic diffuser and immediate neighboring subsonic diffuser. Conditions for stable and unstable flow are presented. The theory developed in the report is in agreement with the experimental data of NACA-TN-3506 and NACA-RM-L50K30. A simple theory for predicting the approximate amplitude of small pressure pulsation in terms of mass-flow decrement from minimum-stable mass flow is developed and found to agree with experiments. Cold-flow tests at a Mach number of 1.94 of ram-jet models having scale factors of 3.15:1 and Reynolds number ratios of 4.75:1 with several supersonic diffuser configurations showed only small variations in performance between geometrically similar models. The predominant variation in steady-flow performance resulted from the larger boundary layer in the combustion chamber of the low Reynolds number models. The conditions at which buzz originated were nearly the same for the same supersonic diffuser (cowling-position angle) configurations in both large and small diameter models. There was no appreciable variation in stability limits of any of the models when the combustion-chamber length was increased by a factor of three. The unsteady-flow performance and wave patterns were also similar when considered on a reduced-frequency basis determined from the relative lengths of the model. The negligible effect of Reynolds number on stability of the off-design configurations was not anticipated in view of the importance of boundary layer to stability, and this result should not be construed to be generally applicable. (author).

Pneumatic bubble aeration reactor and method of using same

Abstract: A pneumatic bubble aeration reactor and method for conditioning bodies of liquid comprising at least one upwelling bubble conduit, at least one return conduit fluidly connected to the upwelling conduit via a fluid reservoir and a secondary gas-diffuser positioned adjacent the top of the return conduit. A liquid driving diffuser introduces oxygen-rich gas bubbles into the upwelling conduit at a velocity sufficient to cause the downward flowing liquid in the return conduit to exceed the natural tendency of the secondary gas to flow upwardly. This driving action is coupled with a reactor geometry to assure a liquid velocity that exceeds the rise velocity of the bubbles, causing the bubbles to reach the exit end of the return conduit. An expansion chamber is provided at the exit end of the return conduit to present a decreasing velocity gradient to the fluid passing through the return conduit. This expansion chamber increases the gas bubble dwell time and allows for recirculation of the gas bubbles from the return conduit into the upwelling conduit. A counter-flow of gas bubbles can also be introduced into the return conduit proximate the exit end thereof. Due to prolonged exposure between the liquid and the gas bubbles within both the upwelling and return conduits, high oxygen absorption efficiency is attained.

Comparison of k–ϵ and algebraic Reynolds stress models for swirling diffuser flow

Abstract: SUMMARY A brief overview of classes of turbulent swirling flow in conical diffusers is given, together with a description of appropriate numerical schemes for each class. Numerical results obtained for the class of moderate swirl in a 20" diffuser and for the class of no swirl in an 8" diffuser are compared with experimental results. The results are obtained using a multi-sweep scheme solving the full steady state time-averaged Navier-Stokes equations. Turbulence quantities are approximated using two types of algebraic Reynolds stress model and two types of k-& model. One of the algebraic Reynolds stress models includes extra production terms associated with the Christoffel symbols in cylindrical co-ordinates, and one of the k-E models includes a swirl-related modification to the E equation. It is demonstrated that the standard k--E model gives poor prediction of the mean flow, and it is necessary to at least use the modified form or one of the two algebraic Reynolds stress models.