Critical Mass-Flow in Orifice-Nozzles at the Disintegration of Superheated Liquids

Author(s):  
K.-E. Wirth ◽  
M. Rossmeissl

Flashing atomization is initiated when the superheated liquid is exposed to a sudden pressure drop below saturation vapor pressure at the prevailing temperature. Superheated atomization is used to enhance atomization where conventional pressurized liquid injection cannot achieve the desired fine sprays. Essentially flashing is initiated by in situ bubble nucleation followed by bubble growth. If the internal flow conditions are such that stable cavitation bubbles can form, then such bubbles promote the atomization of the base liquid already in the capillary of the nozzle. Bubble creation via cavitation can be achieved by changing the nozzle geometry such as the orifice length-to-diameter ratio, the inlet corner radius, the surface conditions of the nozzle material and the flow velocity in the orifice. In case of superheated atomization, the mass flow and thus the flow velocity in the orifice can just be indirectly set by the combination of superheat temperature upstream the nozzle and the difference between high pressure level upstream and ambient pressure downstream the orifice. Consequently the internal geometry and the material of the nozzle are of vital impact on the atomization process of the ejected liquid.

Author(s):  
Sreedevi Aithal ◽  
Venkatesh Aithal ◽  
Joseph Kei ◽  
Shane Anderson

Abstract Objectives The objective of this study was to describe wideband absorbance (WBA) findings in patients with cholesteatomas and retraction pockets (RPs). Design In this prospective study, tympanometry, audiometry, and wideband tympanometry (WBT) were performed on 27 ears with an RP (eight with epitympanic RP and 19 ears with mesotympanic RP), 39 ears with a cholesteatoma (23 ears with epitympanic and 16 ears with mesotympanic cholesteatomas [MCs]), and 49 healthy ears serving as controls. Results Mean WBA at ambient pressure (WBAamb) of both experimental groups was reduced significantly between 0.8 and 5 kHz relative to the control group. The difference between mean WBAamb and mean WBA at tympanometric peak pressure (WBATPP) was greater for the RP (0.12–0.16 between 0.5 and 1.5 kHz) than for the cholesteatoma group (0.03–0.11 between 0.6 and 3 kHz). Mean WBAamb of both epitympanic RP (ERP) and epitympanic cholesteatoma (EC) subgroups was significantly lower than that of the control group. Mean WBATPP of the ERP subgroup attained normal levels as per the control group, while mean WBATPP of EC subgroup was significantly lower than that of the control group at 0.8 to 1.5 kHz and 4 to 5 kHz. In contrast, both mesotympanic RP and MC subgroups demonstrated similar mean WBAamb and WBATPP values. No significant differences in WBAamb and WBATPP results between the RP and cholesteatomas groups were observed. Receiver operating characteristic (ROC) analyses indicated that the area under the ROC curve for distinguishing between the RP and cholesteatomas groups ranged from 0.44 to 0.60, indicating low accuracy in separating the two groups. Conclusion While it is not possible to distinguish between the RP and cholesteatomas groups based on the WBAamb and WBATPP results, it is potentially feasible to differentiate between the EC and ERP conditions. Further study using a large clinical sample is recommended to determine the sensitivity and specificity of the WBA test to identify the EC and ERP conditions.


Author(s):  
Lei Jing ◽  
Ce Yang ◽  
Wangxia Wu ◽  
Shan Chen

The work presented here investigates the impeller matching characteristics and widens the stable operating range of front and rear impellers for an asymmetric entry double sided centrifugal compressor. A numerical approach is employed to analyze the operating characteristics of front and rear impellers, and a strategy to widen the stable operating range of double sided compressor is presented. Firstly, the performance curves of a double sided centrifugal compressor are obtained by simulating the operation of the whole-stage compressor. The result shows that the compressor operating mode switches from parallel mode to single impeller mode automatically with the decrease of the mass flow. Thus, the stable operating range of the compressor is limited. Second, the simulation of a simplified double sided compressor is conducted to reveal the mechanism of the compressor operating mode conversion. It is found that the essential reason for the conversion of the compressor operating mode is the total pressure difference between the front and rear impeller inlets. A proper increase of the rear impeller radii is helpful for improving the impeller power capability, which enables the front and rear impeller to obtain a superior matching relationship in a wider operating range and widens the stable operating range of the compressor. Furthermore, by analyzing the respective performance characteristic curves in various calculation cases, there is a critical mass flow value between the front and rear impellers for compressors with the same flow capability. When one side impeller mass flow is below the critical value, with further decrease of the flow, the pressure ratio characteristic curve of this side rises and enters the stall zone gradually. Thus, the operating mode is converted from parallel mode to single mode. This result further explains the mechanism for extending the stable operating range of a double sided compressor in a wider scope.


2019 ◽  
pp. 359-365
Author(s):  
Tetiana Tsymbaliuk-Skopnenko

The term divergence is used traditionally in linguistics in origin of language and dialectology to denote the distinction between certain idioms. However, the unit under consideration was used in a wider context, because it denotes the process and the consequence that are caused by the distinction of features and properties of objects – something that ultimately leads to the division of the previously indistinguishable, and hence the appearance of new ideas about the world. In word formation, divergence is understood as the differentiation of common-root derivatives in terms of content or peculiarities of their use. Researchers also use the notions of semantic divergence – the difference in the content structure of derivative units with certain semantic nuances, which shows their semantic non-identity. Phraseography – conventionally derivative unit of lexemy lexicography, in this case we must talk about creating the first term by model of the second. For a long time in the scientific literature lexicography was used to refer to the section of linguistics, within which, with the help of certain methods, both lexemes and phraseologisms are described, although these units have different nature. The growth of phraseology as a separate scientific field did not automatically lead to the fixing of the term phrazeography in the national scientific discourse. Modern search engines on the Internet provide information that in this network found over a thousand documents in the Ukrainian language, which includes the word phrazeography. Certainly, this cannot be an example of the frequency of the use of this lexeme, but this fact suggests that in the modern scientific world there is a critical mass for understanding of the phrazeography as a separate scientific field. Some important arguments against this tendency were not found, although in modern university textbook phrazeography information is presented in the section “Phraseology” or at the end of “Lexicsology”, while lexicography as a separate branch, not within the limits of lexicology, has long been entrenched in the educational and scientific literature. And it sounds paradoxical to a certain extent, because it is from phraseology (however, in symbiosis with lexicography), not only the newest Ukrainian phraseology as a science began, the description of phraseological units was one of the first tasks of Ukrainian vocabulary in general. In addition, we note that the term “science about dictionaries” is most often used in the sense of “lexicography”. Since the tradition of non-differentiation of lexicography and phraseology is very strong, it would be expedient (and simply convenient) to use this Ukrainian term for the definition of synthetic understanding of the two branches of philology as a related unity: lexicography (theoretical and practical) and phrazeography (also theoretical and practical). If we accept such a proposal, then there will be no unnecessary confrontation between lexicography and phrazeography, the uncertainty of which leads to many misunderstandings. We can conclude that there is no reason to denote by the term lexicography the whole set of scientific approaches related to the phrazeography description. In Ukrainian linguistics, it is necessary to clearly delineate the terms lexicography and phrazeography, since they, over the last time, consolidated various semantic concepts.


Micromachines ◽  
2020 ◽  
Vol 11 (8) ◽  
pp. 758
Author(s):  
Zhi-xin Gao ◽  
Ping Liu ◽  
Yang Yue ◽  
Jun-ye Li ◽  
Hui Wu

Although check valves have attracted a lot of attention, work has rarely been completed done when there is a compressible working fluid. In this paper, the swing check valve and the tilting check valve flowing high-temperature compressible water vapor are compared. The maximum Mach number under small valve openings, the dynamic opening time, and the hydrodynamic moment acting on the valve disc are chosen to evaluate the difference between the two types of check valves. Results show that the maximum Mach number increases with the decrease in the valve opening and the increase in the mass flow rate, and the Mach number and the pressure difference in the tilting check valve are higher. In the swing check valve, the hydrodynamic moment is higher and the valve opening time is shorter. Furthermore, the valve disc is more stable for the swing check valve, and there is a periodical oscillation of the valve disc in the tilting check valve under a small mass flow rate.


Author(s):  
Juan C. Ramirez ◽  
Suzanne A. Smyth ◽  
Russell A. Ogle

A boiling liquid, expanding vapor explosion (BLEVE) occurs when a pressure vessel containing a superheated liquid undergoes a catastrophic failure, resulting in a violent vaporization of the liquid. The exposure of a pressure vessel to a fire is a classic scenario that can result in a BLEVE. The thermomechanical exergy of a pressure vessel’s contents provides — by definition — an upper bound on the work that can be performed by the system during the explosion. By fixing the values of ambient pressure and temperature (i.e., the dead state), exergy can be interpreted as another thermodynamic property. This rigorous and unambiguous definition makes it ideal to estimate the maximum energy of explosions. The numerical value of exergy depends on the definition of the dead state. In this paper we examine the effect of different definitions for the dead state on the explosion energy value. We consider two applications of this method: the contribution of the vapor head-space to the explosive energy as a function of the fractional liquid fill of the vessel, and the effect of the vessel burst pressure.


2011 ◽  
Vol 115 (1170) ◽  
pp. 471-480 ◽  
Author(s):  
J. Masud

Abstract In this paper the computed flow and performance characteristics at low angle-of-attack (AOA) of an integrated diverterless supersonic inlet (DSI) are presented. The subsonic characteristics are evaluated at M∞ = 0·8 while the supersonic characteristics are evaluated at M∞= 1·7, which is near the design Mach number for the intake. In addition to the external flow features, the internal intake duct flow behaviour is also evaluated. The results of this study indicate effective boundary layer diversion due to the ‘bump’ compression surface in both subsonic and supersonic regimes. At M∞ = 1·7, the shockwave structure (oblique/normal shockwave) on the ‘bump’ compression surface and intake inlet is satisfactory at design (critical) mass flow rate. The intake duct flow behaviour at subsonic and supersonic conditions is generally consistent with ‘Y’ shaped intake duct of the present configuration. The secondary flow structure inside the duct has been effectively captured by present computations. The computed intake total pressure recovery at M∞ = 1·7 exhibits higher-than-conventional behaviour at low mass flow ratios, which is attributed to unique inlet design. Overall computed subsonic and supersonic total pressure recovery characteristics are satisfactory under the evaluated conditions and are also in agreement with wind tunnel test data.


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