/pdf/joint-research-centre-frj77vs64c.pdf

Joint Research Centre

The laminar-turbulent transition zone in the boundary layer

Flow regime transitions due to cavitation in the flow through an orifice

This paper describes the development of a novel proximity gauging technique for soft deposits, exploiting a siphon effect. This non-contact technique has the capability to measure the thickness of soft deposits on a surface in situ and in real time. A theoretical model of performance has been developed and its validity demonstrated by calibration experiments. Local thickness measurements of soft deposits such as whey protein deposit, supermarket butter and sticky foam on metal surfaces had an accuracy of ±20 μm for a deposit thickness of 500 to 1000 μm. The potential of this technique for on-line monitoring of fouling and cleaning processes in liquid environments is demonstrated by preliminary studies of alkali (NaOH) cleaning of whey protein deposits from stainless steel surfaces.



On decrit dans cet article la mise au point d'une nouvelle technique de jaugeage de proximite pour des depots mous, exploitant un effet siphon. Cette technique sans contact a la capacite de mesurer l'epaisseur de depots mous sur une surface in situ et en temps reel. Un modele de performance theorique a ete developpe et sa validite est demontree par des experiences de calibration. Des mesures d'epaisseur locales de depots mous tels que des depots de proteines de petit-lait, du beurre de supermarche et de la mousse collante sur des surfaces metalliques ont une precision de ±20 μm pour une epaisseur de depot de 500 a 1000 μm. Le potentiel de cette technique pour la surveillance en continu des precedes de refoulement et de nettoyage dans des environ-nements liquides est demontre par des etudes prelim-inaires de nettoyage a la soude (NaOH) de depots de proteines de petit-lait sur des surfaces d'acier inoxydable.

Development of a novel non-contact proximity gauge for thickness measurement of soft deposits and its application in fouling studies

Hydrodynamic cavitation and boiling in refrigerant (R-123) flow inside microchannels

Loss Characteristics of Orifices and Nozzles

The critical Reynolds number at which the flow downstream of an orifice or nozzle in a pipe becomes turbulent is an important parameter as it is the demarcating point between purely laminar flow and relaminarising flow. The value of the critical Reynolds number is estimated for sharp-edged orifices, quadrant-edged orifices and long radius nozzles from indirect evidences using mean flow measurements. Different criteria are considered such as the variations of coefficient of discharge, loss coefficient, loss as percentage of piezometric head differential across the meter, and pressure recovery length downstream of the orifice. These criteria identify a range of transition Reynolds number for different orifices and nozzles. The critical orifice Reynolds number is seen to approach a constant value for low values of orifice or nozzle diameter to pipe diameter ratio. The critical Reynolds number increases gradually with increase in edge radius with the nozzle having the highest value.

Critical Reynolds Number For Orifice And Nozzle Flows In Pipes

Shapes Of Grit Chambers To Achieve Certain Velocity-Head Relations With Given Shapes Of Outlet Weirs

Flow past lang radius 1I0::::1es is studied in the Reynolds  number range of 1 to 10,000 based on experiments in all oil recirculation system. The ratio of nozzle outlet diameter to pipe diameter is varied from 0'2 to 0'8. Aspects studied include the coefficient of discharge, sensitivity of the discharge coefficient to marginal shifts in pressure tap location, loss coefficient, loss as function of the meter pressure differential, critical Reynolds number corresponding to the origin of turbulence downstream of the nozzle, setting length, and nature of development of pressure and velocity fields. The contribution contained in the paper fills the gap that exists in literature on the performance of long radius nozzles at low and moderate Reynolds numbers.

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N. S. Lakshmana Rao

Papers

Loss Characteristics of Orifices and Nozzles

Critical Reynolds Number For Orifice And Nozzle Flows In Pipes

Shapes Of Grit Chambers To Achieve Certain Velocity-Head Relations With Given Shapes Of Outlet Weirs

NOZZLE FLOWS AT LOW AND MODERAtE REYNOLDS NUMBERS

Improvement of the "baseless" proportional weir