Prediction of two-phase flow through a safety relief valve

Safety relief valves are necessary elements in any pressurised system. The flow inside the safety relief valve shows a number of interesting, yet complicated, features especially when a two-phase flow is involved. Consequently, developing an efficient and accurate means for predicting the safety relief valve performance and understanding the flow physics is a demanding objective. In this article, the ability of a two-phase mixture model to predict the critical flows of air and water through a safety valve is examined. An industrial refrigeration safety relief valve of ¼” inlet bore size has been tested experimentally over a pressure range of 6–15 barg and air mass qualities from 0.23 to 1 when discharging to near atmospheric conditions for a range of valve lift positions. A two-dimensional mixture model consisting of mixture mass, momentum and energy equations, combined with a liquid mass equation and the standard k-e turbulence model for mixture turbulent transport has been used to predict the two-phase flows though the valve. The mixture model results have been compared with the homogenous equilibrium model and the homogenous non-equilibrium model adopted by the ISO standard. It has been shown that the mixture model can be used satisfactorily to predict the mass flows for the above conditions. Overall, the accuracy of the two-phase air mass flow for given inlet liquid flow rates can be predicted to within 15%

Two-phase discharge flow prediction in safety valves

Safety Relief Valves (SRV) are necessary elements in the protection of any pressurised system and the prediction of the expected discharge flows is an important consideration for the valve sizing to ensure that rupture pressures do not occur. The high speed flows that occur inside the SRV are complex particularly when a two-phase flow is involved and lead to a less capable protection device which result in larger valves compared to single phase flows. In this paper the ability of a CFD based two phase mixture model to predict the critical flows of air and water through a safety valve is examined. An industrial refrigeration safety relief valve of ¼” inlet bore size has been tested experimentally over a pressure range of 6-15 barg and air mass qualities from 0.1-1 when discharging to near atmospheric conditions for a fully open condition. A two-dimensional mixture model consisting of mixture mass, momentum, and energy equations, combined with a liquid mass equation and the standard k- ε turbulence model for mixture turbulent transport has been used to predict the two phase flows through the valve. The mixture model results have been compared with the Homogenous Equilibrium Model (HEM) commonly used for in valve sizing in non flashing two phase flow conditions. The accuracy of the models over the two phase flow range are quantified and discussed

On the experimental testing of fine Nitinol wires for medical devices

Nitinol, a nickel titanium alloy, is widely used as a biocompatible metal with applications in high strain medical devices. The alloy exhibits both superelasticity and thermal shape memory behaviour. Basic mechanical properties can be established and are provided by suppliers; however the true stress–strain response under repeated load is not fully understood. It is essential to know this behaviour in order to design devices where failure by fatigue may be possible. The present work develops an approach for characterising the time varying mechanical properties of fine Nitinol wire and investigates processing factors, asymmetric stress–strain behaviour, temperature dependency, strain rate dependency and the material response to thermal and repeated mechanical loading. Physically realistic and accurately determined mechanical properties are provided in a format suitable for use in finite element analysis for the design of medical devices. Guidance is also given as to the most appropriate experimental set up procedures for gripping and testing thin Nitinol wire

Particle image velocimetry studies of bubble growth and detachment by high speed photography

An understanding of bubble flows is important in the design of process equipment, particularly in the chemical and power industries. In vapour-liquid processes the mass and heat transfer between the phases is dominated by the liquid-vapour interface and is determined by the number, size and shape of the bubbles. For bubble flows these characteristics are often controlled by the generation mechanisms and, since bubble flows are often generated at an orifice, it is important to determine the controlling parameters which dictate how bubbles grow and detach. For bubbles growing at orifices the liquid displacement is an important feature and affects the pressure distribution acting on the bubble and the heat and mass transfer that may occur at the bubble interface. Therefore, in this study, the characteristics of the liquid velocity field are studied experimentally using Particle Image Velocimetry (PIV) during growth, detachment and translation of a bubble being generated at an orifice supplied with a constant mass flow rate of air. The process is transient and occurs over a period of approximately 50 msecs. In order to map the transient flow field a combination of high speed cine and cross correlation PIV image processing has been used to determine the liquid velocity vector field during the bubble growth process. The paper contains details of the PIV technique and presents several of the velocity vector maps calculated

Long I for Thee!

As yonder lone and lovely star Hangs o\u27er the western hills afar And pausing in it\u27s downward flight Longs lingering for the coming night Long I for thee! Long I for thee! The last fond flowers that loved to fling Their fragrance on the branch of Spring And pine beneath the skies of June Mourn not so for the waning Moon As I for thee! As I for thee! The wild bird fills the local groveWith wailings for his absent loveSo every passing breath of AirMust on its buoyant pinions bearSome sigh for thee! Some sigh for thee! That lovely star shall wax and waneThose flowers shall die and bloom againThe sweet bird sing his mate to restSo shall I yet to this fond breast Fold thee, love thee! Fold thee, love thee

An investigation of the two phase flow and force characteristics of a safety valve

The two phase flow of air and water is studied in a safety relief valve commonly used in the industrial refrigeration industry. In some blowdown conditions a valve which has been specified for gas only operation may encounter flows which include liquid droplets, these having been entrained from upstream processes. Of particular interest is the operation under two phase flow conditions which will be dominated by the altered flow capacity and forces acting on the valve. To examine these effects the characteristics of the flow through the valve and the forces acting on the valve disc have been examined for an air water mixtures for a range of pressures, 5-14 bar, and a wide range of gas mass fractions for various different opening positions. These characteristics determine the capacity of the valve to control pressure, the sizing of the spring and the dynamics of the valve during operation. The data on such effects for safety valves is very limited and here we show the trends that result from the introduction of two phase flow mixtures and reflect on the limited previous work in the literature that is available. The tested range of conditions the results indicate that the flow and force characteristics are influenced by liquid injection with a significant influence on the flowrate. The disc forces resulting from the two phase impacts show a small but notable effect from liquid mass fractions. This is in contrast to previous limited data found in the literature

Jeanie Morrison

I\u27ve wandered east, I\u27ve wandered west through many a weary wayBut never, never can forget the love o\u27 life\u27s young dayThe fire that\u27s blawn on Beltane\u27s e\u27enMay weel be black \u27gin YuleBut blacker fa\u27 awaits the heartBut blacker fa\u27 awaits the heart where first fonds love grows cool O dear, dear Jeanie Morrison the thoughts o\u27 bygone yearsstill fling their shadows o\u27er my path and blind my e\u27en with tearsThey blind my e\u27en with saut, saut tears and sair I sick and pineAs memory idly summons up As memory idly summons up the blithe blinks o\u27lang syne. \u27Twas then we lov\u27d ilk ither weel, twas then we twa did partSweet time sad time! twa bairns at schoolTwa bairns and but ae heart!\u27Twas then we sat on ae laigh bank to leir ilk ither learAnd tones, and looks and smiles were shedAnd tones, and looks and smiles were shed remembered ever mair My head rins round and round about my heart flows like a seaAs ane by ane the thoughts rush back o\u27 school time and o\u27 theeO morning life! O morning love! O lightsome days and langWhen hinnied hopes around our heartsWhen hinnied hopes around our hearts like simmer blossoms sprang! I wonder, Jeanie, after yet,When sitting on that bink,Cheek touching cheek, lood locked in loofWhat our wee heads could think?When baith bent down o\u27er ae braid pageWi\u27 ae book on our kneeThy lips were on thy lesson,butMy lesson was in thee. O\u27 mind ye how we hung our heads,Our cheeks brent red wi\u27 shame,Whene\u27er the school-weans, laughing saidWe cleek\u27d thegither hame?And mind ye o\u27 the Saturday(The school then skail\u27t at noon)When we ran aff to speel the braes-The broomy braes o\u27 June? O, mind ye, love, how aft we leftThe deavin\u27 dinsome townTo wander by the breen burnsideAnd hear its waters croon?The simmer leaves hung o\u27er our headsThe flowers burst round our feetAnd in the gloamin o\u27 the woodThe throssil whistled sweet. The throssil whistled in the woodThe burn sang to the treesAnd we, with Nature\u27s heart in tuneConcerted harmoniesAnd on the knowe abune the burnFor hours thegither satIn the silentness o\u27 joy till baithWi\u27 very gladness grat. Ay, ay dear Jeanie MorrisonTears trinkled down your cheekLike dew beads on a rose yet noneHad any power to speak!That was a time, a blessed timeWhen hearts were fresh and youngWhen freely gushed all feelings forthUnsyllabled - unsung! I marvel, Jeanie MorrisonGin I hae been to theeAs closely twined wi\u27 early thoughtsAs ye hae been to meO, tell me gin their music fillsThine ear as it does mineO, say gin e\u27er your heart grows gritWi\u27 dreamings o\u27 langsyne. I\u27ve wandered east, I\u27ve wandered west,I\u27ve borne a weary lotBut in my wanderings far or nearYe never were forgotThe fount that first burst frae this heartStill travels on its wayAnd channels deeper, as it rainsThe love o\u27 life\u27s young day. O, dear, dear Jeanie MorrisonSince we were sindered youngI\u27ve never seen your face, nor heardThe music o\u27 your tongueBut I could hug all wretchednessAnd happy could I dieDid I but ken your heart still dreamedO\u27 bygane days and me! This poem is written professedly in the Scottish dialect. In order to make it more generally understood, the words have been spelled in English, where it has not interfered with the sense; but it contains some expressions which cannot be rendered purely English and belong exclusively to the idiom of the Scottish tongue, a glossary is here appended, in order to make such explanation as it thought necessary to a general appreciation and the full enjoyment of this beautiful ballad. Glossary Beltane \u27en: a highland festival, held on the evening of the first of May, when fires are kindled for the occasionCroon: a continued low sound or murmurDeavin\u27: deafeningDinsome: noisyGin: if, by or againstGin Yule: by ChristmasGloamin: twilight Grat: wept, shed tearsGrit: full to overflowingHinnied: honeyedKnowe: a small, round hillockLeigh bink: low bankLeir ilk ither leer: teach each other learningLoof: palm of the handSaut: saltSindered: separatedSkail\u27t: scatteredSpeel: climbThrossil: thrush, or mavis, one of the sweetest singing birds that inhabit ScotlandYule: Christma

A CFD study on two-phase frozen flow of air/water through a safety relief valve

The air-water two phase critical flows through a safety relief valve commonly used in the refrigeration industry is examined with particular emphasis on the prediction of the critical mass flowrates using CFD based approaches. The expansion of the gas through the valve and the associated acceleration is coupled to the liquid phase and results in changes to the velocity slip with the possibility of influencing the choking conditions and the magnitude of the critical mass flows. These conditions are poorly reported in the literature for safety valves. This paper presents a study where the ability of established two phase multi-dimensional modelling approaches to predict such conditions are investigated. Comparison with the simplified mixture model will show that this model tends to underestimate mass flowrates for medium to high liquid mass fraction. However, the two fluid model can adequately account for the thermal and mechanical non equilibrium for these complex flow conditions with the use of simplified droplet sizing rules

2-(1,4-Dioxo-1,4-dihydro-2-naphthyl)-2-methylpropanoic acid

The sterically crowded title compound, C₁₄H₁₂O₄, crystallizes as centrosymmetric hydrogen-bonded dimers involving the carboxyl groups. The naphthoquinone ring system is folded by 11.5 (1)° about a vector joining the 1,4-C atoms, and the quinone O atoms are displaced from the ring plane, presumably because of steric interactions with the bulky substituent

A CFD study of two-phase frozen flow of air/water through a safety relief valve

The air-water two phase critical flows through a safety relief valve commonly used in the refrigeration industry is examined with particular emphasis on the prediction of the critical mass flowrates using CFD based approaches. The expansion of the gas through the valve and the associated acceleration is coupled to the liquid phase and results in changes to the velocity slip with the possibility of influencing the choking conditions and the magnitude of the critical mass flows. These conditions are poorly reported in the literature for safety valves. This paper presents a study where the ability of established two phase multi-dimensional modelling approaches to predict such conditions are investigated. Comparison with the simplified mixture model will show that this model tends to underestimate mass flowrates for medium to high liquid mass fraction. However, the two fluid model can adequately account for the thermal and mechanical non equilibrium for these complex flow conditions with the use of simplified droplet sizing rules