| Pressure and temperature reducing device is an important equipment to control steam pressure and temperature and in process industry.It has important value on meeting the requirements of users with steam,recycling waste heat and pressure energy,protecting the security of system and equipment.Pressure reducing valve is the core control element of pressure and temperature reducing device.With the construction and development of national key projects,domestic traditional pressure reducing valve can not meet requirements of pressure adjustment and noise control under complex conditions such as high parameter(high pressure and temperature),high flow rage and large pressure ratio.While at present high pressure reducing valve(HPRV)is almost monopolized by foreign companies.Therefore,researches on pressure reducing mechanism and noise control of HPRV under complex conditions such as high parameter have scientific significance and engineering value to promote pressure and temperature reducing technology and equipment,and to break the foreign monopoly of techniques and products.Supported by Major Science and Technology Project of Zhejiang "Development and application of high efficiency and energy saving pressure and temperature reducing technology and device under extreme conditions"(No.2012C11018-1),pressure reducing mechanism and noise control technology of HPRV were researched using numerical simulation and experimental method.The main research content and achivements are as follows:(1)Calculation models of steam flow in HPRV were built,and charcteristics of compressible flow of high pressure and temperature steam were simulated.Flow status and ideal flow characteristic of HPRV were studied.Tests of ideal flow characteristic and parallel flow characteristic of HPRV were carried out to research ideal flow characteristic and parallel flow characteristic.It is shown that ideal flow characteristic of HPRV has linear features.When the tested flow line is in parallel with bypass line,flow characteristic distortion of HPRV occurred and adjustable ratio of HPRV decreases.The numerical simulation and tests agreed well,which indicates that numerical method is valid for anslysis of flow characteristics in HPRV.(2)Flow models of different opening were built.Flow and throttling effects of valve plug and perforated plate were compared at different opening.The transformation of superheat was revealed.Based on basic equations of steady flow,nozzle flow equation and isentropic flow equation were obtained.By simplifying the throttling elements,pressure reducing and energy variation through perforated plates in pipe were studied.It is shown that velocity increases and pressure decreases at throttling elements.Throttling effects of perforated plate is passive that it enhances with valve opening.Numerical results of HPRV are basically in line with nozzle isentropic flow,while irreversible actual flow entails energy loss.Steam adiabatic throttling is a process of entropy increment.The entropy increases more smoothly for more perforated plates,and exergy loss is also smaller.When the pressure ratio of throttling element is smaller than critical pressure ratio,flow behind perforated plate transforms to supersonic flow.The steam superheat decline obviously at throttling elements and superheat of outlet is higher than that of inlet.On this basis,structure of HPRV was improved,and structure design method was proposed.(3)Using LES model,the unsteady flow models in HPRV was built.Aerodynamic noise properties in HPRV were researched.Noise sources,noise directivity,spectrum property of valve without perforated plate and valve with perforated plate were compared.It is shown that acoustic power level behind the valve plug for valve without perforated plate and around the plate for valve with perforated plate is louder,which is the main noise source.Noise directivity curve is of elliptical shape,and downstream noise is larger.Perforated plate helps to reduce downstream noise.It is found that high frequency noise increase with inlet pressure,while low frequency noise increase markedly when the velocity close to speed of sound.(4)FEM models of perforatd plate in pipe were built.Using transfer matrix method the transmission loss of perforated palte was predicted through sound pressure of four points,and relationship between noise characteristics and structural parameters such as distribution,area ratio and thickness were analyzed.Maximum transmission loss of perforated plate was derived.It is shown that more uniform distribution of holes leads to more effective noise control.Maximum transmission loss of perforated plate is related to area ratio.The calculation formula agreed well with FEM results and can be used for transmission loss prediction of perforated plate with holes in rhombic arrangement.Steady region is wider for thinner plate,but control of low frequency noise is poorer.The subsonic flow has no significant influence on transmission loss,but supersonic flow will cause periodic change of transmission loss. |
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