Abstract: Based on the analysis of the fluid noise and the investigation of the noise after the on-the-spot flow control valve is used, the product with low noise is produced by the theory of flow velocity, pressure difference and multi-stage noise reduction. Keywords: noise source, liquid flow rate, cavitation noise, monomer flow rate, multi-stage noise reduction Our leading product - self-operated flow control valve, since the advent of 93 years to now has a full ten years, in this ten Mid-year heating industry colleagues never recognize the understanding, from a one-sided understanding of the system application, making self-flow control valve in heating has played a role. During this decade my company's self-operated flow control valve made two major improvements. From 93 years of using Type II to 98 years, in the first five years, due to its large size and limited installation location, in the first five years, in order to meet the needs of users, we improved our old products in 1999. Produced to ensure that the control performance can be installed at any angle, and the volume reduced by 40%; to the second 5 years in 2002, many users reflect the noise after installation increased than the original, especially in outdoor overhead lines on. In view of this situation, we also organize technical research and development projects, after nearly four months of thousands of tests, we have produced a low-noise, with lock, easy to adjust the flow control valve. The noise from the original 65 ~ 75dB down to 45 ~ 55dB, to meet the needs of different users. Here's what we get in the development process to sum up, for colleagues for reference. First, the noise source analysis In the heating system can not do without pumps, pipes and valves, but these are again the source of noise generated facilities. First speaking, when the liquid flows through the pipeline, turbulence and frictional excitation pressure disturbance will produce noise, especially when the Reynolds number Re> 2400 when the turbulent state, this contains a large number of irregular micro-turbulence turbulence can be said Itself in a "noisy" state. In particular, turbulent flow interacts with the passage of these impeding fluids when flowing through throttling or depressurisation valves, abrupt pipe sections or sharp bends. The sound power level (dB) as a function of flow rate can be expressed as As: △ Lw = 60lg, if the pipeline design can also produce cavitation noise; say the valve, with throttle or pressure limiting valve, is the most influential noise source in the liquid transmission pipeline. When the fluid flow velocity in the pipeline is sufficient, if the valve is partially closed, a large area choke will be formed at the valve inlet, the liquid flow rate will be increased and the internal hydrostatic pressure will decrease in the choke area. When the flow velocity is greater than or equal to the medium critical velocity, Below or equal to the evaporation pressure of the medium, bubbles are formed in the fluid. Bubbles with the liquid flow in the valve downstream of the choke area gradually reduce the velocity, static pressure increases, the bubble has been crushed, causing fluid pressure fluctuations in the irregular, this special turbulence known as cavitation, resulting The noise is called cavitation noise. In the flow of large, high pressure pipeline, almost all of the throttle valve can produce cavitation noise, this cavitation noise down the pipe can be spread far, this random noise can stimulate the valve or pipe The inherent vibration of the movable part, through which these parts act on other adjacent parts, is transmitted to the surface of the pipe, producing a toned sound similar to the metal collision. Cavitation noise power and the flow rate of the seventh power or the eighth power proportional to the valve so to reduce the noise can be multi-stage cascade valve, the purpose is to gradually reduce the flow rate. As we often use the cut-off valve, the use of low into the high flow direction, so when the fluid flow through the valve chamber, it will be under the control valve flap (ie, choke area) to create low-pressure high-speed zone, resulting in bubbles. After the valve and then through the formation of high-pressure low-speed area, the bubble has been squeezed broken cavitation noise. According to the above analysis shows that the pipeline noise, valve noise and liquid flow are related to the state, in other words that pressure and flow rate. Second, the flow rate, pressure noise generated by the survey Below is our field survey data. Tianjin soda plant Chaoyang floor district heat transfer station, heating area of ​​265,000 square meters, laying pipeline: outdoor overhead, the heat exchange station is divided into four loops for. South Area DN250 for the area of ​​132,000 square meters; North District diameter DN250 for the area of ​​108,000 square meters; spring breeze diameter DN200, for an area of ​​12,000 square meters; 34 # building diameter DN150 for the area of ​​8012 Square meter. Households reflect the 34 # floor and spring install the control valve noise. March 3, 2003 We went to the site for testing (equipment ultrasonic flow meter, noise meter), the data are as follows: Measured indoor noise 34 # building, Unit 2,3 57 dB; 60 dB compared with 45 ~ 47 dB for units 1, From the above data, although the flow rate of each unit did not exceed the design requirements, but due to the relative monomer flow rate is too fast, large pressure drop, resulting in cavitation noise generated in the control valve. The pressure difference of 34 # building is 0.06Mpa, while the pressure difference of 1 # building in the southern area is 0.02 Mpa, another reason for the rapid flow rate and large pressure difference is that the distance between 34 # building and the heat exchange station in spring breeze is relatively close . The farthest end of the user entrance distance of about 350 meters, while the most northern and southern areas of the user up to about 1000 meters, with the same system a great disparity, resulting in a large pressure difference at home, the velocity difference is also large. As the pipeline is overhead installation of this cavitation noise and the stent and then resonate so that noise is transmitted to the interior, this situation in the Liaohe Oilfield Shuguang operating area has also occurred. Not only overhead lines, buried pipelines can also produce cavitation and turbulence friction noise. Such as Tianjin Beichen District, a heating district is buried pipeline. After installing the flow control valve noise significantly increased, the measured indoor up to 65 dB. Ask the user that there was also before, but not now large, the control valve removed, the measured indoor up to 58 dB, the reason is due to heat network balance is not good, a single individual pressure drop, the flow rate is too fast. Earlier it was said that cavitation noise and sound power were proportional to the seventh or eighth power of the flow rate, so that although the flow rate was only a little bit lower, the noise was greatly increased. In view of the above situation, we have taken a step-down or step-by-step approach to reducing the pressure headcount and flow rate on Building 34 in the Chaoyang Lou Residential Quarter. First of all, the main branch of the export valve (DN150) has been adjusted, but also the unit door valve has been adjusted. Retest 34 # House home pressure control between 0.03 ~ 0.05Mpa, retest room unit 2 102 has dropped to 35 dB, 101 units down to 40 dB, has to meet the demand. Third, the noise reduction control valve generated As mentioned earlier, the sound power level changes with the flow rate for the relationship △ Lw = 60lg, and from △ P = KVS · G2 can be obtained V =, we can see that when the flow coefficient (KVS) certain , Flow cross-sectional area (πR2) a certain time, the sound power level can also be expressed as △ Lw = 60lg, and self-flow control valve is based on adjusting the pressure to achieve the purpose of controlling the flow. So how to ensure that the pressure drop and achieve the purpose of noise reduction, based on the above measured data and theoretical analysis, we use a multi-stage buck structure. First of all, the manual valve is changed to the inclined screw plug, making the flow of performance can be guaranteed to reduce the flow rate, which is the first level; secondly, the automatic valve to double arc, double valve structure, the fluid flow through the first Valve on the arc surface, and then through the arc surface that is convenient and can reduce the flow of fluid through, which is the second level; and then the fluid through the lower valve under the arc surface and the lower arc This is the third stage . At the same time in the automatic valve flap also with side ribs can guide, but also eliminate the formation of bubbles in the fluid. In order to eliminate the low-pressure high-speed zone caused by choke, we started by adding a damping net at the control valve inlet and manual control to reduce the flow rate and reduce the choke, which can not be tested because the damping net is corrosion-resistant (using stainless steel ), It is easy to cause blockage because of the mesh diameter limitation. We change the automatic valve disc into comb-tooth shape in order to reduce the bubbles formed in the high-speed zone. However, since the shape and strength of comb teeth are not conducive to long-term use, they are not used. Finally, take the structure of multi-level noise reduction. After nearly 1,000 times of tests, we constantly improve the control valve noise from the original 65 ~ 75dB down to the present 45 ~ 55 dB. Through these two technological transformation makes self-flow control valve in the scope of use and has been further expanded. At present, our noise reduction valve has been mass-produced, and has more than 10 customers orders. The general life of a patented product is 30 to 50 years. Self-operated flow control valve has come out in China more than 10 years, has gradually become a universal product. How to let heating users know how to use the product is the direction we continue to work and we will continue to work hard to develop new products to serve the hot users. References 1, "Noise and Vibration Control Program Manual" Machinery Industry Press 2, "HVAC Design Manual" China Building Press 3, "Engineering Fluid Mechanics"
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