Fixed tube heat exchanger consists of tube bundle, tube plate, shell, head, folded plate, etc. Tube bundle ends fixed in the tube plate, the tube can be expanded (the inner hole of the tube with mechanical expansion, so that the tube wall from the inward to outward extrusion and fixed in the tube plate) or welded to the tube plate. The tube bundle is placed within the tube shell, with headers and flanges fixed at both ends. In this way, one fluid flows from the inside of the tube and the other from the outside. The space between the two heads and the tube plate is used to distribute or collect the fluids inside the tube. The two fluids do not mix with each other, but only exchange heat through the tube wall.
Advantages: simple and compact structure, high pressure resistance, low cost and easy to clean the tube side.
Disadvantages: Risk of blockage when the tube is damaged or needs to be replaced.
When the difference between the wall temperature of the tube bundle and the shell or the coefficient of linear expansion of the material is large, a large thermal stress will be generated in the shell and the tube bundle. A flexible compensation ring (also called expansion joint) should be installed on the shell to reduce the thermal stress.
Fixed Tube Heat Exchanger,Tubular Exchanger,Tema Heat Exchanger,Fixed Tube Sheet Heat Exchanger Guangdong Jiema Energy Saving Technology Co.,Ltd , https://www.heatexchangerjiema.com
1 Introduction In a pneumatic system, the intake and exhaust of the cylinder are controlled by the air distribution valve, and the noise generated by the air discharged to the atmosphere through the distribution valve exhaust port is often lower than the noise generated in any part of the pneumatic system Large, and the operation of workers and the surrounding environment have serious injuries and pollution [2]. In view of the universality of the noise, the seriousness of the damage and the urgency of its governance, the author conducted a great deal of experimental research on the noise characteristics. In particular, the problems and trends of the muffler in the noise control were analyzed and clarified The vague awareness of the noise-controlled muffler has been explored for the effective control of this noise in industrial practice. 2 air distribution valve exhaust noise characteristics and requirements of the muffler 2.1 exhaust noise classification exhaust noise is aerodynamic noise. According to the degree of exhaust noise fluctuations, it can be divided into three categories: stable exhaust noise, periodic exhaust noise and intermittent exhaust noise. Stability Exhaust noise is the amount of noise that remains substantially the same throughout the exhaust process, such as the noise generated by the air compressor venting to the atmosphere through the exhaust valve above or below it. The noise is dominated by high frequencies. Periodic exhaust noise means that the exhaust noise periodically changes in size and noise occurs for the most part of the process. Exhaust noise generated during the operation of the internal combustion engine is periodic exhaust noise. The noise is dominated by low frequencies. Intermittent exhaust noise is an extremely striking impact on the size of the noise, producing the next noise pulse longer after the previous noise vanishes, with much less noise than noiseless time. Noise generated by the cylinder exhaust through the air distribution valve is such noise. Pump suction port should be large enough, and should not get into the tank below the surface of a certain depth, to prevent the liquid level down after suction. 2.2 Air distribution valve exhaust noise characteristics 20MN hot forging press clutch cylinder air distribution valve exhaust as an example, the measured noise results shown in Figure 1. After a large number of test results are similar to Figure 1, before the exhaust gas cylinder pressure is higher, the greater the noise, and the sound pressure level at all frequencies have increased, and the low-frequency and high-frequency sound pressure value is higher, The lower IF, the spectrum showed a saddle-shaped curve. Low-frequency noise is generated by a monopole source and the high-frequency part is generated by a quadrupole source. And test results show that the initial noise of the exhaust the largest, later smaller and smaller until it is zero. Although the low-frequency part of the exhaust noise is large, Figure 1 shows that the low-frequency part of the A sound level is below 80dB, the high-frequency part of the A sound level is very high, At present, A sound level is widely used in the world to measure the extent of a noise damage to the human ear. Therefore, the exhaust noise generated by the air distribution valve is still dominated by the high frequency part. When it is controlled, it is controlled by high frequency. 2.3 pairs of air distribution valve exhaust noise muffler requirements According to the characteristics of the noise and plant actual pneumatic equipment in the actual situation, especially for the control of the noise exhaust muffler with the following requirements: (1) a good high-frequency drop Noise performance. (2) aerodynamic performance is good. That is, the exhaust resistance is small, and the exhaust time will not be excessively prolonged after installation of the muffler, or even cause an accident of the equipment. (3) Anti-harsh use of the environment ability. Due to compressed air containing water, oil and other impurities, the use of dust present on site, therefore, in order to improve the life of the muffler, the muffler should have good resistance to water, oil and dust pollution. In addition, due to the strong exhaust impact, high flow velocity, muffler structure should have good impact, vibration and anti-scratch fly ability. (4) has a good structural performance, low cost, easy maintenance, long life. 3 commonly used noise control muffler type and its problems 3.1 orifice injection muffler Institute of Acoustics, Chinese Academy of Sciences, Professor Ma Dao and other scholars, through theoretical and experimental research, put forward a small hole injection control noise theory, the principle is that a Large spout, while maintaining the same displacement under the premise, replaced by many holes instead, and the hole will be high-frequency sound to the human ear is not sensitive to the ultrasound range, so as to achieve the purpose of noise reduction. Hole muffler silencer volume muffler [2] Where xA - blocking situation 0.165D / DOD - nozzle diameter (mm), DO = 1mm. When D ≤ 1mm, xA1, available by conversion [5] ΔL = 27.5-30lgD Thus, within the aperture range, the aperture by half, the amount of silence can be increased by 9dB, taking into account the ease of processing holes , The general election diameter of 1 ~ 3mm holes more appropriate. If the aperture is too large, the noise reduction effect of the hole is poor. If the hole spacing is small, the air flow through the hole will be reunited into a large jet, so that the noise reduction effect worsened. To this end, the hole injection hole center distance should be taken 5 to 10 times the aperture (before injection pressure is higher, the hole center distance should be greater), and the hole center distance for the lowest value of d- - Small hole diameter, usually choose b = (8 ~ 10) d is more appropriate. In order to make the exhaust unobstructed, taking into account the damping effect of the small hole, it is recommended to design the open flow area of ​​the muffler as 1.5 to 2 times the area of ​​the exhaust valve. In summary, the small hole injection muffler, to make it has a certain noise reduction effect, without affecting the normal operation of the pneumatic device, muffler aperture, hole spacing, hole number of the three key parameters must be good . However, the survey found that many of the three key parameters of the muffler used in the factory did not meet the requirements. Shown in Figure 2 for a factory production of air distribution valve muffler, the circumferential hole pitch is 44.5mm, the axial pitch is 13mm, the number of holes 48. The hole diameter d = 2.3mm between 1 ~ 3mm; the hole spacing b in the circumferential direction and the aperture d ratio b / d = 19.3, in the axial b / d = 5.6, therefore, in the axial pitch is a little smaller ; The diameter of the air distribution valve D = 15mm, according to the aforementioned design principles, the total area of ​​the orifice should be 1.5 to 2 times the valve flow area. Thus, the calculation shows that the required number of holes should be 64 to 85 holes, while the muffler shown in Figure 2 is only 48 holes, equivalent to the valve area of ​​?? only 1.13 times the flow area, it will result in row The gas does not flow smoothly, and the actual use of the muffler does not have the problem of poor exhaust. In addition, the axial distance between the holes is too small and the diameter of the hole is 2.3mm. As a result, the actual noise reduction amount is only 7dB. Both of these disadvantages are common As a result of the operation, it causes the operating workers to dismantle them often in practice. Figure 2 orifice injection muffler According to the author of the actual noise control experience, injection of small holes should be more appropriate choice of 1.5mm, the hole spacing should be 8 to 10 times the aperture, the orifice area should be the valve flow area of ​​1.5 ~ 2 times better. In addition, the orifice injection plate should have sufficient strength and stiffness, in the intermittent exhaust flow under the impact of the structure can not produce noise. 3.2 Muffler Muffler Muffler As shown in Figure 3 for the production of a domestic factory air distribution valve muffler, the valve diameter used is 25mm, the total area of ​​40 holes φ5.5 equivalent to 1.936 times the valve flow area, Therefore, the exhaust is very smooth. The hole pitch b = 7.5mm, the hole pitch b and the hole diameter d = 5.5 the ratio of b / d = 1.36mm, the pitch is too small, combined with the aperture of 5.5 mm far more than 1 ~ 3mm, so the noise reduction performance is poor, measured The noise reduction is only 2.5dB. Therefore, should not actively advocate the muffler. Figure 3 porous diffusion muffler 3.3 hole diffuser muffler At present, many of the domestic air distribution valve exhaust port on the use of such muffler, which has the advantages of small size, large amount of noise reduction. This type of muffler with a large number of small pores, the exhaust flow can be filtered into numerous small air flow, the gas pressure is reduced, the flow rate is reduced to reduce the noise so as to achieve the purpose. Such mufflers can be divided into micro-porous sintered type and multi-layer wire mesh type (or known as sieve type), shown in Figure 4, porous sintered type is the metal, plastic or ceramic spherical particles, in a certain Temperature and pressure, sintered in the mold into a microporous (pores as small as silk level) muffler, the most used is currently sintered copper particles. Multi-layer wire mesh type is a good anti-rust function of the copper mesh wrapped around the muffler with good rigidity perforation protection panel to form a multi-layer (up to 20 layers) copper mesh, and then installed outside the metal face Sleeve. Figure 4 Hole diffusion muffler a. Porous sintered b. Multi-layer wire mesh type A large number of test results show that the same size, micro-porous sintered noise reduction significantly larger than the multi-layer wire mesh type, and these two Mufflers of various types have good mid-to-high frequency noise cancellation characteristics. But the porous sintered type hole is too small, use for a period of time, due to the compressed air impurities, oil, water and dust in the environment, causing microporous plugging. During the investigation, it was found that when the pneumatic device was operated at full load for about six months, almost 40% to 50% of the micropores in the microporous muffler were clogged, and fine impurities were difficult to clean when they were drilled in the micropores. Therefore, After a period of time, due to serious blockage, it can only be removed without use, otherwise it will make the exhaust is very smooth and affect the normal work of equipment. For example, the survey found that due to serious blockage of the muffler, resulting in hot forging presses clutches and brakes are not smooth, eventually lead to "boring car" accident, resulting in the use of tens of thousands of dollars had to burn off the mold. Metal mesh muffler, when used after a period of time to open it, the metal mesh impurities with a brush and water rinse, its performance will be restored as ever, so Japan made the air distribution valve exhaust port on the large Most are installed this type of muffler, but must be cleaned regularly. A large number of test results on the test bench show that to ensure that these two mufflers have sufficient flow area so as not to affect cylinder exhaust, the flow area should be 3 to 5 times the rated flow area of ​​the valve, with micro Hole sintered type to take the upper limit, multi-layer metal mesh type to take down the limit. 3.4 purely resistive muffler porous muffler with a porous muffler with good high-frequency sound absorption characteristics, and the exhaust noise is again based on high-frequency noise, so naturally make people think of using a resistive muffler to reduce The noise. Figure 5 shows the structure of the muffler. Figure 5 resistive muffler 1. Perforated guard panels 2. Shell 3. Absorbing material However, the survey found that the actual noise reduction of this muffler is often less than the actual use of the design of the noise reduction, and performance degradation faster, shorter life expectancy . The reasons for the above phenomena mainly in the following three aspects. First of all, due to the high air velocity, the large noise generated by the perforation on the air flow caused by the perforation when passing through the surface of the perforated retaining panel greatly reduces the noise reduction capability. Secondly, due to the intermittent nature of the exhaust gas and the high velocity of flow, strong impact is generated on the structural components in the muffler, causing the components to vibrate and radiate structural noise, thereby reducing the silencing function. In addition, the high-speed impact Airflow attempt to porous porous sound-absorbing material scraping away from the muffler, over time, the muffler will gradually reduce the sound-absorbing material, so that muffler noise reduction. The author at the two steam forging plant used in the British Marseille 1,800 tons hot forging press clutch cylinder exhaust muffler installed on the anatomy found that almost half of its sound-absorbing material is scraped off the fly, so its noise reduction performance is very difference. Finally, the compressed air discharged from the cylinder through the air distribution valve contains a certain amount of oil, water and impurities, dust in the environment of use. Therefore, the survey found that the muffler porous sound-absorbing material surface of the glass cloth and near-surface porous sound-absorbing material in the pores have been oil, cement dirt paste full, long-time use of the porous muffler muffler sound absorption Almost all of the pores of the material are soaked with oil and water, and the porous sound-absorbing material has completely decomposed and decayed, which leads to the serious decrease of the sound-absorbing performance of the porous sound-absorbing material. Therefore, good absorbent and oil absorption porous sound-absorbing material should not be used in the air exhaust noise control muffler. 3.5 Resistant muffler Anti-muffler made of metal plate, with good resistance to water and oil resistance, but the general muffler low-frequency noise reduction performance is good, the main frequency noise performance is poor. Especially for the air distribution valve exhaust port intermittent exhaust noise, high-speed impact airflow in the muffler within the structural components have a strong impact, making it produce vibration and the radiation of structural noise; the other hand, the airflow in the muffler to produce a strong Turbulent phenomena and unstable flow, resulting in air flow noise regeneration, the author in the research and intermittent exhaust noise test bench on a large number of test results show that the pure muffler used in the air distribution valve exhaust noise reduction occasions, The actual amount of noise reduction far less than the design of noise reduction, more serious is sometimes not only not muffler muffler, but will amplify the noise and become a loudspeaker. Therefore, use a resistant muffler in this noise control must be very cautious. As shown in Figure 6 for a factory technical staff forging forging forging machine clutch air distribution valve exhaust muffler schematic design, the design of the noise reduction up to 35dB, and the actual amount of noise Only 7dB. Figure 6 resistance muffler for the current problems in the noise control, the author after a long period of painstaking research, the establishment of the effective control of the noise theory and good performance muffler, successfully applied to a very noisy, and exhaust Resistance demanding mechanical presses clutches and brake exhaust noise control, and in large areas of practical promotion, performance is good. 4 Conclusion (1) air distribution valve noise far exceeds the national standard, the operation of workers and the surrounding environment caused extremely serious injury and pollution, the effective control of the noise is imperative. (2) According to the fluctuation of exhaust noise, it can be divided into stable exhaust noise, periodic exhaust noise and intermittent exhaust noise. The exhaust noise generated by the air distribution valve is intermittent Air noise. (3) Air distribution valve exhaust noise generated by high and low frequency-based, and with the cylinder pressure increases, the total noise level and the noise at all frequencies have increased, and the exhaust early The noise is maximum. (4) air distribution valve exhaust noise control muffler should have good high-frequency noise reduction performance, aerodynamic performance, anti-harsh use of the environment ability, with good structural performance. (5) At present, there are five types of muffler that control the noise, such as small hole injection type, large hole diffusion type, small hole diffusion type, resistivity and resistance type. The more effective types are small hole diffusion type and small size Hole injection type, but the hole diffusion muffler flow area should be 3 to 5 times the valve flow area, and must be regularly cleaned, maintained and replaced. Hole injection type design must make the aperture (1.5mm), pitch (aperture of 8 to 10 times) and the flow area (for the valve through the flow area of ​​1.5 to 2