DESIGN OPTIMIZATION OF INDUSTRIAL STEAM VENT SILENCER FOR BETTER FLOW PROCESS AND NOISE REDUCTION BY CFD AND SIDLAB SIMULATION

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1 DESIGN OPTIMIZATION OF INDUSTRIAL STEAM VENT SILENCER FOR BETTER FLOW PROCESS AND NOISE REDUCTION BY CFD AND SIDLAB SIMULATION Shahid Nadeem #1,, K.S.Shashishekar #2, #1. M.Tech student (Thermal Power Engineering), Department of Mechanical Engineering, Siddaganga Institute of Technology, Tumkur , Mobile no: #2. Professor & Dean, Department of Mechanical Engineering,Siddaganga Institute of Technology,Tumkur , Mobile no: ABSTRACT With the tightening of noise regulations, industrial facilities are required to stay in compliance with regulations, here comes the usage of vent silencers which are mainly used for reduction of the noise coming out from the industrial facilities.there are mainly two aspects in industrial steam vent silencer one is the noise reduction and another is the flow consideration. The flow of steam in the vent silencer is mainly from the inlet diffuser which is designed with multiple number of holes through which the flow takes place. Detailed literature survey has shown that there is a considerable variation in fluid flow pattern inside the steam vent silencer by differing the number of holes and also diameter of holes in the inlet diffuser. This study aims at running the CFD simulation for the steam vent silencer for different number of holes and diameter and hence finding an optimized design for the inlet diffuser for the flow to take place smoothly and henceforth reducing the noise, since we know turbulent flows creates noise. The steam vent silencer model is generated using CATIA V5 R20, pre-processing is carried out using ANSYS WORKBENCH and CFX SOLVER is used for simulation. The vent silencer discussed here is those for a large flow rate, high velocity, high pressure and high temperature used in power plants.the turbulence model used is k-epsilon. Keywords:Diffuser, Vent Silencer, Flow Pattern, k-epsilon Turbulence model. INTRODUCTION SOUND is both a physical phenomenon and the sensation of hearing. By definition, Noise is unwanted sound. One person s sound, rock music, for example, can be another person s noise [1] Excessive noise can be both objectionable and hazardous; hence there is a need to reduce the R S. Publication, rspublicationhouse@gmail.com Page 221

2 noise coming out from any facility. In our case as the noise is coming out from the industrial facilitieslike steam vents, safety relief valve outlets etc, hencevent silencers are used for the noise reduction. Thesevent silencers reduce the noise generated by the expansion of steam from elevated pressures to atmospheric pressures.these are absorptive silencers used to suppress noise generated by high velocity gas streams such as steam vents, safety relief valve outlets, system blow downs and purge outlets etc [2].There are two considerations in the industrial vent silencer one is the noise reduction and another is the flow consideration [3], for any silencer to work effectively the flow through the silencer should be smooth and laminar, the flow in the silencer takes place through the pressurized inlet diffuser which is designed with multiple number of holes to break up the large jet stream of gas into many small jets and provide energy dissipation [3], the characteristics of flow into the silencer is mainly decided through these holes hence there is a need to design the silencer with optimum number of holes and diameter so as to get the flow as smooth as possible. According to the paper entitled steam silencer by M.I. Carlos A. Miranda Herrera [4],equal flow is assumed in all the holes. Because of this, the speed will be reduced in each hole and this will produce a lower Reynoldsnumber Re (less turbulence). In the previous design of the silencer the flow through the diffuser was turbulent due to which there was an inefficiency of the silencer. An attempt is made in this project to try to reduce the turbulent nature of the flow by trying to optimize the design of the diffuser to get a smooth flow. DESIGN The overall size of a vent silencer is directly proportional to the desired noise reduction and the flow rate of the particular gas [5]. Noise reduction depends on the silencer length, while the diameter of the silencer depends on the gas flow rate. These silencers can range from 12 inches up to 12 feet in diameter. In our case the length and the diameter is given for the particular flow rate. A typical vent silencer designed in CATIA for the analysis purpose in this study is shown in figure below Figure 1 shows the CATIA designed model of the vent silencer R S. Publication, rspublicationhouse@gmail.com Page 222

3 The three principal components of the vent silencer are the 1) Pressurized Inlet Diffuser, 2) Plenum Section and 3) Acoustic Tube Module as shown in Figure 1. Each component accomplishes diffusion and smoothing of the flow and an overall reduction of noise. DESIGN REQUIREMENTS Stay away from sonic flow and have a moderate speed. Designing the holes of moderate size because if the holes are too small the speed will be increased and the system may collapse, on the other hand if the holes are too big there will be no pressure drop. No concentrically designed holes. FLOW ANALYSIS The three-dimensional geometry model of the vent silencer is created using a 3D modelingsoftware package(catia V5 R20) as shown in Fig 1.Then the geometry is meshed using3d tetragonalfinite volume based elementsin the ANSYS CFX MESHER, and the simulations are carried out using the commercial finite volumebased CFD package,ansys CFX SOLVER. The standard k-epsilon model is used for simulation of turbulent flow. The main dimensions of the silencer in mmare: Length: Height: 762 Diameter: 762 Diffuser dia: The Flow conditions are: Fluid: Steam Design pressure: Atmospheric pressure Design temperature: C Flow rate: 8 kg/sec Walls: no slip walls. RESULTS & DISCUSSION The CFD simulations are carried out for the silencer with different designs of the pressurized inlet diffuser whose results are shown below: R S. Publication, rspublicationhouse@gmail.com Page 223

4 Figure 2 shows the stream lines for 24 holes offigure 3a shows the streamlines for 24 holes of 30mm dia 30 mm dia. Figure 3b shows the streamline for diffuser Figure 4 shows the streamline for diffuser with holes of 45mm dia holes of 45mm dia Based on simulated results, the velocity streamline for the old design of the silencer with 24 number of holes of 30 mm diameter is shown in Figure 2, wherein the flow through the diffuser is turbulent in nature as can be seen from the figure. Henceforth in order to reduce this turbulence different designs of the diffuser are tried. Results of some of the designs simulated are shown above, first the design of the silencer with 16 number of holes of 30 mm dia on the diffuser is tried whose result is shown in the figure 3a. This design did not gave satisfactory result hence was not suitable for design. Figure 3b shows another design of the silencer with 16 number of holes of 45 mm diameter on the diffuser, the results from this design was comparatively better than the previous designs but still were not satisfactory. At last the design of the silencer with 24 number of holes of 45 mm diameter gave satisfactory result with less turbulent flow as shown in figure 4 and also with higher noise reduction as shown in the results of the SIDLAB noise simulation software below. SIDLAB NOISE SIMULATIONRESULTS. SIDLAB is a1d sound propagation simulation software for complex duct networks. It is based on the two-port theory and compiles a long experience and knowledge of using similar codes for all types of duct acoustic applications in research, teaching and consulting. SIDLAB calculates Transmission Loss for all the silencer designs and hence gives an comparison as to which is a better design with higher Transmission Loss. Sound Transmission loss is defined as the logarithmic ratio of the incident sound power on one side of the barrier( or partition) to the sound transmitted to the other side, higher the Transmission Loss better the design. The results of the Transmission loss are given below. R S. Publication, rspublicationhouse@gmail.com Page 224

5 Figure 5Transmission Loss for present silencer Figure Transmission Loss for silencer with 16 holes of 30mm dia with 24 holes of 30mm dia Figure 7Transmission Loss for silencer Figure 8: Transmission loss result for silencer 16 holes of 45mm dia. with 24 holes of 45 mm dia. As we can see from the above 4 Figures, the results for the silencer with 24 number of holes of 45 mm diameter gave higher Transmission Loss of about 40 db which is higher compared to all other designs which gave a Transmission loss of about 25 to 30 db.hence we can say the design of the silencer with 24 number of holes of 45 mm dia is a better design for the vent silencer. CONCLUSION The objective of this project was to run the simulations for the steam vent silencer with different designs of the pressurized inlet diffuser and find the optimum design for it with different number of holes with different diameter, CFX Solver was used to run the simulations, the results obtained shows the design of the pressurized inlet diffuser with 24 number of holes of 45 mm R S. Publication, rspublicationhouse@gmail.com Page 225

6 diameter gave satisfactory results with flows from the diffuser to the plenum section taking place smoothly and with less turbulence and also the Transmission loss for the design was around 40 db which is higher comparted to all other designs. Hence the design of the diffuser with 24 holes of 45 mm diameter is recommended for the design. FUTURE PROSPECTIVE In this project the design of the diffuser with different number of holes and diameter is taken into account for optimizing the design of the diffuser, furthermore in future the design of the diffuser with different length and diameter can be studied for better optimization of the silencer. Furthermore in these simulations only standard k-epsilon turbulence model is used but in future SST k-omega, realizable k-epsilon turbulence model can be used for better result and a validation of simulation result to experiment data can also be done. REFERENCES 1. Silencer Applications by UNIVERSAL Silencers Co. 2. UNIVERSAL vent silencer a report by universal co. 3. Flow Considerations in Industrial Silencer Design by George Feng, Vadim Akishin and Bruce Huyn. 4. Steam silencers by M.I. Carlos A. Miranda Herrera 5. PULSCO vent silencer- a report by pulsco co. 6. Dr. S. RajaduraiSuresh Natarajan and N.Manikandan s Muffler Pre-Processing Methodology and Comparative Study 7. Middelberg, Barber, T.J., Leong, S. S., Byrne, K.P and Leonardi, E s. Computational Fluid Dynamics Analysis Of The Acoustic Performance Of Various Simple Expansion Chamber Mufflers 8. C.J. Deschampsa, F.C. Possamaib and E.L.L. Pereira s numerical simulation of pulsating flow in Suction mufflers 9. V. KoteswaraRao, Mahesh S. Murthy, S. Arumuga Raja &Dattu Kumar s CFD (Computational Fluid Dynamics) technique to study the suction gas flow through the suction muffler 10. Sanjay s. gosavi, Vinayak m. juge, Mayur m. nadgouda s Optimization of Suction Muffler Using Taguchi s DOE method 11. George Feng,VadimAkishin, Aerodynamic aspects for designing industrial acoustic silencers 12. H.Maheshappa, V.K.Pravin, K.S.Umesh, P.H.Veena s Simulation of the Design of an Exhaust Silencer Stack by CFD 13. Shital Shah Saisankaranarayana K, Kalyankumar S. Hatti Prof. D. G.Thombare s A Practical Approach towards Muffler Design, Development and Prototype Validation 14. Lee Ming Wong G. Gary Wang s Development of an automatic design and optimizationsystem for industrial silencers 15. Ar-15 Reflex Sound Suppressor Modeling And Testingby Christopher Gingrich Daniel Emery Ricky Lynch. R S. Publication, rspublicationhouse@gmail.com Page 226