30120130405017

222 views

Published on

Published in: Technology, Business
0 Comments
0 Likes
Statistics
Notes
  • Be the first to comment

  • Be the first to like this

No Downloads
Views
Total views
222
On SlideShare
0
From Embeds
0
Number of Embeds
1
Actions
Shares
0
Downloads
4
Comments
0
Likes
0
Embeds 0
No embeds

No notes for slide

30120130405017

  1. 1. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME 150 NUMERICAL ANALYSIS OF AIR FLOW VELOCITY STREAMLINES OF AIR CURTAINS Mr Nitin Kardekar Principal, Jayawantrao Sawant Polytechnic, Research Scholar, Singhania University, Rajasthan. Dr. V K Bhojwani Professor JSPM’s Jayawantrao Sawant College of Engineering, Pune Dr Sane N K Research Supervisor, Singhania University ABSTRACT A prototype is developed in the laboratory in order to simulate the conditions of the entrance of the doorway. The air curtain device is mounted above the doorway. An obstacle of human Shape (mannequin) is placed in the doorway to simulate the real time situation. The air curtain blows the air in downward direction. The flow within the air curtain is simulated with commercial computational Fluid Dynamics (CFD) solver, where the momentum equation is modelled with Reynolds-Average Navier-Stokes (RANS), K- ε turbulence model. The boundary condition set up is similar to the experimental conditions. The CFD results are compared and validated against experimental results, after the validation stage and the air curtain velocity profiles are compared for with obstacle situations. The results are obtained in the form of velocity streamlines at different planes. The velocity streamlines are analysed discussed for the two cases reported and discussed in this paper. Key words: Air curtain, Reynolds-averaged Navier – Stokes equation, K- ε turbulence Model, velocity streamlines turbulent kinetic energy INTRODUCTION Air curtain devices provide a dynamic barrier instead of physical barrier between two adjoining areas (conditioned and unconditioned) thereby allowing physical access between them. The air curtain consist of fan unit that produces the air jet forming barrier to heat, moisture, dust, odours, insects etc. The Air curtains are extensively used in cold rooms, display cabinets, entrance of retail store, banks and similar frequently used entrances. Study found that air curtains are also finding applications in avoiding smoke propagation, biological controls and explosive detection INTERNATIONAL JOURNAL OF MECHANICAL ENGINEERING AND TECHNOLOGY (IJMET) ISSN 0976 – 6340 (Print) ISSN 0976 – 6359 (Online) Volume 4, Issue 5, September - October (2013), pp. 150-155 © IAEME: www.iaeme.com/ijmet.asp Journal Impact Factor (2013): 5.7731 (Calculated by GISI) www.jifactor.com IJMET © I A E M E
  2. 2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September portals. According to research by US department of energy by optimising the performance of super market display cabinet air curtain drinks industry used equivalent of 285 tonnes of used in cold storages. In developing countr retail stores, banks are not only limited to mega cities but they suburban’s and small towns. The effects of globalisation are inevitable. The air curtains are no more luxury but are necessary part of business development and economy. Hence study of air curtain with respect to Indian climate is necessary to ensure op leads to energy conservation. The saving of energy (Electrical energy) will be always boon for energy starving country like India. METHODOLOGY In order to analyse the flow of air curtain, it The study of velocity streamlines is essential to ensure that the air curtain does not get weak or breaks at any section. The air flow analysis was carried out using commercial software package ANSYS V13.0 Workbench platform. As shown in Figure 1 the air curtain is Figure 1 Experimental set up without mannequin (Photograph) Figure 3 Meshing Details International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME 151 portals. According to research by US department of energy 1875 MW energy will be saved super market display cabinet air curtains. In 2002 the UK food and used equivalent of 285 tonnes of oil to power its refrigeration units . In developing countries like India; the rise in cold storages, super markets, retail stores, banks are not only limited to mega cities but they have also become an The effects of globalisation are inevitable. The air curtains are no more necessary part of business development and economy. Hence study of air curtain with respect to Indian climate is necessary to ensure optimised performance of air curtains leads to energy conservation. The saving of energy (Electrical energy) will be always boon for In order to analyse the flow of air curtain, it was decided to analyse the velocity streamline The study of velocity streamlines is essential to ensure that the air curtain does not get weak or The air flow analysis was carried out using commercial software package Workbench platform. As shown in Figure 1 the air curtain is without mannequin Figure 2 Geometry Model with obstacle eshing Details Figure 4 Experimental set up with mannequin (Photograph) International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – October (2013) © IAEME MW energy will be saved per year In 2002 the UK food and units with most being like India; the rise in cold storages, super markets, have also become an integral part of The effects of globalisation are inevitable. The air curtains are no more necessary part of business development and economy. Hence study of air curtain with performance of air curtains which would leads to energy conservation. The saving of energy (Electrical energy) will be always boon for nalyse the velocity streamlines. The study of velocity streamlines is essential to ensure that the air curtain does not get weak or The air flow analysis was carried out using commercial software package Geometry Model with obstacle with mannequin (Photograph)
  3. 3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September Figure 5 Plane Definitions mounted on the top of the frame. The doorway frame chosen is 2270 mm in height and 900 mm in width, the breadth of the frame is 290 mm. There are two slits opens in the pushed by the blower in the domain through these slits. The experimentation without insertion of mannequin are carried out first then repeated after placing the mannequin in the flow of air curtain as shown in figure 4. The entire experiment is carried out at isothermal conditions; air at 2 at one atmosphere. The velocity of l CFD analysis, this velocity is representative of air curtain flow velocity. domain is extended (surrounding area) directions of frame openings. The frame walls are treated as impermeable wa walls. It is ensured while choosing the length of air curtain will not cross the boundaries of the domain. is generated (Figure 3) in the workbench. The structured mesh (hexahedron mesh) is used to build the extended domain and flow straightener. The frame portion is meshed with unstructured tetra mesh. The effort was made to mesh the entire domain with structured mesh but due to complex geometry at the flow straightener the frame portion has unstructured mesh. 385443 of which 59589 are tetrahedral cells and 325854 hexahedral cells. The minimum mesh quality is 0.3, total 708 cells falls within this range, as per the CFD Practices this is a good quality mesh. The mesh which is created in t solver available with workbench platform. The flow within the air curtain is simulated within commercial Computational Fluid Dynamics (CFD) solver, where the momentum equation is modelled with Reynolds-Average Navier domain is air at 290 C. The inlet boundary condition used is ‘normal speed’ at 9 m/s, since the actual turbulence data at inlet is currently unavailable, for the present simulation the intensity of 5% (medium intensity) is used to model the inlet turbulence. The outlet condition is assigned to the extended domain walls as average static pressure of 0 gauge magnitude. The computational platform is HP- Pavilion dv6, with The convergence target set at 1e-4 RMS; with continuity target error is 1e target achieved after 167 iterations. RESULT AND DISCUSSION The objective of the air curtain is to restri energy and keep the comfort conditions inside the space as is. The addition of serves as a partition between two spaces International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME 152 Plane Definitions Figure 6 Result Validation on the top of the frame. The doorway frame chosen is 2270 mm in height and 900 mm in frame is 290 mm. There are two slits opens in the domain; the flow jet is pushed by the blower in the domain through these slits. The experimentation without insertion of mannequin are carried out first then repeated after placing the mannequin in the flow of air curtain as xperiment is carried out at isothermal conditions; air at 2 at one atmosphere. The velocity of leaving air from slits is 9 m/s, similar conditions are used for analysis, this velocity is representative of air curtain flow velocity. As shown (surrounding area) to capture the flow of air leaving frame boundaries in directions of frame openings. The frame walls are treated as impermeable walls and are walls. It is ensured while choosing the length of extended domain that the direct transverse flow of he boundaries of the domain. Once the configuration is modelled, the mesh is generated (Figure 3) in the workbench. The structured mesh (hexahedron mesh) is used to build xtended domain and flow straightener. The frame portion is meshed with unstructured tetra mesh. The effort was made to mesh the entire domain with structured mesh but due to complex geometry at the flow straightener the frame portion has unstructured mesh. The total mesh count is which 59589 are tetrahedral cells and 325854 hexahedral cells. The minimum mesh quality is 0.3, total 708 cells falls within this range, as per the CFD Practices this is a good quality mesh. The mesh which is created in the Workbench is internally transferred to CFX solver available with workbench platform. The flow within the air curtain is simulated within commercial Computational Fluid Dynamics (CFD) solver, where the momentum equation is Average Navier-Stokes (RANS), K- ε turbulence model. The default C. The inlet boundary condition used is ‘normal speed’ at 9 m/s, since the actual turbulence data at inlet is currently unavailable, for the present simulation the uniform turbulence intensity of 5% (medium intensity) is used to model the inlet turbulence. The outlet condition is assigned to the extended domain walls as average static pressure of 0 gauge magnitude. The Pavilion dv6, with Intel CORE i3, 2.4 GHz processor, 8 4 RMS; with continuity target error is 1e-4 kg/s. The convergence The objective of the air curtain is to restrict the infiltration of outside air and thus save the energy and keep the comfort conditions inside the space as is. The addition of air curtain which partition between two spaces. Very complicated flow pattern is observed in close vicinity International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – October (2013) © IAEME Result Validation on the top of the frame. The doorway frame chosen is 2270 mm in height and 900 mm in domain; the flow jet is pushed by the blower in the domain through these slits. The experimentation without insertion of mannequin are carried out first then repeated after placing the mannequin in the flow of air curtain as xperiment is carried out at isothermal conditions; air at 290 C ( + 10 C) similar conditions are used for As shown in Figure 2 the to capture the flow of air leaving frame boundaries in lls and are ‘no slip’ extended domain that the direct transverse flow of the configuration is modelled, the mesh is generated (Figure 3) in the workbench. The structured mesh (hexahedron mesh) is used to build xtended domain and flow straightener. The frame portion is meshed with unstructured tetra mesh. The effort was made to mesh the entire domain with structured mesh but due to complex The total mesh count is which 59589 are tetrahedral cells and 325854 hexahedral cells. The minimum mesh quality is 0.3, total 708 cells falls within this range, as per the CFD Practices this is a good quality he Workbench is internally transferred to CFX-Pre, a CFD solver available with workbench platform. The flow within the air curtain is simulated within commercial Computational Fluid Dynamics (CFD) solver, where the momentum equation is turbulence model. The default C. The inlet boundary condition used is ‘normal speed’ at 9 m/s, since the actual uniform turbulence intensity of 5% (medium intensity) is used to model the inlet turbulence. The outlet condition is assigned to the extended domain walls as average static pressure of 0 gauge magnitude. The GHz processor, 8 GB of RAM. 4 kg/s. The convergence ct the infiltration of outside air and thus save the air curtain which observed in close vicinity
  4. 4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME 153 of the air curtain device. The analysis of such a complicated flow is difficult with experiments, whereas CFD can prove handful tool to analyse the flow patterns when validated. The velocity matrix generated with experiments at the centre plane is in good agreement with the CFD results. The Figure 5 shows the result comparison. The validation result justifies the CFD results, and can extend our belief for other flow results which are impossible to judge experimentally. The CFD plots are associated with 3 mid planes, as shown in the Figure 5. To reveal the details of movement of air particle, the streamline are drawn at planes 1, 2 and 3 with and without mannequin. Figure 7, 8 and 9 shows the streamline at plane 1, plane 2 and plane 3 respectively when mannequin is not introduced in the flow path. Straight flow of air particle from top to bottom is observed in all the planes. Above 150 mm from the ground the particles move sideways because the flow hits the ground. The velocity gradually decreased from top to bottom. The air particles from surrounding area gain momentum and get attracted towards the air curtain flow. This is because of higher velocity of air curtain particles; the low Figure 7 Velocity streamline at plane 1 Figure 8 Velocity streamline at plane 2 without obstacle without obstacle Figure 9 Velocity streamline at plane 3 Figure 10 Velocity streamline at plane 1 without obstacle with obstacle (mannequin)
  5. 5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME 154 Figure 11 Velocity streamline at plane 2 Figure 12 Velocity Streamline at plane 3 with obstacle (mannequin) (3D View) pressure region is created and surrounding air particles move towards this region to minimise the pressure difference. The velocity of surrounding particles is very low of the order of 0.0056 m/s. The particles from both surrounding are attracted towards the flow but do not cross the air curtain. Thus air curtain forms a perfect barrier. The surrounding particles leave the flow in their respective surrounding along with air curtain flow. Figure 8 and 9 explains this phenomenon at plane 2 and plane 3 respectively. Figure 10 shows the velocity streamline at plane 1 with obstacle located at the doorway. The streamline are found bend over the mannequin in all the directions. The concentration of streamline is observed on the sideways and rarefaction over front and backside of the mannequin. This explains the high velocity zone on the side of mannequin and low velocity region on front and backside of mannequin. The streamlines get crossed in the region below hands and the legs of the mannequin representing the mixing of surrounding particles and absence of effective air curtain barrier. At the bottom because the flow hits ground and absence of positive air curtain flow, the particle movement is complex. The particles, especially at the front and back of the mannequin are moving in all directions forming spiral movement perpendicular to mannequin instead of flowing downwards straight to ground. The particles on the side of the mannequin escape to sideways forming rouged barrier for both the environments. The boundary layer on the sideways is totally lost because of high velocity and concentration of air particles, and a narrow path between mannequin and side of the doorway. Figure 11 and Figure 12 show the streamlines at plane 2 and plane 3 respectively. At both the planes the streamlines move sideways and again turn back towards the mannequin. The deviation of air particles are found more at plane 2 as compared to plane 3 because of higher velocities and hence higher momentum of air particles at plane 3. No intermixing of air particles is observed up to half way i.e. up to waist height of the mannequin. Thereafter because of no positive flow between legs of the mannequin, the particles tend to cross the mannequin causing weakening of the air curtain barrier. Figure 11 show the Velocity streamline at plane 2 with obstacle. Figure 12 shows the three dimensional view of streamlines at plane 3. The sides of the doorway and the surrounding are hidden from the view. From these figures the location the streamlines can be understood within the flow domain.
  6. 6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 – 6340(Print), ISSN 0976 – 6359(Online) Volume 4, Issue 5, September - October (2013) © IAEME 155 CONCLUSION Numerical analysis of velocity streamlines of flow of air curtain provides valuable data for analysing the performance of air curtain. Functioning of air curtain was found smooth and reliable when the obstacle is not introduced as per the basic need of air curtain. Such performance will definitely ensure the effective separation of two environments. But when obstacle in the form of mannequin is introduced, the streamlines are observed to cross on the other side of the barrier. The crossover of the particle is also observed at the bottom side of door. Thus air curtain performance deteriorates when a person passes through it. From above discussion, it is clear that the air curtain purpose to separate the two environments will not be successful until this crossover of the particles is prevented. If air curtain is installed at the entrance of the shopping mall and daily thousands of customer are passing through the curtain then every time the air curtain barrier is breached causing crossover of air particles. The present paper is highlighting this issue which must be solved. A little improvement in the effectiveness of the air curtain will save the loss of valuable conditioned air. And thus the operating expenses on air conditioning system will be saved. Considering the numbers of installations of air curtain in the entire world, millions of dollars would be saved in energy bills globally. REFERENCES [1] Zhikun Cao Hua Han, Bo Gu,’ A novel optimization strategy for the design of air curtains for open vertical refrigerated display cases’, Applied Thermal Science Engineering, Volume 31, Issue 16, November 2011, pp. 3098-3105. [2] Tassou, S. A. and Pappas, T. C., ‘Numerical Investigations into the Performance of Doorway Vertical Air Curtains in Air-Conditioned Spaces’, ASHRAE Transactions, Vol. 109, No. 1, 2003, pp. 273–279. [3] Homayun K Navaz, Dabiri, D. & R. Faramarzi, M Gharib, D Modarress,’The application of Advanced methods in analysing the performance of the air curtain in a refrigerated display case’, Journal of Fluid Engineering, Vol. 124, September 2002, pp. 756- 764. [4] Julian E Jaramillo, Carles D Perez-Segarra, Orial Lehmkuhl, Assensi Oliva, ‘Detail Numerical study of Turbulent flows in air curtain’ ,Vth European Conference on Computational Fluid Dynamics, ECCOMAS CFD 2010, Lisbon Portugal. June 10. [5] Brandon S Field and Erich Loth, ‘An air curtain along a wall with high inlet turbulence’ Journal of Fluid Engineering, May 2004, pp 126/391. [6] Frank K. Lu, Vijay A. Chauhan, Adam J Pierce, Takayuki Yajin and J Craig Dutton, ‘Numerical model of doorway flow induced by an air curtain’, American Institute of Aeronautics and Astronautics, Vol 35, No. 9, 2009. [7] 'Durbin, P.A. and Pittersson Reif, B.A, 'Stastistical Theory and modelling for Turbulent flows', Wiley, New York 2001. [8] Samir R Traboulsi, Ali Hammoud, M Farid Khalil, ‘Air cirtain Integrity when Misusing the Refrigerated Display Cabinets’, ISSN 1790-5087, Issue 2, Volume 4 April 2009. [9] Mr Nitin Kardekar and Dr Sane N K, ‘Effect of humanoid shaped obstacle on the velocity profiles of flow of air curtain’ International Journal of Mechanical Engineering and Technology, Vol 3, Issue 3, Sept.- Dec. (2012), pp.511-516,(ISSN 0976 – 6340). [10] Nitin Kardekar and Dr Sane N K, “Effect of Humanoid Shaped Obstacle on the Velocity Profiles of Flow of Air Curtain”, International Journal of Mechanical Engineering & Technology (IJMET), Volume 3, Issue 3, 2012, pp. 511 - 516, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359. [11] Nitin Kardekar, Dr. V K Bhojwani and Dr Sane N K, “Experimental Performance Analysis of Flow of Air Curtain”, International Journal of Mechanical Engineering & Technology (IJMET), Volume 4, Issue 3, 2013, pp. 79 - 84, ISSN Print: 0976 – 6340, ISSN Online: 0976 – 6359. [12] Nitin Kardekar, Dr. V K Bhojwani and Dr. Sane N K, “Numerical Analysis of Velocity Vectors Plots and Turbulent Kinetic Energy Plots of Flow of the Air Curtain”, International Journal of Advanced Research in Engineering & Technology (IJARET), Volume 4, Issue 4, 2013, pp. 67 - 73, ISSN Print: 0976-6480, ISSN Online: 0976-6499.

×