30120130405017

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

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


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


In order to analyse the flow of air curtain, it was decided to analyse the velocity streamline


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)


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


nalyse the velocity streamlines.


The air flow analysis was carried out using commercial software package

Geometry Model with obstacle

with mannequin

(Photograph)


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 290C. 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


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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



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


xtended domain and flow straightener. The frame portion is meshed with unstructured tetra


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


mesh. The mesh which is created in the Workbench is internally transferred to CFX



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



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


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



xperiment is carried out at isothermal conditions; air at 290C ( + 1

0C)

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


xtended domain and flow straightener. The frame portion is meshed with unstructured tetra


The total mesh count is

which 59589 are tetrahedral cells and 325854 hexahedral cells. The minimum mesh


he Workbench is internally transferred to CFX-Pre, a CFD



turbulence model. The default

C. The inlet boundary condition used is ‘normal speed’ at 9 m/s, since the actual

uniform turbulence



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



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)



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.



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

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[3] Homayun K Navaz, Dabiri, D. & R. Faramarzi, M Gharib, D Modarress,’The application of Advanced

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[7] 'Durbin, P.A. and Pittersson Reif, B.A, 'Stastistical Theory and modelling for Turbulent flows', Wiley,

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[9] Mr Nitin Kardekar and Dr Sane N K, ‘Effect of humanoid shaped obstacle on the velocity profiles of

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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

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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

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[12] Nitin Kardekar, Dr. V K Bhojwani and Dr. Sane N K, “Numerical Analysis of Velocity Vectors Plots

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ISSN Print: 0976-6480, ISSN Online: 0976-6499.

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study of air curtain

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