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CHEMICAL ENGINEERING TRANSACTIONS

VOL. 46, 2015

A publication of

The Italian Association

of Chemical Engineering
Online at www.aidic.it/cet

Guest Editors: Peiyu Ren, Yancang Li, Huiping Song
Copyright © 2015, AIDIC Servizi S.r.l.,
ISBN 978-88-95608-37-2; ISSN 2283-9216

Numerical Simulation and Experimental Research on Flow
Field of Swirling Cold Air Diffuser

Dongyi Zhou*, Chuping Shi

Department of Mechanical and Energy Engineering, Shaoyang College, Shaoyang, 422000, China
zhoudongyi2005@163.com

Experimental and numerical research was carried out on swirling cold air diffuser. In experimental research,
following the cold air distribution requirements, cold air distribution experiment table was constructed for
testing specimen of swirling cold air diffuser. In numerical research, Fluent software was applied to analog
calculate air distribution of air conditioning room flow field for this air diffuser. The obtained result was
compared with the experimental result, both were in good agreement. It indicated that temperature field and
velocity field is uniform in swirling cold air diffuser room, which supplied theoretical and experimental basis for
actual application of this air diffuser.

1. Introduction
The supply air temperature can reach 4-6ºC in the ice of the cold air system and the small air easily result in
the unevenness of indoor air temperature and caused uncomfortable feeling of cold air blowing (Gusel, L &
Rudolf, R, 2015; Lee, W. S, et al, 2009). At the same time the low surface temperature of air device perhaps is
to condense (Li, P. et al, 2009; Memon, R. A, Chirarattananon, S & Vangtook, P, 2008). Many researchers
have carried out extensive research on the outlet for cold air distribution (Yu, H, et al, 2009 ;). J.S. Elleson
offered a high-current and high-temperature air diffuser, and this kind of low-temperature air diffuser allows jet
of cold air to mix with indoor air in a very short distances and is appropriate to hang in a higher place, but its
diffuser is easy to condense dew. The surface of the diffuser need use special materials to process (Chuah, Y.
K, 2004). In 1993, D. E. Knebel, and d. A. John offered a cold-air nozzle outlet, and proved with lots of
experiments that in most of the load range the outlet can maintain good indoor air circulation, but the air
resistance is larger (Z. Yanlin, et al 1997). Southwest Jiaotong University, Deyuan Cai with others developed a
new kind of cold air diffusers-Windmill-fan inducible diffusers, that is exactly the windmill-fan-induced diffuser
air supply, but the structure was a little complicate with vulnerable and moving parts (Windmill-fan unit) (Liu, J
& Yu, B, 2010; Hong, B. Z, et al, 2004).
Among the available outlet products for cold air distribution currently, there are few products which have the
advantages of simple construction, low cost, good induction ratio, low resistance, non-condensate, small
noise, high performance cost ratio and meanwhile a uniform temperature filed can be provided when it is used
(Zhili, B. Z, 2005). For that we develop a new-style swirling cold air diffuser after an in-depth study. In order to
test the function of this swirling cold air diffuser, we applied computational fluid mechanics software Fluent to
analog calculated the air distribution of air conditioning room flow field, then we did comparison between the
achieved result and the experimental result (Zhou, D, et al, 2010).

2. Swirling cold air diffuser
Profile picture of swirling cold air diffuser see Figure 1, and construction see Figure 2. This diffuser is a circular
vortex chamber structure with the primary air nozzle on tangents and the mixed diffuser on radial direction. In
the center under vortex chamber, there is a secondary return air inlet (L. Zhongqi, 1980). Deflector is provided
on the diffuser. Specimen is made of organic glass, nominal blowing rate is 100 m3/h.

DOI: 10.3303/CET1546164

Please cite this article as: Zhou D., Shi C.P., 2015, Numerical simulation and experimental research on flow field of swirling cold air diffuser,
Chemical Engineering Transactions, 46, 979-984 DOI:10.3303/CET1546164

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3. Numerical simulation of flow field
3.1 Physical model
Assumed flow rate of testing diffuser is 100 m3/h (means primary and secondary air flow rates are theoretical
flow rate of 50 m3/h respectively), induction ratio is designed to 1, inner and outer diameters of annular mixed
air outlet are 200 mm and 300 mm, secondary diffuser diameter is 200 mm. Experiment measures that
temperature is 16.5ºC at mixed air outlet, and 22ºC at return air temperature. The size of air conditioning room
(length*width*height) is 3200 mm*3000 mm*3200 mm, diffuser is installed at the room center and 2.8 m higher
than ground. Diffuser bottom flushes with roof dale. South side in air conditioning room has a window with size
of 2350*1750; other three sides are inner walls. Adjacent room has no air conditioning system. In the room,
thermal load is simulated by electrical heating film which is laid on the ground and can generate heat of 19
W/m2 (Awni. Al., et al, 2015). The Layout of the testing room for diffuser is shown in Figure 3.

Figure 1: Photo of the swirling cold air diffuser

Figure 3: Layout of the testing room for diffuser

Primary air

Secondary back air.
Mixed air

1. Circular room 2.Deflector 3. Center back vent 4.
Tangential nozzle 5.The above air Board 6.The
below air Board 7. Radial inlet
Figure 2: Schematic diagram of the swirling cold
air diffuser

The cold source of experimental device applies the way of making cold by chiller and adding broken ice to
maintain the temperature of storage tank is 1-3ºC, and to adjust spraying volume and cooler’s supply of water
to control the temperature of the supply air.

3.2 Mathematical simulation
turbulence model, which is the most widely used, most tested and most mature numerical simulation

technology, is applied. In order to simplify the problems, the following condition is assumed (Koskela. H, 2004;
Y. Hong, et al, 2015; Xu. j., et al 2015):
(1) All east, west and north walls are all inner walls, assumed their temperatures are constant that is the same
temperature with indoor design temperature 22ºC; south wall is a heating surface, assumed wall temperature
is fixed and 3ºC higher than other walls.
(2) Indoor is stimulated thermal load by electrical heater which is laid on the ground, but ground is adiabatic.
(3) Internal air cannot be compressed.
(4) Air jets parameters of outlet are even, internal air properties are fixed value.
(5) Without considering effect of air leaking, door and windows are closed; tightness inside of air conditioning
room is excellent (Yang, I. H, et al, 2004; T. Wenquan, 2001).
Turbulence model (ASHRAE, 2009):

(1)

Where:

k ε−

( )
k

U S
t xϕ

ρ φ φ
ρ φ φ

 ∂ ∂
+ ∇ = ∇ Γ + ∂ ∂ 

[ ]1 2 31 u u u kϕ ε=

980

Formation item of turbulence kinetic energy:

(2)

(3)

Other parameters selections are shown in reference [6].

3.3 Results and analysis
Room gridding structure sees Figure 4. Temperature field distribution is indicated as Figure 5 to Figure 10.
Figure 5 is the temperature distribution when height Z=2000 mm, Figure 6 is the temperature distribution when
height Z=1800 mm, Figure 7 is the temperature distribution when height Z=1500 mm, Figure 8 is the
temperature distribution on the section when X=1500 mm, Figure 9 is the temperature distribution on the
section when X=160 mm. Figure 10 is the velocity distribution on the section when X=1500 mm, and Figure 11
is the velocity distribution on the section when X=1600 mm.

Figure 4: Room gridding structure

Figure 5: The temperature distribution on the
section when height Z=2000 mm

Figure 6: The temperature distribution on the
section when height Z=1800 mm

Figure 7: The temperature distribution on the
section when height Z=1500 mm

Figure 8: The temperature distribution on the
section when height X=1600 mm

Figure 9: The temperature distribution on the
section when height Y=1500 mm

0 e ee e e
k

ϕ
ε

μ μ
μ μ μ

δ δ
 

Γ =  
 

( )1 , 1, 2, 3ji i
j i j

uu u
G i j

u u u
μ
 ∂∂ ∂

= + =  ∂ ∂ ∂ 

C kμ ρμ
ε

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Figure 10: Velocity distribution on the section
when X=1600 mm

Figure 11: Velocity distribution on the section
when X=1500 mm

4. Experimental research on flow field
4.1 Experimental procedure
Air supply system consists of cold air diffuser, cold air blast pipe, air fan, air regulating and stabilizing device,
cold water spray chamber, surface heat exchanger, ice storage tank and ice maker. Air supply temperature is
8ºC, relative humidity is 95%. Primary air is formed after supply air passing through blast pipe and
overheating, its temperature is 9ºC, and relative humidity is 92% [5].
Generally, the height that is lower than 2 m above ground is the major work area for staff. Therefore, 2 m
height is as a limitation, six different heights with 0.3 m distance are adopted along room vertical direction,
means Z=0.5 m, Z=0.8 m, Z=1.1 m, Z=1.4 m, Z=1.7 m, Z=2.0 m. In horizontal direction, diffuser is considered
as a center point, 10 sets of positions with 0.2m distance are adapted from center to both sides, and totally 60
measuring points. Each measuring point has the copper-constantan thermoelectric couple probe and hot-wire
anemometer to measure temperature and air velocity. See Figure 12.
Room thermal load includes heat output of person, equipment and lights, and heat transmitted from outside to
inside. In experiment, due to outside temperature was low (19ºC), we applied 1.5kw electrical heater (power
self-regulating) to simulate thermal load to keep room heat gain. When indoor temperature is constant, room
can be considered to achieve dynamic thermal equilibrium. Meanwhile, temperature and air velocity can be
measured respectively.

7 5 0 2 5 5 09 5 0 1 3 5 0 1 7 5 0 2 1 5 0

5 0 0

8 0 0

1 1 0 0

1 4 0 0

1 7 0 0

2 0 0 0

D if fu s e rCeiling

Figure 12: The layout of the measuring points of temperature field and speed field

4.2 Measurements
Experimental data in each point are shown in the Figure 13 and Figure 14.

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Figure 13: Temperature of measurement points in the different distance from floor in Figure 12

Figure 14: Temperature of measurement points in the different distance from floor in Figure 12

4.3 Comparison between analog results and experimental results
According to analog results, we can achieve:
(1) Temperature range: 19.2ºC-20.4ºC, maximum temperature difference on measuring point in horizontal
direction is 1.2ºC, and in vertical direction is 0.5ºC, average temperature t=19.91ºC.
(2) Air velocity range: 0.04 m/s-0.20 m/s, below 2 m in people work area, average air velocity v=0.95m/s
According to experimental results, we can find out:
(1) Temperature range: 19.4ºC-20.2ºC, maximum temperature difference on measuring point in horizontal
direction is 0.7ºC, and in vertical direction is 0.4ºC, average temperature t=19.95ºC.
(2) Air velocity range: 0.05 m/s-0.19 m/s, below 2 m in people work area, average air velocity v=0.99 m/s
As shown above, we can see analog results and experimental results are in good agreement.

5. Conclusions
(1) By means of numerical simulating and experimental measuring, temperature field and velocity field are
uniform in the room of swirling cold air diffuser.
(2) Swirling cold air diffuser can evenly mix primary and secondary air in diffuser, but uniformity of air supply in
circumferential direction shall be improved.
(3) Research work in this paper has many shortages, for example, due to condition limitation in experiment,
we cannot obtain enough effective information; more accurate and effective methods have not applied in
calculation, and etc., which shall be improved in the further research.

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Acknowledgments

This project was supported by Hunan education department Foundation under Project 14K087, China, and by
the science and technology office of Hunan Foundation under Project 2014ZK3094, China.

References

ASHRAE, 2009, ASHRAE Handbook-Fundamentals. Atlanta, ON: ASHRAE Inc.
Awni Al., & Hamzeh D., 2015, Analysis of mechanical system ventilation performance in an atrium by

consolidated model of fire and smoke transport simulation. International Journal of Heat and Technology.
30(3), 121-126, DOI: 10.18280/ijht.330318.

Chuah Y.K., Hu, S.C., & Shieh M.F., 2004, A study on the control of surface condensation on a multi-cone
diffuser in cold air distribution applications. Indoor and Built Environment, 13(3), 223-231. doi:
10.1177/1420326X04040648.

Gusel L., & Rudolf R., 2015, Shear stress distribution analysis in cold formed material. Procedia Engineering,
100, 41–45. doi: 10.1016/j.proeng.2015.01.340.

Koskela H., 2004, Momentum source model for CFD-simulation of nozzle duct air diffuser. Energy and
Buildings, 36(10), 1011-1020. doi: 10.1016/j.enbuild.2004.06.013.

Lee W.S., Chen Y.T., Wu T.H., 2009, Optimization for ice-storage air-conditioning system using particle
swarm algorithm. Applied Energy, 86(9), 1589-1595. doi: 10.1016/j.apenergy.2008.12.025.

Li P., Li Y., Seem J.E., 2009 January, Modelica Based Dynamic Modeling of an Air-Side Economizer. In
ASME 2009 International Mechanical Engineering Congress and Exposition (pp. 811-820). American
Society of Mechanical Engineers. doi: 10.1115/IMECE2009-13173.

Liu J., & Yu B., 2010 May, Research on thermal environment in room using separated air-conditioning unit by
supplying low-temperature air. In Networking and Digital Society (ICNDS), 2010 2nd International
Conference on (Vol. 2, pp. 180-185). IEEE. DOI: 10.1109/ICNDS.2010.5479336

Li Z.Q., 1980, Fluid Mechanics, Beijing, ON: China Machine Press.
Memon R.A., Chirarattananon S., Vangtook P. (2008). Thermal comfort assessment and application of radiant

cooling: a case study. Building and environment, 43(7), 1185-1196. doi: 10.1016/j.buildenv.2006.04.025.
Tao W.Q., 2001, Numerical Heat Transfer. Xian, ON: Xian jiaotong university press.
Xu J., Zhou S., Li K., 2015, Analysis of flow field and pressure loss for fork truck muffler based on the finite

volume method. International Journal of Heat and Technology. 30(3), 85-90, DOI: 10.18280/ijht.330312.
Yang I.H., Shin C.B., Kim T.H., Kim S., 2004, A three-dimensional simulation of a hydrocyclone for the sludge

separation in water purifying plants and comparison with experimental data. Minerals Engineering, 17(5),
637-641. doi: 10.1016/j.mineng.2003.12.010.

Yin H., Song D., Li X.Y., Huan P., 2015, Airflow simulation of linear grating lithography workshop. International
Journal of Heat and Technology. 30(2), 109-114, DOI: 10.18280/ijht.330218.

Yu H., Liao C.M., Liang H.M., Chiang K.C., 2007, Scale model study of airflow performance in a ceiling slot-
ventilated enclosure: Non-isothermal condition. Building and environment, 42(3), 1142-1150. doi:
10.1016/j.buildenv.2005.12.004.

Zeng Y.L., Cai D.Y., 1997, A Study on the Cold Air Distribution of the Ice Storage. Journal of Civil,
Architectural & Environmental Engineering. 19(5), 73-77, DOI：10.11835/j.issn.1674-4764.1997.05.015

Zhang H., Li M.F., Qin J., Bai, W., 2004, Application of air diffusers with high induction ratio and low
temperature to a project. Hv & Ac. 34(8), 99-101. doi: 10.3969/j.issn.1002-8501.2004.08.022

Zhang Z.L., Zhang X., Zhang E.Z., 2005, Experiment of condensation on diffusers under low temperature air
supply conditions. Hv & Ac. 35(5), 120-122. doi: 10.3969/j.issn.1002-8501.2005.05.026

Zhou D., Shi C., Yuan, W., 2010 October, Design and Experimental Research on a Novel Cold Air Diffuser. In
Intelligent System Design and Engineering Application (ISDEA), 2010 International Conference on (Vol. 1,
pp. 494-497). IEEE. Doi: 10.1109/ISDEA.2010.14

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