iisrt vincent raj (mech)
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International Journal of Mechanical Civil Automobile and Structural Engineering IJMCAS, Volume 1 Issue 1TRANSCRIPT
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International Journal of Mechanical, Civil, Automobile and Structural Engineering (IJMCAS)
Vol. 1, Issue. 1, April 2015 ISSN (Online): 2395-6755
27
Abstract: In this world of ever increasing demand for the
new technology, refrigeration and air-conditioning are
becoming the vital area of research and development. The
project is concerned with the use of computational fluid
dynamics as a tool to simulate, study and compare the
pressure drop and flow of the refrigerant R407c,r407b with
that of the R12 in a S shaped coil. Here we have concluded
that the alternative refrigerants possess better characteristics
in the pressure drop and flow pattern than that of the R12
refrigerant.
Key words: refrigerants, pressure drop, flow pattern, CFD
I.INTRODUCTION
A refrigeration process indicate the change of
thermodynamic properties of the refrigerant and the
energy transfer between the refrigerant and the
surroundings.
[8]Chlorofluorocarbons and Hydro
Chlorofluorocarbons have been widely used in
refrigeration and air conditioning systems. The
Montreal protocol and Kyoto summit has agreed that
these refrigerants should be phased out and new
ozone-friendly refrigerants should be replaced. HFC
refrigerants like R134a and zeotropic refrigerants like
R407c are introduced to replace R12 and R22
respectively.
[10]In order to achieve optimum performance
an accurate design technique is necessary for the
prediction of pressure drop and flow pattern through
S shaped coil used in refrigeration and air-
conditioning systems. Computational fluid dynamics
can be used as a tool to estimate or enhance our
understanding of pressure losses in coil prior to
construction. The CFD would allow different type of
working fluid and coil of various geometrics to be
explained.
[5] CFD packages used for the simulation
were the gambit 2.2.30 and fluent 6.2.16. Gambit has a
single interface for geometry creation and meshing that
brings together all of fluent preprocessing technologies
in one environment. [3]Fluent is another software used
for simulation visualization and analysis of fluid flow
heat and mass transfer and chemical reactions.
II.CARNOT REFRIGERATION CYCLE
[4]Carnot refrigeration cycle is a completely
reversible cycle, hence is used as a model of perfection
for a refrigeration cycle operating between a constant
temperature heat source and sink. It is used as a
reference against which the real cycles are compared.
The basic Carnot refrigeration system for a
pure vapour consists of four components: compressor,
condenser, turbine and evaporator.
III.PRESSURE LOSS IN COILS
[9]Pressure drop is a term used to describe the decrease in pressure from one point in a tube to another
point downstream. Pressure drop is of frictional
forces on the fluid as it flows through the tube. The
frictional forces are the reason to cause resistance to
flow. The main factors impacting the resistance to the
fluid flow are fluid velocity and fluid viscosity.
Geometric pressure drop deals with the parameters
such as length, diameter of the pipe.
[10]A theoretical analysis of S-shaped coil was
carried out for the single phase flow and the pressure
drop was calculated by summing the frictional pressure
loss and geometric pressure loss due to change in
momentum within the liquid/Vapour mixture. For
calculations pressure loss can be estimated as:
(
)
Where,
Simulation of Pressure Drop of Alternative Refrigerants inside
evaporator Coil using CFD T.Balasubramanian
1, M.Vincent Raj
2, V.Nikshith
3 R.Vijay
4
2,3,4UG Student, Department of Mechanical Engineering, St.Josephs College of Engineering, Chennai, INDIA
1Department of Mechanical Engineering, St.Josephs College of Engineering, Chennai, INDIA
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International Journal of Mechanical, Civil, Automobile and Structural Engineering (IJMCAS)
Vol. 1, Issue. 1, April 2015 ISSN (Online): 2395-6755
28
f - Friction coefficient D - Pipe diameter
k - Roughness factor
Re - Reynolds number
Co - Loss coefficient for the bends (1.47)
- Density of refrigerant (kg/m3) Ls - Length of the coil
IV.SIMULATION AND WORK
The various property of the refrigerants were given below in the table 1.
Table. 1, Property of the refregerants
REFRIGERANTS/
PROPERTIES(LIQUID) R12 R407c R407b
DENSITY( kg/m3) 1.437 1.237 1.287
VISCOSITY(m2/s) 3.13E-07 2.08E-
07 2.08E-07
SPECIFIC HEAT(j/kg-
k) 938.8 1408 1322
THERMAL
CONDUCTIVITY
(W/m-k)
0.07591 0.1009 0.08361
HGWP 3.1 0.66 0.47
ODP 1.0 0 0
The study of pressure drop in the S shaped coil
include the following procedure to compute and
simulate
Gambit 2.2.30 is used as a preprocessor tool
to design the 2D S shaped coil.
The 2D model was then meshed optimally
taking the bend and wall into consideration.
The meshed 2D is then defined for its
boundary condition.
At last the 2D meshed model is exported to
fluent as file.msh
The 2D meshed model is checked for the
mesh
The model is standardized for its units.
The various parameters which has been
defined in the fluent is given as
Solver: Segregated
Viscosity: Epsilon model
Energy equation: On
The model is initialized and the residual is
monitored to check for the convergence.
Thus the model is solved.
V.SIMULATION RESULTS
Fig. 1.1, Pressure contour of the R12 refrigerant
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International Journal of Mechanical, Civil, Automobile and Structural Engineering (IJMCAS)
Vol. 1, Issue. 1, April 2015 ISSN (Online): 2395-6755
29
Fig. 1.2, Velocity contour of the R12 refrigerant
Fig. 1.3, R12 liquid
Fig. 2.1, Pressure contour of the R407b refrigerant
Fig. 2.2, Velocity contour of the R407b refrigerant
Fig. 2.3, R407b liquid
Fig. 3.1, Pressure contour of the r407c refrigerant
Fig. 3.2, Velocity contour of the R407c refrigerant
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International Journal of Mechanical, Civil, Automobile and Structural Engineering (IJMCAS)
Vol. 1, Issue. 1, April 2015 ISSN (Online): 2395-6755
30
Fig. 3.3, R407c liquid
VI.MODEL CALCULATION
Pressure drop of refrigerant through an S-
shaped coil for R12 liquid,
1.
Where,
Co - Loss coefficient for the bends (1.47)
- Density of refrigerant (kg/m3) U - Mean velocity (10 m/s)
Pgs =1047*0.5*1.237*102
Pgs =90.9195 KPa
2.
Where,
f - Friction coefficient
D - Pipe diameter (0.02 m) k - Roughness factor (10.2*E-4)
Re - Reynolds number
f =0.25/ (log (2.5*106/3.7*0.015) +
(5.74/890782.520.9))2
f=1.45*10-2
3. (
)
Where,
P=Pressure through the coil Lc=Length of the coil
P= (0.07227*1.4*1237.102/2*0.02)+90.9195 P=247 Pa And the total pressure drop of each
refrigerants were tabulated in the table 2.
Table. 3, Total pressure drop
REFRI
GERA
NTS
DE
NSI
TY
(kg/
m)
VEL
OCI
TY
(m2/
s)
GEO
MET
RIC
PRE
SSU
RE
DRO
P
(KPa
)
REY
NOL
DS
NU
MB
ER
(Re)
FRIC
TION
COEF
FICIE
NT
(f)
TOT
AL
PRE
SSU
RE
DR
OP
(KP
a)
R12 liquid
1.437
3.13E-07
105.6195
6.09E05
1.48 E02
247
R407c
liquid
1.2
87
2.08
E-07
90.91
95
8.9
E05
1.45
E02
211
R407b
liquid
1.2
87
2.08
E-07
94.59
45
9.2
E05
1.45
E02
219
VII.RESULT AND CONCLUSION
The comparison of the pressure loss and velocity of the various eco-friendly refrigerants that
were taken for the study is shown as a simulation in the
(fig1.1, fig1.2, fig1.3, fig2.1, fig2.2 fig2.3, fig3.1,
fig3.2, and fig3.3). And (table 3) shows that the
relationship between theoretical pressure drop and
predicted pressure-drop using CFD when considering
the liquid flow.
Table. 3, Pressure loss
REFRIGERANT P PRESSURE LOSS
(Pa)
R12 R407b R407c
CFD LIQUID 243 221 204
THEORY
LIQUID
247 219 211
From table 3 it has shown that the
performance of the new eco-friendly
refrigerants R407b, R407c to be better than of
R12 refrigerant.
VIII.REFERENCES
1. Hand book of air-conditioning and refrigeration-----Shan K Wang
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International Journal of Mechanical, Civil, Automobile and Structural Engineering (IJMCAS)
Vol. 1, Issue. 1, April 2015 ISSN (Online): 2395-6755
31
2. Refrigeration and air conditioning-Ahmadul Ameen
3. Fluent work guidefluent inc
4. Refrigeration and tables and chartsC.P. Kothandaraman
5. WWW.CFD-online.com.
6. www.wikipedia.org
7. www.howstuffworks.com
8. www.refexrefrigerant.com
9. Journal: Pressure drop of HFC
refrigerants inside evaporator and
condenser coils as determined by CFD
by S.J. Smith*, L. Shao, S.B.Ri at
Institute of Building Technology
10. Analytical study of evaporator coil in humid environment S.Y. Liang,
M. Liu, T.N. Wong *,
G.K. Nath