IISRT Vincent Raj (Mech)

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



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



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



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



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

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IISRT Vincent Raj (Mech)

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