experimental investigation of tube in tube helical coil ...tube helical coil heat exchanger 6.1...

4437

www.ijifr.com Copyright © IJIFR 2015

Research Paper

International Journal of Informative & Futuristic Research ISSN (Online): 2347-1697

Volume 2 Issue 12 August 2015

Abstract

This Present work represents an Experimental studies for a counter flow tube in tube helical coil heat exchanger where hot water flows through the inner tube and cold water flows through the outer tube. An experimental setup will be used for the estimation of the heat transfer characteristics. A wire will wound over the inner tube to increase the turbulence in turn increases the heat transfer rate. The analysis deals with the pitch variation of the internal wound wire and its result on the heat transfer rate. From Experimental results, heat transfer rate, LMTD, overall heat transfer coefficient, efficiency and Reynolds number, Nusselt number, Friction factor will be calculate.

1. Introduction

To transfer the heat between two fluids Heat exchanger is used which may be in direct contact or

may flow separately in two tubes or channels. We find numerous applications of heat exchangers in

day today life. For example condensers and evaporators used in refrigerators and air conditioners.

In thermal power plant heat exchangers are used in boilers, condensers, air coolers and chilling

towers etc. Similarly the heat exchangers used in automobile industries are in the form of radiators

and oil coolers in engines. Heat exchangers are also used in large scale in chemical and process

industries for transferring the heat between two fluids which are at a single or two states.

Ganesh B. Mhaske 1

M.Tech. Student Department Of Mechanical Engineering Matoshri College of Engineering and Research Center Nashik, India

D. D. Palande 2

Associate Professor Department Of Mechanical Engineering Matoshri College of Engineering and Research Center Nashik, India

Experimental Investigation Of Tube

In Tube Helical Coil Heat Exchanger

Paper ID IJIFR/ V2/ E12/ 018 Page No. 4437-4448 Subject Area Mechanical

Engineering

Key Words Tube-In-Tube Helical Coil, Nusselt Number, Wire Wound, Reynolds Number,

Dean Number, Dead Zone, Efficiency

Received On 05-08-2015 Accepted On 17-08-2015 Published On 18-08-2015

4438

ISSN (Online): 2347-1697 International Journal of Informative & Futuristic Research (IJIFR)

Volume - 2, Issue - 12, August 2015 24th Edition, Page No: 4437-4448

Ganesh B. Mhaske , D. D. Palande :: Experimental Investigation Of Tube In Tube Helical Coil Heat Exchanger

2. Helical Coil Heat Exchanger- A Review

Recent developments in design of heat exchangers to full fill the demand of industries has led to the

evolution of helical coil heat exchanger as helical coil has many advantages over a straight tube.

Advantages

a. Heat transfer rate in helical coil are higher as compared to a straight tube heat exchanger.

b. Compact structure. It required small amount of floor area compared to other heat

exchangers.

c. Larger heat transfer surface area.

Applications a. Heat exchangers with helical coils are widely used in industries. The most common

industries where heat exchangers are used a lot are power generation plants, nuclear plants,

process plants, refrigeration, heat recovery systems, food processing industries, etc.

b. Helical coil heat exchanger is used for residual heat removal system in islanded or barge

mounted nuclear reactor system, where nuclear energy is used for desalination of sea water.

c. In cryogenic applications including LNG plant.

Table.1 Summary of Tube-In-Tube Helical Coil Heat Exchanger

S. N

o.

Author

&

Year

Title

Mate

rial

Of

Coil

Inner

Tube

Diameter

(mm)

Outer Tube

Diameter (mm)

Rad

ius

of

Cu

rvatu

re

(mm

)

Cu

rvatu

re R

ati

o

Pit

ch o

f th

e co

il

(mm

)

No. of

Tu

rns

Un

fold

Len

gth

(

m)

do

di

Th

ick

nes

s D0

DI

Th

ick

nes

s

1.

Rennie T.J,

Raghavan G.S.V (2002)

Laminar

parallel flow in a

tube-in-tube

helical heat

exchanger

Sta

inle

ss

Ste

el

80

68

12

115

100

15

800

0.0

625

115

- -

2.

Rennie T.J,


Experimental

studies of a

double pipe

helical heat

exchanger

Co

pper

9.5

8.7

0.8

15.9

15.1

0.8

235.9

0.0

33

- - -

3.

Rennie T.J,


Effect of fluid

thermal properties

on the heat

transfer

characteristics in a

doublepipe helical heat exchanger;

Sta

inle

ss S

teel

80

68

12

11

100

15

800

0.0

62

5

115

- -

4439




4.

Kumar V,

Saini S, Sharma

M, Nigam K. D. P.(2006)

Pressuredrop

and heat transfer

study in tube-in-

tube helical heat

exchanger

Ss3

16

25.4

24.2

1.2

50.8

49.6

1.2

762

0.0

33

100

4

10

5.

Kumar V,

Faizee B,

Mridha M,

Nigam K. D. P.(2008)

Numericalstud

ies of a tube-in-

tube helically

coiled heat exchanger

S

s31

6

25

.4

24

.2

1.2

50

.8

49

.6

1.2

76

2

0.0

33

10

0

4

10

6

Gabriela

Huminic, Angel

Huminic.(2011)

Heat

transfercharacteri

stics in double

tube helical heat

exchangers

usingnanofluids Sta

inle

ss S

teel

46

40

6

11

5

10

0

15

80

0

0.0

62

5

11

5

- -

7

Jayakumar J. S,

Mahajani S. M,

Mandal J. C,

Vijayan P.K,

Bhoi R.(2008)

Experimental and

CFD estimation

of heattransfer in

helically coiled

heat exchangers

Ss3

16

10

- - -

12.7

-

150

0.0

423

30

- -

Concluding Remarks from Literature Review

From the literature I find that so much work had been done to find heat transfer characteristic of

helical coil heat exchanger with constant wall temperature and constant heat flux conditions. Also

by changing the working fluid heat transfer relation were found. But effect of pitch variation of the

internal wounded wire and its result on the heat transfer rate is not explained properly. In the

present work the performance of a Tube-in-tube helical coil heat exchanger for a water–water

counter current flow system will be going to study experimentally. The effect of the fluid flow rate

on the heat transfer and hydrodynamics is going to study in the tube as well as in the annulus. In the

present work four turns of coils is consider and also copper wire is to be introduce in the annulus

area of the Tube-in-tube helical coil heat exchanger.

3. Problem Statement Conventional heat exchangers are large in size and heat transfer rate is also less and in conventional

heat exchanger dead zone is produce which reduces the heat transfer rate and to create turbulence in

conventional heat exchanger some external means is required and the fluid in conventional heat

exchanger is not in continuous motion with each other. Tube in tube helical coil heat exchanger

provides a compact shape with its geometry offering more fluid contact and eliminating the dead

zone, increasing the turbulence and hence the heat transfer rate. Helical coiled heat exchangers are

used in order to obtain a large heat transfer per unit volume and to enhance the heat transfer rate on

the inside surface. In present study, Experimental investigation will be carry out for a counter flow

tube in tube helical coil heat exchanger where hot water flows through the inner tube and cold water

flows through the outer tube. Therefore, we switch towards tube in tube helical coil heat exchanger

for better performance than conventional heat exchangers.

4440




4. Objectives The objective of this work is to Experimental analysis of tube in tube helical coil heat exchanger

and find out heat transfer rates, LMTD, overall heat transfer coefficient and Reynolds number,

Nusselt number, friction factor for counter flow arrangement.

5. Scope There are many limitations of conventional heat exchanger like large in size, heat transfer surface is

also less, the fluid which is not in continuous motion with each other, they produce dead zone and

due to that heat transfer is also less. To overcome these limitations Experimental and CFD analysis

for a counter flow tube in tune helical coil heat exchanger will be carry out and compare its results

with conventional heat exchangers from available literature.

6. Experimental Setup

Figure 1: Layout of Experimental-Setup Tube-In-Tube Helical Coil Heat Exchanger

Figure 2: Actual Experimental-Setup Tube-In-Tube Helical Coil Heat Exchanger

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6.1 Experimental-Setup consists of following parts

Tube-In-Tube Helical Coil Heat Exchanger

Tank with thermostatic heater

Water Reservoir

Flow Control valve

Pressure Indicator

J-Type thermocouples

Cold tap water will be used for the fluid flowing in the outer tube. The water in the outer tube will

be circulated. The flow will control by a valve, allowing flows to be control and measure between

200 and 500 LPH. Hot water for the inner tube was heated in a tank with the thermostatic heater set

at 600C. This water will be circulated via pump. The flow rate for the inner tube will control by

flow metering valve as described for the outer tube flow. Flexible PVC tubing will use for all the

connections. J-Type thermocouples will insert into the flexible PVC tubing to measure the inlet and

outlet temperatures for both fluids. Temperature data will be recorded using a creative temperature

indicator. The fluid properties of the working fluid (water) was assumed to be constant throughout

the analysis with respect to temperature and presented in the table 1.a

Table 1: The fluid properties of the working fluid (water)

6.2 Construction of Tube-in Tube Helical coil Heat Exchanger

Material

The tube of the heat exchanger is made up of copper for maximize the heat transfer, because copper

has good thermal conductivity. Also the properties of the copper were also remains constant

throughout the analysis. It is represented in table 2.

Table 2: Properties of copper

Description Value Units

Density 8978 kg/m3

Specific Heat Capacity 381 J/kg-K

Thermal Conductivity 387.6 W/m-K

During Construction of Tube-in Tube Helical coil Heat Exchanger following parameters are

taken into considerations

• Effect of curvature ratio on heat transfer

• The Influence of pitch of coil on heat transfer

• Influence of the tube diameter change on heat transfer characteristics

• Influence of the number of coils on the overall heat transfer coefficient.

Actual Selected Dimensions from summary of tube-in-tube helical coil heat exchanger. To increase

heat transfer rate, we have to increase the curvature ratio.

Description Value Units

Viscosity 0.001003 kg/m-s

Density 998.2 kg/m3

Specific Heat Capacity 4182 J/kg-K

Thermal Conductivity 0.6 W/m-K

4442




Figure 3 :Tube-In-Tube Helical Coil Heat Exchanger

6.3 Data Deduction

In present investigation work the heat transfer coefficient and heat transfer rates were determined

based on the measured temperature data. The heat is flowing from inner tube side hot water to outer

tube side cold water.

Mass flow rate of hot water (Kg/sec): mH = QHOT(LPH) × 𝜌 (Kg/m3)

Mass flow rate of hot water (Kg/sec) mC = QCOLD(LPH) × ρ (Kg/m3)

Velocity of hot fluid (m/sec)

VH = 𝑄𝐻𝑂𝑇/(1000×Area)

Heat transfer rate of hot water (J/sec) qH = mH×CP× ΔtHOT× 1000

Heat transfer rate of cold water (J/sec) qC = mC×CP×tCOLD× 1000

Average heat transfer rate Qavg = (qH+ qC)/2

The heat transfer coefficient was calculated with, 𝑈𝑜 =𝑞/ (𝐴×𝐿𝑀𝑇𝐷)

The overall heat transfer surface area was determined based on the tube diameter and developed

area of heat transfer which is A= 0.22272m2, The total convective area of the tube keep constant

for two geometry of coiled heat exchanger. LMTD is the log mean temperature difference, based on

the inlet temperature difference ΔT1, and outlet temperature difference ΔT2,

LMTD=(Δ𝑇1−Δ𝑇2)/ (ln (Δ𝑇1/Δ𝑇2))

The overall heat transfer coefficient can be related to the inner and outer heat transfer coefficients

by the following equation ,

1/𝑈0= (𝐴0/𝐴𝑖ℎ𝑖)+(𝐴0×ln(𝑑𝑜/𝑑𝑖)/2𝜋𝐾𝐿)+(1/ℎ𝑜)

Dimensional parameters Heat

Exchanger

di,mm 10

do,mm 12

Di,mm 23

Do,mm 25

Curvature Radius,mm 125

Stretch Length,mm 3992

Wire diameter, mm 1.5

Curvature ratio 0.1

No. of Turns 4

Table 4 : Dimensional Parameters of Heat Exchanger

Dimensional parameters Heat

Exchanger

di,mm 10

do,mm 12

Di,mm 23

Do,mm 25

Curvature Radius,mm 125

Stretch Length,mm 3992

Wire diameter, mm 1.5

Curvature ratio 0.1

No. of Turns 4

4443




Where di and do are inner and outer diameters of the tube respectively. k is thermal conductivity of

wall material and L, length of tube(stretch length) of heat exchanger. After calculating overall heat

transfer coefficient, only unknown variables are hi and ho convective heat transfer coefficient inner

and outer side respectively, by keeping mass flow rate in annulus side is constant and tube side

mass flow rate varying,

hi= CVin

Where Vi are the tube side fluid velocity m/sec., the values for the constant, C, and the exponent, n,

were determined through curve fitting. The inner heat transfer could be calculated for both circular

and square coil by using Wilson plot method. This procedure is repeated for tube side and annulus

side for each mass flow rate on both helical coils.

The efficiency of the heat exchanger was calculated by,

𝜂 = (1 − 𝑒−𝛼)/ (1 –(𝐶𝑚𝑖𝑛/𝐶𝑚𝑎𝑥 )x 𝑒−𝛼)

The Reynolds number

Re= (𝜌×V×D) /𝜇

Dean number,

De= ((𝜌×V×D) / ) x (𝐷/2𝑅) ½

Friction factor,

(Δ𝑃×𝐷) / (2×𝜌×𝑉2×𝐿)

Table 4: Observations for Cold Water Flow Rate = 480 LPH

Sr.

No.

Hot water

flow rate

(LPH)

Cold Water

Temperature(0c)

Hot Water

Temperature(0c) Δt1

(0c)

Δt2

(0c)

LMTD

(0c)

Tinlet Toutlet Tinlet Toutlet

COLD WATER FLOW RATE = 480 LPH

1 120 30 36 60 40.1 24 10.1 16.06

2 240 30 38 60 42.2 22 12.2 16.62

3 360 30 40 60 45.4 20 15.4 17.14

4 480 30 42 60 47 18 17 17.49

CALCULATIONS:

dio = 0.012 m

dii =0.010 m

AH = (

4) dii

2

=0.0000785

AC = (

4) (dOI

2- dio

2)

=(

4) (0.023

2- 0.012

2)

=3.023 10-4

Heat transfer area = inner side of inner coil (Ai)

= *dii*L = 0.157m2

outer side of inner coil (Ao) = *dio*L = 0.1884m2

wire flow area(Aw) =Aw = ( /4) *dw2xL = ( /4)* 1.5

2x5

4444




Aw = 8.83x10-6

m2

Ai and Ao are the inner and outer tube surface areas

ΔT1 = T3-T2

ΔT1 =60-36

ΔT1 =240C

ΔT2 = T4-T1

ΔT2 =40.1-30

ΔT2 =10.10C

LMTD =( ΔT1- ΔT2)/(ln(ΔT1/ ΔT2))

LMTD =(24-10.1) / (ln(24 / 10.1))

LMTD = 16.060C

Mass flow rate of hot water(Kg/sec)

Mh = QHOT(LPH)* ρ (Kg/m3)

Mh = [QHOT(LPH)*10-3* ρ (Kg/m

3)] / 3600

Mh = [120*10-3

* 983] / 3600

Mh = 0.0327 Kg/sec

Mass flow rate of coldwater(Kg/sec)

Mc = QCOLD(LPH)* ρ (Kg/m3)

Mc = [QCOLD(LPH)*10-3* ρ (Kg/m

3)] / 3600

Mc = [480*10-3

* 1000] / 3600

Mc =0.133 Kg/sec

Velocity of hot fluid (m/sec)

VH = QHOT / [1000*AREAHOT]

VH = 120 / [1000*0.0000785*3600]

VH =0.4246 m/sec

Heat transfer rate of hot water(J/sec)

qh = Mh*CP*(T3-T4)*1000

qh = 0.0327*4.186*(60-40.1)*1000

qh =2723.95 J/sec

CP =4.186 KJ/Kg K

Heat transfer rate of cold water(J/sec)

qc = Mc*CP*(T2-T1)

qc = 0.1333*4.186*(36-30)*1000

qc = 3340.42 J/sec

CP =4.186 KJ/KgK

Average heat transfer rate

Qavg =(qH+ qC)/2

Qavg = (2723.95+3340.42) / 2

Qavg = 3032.18 J/sec

Overall heat transfer coefficient W/m2K

U0 = qC/ [(heat transfer area + wire area)*LMTD]

U0 = 3340.42/ [(0.157+8.83*10-6

)*16.06]

U0 = 1324.74 W/m2K

Reynolds number

4445




Re = (ρ*V*D) / μ

Where

Dynamic viscosity (μ) = 0.000798 (N·s/m²)

Re = 983*0.4246*0.01/0.000798

Re = 5230.34

Dean no. =

√

ρ = density of the fluid

μ = dynamic viscosity

V=axial velocity scale

D=diameter (other shapes are represented by an equivalent diameter)

R=radius of curvature of the path of the channel.

De = Re *(r/R)0.5

De = 5230.34 *(0.1)0.5

De = 1689.89

*Using the Wilson plot method

For 6mm pitch 480 LPH

Average convection coefficient= Rov = Ri + Rw+ Ro

Where

Ri= internal convection resistance

Rw= the tube wall resistance

Ro= external convection resistance

Rov=1 / (hi*Ai)+ [ln(d0/di)/(2 KwLw)]+1/ h0A0

Where

hi and ho are the internal and external convection coefficients,

di and do are the inner and outer tube diameters,

Kw is the tube thermal conductivity,

Lw is the tube length

Ai and Ao are the inner and outer tube surface areas

By reference of Wilson Plot

ROV= (SLOPE)/V0.8

+C1

SLOPE== (Y2-Y1)/(X2-X1)

C1 = 0.0061

ROV=0.006059/0.427308+0.0061

ROV= 0.01806

C2=1/((ROV-C1)*A0*V0.8

)

C2 = 1/((0.01806-0.0061)*0.1884*0.42730.8

)

C2 = 876.19

Convection coefficient

hi=C2*V0.8

hi=876.19*0.42730.8

hi = 443.80 W/m2K

Nusselt number

Nu=(hi*D)/KW

Nu=(443.80*0.01)/0.628

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Nu=7.06

For outer side

RW=[ln(d0/di)/(2 KcuLw)]

RW=[ln(0.012/0.010)/(2 *387*5)]

RW = 0.00015

RO=C1-RW

RO = 0.00595

Heat transfer coefficient

hO=1 / RO*0.1884

hO=892.07 W/mK

Nusselt number

Nu=(hO*D)/KW

Nu =(892.07*0.02)/0.628

Nu = 28.40

Velocity of cold water (m/sec)

V= qC/(A*ρ)

Vc = 0.1333/ (3.023*10-4*1000)

Vc= 0.4410 m/sec kinematic viscosity (m²/s)

ν=μ/ρ

ν is the kinematic viscosity

ν= 0.000789/1000

ρCOLD WATER=1000 Kg/m3

OUTSIDE REYNOLD NUMBER

Re= (V*D) /ν

Re=3530.54

OUTSIDE DEAN NUMBER

Dean no.=

√

ρ =is the density of the fluid

μ =is the dynamic viscosity

V=is the axial velocity scale

D=is the diameter (other shapes are represented by an equivalent diameter)

De = Re *(r/R)0.5

De = 11164.55

Friction factor

DH = (doo-dio)

DH = (0.0235-0.0125)

DH = 0.011

f = (ΔP*DH) / (2*ρ*V2*L )

f = (0.5*105*0.011)/(2*1000*0.4410

2*5)

f = 0.2827

Efficiency of Heat Exchanger (η):

e= exponential

C=capacity factor

4447




C=(Cmin)/(Cmax)

=(mH*Cp) / (mc*Cp)

=(0.0327*4.186) / (0.133*4.186)

=0.2458

NTU=U*A /(mh*cp)H

=(1324.74*3.023*10-4

) /(0.0327*4.186)

=2.925

η =(1-e-(1-c)NTU

)/(1-c* e-(1-c)NTU

)

η = 95.46 %

Table 5: Results obtained for Cold water flow rate =480 LPH

Parameters 120 LPH 240 LPH 360 LPH 480 LPH

For Inner Side of Inner Tube

LMTD(0c) 16.06 16.62 17.14 17.49

MH(Kg/sec) 0.0327 0.0655 0.0983 0.131

Mc(Kg/sec) 0.133 0.133 0.133 0.133

VH(m/sec) 0.4246 0.8492 1.2738 1.6985

qH(J/sec) 2723.95 4880.45 6007.66 7128.25

qc(J/sec) 3340.42 4453.90 5567.38 6680.85

Qavg(J/sec) 3132.18 4667.17 5787.52 6704.70

Uo(W/m2k) 1324.74 1706.81 2068.70 2432.74

Re 5230.34 10460.69 15691.04 20922.02

De 1689.89 3307.96 4961.94 6616.11

C1 0.0061 0.00540 0.00490 0.00396

Rov 0.01806 0.01230 0.00548 0.00792

Nu 7.06 12.24 16.93 21.34

For Outer Side Of Inner Tube (Annulus area)

Rw 0.00015 0.00015 0.00015 0.00015

Ro 0.00595 0.00525 0.00475 0.00381

ho(W/m2k) 892.07 1011.02 1117.44 1393.13

Nu 28.40 32.198 35.58 44.37

Vc(m/sec) 0.4410 0.4410 0.4410 0.4410

Re 11164.55 11164.55 11164.55 11164.55

De 3530.54 3530.54 3530.54 3530.54

References [1] D.G.Prabhanjan, G.S.V., Raghavan and T.J.Rennie, Comparison of heat transfer rates between a straight

tube heat exchanger and a helically coiled heat exchanger, Heat and mass transfer, Vol. 29, No. 2,

(2002), pp.185-191.

[2] T.J. Rennie, D.G. Prabhanjan, Laminar parallel flow in a tube-in-tube helical heat exchanger, in AIC

Meeting, 2002.

[3] D.G.Prabhanjan, G.S.V., Raghavan and T.J.Rennie, Natural convection heat transfer from helical coiled

tubes, International Journal of Science, Vol. 43, No. 4, (2004), pp. 359-365.

[4] T.J. Rennie, V.G.S. Raghavan ,Experimental studies of a double-pipe helical heat exchanger,

Experimental Thermal and Fluid Science,29 (2005) 919–924.

[5] J.R.Timothy., G.S.Vijaya, Numerical studies of a double-pipe helical heat exchanger, Applied Thermal

Engineering, Vol. 26, (2006), pp. 1266-1273.

4448




[6] T.J. Rennie, V.G.S. Raghavan,Effect of fluid thermal properties on heat trans-fer characteristics in a

double pipe helical heat exchanger. Int J Therm Sci, 2006 b; 45:1158–65.

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Chem. Eng. Sci. 61 (2006) 4403e4416.

[8] J.S. Jayakumar, S.M. Mahajani, J.C. Mandal, Experimental and CFD estimation of heat transfer in

helically coiled heat exchangers, Chemical engineering research and design, Vol. 86, (2008), pp. 221-

232.

[9] V. Kumar, B. Faizee, M. Mridha, K.D.P. Nigam, Numerical studies of a tube– in-tube helically coiled

heat exchanger, Chem. Eng. Proc. 47 (2008) 2287–2295.

[10] Jung-Yang San*, Chih-Hsiang Hsu, Shih-Hao Chen, Heat transfer characteritics of a helical heat

exchanger, Applied Thermal Engineering 39 (2012) 114e120, Jan 2012.

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Thesis, NIT Rourkela, India, (2013), pp. 1-33.

[12] Mr G.B.Mhaske and D.D.Palande, “Experimental Investigation of Heat Transfer Analysis of Tube in

Tube Helical Coil Heat Exchanger” ,Open/ MPGCON, Jully 2015, (Pg:1 -7)

experimental investigation of tube in tube helical coil ...tube helical coil heat exchanger 6.1...

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