A PATH FOR HORIZING YOUR INNOVATIVE WORK EXPERIENTIAL INVESTIGATION … · EXPERIENTIAL...

Research Article ISSN: 2319-507X K Anand, IJPRET, 2014; Volume 2 (6): 64-82 IJPRET

Available Online at www.ijpret.com

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INTERNATIONAL JOURNAL OF PURE AND APPLIED RESEARCH IN ENGINEERING AND

TECHNOLOGY A PATH FOR HORIZING YOUR INNOVATIVE WORK

EXPERIENTIAL INVESTIGATION OF SHELL AND TUBE HEAT EXCHANGER USING KERN METHOD

K ANAND1, V K PRAVIN2, P H VEENA3

1. Thermal Power Engg., Dept. of Mechanical Engg. PDACE Gulbarga

2. Thermal Power Engg, VTU Regional Centre Gulbarga.

3. Dept of mathematics, Smt V G women's college, Gulbarga

Accepted Date: 13/01/2014 ; Published Date: 01/02/2014

\

Abstract: Heat exchangers are one of the most important heat transfer apparatus that find its use in

industries like oil refining, chemical engineering, electric power generation etc. Shell-and-tube types of heat

exchangers (STHXs) have been commonly and most effectively used in Industries over the years. This paper

analyses the conventional heat exchanger thermally using the Kern method. In the present study, a water to

water STHE wherein, hot water flows inside the tubes and cold water inside the shell is used to study and

analyze the heat transfer coefficient and pressure drops for different mass flow rates and inlet and outlet

temperatures, using Kern Method. The Kern method gives maximum heat transfer coefficient and less pressure

drop, providing an more realistic estimates of heat transfer and pressure drops.

Keywords: STHE, Heat transfer coefficient, shell &Tube heat exchanger, Pressure Drop, TEMA, kern’s method

Corresponding Author: Mr. K ANAND

Access Online On:

www.ijpret.com

How to Cite This Article:

K Anand, IJPRET, 2014; Volume 2 (6): 64-82

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INTRODUCTION

A heat exchanger is a piece of equipment built for efficient heat transfer from one medium to another. The media may be separated by a solid wall, so that they never mix, or they may be in direct contact [1].

Heat exchangers are commonly manufactured to the standards set forth by TEMA, the Tubular Exchangers Manufacturers Association [2].TEMA, in cooperation with users and manufacturers, establishes a common set of guidelines for the construction methods, tolerances and practices to be employed.

The major components of STHE exchanger are tubes (tube bundles), shell, front end head, rear end head, baffles and tube sheets. The standard of the Tubular Exchanger Manufacturers Association (TEMA) describe various components in detail of shell and tube heat exchanger (STHE) [3]. Shell and tube heat exchangers are the most used heat transfer equipment in industrial processes. They are also easily adaptable to operational conditions. In this way, the design of shell and tube heat exchangers is a very important subject in industrial processes.

In STHE heat exchange between hotter and colder fluid is done. Fluid flowing through tubes is called – tube fluid, and fluid flowing around tube bundle is called – shell side fluid. Baffles, placed in shell side space, are providing the cross flow direction of shell side fluid and so the more intensive heat exchange between fluids could be realized [4]. STHE's usually have combined fluid flow, which means that there is parallel in one, and counter flow in other part of the exchanger [5].

TYPES OF HEAT EXCHANGER

The following are the different types of heat exchanger.

Shell and tube heat exchanger

Plate heat exchanger

Plate and shell heat exchanger

Adiabatic wheel heat exchanger

Plate fin heat exchanger

Pillow plate heat exchanger



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Fluid heat exchangers

Waste heat recovery units

Double pipe heat exchanger

SHELL AND TUBE HEAT EXCHANGER

shell and tube heat exchangers consist of a series of tubes. one set of these tubes contains the fluid that must be either heated or cooled. the second fluid runs over the tubes that are being heated or cooled so that it can either provide the heat or absorb the heat required. a set of tubes is called the tube bundle and can be made up of several types of tubes: plain, longitudinally finned, etc. shell and tube heat exchangers are typically used for high-pressure applications (with pressures greater than 30 bar and temperatures greater than 260 °c). This is because the shell and tube heat exchangers are robust due to their shape. Several thermal design features must be considered when designing the tubes in the shell and tube heat exchangers

In designing shell and tube heat exchangers, to calculate the heat exchange area, different methods were proposed. Methods proposed for shell side design are as follows:

Kern Method

Taborek Method

Donohue Method

Bell’s Method

Bell Delaware Method

Tinker Method

Devore’s Method

Mueller Method

Wills and Johnson Method

Among the all method, the Kern method provided a simple method for calculating shell side pressure drop and heat transfer coefficient. However, this method cannot adequately account



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the baffle to shell and tube to baffle leakage. The concept of the kern was originally proposed by Tinker [6].

The kern method was based on experimental work on commercial exchangers with standard tolerances and will give a reasonably satisfactory prediction of the heat-transfer coefficient for standard designs. The prediction of pressure drop is less satisfactory, as pressure drop is more affected by leakage and bypassing than heat transfer. The shell-side heat transfer and friction factors are correlated in a similar manner to those for tube-side flow by using a hypothetical shell velocity and shell diameter. As the cross-sectional area for flow will vary across the shell diameter, the linear and mass velocities are based on the maximum area for cross-flow: that at the shell equator. The shell equivalent diameter is calculated using the flow area between the tubes taken in the axial direction (parallel to the tubes) and the wetted perimeter of the tubes [7].

The method used by D.Q. Kern is simple and more explanative. All the parameter related to heat exchanger are obtained in well manner and brief without any complication as compared to other method, the calculation process is quite and simple detailed. This method gives more accurate and exact values. Hence by using this method we get accurate results when compared to other method.

EXPERIMENTAL SETUP OF SHELL AND TUBE HEAT EXCHANGER

Figure 1: schematic diagram of shell and tube heat exchanger



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The principal components of an STHE are:

Shell: Shell diameter should be selected in such a way to give a close fit of the tube bundle. In this setup the shell diameter is usually taken as 0.2m and is made of Stainless steel.

Tubes : Tube OD of ¾ and 1‟‟ are very common to design a compact heat exchanger. With increase in number of tubes, the heat transfer coefficient is increased. Stainless steel is commonly used tube materials.

Tube pitch: Tube pitch is the shortest centre to centre distance between the adjacent tubes. The tubes is generally triangular patterns (pitch).

Tube passes: The number of passes is chosen to get the required tube side fluid velocity to obtain greater heat transfer co-efficient and in this setup 2 passes is chosen.

Baffles: Baffles are used to increase the fluid velocity by diverting the flow across the tube bundle to obtain higher transfer co-efficient. In this experiment four baffles are used.

Rota meter: In this setup two rotameter are used. One is for measuring mass flow rate on shell side and another for tube side. The readings will appear in digital form.

REF NO DESCRIPTION

1 WATER LEVEL INDICATOR

2 PRESSURE RELIEF VALVE

3 PRESSURE GAUGE

4 HEATER

5 TUBE

6 WATER OUTLET

7 ROTAMETER

8 PUMP

9 WATER TANK

10 SHELL



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Pumps: Two pumps are used of half HP pump.

Heater: heater is provided on one side of tank, to heat water. The hot water is supplied to shell or tube depending upon requirement.

KERN’S DESIGN PROCEDURE

Shell and tube heat exchanger is designed by trial and error calculations. The procedure for calculating the shell-side heat-transfer coefficient and pressure drop for a single shell pass exchanger is given below The main steps of design following the Kern method are summarized as follows:

STEP 1: Calculating the area of cross flow As, for hypothetical row of tubes at the shell Equator, given by

As = (Pt – Do)*Ds*Lb /Pt

STEP 2: Calculate shell side mass velocity Gs and linear velocity Us.

Gs = ms / As

or

Us = Gs / ρs

STEP 3: Calculate the shell side equivalent diameter De.

For square pitch:

De = [4*(Pt2 – (π/4)* Do

2] / (π* Do)

For triangular pitch:

De = [4*(Pt2*√3)/4 – (π* Do

2)/8] /

[(π*Do)/2]

STEP 4: Calculate shell side Reynolds number Res.

Res = (Gs* De) / μs

Or



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Res = (Us* De* ρs) / μs

STEP 5: Calculate shell side Prandtl number Prs.

Prs = (Cps*μs) / Ks

STEP 6: Calculate the shell side heat transfer coefficient hs

hs = 0.36*( Ks / De)* (Re^0.55)*(Pr^0.33)*(μs / μw)^0.14

Note: The value of (μs / μw) ^0.14 = 1, for water.

CALCULATION OF SHELL SIDE PRESSURE DROP

STEP 7: Calculate the number of baffles on shell side Nb.

Nb = Ls / (Lb + tb) – 1

STEP 8: Calculate the friction factor f.

f = exp 0.576 – (0.19*Ln Res)

STEP 9: Calculate the shell side pressure drop ΔPs.

ΔPs = [4* f* Gs2* Ds*( Nb+1)] / [2* ρ*

De*×(μs / μw)^0.14]

Or = [f* Gs2* Ds*( Nb+1)] / [2* ρs* De*(μs/ μw)^0.14]

CALCULATION OF TUBE SIDE HEAT TRANSFER COEFFICIENT

STEP 1: Calculate the tube side cross flow section area At.

At = (π* Di2) / 4*(Nt / 2)

STEP 2: Calculate the tube side mass velocity Gt and linear velocity Ut.

Gt = mt / At

Or

Ut = Gt / ρt

STEP 3: Calculate the tube side Reynolds number Ret.



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Res = (Gt* Di) / μt

Or

Ret = (Ut* Di* ρt) / μt

STEP 4: Calculate the tube side Prandtl number Prt.

Prt = (Cpt*μt) / Kt

STEP 5: Calculate the friction factor f.

f = (1.58*Ln Ret) – 3.28 ^ (-2)

STEP 6: Calculate the tube side Nusselt number Nut.

Nut = (f /2)*(Ret -1000)* Prt / 1+ (12.7*√(f /2)*(Prt ^ (2/3))-1)

STEP 7: Calculate the tube side heat transfer coefficient hi.

hi = (Nut * Kt) / Di

CALCULATION OF TUBE SIDE PRESSURE DROP

STEP 8: Calculate the pressure drop on the tube side ΔPt.

ΔPt = [(4* f* Lt* np) / Di + (4* np)]*[(ρt*

Ut2) / 2]



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Experimental investigation:

Shell side

Sl. no Quantity Symbol Value

1 Shell side fluid Water

2 Shell side Mass flow rate(kg/sec) Mt 0.060

3 Shell ID(m) Ds 0.2

4 Shell length(m) Ls 0.800

5 Tube pitch(m) Pt 0.03

6 No. of passes n 1

7 Baffle spacing(m) Lb 0.2

8 Mean Bulk Temperature(oC) ∆T

9 No. of baffles N 4

Tube side

Sl. no Quantity Symbol Value

1 Tube side fluid Water

2 Tube side Mass flow rate (Kg/sec)

Mt 0.060

3 Tube OD (m) Do 0.019

4 Tube ID(m) Di 0.016

5 Tube thickness(m) Tp 0.0162

6 Number of Tubes N 18



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7 Tube length(m) Lt 0.825

Fluid Properties of water

Sl. no Property Unit Cold water shell side Hot water tube side

1 Specific Heat (Cp) KJ/kg. K 4.187 4.187

2 Thermal conductivity (k)

W/m. K 0.00098 0.00098

3 Density (ƍ) kg/m. s 1000 1000

4 Viscosity (Ω) kg/m3 0.00088 0.00086

CALCULATION

For 3rd reading,

SHELL SIDE HEAT TRANSFER COEFFICIENT

As = (Pt – Do)*D*Lb /Pt

= (0.03-0.01924)*0.2*.2/(0.03)

= 0.01435 m2

Gs = ms / As

= 0.0354/0.01435

= 2.47 Kg/m2 sec

De = [4*(Pt2*√3)/4 – (π* Do

2)/8] / [(π*Do)/2]

=[4(0.032*√3/4(π*0.019242)/8]/[(π*0. 0924)/2]

= 0.0325m

Res = (Gs* De) / μs



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= (2.47/0.0325)/0.00088

= 91.2

Prs = (Cps*μs) / Ks

= (4.187*0.00088)/0.00098

= 3.76

hs = 0.36*( Ks / De)* (Re^0.55)*( Pr^0.33)* (μs / μw)^0.14

=0.35*(0.00098/0.0325)*(91.20.55)*(3.760.33)*1

= 0.201 W/m2oK

CALCULATION OF SHELL SIDE PRESSURE DROP

Nb = Ls / (Lb + tb) – 1

= 0.800/(0.2+0.00162)-1

Nb+1= 3.96

f = exp 0.576 – (0.19*Ln Res)

= exp 0.567-(0.19*Ln*91.2)

= 0.754

ΔPs = [f* Gs2* Ds*( Nb+1)] / [2* ρs* De*(μs

/ μw)^0.14]

=[0.754*(2.472)*0.2*3.96]/ [2*1000*0.0325*1]

= 0.056Pa

CALCULATION OF TUBE SIDE HEAT TRANSFER COEFFICIENT

At = (π* Di2) / 4*(Nt / 2)

= (π*0.0162)/4*(18/2)

= 0.00180 m2



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Gt = mt / At

= 0.0291/0.00180

= 16.17 Kg/m sec

Ut = Gt / ρt

= 16.17/1000

= 0.01617 m/sec

Res = (Gt* Di) / μt

= (16.17*0.016)/0.00086

=300.83

Prt = (Cpt*μt) / Kt

= (4.187*0.00086)/0.00098

= 3.67

f = (1.58*Ln Ret) – 3.28 ^ (-2)

= (1.58*Ln 300.83)-3.28^(-2)

= 0.0304

Nut = (f /2)*(Ret -1000)* Prt / 1+

(12.7*√ (f /2)*(Prt ^ (2/3))-1)

=(0.0304/2)*(300.83-1000)*3.67]/1+(12.7*√ (0.0304/2)*(3.672/3- 1)

=-12.4

hi = (Nut * Kt) / Di

= (-12.4*0.00098)/0.016

= -0.78 W/m2 0K



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CALCULATION OF TUBE SIDE PRESSURE DROP

ΔPt = [(4* f* Lt* np) / Di + (4* np)]*[(ρt*

Ut2) / 2]

=[(4*0.0304*0.825*2)/0.016+(4*2)]*[( 100 0*0.016172)/2]

= 2.685Pa

Results & Graphs

Sl.no Shell side R1 R2 R3 R4 R5

1 Ms 0.026 0.030 0.035 0.040 0.044 2 Tci 32.8 33 33.1 33.1 33.2 3 Tco 34.6 34.7 34.9 35 35.5 4 Res 66.93 76.45 91.12 102.4 115.3 5 Pts 3.76 3.76 3.76 3.76 3.76 6 Ho 0.17 0.183 0.201 0.214 0.229

7 ΔPa 0.032 0.041 0.056 0.069 0.086 8 Uc 0.151 0.164 0.187 0.211 0.236

Sl.no Tube side R1 R2 R3 R4 R5 1 Mt 0.020 0.023 0.029 0.035 0.040 2 Thi 49.8 52.6 54.4 54.8 55.8 3 Tho 34.9 34.7 34.6 34.5 34.2 4 Ret 206.7 238.8 300.8 376.2 419.6 5 Prt 3.674 3.674 3.674 3.674 3.674 6 hi -1.106 -1.002 -0.842 -0.693 -0.62 7 ΔPa 1.456 1.836 2.684 3.91 4.711



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FIGURE 1: REYNOLDS NUMBER V/S MASS FLOW RATE ON SHELL SIDE

FIGURE 2: HEAT TRANSFER COEFFICIENT V/S MASS FLOW RATE

0

20

40

60

80

100

120

140

0.0267 0.03 0.035 0.04 0.044

REYN

OLD

S N

UM

BER

MASS FLOW RATE

0.000

0.050

0.100

0.150

0.200

0.250

0.000 0.010 0.020 0.030 0.040 0.050

HEA

T TR

ANSF

ER C

OEF

FICI

ENT

MASS FLOW RATE



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FIGURE 3: PRESSURE DROP V/S HEAT TRANSFER COEFFICIENT

FIGURE 4: OVER ALL HEAT TRANSFER COEFFICIENT V/S REYNOLDS NUMBER

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.1

0 0.05 0.1 0.15 0.2 0.25

PRES

SURE

DRO

P

HEAT TRANSEFR COEFFICIENT

0

0.05

0.1

0.15

0.2

0.25

0 50 100 150 200 250 300 350 400 450

OVE

R AL

L H

EAT

TRAN

SFER

CO

EFFI

CIEN

T

REYNOLDS NUMBER



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FIGURE 5: MASS FLOW RATE V/S PRESSURE DROP ON TUBE SIDE

FIGURE 6: REYNOLDS NUMBER V/S OVER ALL HEAT TRANSFER COEFFICIENT ON TUBE SIDE

CONCLUSION

It is found that among the all method, the Kern method provided a simple method for calculating shell side pressure drop and heat transfer coefficient.. By this experimentation it is clear that heat transfer coefficient and various thermal parameters can be calculated and analyzed up to higher accuracy as compared to the other methods.

NOMENCLATURE

0

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

0 1 2 3 4 5

MAS

S FL

OW

RAT

E

PRESSURE DROP

050

100150200250300350400450

0.151 0.164 0.187 0.211 0.236

REYN

OLD

S N

UM

BER

OVER ALL HEAT TRANSFER COEFFICIENT



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As = Area of the shell side cross flow section (m2).

At = Area of the tube side cross flow section (m2).

Pt = Tube pitch (m).

Do = Tube outside diameter (m).

Di = Tube inside diameter (m).

Ds = Shell inside diameter (m).

Lb = Baffle spacing (m)

Ls= Length of shell (m).

Lt = Length of tube (m).

tb = Tube thickness (m).

Gs =Shell side mass velocity (kg/ m2-s).

Gt = Tube side mass velocity (kg/ m2-s).

Us = Shell side linear velocity (m/s).

Ut = Tube side linear velocity (m/s).

ms= Mass flow rate of the fluid on shell side

(kg/s).

mt= Mass flow rate of the fluid on tube side (kg/s).

ρs = Shell side fluid density (kg/m3).

ρt = Tube side fluid density (kg/m3).

De= Shell side equivalent diameter (m)

Res= Shell side Reynolds number.

Ret = Tube side Reynolds number.

Prs = Shell side Prandtl number.



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Prt = Tube side Prandtl number

μs = Shell side fluid Viscosity (N-s/ m2).

μt = Tube side fluid viscosity (N-s/ m2).

μw= Viscosity a wall temperature (N-s/ m2).

Cps= Shell side fluid heat capacity (kJ/kg’K).

Cpt = Tube side fluid heat capacity (kJ/kg’K).

Ks = Shell side fluid thermal conductivity (kJ/s-m’K).

Kt = Tube side fluid thermal conductivity (kJ/s-m’K).

hs = Shell side heat transfer coefficient (W/ m2’K).

hi = Tube side heat transfer coefficient (W/ m2’K).

Nb= Number of baffles.

Nt = Number of tubes.

f = Friction factor.

ΔPs= Shell side pressure drop (Pa).

ΔPt =Tube side pressure drop (Pa).

np = Number of tube passes.

REFERENCE

1. Su Thet Mon Than, Khin Aung Lin, Mi Sandar Mon, 2008, Heat exchanger design, Proceedings of world academy of science, Engineering and technology, 36: 619-626.

2. The Tubular Exchanger Manufacturers Association at: www.tema.org.

3. Mukherjee R, Effective design Shell and Tube Heat exchangers, Chemical Engg Progress, (1998), 1-8

4. Gaddis, E., Gnielinski, V.: Pressure drop on the shell side of shell-and-tube heat exchangers with segmental baffles, Chemical Engineering and Processing 36, pp. 149-159, 1997.



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5. R. J. Gudmundur, S. Lalot, O. P. Palsson and B. Desmet, Int. J. Heat Mass Transfer., 50, 2643 (2007).

6. Tinker t. (1951) “shell-side characteristic of shell-and-tube heat exchangers”, parts ii, iii, and in: proceedings of general discussion on heat transfer, institute of mechanical engineers and american society of mechanical engineers, london, new york, pp. 89.

7. Kern d.q. (1950), “process heat transfer”, mcgraw hill, new york.

8. Frass a.p. (1989), “heat exchanger design”, john wiley & sons, new york.

9. Xuan, Y.M., Li, Q., (2003). Investigation on convective heat transfer and flow features of nanofluids, ASME J. Heat Transfer, 125, 151-155

10. Bhowmik, H., Lee, Kwan-Soo, 2009, Analysis of Heat Transfer and Pressure Drop Characteristics in an Offset Strip Fin Heat Exchanger. International Communications in Hea and Mass Transfer, vol.36, no.3:p 259-263

11. Bell k. j. delaware method for shell-side design, in: serth r.w., process heat transfer principles and applications, elsevier science & technology books, 2007, pp. 1

12. Huang, L., Wen, J., Karayiannis, T., Mathews, R.: Cfd modelling of fluid flow and heat transfer in a shell and tube heat exchanger, Phoenics Journal, Vol. 9, No. 2, pp 181 ÷ 209, 1996.

13. Hobler, T, Heat transfer and heat exchangers, WNT, Warszawa, 1979.

14. Peng B, Wang Q.W., Zhang C., An experimental Study of shell and tube heat exchangers with continuous Helical baffles, ASME Journal of Heat transfer, (2007).

15. S. Lalot and H. Palsson, Int. J. Therm. Sci., 49, 675 (2010).

16. M. S. Abd-Elhady, C. C.M. Rindt, J.G. Wijers, A. A. Van Steenhoven, E. A. Bramer and H. T. Van der Meer, Int. J. Heat Mass Transfer, 47, 943 (2004).

A PATH FOR HORIZING YOUR INNOVATIVE WORK EXPERIENTIAL INVESTIGATION … · EXPERIENTIAL...

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