Analytical and CFD analysis of Shell and tube heat Exchanger with Segmental and Helical Baffles

Download Full-Text PDF Cite this Publication

Text Only Version

Analytical and CFD analysis of Shell and tube heat Exchanger with Segmental and Helical Baffles

Netra Ravindra Lagad

Aishwarya Shivachandar

Jyoti Sharad Bodhale

Student,SAE

Student,SAE

Student,SAE

Pune

Pune

Pune

Abstract The development and performance optimization of shell and tube heat exchanger is an issue of great challenge and part of emerging nascent technology. The performance optimization would serve a great contribution to placate the inflated operating costs as well as energy crisis. This paper showcases all the empirical results obtained from the real time system analysis in various working conditions. Further it represents comparison for several shell-and-tube heat exchangers with segmental baffles as well as helical baffles with baffle angle parametric variation. The system identification has been carried out by two methods viz. Theoretical analysis and CFD analysis. The combined results with respect to same shell-side flow rate show that, the heat transfer coefficient of the heat exchanger with helical baffles is higher than that of the heat exchanger with segmental baffles while the shell-side pressure drop of the former is even much lower than that of the latter. Further enhancement techniques should be incorporated in order to enhance shell-side heat transfer based on the same flow rate. The comparative analysis of heat transfer coefficient per unit pressure drop shows that the Segmental Baffle Heat exchanger have significant performance advantage over Segmental Baffle Heat exchanger for the same geometrical configurations. The performance enhancement of heat exchanger with helix baffle angle optimization could be considered as an innovation.

KeywordsCFD analysis, helical baffles, shell-side flow rate, heat transfer coefficient, pressure drop.(keywords)

I.INTRODUCTION

A heat exchanger is equipment built for efficient heat transfer from one medium to another. The media may be separated by a solid wall to prevent mixing or they may be in direct contact. They have numerous applications and are widely used in space heating, refrigeration, air conditioning, power plants, chemical plants, petrochemical plants, petroleum refineries, natural gas processing, and sewage treatment.

The performed work is based on the analysis of Shell and tube heat exchanger, that contains two separated fluids at different temperatures flowing through the heat exchanger: one through the tubes (tube side) and the other through the shell around the tubes (shell side). Several design parameters and operating conditions influence the optimal performance of a shell-and-tube heat exchanger.

The baffle configuration is selected on the basis of size, cost, and ability to lend support to the overhung tube bundles. In the presented work helical baffles are considered over segmental baffles for numerous advantages such as:-

  • Increased heat transfer rate/ pressure drop ratio.

  • Reduced bypass effects.

  • Reduced shell side fouling.

  • Prevention of flow induced vibration.

  • Reduced maintenance

    Helical baffles are advantageous because high pressure drop occurs since the segmental baffles make fluid perpendicularly impact the shell wall and the tubes, leading to an increased power load which is overcome by helical baffles.

    1. PROBLEM STATEMENT

      Comparative Analysis of Shell and Tube Heat Exchangers with Segmental Baffles and Helical Baffle Configurations in reference to Heat Transfer Co-efficient and Pressure Drop using Analytical and CFD analysis and identifying the most suitable Baffle angle Configuration for Industrial Application.

    2. LITERATURE REVIEW

      Literature review for the present study includes the guidelines which are as follows:-

      1. Mustansir Hatim Pancha et al,"Comparative Thermal Performance Analysis of Segmental Baffle Heat Exchanger with Continuous Helical Baffle Heat Exchanger using Kern method"Pub no.ISSN/2248/9622.Pub Date-July-august 2012:- With segmental baffles, most of the overall pressure drop is wasted in changing the direction of flow, while helical baffle focus on better conversion of pressure drop into heat transfer that is, higher Heat transfer co-efficient to Pressure drop ratio. Also the undesirable effects such as dead spots/zones of recirculation causes fouling, high leakage flow and large cross flow, are avoided.

      2. Qiuwang Wang et al,Shell and tube heat exchanger with helical bafflesPub no.US 2011/0094720.Pub. Date- Apr.28,2011:- Power load present in segmental baffle can be reduced by helical baffles. The invention provides 2 methods of manufacturing of continuous helical baffles. The flow pattern in helical reduce fouling and increase the service life.

      3. B.Peng et al, "An Experimental study of shell and tube heat exchanger using continuous helical baffles, "Journal of Heat transfer Volno.-129/1425,October 2007:- Helical baffles prevent the flow induced vibration. The use of continuous helical baffles results in nearly 10% increase in heat transfer coefficient compared with those with the conventional segmental baffles for the same shell side pressure drop.

    3. ANALYTICAL CALCULATIONS

      This section represents all the equations and formulae

      (T )lmtd 12 33 0C

      used in designing the shell side, tube side, segmental baffles and helical baffles heat exchanger. The values obtained are listed below and sample calculation for one Configuration (25o

      T Ft * Tlmtd

      Ft =Correction factor

      …(7)

      baffle angle) for helical baffle heat exchanger is shown.

      Geometrical parameters Shell

      Shell diameter (inner diameter)=92.5mm Thickness=1.25mm

      Tube

      Outer Diameter=12.7mm Length=245mm Thickness=0.37mm Pitch= 27.5mm Segmental baffles

      Helical baffle angles- 15 , 25 , 35 , 45

      Boundary conditions

      Ambient air temperature (inlet air temp)=25C Water inlet temp=55C

      Inlet mass flow rate of air=0.1025kg/sec Inlet mass flow rate of water=0.052kg/sec

      General Calculations

      1. Heat Transfer Rate

        Heat transfer rate, Outlet temperature of water and LMTD are the parameters which forms the base for the calculations of both shell and tube side primary calculations.

        Q ma C pa Ta

        Q =3714.14 KJ/hr

      2. Outlet Temp Of Water

        Q mwCpwTw

        Qair Qwater

        Q / mwCpw Tw

        …(1)

        2.1 Calculation for shell side pressure drop [1]

        2.2 Calculation for tube side pressure drop [1]

        1. Flow area

        a ID C ' B (8)

        s 144 PT

        as =0.02725 ft2 2.Mass Velocity

        G M s (9)

        s As

        G =29851.77 lb/hr ft2

        s

        R DsGs (10)

        es

        Re =140486.98

        s

        fG 2 D N 1

        P s s (11)

        s 5.22 1010 D S

        e s

        Ps =7.31 psi

        Allowable

        Pressure drop=0.00731 kpsi

        N a' t

        a t (12)

        t 144n

        at =0.0042 ft2

        G M t (13)

        t a

        t

        G =92909.07 lb/hr ft2

        t

        R DtGt (14)

        et

        Re =2994.58

        t

        fG 2 Ln

        P t (15)

        t 5.221010 D S

        t t

        Pt =0.0310 psi

        2

        P 4nV 62.5 (16)

        r s 2g ' 144

        Pr =0.00258 psi

        PT Pt Pr (17)

        PT =0.03358 psi

        Allowable

        Pressure Drop=003358 psi

        1. Reynolds Number

        2. Pressure Drop

        1. Flow Area

        2. Mass velocity

        3. Reynolds Number

        4. Tube Side Pressure Drop

        5. Return Pressure Drop

        6. Total Pressure Drop

        2.1 Calculation for shell side pressure drop [1]

        2.2 Calculation for tube side pressure drop [1]

        1. Flow area

        a ID C ' B (8)

        s 144 PT

        as =0.02725 ft2 2.Mass Velocity

        G M s (9)

        s As

        G =29851.77 lb/hr ft2

        s

        R DsGs (10)

        es

        Re =140486.98

        s

        fG 2 D N 1

        P s s (11)

        s 5.22 1010 D S

        e s

        Ps =7.31 psi

        Allowable

        Pressure drop=0.00731 kpsi

        N a' t

        a t (12)

        t 144n

        at =0.0042 ft2

        G M t (13)

        t a

        t

        G =92909.07 lb/hr ft2

        t

        R DtGt (14)

        et

        Re =2994.58

        t

        fG 2 Ln

        P t (15)

        t 5.221010 D S

        t t

        Pt =0.0310 psi

        2

        P 4nV 62.5 (16)

        r s 2g ' 144

        Pr =0.00258 psi

        PT Pt Pr (17)

        PT =0.03358 psi

        Allowable

        Pressure Drop=0.03358 psi

        1. Reynolds Number

        2. Pressure Drop

        1. Flow Area

        2. Mass velocity

        3. Reynolds Number

        4. Tube Side Pressure Drop

        5. Return Pressure Drop

        6. Total Pressure Drop

        …(2)

        …(3)

      3. Logarithemic Mean Temp Difference

        R=2

        T T

        R s1 s2

        Tt2 Tt1

        …(4)

        T T

      4. Sample baffle calculation for baffle angle 250 is shown

      S=0.25

      (T)lmtd

      S t 2 t1

      Ts1 Tt1

      T1t2T2t1

      T1t2

      lnT2t1

      …(5)

      …(6)

      below:

      1. Tube Clearance (C)

        C = Pt Dot C=0.0148 m

      2. Baffle Spacing (Lb)

        Lb = . Dis . tan Lb=0.1355 m

      3. Cross-flow Area (AS)

        (18)

        (19)

        A = (D .C . L ) / P

        1. Baffle configurations:

          ICNTE-2015 Conference Proceedings

          S is B t

          (20)

          AS=0.006745 m2

        2. Equivalent Diameter (DE)

          t

          t

          DE = 4 [ ( P 2 .Dot2 / 4 ) / ( .Dot) DE=0.06312 m

        3. Maximum Velocity (Vmax)

          V Ms

          (21)

          (22)

          Various baffle configurations are tested for optimum results and the baffle angle CFD models are as follows:

          A

          A

          max

          s

          Vmax=12.35 m/sec

        4. Reynolds number (Re)

          Re = ( .Vmax .DE) / Re= 46198.92

        5. Prandtl number (Pr)

          Pr =0.7038

        6. Heat Transfer Co-efficient (o)

          o = (0.36 .K . Re0.55 . Pr0.33) / R.DE o= 50.8764 W/m2K

        7. No. of Baffles (Nb)

          Nb = Ls / (Lb + SB) Nb = 2.39=3

        8. Pressure Drop (PS)

      s

      s

      PS=[4.f.M 2.Dis.(Nb+1)]/(2..DE) PS=0.1196 KPa

      (23)

      (24)

      (25)

      (26)

      VI. CFD ANALYSIS

    4. HEAT EXCHANGER AND BAFFLE CONFIGURATION

      The Baffle Configurations used for Theoretical and CFD purpose are listed as follows:

      1. Segmental Baffle Heat Exchanger

        Segmental Baffle Heat Exchanger is a type of shell and tube heat exchanger which has a Quadrant shaped baffle segments that are arranged at right angle (900) to the tube axis in a sequential pattern that guide the shell side flow over the tube bundle.

        Computational fluid dynamics, abbreviated as CFD, is a branch of fluid mechanics which uses numerical methods and algorithms to solve and analyze problems that involve fluid flow. We have used software named SOLIDWORKS 2013for the analysis of the Helical Baffles in the Shell and Tube Heat Exchangers.

        CFD analysis is performed on the developed solid model with the baffle angle 15o, 25o, 35o, 45o. CFD results for segmental and optimum helical angle (25o) are shown below.

        Pressure analysis:-

        Segmental Baffle Configuration

      2. Helical Baffle Heat Exchanger

Helical Baffle Heat Exchanger is a type of shell and tube heat exchanger which has a Helical shaped baffle segment which are arranged at Helix angle (150,250,350&450) to the tube axis in a sequential pattern that guide the shell side flow over the tube bundle. The visual representation of the Helical Baffle over the tubes is similar to a spring wound around the rod/tube.

Pressure Trajectory (segmental baffle)

Pressure Contour (segmental baffle)

The pressure drop is 152655.07-

147230.63 =

5420Pa

250 Helical Baffle Configuration

250 Helical Baffle Conf

ICNTE-2015 Conference Proceedings

iguration

Pressure Trajectory (250 baffle)

The pressure drop Temperature Trajectory (250 baffle)

is 147553.09-

147130.93 =

423Pa

Pressure Contour (250 baffle)

Thermal Analysis:-

Most effective temperature rise is studied which also contributes to the selection of the optimum baffle angle configuration from the following analysis.

Segmental Baffle Configuration

Temperature Contour (250 baffle)

  1. RESULTS AND VALIDATION

    This section combines the results obtained from theoretical analysis and CFD analysis. The results are then compared by plotting graphs and final conclusions have been found which are shown below.

    Comparative Results for Heat Transfer Coefficient

    Temperature Trajectory (segmental baffle)

    Temperature Contour (segmental baffle)

    Theoretical Results

    GrappHeat Transfer Co-efficient vs. Helical Angle(Theoretical)

    CFD Results

    GrappHeat Transfer Co-efficient vs. Helical Angle(CFD)

    TABLE 1: COMPARISON OF HT COEFFICIENT

    Comparative Results drop

    HELIX ANGLE

    H.T. COEFFICIENT

    (W/sq m. K) Theoretical

    H.T. COEFFICIENT

    (W/sq m. K) CFD

    NUMBER OF REVOLUTI ONS

    0 (Segme ntal baffle)

    87.65

    86.993

    6

    15

    118.77

    112.471

    4

    25

    87.47

    68.250

    3

    35

    70.15

    50.827

    2

    45

    57.906

    30.548

    1

    HELIX ANGLE

    H.T. COEFFICIENT

    (W/sq m. K) Theoretical

    H.T. COEFFICIENT

    (W/sq m. K) CFD

    NUMBER OF REVOLUTI ONS

    0 (Segme ntal baffle)

    87.65

    86.993

    6

    15

    118.77

    112.471

    4

    25

    87.47

    68.250

    3

    35

    70.15

    50.827

    2

    45

    57.906

    30.548

    1

    Theoretical Results

    ICNTE-2015 Conference Proceedings

    for Heat Transfer per unit pressure

    CFD Results

    The above result give us a clear idea that the Helical baffle heat exchanger has far more better Heat transfer coefficient than the conventional segmental Heat Exchanger.

    Comparative Results for Pressure Drop.

    Grapp The ratio of Heat Transfer co-efficient per unit pressure drop Vs Helix angle(Theoretical)

    Grapp The ratio of Heat Transfer co-efficient per unit pressure drop Vs Helix angle(CFD)

    Theoretical Results

    GrappPressure Drop vs. Helical Angle(Theoretical)

    CFD Results

    Graph4Pressure Drop vs. Helical Agle(CFD)

    TABLE 3:COMPARISON OF HEAT TRANSFER PER UNIT PRESSURE DROP

    HELIX ANGLE

    o/ PS Theoretical

    o/ PS CFD

    NUMBER OF REVOLUTIONS

    0 (Segmental baffle )

    0.0183

    0.0174

    6

    15

    0.1084

    0.0886

    4

    25

    0.2424

    0.1613

    3

    35

    0.3638

    0.2500

    2

    45

    0.6771

    0.3090

    1

    The ratio of Heat Transfer co-efficient per unit pressure drop for helical baffle is higher as compared to segmental

    TABLE 2: COMPARISON OF PRESSURE DROP

    HELIX ANGLE

    PRESSUR E DROP PS (Pa)

    Theoretical

    PRESSUR E DROP PS (Pa) CFD

    NUMBER OF REVOLUTIO NS

    0(Segmenta l baffle)

    4780

    5420

    6

    15

    1095.73

    1270

    4

    25

    360.84

    423

    3

    35

    192.8

    204

    2

    45

    85.51

    98.72

    1

    The above result indicates that the pressure drop Ps in a helical baffle heat exchanger is appreciably lesser as compared to Segmental baffle heat Exchanger due to increased cross- flow area resulting in lesser mass flux throughout the shell, and also different baffle geometry.[Graph 3 and 4]

    baffle heat exchanger. [Graph 5 and 6]

  2. CONCLUSION

In this project, numerical simulations of Helical baffle heat exchanger with different helix angles are performed to reveal the effects of baffle helical angle on the heat transfer and pressure drop characteristics. This provides an optimal helix angle for the required range of heat transfer coefficient and available pumping power. The major findings are summarized as follows:

  1. In the present work, an attempt has been made to modify the existing Kern method which is originally used for Segmental baffle heat exchangers, so as to use it for continuous helical baffle heat exchanger. The Kern method available in the literature is only for the conventional segmental baffle heat exchanger, but the modified formula used to approximate the thermal performance of Helical baffle Heat Exchangers give us a clear idea of their efficiency and effectiveness.

  2. By Theoretical analysis the maximum heat transfer co- efficient obtained for segmental baffles is 87.65 W/sqmK and for 15 helical baffles the maximum obtained heat transfer coefficient is 118.77 W/sqmK and by using CFD analysis the maximum heat transfer co-efficient obtained for segmental

    baffles is 86.993 W/sqmK and 112.471 W/sqmK for 15 helical baffles. By Theoretical analysis the pressure drop obtained for segmental baffles is 4780 Pa and for 45 helical baffles the minimum pressure drop obtained is 85.51 Pa and by using CFD analysis pressure drop is 5000 Pa for segmental baffles and minimum pressure drop for 45 helical baffles being 98.72 Pa respectively.

    The values obtained by analytical writing and CFD analysis are in good agreement.

  3. The optimum helical angle can be determined by comparing the values obtained from graph of Heat Transfer per unit pressure drop. With decrease in helical angle, though there is increase in heat transfer coefficient but this also leads to increase in the shell side pressure drop. Hence, 250 is considered to be the optimum helical angle for Industrial purpose heat exchangers.

ACKNOWLEDGMENT

This work was financially supported by a grant from the Air dynamics Pune, India. The authors thank to management of Sinhgad Academy of Engineering Kondhwa, Pune for providing technical and managerial support to execute research work.

ICNTE-2015 Conference Proceedings

R

R

EFERENCES

  1. Donald Q. Kern, Process Heat Transfer, McGraw Hill.

  2. Prof.SunilkumarShinde*,MustansirHatimPancha**, Comparative Thermal Performance Analysis of Segmental Baffle Heat exchanger with Continuous Helical Baffle Heat Exchanger using Kern Method,(Ijera),Vol.2., Issue 4, July-August 2012,Pp.2264- 2271 .

  3. Qiuwang Wang et al,"Shell and Tube Heat Exchanger with Helical BafflesPub no.US 2011/0094720.Pub. Date- Apr.28,2011.

  4. Bashir.I.Master et al,Fouling mitigation using helixchanger heat exchangers. Date:-2003

  5. Mayankvishwakarma , Performance Evaluation Of A helical Baffle Heat Exchanger Date: June 2013

  6. JurandirPrimo,Shell and Tube Heat Exchanger

  7. Qiuwang Wang et al, "Shell-side heat transfer enhancement for shell-and-tube heat exchangers by helical baffles" Chemical Engineering Transactions Volume 21, 2010

  8. Sunil S. Shinde et al, "Numerical comparison on shell side performance of Helixchanger with Center tube with different Helix angles. International Journal of Scientific and Research Publications, Volume 3, Issue 8, August 2013

  9. B.Peng et al,"An Experimental study of Shell and Tube Heat exchanger using continuous Helical Baffles",Journal of Heat Transfer Vol no:- 129/1425, October 2007.

  10. Sunil S. Shinde et al, " Numerical Comparison on Shell Side Performance of Helixchanger with center tube with different helix angles, International Journal of Scientific and Research Publications, Volume 3, Issue 8, August 2013

  11. MayankVishwakarma et al,"Thermal Analysis of Helical Baffle in Heat Exchanger", International Journal of Science and Research (IJSR), Volume 2 Issue 7, July 2013

Leave a Reply

Your email address will not be published. Required fields are marked *