INTERNATIONALMechanical Engineering and Technology (IJMET), ISSN 0976 – International Journal of JOURNAL OF MECHANICAL ENG...
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) V...
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) V...
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) V...
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) V...
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) V...
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) V...
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) V...
International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) V...
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A practical approach to design and optimization of single phase liquid to liquid shell and tube heat exchanger

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A practical approach to design and optimization of single phase liquid to liquid shell and tube heat exchanger

  1. 1. INTERNATIONALMechanical Engineering and Technology (IJMET), ISSN 0976 – International Journal of JOURNAL OF MECHANICAL ENGINEERING 6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME AND TECHNOLOGY (IJMET)ISSN 0976 – 6340 (Print)ISSN 0976 – 6359 (Online) IJMETVolume 3, Issue 3, September - December (2012), pp. 378-386© IAEME: www.iaeme.com/ijmet.asp ©IAEMEJournal Impact Factor (2012): 3.8071 (Calculated by GISI)www.jifactor.com A PRACTICAL APPROACH TO DESIGN AND OPTIMIZATION OF SINGLE PHASE LIQUID TO LIQUID SHELL AND TUBE HEAT EXCHANGER Ajeet Kumar Rai * and Mustafa S Mahdi** *Deptt of Mech. Engg. SSET, SHIATS-DU Allahabad (U.P.) INDIA-211007 **Deptt of Mech. Engg. University of Diyala, Republic of Iraq-32001 E mail-raiajeet@rediffmail.com, Mustafa.sabah@yahoo.com ABSTRACT In this paper a method for thermal-hydraulic design of single phase liquid to liquid shell and tube heat exchanger is established based on Tinker method. Modification suggested by Kern and Kakac are also incorporated. A computer program has been developed to ease the design procedure. The program determines the overall dimensions of the shell, the tube bundle, and optimum heat transfer surface area required to meet the specified heat load by utilizing the allowable shell-side pressure drop and other optimum parameters like fixed tube side velocity and fixed baffle cut. The capability of the proposed model was verified through a case study of a shell and tube heat exchanger used in a locomotive for cooling of the lubricating oil of the engine. The design shows a comparable result with the case study with deviation of 10%. Keywords: Heat exchanger; Shell and tube; Sizing; Single-phase flow INTRODUCTION Shell and tube heat exchanger have a wide application, it is worth noting that more than ninety percent of heat exchangers used in industry are of the shell and tube heat exchanger type as these heat exchangers are capable of handling a quite high load in a moderate size, they offer a great flexibility to meet almost any service requirement, they can be designed for handling high pressures and they can be easily cleaned. Consequently many researches and investigation are done towards establishing better and efficient design procedures with optimization with its characteristics and cost. Kern [1] provided a simple method for calculating shell side pressure drop and heat transfer coefficient. However, this method cannot adequately account the baffle to shell and tube to baffle leakage. The concept of considering the various streams through the exchangers was originally proposed by Tinker 378
  2. 2. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME[2]. He suggested a schematic flow pattern, which divided the shell side flow in a number ofindividual streams. Tinker’s original analysis was quite complex and hard to understand but itpresents a much better approximation than the analysis given by Kern, a simplified form ofTinker’s analysis is present by Frass [3], which is suitable for computer program, which hasbeen depended on this work for thermal and hydraulic design. In the context of developmentof new design technique, this work presents a design and optimization procedure integratewith an practical design guidelines with the help of simple user friendly computer program.METHOD Design strategy: Shell and tube heat exchanger design is an inherently iterative process;the main steps can be summarized as follows: (1) Obtain an initial configuration for the heatexchanger. (2) Obtain a thermal and hydraulic design which is suitable for given data. (3)Iterate until acceptable design is obtained. (4) Optimize the design by testing all the designparameters to get an optimum and economic design; this can be done by using the computerprogram that has been developed in this work.Thermal and hydraulic design: In thermal design, the heat exchanger is sized, which meansthat all the principal construction parameters such as shell diameter, number of tubes, tubelength, tube, baffle spacing and cut, are determined as the following procedure:1- Calculate the total number of tubes ‫ݓ‬ଵ ݂ଵ ∗ ‫ܰ ∗ ܮ‬ଵ ଷ݊= ∗ඨ 1.11 ߩଵ ∗ ݀௜௡ ∗ ∆ܲଵUse 2.25 m/s as a fluid velocity in tube side which is the most efficient velocity to utilize theallowable pressure drop to heat transfer coefficient for determination of Reynolds numberthat required for determination of friction factor[4].2- Calculate the tube matrix diameter and shell inside diameter [5]. 0.87 ‫ݏ‬݀௠ = 0.637 ∗ ඨ ∗ [ߨ ∗ ݀௢௨௧ ∗ ݊ ∗ ( )ଶ ]଴.ହ 0.9 ݀௢ ݀௦ = ݀௠ ∗ 1.0753- Calculate nozzles diameter [1].݀ே = ݀௦ ∗ 0.24- Calculation of correction factors to allow the deviation from ideality for shell side, eachbaffle cut has a particular correction factors [3], however in present work the baffle cut isfixed to 25% as it’s the most efficient cut so the correction factors is:M = 0.88, ܰ௛ = 0.54, Y = 4.7, ܰ௣ = 0.3‫ܨ‬௛ = (1 + ܰ௛ ∗ ඥ݀௦ ⁄‫ି)ݏ‬ଵ‫ܨ‬௣ = (0.8 + ܰ௣ ∗ ඥ݀௦ ⁄‫ି)ݏ‬ଵ5- Calculate the coefficients ‫ܥ‬௔ and ‫ܥ‬௕ which use in calculation of ‫ܩ‬ଶ , ℎଶ and ݂ଶ . this step ℎadopted from the experimental work of Tinker [2].‫ܥ‬௔ = ଴.ହ଺ ‫ܩ‬௛Where for this step 379
  3. 3. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME 24ℎ= ݀௢ ଵ ߤ ∗ ܲ‫ݎ‬ଶ ିଷ ∗ (ߤ )ି଴.ଵସ ݇ଶ ௪ ܴ݁ଶ ∗ ߤଶ ∗ ‫ܯ‬And‫ܩ‬௛ = ݀௢∗ ‫ܨ‬௛And for ‫ܥ‬௕ 0.8‫ܥ‬௕ = ି଴.ହଷ ‫ܩ‬௣ ܴ݁ଶ ∗ ߤଶAnd‫ܩ‬௣ = ݀௢ ∗ ‫ܨ‬௣6- Calculate the logarithmic mean temperature difference.‫ܶܨ ∗ ܦܶܯܮ = ܦܶܯܮ‬ ∆ܶଶ − ∆ܶଵ‫= ܦܶܯܮ‬ ݈‫ܶ∆(݃݋‬ଶ ⁄∆ܶଵ ) ൫√ܴ ଶ + 1൯ ln (1 − ‫)ݏܴ − 1(⁄)ݏ‬‫= ܶܨ‬ 2 − ‫ ܴ√ − 1 + ܴ(ݏ‬ଶ + 1) (ܴ − 1) ݈݊ 2 − ‫ + 1 + ܴ(ݏ‬ඥܴ ଶ + 1) 1.86 ∗ ‫ܥ‬௔ ∗ ߨ ∗ ݀௢ ∗ ∆ܲଶ ‫ܷ ܦܶܯܮ‬ ߤ7- Calculate shell side mass flow rate through the tube bundle‫ܩ‬ଶ ଷି௔ି௕ = ∗ ∗ ∗ ( )଴.ଵସ ‫ܥ‬௕ ∗ (‫݀ − ݏ‬଴ ) ∗ ‫ܨ‬௣ ∗ (1 − ‫݀⁄ܪ‬௦ ) ∗ (1 + ܻ(‫݀⁄ݏ‬௦ )) ∗ ܿ௣ଶ ଶ ∆‫ݐ‬ଶ ℎଶ ߤ௪௎௛మ is the ratio of overall heat transfer coefficient to shell side heat transfer for first design itcan be approximate to unity from the fact that the most shell and tube heat exchangers areemploying organic liquid in the shell side and cooling water is insensitive to the tube side hthis makes possible a simplifying approximation [3].8- Calculate Reynolds number for shell side that modified to the calculation of frictionfactor ܴ݁௣ and heat transfer coefficient ܴ݁௛ [2]. ‫ܩ‬ଶ ∗ ݀௢ ∗ ‫ܨ‬ ௣ܴ݁௣ = ߤଶ ‫ܩ‬ଶ ∗ ݀௢ ∗ ‫ܨ‬௛ܴ݁௛ = ߤଶ ∗ ‫ܯ‬9- Calculate shell side friction factor݂ଶ = ‫ܩ‬௣ ௕ ∗ ‫ܥ‬௕10- Calculate shell side heat transfer coefficientℎଶ = ‫ܥ‬௔ ∗ ‫ܩ‬௛ ௔ ܳ11- Calculate of baffle spacing݈= ଴.ହ ∗ (‫ܿ ∗ ݐ∆ ∗ ) ܩ( ∗ ) ݀ − ݏ‬ ‫ܥ‬௠ ∗ ݊ ௢ ଶ ଶ ௣ଶ 380
  4. 4. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME 2 ∗ ∆ܲଶ ∗ ߩଶ ∗ ‫ܥ‬௠12- Calculate baffles numberܰଶ = ߤ ݂ଶ ∗ ‫ܩ ∗ ܨ‬ଶ ∗ ݊଴.ହ ∗ (1.075 ∗ (1 − ‫݀⁄ܪ‬௦ ) ∗ (1 + ܻ(‫ݏ‬ൗ݀௦ )) ∗ (ߤ )଴.ଵସ ଶ ௣ ଶ ௪13- Calculate tube length of the heat exchanger‫ܰ ∗ ݈ = ܮ‬ଶThis is the step to check the value of the assumed length, which it was necessary to assumedit to precede the calculation; it is provide the bases for the second trail, where the secondassumed value should be closer and higher to the value of calculated length. ݇ଵ ∗ ܰ‫ݑ‬14- Calculate tube side heat transfer coefficient.ℎଵ = ݀௜௡ ‫ݓ‬ଵ15- Calculate tube side mass flow rate.‫ܩ‬ଵ = ݊ ߨ ∗ ∗ ݀௜௡ ଶ ܰଵ 416- Calculate tube side pressure drop ݂ଵ ∗ ‫ܩ‬ଵ ଶ ∗ ‫ܰ ∗ ܮ‬ଵ∆ܲଵ = 2 ∗ ߩଵ ∗ ݀௜௡ 1 1 117- Calculate the overall heat transfer coefficientܷ = ( + + )ିଵ ℎଶ ℎଵ ܶ௖19- Calculate the total heat transfer area, for the purpose of cost estimation‫݀ ∗ ߨ ∗ ݊ = ܣ‬௢ ∗ ‫ܮ‬Following above steps are the calculations of thermal design, which find the dimensions ofthe heat exchanger and the quantity of some feature, such as nozzles, baffles, shell and tubes.As it seems very lengthy and the error is not avoidable in manual calculation and the iterationis required to get the final and optimum design of given data which makes the design verylengthy. Therefore a computer program is developed in present work to ease the calculationand minimize the time. This would make the design an enjoyable task to get the optimumdesign with the help of computer.A C code is developed based on the method described above. Baffle cut is fixed to 25% asit’s the most efficient cut and for simplicity. The program allows the user to choose thedifferent fluid for shell and tube side. The flow diagram of the computer program isillustrated in the Fig. 1.RESULT AND DISCUSSION The performance of the proposed model is illustrated through the analysis of the resultsobtained in an example of design tasks and comparing the solution reached with a shell andtube heat exchanger that employed in a locomotive for cooling the lubricating oil of theengine, the data had taken from diesel locomotive works, Varanasi. And the heat exchanger isemploying to maintain the lubricating oil temperature between 65.6 C° and 60 C°. Therequirement data to design the shell and tube heat exchanger is illustrated in table (1). Table(2) shows three columns. Run1 (with the same data of locomotive heat exchanger column)gives the acceptable design for a given data that the length assumed was 1.4 m and the 381
  5. 5. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEMEcalculated length is 1.37 m which it is quite close to the assumed one. The last column showthe result of real heat exchanger (DLW, Varanasi) the design result is comparable with adeviation of 5-10%. Run2 contains the result of different input data (different in tubediameters only in Run1=0.019, in Run2=0.025) and is an example of how the designers(users) can use the program and examine the variable input parameters to get an optimumdesign for a particular task, following are the difference observed between Run1 and Run2:(1)The heat exchanger first cost has increased due to the increase in the heat transfer area. (2)Tube side heat transfer coefficient is not much affected with the change due to the factthat the velocity in tubes in both cases had been fixed at 2.25 m/s.(3)Shell side heat transfer coefficient is decreased.(4)Tube side pressure drop is less in Run2.(5)The overall heat transfer coefficient has decreased in Run2.This comparison shows that Run1 is the optimum design, which has a better utilization ofallowable pressure drop to heat transfer coefficient, which Leads to a more economic design(less heat transfer area or the smaller heat exchanger) for a particular heat load.Table 1 Data of case study Heat load = 211000 W Flow configuration = 2 passes Matrix geometry = triangular pitch Tube size (m) = 0.019m outside diameter, 0.0166 inside diameter shell tube Temperature in ( ௢ ‫) ܥ‬ Fluid oil water 65.6 32.2 Temperature out ( ௢ ‫)ܥ‬ 60 43.52 Density (݇݃/݉ ଷ ) Allowable pressure drop (Pa) 14000 10355 Heat capacity (‫)݇ .݃݇⁄ܬ‬ 849 993 2100 4200 Thermal conductivity (‫)݇ .݉⁄ݓ‬ Viscosity (Pa . s) 0.031 0.00075 0.156 0.614 Total flow rate (kg/s) 18.2 60 382
  6. 6. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME Figure 1 Flow chart of the program Table 2 Thermal-hydraulic result Geometry present work present work Locomotive Run1 Run2 SHTH no. of tubes 241 138 253 shell diameter (m) 0.439 0.438 0.4439 nozzles diameter (m) 0.088 0.087 N.A. baffle spacing (m) 0.274 0.29 0.25 baffle cut 25% 25% 34% baffle number 5 8 6 tube length (m) 1.37 2.4 1.5 heat transfer area (݉ଶ ) 19.7 25.28 N.A. tube side heat coefficient (ܹ ⁄݉ଶ . ଴ ‫)ܥ‬ tube side pressure drop (Pa) 10167 9674.3 N.A. shell side heat coefficient(ܹ ⁄݉ଶ . ଴ ‫)ܥ‬ 8278 7755.4 N.A. over all heat coefficient(ܹ ⁄݉ଶ . ଴ ‫)ܥ‬ 456.88 413.8 N.A. 429.03 390.13 N.A.(N.A.= not available) 383
  7. 7. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEMECONCLUSION The design strategy is based mainly on Tinker method which provides a goodprediction for shell side flow. The design model was very close to the ideality. Theoptimization strategy is based on two things, (i) assumptions made for tube side velocity,utilization of all shell side pressure drop, and the fixed baffle cut. And (ii) the need of acomputer aided design, that can be used to examine all the design parameters for a given heatload to get the economic design. This work and specially the computer program is useful forboth the customers and the designers. A customer can get a first idea about the size and thecomponent of the required heat exchanger and can select it from hundreds of the heatexchangers provided in manufacturer’s catalogues. And for the designer to test all the designparameters to get an economical design, and this can be made easily with the help of thecomputer program.NOMENCLATUREQ Heat load (ܹ) The area of heat transfer (݉ଶ )݊A‫ ݓ‬ Total number of tubes݂ Total flow rate (݇݃/‫)ݏ‬‫ܮ‬ Flow friction factor݀௜௡ Tube length (݉)݀௢ Tube inside diameter (݉)ܰଵ Tube outside diameter (݉)݀௠ Number of tube side passesܴ݁ Diameter of circle circumscribed (݉)ܴ݁௣ Reynolds numberܴ݁௛ Reynolds number for pressure drop calculations݀௦ Reynolds number for heat transfer coefficient calculations݀ே Shell diameter (݉) Nozzle diameter (݉)‫ ܯ‬ Ratio of the effective flow passage area for cross flow through the tube matrix to the total flow passage area ܻ A factor which when multiplied by ‫݀⁄ݏ‬௦ gives the ratio of the baffle window pressure drop to the tube matrix pressure drop for‫ݏ‬ the shell side flow Tube spacing (݉)‫ܨ‬௣ Fraction of the shell side flow passing through the tube matrix for the determination of the pressure dropܰ௣ Factors used in the calculation of ‫ܨ‬௣‫ܨ‬௛ Fraction of the shell side flow passing through the tube matrix for the determination of the heat transfer coefficientܰ௛ Factors used in the calculation of ‫ܨ‬௛ 384
  8. 8. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME‫ܩ‬௣ Shell side mass flow rate for the determination of pressure drop (݇݃⁄݉ ଶ ‫)ݏ‬‫ܩ‬௛ coefficient (݇݃⁄݉ଶ ‫)ݏ‬ Shell side mass flow rate for the determination of heat transfer‫ܥ‬௕‫ܥ‬௔ Coefficient in step 5ℎ Heat transfer coefficient (ܹ ⁄݉ ଶ ݇) Coefficient in step 5‫ܦܶܯܮ‬ cold fluids ( ௢ ‫) ܥ‬ The logarithmic mean temperature difference between the hot and‫ܶܨ‬ Correction factor applied to calculate ‫ܦܶܯܮ‬௦௛௘௟௟ ௔௡ௗ ௧௨௕௘ܿ௣ Specific heat (‫)݇݃݇⁄ܬ‬∆‫ݐ‬ଶ The temperature difference at shell side ( ௢ ‫) ܥ‬݈‫ܥ‬௠ Baffle spacing (݉) The square root of (average number of tubes per transverse row/number of‫ ܩ‬ Mass flow rate (݇݃⁄݉ ଶ ‫)ݏ‬ tubes rows)ܰଶܰ‫ݑ‬ Baffles number݇ Thermal conductivity (ܹ ⁄݉ ݇ ) Nusslet numberܲ‫ ݎ‬ܶ௖ Prandtl number wall by the tube thickness (ܹ ⁄݉ ଶ ݇) Tube conductance obtained by dividing the thermal conductivity of theܷ Overall heat transfer coefficient (ܹ ⁄݉ଶ ݇ )ܾ௪ ݇௪ Tube-wall conductivity (ܹ ⁄݉ଶ ݇) Tube-wall t thickness (݉)‫ݒ‬ Fluid velocity (݉⁄‫)ݏ‬ߤ Greek symbols∆ܲ Fluid viscosity (ܲܽ ‫)ݏ‬ߩ Fluid density (݇݃⁄݉ଷ ) Pressure drop (ܲܽ)REFRENCES 1. Kern D.Q. (1950), “Process heat transfer”, McGraw Hill, New York. 2. Tinker T. (1951) “Shell-side characteristic of shell-and-tube heat exchangers”, Parts II, III, and I, in: Proceedings of General Discussion on Heat Transfer, Institute of Mechanical Engineers and American Society of Mechanical Engineers, London, New York, pp. 89. 3. Frass A.P. (1989), “Heat Exchanger Design”, John Wiley & sons, New York. 4. 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. 145. 5. Kakac S., Hongtan L. (2002), “Heat exchangers selection, rating and thermal design”, CRC Press. 385
  9. 9. International Journal of Mechanical Engineering and Technology (IJMET), ISSN 0976 –6340(Print), ISSN 0976 – 6359(Online) Volume 3, Issue 3, Sep- Dec (2012) © IAEME 6. El-Fawal, Fahmy and Taher. (2011), “Modelling of Economical Design of Shell and Tube Type Heat Exchanger Using Specified Pressure Drop”, Journal of American Science, Vol 7, pp. 32-40. 7. Polley G.T., Shahi M.H. and Nunez M.P. (1991), “Rapid design algorithms for shell and tube and compact heat exchangers”, Trans Chem, Vol. 69(A), November, pp. 435-444. 8. Kara Y. A., Guraras O. (2004), “A computer program for designing of shell-and-tube heat exchangers”, Elsevier Applied Thermal Engineering, Vol. 24, PP. 1797–1805. 9. Adelaja, Ojolo and Sobamowo M. G. (2012), “Computer Aided Analysis of Thermal and Mechanical Design of Shell and Tube Heat Exchangers”, Advanced Materials Research, Vol. 367, pp. 731-737. 10. LEONG K. C., TOH K. C. (1998), “Shell and Tube Heat Exchanger Design Software for Educational Applications”, Int. J. Engng Ed. Vol. 14[3], pp. 217-224. 11. Incropera F.P., Dewitt D.P. (1988), “Fundamentals of heat transfer”, John Wiley & sons, New York. 12. Serth R.W. (2007), “Process heat transfer principles and applications”, Elsevier Science & Technology Books. 13. Poddar T.K. and Polley G.T. (1996), “Heat Exchanger Design through Parameter Plotting”, Transactions of the Institution of Chemical Engineers, Vol. 74[A], pp 849– 852. 386

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