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IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com

IJERA (International journal of Engineering Research and Applications) is International online, ... peer reviewed journal. For more detail or submit your article, please visit www.ijera.com

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  • 1. Professor Sunil S.Shinde, Swapnil R. Jayale, Dr.S.Pavithran / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.437-443 The Software For Thermal Analysis Of Helixchanger With Modification In Kern Method Professor Sunil S.Shinde*, Swapnil R. Jayale**,Dr.S.Pavithran*** *(Department of Mechanical Engineering, Vishwakarma Institute of Technology, Pune, India.) ** (B.Tech, Department of Mechanical Engineering, Vishwakarma Institute of Technology, Pune, India.) ***(Department of Mechanical Engineering, Vishwakarma Institute of Technology, Pune, India.)ABSTRACT Keywords- Kern method, heat transfer Heat exchangers are important heat & coefficient per unit pressure drop, helical bafflemass transfer apparatus in oil refining, chemical heat exchanger, helix angle, increased heatengineering, environmental protection, electricpower generation etc. Among different types of transfer coefficient, reduced pressure drop andheat exchanger, shell-and-tube heat exchangers software.(STHXs) have been commonly used in Industries.The thermal analysis of conventional heat I. INTRODUCTIONexchanger has been done using Kern method. This Heat exchangers are commonly used as oilmethod is proven & has been verified by other coolers, power condensers, preheaters and steamresearchers. Thermal analysis of helixchanger-a generators in both fossil fuel and nuclear-basedheat exchanger with helical baffles hasn’t been energy production applications. They are also widelydone using Kern method. used in process applications and in the air The present work modifies the existing conditioning and refrigeration industry. AlthoughKern method used for conventional heat they are not specially compact, their robustness andexchanger, taking into consideration the helical shape make them well suited for high pressuregeometry of helixchanger. The thermal analysis of operations. In view of the diverse engineeringHelixchanger using Kern method which gives applications and basic configuration of heatclear idea that the ratio of heat transfer coefficient exchanger, the thermal analysis and design of suchper unit pressure drop is maximum in exchangers form an integral part of the undergraduatehelixchanger as compared to segmental baffle heat mechanical and chemical engineering curricula ofexchanger. The Helixchanger analysis for most universities. Final year undergraduate coursesdifferent helix angles shows that, the heat transfer often include an elective subject for thermal design ofcoefficient decreases with increase in helix angle. heat exchangers.This decides the optimum helix angle for Reflecting the growing trend of usingHelixchanger. The Helixchanger eliminates computers for design and teaching, computerprinciple shortcomings caused by shell side zigzag software for the design and optimization of heatflow induced by conventional baffle arrangement. exchangers is needed. These softwares are written toThe flow pattern in the shell side of the heat reinforce fundamental concepts and ideas and allowexchanger with continuous helical baffle was design calculations for generic configurations with noforced to rotational & helical due to geometry of reference to design codes and standards used in thecontinuous helical baffles, which results in heat exchanger industry.significance increase in heat transfer coefficient This paper describes user-friendly computerper unit pressure drop in the heat exchanger. software developed for the thermal analysis of helical A software for the thermal analysis of baffle heat exchanger based on the open literaturehelixchanger developed in a visual basic Kern method. The use of this software will bridge theprogramming environment. Its user-friendly input gap between engineering practice and teaching offormat makes it an excellent tool for the teaching, shell and tube heat exchanger design.learning and preliminary design of helixcanager.Design methodology is based on the open II. INTRODUCTION TO SHELL AND TUBE HEATliterature Kern method while calculations adhere EXCHANGERclosely to the methodology prescribed by the latest Shell and tube heat exchangers still take aTEMA standards for industry practice. It is hoped noted place in many industrial processes. They arethat the software will bridge the gap between the widely used because of their robust and flexibleteaching of engineering fundamentals and the design. However, conventional heat exchangers withexisting industry practice of helixchanger design. segmental baffles in shell side have some shortcomings resulting in the relatively low 437 | P a g e
  • 2. Professor Sunil S.Shinde, Swapnil R. Jayale, Dr.S.Pavithran / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.437-443conversion of pressure drop into a useful heat exchanger is built from expensive special materialstransfer. such as titanium or nickel. The helixchanger – heat exchanger withshell side helical flow eliminates principle B. Lower pressure drop:shortcomings caused by shell side zigzag flow Pumping costs are dependent on pressureinduced by conventional baffle arrangements. Both drop within an exchanger. Therefore the lowerhydrodynamic studies and testing of heat transfer and pressure drop means lower operating costs. Normallythe pressure drop on research facilities and industrial devices or surfaces that provide high heat transferequipment showed much better performance of coefficients also give high pressure gradients i.e. thehelically baffled heat exchanger when compared with pressure drop per unit length of flow path.conventional ones. The new design causes near plug Exchangers designed to give enhanced performance,flow conditions and reduces dead zones within the however require shorter flow paths to achieve a givenshell space. These results in relatively high value of duty. It is therefore possible that these exchangersshell side heat transfer coefficient, low pressure drop, have a high pressure gradient but not so high pressureand low shell side fouling. Thus the helixchanger drop.exhibits much more effective way of converting a However, the segmental baffles have somepressure drop in to a useful heat transfer than adverse effects such as large back mixing, fouling,conventional heat transfer.[1] high leakage flow, and large cross flow. In addition, segmental baffles bring on significant pressure drop across the exchanger when changing the direction of flow. Recently, a new type of heat exchanger with helical baffles has been proposed to improve the performance on the shell side [6]. Compared to the conventional segmental baffled shell and tube exchanger Helixchanger offers the following general advantages:  Increased heat transfer rate/ pressure drop ratio  Reduced bypass effects.  Reduced shell side fouling.  Prevention of flow induced vibration.  Reduced maintenance C. Research aspectsFigure – 2 : Helixchanger Research on the helixchanger has forced on two principle areas.III. DESIRABLE FEATURES OF HEAT  Hydrodynamic studies on the shell side andEXCHANGERS:  Heat transfer and pressure drop studies on small In order to obtain maximum heat exchanger scale and full industrial scale equipment.performance at the lowest possible operating and Hydrodynamic studies were aimed atcapital costs without comprising the reliability, the investigation of relation between the fluid streamfollowing features are required of an exchange. momentum changes and heat transfer rate. With these tests, the influence of stagnant zones on the effective use of available heat transfer area and on theA. Higher heat transfer coefficient and larger deviation from plug flow ideal could be investigated.heat transfer area: These two factors increase the heat transfer The experimental method was based on stimulusrate for a given temperature difference and therefore response techniques modified for the specificimprove the heat exchanger effectiveness or purpose. Hydrodynamic studies on the helixchangertemperature approach. showed encouraging results- a low degree of back A high heat transfer coefficient can be mixing and nearly negligible dead volume. [10]obtained by using heat transfer surfaces, which The research program for heat transfer andpromote local turbulence for single phase flow or pressure drop tests was guided by results of thehave some special features for two phase flow. Heat hydrodynamic studies. Test units with optimumtransfer area can be increased by using larger baffle arrangement (20°-40° helical angles) wereexchangers, but the more cost effective way is to use investigated.[6]a heat exchanger having a large area density per unit The shell side heat transfer coefficientexchanger volume. Foe some duties, such as those against the shell-side pressure drop, which offers ainvolving a gaseous phase, secondary heat transfer measure of conversion efficiency of the conventionalarea is also useful. High area densities become segmental baffles as compared to that of helicaleconomically even more attractive when an baffles offer much higher conversion efficiency for converting a given pressure drop to heat transfer than 438 | P a g e
  • 3. Professor Sunil S.Shinde, Swapnil R. Jayale, Dr.S.Pavithran / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.437-443the conventional segmental baffle. An interesting in baffles with the same position are importantfigure is the dramatic improvement in conversion parameters. Baffles pitch angle (φS) is the angleefficiency for the helical baffles at a helix angle of between flow and perpendicular surface on40°. This dramatic improvement at 40° helix angle exchanger axis and Hs is space between twowas confirmed by several repeated measurements. following baffles with the same situation. TheseRecently, flow visualization tests offered some parameters are shown in Figure - 5.1expiation for this phenomenon. The boundary layeron the tube surface follows the helical path and itappears to be fully developed just around a helixangle of 40°.D. Design aspects: An optimally designed helical bafflearrangement depends largely on the heat exchangeroperating conditions and can be accomplished byappropriate design of helix angle, baffle overlapping, Figure - : A schematic of heat exchangers withand tube layout. The cross sectional area of shell side helical baffles (left), pitch angle (φS) and baffleflow channel is determined primarily by the shell space (Hs) (right).inside diameter, tube outside diameter, tube layout Optimum design of helical baffle heatand helix angle. A wide range of flow velocities can exchangers is depended on operating condition ofbe achieved by variation of helix angle, analogous to heat exchanger, and it can be followed and completedvariation of baffle spacing and baffle cut in by consideration of proper design of pitch angle,segmentally baffled heat exchanger. The overlapping overlapping of baffles and tube‟s layout. Changingof helical baffles is the parameter that can the pitch angle in helical baffle system can createsubstantially affect the shell side flow pattern. wide range of flow velocities as the baffle space andEspecially in case where adjacent baffle touch at the baffle cut in traditional heat exchangers. Moreover,perimeter, the large triangular free flow area between overlapping of helical baffles is a parameter that canthe baffles can cause a bypass stream with significant affect significantly on shell side flow pattern.longitudinal flow component. In order to counter this, Heat transfer coefficients and pressure dropbaffle overlapping is used to minimize the bypass calculations are the main part of design of heatstream. exchangers with a given duty. In traditional In the original method an ideal shell-side approaches such as Kern and Bell–Delaware methodsheat transfer coefficient is multiplied by various a design starts with a specified primary guess for thecorrection factors for flow distribution and the non- overall heat transfer coefficient and geometry ofidealities such as leakage streams, bypass stream etc. exchanger so that at the end of one run offor helical baffle geometry it is suggested that some calculations the pressure drops are re-calculated andcorrection factor are not required; at the same time compare with the maximum available pressure dropsnew are introduced given in a process. IV. THERMAL ANALYSIS OF HELICAL BAFFLE HEAT EXCHANGER In the current paper, thermal analysis has been carried out using the Kern‟s method. The thermal parameters necessary to determine the performance of the Heat Exchanger have been calculated for Segmental baffle heat Exchanger following the Kern‟s method, and suitable modifications made to the method then allow us toFigure - 3: Helixchanger flow pattern apply it for the helical baffle Heat Exchanger which is the subject area of interest. Also, the comparativeImportant Parameters: analysis, between the thermal parameters of the two  Pressure Drop Heat exchangers has been carried out, that clearly  Baffles pitch(Helix indicates the advantages and disadvantages of the two angle) angle (φS) Heat Exchangers.  Baffle space (Hs)  Surface area (A) 4.1 Heat Exchanger Data at the shell side  Heat transfer coeff. (h) Table 1. Input data – Shell Side In designing of helixchangers, pitch angle,baffle‟s arrangement, and the space between two 439 | P a g e
  • 4. Professor Sunil S.Shinde, Swapnil R. Jayale, Dr.S.Pavithran / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.437-443 6. Number of Tubes 24 Cold Hot 7. Tube side nozzle ID 0.101 m SynbolProperty Unit Water Water (Shell) (Tube) Mean Bulk 8. (MBT) 30 ˚C TemperatureSpecific KJ/kg. Cp 4.178 4.178Heat K 4.3 Fluid PropertiesThermal Table 3: Fluid properties K W/m. K 0.6150 0.6150ConductivityViscosity µ kg/m. s 0.001 0.001Prandtl‟s Pr - 5.42 5.42NumberDensity Ρ 1 kg/m3 996 996 Symbol Quantity ValueS. No.1. Shell side fluid Water2. Volume flow rate ( s) 60 lpm3. Shell side Mass flow rate ( s) 1 kg/sec Figure - 4 plot of „f‟ as a function of shell-side Reynold‟s number4. Shell ID (Dis) 0.153 m5. Shell length (Ls) 1.123 m 4.4 Thermal analysis of Helical Baffle Heat6. Tube pitch (Pt) 0.0225m Exchanger :7. No. of passes 1 (Baffle Helix Angle 25˚)8. Baffle cut 25% 1. C‟ = 0.0105 2. Baffle Spacing (Lb)9. Baffle pitch (LB) 0.060 m Lb = π ∙ Dis ∙ tan ф …(where ф is the helix angle = 25˚)10. Shell side nozzle ID 0.023 m = π ∙ 0.153 ∙ tan 25 = 0.224111. Mean Bulk Temperature (MBT) 30 ˚C 3. Cross-flow Area (AS) AS = ( Dis ∙ C‟ ∙ LB ) / Pt = ( 0.153 ∙ 0.0105 ∙ 0.2241 ) / 0.022512. No. of baffles (Nb) 17 = 0.016 m2 4. Equivalent Diameter Shell side Mass velocity / kg / DE = 0.04171 m.13. ( F) mass flux (m2s) 5. Maximum Velocity (V max) Vmax = s / As4.2 Heat Exchanger data at the tube side = 0.001 / (0.016)Table 2. Input data – Tube side = 0.0625 m/s 6. Reynold‟s number (Re) Re = (ρ ∙ Vmax ∙ DE) / μ Symbol Quantity Value = (996 ∙ 0.0625 ∙ 0.04171) / 0.001S. No. = 2596.44 7. Prandtl‟s no.1. Tube side fluid Water Pr = 5.42 ( t) 8. Heat Transfer Co-efficient (αo)2. Volume flow rate 10 lpm. αo= (0.36 ∙ K ∙ Re0.55 ∙ Pr0.33) / R ∙ DE Tube side Mass flow 0.17 = (0.36 ∙ 0.6150 ∙ 2596.440.55 ∙ 5.420.33) / 0.041713. ( t) = 699.94 W/m2K rate kg/sec 8. No. of Baffles (Nb)4. Tube OD (Dot) 0.0120 m Nb= Ls / (Lb + ∆SB)5. Tube thickness 0.0013 m = 1.123 / (0.2241 + 0.005) ≈5 440 | P a g e
  • 5. Professor Sunil S.Shinde, Swapnil R. Jayale, Dr.S.Pavithran / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.437-443 9. Pressure Drop (∆PS) it can be saved into excel background which can be ∆PS = [4 ∙ f ∙ F2 ∙ Dis ∙ (Nb + 1)] / (2 ∙ ρ ∙ DE) conveniently used analysis of the heat exchanger. = 15.52 Pa This feature is useful for the generation of design = 0.01552KPa reports. Detailed calculation steps are also availableV. THE SOFTWARE FOR THERMAL ANALYSIS to facilitate the understanding of concepts used in theOF HELIXCHANGER design. This feature sets this software apart from most commercial packages which behave like blackA. Introduction boxes and have no pedagogical use. A software for the thermal analysis ofhelixchanger developed in a visual basicprogramming environment. Its user-friendly input D. Tutorial Step1:format makes it an excellent tool for the teaching,learning and preliminary design of helixcanager. Double click on the HXDE.xlsm file. ADesign methodology is based on the open literature visual basic window will appear on the screen. It contains various tabs. After clicking on each tab aKern method while calculations adhere closely to the new window will appear. This new window willmethodology prescribed by the latest TEMAstandards for industry practice. It is hoped that the either takes some input from user or it shows thesoftware will bridge the gap between the teaching of result. For thermal analysis of helix changer firstengineering fundamentals and the existing industry click on the Parameters tab.practice of helixchanger design. Reflecting thegrowing trend of using computers for design andteaching, computer software for the design andoptimization of heat exchangers is needed. Thesesoftwares are written to reinforce fundamentalconcepts and ideas and allow design calculations forgeneric configurations with no reference to designcodes and standards used in the heat exchangerindustry.B. Description of Software Step2:The shell and tube heat exchanger design software is As user clicks on the parameters tab, It willdeveloped for use in the teaching of thermal design of ask the user “If you want to change the previouslyshell and tube heat exchangers usually at the senior entered input then click YES else NO”. Theundergraduate level of a mechanical or chemical following window will appear on the screen once youengineering course. It may also be used for the click on YES button. In this window user has to enterpreliminary design of shell and heat exchangers in several input parameters which are needed for furtheractual industrial applications. Developed in Visual analysis. After entering all the parameters click onbasic programming environment, the Microsoft the BACK button.Windows-based Software can be compatible forpersonal computer with at least 250 MB of RAM andat least 2MB of free hard disk space.C. Components of the software The software consists of five options viz.Parameter, Calculations, Sketch, Plots and Print. Thecalculation option allows user to get thermal analysisof the shell and tube heat exchanger to be determinedbased on inputs of fluids temperatures, flow rates,helix angle and dimensional constraints. The user cancall out a sketch screen showing the differentgeometrical configurations of helical baffle heatexchangers. Thermo physical properties of commonfluids are included in the software. The existingdatabases of fluid properties cater for water. Thesoftware allows for user input of thermo physicalproperties of fluids. The inputs taken from user are in Step3:SI system. One more feature is set in this software As you click on the CALCULATIONapart from most software developed for educational button, a new window will appear. Read the noteapplications. Firstly, it calculates different parameters which is mentioned in this window. The inputs whichlike pressure drop, heat transfer coefficient of the are varying every time are taken from the user in thisheat exchanger for particular set of input given. Then step. Enter the shell side and tube side inputs in the 441 | P a g e
  • 6. Professor Sunil S.Shinde, Swapnil R. Jayale, Dr.S.Pavithran / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.437-443respective boxes. The unit in which the input main window.parameter is to be entered is shown. Helix angle alsocan be varied. After entering all varying inputs, clickon calculation button. A new frame will appear in thesame window which will give you all calculatedparameters for particular input. To save thiscalculated results click on the button is shown in“SET OF READINGS” frame. To close this windowat any instant, drag the window to the left side andthen close it. After closing this window background Step 6:calculation Excel sheet will appear. In this sheet user Pressure drop and heat transfer coefficient iscan view the calculations. calculated for varying mass flow rate and helix angle. The calculated values are shown in table for respective mass flow rate and helix angle. From these results various graphs are plotted. User will get print for the saved data after clicking on the print button. It contains all varying parameter and calculated results for respective input parameter. VI. SOFTWARE UTILIZATION IN DESIGN EDUCATION The software is suitable for teaching thermal design of shell and tube heat exchangers to senior undergraduate students in mechanical and chemicalStep 4: engineering and also to train new graduate engineers The sketch of helical baffle heat exchanger in thermal design. Students may be asked to use theis shown in this window. This window will appear software to undertake a few mini projects in shell andafter clicking SKETCH button in the main window. tube heat exchanger design.This sketch shows the flow pattern in the helicalbaffle heat exchanger. The baffle which is shown in VII. LIMITATIONS OF THE SOFTWAREthe 3-d diagram is continuous helical baffle. Since the software is developed in the college with limited manpower and financial resources, it will not have the aesthetic appearance and database of commercially developed ones. At present, thermo physical properties of two fluids are stored in the database. It is a simple though tedious task of incorporating more fluid data into the software. This limitation does not hinder the use of the software and in fact allows the student the opportunity to search for thermo physical data of fluids encountered in engineering applications.Step 5: The calculated results for varying input VIII. CONCLUDING REMARKSparameter are saved in the background. From these Software has been developed for the thermalresults various graphs are plotted. These graphs are design of helical baffle heat exchanger based on thevisible to user after clicking on PLOT button in the Kern method. Students can use it to learn the basics of helical baffle heat exchanger at their own pace. As with the case of all software, it is always in a constant state of development. The addition of a mechanical design and optimization are some of the enhancements are needed in this software. It is hoped that the software will bridge the gap between the 442 | P a g e
  • 7. Professor Sunil S.Shinde, Swapnil R. Jayale, Dr.S.Pavithran / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com Vol. 2, Issue 5, September- October 2012, pp.437-443teaching of fundamentals and industry practice of [2]. Mukherjee R, Effectivedesign Shell andhelical baffle heat exchanger design. Tube Heat exchangers, Chemical EnggNomenclature Progress, (1998), 1-8. [3]. Gang Yong Lei, Ya-Ling He, RuiLi, Ya-Fu Gao, Effects of baffle inclination angle on Symbol Quantity Units flow and heat transfer of a heat exchanger with helical baffles,ScienceDirect-Chemical Engineering and Processing,(2008), 1-10. As Shell Area m2 [4]. Peng B, Wang Q.W., Zhang C., An LB Baffle Spacing m experimental Study of shell and tube heat Cp Specific Heat kJ/kgK exchangers with continuous Helical Dot Tube Outer Diameter m baffles,ASME Journal of Heat transfer, (2007). Dis Shell Inner Diameter m [5]. Hewitt G.F, Shires G.L., Bott T.B., Process DE Equivalent Diameter m heat transfer, (CRC press), 275-285. Heat Transfer Co- αo [6]. Master B.I, Chunagad K.S. Boxma A.J. Kral efficient D, Stehlik P, Most Frequently used Heat Nb Number of Baffles - exchangers from pioneering Research to Pr Prandtl‟s No. - Worldwide Applications, vol. No.6, (2006), PT Tube Pitch m 1-8. Re Reynold‟s Number - [7]. Prithiviraj, M., and Andrews, M. J, Three Total shell side Dimensional Numerical Simulation of Shell- ∆PS Pa pressure drop and-Tube Heat Exchangers, Foundation and μ Dynamic viscosity Kg∙s/m2 Fluid Mechanics, Numerical Heat Transfer ρ Fluid Density kg/m3 Part A - Applications, 33(8), 799–816, Maximum Tube (1998). Vmax m/s [8]. Serth Robert W.,Process heat transfer Velocity principles and application, ф Helix Angle - ISBN:0123735882, 246-270, (2007). [9]. WadekarVishwasEnhanced and CompactACKNOWLEDGEMENTS Heat exchangers – A Perspective from The authors would like to acknowledge process industry, 5th internationalBCUD, University of Pune for providing necessary conference on Enhanced and Compact Heatfinancial support (Grant no. BCUD/OSD/184/09). exchangers: Science, Engineering and Technology, 35-41, (2005).REFERENCES [10]. Wang Qui, Dong Chen Gui, Xu Jing, PengJi [1]. Andrews Malcolm, Master Bashir, Three Yan,Second-Law Thermodynamic Dimensional Modeling of a Helixchanger Comparison and Maximal Velocity Ratio Heat exchanger using CFD, Heat Transfer Design Of Shell-and-Tube Heat Exchanger Engineering, 26(6), (2005), 22-31. With Continuous Helical Baffles, ASME journal, 132/101801, 1-8, (2010). 443 | P a g e