INTERNATIONAL JOURNAL OF PURE AND APPLIED RESEARCH IN ENGINEERING AND TECHNOLOGY

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1 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 ANAND 1, V K PRAVIN 2, P H VEENA 3 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: PAPER-QR CODE How to Cite This Article: 64

2 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 65

3 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 66

4 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 67

5 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 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. 68

6 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 A s, for hypothetical row of tubes at the shell Equator, given by A s = {(P t D o )*D s *L b} /P t STEP 2: Calculate shell side mass velocity G s and linear velocity U s. G s = m s / A s or U s = G s / ρ s STEP 3: Calculate the shell side equivalent diameter D e. For square pitch: D e = [4*(P 2 t {(π/4)* D 2 o }] / (π* D o ) For triangular pitch: D e = [4*{(P 2 t * 3)/4} {(π* D 2 o )/8}] / [(π*d o )/2] STEP 4: Calculate shell side Reynolds number R es. Or R es = (G s * D e ) / μ s 69

7 R es = (U s * D e * ρ s ) / μ s STEP 5: Calculate shell side Prandtl number P rs. P rs = (C ps *μ s ) / K s STEP 6: Calculate the shell side heat transfer coefficient h s h s = 0.36*( K s / D e )* (R e^0.55)*(p r^0.33)*{(μ s / μ w )^0.14} Note: The value of (μ s / μ w ) ^0.14 = 1, for water. CALCULATION OF SHELL SIDE PRESSURE DROP STEP 7: Calculate the number of baffles on shell side N b. N b = {L s / (L b + t b )} 1 STEP 8: Calculate the friction factor f. f = exp {0.576 (0.19*Ln R es )} STEP 9: Calculate the shell side pressure drop ΔP s. ΔP s = [4* f* G 2 s * D s *( N b +1)] / [2* ρ* D e * {(μ s / μ w )^0.14}] Or = [f* G 2 s * D s *( N b +1)] / [2* ρ s * D e *{(μ s / μ w )^0.14}] CALCULATION OF TUBE SIDE HEAT TRANSFER COEFFICIENT STEP 1: Calculate the tube side cross flow section area A t. A t = {(π* D 2 i ) / 4}*(N t / 2) STEP 2: Calculate the tube side mass velocity G t and linear velocity U t. Or G t = m t / A t U t = G t / ρ t STEP 3: Calculate the tube side Reynolds number R et. 70

8 Or R es = (G t * D i ) / μ t R et = (U t * D i * ρ t ) / μ t STEP 4: Calculate the tube side Prandtl number P rt. P rt = (C pt *μ t ) / K t STEP 5: Calculate the friction factor f. f = {(1.58*Ln R et ) 3.28} ^ (-2) STEP 6: Calculate the tube side Nusselt number N ut. N ut = {(f /2)*(Ret -1000)* P rt } / {1+ (12.7* (f /2)*(P rt ^ (2/3))-1)} STEP 7: Calculate the tube side heat transfer coefficient h i. h i = (N ut * K t ) / D i CALCULATION OF TUBE SIDE PRESSURE DROP STEP 8: Calculate the pressure drop on the tube side ΔP t. ΔP t = [{(4* f* L t * n p ) / D i } + (4* n p )]*[(ρt* U 2 t ) / 2] 71

9 Experimental investigation: Shell side Sl. no Quantity Symbol Value 1 Shell side fluid Water 2 Shell side Mass flow rate(kg/sec) Mt Shell ID(m) Ds Shell length(m) Ls Tube pitch(m) Pt No. of passes n 1 7 Baffle spacing(m) Lb Mean Bulk Temperature( o C) 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 Tube OD (m) Do Tube ID(m) Di Tube thickness(m) Tp Number of Tubes N 18 72

10 7 Tube length(m) Lt Fluid Properties of water Sl. no Property Unit Cold water shell side Hot water tube side 1 Specific Heat (Cp) KJ/kg. K Thermal conductivity (k) W/m. K Density (ƍ) kg/m. s Viscosity (Ω) kg/m CALCULATION For 3 rd reading, SHELL SIDE HEAT TRANSFER COEFFICIENT A s = {(P t D o )*D*L b } /P t = {( )*0.2*.2}/(0.03) = m 2 G s = ms / A s = / = 2.47 Kg/m 2 sec D e = [4*{(P 2 t * 3)/4} {(π* D 2 o )/8}] / [(π*d o )/2] =[4{( * 3/4}{(π* )/8]/[(π* )/2] = m R es = (G s * D e ) / μ s 73

11 = (2.47/0.0325)/ = 91.2 P rs = (C ps *μ s ) / K s = (4.187* )/ = 3.76 h s = 0.36*( K s / D e )* (R e^0.55)*( P r^0.33)*{ (μ s / μ w )^0.14} =0.35*( /0.0325)*( )*( )*1 = W/m 2o K CALCULATION OF SHELL SIDE PRESSURE DROP N b = {L s / (L b + t b )} 1 = {0.800/( )}-1 Nb+1= 3.96 f = exp {0.576 (0.19*Ln R es )} = exp {0.567-(0.19*Ln*91.2)} = ΔP s = [f* G 2 s * D s *( N b +1)] / [2* ρ s * D e *{(μ s / μ w )^0.14}] =[0.754*( )*0.2*3.96]/ [2*1000*0.0325*1] = 0.056Pa CALCULATION OF TUBE SIDE HEAT TRANSFER COEFFICIENT A t = {(π* D 2 i ) / 4}*(N t / 2) = {(π* )/4}*(18/2) = m 2 74

12 G t = m t / A t = / = Kg/m sec U t = G t / ρ t = 16.17/1000 = m/sec R es = (G t * D i ) / μ t = (16.17*0.016)/ = P rt = (C pt *μ t ) / K t = (4.187* )/ = 3.67 f = {(1.58*Ln R et ) 3.28} ^ (-2) = {(1.58*Ln )-3.28}^(-2) = N ut = {(f /2)*(Ret -1000)* P rt } / {1+ (12.7* (f /2)*(P rt ^ (2/3))-1)} ={(0.0304/2)*( )*3.67]/{1+(12.7* (0.0304/2)*(3.67 2/3-1)} =-12.4 h i = (N ut * K t ) / D i = (-12.4* )/0.016 = W/m 2 0 K 75

13 CALCULATION OF TUBE SIDE PRESSURE DROP ΔP t = [{(4* f* L t * n p ) / D i } + (4* n p )]*[(ρt* U t 2 ) / 2] =[{(4*0.0304*0.825*2)/0.016}+(4*2)]*[( 100 0* )/2] = 2.685Pa Sl.no Shell side R1 R2 R3 R4 R5 1 Ms Tci Tco Res Pts Ho ΔPa Uc Results & Graphs Sl.no Tube side R1 R2 R3 R4 R5 1 Mt Thi Tho Ret Prt hi ΔPa

14 REYNOLDS NUMBER MASS FLOW RATE FIGURE 1: REYNOLDS NUMBER V/S MASS FLOW RATE ON SHELL SIDE HEAT TRANSFER COEFFICIENT MASS FLOW RATE FIGURE 2: HEAT TRANSFER COEFFICIENT V/S MASS FLOW RATE 77

15 PRESSURE DROP HEAT TRANSEFR COEFFICIENT FIGURE 3: PRESSURE DROP V/S HEAT TRANSFER COEFFICIENT OVER ALL HEAT TRANSFER COEFFICIENT REYNOLDS NUMBER FIGURE 4: OVER ALL HEAT TRANSFER COEFFICIENT V/S REYNOLDS NUMBER 78

16 MASS FLOW RATE PRESSURE DROP FIGURE 5: MASS FLOW RATE V/S PRESSURE DROP ON TUBE SIDE REYNOLDS NUMBER OVER ALL HEAT TRANSFER COEFFICIENT 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 79

17 A s = Area of the shell side cross flow section (m 2 ). A t = Area of the tube side cross flow section (m 2 ). P t = Tube pitch (m). D o = Tube outside diameter (m). D i = Tube inside diameter (m). D s = Shell inside diameter (m). L b = Baffle spacing (m) L s = Length of shell (m). L t = Length of tube (m). t b = Tube thickness (m). G s =Shell side mass velocity (kg/ m 2 -s). G t = Tube side mass velocity (kg/ m 2 -s). U s = Shell side linear velocity (m/s). U t = Tube side linear velocity (m/s). m s = Mass flow rate of the fluid on shell side (kg/s). m t = Mass flow rate of the fluid on tube side (kg/s). ρ s = Shell side fluid density (kg/m 3 ). ρ t = Tube side fluid density (kg/m 3 ). D e = Shell side equivalent diameter (m) R es = Shell side Reynolds number. R et = Tube side Reynolds number. P rs = Shell side Prandtl number. 80

18 P rt = Tube side Prandtl number μ s = Shell side fluid Viscosity (N-s/ m 2 ). μ t = Tube side fluid viscosity (N-s/ m 2 ). μ w = Viscosity a wall temperature (N-s/ m 2 ). C ps = Shell side fluid heat capacity (kj/kg K). C pt = Tube side fluid heat capacity (kj/kg K). K s = Shell side fluid thermal conductivity (kj/s-m K). K t = Tube side fluid thermal conductivity (kj/s-m K). h s = Shell side heat transfer coefficient (W/ m 2 K). h i = Tube side heat transfer coefficient (W/ m 2 K). N b = Number of baffles. N t = Number of tubes. f = Friction factor. ΔP s = Shell side pressure drop (Pa). ΔP t =Tube side pressure drop (Pa). n p = 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: The Tubular Exchanger Manufacturers Association at: 3. Mukherjee R, Effective design Shell and Tube Heat exchangers, Chemical Engg Progress, (1998), 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 ,

19 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 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, 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 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 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 , Hobler, T, Heat transfer and heat exchangers, WNT, Warszawa, 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). 82