PERFORMANCE ANALYSIS OF DIFFERENT HEAT EXCHANGER DESIGN USING CFD SIMULATION 1 KVENUMADHAV 2 SUDHANSHU KUMAR

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1 PERFORMANCE ANALYSIS OF DIFFERENT HEAT EXCHANGER DESIGN USING CFD SIMULATION 1 KVENUMADHAV 2 SUDHANSHU KUMAR 3 CHANDRASHEKAR GOUD.V 1 PG Scholar, Department of MECH, Aurora s Scientific, Technological and Research Academy madhav.venu564@gmail.com 2 Assistant Professor, Department of MECH, Aurora s Scientific, Technological and Research Academy sudhanshuk27@gmail.com 3 Associate Professor, Department of MECH, Aurora s Scientific, Technological and Research Academy csgoud10@gmail.com ABSTRACT A heat exchanger is a device used to transfer energyfrom two or more fluids, from a solid surface and a fluid, or from solid particulates and a fluid, at distinctive temperatures and which are in thermal contact. Heat exchangers are one of the important engineering devices in process industries since the efficiency and economy of the process largely depend on the performance of the heat exchangers. In the present study, Double Helical Circular Pipe Heat Exchanger has been designed and analyzed to get maximum Effectiveness. Further, materials of this design have also been varied and analyzed. The materials are considered as Steel, Aluminium, and Copper. The design Double Helical Circular Pipe Heat Exchanger has been done using SolidWorks software. Then analysis is carried out using ANSYS software. After doing analysis in ANSYS software, it has been observed that, (i) Counterflow Heat Exchanger has greater Effectiveness than Parallel flow for all materials, (ii) Copper is best suited material for the heat exchanger as it is giving more effectiveness than Aluminium and Steel, (iii) And Steel is giving less effectiveness than Aluminium. 1.0 Introduction A heat exchanger is a device used to transfer heat between one or more fluids. The fluids may be separated by a solid wall to prevent mixing or they may be in direct contact. They are widely used in space heating, refrigeration, air conditioning, power stations, chemical plants, petrochemical plants, petroleum refineries, naturalgas processing, and sewage treatment. The classic example of a heat exchanger is found in an internal combustion engine in which a circulating fluid known as engine coolant flows through radiator coils and air flows past the coils, which cools the coolant and heats the incoming air. 1.1 Classification of Heat Exchangers There are many types of heat exchangers. Some of them are. Shell and Tube Heat Exchanger Plate Heat Exchangers Plate and Shell Heat Exchanger Pillow Plate Heat Exchanger Fluid Heat Exchangers

2 Dynamic Scraped Surface Heat Exchanger Plate and Fin Heat Exchanger Spiral Heat Exchanger Concentric Tube Heat Exchangers (i) Classification of Heat Exchangers According to the Flow Direction a) parallel flow b) Cross flow c) Counter flow (ii) Classification of Heat Exchangers According to the construction Tubular Heat Exchangers Tubular heat exchangers are built of mainly of circular tubes there are some other geometry has also been used in different applications. Double Pipe Helical Heat Exchanger The double pipe or the tube in tube type heat exchanger consists of one pipe placed concentrically inside another pipe having a greater diameter. The flow in this configuration can be of two types: parallel flow and counter-flow. It can be arranged in a lot of series and parallel configurations to meet the different heat transfer requirements. Double coil heat exchanger is widely used; knowledge about the heat transfer coefficient, pressure drop, and different flow patterns has been of much importance. Fig: Double Pipe Helical Heat Exchanger Advantages of Coils 1. Helical coils give better heat transfer characteristics, since they have lower wall resistance & higher process side coefficient. 2. The whole surface area of the curved pipe is exposed to the moving fluid, which eliminates the dead-zones that are a common drawback in the shell and tube type heat exchanger. 3. A helical coil offers a larger surface area in a relatively smaller reactor volume and a lesser floor area. 4. The spring-like coil of the helical coil heat exchanger eliminates thermal expansion and thermal shock problems, which helps in high pressure operations. 5. Fouling is comparatively less in helical coil type than shell and tube type because of greater turbulence created inside the curved pipes. (ii) Disadvantages of coils 1. For highly reactive fluids or highly corrosive fluid coils cannot be used, instead jackets are used. 2. Cleaning of vessels with coils is more difficult than the cleaning of shells and jackets. 3. Coils play a major role in selection of agitation system. Sometimes the densely packed coils can create unmixed regions by interfering with fluid flow. 4. The design of the helical tube in tube type heat exchanger is also a bit complex and challenging. (iii) Applications of Helical coils Use of helical coil heat exchangers in different heat transfer applications: 1. Helical coils are used for transferring heat in chemical reactors because the heat transfer coefficients are greater in helical coils as compared to other configurations. 2. The helical coils have a compact configuration, and because of that they can be readily used in heat transfer application with space limitations, for example, marine cooling systems, central cooling,

3 cooling of lubrication oil, steam generations in marine and industrial applications. 3. The helical coiled heat exchangers are used widely in food and beverage industries 4. Helical coil heat exchangers are often used as condensers in used in HVACs due to their greater heat transfer rate and compact structure. 5. Helical coiled tubes are used extensively in cryogenic industry for the liquefaction of gases. 6. Used in hydro carbon processing, recovery of CO2, cooling of liquid hydrocarbons, also used in polymer industries for cooling purposes. 1.2 Materials Used For Heat Exchangers A variety of materials are used in the design of tube heat exchangers, including carbon steel, stainless steel, copper, bronze, brass, titanium and various alloys. Generally, the outer shell is made of a durable, high strength metal, such as carbon steel or stainless steel. Inner tubes require an effective combination of durability, corrosion resistance and thermal conductivity. Regular materials used in their construction are copper, stainless steel, and copper/nickel alloy. Other metals are used in device fittings, end bonnets and heads. 1.3 Computational Fluid Dynamics Usually abbreviated as CFD, is a branch of fluid mechanics that uses numerical analyze and algorithms to solve and analyze problems that involve fluid flows. The fundamental basis of almost all CFD problems are the Navier Stokes equations which define any single-phase (gas or liquid, but not both) fluid flow. 1.4 Introductions to ANSYS ANSYS delivers innovative, dramatic simulation technology advances in every major Physics discipline, along with improvements in computing speed and enhancements to enabling technologies such as geometry handling, meshing and postprocessing. 1.5Introduction to SolidWorks SolidWorks is mechanical design automation software that takes advantage of the familiar Microsoft Windows graphical user interface. It is an easy-to-learn tool which makes it possible for mechanical designers to quickly sketch ideas, experiment with features and dimensions, and produce models and detailed drawings. 1.6 Literature Review In this chapter, some important research work has been surveyed on Heat Exchanger. This chapter helps to find the recent development in the area of heat exchanger. This also helps to find out the gap in research work on heat exchanger. Daniel Flórez-Orrego, Walter Arias, Diego Lopez and Hector Velasquez have worked on the single phase cone shaped helical coil heat exchanger. The study showed the flow and the heat transfer in the heat exchanger. An empirical correlation was proposed from the experimental data for the average Nusselt number and a deviation of 23% was found. For the cone shaped helical coils an appreciable inclination of the velocity vector components in the secondary flow was seen, even though the contours of velocity were similar. The study showed that some of the deviations and errors were due to the nonuniform flame radiation and condensed combustion products which modified the conditions of the constant wall heat fluxassumptions.the correlations for the Nusselt number values were not totally reliable. There was no proper data available for the effect of the taper in the local Nusselt number and

4 also the effect of curvature ratio, vertical position and the pitch of the heat exchanger. Timothy J. Rennie studied the heat transfer characteristics of a double pipe helical heat exchanger for both counter and parallel flow.both the boundary conditions of constant heat flux and constant wall temperature were taken. The study showed that the results from the simulations were within the range of the pre-obtained results. For dean numbers ranging from 38 to 350 the overall heat transfer coefficients were determined. The results showed that the overall heat transfer coefficients varied directly with the inner dean number but the fluid flow conditions in the outer pipe had a major contribution on the overall heat transfer coefficient. The study showed that during the design of a double pipe helical heat exchanger the design of the outré pipe should get the highest priority in order to get a higher overall heat transfer coefficient. Jayakumar J.S observed that the use of constant values for the transfer and thermal properties of the fluid resulted in inaccurate heat transfer coefficients. Based on the CFD analysis results a correlation was developed in order to evaluate the heat transfer coefficient of the coil. In this study, analysis was done for both the constant wall temperature and constant wall heat flux boundary conditions. The Nusselt numbers that were obtained were found to be highest on the outer coil and lowest in the inner side. Various numerical analyses were done so as to relate the coil parameters to heat transfer. The coil parameters like the diameters of the pipes, the Pitch Circle Diameters have significant effect on the heat transfer and the effect of the pitch is negligible. Patel H. S. ** Makadia R. N.[1] A Review on Performance Evaluation and CFD Analysis of Double Pipe Heat Exchanger Double pipe heat exchanger is one of simplest type of heat exchanger, generally used for the purpose of sensible heating or cooling. In this paper it describes the different techniques which may help to enhance the heat transfer rate. Heat exchangers are modified in space of annular, also using Nano particle in water and compared with the conventional heat exchanger. Double pipe heat exchanger is practically investigated and results are validated with ANSYS CFX software. Results shows that heat transfer rate of modified heat exchanger are higher than the conventional heat exchanger. As Nano particles dispersed in water can significantly enhance heat transfer rate and also heat transfer rate increase with increase of mass flow rate. From the above literature survey it may conclude that heat transfer augmentation techniques is successful to increase heat transfer performance of double pipe heat exchanger. Heat exchanger with the modification of extended surfaces, twisted tape, and louvered strips are resulted greater heat transfer rate as compared to heat exchanger without modification. As Nanoparticles water can significantly enhance the convective heat transfer and heat transfer rate increases with the increase of mass flow rate. Antony luki.a, Ganesan.M [2] Flow Analysis and Characteristics Comparison of Double Pipe Heat Exchanger Using Enhanced Tubes In this investigation, augmented surface has been achieved with dimples strategically located in a pattern along the tube of a concentric tube heat exchanger with the increased area on the tube side. Augmented surfaces to increasing the heat transfer coefficient with a

5 consequent increase in the friction factor. In this analysis to modify the inner tube of double pipe heat exchanger using dimpled tube. The concentric tube heat exchanger is design from Juin Chen a.et.al. Correlation. In this design the inner tubes consider as the hot flue gas and outer tube is nano fluid. Here In this study the properties of nano fluid from the alumina as the nano fluid with ethyl glycol as the base fluid. a. From this design calculation the heat transfer co efficient is increased compared to plain concentric tube heat exchanger. Similarly the effectiveness is 8% increased compared to plain concentric tube heat exchanger. The theoretical results show that the using dimpled tube in concentric tube heat exchanger gives better performance. The modeling and analysis is carried out to vary the dimple tube cross sections, ellipsoidal and spherical shapes using CFD. Finally the enhanced dimple tube is compare with the theoretical, analytical and analysis the results. From the above literature survey it may conclude that Augmented surfaces to increasing the heat transfer coefficient with a consequent increase in the friction factor. Here investigation dimpled tube is used. From theoretical calculation the overall heat transfer coefficient is increased and also effectiveness of the dimpled tube with concentric tube heat exchanger is increased 8% compare to plain tube concentric tube heat exchanger. Usman Ur Rehman studied the heat transfer and flow distribution in a shell and tube heat exchanger and compared them with the experimental results. The model showed an average error of around 20% in the heat transfer and the pressure difference. The study showed that the symmetry of the plane assumption worked well for the length of the heat exchanger but not in the outlet and inlet regions. The model could be improved by using Reynolds Stress models instead of k-ε models. The heat transfer was found to be on the lower side as there was not much interaction between the fluids. The design could be improved by improving the cross flow regions instead of the parallel flow. 2.0Modeling and Designing of Heat Exchanger Modeling of Double Helical Circular Pipe Heat Exchanger Fig: Profile of Helix Fig: Using Sweep command, Inner Pipe Fig : Generation of Outer Pipe, Double Helical Circular Pipe 3.0 SIMULATION Analysis of Heat Exchangers

6 Analysis has been carried out using ANSYS software considering four different cross-sectional pipes under similar boundary conditions. The different crosssection Heat exchangers are Double Helical Circular Pipe, Double Rectangular Pipe, Double Straight Circular Pipe, and Double Straight Rectangular Pipe. Steel, Copper and Aluminum are used as pipe material. Boundary conditions used for analysis are shown in table 1 Table.1: Boundary Conditions 3.1 Analysis of Double Helical Circular Pipe Heat Exchangerusing Steel under Parallel flow (i) Geometry tool features and outer wall is named as adiabatic wall as shown in fig Fig: Name selection for Parallel flow (iv)model: Viscous model is selected as k-epsilon (2 equations). (v) Materials: Materials are edited/created as per boundary conditions from fluent database. (vi)boundary Condition: The inlet and outlet conditions are defined as velocity inlet and pressure outlet. The walls are separately specified by respective boundary conditions. No slip condition is considered for each wall. Except for tube walls, each wall is set to zero heat flux condition. (vii) Run Calculation: The number of iterations has been set to 500. Simulation results of Temperature, Pressure, and Velocity are shown in table no 2. Table 2: Simulation Results (ii)meshing Fig: Geometry for Meshing (viii) Vectors: The vectors give an idea of flow separation at several parts of the heat exchanger. Fig: Meshing Operation (iii)name selection: The names for walls, inlets, outlets, and fluids are assigned using face and body

7 Table 3: Simulation Results Vectors: (c) Fig: Double Helical Circular Pipe Parallel flow-vector View Temperature, Pressure, (c) Velocity 3.2 Analysis of Double Helical Circular Pipe using Steel under Counterflow The only change in the analysis of Counterflow is name selection. As the two streams flow in opposite directions in Counterflow, the inlets and outlets of hot and cold fluids are interchanged. The remaining steps like Meshing, Models, Material selection, Cell zone conditions, Boundary conditions, Solution initialization, and Run calculation are same as done in case of Parallel flow. Simulation results of Temperature, Pressure, and Velocity are shown in table no 3. (c) Fig: Double Helical Circular Pipe Counter flow-vector View Temperature, Pressure, (c) Velocity 3.3 Analysis of Double Helical Circular Pipe Heat Exchanger using Aluminium under Parallel flow

8 Simulation results of Temperature, Pressure, and Velocity are shown in table no4. Table 4: Simulation Results The only change in the analysis of Counterflow is name selection Simulation results of Temperature, Pressure, and Velocity are shown in table no.5. Table 5: Simulation Results Vectors: Vectors: (c) Fig: Double Helical Circular Pipe Parallel flow-vector View Temperature, Pressure, (c) Velocity 3.4 Analysis of Double Helical Circular Pipe Heat Exchanger using Aluminium under Counterflow Fig: Double Helical Circular Pipe Counterflow-Vector View Temperature, Pressure, (c) Velocity

9 3.5 Analysis of Double Helical Circular Pipe Heat Exchanger using Copper under Parallel flow Materials of inner and outer pipes are changed from Steel to Copper. Simulation results of Temperature, Pressure, and Velocity are shown in table no Analysis of Double Helical Circular pipe Heat Exchanger using Copper under Counterflow The only change in the analysis of Counterflow is name selection. Simulation results of Temperature, Pressure, and Velocity are shown in table no7. Table 7: Simulation Results Vectors: Vectors: (c) Fig: Double Helical Circular Pipe Parallel flow-vector View Temperature, Pressure, (c) Velocity (c)

10 Fig: Double Helical Circular Pipe Counter flow-vector View Temperature, Pressure, (c) Velocity 4.0 Results and Discussion In the present study, Modeling and Analysis has been carried out on Double Helical Circular Pipe Heat Exchanger. Further materials of this design have also been varied and analyzed. ANSYS Fluent software is used to analyze the Effectiveness of heat exchanger and calculated. Effectiveness Calculations: (i) Analysis of Double Helical Circular Pipe Heat Exchangerusing Steel under Parallel flow A h = πr i 2 = m 2 A c = π(r o 2 - r i 2 ) = m 2 Mass flow rate M h = ρa h V = = kg/s M C = ρa c V = = kg/s Heat Capacity rates C h = (C p ) h M h = w/k C c = (C p ) c M c = w/k Heat capacity Ratio R = C min / C max = C h / C c = As, Q = UAθ m Finding UA from the above equation, first Calculated Q and θ m values and substituted. Actual Heat Transfer rate, Q = C min (T h1 - T h2) = ( ) = watts θ 1 - θ 2 θ m = ln(θ 1 /θ 2 ) θ 1 = (T h1 - T c1 ) = = 50 K θ 2 = (T h2 - T c2 ) = = K θ m = 35.80, UA = Q / θ m = NTU = UA / C min = Effectiveness: {-NTU (1+R)} 1 e ε = 1+R ε = Heat capacity, Q = ε C min (T h1 - T c1 ) = ( ) = watts (ii) Analysis of Double Helical Circular Pipe Heat Exchanger using Steel under Counterflow Cross-sectional areas of each fluid flow A h = πr i 2 = m 2 A c = π(r o 2 - r i 2 ) = m 2 Mass flow rate M h = ρa h V = = kg/s M C = ρa c V = = kg/s Heat Capacity rates C h = (C p ) h M h = w/k C c = (C p ) c M c = w/k Heat capacity Ratio R = C min / C max = C h / C c = As, Q = UAθ m Finding UA from the above equation, first Calculated Q and θ m values and substituted. Actual Heat Transfer rate, Q = C min (T h1 - T h2) = ( ) = watts θ 1 - θ 2 θ m = ln(θ 1 /θ 2 ) θ 1 = (T h1 - T c2 ) = = K θ 2 = (T h2 - T c1 ) = = K θ m = 35.82, UA = Q / θ m = NTU = UA / C min = Effectiveness

11 {-NTU (1-R)} 1 e ε = {-NTU (1-R)} 1-R e ε = Heat capacity, Q = ε C min (T h1 - T c1 ) = ( ) Effectiveness PF-[Y VALUE] CF-[Y VALUE] = watts The Effectiveness value for Aluminium and Copper also calculated in the same manner as calculated for Steel. The following table shows Effectiveness values of Double Helical Circular Pipe Heat Exchanger using different materials. Table 8: Effectiveness values of Double Helical Circular Pipe Heat Exchanger Geometry Material Effectiveness Parallel Counterflow flow Helical Circular Pipe Steel Aluminium Copper On the basis of Table no 1, the plots has beenplotted for Effectiveness as shown below Effectiveness CF-[Y VALUE] PF-[Y VALUE ] Steel Effectiveness (c) Fig: Plots showing Effectiveness for Different Materials 5.0 Conclusions 1. It has been observed that, Counterflow Heat Exchanger has greater Effectiveness than Parallel flow for three materials. 2. It has been observed that, Copper is best suited material for the heat exchanger, as it is giving more effectiveness than Aluminium and Steel. 3. And Steel is giving less effectiveness than Aluminium and Copper. 6.0 References 1. Experimental and CFD study of a single phase cone-shaped helical coiled heat exchanger: an empirical correlation. By Daniel Flórez-Orrego, ECOSJune 26-29, Helically Coiled Heat Exchangers by J.S.Jayakumar. Aluminium PF-[Y VALUE] CF-[Y VALUE] Copper

12 3. Numerical and Experimental Studies of a Double pipe Helical Heat Exchanger by Timothy John Rennie, Dept. of Bio-resource Engg. McGill University, Montreal August Experimental and CFD estimation of heat transfer in helically coiled heat exchangers by J.S. Jayakumar, S.M. Mahajani, J.C. Mandal, P.K. Vijayan, and Rohidas Bhoi, 2008, Chemical Engg Research and Design Heat Transfer Optimization of Shell-and-Tube Heat Exchanger through CFD Studies by Usman Ur Rehman, 2011, Chalmers University of Technology. 6. Structural and Thermal Analysis of Heat Exchanger with Tubes of Elliptical Shape by Nawras H. Mostafa Qusay R. Al-Hagag, IASJ, 2012,Vol-8 Issue Numerical analysis of forced convection heat transfer through helical channels Dr. K. E. Reby Roy, IJEST, and July-2012 vol Minton P.E., Designing Spiral Tube Heat Exchangers, Chemical Engineering, May 1970, p Noble, M.A., Kamlani, J.S., and McKetta, J.J., Heat Transfer in Spiral Coils, Petroleum Engineer, April 1952, p Heat Transfer Analysis of Helical Coil Heat Exchanger with Circular and Square Coiled Pattern by Ashok B. Korane, P.S. Purandare, K.V. Mali, IJESR, June 2012, vol-2, issue-6.