Computational Fluid Dynamics Simulation of Laminar Flow in a Concentric Tube Heat Exchanger - Report Example

School of Engineering Griffith University 6007ENG – Industry Affiliates Program Computational Fluid Dynamics Simulation of Laminar Flow In A Concentric Tube Heat Exchanger Othman A J M JAMAL 2891220 Date of Submission (Include Year and Semester) Griffith University Dr. Peter Woodfield A report submitted in partial fulfillment of the degree of Bachelor of mechanical engineering The copyright on this report is held by the author and/or the IAP Industry Partner. Permission has been granted to Griffith University to keep a reference copy of this report. TABLE OF CONTENTS Project Background Concentric tube heat exchangers are low-cost, effective devices used for heat transfer in many industrial processes. In the third-year undergraduate engineering course 3505ENG Heat and Mass Transfer at Griffith University, many students have found that the double-pipe heat exchangers in the laboratory performed better than expected from theory particularly for laminar flow conditions. This research will investigate and compare the outcomes from theory and experiments for a double pipe heat exchanger. Furthermore, Computational fluid dynamics (CFD) simulation will be used for this comparison as well as enhancing the design further. The objective of this heat exchanger is to cool water which is initially at 60 °C flowing at 1.5 L/min to below 50 °C. The hot water will be cooled by a cold water at 20 °C and flowing at 3.6 L/min. Heat exchangers are used when transferring temperatures from one body to another. The double pipe heat exchange is a simple, affordable and socially accepted heat exchanger. The double pipe heat exchanger has one fluid flowing through a pipe while the other fluid flows between the pipe and another enclosing pipe hence the name concentric pipe connection (Figure1). The flow inside the exchanger can either be counter-current or co-current current flow (Incropera, Dewitt, Bergman, & Lavine, 2013). In this research a counter current flow method will be used as showing in Figure 1. The inner pipe in figure 1 carries the hot water and labelled as H while the cold water flows in the annulus and labelled as C. Figure 1: schematic diagram of the concentric tube heat exchanger with counter flow The Computational Fluid Dynamics (CFD) involves the application of data structures and numerical analysis during the analysis and solution of problems that involve fluid flow. (Hoffmann, & Stein, 2002). The results of the flow evaluation are presented in terms of wall temperature as well as the axial fluids variations. The flow in the double heat exchanger is normally steady until changes are done on the temperature at the inlet or the flow rate. The heat capacity ratio of both liquids and height of the exchanger also has a significant influence on the analysis (Nunge, & Gill, 1966). The process of analysing the heat exchanger begins with a balance of the material and energy. To obtain a complete balance of the energy a few assumptions are done. One, the energy lost from the two pipes or from the u-tube bend to the surroundings is negligible. The transfer of heat from one stream to another is facilitated by the forced convection. The heat energy transferred through the walls of the pipe is conveyed to the stream as it flows. In that way the gradient of the temperature is well maintained. The amount of heat transferred changes with the changes in the pipe conditions such as the fluid properties, the temperatures at the intake, the flow rates as well as the composition of the fluid (Duangthongsuk & Wongwises, 2009). The cost to purchase and work with the concentric tube heat exchangers is low as compared to others and in addition very effective. For this reason, most of the processing industries have adopted the concentric tube heat exchangers for their production process (kk, 2017). Purpose of the Project the purpose of this project is to systematically investigate the performance of a double pipe heat exchanger using computational fluid dynamics and compare this with results from theory and experiment. The outcome results from the experiment explain why the concentric tube heat exchangers in the lab perform better than what is expected. In addition, the results will help in recommending on the best way on how to improve the double pipe heat exchanger to obtain more desired results. Through the project, the cold water flow will be minimized to below 3.6L/min. The project also acts to reduce the temperature of the hot water at the exit to 50o C or below. The prototype will significantly help to explain the process of the design in a more concise manner. In addition, the performance of the design in the experiment will be compared to other heat exchangers available. The comparison helps to evaluate the market prices for the device to be used for the project. The calculations computed from the experiment helps to determine the coefficient of the overall heat transferred between the inner and the outer pipe. The coefficient takes into account the convective and conductive resistances between the inner and outer pipe. expected project outcomes The project is set to systematically investigate the performance of the double pipe heat exchanger by use of computational fluid dynamics and compared with theory and experimental knowledge. The values/data from the simulation should be able to imitate the real project outcomes of: i. Minimizing cold water flow rate below 3.6 L/min. ii. Achieve an exit hot water flow rate below 50o C. The performance of this heat exchanger should be to make sure that these conditions are met and that the results are being delivered as intended. The simulated project design should be able to deliver results as those of the real project designed in the lab (Griebel, Dornseifer & Neunhoeffer, 1998). The Expected results should look like: Experimental CFD Analytical Methodology to be Adopted and Project Schedule The project involved the design and implementation of a double pipe heat exchanger then followed by the testing of this design. Moreover, using CFD simulation has more advantages as compared to experiments and theories, some of the advantages are summarized below: FIGURE 2: SHOWING COMPARISON BETWEEN EXPERIMENTS AND CFD SIMULATION Equipment and human resource are difficult and expensive to transport as compared to CFD software that is portable and easy to use/modify. Finally, enhancing the heat exchanger. The plan is to deliver this project within 14 weeks. Therefore the project task work will be by presented using the Gantt chart. The performance test by use of CFD is a process that uses numerical analysis to solve problems involving fluid flows. Computers perform the calculations necessary to simulate the interaction of fluids with surfaces defined by set parameters. The following are descriptions and justifications as to why a decision on the chosen tasks was considered and why they were the tasks were handled the way they have been handled. Designing & experimenting The heat exchanger will be designed from the available materials in the mechanical engineering lab at Griffith University. The experiments will be done twice to ensure the data are reliable. Furthermore, a data logger will be used while reading the change in temperatures to check for transient effects and improve the accuracy of the results. Theoretical calculations Some of the dimensions to be considered include: FIGURE 3: FIGURE SHOWING IMPORTANT DIMENSIONS OF THE HEAT EXCHANGER Some important formulas are: CFD simulation objectives Computational Fluid Dynamics is the art of replacing Partial Differential Equations that represent conservation laws for momentum, mass, and energy by a set of algebraic equations that can be solved by the use of digital computers. CFD provides the mostly qualitative prediction of fluid flows by: Mathematical modeling (Pdes) Software tools (Pre-, Post processing utilities) Numerical methods (discretization) CFD is an interdisciplinary research area and follows the analysis process as below: 1. Problem Statement-where information about the flow is obtained 2. Mathematical model-PDE+IC+BC 3. Mesh generation 4. Space Discretization 5. Time discretization 6. Iterative solving 7. The CFD software-implementing and debugging 8. Simulating 9. Post process 10. Verification Ethics Issues Related to the Project This research has no ethical issue as discussed previously with the academic supervisor. REFERENCES Duangthongsuk, W., & Wongwises, S. (2009). Heat transfer enhancement and pressure drop characteristics of TiO 2–water nanofluid in a double-tube counter flow heat exchanger. International Journal of Heat and Mass Transfer, 52(7), 2059-2067. Dym, C. L., Little, P., Orwin, E. J., & Spjut, E. (2009). Engineering design: A project-based introduction. John Wiley and sons. Griebel, M., Dornseifer, T., & Neunhoeffer, T. (1998). Numerical simulation of fluid dynamics: a practical introduction. Society for Industrial and Applied Mathematics. Hoffmann, A. C., & Stein, L. E. (2002). Computational fluid dynamics. In Gas Cyclones and Swirl Tubes (pp. 123-135). Springer Berlin Heidelberg. kk, S. (2017). Comparison between four types of heat exchangers. Inclusive-science-engineering.com. Retrieved 16 July 2017, from http://www.inclusive-science-engineering.com/comparison-between-four-types-of-heat-exchangers/ Nunge, R. J., & Gill, W. N. (1966). An analytical study of laminar counterflow double‐pipe heat exchangers. AIChE Journal, 12(2), 279-289. Veldman, A. E. P. (2001). Computational fluid dynamics. Lecture Notes, University of Groningen, The Netherlands. (will not use this) Incropera, F., Dewitt, T., Bergman, T., & Lavine, A. (2013). Principles of heat and mass transfer (seventh ed.). 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