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Transient boiler heat exchanger thermal behaviour analysis
Includes bibliographical references.
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| Main Author: | |
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| Other Authors: | |
| Format: | Thesis |
| Language: | English |
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Department of Mechanical Engineering
2015
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| _version_ | 1867613844178731009 |
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| access_status_str | Open Access |
| author | Gwebu, Excellent Zibhekele |
| author2 | Jestin, Louis |
| author_browse | Gwebu, Excellent Zibhekele Jestin, Louis |
| author_facet | Jestin, Louis Gwebu, Excellent Zibhekele |
| author_sort | Gwebu, Excellent Zibhekele |
| collection | Thesis |
| description | Includes bibliographical references. |
| format | Thesis |
| id | oai:open.uct.ac.za:11427/13230 |
| institution | University of Cape Town (South Africa) |
| language | eng |
| last_indexed | 2026-06-10T12:42:36.158Z |
| license_str | Not specified — see source repository |
| provenance_str_mv | Harvested via OAI-PMH from UCTD — University of Cape Town Open Access Repository |
| publishDate | 2015 |
| publishDateRange | 2015 |
| publishDateSort | 2015 |
| publisher | Department of Mechanical Engineering |
| publisherStr | Department of Mechanical Engineering |
| record_format | dspace |
| source_str | UCTD — University of Cape Town Open Access Repository |
| spelling | oai:open.uct.ac.za:11427/13230 Transient boiler heat exchanger thermal behaviour analysis Gwebu, Excellent Zibhekele Jestin, Louis Mechanical Engineering Includes bibliographical references. Coal fired power plants that were built in the past four decades are aging. The main aging mechanisms are creep and thermal fatigue. Creep results from the high temperatures at which the components operate. Thermal fatigue is due to thermal stresses and these stresses result from temperature gradients within the material. Cycling of these thermal stresses accelerate the creep in a process called creep- fatigue aging. The boiler and its final heat exchangers and headers are the main components that are affected by these mechanisms. The aging of these components results in high maintenance costs, reduction of the plant reliability and availability, and contribute to increased safety risks for the plant and personnel. Therefore, there is a need to understand the steady state and dynamic behaviour of the components of these plants in order to predict the stresses that the material experience. This report discusses an investigation to the possibility of modelling the thermal dynamic behaviour of typical boiler heat exchanger components which have to withstand the highest temperature of a Pulverised Fuel Rankine cycle power plant. Thus, illuminating the issues that need to be addressed in modelling such heat exchangers. Modelling approaches of heat exchangers are systematically presented, starting with the use of exact analytical solutions. This is followed by the application of finite volume numerical method. Finishing off with the use of the Flownex software. The exact analytical solutions are used to characterise the transient temperature distribution in solid materials with simplified heat transfer, highlighting the dependence of the solutions on the Fourier number and Biot number. These solutions are further used to calculate thermal stresses generated in the material, illustrating the relationship between thermal stresses and temperature gradients. Furthermore, a finite volume solution is applied to modelling an infinitely long tube. I t is illustrated that for transient conduction heat transfer problems, the solution depends on both physical space discretisation and time- wise discretisation. The numerical solution is verified against the exact analytical solution. Finally, the Flownex software is used to illustrate the issues that need to be addressed when modelling the transient behaviour of a heat exchanger . For this purpose only the average area discretisation scheme is used since it allows for any generic solid structure to be modelled, provided that the appropriate level of discretization is applied. The Flownex modelling starts by modelling transient conduction heat transfer within an infinitely long tube. The Flownex solution is verified against the finite volume numerical solution. The Flownex solution depends on thickness discretisation, especially for thick cylindrical components. Finite tubes are also modelled on Flownex including axial discretisation and layout simplification of the tubes. Flownex is also used to model a heat exchanger bundle using two methods; a tube by tube method and a method that involves the combination of all ii the tubes into one tube. The product of the thermal resistance and the capacitance of the system governs the transient simulations for both methods. 2015-07-01T08:57:20Z 2015-07-01T08:57:20Z 2014 Master Thesis Masters MSc http://hdl.handle.net/11427/13230 eng application/pdf Department of Mechanical Engineering Faculty of Engineering and the Built Environment University of Cape Town |
| spellingShingle | Mechanical Engineering Gwebu, Excellent Zibhekele Transient boiler heat exchanger thermal behaviour analysis |
| thesis_degree_str | Master's |
| title | Transient boiler heat exchanger thermal behaviour analysis |
| title_full | Transient boiler heat exchanger thermal behaviour analysis |
| title_fullStr | Transient boiler heat exchanger thermal behaviour analysis |
| title_full_unstemmed | Transient boiler heat exchanger thermal behaviour analysis |
| title_short | Transient boiler heat exchanger thermal behaviour analysis |
| title_sort | transient boiler heat exchanger thermal behaviour analysis |
| topic | Mechanical Engineering |
| url | http://hdl.handle.net/11427/13230 |
| work_keys_str_mv | AT gwebuexcellentzibhekele transientboilerheatexchangerthermalbehaviouranalysis |