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Development of a Semi-Analytical Model Based on the Duhamel Method and the Superposition Principle for the Simulation of Earth-Air Heat Exchanger to Enhance Gas Turbine Performance

Bahmani, Mohammad Hossein | 2024

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 57702 (08)
  4. University: Sharif University of Technology, International Campus, Kish Island
  5. Department: Mechanical Engineering
  6. Advisor(s): Hakkakifard, Ali; Moosavi, Ali
  7. Abstract:
  8. In response to pressing energy crises and environmental concerns, enhancing the performance of existing energy conversion systems, such as gas turbines, and tapping into renewable resources have become critical imperatives. Escalating ambient temperatures poses a notable challenge, hampering the efficiency of gas turbines. This study rigorously explores the feasibility of Earth to Air Heat Exchangers (EAHEs) as a pragmatic solution to cool gas turbine inlet air. This study has two main parts. In the first part, this study puts forward a novel hybrid analytical-numerical model for predicting the performance of HGHEs and in the second part, an exhaustive techno-economic analysis is employed to evaluate the long-term operational viability of EAHE for gas turbine inlet air cooling system. The proposed approach is based on Duhamel’s theorem, modified infinite line source method, and superposition principles that allow fast and straightforward simulation. The suggested model also considers the heat balance on the ground surface, including the convection and radiation heat transfer. The thermal interference between adjacent pipes is also considered via the superposition method. The computational time and performance of the proposed approach are evaluated via several benchmark cases and are compared with the results of a three-dimensional CFD model. The results depicted that the present model can predict well the transient performance of linear HGHEs with various pipe arrangements. Moreover, according to the obtained results, the proposed semi-analytical method is up to 50 times faster than the CFD approach. In addition, the proposed model is easier to code and does not require mesh generation. These features make this method to be more practical for engineering applications. In the second part of current study, the EAHE as the gas turbine inlet air cooling system in investigated. Employing the Taguchi method, the study optimizes the system geometry and pipe arrangement, focusing on four key control factors: pipe diameter, spacing, length and depth. The pivotal optimization criterion is the Levelized Cost of Energy (LCOE), encompassing thermal performance and economic viability. The Net Present Value (NPV) and Discounted Payback Period provide supplementary insights into the economic prospects. Integral to the study is a novel and intricate hybrid analytical-numerical model that simulates the long-term transient operation of EAHE. Findings from a detailed case study unveil an optimized scenario yielding a LCOE amounting to 0.071 $/kWh, accompanied by a substantial NPV of 4.5 million dollars
  9. Keywords:
  10. Gas Turbines ; Earth to Air Heat Exchanger ; Levelized Energy Cost (LEC) ; Taguchi Method ; Duhamel’s Theorem ; Computational Fluid Dynamics (CFD) ; Ground Heat Exchanger

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