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Towards Understanding the Heat Transfer Behavior of Dense Granular Media
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| 자료유형 | 학위논문 |
|---|---|
| 서명/저자사항 | Towards Understanding the Heat Transfer Behavior of Dense Granular Media. |
| 개인저자 | Chilamkurti, Yesaswi Narendra. |
| 단체저자명 | North Carolina State University. |
| 발행사항 | [S.l.]: North Carolina State University., 2019. |
| 발행사항 | Ann Arbor: ProQuest Dissertations & Theses, 2019. |
| 형태사항 | 127 p. |
| 기본자료 저록 | Dissertations Abstracts International 81-03B. Dissertation Abstract International |
| ISBN | 9781085644341 |
| 학위논문주기 | Thesis (Ph.D.)--North Carolina State University, 2019. |
| 일반주기 |
Source: Dissertations Abstracts International, Volume: 81-03, Section: B.
Advisor: Hopkins, Douglas |
| 이용제한사항 | This item must not be sold to any third party vendors. |
| 요약 | Over the past few decades, granular media is gaining attention as a viable option for heat transfer fluids (HTFs). From applications in chemical/material processing industries to state-of-the- art Concentrated Solar Power technologies, many research efforts are studying the use of ceramic particles to maximize the heat transfer efficiency of their systems. In addition, these particle-based HTFs can also serve as thermal storage media and pose limited safety concerns. Hence it is important to understand the particle-scale physics of granular media. With this motivation, the current work focusses on analyzing the different flow and heat transfer mechanisms in densely packed granular media.In the early stages of the work, experimental techniques were employed to understand gravity-driven flow behavior of granular media in vertical circular tubes. Using these results as bench-mark data, computational studies were then implemented to gain deeper insights into the flow. The motion of particles was resolved with a Lagrangian approach using the high-fidelity Discrete Element Method (DEM). These preliminary studies helped in gaining an understanding of the velocity, packing fraction and pressure profiles in gravity-driven dense flows. Literature suggests that the heat transfer behavior of granular media is primarily restricted by the discrete nature of these flows. While previous works acknowledged a relatively high thermal resistance near the wall compared to the bulk of the flow, there was not an in-depth analysis of this phenomenon. Thus, DEM computational studies were conducted to incorporate the microstructure of particles in modelling the wall-adjacent thermal resistance for vertical dense granular flows.To study the heat transfer behavior of granular media, unlike the flow simulations, a two-way coupled computational strategy is mandatory. Hence, the DEM approach is coupled with a Finite-Volume (FV) approach to solve for the heat transfer of both particles and the interstitial air, respectively. The Open-Source library CFDEM Coupling짰 was used in the current study to join the Finite Volume PISO solver of OpenFOAM짰 and the DEM solver of LIGGGHTS짰. Theoretical analyses in the literature suggest the existence of several modes of heat transfer in flowing granular media. Since it is beyond the scope of the current work to analyze all of them, the CFD-DEM heat transfer studies conducted here are restricted to static bed configurations. It was observed that the available heat transfer closure models severely underestimate the thermal behavior. Hence other multi-scale modelling approaches were explored to address these issues. Particle-Resolved Direct Numerical Simulations (PR-DNS) were conducted to obtain high fidelity observations of different particle-scale heat transfer mechanisms. In addition to the conduction and convection heat transfer, an entirely different mechanism of heat transfer was observed in these simulations. This phenomenon - streaming heat transfer - was found to play a significant role in the overall thermal behavior of packed beds. Characteristics of this mechanism were carefully observed, and a theoretical model was developed to capture its behavior. The PRDNS results were used to fine-tune the developed model to make it applicable over a wide range of thermal properties, particle sizes and bed packing fractions. Finally, this model was implemented in the CFD-DEM framework as another closure model. Studies were then conducted to analyze the relative contribution of each heat transfer mode for different thermal properties and void fractions. Further observations were also made to analyze the variation of the effective thermal conductivity of static beds with different thermal and geometrical properties. Thus, the proposed CFD-DEM framework was found to serve as a first step in estimating the particle-scale heat transfer mechanisms with less computational expenditure, which can be implemented for mostfuture granular systems. |
| 일반주제명 | Mechanical engineering. |
| 언어 | 영어 |
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