Modelling and infrared thermal imagery of hot particle curtains

Afshar, Sepideh (2015) Modelling and infrared thermal imagery of hot particle curtains. PhD thesis, James Cook University.

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Abstract

In this research, the behaviours of hot particle curtains are investigated experimentally and numerically. An introduction to particle curtains and their importance in industry is given in Chapter 1, where the broad research aims are stated. These include developing a CFD model of hot particle curtains, to experimentally characterising the curtain bulk properties, and assessing the reliability of experimental methods and predictability of CFD modelling techniques.

Chapter 2 provides a literature review which first outlines typical industrial drying equipment and emphasises flighted rotary dryers, because they are examples of a device in which particle curtains are critical to their performance. Various approaches to modelling flighted rotary dryers were discussed and in particular, the methods used to model particle curtains were outlined. CFD was identified as a powerful tool for modelling particle curtains within flighted rotary dryers. The various Computational Fluid Dynamics (CFD) approaches were described and Eulerian-Eulerian was selected for further consideration because of its simplicity and potential for extracting bulk property predictions. Examples of modelling particle curtains in the literature were discussed in order to choose the most effective methods and equations. Drag and heat transfer were emphasised.

In this thesis, hot particle curtains were simulated using Eulerian-Eulerian CFD. Chapter 3 presents CFD models to generate single particle curtains which are bounded by a rectangular box with slot widths varying between 20mm and 80mm. Particles with mean diameters of 290μm, 400μm and 610μm were modelled. The single particle model in the absence of internal heat conduction, widely used in modelling particle curtains in flighted rotary dryers, was also presented for comparison. Centreline particle temperature profiles from CFD simulations were compared to those derived using the single particle model. The base CFD model was used to derive Reduced Order Models (ROM) suitable for implementation in larger scale process models. Furthermore, CFD simulations of the effects of particle mass flow, particle size, and particle slot width on temperature profiles and heat loss, were investigated using analysis of variance techniques. Good agreement was found between CFD and single particle at low mass flow rates and small particle sizes, but the single particle model was not able to predict the behaviour of particles in curtains at larger particle sizes and higher mass flow rates. A ROM correlation was developed to enable the single particle model to be used as a basis for predicting curtain behaviour. Key properties of particle curtains that were modelled included residence time, curtain area and average solid volume fraction. Methodologies based on image analysis techniques to identify the edges of the curtain from CFD data were also described.

Chapter 4 describes experimental apparatus and methods used to generate hot particle curtains. The primary apparatus consisted of a hopper, perforated plates, wire mesh screens, scale indicator, data logger and oven. Chapter 4 describes the methods used to heat the glass beads, and to ensure particles discharge from the hopper is uniform and consistent. The rate at which particles were discharged was recorded using scale indicator. Infrared and visible cameras were described, and the methods used to capture hot particle curtain images were outlined. The infrared camera was used to capture the temperature of particles. High speed photography, used to measure the initial velocities of the particles was described. Direct thermocouple measurements were outlined.

A variety of image processing techniques to manipulate and filter raw image data were described in Chapter 5. Centreline temperatures and 2D infrared temperature profiles were two key curtain attributes examined in this research. Repeatability of temperature profiles using infrared thermography and thermocouple measurements in various examples was investigated. Thermography repeatability error varied between 0.9% and 2%, and a good repeatability was obtained in thermocouple measurements. Furthermore, the reliability of infrared thermography was investigated qualitatively and quantitatively. The qualitative analysis examined the effect of curtain depth on infrared recorded temperatures at two particle sizes (290μm and 610μm) and varying curtain depths (1.5cm to 15cm). It was found that thermal images were significantly affected by background ambient temperature. Quantitative analysis of the background effect using direct comparison between thermocouple data and thermography was described. There was a good agreement between infrared and thermocouple measurements for the smallest particles (290μm) at both high and low mass flow rates. However, a substantial mismatch was found for the largest particle sizes (610μm). Thermographic models which include data from visible images of curtains were developed to predict true particle temperatures. A final model for each particle size was selected, which was capable of more reliable temperature predictions.

Results and discussion of raw and modelled infrared thermography and CFD model predictions were provided in Chapter 6. The effects of particle size, mass flow rate and slot width on both centreline temperature profiles and 2D infrared thermographic images were examined. The reliability of infrared thermography was investigated, and trends in thermal characteristics of the hot curtains were presented. Results comparing curtain shape derived from both CFD and thermographic data were presented. The strengths and weaknesses of methodologies developed in this thesis, such as the gradient technique in edge detection were discussed in Chapter 6. Methodologies used to extract curtain edge locations from both CFD and thermographic data were successful. A good agreement was found between CFD and thermography curtain edge locations. However, the CFD model failed to predict the edges of the curtain at large slot widths (60mm).

Thermographic data was used to describe conditions where heat transfer in particle curtains can be maximised. A hybrid CFD model was introduced to examine the impact of internal heat conduction of particles because this was recognised to be a model deficiency. Chapter 7 presents the conclusions and recommendations of the research.

Item ID: 45964
Item Type: Thesis (PhD)
Keywords: computational fluid dynamics, computational heat transfer, convection, curtain, drag, drying, Eularian-Eularian, fluid mechanics, heat transfer, infrared thermography, particle curtains, particle dynamics, particles, reduced order model, residence time, thermal energy
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Publications arising from this thesis are available from the Related URLs field. The publications are:

Afshar, Sepideh, Sheehan, Madoc, and Fazlollahi, Amir (2015) Using CFD to derive reduced order models for heat transfer in particle curtains. Progress in Computational Fluid Dynamics, 15 (2). pp. 71-80.

Afshar, Sepideh, and Sheehan, Madoc (2013) CFD and experimental study of convectional heat transfer in free falling particle curtains. In: Proceedings of the 11th International Conference of Numerical Analysis and Applied Mathematics (1558), pp. 2005-2008. From: ICNAAM 2013: 11th International Conference of Numerical Analysis and Applied Mathematics, 21-27 September 2013, Rhodes, Greece.

Afshar, Sepideh, and Sheehan, Madoc (2012) Using CFD to simulate heat transfer in particle curtains. In: Ninth International Conference on CFD in the Minerals and Process Industries, pp. 1-7. From: Ninth International Conference on CFD in the Minerals and Process Industries, 10-12 December 2012, Melbourne, Australia.

Date Deposited: 05 Oct 2016 05:26
FoR Codes: 09 ENGINEERING > 0915 Interdisciplinary Engineering > 091501 Computational Fluid Dynamics @ 33%
09 ENGINEERING > 0915 Interdisciplinary Engineering > 091502 Computational Heat Transfer @ 33%
09 ENGINEERING > 0915 Interdisciplinary Engineering > 091504 Fluidisation and Fluid Mechanics @ 34%
SEO Codes: 85 ENERGY > 8505 Renewable Energy > 850506 Solar-Thermal Energy @ 34%
85 ENERGY > 8507 Energy Conservation and Efficiency > 850703 Industrial Energy Conservation and Efficiency @ 33%
85 ENERGY > 8598 Environmentally Sustainable Energy Activities > 859805 Management of Solid Waste from Energy Activities @ 33%
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