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Development of convection in high-temperature coil annealing furnaces using rotating cylinders technique

Fatla, Oula 2019. Development of convection in high-temperature coil annealing furnaces using rotating cylinders technique. PhD Thesis, Cardiff University.
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Abstract

The formation of hotspots in HTCA furnaces presents significant engineering challenges. The problem occurs due to lack of fluid recirculation to distribute the heat inside the furnace uniformly. The problem exaggerates when the hotspots cause electrical failure in the heating elements leading to a long process duration and high energy consumption to compensate the thermal deficiency. Therefore, it is important to investigate opportunities for improving fluid mixing in the HTCA furnace to eliminate the formation of hotspots. The main objective of this thesis is to investigate generating fluid flow inside the HTCA furnace. With generating fluid recirculation, the advantages are twofold: it enhances fluid mixing and promotes convection. In this study, a rotating cylinders technique was proposed to generate the fluid recirculation inside the furnace during the annealing process of the grain-oriented electrical steel. The thesis begins with a survey of the energy consumption in the HTCA furnace to set the energy benchmarks. The survey revealed that an annealing process with electrical failure consumed about 8000 kWh extra higher than that of a standard annealing process. The thesis also presents an experimental investigation which was designed to test the validity of the proposed technique on controlling the flow around it when it is placed in a cross flow. The results confirmed that the technique is quite capable of generating flow instabilities around them. A numerical investigation was conducted to simulate the rotating cylinder during the annealing cycle. Six different cylinder arrangements were tested to select the configuration that can offer the best fluid recirculation inside the furnace. Four different rotational rates were used 100, 150, 200, and 250 rad/sec. The results show that a turbulent flow can be generated due to cylinder rotation and its intensity proportional to the cylinder’s rotational rate. The optimal cylinder layout was then tested using a transient model created for this process to examine the effect of the proposed technique on the cycle duration. It was iv found that the optimal cylinder configuration can save the process at least one hour of the heating-up segment.

Item Type: Thesis (PhD)
Date Type: Submission
Status: Unpublished
Schools: Engineering
Uncontrolled Keywords: HTCA Furnaces; Rotating Cylinder Technique; Generating Fluid Mixing; Convection Enhancement; CFD.
Date of First Compliant Deposit: 30 July 2019
Last Modified: 30 Jul 2019 09:34
URI: http://orca.cf.ac.uk/id/eprint/124561

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