Abstract

In order to replace hazardous molten lead baths in the heat treatment of carbon steel wire with environmentally friendly fluidized bed furnaces a better understanding is needed of their heat transfer rates. There has been considerable work done in examining heat transfer rates to large cylinders immersed in fluidized beds, and some on wire sized ones as well, but all previous studies have been conducted on static cylinders. In order to gain a deeper understanding of heat transfer rates to a moving wire immersed in a fluidized bed furnace an apparatus has been constructed to move a wire through a fluidized bed. The heat transfer rates were calculated using the difference in inlet and outlet temperatures, wire speed and the bed temperature. As predicted, correlations for static wire were found to under-predict heat transfer rates at higher wire speeds, so a new correlation was developed by modifying an existing one.

Highlights

  • ˆ To develop a model capable of determining the average heat transfer coefficient and Nusselt number based on available parameters such as inlet, outlet and bed temperatures, as well as wire speed

  • The mixture of 70 and 80 grit particles were newly introduced in this work, and their properties were determined in the following manner: the mean particle diameter was determined

  • While the behavior exhibited in beds of different particles is not identical, there is an overall trend that shows Nusselt numbers increasing with

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Summary

Introduction

This study is primarily focused on heat transfer rates and their relation to wire speeds, but fluidization velocity is a parameter of interest, albeit to a lesser extent. Previous work by Friedman et al (2006) and Masoumifard et al (2008) has shown that for small immersed cylinders, such as the ones in this study, fluidizing velocity does not influence Nusselt number past 2.5 × Umf. Previous work by Friedman et al (2006) and Masoumifard et al (2008) has shown that for small immersed cylinders, such as the ones in this study, fluidizing velocity does not influence Nusselt number past 2.5 × Umf This was confirmed with a set of tests in the present work. To ensure the validity of the tests, it is important to know the fluidizing velocity within a certain threshold. The current flow rate can be calculated using the following:

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