Analysing the Contact Conduction Influence on the Heat Transfer Intensity in the Rectangular Steel Bars Bundle

Abstract

Bundles of steel bars, besides metal foams, are an example of cellular solids. Such bundles constitute a charge during the heat treatment of bars. The paper presents a mathematical model of transient heat transfer in a bundle of rectangular steel bars based on the energy balance method. The key element of this model is the procedure of determining the effective thermal conductivity using the electrical analogy. Different mechanisms of heat transfer occurring within the analysed medium (conduction in steel and contact conduction) are assigned corresponding thermal resistances. The discussed procedure involves expressing these resistances with the use of arithmetic relationships describing their changes in the temperature function. Thermal contact resistance has been described with the use of the relationships determined experimentally. As a result of the performed calculations, the influence of contact conduction between the adjacent bars and bundle arrangement on its heating time was established. The results of the calculations show that the heating time of bundles can be lowered by 5–40% as a result of a decrease in the thermal contact resistance. This effect depends on the bar size and bundle arrangement. From the practical point of view, the analysed problem is connected with the optimization of the heat treatment processes of steel bars.

Experimental Investigations of Effective Thermal Conductivity of the Selected Examples of Steel Porous Charge

“…This resistance is dependent, among other things, on the actual contact area A r [43,44]. In the packed beds of the porous charge, this surface depends on the shape of the components and their work accuracy [45]. Any shape errors, and in the case of long components, especially the lack of rectilinearity, leads to a reduction in this surface.…”

The Review of Chosen Methods Used to Investigate Heat Transfer in a Steel Porous Charge

“…Using the model of thermal conductivity, it is possible to analyse the transient temperature field in the treated charge. This type of model, based on the method of energy balance dealing with a charge of rectangular steel bars, was described in [58]. It is a convenient tool, the results of which can contribute to the reduction in energy consumption and emission of pollutants as well as to the increase in production capacity and quality improvement of the finished products.…”

“…In the case of solid elements, the basic thermal property of the treated charge is the thermal conductivity of steel k s [8,9]. However, in many situations, the treated charge has a porous structure [10,11]. Such charges are two-phase granular media with a solid metal skeleton and voids filled with gas.…”

Experimental and Theoretical Studies of the Thermal Contact Conductance for Bundles of Round Steel Bars

“…Bundles of steel bars encountered in metallurgical heat treatment processes are a specific example of such media [8,9]. The bundles of bars presented in Figure 1 are a kind of steel porous charge [10,11].…”