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

Abstract

In many cases of heat treatment of steel products, the heated charge has a porous structure. The examples of such charges include bundles of long steel components e.g., bars. The basic thermal property of the charge in this form is effective thermal conductivity kef. This paper presents the results of experimental examinations of effective thermal conductivity of the porous charge, which is composed from various types of steel long components. Due to the specific nature of the samples, a special measurement stand was constructed based on the design of a guarded hot plate apparatus. The measurements were performed for sixteen different samples across a temperature range of 70–640 °C. The porosity of the samples, depending on the type of components used, ranged from 0.03 to 0.85. Depending on these factors, the effective thermal conductivity ranged from 1.75 to 8.19 W·m−1·K−1. This accounts for 0.03 to 0.25 of the value of thermal conductivity of the solid phase of the charge, which in the described cases was low-carbon steel. It was found that the effective thermal conductivity rises linearly with temperature. The intensity of this increase and the value of coefficient kef depend on the transverse dimension of the components that form the charge. The results may represent the basis for the validation of various models of effective thermal conductivity with respect to the evaluation of thermal properties of the porous charge.

Experimental Investigation of Thermal Contact Conductance in a Bundle of Flat Steel Bars

“…The maximal measurement uncertainty of the effective thermal conductivity at the used experimental stand was 4.6% [13].…”

“…A custom experimental stand-a general view of which is shown in Figure 2a-was used for the measurement [13]. This stand consists of: a heating chamber, a temperature…”

“…A custom experimental stand-a general view of which is shown in Figure 2a-was used for the measurement [13]. This stand consists of: a heating chamber, a temperature measurement system, a control system (consisting of the main heater and guarded heaters) and a cooling system.…”

“…The problem of heat transfer in round bar bundles has been widely analysed by the authors. The works published in this field concerned: determination of the effective thermal conductivity [13][14][15], heat conduction [16], thermal radiation [17][18][19] and free convection [20]. The present article is concerned with the problem of heat transfer in a bundle of flat bars.…”

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

“…The measurements were performed with the use of a custom experimental stand, designed as recommended by the ASTM standards [35,36]. The details on the structure of the stand and measurement procedure, in this case, were described in [37]. The maxi- The measurements were performed with the use of a custom experimental stand, designed as recommended by the ASTM standards [35,36].…”