Determination of the Radiation Exchange Factor in the Bundle of Steel Round Bars

Abstract

A method to obtain a radiation exchange factor FR in the bundle of steel round bars is presented. This parameter is required for determination of the radiative thermal conductivity krd, which is one of the basic thermal properties of the bar bundles. In the presented approach, the analyzed parameter is calculated indirectly. The initial point for calculations is the geometric model of the medium defined as a unit cell. Then, for the elements present in this cell, the thermal resistance of both conduction and radiation is determined. The radiation resistance is calculated from the radiosity balance of the surfaces enclosing the analyzed system. On this basis, the radiation thermal conductivity krd is calculated. Next, taking into account the bar diameter, the value of parameter FR is also determined. The analysis is performed at the process temperature range of 200 to 800 °C for three bar diameters: 10, 20 and 30 mm, and for the three porosities of the bundle. Different emissivity of bars in the range of 0.5 to 0.9 was also taken into account. Finally, a relationship that allows calculating the FR factor correlated with the emissivity of the bars and the bundle porosity was established. The krd obtained from the methodology presented and compared with the values calculated directly do not exceed 9%; however, after averaging over the entire temperature range of the process, the difference does not exceed 0.2%.

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

“…This is caused by the phenomenon of thermal radiation between the surfaces of the adjacent components. The intensity of this process is nearly proportional to the third power of the mean absolute temperature of the surfaces that exchanges heat [16,38,39].…”

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

“…The bundles with can have an external or mixed porosity due to the geometry of individual elements. The bundles with an external porosity relate to various types of bars (round, square or flat ones), whereas the charge, which is characterised by a mixed porosity, is made up of hollow components, such as pipes or rectangular sections [12,13]. The second group is coils, which are formed by heated sheets, tapes, wires or blanks [14,15].…”

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

“…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.…”