COMPARISON OF HEAT TRANSFER PROPERTIES OF DRY SAND AND MAGNESIUM OXIDE POWDER BY SINGLE-PROBE METHOD

Abstract

The use of magnesium oxide (MgO) powder in electrical heating appliances is based on its thermal and electrical insulating properties. However, dry sand, which is readily available and free on the surface horizon than MgO powder also possesses good thermal and electrical insulating properties that could be utilized in the fabrication of electrical heating devices. In this study, we determined and compared heat transfer properties of dry fine-medium sand (0.125-0.50 mm) and dry coarse sand (0.50-1.00 mm) with those of MgO powder, using the single-probe method. Electrical heating equipment was designed and fabricated with a heating element that generated a heat flux of 18.05Wm-1. From the results obtained, the thermal conductivities of dry fine-medium sand, dry coarse sand and MgO powder were found to be 0.21 m-1K-1, 0.22 Wm-1K-1 and 0.36 Wm-1K-1 respectively. Temperature increase per second were also obtained and found to be 4.75 × 10-2 Ks-1 in dry fine-medium sand, 4.28 × 10-2 Ks-1 in dry coarse sand and 2.03 × 10-2 Ks-1 in MgO powder. Thus, while it took MgO powder 472 s to warm from 30 oC to 40 oC, it took dry coarse sand and dry fine-medium sand only 229 s and 205 s respectively to warm through the same temperature range.