**4.3 Behavior of IHTC for the given Al 6061**

The behavior of the sample rectangular cast was considered as it summarizes most of the heat transfer modes in solidification of the cast. On pouring the IHTC was found to be 370 W/m2 K at 90 s, the higher initial surface heat flux was due to a perfect thermal contact. As further solidification starts, vaporization takes place in the sand mold because of the moisture content, presence of hydrogen release along with metal oxides across the interface and the reduction of specific volume of metal creates an air gap and decreases the value of IHTC rapidly to a minimum value of 163 W/m<sup>2</sup> K at 130 s. The shrinkage of metal causes release of latent heat and rise in the IHTC, then heat transfer reduces once the solid skin is formed [10]. Again the inner metal leaks and flows out from the solid skin to outside and gets cooled which again releases latent heat and so IHTC increases and decreases. Continuous rise and fall of the IHTC shows peak formation, which is shown till the end of solidification. The fourth peak value of 1718 W/m<sup>2</sup> K at 600 s and further again at 720 s the IHTC reached the highest peak value of 1918 W/m2 K. The vapor pressure developed in the sand mold is due to the escape of moisture content to the ambient, which is sufficient to allow the heat to flow from the solidifying metal to sand mold hence the sharp rise in IHTC is observed in the final stage of solidification. Not only vapor pressure but also huge temperature differences causes high heat flows. Due to the thermal resistance induced, as the metal solidifies and contracts, a fall in the IHTC is vividly observed.
