Air gap formation during solidification greatly affects interfacial heat transfer and both must be understood quantitatively for accurate numerical simulation of casting processes, which are needed for fundamental understanding to enable quality improvements. Displacement and temperature in a 23 kg steel ingot and mold were measured simultaneously during solidification using a new experimental system. Interfacial heat transfer coefficients were extracted from the measurement results using an inverse heat conduction model. The evolution of temperature, air gap thickness, and interfacial heat transfer coefficients (IHTC) were quantified during this ingot casting process. The air gap forms earlier and grows larger on the narrow side than on the width side of the ingot. Interfacial heat transfer can be divided into four stages. In the first stage, there is good contact between the steel shell and the mold, so there is no air gap, and IHTC is high: 2700 to 3000 W m⁻² °C⁻¹. In the second stage, an air gap starts to form, so heat transfer decreases sharply. In the third stage, as the air gap thickness continues to grow, its effect weakens. In the fourth stage, even as the air gap continues to grow, IHTC remains almost constant at about 600 W m⁻² °C⁻¹. The IHTC can be predicted reasonably well with a simple equation based on conduction across the measured gap thickness, radiation, and contact resistance based on the measured roughness of the cast surface. Conduction is more important than radiation across the gap, accounting for about seventy percent of the effective IHTC at later times when the gap is large.

凝固过程中气隙的形成会极大地影响界面传热，并且必须定量地理解两者，才能对铸造过程进行精确的数值模拟，这对于基本了解以提高质量是必不可少的。使用新的实验系统，同时测量了凝固过程中23千克钢锭和铸模中的位移和温度。使用逆导热模型从测量结果中提取界面传热系数。在铸锭过程中，对温度，气隙厚度和界面传热系数（IHTC）的变化进行了定量。气隙较早地形成，并且在铸锭的窄侧上比在宽度侧上更大。界面传热可分为四个阶段。在第一阶段⁻²  °C ^-1。在第二阶段，开始形成气隙，因此热传递急剧下降。在第三阶段，随着气隙厚度的不断增加，其作用减弱。在第四阶段，即使气隙继续增加，IHTC仍几乎保持恒定在600 W m ^-2  °C ^-1左右。通过一个简单的方程式，可以基于在测得的间隙厚度范围内的传导率，辐射和基于测得的铸件表面粗糙度的接触电阻，用一个简单的方程式对IHTC进行合理的预测。传导比跨越间隙的辐射更为重要，在间隙较大时，传导约占有效IHTC的70％。