Measuring thermal contact resistance under an impacting droplet of molten metal

An experimental investigation was performed on the thermal contact resistance values between molten metal droplets and metal substrates. Droplet impact was photographed and substrate surface temperature variation under the impacting droplet was measured using ultra fast temperature sensors that were developed especially for the purposes of this research. The thermal contact resistance during the first few milliseconds of impact was obtained by matching measured surface temperature variation with an analytical solution of the 1-D transient conduction equation. The process was repeated for different surface roughness, different impact velocity and different surface contaminations. An analytical model was developed in order to predict the contact resistance values by estimating the true area of contact between liquid metal and a rough solid. The test results agreed well with the analytical model predictions. Thermal contact resistance increased moderately with an increase in surface roughness, decrease in contact pressure and the presence of surface contaminations.