Experimental and numerical investigation of contact heat transfer between a rotating heat pipe and a steel strip

A new concept for energy efficient annealing of steel strip comprises of multiple rotating heat pipes. Each heat pipe extracts heat from the cooling strip which is reused to increase the temperature of the heating strip. In this context, the heat transfer between the steel strip and the rotating heat pipe is investigated. When the strip is transported over the heat pipe, gas entrains in the gap. The gas compresses into a uniform gas layer. The contact heat transfer deteriorates due to this phenomenon. A numerical model to quantify the heat transfer between the surfaces is developed. Since there is no direct way to quantify the heat transfer between two moving surfaces, the problem is divided into a gas entrainment and a heat transfer part. The model is validated with experiments executed on a rotating heat pipe test rig. The validation was made varying the strip thickness, specific tension and strip velocity. The results show a uniform gas layer forming within the first 1° of the 180° wrap angle in all cases. The heat transfer is dominated by gas conduction. Results for the uniform gas layer region yield heat transfer coefficients in the range between 4000 and 20,000 W/m²·K.