Influence of impingement temperature and nozzle geometry on heat transfer -: Experimental and theoretical analysis

Based on the earlier studies the most common empirical correlations in the literature predict the impingement heat transfer coefficients rather well at low (close to 100 C) temperatures, but get inaccurate at higher temperatures. Impingement temperatures used in paper drying applications are typically 300 to 700degreesC, and there has been a need to improve the existing heat transfer correlations at high temperature area. This study presents experimental results of impingement heat transfer measurements with a laboratory-scale heat transfer test rig. Five nozzle configurations were measured. The parameters varied in the investigation were nozzle-to-plate distance, nozzle open area, nozzle diameter, impingement velocity and impingement air temperature. Regression model of heat transfer was developed based on the measurement data. A correction factor including the impingement and heat receiving surface temperatures is proposed. The correction factor can be used to improve the existing correlations at large jet to heat receiving surface temperature differences.