Volume 6, Issue 4 (April 2009)
Experimental Technique for Heat Transfer Measurements on Fast Moving Sprayed Surfaces
An experimental technique for the measurements of heat transfer distribution at spray cooled surfaces is described. The measurements were done at moving surfaces up to a velocity of 12 m/s. The samples of different cross sections (flat, profile, rail, etc.) can move linearly. Different approaches are used for the measurements of heat transfer coefficient (HTC) distribution or heat flux distribution at rotating cylindrical body. An inverse task for the computation of surface temperature, HTC, and heat flux distribution obtained from the measurements conducted for internal transient temperature is described. The paper describes necessary demands on experiment configuration and temperature measurements when studying highly transient processes (fast moving objects under spraying nozzles or high circumferential velocities of rotating surface). The results of HTC distribution for spray cooling are shown and are compared to water impingement density. Influence of water impingement density, water pressure, spray configuration, and surface velocity is studied. Examples for water nozzles and for mist nozzles (water-air) are given. Emulsions and oils are beneficial for some industrial applications of spray cooling. The cooling experiments performed with these liquids provide information about decrease of cooling intensity even for a low concentration of the oils in water. The results comparing the cooling properties of these liquids and their comparison to water are presented.