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Proceedings of the Seventh International Conference on Liquid Atomization and Spray Systems

ISBN Druckformat: 89-950039-2-8

Transient Cooling of High Temperature Metal Surface with Impinging Water Sprays


The experimental heat transfer data of a transient cooling for a horizontal heated metal surface with vertically impinging water sprays has been investigated. The measurements of spray characteristics such as droplets size and velocity at various height downstream of spray nozzle were conducted by using Phase Doppler Particle Analyzer (PDPA). A full-cone nozzles with orifice diameter of 1.4∼2.3 mm were used at supply pressure of water ranging of 0.1∼0.4 MPa. The distribution of droplets size, velocity and mass velocity were measured from 0∼0.5 m downstream of spray nozzle. A copper specimen of dimensions 0.1×0.1×0.03 m was used as a heat transfer target. The specimen was heated up to 750 °C and exposed horizontally to the water spray. The spray nozzle was set up vertically above the heat transfer surface and the spray angle was traversed from 0 to 60° in respect of vertical. The temperature history at two positions inside the specimen were recorded with data acquisition system, the first at 3 mm from the upper surface and the second at center of specimen. The surface temperature and heat flux were estimated numerically by solving inverse heat conduction model. An iteration method is presented to estimate the temperatures distribution inside the specimen at time interval of 10-3 s. The evaporation heat transfer coefficient was assumed to obtain the temperatures distribution inside the specimen and adjusted to give temperature difference 0.01 °C between measured and estimated values. The boiling curves of transient cooling at different spray characteristics were obtained. The effect of spray characteristics and spray angle on surface heat flux were investigated. The cooling time is more speed at spray impinging angle α=30° than vertical at We ≤ 10 and mass velocity ≤ 0.143 kg/(m2 ∙ s). The mass velocity of water is the most dominant parameter in film boiling region. The droplet size and impinging velocity has a little effect at high surface temperature, but the evaporation heat transfer decreased with increasing spray angle from vertical. A generalized correlation for evaporation heat transfer for vertical and inclined impinging water sprays has been obtained.
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