Experimental identification and a model of a local heat transfer coefficient for water – Air assisted spray cooling of vertical low conductivity steel plates from high temperature

摘要

A local heat transfer coefficient (HTC) has been determined for six cases of vertical plates cooling by the water-air assisted sprays. Full cone 60° nozzle operating under pressure of 0.1, 0.25 and 0.4?MPa has been employed. The plates have been made from the Inconel alloy and stainless steel. The Inconel alloy differs to some extend in thermophysical properties from stainless steel. Plate temperature has been measured with thermocouples at 25 points distributed over 1/4 of the cooled surface. The inverse solutions have given HTC as function of surface coordinates and time. The HTC maximum has varied from 3 to 10 kW/(m2?K) over water stream zone. The critical heat flux ranging from 600?kW/m2to 2.5?GW/m2has been obtained depending on pressure, location and plate material. Based on a large set of HTC a model of local HTC as function of pressure, surface temperature and distance from the stagnation point has been developed. The HTC model depends on 15 coefficients which has been determined for Inconel and stainless steel. The HTC model has been validated. Energy extracted from the plate surface and temperature distributions predicted by the model have been compared to data obtained from inverse solutions and temperature measurements. It has been concluded that the model accuracy is sufficient for simulations of water spray cooling of low conductivity steels from 1200?°C to 50?°C.