HEAT TRANSFER COEFFICIENT DURING SPRAY COOLING OF VERY HOT SURFACES BY FLAT NOZZLES

článek ve sborníku mimo WoS a Scopus

en

An experimental investigation of spray cooling intensity was carried out to determine the heat transfer coefficient for different spray characteristics on a moving steel surface above the Leidenfrost point. The austenitic steel plate, which had an initial temperature of 1200°C, was cooled by a nozzle moving at a speed of 1 m·min-1 and spraying upwards onto the cooled surface at a distance of 250 mm. To discover the influence of different spray characteristics, flat nozzles were used, which can be sorted into two groups. Each group is comprised of one water nozzle and one mist nozzle tested at two air pressures. The first group operated with a water flow rate of 11 l·min-1 and the second group with a rate of 6 l·min-1 . The nozzles in each group were chosen to give different spray characteristics, while the water flow rate and spray angle are the same for the whole group, therefore the effect of the other parameters of the spray should be revealed and not the water flow rate only. Measurements of heat transfer coefficient (HTC), water impingement density, impact pressure distribution and droplets diameter and velocity are evaluated and used to assess the main factors influencing HTC. The experiments confirmed that the character of cooling intensity differs for different air pressures in one mist nozzle when the water flow rate remains unchanged. It is therefore necessary to find the correlation between HTC and the other parameters rather than only the water flow rate (or water impingement density).

An experimental investigation of spray cooling intensity was carried out to determine the heat transfer coefficient for different spray characteristics on a moving steel surface above the Leidenfrost point. The austenitic steel plate, which had an initial temperature of 1200°C, was cooled by a nozzle moving at a speed of 1 m·min-1 and spraying upwards onto the cooled surface at a distance of 250 mm. To discover the influence of different spray characteristics, flat nozzles were used, which can be sorted into two groups. Each group is comprised of one water nozzle and one mist nozzle tested at two air pressures. The first group operated with a water flow rate of 11 l·min-1 and the second group with a rate of 6 l·min-1 . The nozzles in each group were chosen to give different spray characteristics, while the water flow rate and spray angle are the same for the whole group, therefore the effect of the other parameters of the spray should be revealed and not the water flow rate only. Measurements of heat transfer coefficient (HTC), water impingement density, impact pressure distribution and droplets diameter and velocity are evaluated and used to assess the main factors influencing HTC. The experiments confirmed that the character of cooling intensity differs for different air pressures in one mist nozzle when the water flow rate remains unchanged. It is therefore necessary to find the correlation between HTC and the other parameters rather than only the water flow rate (or water impingement density).

SPRAY COOLING – MIST NOZZLES – HEAT TRANSFER COEFFICIENT – FLAT NOZZLE – EXPERIMENT – COOLING INTENSITY – VERY HOT SURFACES

20.10.2021

Associazione Italiana di Metallurgia

Italy

978-88-98990-24-5

1–10

10