Experimental investigation of air-atomized spray with aqueous polymer additive for high heat flux applications

The experimental investigation of using a water based polymer additive to enhance the spray cooling performance of hot steel plate, has been carried out in the current research. This is essentially important to produce high-strength steel on the run-out table (ROT) of a Hot Strip Mill. The ultra-high heat flux cooling system has been developed using an air-atomized spray, containing dissolved polyvinylpyrrolidone (PVP) in water at different concentration ranges between 10 and 150 ppm and compared with the cooling performance of pure water. To understand the heat transfer mechanism of aqueous polymer solutions, the physical properties such as surface tension, viscosity and thermal conductivity were measured. The cooling experiments were conducted using an AISI 304 stainless steel plate of 6 mm thickness initially kept at a temperature above 900 °C, where the Leidenfrost effect is predominant. In these experiments, the transient temperature data during cooling has been measured with three subsurface thermocouples and this time-temperature history has been used to estimate the surface temperature and the surface heat flux histories using a commercial inverse heat conduction software namely, INTEMP. The results explain that the polymer solution has a significant effect on the enhancement of surface heat flux, critical heat flux, as well as the cooling rate of the test plate. It was observed that an increase in the polymer concentration increases the heat transfer rate up to an optimal concentration; after which it results in a reduction in the rate. A maximum cooling rate of 253 °C/s was obtained with a critical heat flux of 4.212 MW/m2, which can be termed as the higher range of an 'Ultrafast cooling' process. Overall, the aqueous polymer solution can serve as a better heat transfer fluid for high heat flux applications.