(262b) Spray Cooling of Hot Steel Plate Using Water Based TiO2 Nanofluid

Samarshi Chakraborty ^a, Surjya Kanta Pal ^b, Sudipto Chakraborty ^a

^aDepartment of Chemical Engineering, Indian Institute of Technology Kharagpur, India.

^bDepartment of Mechanical Engineering, Indian Institute of Technology Kharagpur, India.

Abstract

With the progress in the nanotechnology, in past two decade synthesis of nano-sized particle has become well known reality and with ever increasing demand in heat transfer application and thermal engineering sector, high performance cooling is the need of the hour. Engineered coolant such as nanofluids [1] (particle size less than 100 nm) provides much improved thermo-physical properties (thermal conductivity, surface tension) as compared to conventional coolant (i.e. water, ethanol, etc.) therefore can be implemented for various industrial applications such as power production, air conditioning system, electronics, and steel manufacturing process. On the other hand, spray cooling process is a known technique faster heat extraction in numerous industrial applications, such as electronics, metal manufacturing. Cooling rate at run-out table (Temperature range 900^o-600^o C) helps to achieve desired metal microstructure which in turn leads to improved mechanical properties [2]. The experimental condition maintained during current study is similar to the condition present during the heat treatment of hot steel strip at the run out table. In the present work, TiO₂ nanofluid and spray cooling technique are used to enhance the heat transfer rate of a hot steel plate (initial plate temperature >900^oC) in the aforementioned temperature region. TiO₂ nanoparticle used in this study was synthesized using co-precipitation method [3]. Effect of varying nanoparticle concentration on thermo-physical properties (thermal conductivity, surface tension and viscosity) of nanofluid has been studied in details. A stainless steel plate with a dimension of 10 cm (length) × 10 cm (breadth) × 6 mm (thickness) were used throughout the experiment. A full cone spray nozzle (Manufacturer: Lechler 460-843-17-CG) with a spray angle of 45^o were used during the experiment. The coolant flow rate and spray height were maintained at 16 lpm and 6 cm, respectively. The transient temperature-time data were measured by three K type thermocouple and recorded via data acquisition system (NIcDAQ-9174 and NI 9211 card) for further processing. An inverse heat conduction solver named INTEMP [4] were used to calculate surface temperature and heat flux from the recorded data. The experimental results reveal that with addition of TiO₂ nanoparticle in water, surface cooling rate increases as compared cooling rate achieved by water. However, with increasing surface cooling rate is observed up to an optimum concentration beyond which it starts to decrease again. Maximum cooling rate of 151.4^oC/s was achieved at nanoparticle concentration of 40 ppm which is greater than that achieved by water. Therefore, it can be concluded that TiO₂nanofluid can act as superior coolant in run-out table cooling operation for achieving greater cooling rates.

Table 1: Thermo-physical properties of TiO₂nanofluid at optimum concentration

Keywords: Spray cooling; TiO₂nanofluid; Steel.

Reference:

[1] S.U.S. Choi, Enhancing thermal conductivity of fluids with nanoparticles, in: American Society of Mechanical Engineers, Fluids Engineering Division (Publication) FED, 1995, pp. 99-105.

[2] S.D. Cox, S.J. Hardy, D.J. Parker, Influence of runout table operation setup on hot strip quality, subject to initial strip condition: heat transfer issues, Ironmaking & Steelmaking, 28 (2001) 363-372.

[3] R. Saleh, N. Putra, R.E. Wibowo, W.N. Septiadi, S.P. Prakoso, Titanium dioxide nanofluids for heat transfer applications, Experimental Thermal and Fluid Science, 52 (2014) 19-29.

[4] D.M. Trujillo, H.R. Busby, Practical Inverse Analysis in Engineering with 3.5 Disk, CRC Press, Inc., 1997.