Title of Invention	A COOLING PROCESS WITH NANOFLUID FOR COOLING THE STRIP IN THE RUN OUT TABLE OF THE HOT STRIP MILL
Abstract	The invention relates to a cooling process with nanofluid for cooling the strip in the run out table of hot strip mill comprising dispersing the nanocrystalline particles in the fluid characterized in that the said coolant will increase the heat dissipation from the strips as the dispersion of the solid particles in the base medium increases thermal conductivity.

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FIELD OF THE INVENTION The present invention relates to a cooling process with nanofluid for cooling the strip in the run out table of hot strip mill. The invention also relates to a precursor of the development of a cooling agent by nanotechnology. The present invention is intended to be practiced only with the addition of nanofluid. BACKGROUND OF THE INVENTION In the existing practice, slabs are heated in hot strip mill (HSM) and soaked at an elevated temperature (~1200°C) in the furnace, and are subject to subsequent reductions in the Roughing and Fining Mill. The resultant strip coming out from the finishing mill is then cooled on the Run-out Table (ROT) using laminar water jets from the Finishing Rolling Temperature (FRT) (~890°C) to the coiling temperature (~600°C). The coiling temperature (CT) and the cooling rate (CR) are important paramenters at the end of the rolling and mechanical properties in turn. Laminar cooling is an efficient method of cooling for a hot strip for the reason of high value of local heat transfer coefficient between cooling water and hot strip. A Run-out Table (ROT) in a hot strip rolling has a laminar cooling system between the last finishing stand and the down coiler and cooling of the length of the strip over the length of coil is performed in the ROT. The microstructure of the grain size of the strip rolled in Hot Strip Mill is decided by the cooling rate over the length of the coil. The metallurgical transformation from austenite phase to ferrite phase in the grain brings a dramatic change in the mechanical properties of the strip during ROT cooling of the strip. The quality of the final product or the hot strip coil can change for a variation of cooling rate or the coiling temperature. Hence, the cooling rate is important as it in turn determines the metallurgical properties and mechanical properties. If the Mechanical property is uniform or almost same over the length of the coil, the tensile strength, Ultimate tensile strength and % Elongation of the coil is same at every point, which can guarantee better performance of the coil for use. Uniform mechanical properties over the length can be achieved by uniform cooling rate. To have the uniform mechanical property over the length of the coil, the steel manufacturers must ensure the uniform cooling rate over the length of the coil in the ROT of a Hot Strip Mill. The cooling of strip in the hot strip mill in laminar cooling by water exhibits a complete description of heat transfer mechanism. The nature of heat transfer from the bed of ROT is complex as it involves several modes of heat transfer. The strip coming out of the last finishing stand is exposed to air-cooling for a short distance (about 10 meter in the existing steel plants) before it meets first water jet at ~25°C from each cooling bank impinges on the surface of the running strip. Once it hits the hot surface, the strip at a temperature of above 800°C meets water at a temperature of 25°C. This gives rise to boiling heat transfer, which is normally described by boiling curve, as shown in Fig.2. Nukiyama [1] studied first the phenomenon of the boiling heat transfer which is heat transfer to water boiling on submerged metal surface and then elucidate the idea of boiling phenomenon. In case of water impingement on hot strip, there are several vies prevalent in the literature as described earlier and the exact nature of heat transfer is not known very precisely as the change of heat flux and the temperature change is very fast due to the boiling phenomenon and experimental studies for this case are always performed with high speed camera. The different regimes of heat transfer are illustrated in Figure 3 for a water jet impinging on a stationary strip. In zone, I just below the impinging jet, the single phase convection prevails as the jet temperature is very low compared to the high temperature of strip. Outside the stagnation region, the strip temperature increases and boiling starts. Regime II is marked with start of nucleate boiling. And this regime II separates the film-boiling region (Regime III) from the single phase forced convection. A situation occurs when the water jet falling on the vapor layer coalesce to form agglomerated pool due to surface tension and gives rise to regime IV. The pools are found to run away from the strip in a random-walk fashion till they evaporate or lost from the edge of the strip. Heat transfer outside these agglomerated pools takes place by radiation and convection from the dry strip surface. Instead of using water, nanofluid has been perceived as the cooling agent. It is a suspension of solid particles in the size of nanometer. The dispersion of the solid particles in the base medium increases the thermal conductivity. With the addition of 4% volume of cupric oxide nanoparticles. The ethylene glycol exhibits an increase of its thermal conductivity by 40%. Similarly the large amount of increase of the thermal conductivity is noticed by the addition of aluminum oxide nanoparticles dispersed in water. Compared to the normal cooling water the thermal conductivity of the nanofluid is higher and it offers a great promise as a cooling agent for the future. Nanofluids can be described as the coolant for the future. Any particle with the size less than 100 nanometers (nm) falls under the consideration of nanotechnology. Choi [2] has experimentally shown the behaviour of nanoparticles as highly conductive particles. Nanofluids is a solution of nanoparticles of very low volume fraction distributed in quiescent base fluid. It has been found that the 30 nm diameter in volume 0.001 to 6 percent creates thermal conductivity of nanofluid solution as the three times of the base fluid by Choi et al.[3] Eastman et al. [4], Patel et al. [5]. In the study by Choi et al [3] and Eastman et al. [4] the anomalous behaviour in the increase of the thermal conductivity of nanofluid has been reported where the study was related to carbon nanotube and copper nanoparticles. Their findings have stimulated the idea of novel use of nanofuids for better heat transfer mechanism. People have started applying nanofluids in the area of medicine and biomedical engineering. Traditional mathematical model and correlation for thermal conductivity has been found in literature from the work of Maxwell [6] and Hamilton and crosser [7]. Recent attempt to evaluate and establishing a new correlation for the same has been proposed from the experimental work of Xuan and Li [8]. Keblinski et al. [9] have proposed four possible mechanism to provide physical explanation for the increase of thermal conductivity. The four mechanism can be summarized as (1) Brownian motion of the nanoparticles (2) Molecular level layering of the liquid at the liquid / particle interface (3) Clustering effect from the nanoparticles (4) the nature of heat transport in the nanoparticles. The thermal conductivity of metal oxide nanofluids are found to be higher than the base fluid in the work of Lee et al. [10]. Several novel models have been explored for expressing the effective thermal conductivity in recent times. A new model based on Brownian motion of the suspended particles has been developed to explain the effect of the size and temperature on thermal conductivity by Jang and Choi [11]. However, the Limited data obtained from experimental results are used to prove the validity of the most of the correlation developed. Based on Maxwell's theory and average polarization theory, Xue [12] has formulated a thermal conductivity model, which has been compared with the experimental results. Kumar et al. [13] have shown by means of a stationary particle model that thermal conductivity is dependent of the particle size and volumetric concentration. By considering the particle size and the interfacial properties, a correlation has been developed for the calculation of thermal conductivity of nanofluids with interfacial shell by Xue et. Al [14]. Xuan et al [15] analysed the enhanced heat transfer of nanofluids with the help of a dispersion model. In general , it is believed that the advantages of nanofluids are the reduced size and reduced cost. The reason of enhanced heat transfer performance of nanofluids may be attributed to the characteristics of nanoparticles for (1) increased surface area and heat capacity of the fluid (2) more collisions and interaction amongst fluid, particles and flow passage surface enhance the heat transfer performance of nanofluids (3) more turbulence and mixing fluctuation of the fluid. Thus, the above-mentioned prior arts suggest that the thermal conductivity of nanofluids is function of the particle size and interfacial properties. In most of the earlier studies, the focus was concentrated on the study of thermal conductivity or the development of stable nanofluid. It is therefore the object of the invention to achieve the stable form of the nanofluid in a laboratory study for the effective use of nanofluid to achieve the benefit of higher conductivity and translating the same achievement to the application in the plant scale. Another object of the invention is to produce the desired higher rate of cooling in a strip vis- avis the wider range of metallurgical products in a hot strip mill. Although this study is concentrated for the specified plant, the same development can be applied for other plant with required tuning. It is therefore the object of the invention to provide a method for achieving a faster cooling rate which will ensure the coiling temperature in the hot strip mill to be low. List of references The prior state of art of using nanofluids are referred as follows :- [1] Nukiyama, S., 1934, "The Maximum and Minimum Values of Heat Transmitted from Metal to Boiling Water under Atmospheric Pressure", J. Japan Soc. Mech. Eng., 37, pp. 367-374 (Translation: Int. J. Heat Mass Transfer, 9, 1419, 1966) [2] S. Chou, 1995, Enhancing thermal conduction of fluids with nanoparticles, FED 231, 99-103. [3] Choi, S.Z. Zhang, W Yu, F. Lockwood and E. Grulke, 2001, Anomolously hermal conductivity enhancement in nanotube suspensions, Appl. Phs. Lett. 79(14), 2252- 2254. [4] Eastman, J,A, Choi, U,S,Li,S,Yu, W & Thompson, L,J,2001, "Anomalaously increased effective thermal conductivities of ethylens glycol-based nanofluide containing copper nanoparticles", Appl. Phys. Lett, vol. 76, no.6, pp.718-720. [5] Patel H., S. Das, T. Sundararajan, A. Sreekumaran, B. George & T. Pradeep, 2003. Thermal conductivities of naked and monolayer protected metal nanoparticle based nanofluids: Manifestation of anomalous enhancement and chemical effects. Appl. Phs.Lett.83(14), 2931-2933. [6] Maxwell, J.G, 1904. A Treatise on Electricity and Magnetism, second ed.oxford University Press, Cambridge, pp.435-441. [7] Hamiton R.& 0. Crasser, 1962, Thermal conductivity of heterogeneous two- componecnt system, I & EC Fundamentals, 125(3), 187-191. [8] Xuan Y. & Li,2000, Heat transfer enhancement of nanofluids. Int. J Heat Fluid Flow 21, 58-64. [9] Keblinski, P., Phillpot, S.R., Choi, S.U.-S., Eastman, J.A., 2002. Measuring of heat flow in suspension of nono-sized particles (nanofluids) Int. J. Heat Mass Transfer 45, 855- 863. [10] Lee, S. Choi, S.U.S., and Eastman, J.A., Measuring Thermal Conductivity of Fluids Condtaining Oxide Nanoparticles, J.Heart Trabfer, vol. 121. pp.280-289, 1999. [11] Jang S.P., and Choi S.U.S., Role of Brownian Motion in the Enhanced Thermal Conductivity of Nanofluids, Applied Physics Letters, Vol.84, no 21, pp 4316-4318,2004. [12] Xue, Q.Z., Model for Thermal Cxnductivity of Nonofluids, Physics Letters, A, Vol.307 (2003), pp. 313-317 [13] D.H. Kumar. H.E. Patel, V.R.R Kumar, T. Sundararajan, T. Pradeep and S.K. Das, Model for Heat Conduction in Nanofluids, Physical review Letters, Vol. 93 (2004), pp. 144301-1-4 [14] Xue Q. and Xu. W-M., A Model of thermal Conductivity of Nanofluids with interfacial shells, Materials Chemistry and physics, Vol.90 (2005), P. 298. [15] Xuan Y. and Li, Q., Heat Transfer Enhancement of Nanofluids, International Journal of Heat and fluid Flow, Vol.21(2000), pp.58-64. OBJECT OF THE INVENTION It is therefore the object of the invention to provide a method of achieving faster cooling rate over the length of the coil in a hot strip mill by a nanofluid to ensure the lower coiling temperature of the strip. Another object of the invention is to enhance formation of dual phase steel of ferrite- pearlite with optimized grain size and tensile strength at low coiling temperature and thus ensuring wider range of products from a hot strip mill with optimized mechanical and metallurgical properties. DESCRIPTION OF THE IN VENTION The cooling of the strip in the bed of run out table requires a large amount of heat dissipation as the strip temperature is required to be reduced from a temperature range of 880-910°C over a length_of 90 ~ 100 metre. The heat conductivity of water is not very high. The addition of nano-particles with a lower volume concentration in water / base fluid or the suspension of nanoparticles makes the solution an efficient heat conducting liquid. The use of nanofluids increases the thermal conductivity by an amount 40 %. A nanofluid suspension is prepared in the laboratory. The nanofluid prepared from laboratory scale is proposed for use in the cooling of hot strip. This was tested first in a laboratory scale, where the strip from the hot strip mill is heated to a temperature of 900°C and thereafter the strip is cooled by nanofluid. The temperature of the strip is monitored with the time. This invention as a cooling method is specifically developed for hot plate or strip. The proposed invention is applicable to other hot strip mill, provided the similar conditions prevail. The invention has been developed on study of surface temperature of the strip to obtain an efficient cooling method. The steps in the cooling method involved are: • Formation of nanofluid. • Study of the cooling phenomena of hot strip by the use of nanofluid. • Determination of the cooling rate. BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS FIG. 1. Represents general layout of existing strip cooling system in ROT of HSM. FIG. 2. Represents the boiling curve. FIG. 3. Heat Transfer regimes adjacent to a jet impinging on a hot strip FIG. 4. Experimental setup before modification. FIG. 5. Experimental setup after modification. FIG; 6. Plate placed on refractory before pouring nanofluid on it. FIG. 7. Comparison of cooling curves of water and different concentration of nanofiuid, Al203. FIG. 8. Comparison of cooling curves of water, Al203 and clay. DETAILED DESCRIPTION OF THE INVENTION Preparation of nanofiuid : A nanofiuid proposed has been prepared in the laboratory from Alumina nanopartides. Commercially available nanopartides are used for the preparation of the nanofiuid. Commercial nanopartides are procured for alumina. Different concentration of alumina has been prepared. A dispersant of Sodium Hexa-Metaphosphate has been added in the nanofiuid which maintains the stability. For the experimental purpose concentration of 0.5% and 1% has been used. Similarly solution of clay has been prepared. EXPERIMENTAL WORK WITH NANOFLUID: Fig. 4 is the experimental set up that was conceived at the beginning for the cooling of the strip. In this set up, refractory bricks are shown which are used for keeping the hot once the plate is heated inside the furnace upto a desired temperature of 950°C. The same set up has been modified and shown in Fig.5. The plate (a part of the strip from hot strip mill) is fitted with the two K-type thermocouples. The leads of the thermocouples are connected to the data acquisition system and in turn to a computer. The temperature recorded from the thermocouples of the hot plate is stored by the data acquisition. The plate/strip along with the connecting leads is placed inside the furnace for heating upto a temperature of 950°C. It takes about 20 minutes in the furnace to soak the plate. Following the heating of the strip is taken out. Figure 6 shows that the plate is being placed on the refractory bricks after the plate has been taken out from the furnace. Then the solution of the nanofluid is allowed to pour through the jet on the surface of the hot strip. The thermocouple attached to the strip is meant for reading the temperature of the strip with the addition of the nanofluid. The time variation of the strip temperature is recorded to study the cooling behaviour of the strip with the help of nanofluid. For comparison purpose water was used separately to cool the strip. The study is carried out with a 4 mm thick steel plate. Figure 7 depicts the comparison of cooling curve of water and nanofluid of aluminium oxide with 0.5% by wt and 1% by weight. The different concentration of Aluminium oxide, i.e. 0.5% and 1.0% has been used in the cooling experiment. It has been found the nanofluid with higher concentration i.e., 1% by weight of aluminium oxide has cooled the plate at a faster rate compared to the water that is also used for cooling. The initial drop in the temperature before the pouring of nanofluid or water is due to furnace drop-out temperature. As can be found from the results shown in Fig. 7, the quick nature of the dropping of the strip surface temperature has been manifested when the strip is cooled by Aluminium oxide. The same study has been done with silica of different concentration. This result has been shown in Fig. 8. Similar to Fig. 7, fig. 8 shows the nature of the cooling of the strip by clay with different concentration. Even in this case, the gradient of cooling is not steep when clay is used. For comparison purpose the influence of clay at different concentration in the base fluid of water could not cool at a faster rate. The experimental facility in the said laboratory scale will be upscaled and used for cooling the hot strip in the plant with the use of nanofluid. The prepared nanofluid will be used to cool the strip in the plant. Although the study is performed in the laboratory scale, this technology is targeted for cooling the full scale strip in the run out table of the hot strip mill. The pyrometer in the hot strip mill is the instrument for recording the temperature. If Fig 7 and Fig. 8 are observed carefully, it may be noted that the nanofluid of Aluminium oxide is more effective in cooling the strip compared to water. We claim 1. A cooling process with nanofluid for cooling the strip in the run out table of the hot strip mill comprising; - dispersing the nanocrystalline particles in the fluid by suspension of the fluid, the nanofluid having concentration .5-1% by weight of aluminium oxide characterized in that the said coolant will increase the heat dissipation from the strips as the dispersion of the solid particles in the base medium increases thermal conductivity. 2. The process as claimed in claim 1 uses nanofluid to produce the higher amount of heat dissipation from the strip surface of the hot strip mill where the cooling fluid would enhance the more dissipation due to its property. 3. The nanofluid coolant as claimed in claim 1 wherein a dispersant of sodium hexa-meta phosphate has been added in the nanofluid to maintain stability. ABSTRACT DEVELOPMENT OF A NEW COOLANT FOR RUN OUT TABLE OF HOT STRIP MILL The invention relates to a cooling process with nanofluid for cooling the strip in the run out table of hot strip mill comprising dispersing the nanocrystalline particles in the fluid characterized in that the said coolant will increase the heat dissipation from the strips as the dispersion of the solid particles in the base medium increases thermal conductivity.

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