FIELD Of THE INVENTION
The present invention generally relates to reuse of nanoparticle formulations used In steel plant for cooling of hot steel plate. More particularly the Invention relates to a sedimentation process to separate constituent particles In a stable nano fluid formulation for enhancing the usage life of the formulation.
IACKGROUND OF THE INVENTION
It is generally known that use of nano-sized metal-oxldes Increases thermal conductivity and heat transfer properties of base fluids e.g. water, ethylene glycol, forms the basis of nanofluids. Since the early 90's, nanoflulds have been projected as the next generation fluids capable of Increasing heat transfer rate compared to normal fluids under a given set of conditions. However, commercial applications of nonofluld technology have not been realized until recently [1] for cooling of hot steel plates, emulating the condition of hot steel strips in Hot strip

Mill of a Steel Plant. In these applications, the nanofluid is known to have one¬time use, and then disposed off. However, for effective commercial applications, nanofluid formulations need usage-continuity, which inter alia raises a new disadvantage of contamination of the formulation after several cycles at which point, the nana particles must be separated from the circuit and reused if possible. This poses a challenge and one of the possible solutions could be to allow the nanopartides to settle at the bottom using preferably an effective flocculant.
ORJECTS Of THE INVENTION
It is therefore an object of the invention to propose a sedimentation process to separate constituent particles in a stable nanofluid formulation for enhancing the usage life of the formulation.
Another object of the invention is to propose a sedimentation process to separate constituent particles in a stable nanofluid formulation for enhancing the usage life of the formulation which replaces the metallic nanopartides in the formulation with new metallic nanopartides.
A further object of the invention is to propose a sedimentation process to separate constituent particles in a stable nanofluid formulation for enhancing the usage life of the formulation in which mechanical energy is supplied from external source to expedite the separation.

A still further object of the invention is to propose a sedimentation process to separate constituent particles in a stable nanotluid formulation for enhancing the usage life of the formulation, in which one of used ultrasonic horn, ultrasonic bath or electromagnetic stirrer is used to supply mechanical energy.
SUMMARY Of THE INVENTION
Accordingly, there is provided a process for separating nanoparticles from a stable nanofluid formulation using other metallic nanoparticles under variable process conditions wherein nanoparticles consist of particles having dimension less than at least 100 nm, wherein the nanofluid formulation comprises a class of fluid synthesized homogeneousyy dispersed in base fluid, and wherein the base fluid comprises one of water, ethylene glycol and light oils, the method comprising:
adding other metallic nanoparticles with concentration between 0.01 to 10 wt% into the nanofluid formulation, and application of external mechanical energy.
The sedimentation process uses silver nanoparticles into a stable Ti02 nanofluid. The process achieves a quick rate of sedimentaiion using the principle of metal ion absorption at aqueous metal oxide Interface.

BRIEF DESCRIPTION OF THE ACAMPAlYTNG DRAWING
Fig. 1 - Graphically exhibits particle size-distribution of silver nanoparticles as measured.
Fig. 2 - a graphical representation of settling time vs ultrasonication time for different concentrations of silver addition in Ti02 nanofluid.
Fig. 3 - schematic of interaction between n-Ag and Ti02 nanoparticles in water.
Fig.4-XRD of a typical sedimentation sample collected after completion of the process according to the invention.
DETAILED DESCMPTION OF THE INVENTION
Ti02 nanofluid of a fixed concentration was collected from test rig after performing repeated cooling experiments on hot steel plate. The nanofluid samples were stable for the duration of this work. Details of the experiment and the nanoparticle used are discussed elsewhere [1].
Particle size distribution of silver nanoparticles is measured using Nanoparticle Tracking Analysis Technique (Nanoslght LM20). The particle size of the silver nanoparticles as shown in Fig. 1 is Widely distributed from 25 nm to 180 nm.

Silver nanoparticles were added to Ti02 nanofluid in three different concentrations. After the addition of silver nanoparticles, the samples are mechanically stirred using an electromagnetic stirrer to ensure optimum dispersion of silver nanoparticles. After stirring, the nanofluid was ultrasonicated for different times starting from 10 minutes to several hours. The sedimentation behavior of the ultrasonically treated nanofluld was then observed. It was observed that beyond 20 minutes of ultrasonlcation time (UT), there is no significant change in the settling behavior of the treated TiO2 nanofluid. The process was repeated for ultrasonication times of 10, 20 and 30 minutes. The settling behaviour of a sample of TiO2 nanafluid used, was also monitored simultaneously. After each step of the experiment, i.e. (i) after collecting TiO2 nanofluid from the text rig, (Ii) after adding silver nanoparticles (iii) after ultrasonication treatment (iv) at the end of the sedimentation experiment pH of the solution was measured using a digital ph meter. samples of sediments were collected after the process completion to cany out X-ray diffraction study on them.
Figure 2 shows a graph on settfing time vs varying silver nanoparticle concentration taking UT as a parameter. It can be clearly seen that the effect of ultrasonication is less pronounced beyond a certain concentration of silver. The pH of the experimental TiO2 nanofluid collected from the test rig was measured as 7.00. Since, the isoelectrlc point of TiO2 is 6.2[5], it contains negative surface charge. This is considered as the working pH for the work since this is the suitable pH for any operation in plant condition. Metallic silver does notdissociate into silver ion (Ag+) readily, but In this case the silver nanoparticle

due to its higher surface energy leaves an electron and reduces to metallic silver (AgO), the fact that the pH of the solution increases (Table 1) after addition of silver corroborates this. The possible reaction is given as,

These Ag+ ions act as counter ion to the negatively surface charged TiO2 nanopartidles and ultimately neutralizes the surface charge ( Rg 3). The surface charge neutralization of TiO2 nanopartidles result in formation of TiO2 coagulant. These coagulants are heavier and easy to settle
XRD of a typical sedimentation sample is shown in Rg 4 and its shows the peaks of both TiO2 and silver for example peaks at 2θ=25.87° belongs to (011) plane of anatase TiO,, at 28=27.9° belongs to (110) plane of Rutile phase of TiO2 and at 28=38.11° belongs to (111) plane of metallic silver. Such silver TiO2 composites have very novel applications for its phOto activity and antibacterial property, so recovered TiO2 materials can also be used as secondary products for such applications.

Reference Patents
• Rapidly disintegrating tables comprising titanium dioxide nano-powders, 1044/KOLj09 dt. 7.08.2009.
• A Process and Apparatus for application of Coolants to achieve Higher Cooling Rates in the Water Boxes of a Wire Rod Mill - 291/KOL/2009 dt. 16.02.2009.
• A method and Apparatus for achieving higher cooling rates of a gas dUring bypass cooling in a batch annealing furnace of a cold rolling mills 292/KOL/2009 dt.16.02.2009.
• A Process and an apparatus for Large-scale synthesis of nano-fluids 293/KOL/2009 dt. 16.2.2009.
• A method for Faster Cooling Rate by a New Medium For Run Out Table of Hot StrIp Mill (Application No.430/KOL/07).
Reference
[1] Subhrakanii Chakraborty, Anirban Chakraborty, Sumltesh Das, Tridibesh Mukerjee, Debashish Bhattacharjee, Ranjit Kumar Ray, ISU International, 50 (2010), 12+-127).

WE CLAIM:
1. A process for separating nanoparticles from a stable nanofluid formulation
using other metallic nanoparticles under variable process conditions,
wherein nanoparticles consist of particles having dimension less than at
least 100 nm, wherein the nanaftuld formulation comprises class of fluid
synthesized homogenously dispersed in base fluid, and wherein the base
fluid comprises one of water, ethylene glycol and light oils, the method
comprising:
adding other metallic nanoparticles with concentration between 0.01 to 10wt% into the nanofluld formulation; and application of external mechanicl energy.
2. The process as claimed in claim 1, wherein the variable process parameters include solution temperature, pH and mechanical energy supplied externally.
3. The process as claimed in claim 1, wherein the solution temperature ranges between 4 to 65° C, and wherein pH of the solution is between 4 to 11.
4. The process as claimed in claim 1 or 2, wherein the supplied mechanical energy is between 50 watt to 200 watts.

5. The process as claimed in claim 1, wherein the nanoparticle formulation comprises different metallic and non metallic oxides with variable particle size.
6. The process as claimed in claim 5, wherein the different metallic oxides comprise titanium, aluminum, silver, zinc, magnesium, copper and iron oxide.
7. The process as claimed In daim 5, wherein the different non-metallic oxides comprise silicon and Zirconium oxide.
8. The process as claimed in claim 5, wherein variable particle sizes of nanopartlcles is between 5 to 100 nm.
9. The process as claimed In daim 1, wherein metallic nanoparticte comprise silver, gold and copper.

10. A process for separating nanoparticles from a stable nanofluid formulation using other metallic nanoparticles under variable process conditions substantially as herein described and illustrated with reference to the accompanying drawings.