WO2016203334A1

WO2016203334A1 - Carbon nanotubes based hybrid automotive coolant

Info

Publication number: WO2016203334A1
Application number: PCT/IB2016/053253
Authority: WO
Inventors: Amitabh Kumar JAIN; Srinivas VADAPALLI; Annaji Rajiv Kumar TOMPALA; Venkat Chalapathi Rao Peddy; Venkateswarlu Choudary Nettem; Sri Ganesh GANDHAM
Original assignee: Hindustan Petroleum Corporation Limited
Priority date: 2015-06-15
Filing date: 2016-06-03
Publication date: 2016-12-22

Abstract

A composition is provided. The composition includes carbon nanotubes (CNTs) and a base fluid. The carbon nanotubes are dispersed in the base fluid. The carbon nanotubes are functionalized prior to the dispersion of the carbon nanotubes the base fluid. A method for preparing a composition is provided. The method includes subjecting carbon nanotubes (CNTs) to a ball milling process to reduce the length of the CNTs; oxidation of the ball milled CNTs to functionalize the CNTs, and dispersion of the oxidized ball milled CNTs in a base fluid.

Description

CARBON NANOTUBES BASED HYBRID AUTOMOTIVE COOLANT

BACKGROUND

Field

[0001] The subject matter in general relates to coolant additives. More particularly, but not exclusively, the subject matter relates to dispersion of carbon nanotubes in coolant to enhance the functionality/properties of the coolant.

Description of related field

[0002] Coolants have been widely used in automotive engines to prevent the engine from overheating, by transferring the heat generated within the engine. Traditional coolants used in an automotive vehicle may be a fluid such as water or ethylene glycol to which various additives were added to enhance the thermal heat transfer efficiency rate of the fluid. However such fluids have certain demerits.

[0003] Dispersion of nanoparticles in a base fluid is known in the art. The nanoparticles dispersed in the base fluid may be a metal or metal oxide. It has been observed that, the use of metal nanoparticles in the base fluid may result in theproduction of insoluble corrosion products that may block the radiator and reduce the heat transfer rates. Furthermore, it had been observed that metal oxide particles like Α1₂0₃ and Si0₂ may erode the seal of a radiator, thereby leading to leakage of the coolant due to their extreme hardness property.

[0004] In order to address the aforementioned problem, metal or metal oxide nanoparticles were replaced by carbon nanotubes, since the carbon nanotubes did not react with the base fluid, did not react under oxidative environment and had low hardness property. However, the aforementioned technique had certain disadvantages. The carbon nanotubes being hydrophobic in nature, are not soluble in any known base fluid in the prior art. The length of the carbon nanotubes is another hindrance for proper dispersion of the carbon nanotubes in the base fluid. Therefore, surfactants have been used to stabilize the dispersion of the carbon nanotubes in the base fluid. However, the use of surfactants had resulted in formation of large amount of foam.

[0005] In light of the foregoing discussion there may be a need for an effective composition, which may address the aforementioned problems.

SUMMARY

[0006] In an embodiment, a composition is provided. The composition may include carbon nanotubes and a base fluid. The carbon nanotubes are dispersed in the base fluid. The carbon nanotubes may be functionalized prior to dispersion in the base fluid.

[0007] In another embodiment, a method for preparing a composition is provided. The composition may be prepared by subjecting carbon nanotubes to a ball milling process to reduce the length of the carbon nanotubes. The ball milled carbon nanotubes are oxidized to functionalize the carbon nanaotubes. Further, the oxidized carbon nanotubes are dispersed in a base fluid.

BRIEF DESCRIPTION OF DRAWINGS

[0008] Embodiments are illustrated by way of example and not limitation in the Figures of the accompanying drawings, in which like references indicate similar elements and in which:

[0009] FIGs. 1A- IB are graphs illustrating the variation of viscosity with change in temperature on dispersion of various concentration of CNTs in a base fluid diluted with water in the ratk>70:30 (water : base fluid) and 50:50 respectively;

[0010] FIGs. 2A- 2B shows the effect of shear rate on a shear stress at a temperature of 55°C on dispersion of various concentration of CNTs in a base fluid diluted with water in the ratio 50:50 (water : base fluid) and 70:30 (water : base fluid) respectively;

[0011] FIGs. 2C- 2D shows the effect of shear rate on the shear stress at a temperature of 90°C on dispersion of various concentration of CNTs in the base fluid diluted with water in the ratio 50:50 (water : base fluid) and 70:30 (water : base fluid) respectively;

[0012] FIGs. 3 A - 3D are graphs illustrating the variation of thermal conductivity with temperature change on dispersion of CNTs in a base fluid diluted with water in the ratio 70:30 (water : base fluid) and 50:50 respectively; and [0013] FIGs.4A - 4B are graphs illustrating variation in cumulative weight loss within an exposure time on dispersion of CNTs in a base fluid diluted with water in the ratio 50:50 (water: base fluid) and 80:20 to determine the rate of erosion respectively. DETAILED DESCRIPTION

[0014] Embodiments relate to the field of coolant additives. More particularly, but not exclusively, embodiments may relate to dispersion of carbon nanotubes in the coolant to enhance the functionality /properties of the coolant.

[0015] In an embodiment, a composition is disclosed, which may be used as coolant for automotive engines. The composition disclosed may include carbon nanotubes, a hybrid coolant as a base fluid and a coupling agent. The carbon nanotubes used are reduced in length by a mechanical process. The carbon nanotubes so obtained are further oxidized for addition of functional groups on the surface of the carbon nanotubes. A coupling agent is mixed with the functionalized carbon nanotubes, prior to the dispersion of the carbon nanotubes in the base fluid. The coupling agent helps in stabilizing the dispersion of the carbon nanotubes in the base fluid.

[0016] The following detailed description includes references to the accompanying drawings, which form a part of the detailed description. The drawings show illustrations in accordance with example embodiments. These example embodiments, which may be herein also referred to as "examples" are described in enough detail to enable those skilled in the art to practice the present subject matter. The embodiments can be combined, other embodiments can be utilized, or structural, logical, and design changes can be made without departing from the scope of the claims. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope is defined by the appended claims and their equivalents.

[0017] In this document, the terms "a" or "an" are used, as is common in patent documents, to include one or more than one. In this document, the term "or" is used to refer to a nonexclusive "or," such that "A or B" includes "A but not B," "B but not A," and "A and B," unless otherwise indicated. [0018] In an embodiment, a composition including carbon nanotubes, a base fluid, and a coupling agent is provided. The composition disclosed has enhanced properties, which may include high thermal conductivity, anti corrosive properties, and cavitation erosion, among others.

[0019] In an embodiment, the composition may also be referred as a nanofluid. [0020] In an embodiment, the carbon nanotubes (CNTs) used in the composition is a multi walled carbon nanotube (MWCNT). It shall be noted that a person skilled in the art may use others types of carbon nanotubes for example, single walled carbon nanotube (SWCNT) in the disclosed composition.

[0021] The carbon nanotubes used in the composition are synthesized by a chemical vapour deposition method (CVD). The CVD method is well known in the art, and therefore has not been described in detail. It shall be noted that, the carbon nanotubes may be synthesized by other process, such as arc discharge, laser ablation, flame synthesis, and high pressure carbon monoxide, among others.

[0022] The multi walled carbon nanotubes (MWCNTs) with diameter 20 nm to 50 nm and length 10 microns to 25 microns are synthesized by the aforementioned process i.e. CVD method. The MWCNTs formed are of long length, which is undesirable. The long length of the MWCNTs may result in entanglement of the MWCNTs, thereby forming agglomerates in the base fluid. The formation of agglomerates in the base fluid may result in poor dispersion of the MWCNTs in the base fluid. [0023] In an embodiment, the length of the MWCNTs is reduced prior to dispersion of the MWCNTs in the base fluid. The MWCNTs are subjected to a mechanical process. As an example, ball milling process is used to reduce the length of the MWCNTs. The ball milling process is performed for a time period ranging from 12 hours to 16 hours.

[0024] In an embodiment, the length of the MWCNTs is reduced to about 1 micron, after ball milling the MWCNTs. It shall be noted that, the ball milling process is not described in detail as the ball milling process is a well known process.

[0025] Carbon nanotubes produced by the CVD method are hydrophobic in nature. Due to its hydrophobic nature, the MWCNTs are not soluble or less soluble in any solvent. Further, the MWCNTs may have poor adhesion to the base fluid. [0026] In an embodiment, MWCNTs are chemically modified to overcome the aforementioned problem. The MWCNTs are chemically modified by oxidation process. The oxidation of the MWCNTs facilitates the introduction of functional groups on the surface of the MWCNTs. The functional groups may include polar groups such as -COOH, and -OH groups, among others. The oxidized MWCNTs will be hydrophilic in nature, thereby facilitating improved solubility of the MWCNTs in the base fluid.

[0027] In an embodiment, the MWCNTs are oxidized after the MWCNTs are subjected to the ball milling process. The ball milled MWCNTs are oxidized in an acidic medium.

[0028] In an embodiment, the MWCNTs are refluxed in the acidic medium to carry out the oxidation process. The acidic medium may be a solution, which is a mixture of sulphuric acid and nitric acid in the ratio 4: 1. The MWCNTs are refluxed in the acidic medium for about 3- 4 hours at a temperature maintained between 107 °C and 108 °C.

[0029] In an embodiment, the time period to carry out the reflux process is restricted to the aforementioned range, as the oxidation of the MWCNTs for prolonged time period may damage the structure of the MWCNTs. Further, other acids such as, perchloric acid may also be used to oxidise the MWCNTs.

[0030] After the completion of the reflux process, the solution of MWCNTs is washed with water to neutralize the pH of the solution. The solution is further filtered to separate the MWCNTs. The residual MWCNTs obtained after filtration is dried under vacuum conditions to get oxidized MWCNTs powder. [0031] In an embodiment, dispersion of the oxidized MWCNTs in the base fluid may enhance the functionality or properties of the composition. The base fluid may include ethylene glycol, sebasic acid, tolyltriazole, sodium nitrite, and sodium hydroxide.

[0032] The base fluid is prepared by mixing chemicals such as sebasic acid, tolyltriazole, sodium nitrite, and sodium hydroxide in ethylene glycol. Weighed quantity of the aforementioned chemicals are added in the weighed quantity of ethylene glycol and mixed thoroughly in a bath sonicator.

[0033] In an embodiment, the base fluid may also be referred as a hybrid coolant. The base fluid may be composed of 90 - 95% of ethylene glycol, 2 - 5 % of sebasic acid, 0.05 - 0.3 % of tolyltriazole, 1 - 3 % of sodium nitrite, and sodium hydroxide to maintain the pH of the base fluid to about 8.5.

[0034] The weight percent of carbon nanotubes to be dispersed in the base fluid may be between 0.025 and 0.1 % of the base fluid. [0035] In an embodiment, the base fluid may be diluted with water. The base fluid may be diluted with water in the ratio 20:80 (base fluid: water), 30:70(base fluid: water), or 50:50 (base fluid: water). The base fluid may be used in automotives upon dilution with water.

[0036] In an embodiment, the base fluid may be diluted with water in the ratio 20 to 50:80 to 50 (base fluid: water). [0037] In an embodiment, the composition may include a coupling agent. The coupling agent added to the composition helps in stabilizing the CNT's dispersion in the base fluid.

[0038] In an embodiment, Gum Arabic is used as a coupling agent. The addition of gum Arabic improves the adhesion behaviour of the CNTs with the base fluid.

[0039] In an embodiment, the amount of Gum Arabic used is based on the amount of CNTs being used. The amount of gum Arabic and CNTs used is in the ratio 1:1. Equal amount of gum Arabic and CNTs are mixed in water; the mixture so obtained is sonicated for about 45 minutes.

[0040] In an embodiment, the CNTs so obtained are dispersed in the base fluid.

[0041] In an embodiment, the CNTs so obtained are dispersed in the diluted base fluid. [0042] The composition may be prepared by dispersing a mixture of carbon nanotubes and the coupling agent in the base fluid using a physical agitation method. The agitation method facilitates the formation of a stable suspension of the carbon nanotubes in the base fluid. The physical agitation methods may include high shear mixing, such as with a high speed mixer, homogenizers, micro fluidizers, high impact mixing, and ultrasonication methods. [0043] In an embodiment, the physical agitation method used is preferably ultrasonication. The mixture may be sonicated in a probe type sonicator at a frequency of 10 KHZ at a power level of 100 W.

[0044] The addition of gum Arabic helps in improving the stability of the CNTs in the base fluid, however if the ratio of Gum Arabic exceeds the aforementioned ratio, it may result in the formation of large amount of foam, which is undesirable.

EXAMPLES [0045] The following examples illustrate the improved thermal heat conductivity, anti- corrosive properties and stability of the composition. The following examples are given for illustration purpose only, and should not be construed as the limiting the scope of the present invention. To carry out the study, the base fluid is diluted with water in the ratio 80:20 (water : base fluid), 70:30 (water : base fluid), and 50:50 (water : base fluid) to analyse the various properties of the composition.

[0046] The stability of the composition is measured using dynamic light scattering techniques in terms of changes in zeta potential. Zeta potential is a key indicator to determine the stability of colloidal suspension. Table 1 provided below shows an increase in the value of zeta potential after time span of two months, as compared to the value of zeta potential in the first day upon dispersion of CNTs in the base fluid. Further, the value of zeta potential also increases upon agitation.

Table 1

[0047] In an embodiment, the stability of the composition is achieved by adding the coupling agent. A foaming tendency test as per ASTM D 1881 to check the foam break time for the composition was performed. From Table 2 provided below it has been observed that, the foam break time for the composition are within normal limits i.e. less than 5 seconds, and hence CNTs dispersed along with Gum Arabic is used for further analysis.

Table 2

[0048] Measurement of viscosity:

The viscosity of the composition was measured with Wells-Brookfield Cone and Plate Viscometer. FIGs 1A -IB are graphs showing a variation in viscosity with the change in temperature. A mixture of water and the base fluid without CNTs, in the ratio 50:50(water : base fluid) and 70:30(water : base fluid) were considered as a reference sample for the study. In the graph, X axis represents temperature and Y axis represents viscosity. From the graph plotted, it has been observed that, with an increase in the temperature, the viscosity decreases. Further, a moderate increase in the viscosity is observed when the mass fraction of the carbon nanotubes is more than 0.05%. Furthermore, the flow behaviour index of the composition is evaluated. FIGs 2A- 2B are graphs showing a variation of shear stress with shear rate for the CNTs dispersed base fluid(composition) at a temperature 55° C respectively. A mixture of water and the base fluid without CNTs in the ratio 50:50 (water : base fluid) and 70:30 ( water : base fluid) were considered as a reference sample for the study carried out at 55° C and 90°C. FIGs 2C- 2D are graphs showing a variation of shear stress with shear rate for the CNTs dispersed base fluid/composition at a temperature 90° C respectively. In the graph X axis, represents the shear rate in seconds, and Y axis represents the shear stress in N/m . From the graphs plotted, it has been observed that, the shear stress and shear rate are varying almost linearly with intercept towards the origin, which is the characteristic of Newtonian fluids.

[0049] Thermal conductivity measurement

A thermal analyzer KD2 pro had been used to measure the thermal conductivity of the CNTs dispersed base fluid. The thermal analyzer KD2 pro uses the transient line heat source method to measure the thermal conductivity. Further, the thermal conductivity was measured in the temperature range of -50°C to 150°C within an accuracy of 5 %. Graphs illustrated in FIGs 3A and 3B show an increase in the thermal conductivity of the CNTs dispersed base fluid. In this graph, the X axis represents temperature in Celsius, and Y axis represents the thermal conductivity in watts per meter kelvin ((W/ (m. K)). A mixture of water and the base fluid without CNTs, in the ratio 70:30 and 50:50 were considered as a reference sample for the study. It has been observed that, with an increase in the weight fraction of CNTs from 0.025% to 0.1%, the thermal conductivity of the CNTs dispersed base fluid increases as compared to the reference sample. [0050] Heat transfer studies on test rig: A heat exchanger test rig was performed to analyse the improvement of heat transfer with the dispersion of the carbon nanotubes in the base fluid. The improvement of the heat transfer was evaluated by using calorimetric method. The test rig includes a car radiator (air to liquid heat exchanger) placed in a wind tunnel to simulate the actual radiator conditions. The test rig used in the study was an air cooled heat exchanger similar to a car radiator (used in Maruti Suzuki Alto Engine).

Experimental conditions: Air velocity 5 - 15 m s ( 18 KM/hr to 54 KM/hr)

Flow rate of fluid 10 LPM to 20 LPM

Temperature of fluid 80 °C to 105 °C

Evaluation of mean heat transfer coefficient, hi or hnf: q = mC [T_hl - T_hl\ = A. (Τ_Β - T_w ))=U_l A. AT_lm

Where ΔΓ.

CI - cold water inlet, C2- cold water outlet, HI -hot water inlet, H2- hot water outlet, m = Mass flow rate (kg/sec), Cp = Specific heat (kJ/kg-K), nf = nanofluid, T_Hi = Temperature of water at inlet of radiator in °C, T_H2 = Temperature at outlet of radiator in °C, A = Heat transfer area in m², Tci = Temperature at inlet of air to radiator in °C, Tc₂ = Temperature of air at outlet of air in °C, ΔΤ = Temperature difference, lm = logarithmic mean, q = heat transfer rate in W, i = Inside.

Evaluation of overall heat transfer coefficient, Ui

It is evaluated using the following equation q = mC [T_hl - T_h7 \= A. (Τ_Β - T_w ))=U_l A, AT_lm where, Cp = Specific heat (kJ/kg-K), nf = nanofluid, m = Mass flow rate in kg/sec, T_Hi = Temperature of water at inlet of radiator in °C, T_H2 = Temperature at outlet of radiator in °C, A = Heat transfer area in m , i = Inside, T_B = Bulk mean temperature, Tw = wall temperature in °C, U = Overall heat transfer coefficient in W/m -K, ΔΤ = Temperature difference, lm = logarithmic mean, and hi = Heat transfer coefficient in W/m -K. The heat transfer studies were conducted with a mixture of base fluid and water in the ratio's 30:70 and 50: 50 in which 0.025 %, 0.05 % and 0.1 % CNTs were dispersed.

Tables 3A- 3C and 3D- 3F represent test results for water: base fluid (70:30) and water: base fluid (50:50) in different velocities to evaluate the heat transfer coefficient. Table 3A: Water: base fluid (70:30), velocity- 5m/s:

Table 3B: Water: base fluid (70:30), velocity - lOm/s:

Table 3C: Water: base fluid (70:30), velocity- 15m/s

Ui Ui Ui Ui

W/m²- W/m²- % W/m²- % W/m²- % K K change K change K change

500 512.21 609.92 16.02 679.52 24.62 697.9 26.61

1000 591.81 674.57 12.27 760.02 22.13 789.6 25.05

1500 671.41 739.22 9.17 840.52 20.12 881.3 23.82

2000 751.01 803.87 6.58 921.02 18.46 973 22.82

2500 830.61 868.52 4.36 1001.52 17.07 1064.7 21.99

15

m/s 3000 910.21 933.17 2.46 1082.02 15.88 1156.4 21.29

Average 711.21 771.545 7.82 880.77 19.25 927.15 23.29

Table 3D: Water: base fluid (50:50), velocity- 15m/s

Table 3E: Water: base fluid (50:50), velocity- lOm/s

500 389.6 489.19 20.36 557.63 30.13 589.16 33.87

1000 451.35 539.09 16.28 614.63 26.57 664.76 32.10

1500 513.1 588.99 12.88 671.63 23.60 740.36 30.70

2000 574.85 638.89 10.02 728.63 21.11 815.96 29.55

2500 636.6 688.79 7.58 785.63 18.97 891.56 28.60

10

m/s 3000 698.35 738.69 5.46 842.63 17.12 967.16 27.79

Average 543.975 613.94 11.40 700.13 22.30 778.16 30.09

Table 3F: Water: base fluid (50:50), velocity- 15m/s

In the above tables, V represents velocity and Re represents Reynolds number. From the results presented in the above table, it may be concluded that, as the velocity and Reynolds number increases, the overall heat transfer coefficient decreases. However, it has been also observed that, the overall heat transfer coefficient increases as the weight fraction of the carbon nanotubes increases.

[0051] Corrosion Test:

Corrosion of metals present in an engine cooling systems by conventional coolants such as mixture of water and ethylene glycol is very common. Corrosion may result by an electrochemical or a chemical attack by agents that may be present in the surrounding atmosphere. Corrosion may result in disintegration of the surface and material loss due to either the conversion of the component metal into a less adherent material, or the dissolution of the material into the environment itself. In order to evaluate the anti corrosive properties of the CNTs dispersed base fluid, various tests had been performed. The test performed includes glassware corrosion tests, corrosion of Cast Aluminium Alloys, and cavitation corrosion test.

[0052] a) Glassware corrosion test as per ASTM D 1384: Glassware corrosion test was performed to analyse the corrosion inhibitive properties of the CNTs dispersed base fluid (composition). In this test, the corrosion inhibitive properties of the CNTs dispersed base fluid/ composition was evaluated for metals that may be present in engine cooling systems Viz., copper, solder, brass, cast iron, mild steel and aluminium. The metals disclosed were totally immersed in aerated CNTs dispersed base fluid/composition mixed with corrosive water for 336 hrs (14 days) at 88°C. Based on the weight change incurred by the metals, the corrosion inhibitive properties of the CNTs dispersed base fluid (composition) was evaluated.

Following equation is used to calculate the weight loss incurred by each of the metal:

Final reported Weight loss = (Initial weight -weight at end of test) - (Cleaning blank - Cleaning blank re-cleaned alongside of end of test specimen)

Each of the tables presented below represent the weight loss incurred by each of the metals, upon treating each of the metals with the CNTs dispersed base fluid. The base fluid used in the study is diluted with water in the ratio 80:20 (water: base fluid), 70:30, and, 50:50 and the analysis of the study is provided in Table 4A - 4C respectively.

Table 4A- Water: Base fluid (80:20) with CNTs

Table 4B- Water: Base fluid (70:30) with CNTs

Table 4C: Water: Base fluid (50:50) with CNTs

The values of the corrosion test provided in the above table are well below the standard values prescribed by SAE standard given in the following table. This indicates that, the CNTs dispersed in the base fluid may resist corrosion.

[0053] b) Heat transfer corrosion of cast Aluminium Alloys as per ASTM D4340: Corrosion of Cast Aluminium Alloys is evaluated under high heat transfer conditions using ASTM D 4340 with the base fluid dispersed with CNT. In this test method, a heat flux is established through a cast aluminium alloy typical of that used for engine cylinder heads under a pressure of 193 kPa. The temperature of the aluminium specimen is maintained at 135°C and the test is continued for 1 week (168 h). The effectiveness of the coolant for preventing corrosion of the aluminium under heat-transfer conditions is evaluated on the basis of the weight change of the test specimen (aluminium).

Heat transfer corrosion is reported in terms of weight loss of the test specimen during the test. The heat-transfer corrosion rate (R) is calculated as follows.

R = (W_b - W_a) X 1000/ A

R = corrosion rate, mg/cm /week, W_b= weight of test specimen before test in grams,

W_a= weight of test specimen after test in grams

B = weight loss of blank in grams,

A = heat-flux surface area inside O-ring, cm .

Table 5

11 Base fluid: water (50:50) + 1.5 0.065 0.05% CNTs

12 Base fluid: water (50:50) + 1.75 0.076

0.025% CNTs

From the test results provided in the above table, it has been observed that the values of the corrosion test are well below the standard values prescribed by SAE standard given in the following table. This indicates that, the CNTs dispersed in the base fluid may resist corrosion of Cast Aluminium Alloys.

[0054] Cavitation erosion test per ASTM G 32 code: This test method is used to estimate the relative resistance of materials (specimen) to cavitation erosion. To determine the resistance to cavitation erosion, standard tests as per ASTM G-32 were conducted at a test frequency of 20 KHz. The cavitation erosion is measured in terms of weigh loss of the materials. In this method, the specimen was immersed in the base fluid dispersed with CNTs of various weight fractions. Further, face of the specimen was subjected to high frequency ultra-sonic waves for a predetermined time period (1 hr) also referred as exposure time. The test cycles were repeated for 10 hours in order to obtain a history of mass loss versus time (exposure time). [0055] FIGs.4A - 4B are graphs illustrating variance in cumulative weight loss within an exposure time on dispersion of CNT's in a base fluid diluted with water in the ratio 50:50 (water: base fluid) and 80:20 (water : base fluid), to determine the rate of erosion. In the graph, X axis represents exposure time in hours, and Y axis represents cumulative weight loss in mg. From the graph, it has been observed that, the cumulative weight loss of the specimen increases as the exposure time of the specimen increases. It has also been observed that, there is an insignificant change in the weight loss incurred by the specimen, with the dispersion of CNT's in the base fluid. Moreover, upon comparing the graphs 4A and 4B, it has been observed that, cumulative weight loss incurred by the specimen is less when the ratio of water: base fluid is 50:50 as compared to 80:20. It may be construed that, upon increasing the ratio of the base fluid on dilution with water, the cumulative weight loss incurred by the specimen is comparatively less.

Table 6: Cavitation test

It has been observed that, on dispersion of CNTs in the base fluid diluted with water in the ratio 50:50 (water: base fluid), and 80:20(water: base fluid) the rate of erosion is less, as compared to the rate of erosion occurred in the diluted base fluid.

[0056] Although, embodiments have been described with reference to specific example embodiments, it will be evident that various modifications, arrangements of components and changes may be made to these embodiments without departing from the broader spirit and scope of the pointing instrument described herein. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.

[0057] Many alterations and modifications of the present invention will no doubt become apparent to a person of ordinary skill in the art after having read the foregoing description. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. It is to be understood that the description above contains many specifications; these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the personally preferred embodiments of this invention. Thus the scope of the invention should be determined by the appended claims and their legal equivalents rather than by the examples given.

Claims

CLAIMS We claim:

1. A composition comprising:

carbon nanotubes dispersed in a base fluid, wherein the carbon nanotubes are functionalized prior to dispersion of the carbon nanotubes in the base fluid.

2. The composition according to claim 1, wherein the base fluid comprises of ethylene glycol, sebasic acid, tolyltriazole, sodium nitrite, and sodium hydroxide.

3. The composition according to claim 2, wherein the base fluid is composed of 90 - 95% of ethylene glycol.

4. The composition according to claim 2, wherein the base fluid is composed of 2 - 5 % of sebasic acid.

5. The composition according to claim 2, wherein the base fluid is composed of 0.05 - 0.3 % of tolyltriazole.

6. The composition according to claim 2, wherein the base fluid is composed of 1 - 3 % of sodium nitrite.

7. The composition according to claim 2, wherein the base fluid is composed of sodium hydroxide to maintain the pH of the base fluid to 8.5.

8. The composition according to claim 1, wherein the base fluid is a hybrid coolant.

9. The composition according to claim 1, wherein the weight percent of carbon nanotubes is between 0.025 and 0.1 % of the base fluid.

10. The composition according to claim 1, wherein the composition further comprises of a coupling agent to improve the stability of the carbon nanotubes dispersed in the base fluid.

11. The composition according to claim 9, wherein the coupling agent used is gum arabic, wherein the ratio of Gum Arabic and carbon nanotubes is 1: 1.

A method for preparing a composition, the method comprising; subjecting carbon nanotubes to a ball milling process to reduce the length of the carbon nanotubes;

oxidizing the ball milled carbon nanotubes to functionalize the carbon nanotubes; and

dispersing the oxidized carbon nanotubes in a base fluid.

The method according to claim 12, wherein ball milling process is carried out for a time period of 12 hours to 16 hours.

The method according to claim 12, wherein the length of carbon nanotubes is reduced to about 1 micron.

The method according to claim 12, wherein the carbon nanotubes used is multi walled carbon nanotubes.

The method according to claim 12, wherein the carbon nanotubes are refluxed in an acidic medium for a time period of 3 hours - 4 hours to obtain oxidized carbon nanotubes.

17. The method according to claim 16, wherein the acidic medium is a mixture of sulphuric acid and nitric acid in the ratio 4: 1.

18. The method according to claim 12, wherein the base fluid is a mixture of ethylene glycol, sebasic acid, tolyltriazole, sodium nitrite, and sodium hydroxide.

19. The method according to claim 12, the method further comprising addition of coupling agent to the oxidized carbon nanotubes in the ratio 1:1 prior to dispersion of the oxidized carbon nanotubes in the base fluid. The method according to claim 19, wherein the oxidized carbon nanotubes and the coupling agent are mixed in water and sonicated for about 45 minutes.

The method according to claim 19, wherein the coupling agent used is Gum Arabic.