FIELD OF THE INVENTION
The present invention relates to synthesis of hybrid carbon nano-materials. More particularly, it relates to thermal conductivity characteristics of hybrid carbon nano-materials dispersed in heat-exchange fluids/engine coolant base fluid for automotive applications. Further, the invention relates to a stable process for producing an improved heat transfer fluid.
BACKGROUND OF THE INVENTION
Nano-fluids are potential heat transfer fluids with enhanced thermophysical properties and heat transfer properties, which can be applied in many devices for better thermal performances. Specific application of nano-fluids are in engine cooling, solar water heating, cooling of electronics, cooling of transformer oil, improving diesel generator efficiency, cooling of heat exchanging devices, improving heat transfer efficiency of chillers, domestic refrigerator-freezers, cooling machines, in nuclear reactor, etc.
Choi et al. have reported a 150 % thermal conductivity enhancement of poly (a-olefin) oil with the addition of MWNT at 1 % volume fraction. Similarly, a 200 % thermal conductivity enhancement for poly (a-olefin) oil containing 0.35 % (v/v) MWNT is reported. An enhancement in thermal conductivity of 12.4 % for CNT-ethylene glycol suspensions at a volume fraction of 1 % is reported. But there is no report on the thermal properties of hybrid carbon nanomaterials dispersed in heat-exchange fluids/engine coolant base fluid.
OBJECTS OF THE INVENTION:
In view of the foregoing limitations inherent in the prior-art, the object of the invention is to synthesized heat-exchange nano fluids/engine coolant that can provide high thermal conductivity even at low volume fraction of less than

0.02% of hybrid carbon nano-materials without the use of surfactants. The prepared heat-exchange fluids/engine coolant nano-fluid should have high stability even at 120°C with no settlement.
SUMMARY OF THE INVENTION
In view of the foregoing shortcomings inherent in the prior-art, the object of the invention is to provide a nanomaterial engine coolant mixture which overcomes the drawbacks inherent in the prior art while offering some additional advantages.
According to the invention the nanomaterial engine coolant mixture is a mixture of hybrid carbon nano-material (HCN) and an engine coolant, the HCN is in proportion of 0.015 volume % of the engine coolant, the engine coolant is in proportion of 70:30 for water: coolant (by weight) respectively. The coolant is a mixture of 95-96 % of ethylene glycol (EG), 2-3 % of Organic Additives (OAT) and 1-2 % of water (all by wt. %). The HCN is obtained by an ultrasonication of 2D Hydrogen Exfoliated Graphene (HEG) and a 1D CNT in deionized water for 30-40 min. followed by stirring for 12-13 hrs. The HCN can be optionally doped with Nitrogen.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWlNG
FIG. 1(a) shows X-ray diffraction pattern of 1D CNT, 2D HEG and CNT-HEG (HCN).
FIGS. 1(b) & 1(c) shows SEM and TEM image of CNT-HEG (HCN) respectively. FIGS. 2(a) - 2(c) shows digital photographs of engine coolant and nanomaterial engine coolant mixture for their comparison in terms of stability, thermal stability and thermal stress.

FIGS. 3(b) & 3(b) shows graphical comparison between the engine coolant and nanomaterial engine coolant mixture in terms of thermal conductivity and specific heat.
DETAILED DESCRIPTION OF THE INVENTION
Various embodiments of the invention provide a nanomaterial engine coolant mixture, the nanomaterial engine coolant mixture comprises a mixture of hybrid carbon nano-material (HCN) and an engine coolant, the HCN being in proportion of 0.015 volume % of the engine coolant, the engine coolant being in proportion of 70:30 for water: coolant (by weight) respectively, the HCN being obtained by an ultrasonication of 2D Hydrogen Exfoliated Graphene (HEG) and a 1D CNT in deionized water for 30-40 min. followed by stirring for 12-13 hrs., the HCN being optionally doped with Nitrogen, the coolant being a mixture of 95-96 % of ethylene glycol (EG), 2-3 % of Organic Additives (OAT) and 1-2 % of water (all by wt. %).
In accordance with an embodiment of the invention Hybrid carbon nano-material (HCN) is prepared by an ultrasonication of 2D Hydrogen Exfoliated Graphene (HEG) and a 1D CNT in deionized water for 30-40 min. followed by stirring for 12-13 hrs.
The 1D CNTs are prepared by decomposing acetylene gas on MmNi3 catalyst particles using Chemical Vapour Deposition (CVD) unit at 750 °C. 1D CNTs are first air oxidised to remove amorphous carbon and then further treated with cone. HN03 acid (for atieast 3 hrs.) washed several times with deionized water, filtered, and dried in vacuum to remove catalyst impurities. Purified 1D CNTs are acid functionalised by using mixture of H2S04:HN03 (3:1) to attach oxygen containing functional groups (-COOH, -C=0, and -OH).
The oxidation treatment promoted by H2S04:HN03 (3:1) invariably depends on acid exposure time; hence, the reflux period of 1D-CNT is varied from 1 to 2 hrs. to induce the formation of functional groups.

This formation of the functional groups in the 1D CNT induces hydrophilicity.
To prepare 2D Hydrogen Exfoliated Graphene (HEG), Hydrogen exfoliation technique is implemented to reduce graphitic oxide (GO) to Graphene. This GO is prepared by Hummer's method.
Further Graphene is functionalised by 0.5 wt % of cationic polymer Polydiallyldimethylammonium chloride (PDDA) to attach positive functional groups at the surface of Graphene.
The HCN can be optionally doped with Nitrogen. The Nitrogen doping is configured to properly disperse the 2D HEG and the 1D CNT. Doping is done on the resultant hybrid mixture of 1D CNTs and 2D HEG i.e. HCN. The Nitrogen doping is done by uniformly wrapping polypyrrole over the surface of HCN followed by pyrolysis at 800 °C under the inert atmosphere of Argon.
Using HCN, a nanomaterial engine coolant mixture is prepared by mixing the HCN with an engine coolant in ambient condition. The HCN is in a proportion of 0.015 volume % of the engine coolant. The engine coolant being in proportion of 70:30 for water: coolant (by weight) respectively.
The coolant used is a mixture of 95-96 % of ethylene glycol (EG), 2-3 % of Organic Additives (OAT) and 1-2 % of water (all by wt. %).
The HCN is characterized by XRD, field emission scanning microscope (FESEM) and transmission electron microscope (TEM).
X-ray diffraction pattern of 1D CNT, 2D HEG and HCN (1DCNT- 2DHEG) are shown in FIG. 1(a). XRD pattern of 1D CNT shows the intense peak at 26.5° corresponding to C (002) plane. This intense peak confirms the crystalline nature of 1D CNT. XRD pattern of 2D HEG shows the broadening from 16° to 36.5°. The broadening in XRD pattern of 2D HEG reveals that the interlayer spacing has increased in 2D HEG compared to graphite. It also suggests the loss of long

range order in HEG. XRD pattern of CNT-HEG (HCN) shows the intense peak at 26.5° due to the presence of crystalline CNT along with broadening from 16° to 36.5° because of the presence of HEG. This XRD pattern confirms the formation of HCN.
The surface morphology of the sample is studied using transmission electron microscopy. FIG. 1(b) shows the SEM image of CNT-HEG (HCN) and confirms the intercalation of CNT between the Graphene sheets. FIG. 1(c) shows the TEM image of CNT-HEG. The high magnified image confirms the presence of CNT and HEG in hybrid composite.
Shown in FIG. 2(a) Digital photographs of (1) engine coolant fluid which is a mixture of 70% water and 30% coolant and (2) nanomaterial engine coolant mixture. The picture (2) is taken after 2 month of synthesis of nanomaterial engine coolant mixture. This shows that the nanomaterial engine coolant mixture is stable after 2 months, which indicates the hybrid carbon nanomaterial suspension is stable.
Further, the thermal stability of nanomaterial engine coolant mixture is studied by heating the nano material engine coolant mixture at different temperatures from 40°C to 120°C. FIG. 2(b) shows the thermal stability photographs of (11) engine coolant and (12-16) nanomaterial engine coolant mixture heated (12) at 40°C, (13) at 60 °C, (14) at 80 °C, (15) at 100 °C, and (16) at 120 °C.
Further, thermal stress study has been carried out by allowing nanomaterial engine coolant mixture to go through heating and cooling cycles. For this study, nanofluid nanomaterial engine coolant mixture is first heated to 40°C and allowed to cool down at room temperature. Once it is reached to room temperature, the same nanomaterial engine coolant mixture is again heated to 60°C and allowed to cool down at room temperature. The procedure is continued till 120°C. Digital photograph has been taken after 4 days, which shows the

suspension is stable following thermal stress study (see FIG. 2(c)). (Ill) is the coolant fluid which is a mixture of 70% water and 30% coolant, (112) and (113) is the nanomaterial engine coolant mixture when heated to 120 deg. C and at 30 deg. C.
In thermal conductivity measurements of nanomaterial engine coolant mixture, the transient hot-wire technique is the most commonly used method. In this study, Hot Disk TPS 2500S based on transient hot-wire technique is used. The thermal conductivity of engine coolant is first measured. All measurement is carried out by varying temperature from 30°C to a maximum of 120°C. The thermal conductivity measurements are done for temperatures ranging from 30›šššš››…œœœœœœœœœ‚‚‚‚□C to 70□›………C (see FIG. 3a). The thermal conductivity enhancement for the temperature range is about 10% - 15%. Further, specific heat of the sample is investigated and the measurements are shown in FIG. 3b.
Advantages
The nanomaterial engine coolant mixture obtained provides high thermal conductivity even at low volume fraction of less than 0.02% without the use of surfactants. The prepared engine coolant mixture has high stability even at 120°C with no settlement.

We Claim:
1. A nanomaterial engine coolant mixture, the nanomaterial engine coolant
mixture comprising:
a hybrid carbon nano-material (HCN) and an engine coolant, the HCN being in proportion of 0.015 volume % of the engine coolant, the engine coolant being in proportion of 70:30 for water : coolant (by weight) respectively, the HCN being obtained by an ultrasonication of 2D Hydrogen Exfoliated Graphene (HEG) and a 1D CNT in deionized water for 30-40 min. followed by stirring for 12-13 hrs., the HCN being optionally doped with Nitrogen, the coolant being a mixture of 95-96 % of ethylene glycol (EG), 2-3 % of Organic Additives (OAT) and 1-2 % of water (all by wt. %).
2. The nanomaterial engine coolant mixture as claimed in claim 1, wherein the 1D CNT is prepared by decomposition of acetylene gas on MmNi3 catalyst particles in CVD unit at 750 deg. C.
3. The nanomaterial engine coolant mixture as claimed in claim 2, wherein the 1D CNT is air oxidised to remove amorphous carbon and further treated with conc. HNO3 acid to remove catalyst impurities.
4. The nanomaterial engine coolant mixture as claimed in claim 3, wherein the 1D CNT is acid functionalised by using mixture of H2S04:HN03 (3:1) to attach oxygen containing functional groups -COOH, -C=O, and -OH.
5. The nanomaterial engine coolant mixture as claimed in claim 1, wherein the 2D Hydrogen Exfoliated Graphene (HEG) is prepared by Hummer's method by reducing graphitic oxide (GO) to Graphene.

6. The nanomaterial engine coolant mixture as claimed in claim 5, wherein the Graphene is functionalised by cationic polymer Polydiallyldimethylammonium chloride (PDDA) to attach positive functional groups at surface of Graphene.
7. The nanomaterial engine coolant mixture as claimed in claim 1, wherein doping is done by uniformly wrapping polypyrrole over surface of HCN followed by pyrolysis at 800 °C under inert atmosphere of Argon.