3RD INTERNATIONAL CONGRESS ON TECHNOLOGY - ENGINEERING & SCIENCE - Kuala Lumpur - Malaysia (2017-02-09)

Comparison Of Thermal Characteristic Of Grinded Graphene By Physical Method

The nano-fluid refers to the new concept of pure heat transferring fluids in which the nm sized solid particles of excellent heat conductivity are dispersed stably and, owing to its excellent heat conductive property, it is expected to be a heat exchanging medium for the next generation. [1] The graphene is one of the allotropes of the Carbon (Atomic No. 6 in the periodic table), and it is the 2-dimensional allotrope comprising the hexagonal lattice like the shape of honeycomb in which individual atoms of carbon are linked by the sp2 bond [1]. Lee et al.[5] reported the Young’s modulus of graphene to be 1 TPa, 5-times higher than that of steel, together with its light transmittance to be reduced by 2.3% per its sole layer (= the 97.7% transparency of single layer of the graphene). Besides, the very stable structural and chemical properties of graphene have been reported together with its remarkable thermal conductivity as an excellent heat conductor. [1-4][6][7] This study was designed to examine the physical disintegration of graphene, the excellent heat conductor, by using the planetary ball mill, the simple and convenient means to produce particles arbitrarily. The conditions for the disintegration of graphene were distinguished by the rotation of planetary ball mill (200 rpm, 400 rpm, and 600 rpm) and by the duration of its operation (30 min., 60 min., and 90 min.). The graphene disintegrated respectively according to each combination of above conditions were then used for the preparation of corresponding nano-fluids to examine respective thermal properties. Figure 1 (a) illustrates the results of the PSD measurements obtained from samples of the graphene disintegrated according to each predetermined experimental condition. The measurement of average particle size of the original raw graphene was 1087.2nm. This was reduced to 479.2nm, 412.2nm, and 440.7nm by the disintegration lasted for 30 minutes. The measurements were 328.2nm, 518.7nm, and 715nm after the disintegration continued for 60 minutes. The 90 minutes of the duration of disintegration yielded the measurements of average particle size of 557.2nm, 666.4nm, and 757.5nm. Figure 1 (b) shows the graph of the measurements of thermal conductivities of nano-fluids prepared from each condition. The thermal conductivity of original graphene was higher than that of distilled water but it became lower than that of the disintegrated graphene. The causes laid behind this result were estimated that they could be the coagulation and big particle size of graphene and the irregular dispersion thereof. The highest thermal conductivity was resulted from the condition of 200rpm during 30 min from the sample of the identical condition to that rendered the smallest average particle size of graphene represented in Figure 1 (a). Thereby the inverse proportionality of the average particle size of graphene to the degree of thermal conductivity thereof was identified. By taking the PSD measurements represented in Figure 1 (a) and the measurements of thermal conductivity represented in Figures 1 (b) into account, the thermal conductivity to be increasing inverse proportionally to the size of particles was identified, the well-known relationship between the lower level of particle size corresponding to higher level of thermal conductivity.[8]
Gwi-Nam Kim, Ji-Hye Kim, Won-Jo Park, Sun-Chul Huh