19.2 Material and Specimen Geometry In the current study nano-composites made of Poly(2-vinyl pyridine) (97k) polymer and SiO2 particle is considered. The particles are first treated with two different solutions, Methyl Ethyl Ketone (MEK) and Pyridine (PYR), and their effect on the thermal conductivity of the composites has been investigated. The fabrication process can be obtained elsewhere [9], and here it is presented briefly. First, polystyrene chains are attached to the surface of the spherical silica nanoparticles (diameter of 14 and 50 nm). The functionalized particles are mixed with a monodisperse polystyrene matrix with different volume ratios. Then the mixture is casted in an 8 mm diameter cylindrical mold and let cured in room temperature. Through this process, nano-composites containing of 14 and 50 nm diameters SiO2 and different volume fractions (10, 20, 30, 40, 45 and 50 %) are fabricated. Typical SEM images of the nano-composites made with two different methods are shown in Fig. 19.1, from the figure it is clear that the particles functionalized with Methyl Ethyl Ketone are well dispersed. 19.3 Experimental Method A unidirectional/linear heat transfer apparatus is used to measure the thermal conductivity of the nano-composites described above. The apparatus mainly consists of a heat source, heat sink, two conductive brass rods, and eight thermocouples to monitor the temperature flow through and across the cross section of the specimen. This apparatus is arranged so that, the electric heat source, is directly connected to a brass bar in one end and a heat sink, continuously running tap water, is connected to the other brass bar. The specimen is sandwiched between these two 8 mm diameter brass rods above and below. The sectioned schematic diagram of the experiment set up is shown in Fig. 19.2. Where T1–T8 are the thermocouples to measure the in situ temperatures, HSo is the heat source, HSi is the heat sink and IM is the intermediate module. To insure a unidirectional heat transfer, the entire system is insulated using a Teflon jacket. During the experiment, the temperature is varied by manually adjusting the voltage input into the system. The specimens are tested at three different temperatures, and the effect of temperature on the thermal conductivity is investigated. Using the steady state linear heat equation given in Eq. 19.1, the thermal conductivity of the specimen (Ke) can be calculated from the known thermal conductivity of brass rod, KBrass, and the temperatures measured. Ke ¼KBrass ΔXSpeci ΔXBrass TL T5 TH TL ð19:1Þ whereKBrass is thermal conductivity of the brass, ΔXSpeci is thickness of the specimen; ΔXBrass is the distance between the position of the thermocouple and the tip of the brass conductor, which is in contact with the specimen. TL is the temperature at the lower surface of the specimen, and TH is the temperature at the top surface of the specimen. Fig. 19.1 SEM image of nanocomposites prepared (a) pyridine and (b) methyl ethyl ketone (prepared by Prof. Sanat Kumar group) 152 A. Tessema and A. Kidane
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