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Optical Measurements for Phase Change Heat Transfer
Published in Josua P. Meyer, Michel De Paepe, The Art of Measuring in the Thermal Sciences, 2020
Jungho Kim, Iztok Golobič, Janez Štrancar
A test section that enables the measurement of heat flux and temperature as well as flow visualization during flow boiling is shown in Figure 11.7. The fluid flowed through a 6-mm-ID/8-mm-OD sapphire tube. The test section was oriented vertically, and the inlet stream and outlet stream could be reversed to achieve both upward flow and downward flow. A polyethylene terephthalate film with Carbon NanoBud conductive layer (Canatu Carbon NanoBud (CNB) Flex Film, 100 W/sq) was attached to the outside of the sapphire tube, so it could be heated. One half of the inner surface was covered with a tape (3M 8911) onto which TSP and a NiCr layer were attached, so heat transfer could be measured. The NiCr was used in this application as an opaque layer only. Germanium/TSP dots were used to measure the temperature at the 3M tape–sapphire interface. The other half of the tube was covered using a similar laminate, but without the TSP/adhesive/NiCr and allowed for flow visualization. Silver paint was used to make electrical connections to copper electrodes on either end of the heaters. The Phantom camera was used to measure the TSP intensity, and a second camera was used to simultaneously visualize the flow.
Curved and zipped graphene nanoribbons
Published in Shih-Yang Lin, Ngoc Thanh Thuy Tran, Sheng-Lin Chang, Wu-Pei Su, Ming-Fa Lin, Structure-and Adatom-Enriched Essential Properties of Graphene Nanoribbons, 2018
Shih-Yang Lin, Ngoc Thanh Thuy Tran, Sheng-Lin Chang, Wu-Pei Su, Ming-Fa Lin
Whether a composite system of carbon nanotube/graphene nanoribbon can exhibit the rich and unique properties deserves a closer discussion. As a result of the rapid advance in chemical analysis techniques, the nanoscale carbon hybrid materials have been successfully synthesized in experimental laboratories, such as, encapsulated C60 in single-walled carbon nanotube [320], a 1D carbon chain inside a multi-walled carbon nanotubes [394], graphene/carbon nanotube hybrid [346,381,383], and carbon-nanobud hybrid [250]. A commensurate graphene nanotube-nanoribbon hybrid system is formed, when an armchair (zigzag) nanotube is adsorbed on a zigzag (armchair) nanoribbon by the weak van der Waals interactions. According to the first-principles calculations [178,179], the geometric, electronic and magnetic properties strongly depend on the interlayer distance, stacking configuration and spin orientation. The structural stability is examined to be dominated by the charge transfer of 2pz orbitals between two sub-systems. The significant interlayer atomic interactions can greatly modify the low-lying band structures, e.g., the creation of subband spacings and band-edge states, and the destruction of spin/state degeneracy. For armchair nanotube/zigzag nanoribbon hybrids, a pair of intersecting linear bands become two separated parabolic ones with a small energy gap sensitive to the nanotube location. The antiferromagnetic configuration is steadier than the ferromagnetic one for all nanotube locations. Furthermore, the spin degeneracy is lifted when the nanotube is close to the zigzag edge. On the other hand, zigzag nanotube/armchair nanoribbon hybrids exhibit the non-magnetic configuration. The low-energy double degeneracy associated with the cylindrical symmetry is broken by the interlayer 2pz -orbital interactions. The predicted essential properties of carbon nanotube-nanoribbon hybrids require further experimental examinations.
Using a modified single-phase model to predict microgravity flow boiling heat transfer in the bubbly flow regime
Published in Experimental Heat Transfer, 2021
Michel T. Lebon, Caleb F. Hammer, Jungho Kim
Heat flux and temperature as well as flow visualization were measured in the test section shown in Figure 1. The fluid flowed through a 6 mm ID/8 mm OD, 120 mm long sapphire tube. The tube is recessed 2.5 mm into Hydlar-Z endcaps on either end and sealed using O-rings. A PET (polyethylene terephthalate) film coated with a transparent Carbon NanoBud conductive layer (Canatu CNB Flex Film, 100 Ω/sq) was attached to the outside of the sapphire tube so it could be resistively heated. Silver paint was used to make electrical connections to copper electrodes on either end of the heaters. Roughly 5 mm of heat shrink was used to insulate each electrical connection, allowing 105 mm of the sapphire tube to be visualized. One half of the inside surface was covered with a PET 3 M tape (3 M 8911) onto which TSP and an opaque NiCr layer were attached so wall temperature could be measured (Figure 2). The other half of the tube was covered using the same 3 M tape but without the TSP/NiCr to allow flow visualization. The opaque layer was included to block the excitation light from reflecting off bubbles within the flow and changing the TSP illumination intensity. Access to opposite sides of the tube allows the acquisition of temporally and spatially synchronized wall temperature and flow visualization videos, enabling direct correlation of flow/bubble phenomena with temperature fluctuations. The TSP was encapsulated between two layers of 5 micron thick adhesive (3 M 82600) to protect it. A submicron thick, opaque germanium layer was deposited using an electron beam evaporator onto the adhesive side of the tape in a 1 mm diameter dot pattern at 10 mm spacing. TSP was painted onto the dots and used to measure the temperature at the 3 M tape/sapphire interface. The temperature profile at the tape-sapphire interface could be interpolated from the dot temperature values spaced 10 mm apart due to the high thermal conductivity of the sapphire. The measured temperature difference between dots during flow boiling tests was small enough to justify the dot spacing used. The temperature gradient between dots never exceeded 0.05°C/mm, while the minimum temperature gradient at the wall-fluid interface was ~5°C/mm. Measured properties of the acrylic adhesive and sapphire properties are summarized in Table 1.