China 
Africa 
Explore chapters and articles related to this topic
Motor Cooling
Published in Wei Tong, Mechanical Design and Manufacturing of Electric Motors, 2022
More recently, a new advanced material called Pyriod® HT pyrolytic graphite has been developed for enhancing heat transfer in electronic cooling. With a single crystalline structure and a high purity (99.999%), the thermal conductivity of the material can be as high as 1,700 W/m·K [11.16], which is about four times higher than that of copper and seven times of aluminum (205–250 W/m·K at room temperature). Moreover, this material exhibits four times the ability to sustain tensile load than natural graphite material, nearly five times the flexural load and six times Young’s modulus. The material can work at extremely high temperature, up to 3,300°C. Because of its superior thermal and mechanical properties, Pyriod HT can be used for thermal management applications in a variety of industries including aerospace, defense, electronic, automobile, medical device, and power generation.
Thermal Analysis of Fuel Elements
Published in Neil E. Todreas, Mujid S. Kazimi, Nuclear Systems Volume I, 2021
Neil E. Todreas, Mujid S. Kazimi
In a medium that is isotropic with regard to heat conduction, k is a scalar quantity that depends on the material, temperature and pressure of the medium. In a nonisotropic medium, thermal behavior is different in different directions. Highly oriented crystalline-like materials can be significantly anisotropic. For example, thermally deposited pyrolytic graphite can have a thermal conductivity ratio as high as 200:1 in directions parallel and normal to basal planes. For anisotropic and nonhomogeneous materials, k is a tensor which in Cartesian coordinates is written as k¯¯=(kxxkxykxzkyxkyykyzkzxkzykzz)
Quantum Mechanics of Graphene
Published in Andre U. Sokolnikov, Graphene for Defense and Security, 2017
Synthetically, graphite has been produced from carbonaceous materials at high temperatures and pressure. The process is called HOPG (Highly Oriented Pyrolytic Graphite) which means that pyrolytic graphite is received by thermal decomposition of hydrocarbon gas on a heated substrate. Pressure is also applied in order to improve the quality. The subsequent annealing under compression gives HOPG. The typical temperatures range from 2800°C to 3500°C and pressures are in the range of 4000 to 5000 psi. Pyrolytic graphite (carbon) is a material which is close to graphite that has covalent bonding between the layers as a result of defects in its production. The typical production process includes heating of hydrocarbon almost to its temperature of decomposition and then permitting the graphite to crystallize. The angular misalignment of the crystal is improved by annealing of the graphite at temperature of 3300°C. As a result, we have a specimen about 1 mm long (0.1 μm in c-direction). Graphite in general has a lamellar structure, i.e. a microstructure that is composed of thin, alternating layers of various materials which exist in the form of lamellae. Similar to other layered materials, it consists of stacked planes. The forces within the lateral planes are much stronger than between the planes. Because of this, HOPG cleaves like mica. In an atomic resolution scanning tunneling microscopy there are several typical images: one is a close-packed array where each atom is surrounded by six nearest neighbors. The distance between them is 0.246 nm. The hexagonal rings have the center to center distance of 0.1415 nm (see Fig. 4.6).
Corrosion resistance of pyrolytic graphite in LiCl-KCl-UCl3 molten salt for pyrochemical reprocessing application
Published in Corrosion Engineering, Science and Technology, 2018
B. Madhura, Ch. Jagadeeswara Rao, E. Vetrivendan, S. Ningshen, C. Mallika, U. Kamachi Mudali
Pyrolytic graphite is a highly oriented dense and crystalline form of carbon, obtained from thermal decomposition of hydrocarbons at temperatures above 2473 K. The graphite synthesised by pyrolytic cracking results in a pore-free material with high density (∼2.2 g cm−3) and a high degree of crystalline orientation (anisotropy) [12–15]. Pyrolytic graphite exhibits superior corrosion and oxidation resistances and anisotropy in thermal and electrical properties compared to conventional graphite forms [16]. Nevertheless, the compatibility and corrosion behaviour of the PyG in LiCl-KCl-UCl3 molten salt for the pyrochemical reprocessing application have not been pursued earlier and thus, understanding the degradation mechanism in PyG under such corrosive environment is highly desirable.
Flow Simulations in a Pebble Bed Reactor by a Combined DEM-CFD Approach
Published in Nuclear Science and Engineering, 2018
Sijun Zhang, Xiang Zhao, Zhi Yang
The development of reliable, clean, safe, and affordable energy resources has gained more attention and renewed interest all over the world when the reduction of global climate change has been pursued. As the only large-scale emission-free energy resource, nuclear power has been considered to be a very promising option and has become even more attractive with the reintroduction of the pebble bed reactor (PBR) to this field. A PBR uses pyrolytic graphite pebbles as the neutron moderator and an inert gas such as helium as the coolant. The helium gas is heated at very high temperature and used to drive a turbine to generate electricity. Compared with the traditional light water reactor, the PBR has lower risk and higher thermal efficiency. In a PBR, the pebbles are randomly packed in a cylindrical vessel. Thorough knowledge of the packing structures is essential to understand the fluid flow and heat transfer in a PBR and subsequently assess the safety.
Recent advancement on thermal management strategies in PEM fuel cell stack: a technical assessment from the context of fuel cell electric vehicle application
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2022
Dinesh Kumar Madheswaran, Arunkumar Jayakumar, Edwin Geo Varuvel
In this approach, thermal conductive materials for bipolar plates (BPPs), GDL, and Membrane-Electrode-Assembly (MEA) are used as heat spreaders. Given that, the contact resistance between the BPP and the GDL causes Ohmic polarization, accounting for 10% of the total heat generated (Bahru, Shaari, and Mohamed 2020). Therefore, the thermal conductivity of the material used for PEMFC components is inevitable. Bipolar plates are normally made of graphite, where metals and polymer composites come up as alternates (Wlodarczyk 2019). Pyrolytic graphite sheets are used as BPPs, for being light-weight and possess good thermal conductivity (Wen et al. 2011). Copper BPPs, having exceptional thermal conductivity of 400 W m−1 K−1, is widely employed as heat spreaders (Tetuko et al. 2018) and aluminum is an alternative for heat spreaders for compact stacks, due to its optimal conductivity (200 Wm−1K−1) and density (Garraín and Lechón 2014). Graphene and Carbon Nanotube (CNT), with high thermal conductivity (300–500 Wm−1K−1) is also used as a high-rate heat spreader (Liu et al. 2012). Low-density graphite-based material (600 Wm−1K−1) and pyrolytic graphite (1000 Wm−1K−1) has also been employed (Liao et al. 2017). CNT/Carbon Fiber (CF)/graphite filled polycarbonate (PC) BPP for low-temperature PEMFCs was used by NaNaji et al. (2019). The hybrid PCs demonstrated thermal conductivity of 1.7 W m−1 K−1 is attained for CF and CNT loading nearer to their percolation thresholds ensuring better thermal efficiency.