Showing papers on "Heat pipe published in 2015"

Thermal Design: Heat Sinks, Thermoelectrics, Heat Pipes, Compact Heat Exchangers And Solar Cells

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Heat utilisation technologies: A critical review of heat pipes

Abstract: In electrical or thermal appliances, heat (thermal energy) must either be added into or removed from a system to maintain operational stability. Heat pipes can enhance the heat transfer capabilities without needing a significant temperature gradient between heat sources and heat sinks. The effectiveness of heat pipes is due to the latent heat of phase change of the working fluid within (i) condensation and (ii) evaporation stages. The latent heat of phase change greatly exceeds the sensible heat capacity. Heat pipes may rely on gravity, wicks, centrifugal force or in some cases even a magnetic field to help return condensate flow from the condenser to the evaporator. Wicks in heat pipes are classified into three groups: sintered, groove and mesh types. This review attempts to cover various types of heat pipes such as thermal diodes, variable conductance, pulsating, etc. The application of nanotechnology in heat pipes can be separated into two groups: nanoparticles and nanobubbles, with the latter receiving considerably less attention than the former. The hybridisation of heat pipe technology is also possible and has been discussed along with its future research potential.

Additive manufacturing of heat exchangers: A case study on a multi-layered Ti–6Al–4V oscillating heat pipe

Abstract: Additive manufacturing (AM) allows for layer-by-layer fabrication of complex metallic parts with features typically unobtainable via conventional manufacturing. For heat exchangers, such complex features are desirable for enhancing their heat transfer capability and conformability to specific applications. In this case study, Selective Laser Melting (SLM), a laser-based additive manufacturing process, was utilized to fabricate a compact (5.08 cm × 3.81 cm × 1.58 cm) flat-plate oscillating heat pipe (FP-OHP) with innovative design features, including a Ti–6Al–4V casing and a closed-loop, circular mini-channel (1.53 mm in diameter) consisting of four interconnected layers. Venting holes were integrated to intersect each layer to allow for a unique layer-by-layer, plug-and-pressurize de-powdering procedure. The device channel surface was inspected via Scanning Electron Microscopy (SEM) – and it was found that the channel wall consisted of partially un-melted particles, as well as amorphous melt regions; surface characteristics influential on surface/fluid capillarity and heat transfer. This study also highlights important design and manufacturing concerns encountered during SLM of channel-embedded parts, such as channel surface quality and de-powdering. The Ti–6Al–4V FP-OHP was found to operate successfully with an effective thermal conductivity of approximately 110 W/m K at a power input of 50 W; demonstrating a 400–500% increase relative to solid Ti–6Al–4V.

Oscillating Heat Pipes

Abstract: Introduction.- Fundamentals.- Oscillating Flow and Heat Transfer of Single Phase in Capillary Tubes.- Oscillating Motion and Heat Transfer Mechanics of Oscillating Heat Pipes.- Factors Affecting Oscillating Motion and Heat Transfer in an OHP.- Visualization of Oscillating Heat Pipes.- Nanofluid Oscillating Heat Pipe.- Experiment and Manufacturing Considerations.- Conventional Heat Pipes.

Heat Pipe for Aerospace Applications—An Overview

Abstract: The paper presents an overview of heat pipes, especially those used in different space missions. Historical perspectives, principles of operations, types of heat pipes are discussed. Several factors have contributed to the science and technology of the present state-of-Art heat pipe leading to the development of loop heat pipes, micro and miniature heat pipes and micro loop heat pipes. The paper highlights the advancement of heat pipe for hypersonic cruise vehicles, loop heat pipes with higher conductance in 10 K range, heat pipe switches for temperature control of the spacecraft electronics.

Two-Phase Thermal Ground Planes: Technology Development and Parametric Results

Abstract: Defense Advanced Research Project Agency's (DARPA's) thermal ground plane (TGP) effort was aimed at combining the advantages of vapor chambers or two-dimensional (2D) heat pipes and solid conductors by building thin, high effective thermal conductivity, flat heat pipes out of materials with thermal expansion coefficients that match current electronic devices. In addition to the temperature uniformity and minimal load-driven temperature variations associated with such two phase systems, in their defined parametric space, flat heat pipes are particularly attractive for Department of Defense and commercial systems because they offer a passive, reliable, light-weight, and low-cost path for transferring heat away from high power dissipative components. However, the difference in thermal expansion coefficients between silicon or ceramic microelectronic components and metallic vapor chambers, as well as the need for a planar, chip-size attachment surface for these devices, has limited the use of commercial of the shelf flat heat pipes in this role. The primary TGP goal was to achieve extreme lateral thermal conductivity, in the range of 10 kW/mK–20 kW/mK or approximately 25–50 times higher than copper and 10 times higher than synthetic diamond, with a thickness of 1 mm or less.