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Heat Pipes
Published in Juan Cepeda-Rizo, Jeremiah Gayle, Joshua Ravich, Thermal and Structural Electronic Packaging Analysis for Space and Extreme Environments, 2021
Juan Cepeda-Rizo, Jeremiah Gayle, Joshua Ravich
CSHPs are designed to operate at extremely cold temperatures and like VCHPs can be turned off. The off mechanism happens by trapping the liquid in a separate bottle external to the heat pipe and reintroducing the liquid to turn the heat pipe back on. They can be arranged to work as thermal diodes, so heat travels in one direction and cannot travel back in the opposite direction. They are beneficial for uses on devices like focal plane arrays or cryogenic charged coupled device (CCD) that on occasion require an annealing process, in which the device is heated above around room temperature, then cooled down to cryogenic levels. They are also used when devices require de-icing. Without the ability to turn off the heat pipe, annealing and de-icing from cryogenic temperatures would require the entire radiator to be warmed up to room temperature, wasting a lot of power.
Nanoscale Energy Transport
Published in Klaus D. Sattler, st Century Nanoscience – A Handbook, 2019
Jafar Ghazanfarian, Zahra Shomali, Shiyun Xiong
Metamaterials are tunable manipulated materials with artificial structures, which possess some specific thermal characteristics which cannot be seen in common daily life applications. Some of mostly used thermal metamaterials are as follows: Thermal cloak: Eliminates the thermal gradient in a specific region and molds the flow of heat around a zone.Thermal diode or thermal rectifier: Blocks the flow of heat in one direction. The thermal rectification happens when the heat flows in one direction easier than the opposite direction.Thermal rotator: Changes the direction of temperature gradient in a zone.Thermal concentrator: Maps the heat transfer from a larger zone to a smaller region.Thermal camouflage: Hides the existence of temperature gradient in a region.
Nanoscale simple fluid flows
Published in Zhigang Li, Nanofluidics, 2018
A diode is a device or structure that allows flows in a specific, say, the forward, direction but blocks flows in the backward direction. A diode is a special case of a rectifier, which allows flows in both the forward and the backward directions but with different flow rates. The ratio of the flow rates (or pressure drops) in the two directions is referred to as the diodicity, Di, which characterizes the performance of fluidic rectifiers. Once flows in one of the directions are completely blocked, a rectifier works as a diode. A semiconductor diode permits electron flows, i.e., electric current, in one direction, while blocking electron flows in the opposite direction. In electronics, electronic diodes can be used to control electric currents in desired directions, which are important in the design of various circuits (Sze and Ng, 2007). In thermal systems, if heat flows can be regulated in a unidirectional manner, thermal diodes can be designed (Li et al., 2004).
Positive temperature coefficient of the thermal conductivity above room temperature in a perovskite cobaltite
Published in Science and Technology of Advanced Materials, 2022
Atsunori Doi, Satoshi Shimano, Markus Kriener, Akiko Kikkawa, Yasujiro Taguchi, Yoshinori Tokura
Solid state thermal diodes simply consist of two materials which have thermal conductivities with different temperature dependence [2–6]. A schematic illustration is shown in Figure 1(a). Two materials A and B are connected directly in the thermal diode. As shown in Figure 1(b), material A (B) is assumed to have a positive (negative) temperature coefficient of the thermal conductivity, i.e. its thermal conductivity increases (decreases) as the temperature is elevated. When a thermal gradient is applied from material A to material B, the effective thermal conductivity exhibits a relatively large magnitude for this forward direction. On the other hand, when an opposite-direction thermal gradient is applied from material B to material A, the effective thermal conductivity is relatively low for this configuration. Consequently, directional dependence of heat transport emerges in the thermal diode.
Heat transfer and fluid flow characteristics in multistaged Tesla valves
Published in Numerical Heat Transfer, Part A: Applications, 2018
Piyush R. Porwal, Scott M. Thompson, D. Keith Walters, Tausif Jamal
Unlike previously employed geometries and features employed in miniature or microchannels for heat transfer enhancement, the current study investigates the potential of a Tesla valve to function as a mini-to-micro-type heat exchanger along with its fluid rectification capabilities. A 10-staged MSTV is numerically examined using 3D CFD to determine relevant trends in heat transfer and pressure drop characteristics. Along with pressure (or fluidic) diodicity, the concept of a thermal diodicity is introduced and utilized for quantifying the thermal diode capability of Tesla valves. Thermal diodes allow preferentially enhanced heat transfer rates depending on flow direction which can be of importance for various applications, especially aerospace. Correlations for MSTV design and performance in terms of Nusselt number, friction factor, pressure diodicity, and thermal diodicity are derived.