LAMINAR HEAT TRANSFER TO CAVITIES IN HYPERSONIC LOW DENSITY FLOW

Aerogel fiber, with the characteristics of ultra-low density, ultra-high porosity, and high specific surface area, is the most potential candidate for manufacturing wearable thermal insulation material. However, aerogel fibers generally show weak mechanical properties and complex preparation processes. Herein, through firstly preparing a cellulose acetate/polyacrylic acid (CA/PAA) hollow fiber using coaxial wet-spinning followed by injecting the silk fibroin (SF) solution into the hollow fiber, the CA/PAA-wrapped SF aerogel fibers toward textile thermal insulation were successfully constructed after freeze-drying. The sheath (CA/PAA hollow fiber) possesses a multiscale porous structure, including micropores (11.37 ± 4.01 μm), sub-micron pores (217.47 ± 46.16 nm), as well as nanopores on the inner (44.00 ± 21.65 nm) and outer (36.43 ± 17.55 nm) surfaces, which is crucial to the formation of a SF aerogel core. Furthermore, the porous CA/PAA-wrapped SF aerogel fibers have many advantages, such as low density (0.21 g/cm3), high porosity (86%), high strength at break (2.6 ± 0.4 MPa), as well as potential continuous and large-scale production. The delicate structure of multiscale porous sheath and ultra-low-density SF aerogel core synergistically inhibit air circulation and limit convective heat transfer. Meanwhile, the high porosity of aerogel fibers weakens heat transfer and the SF aerogel cellular walls prevent infrared radiation. The results show that the mat composed of these aerogel fibers exhibits excellent thermal insulating properties with a wide working temperature from −20 to 100 °C. Therefore, this SF-based aerogel fiber can be considered as a practical option for high performance thermal insulation.

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Heat Transfer in Circuit Boards with Low-Density Area Occupancy

2019 25th International Workshop on Thermal Investigations of ICs and Systems (THERMINIC) ◽

10.1109/therminic.2019.8923465 ◽

2019 ◽

Author(s):

Ilja Alkov ◽

Michael Jansen ◽

Gunther Andreas Gerhold

Keyword(s):

Heat Transfer ◽

Low Density ◽

Circuit Boards ◽

Density Area ◽

Low Density Area

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Surface pressures and their corrections for the flow past a finite-length plate in supersonic low density flow

Journal of Fluid Mechanics ◽

10.1017/s0022112079001403 ◽

1979 ◽

Vol 95 (1) ◽

pp. 177-187 ◽

Cited By ~ 1

Author(s):

S. L. Gai

Keyword(s):

Experimental Study ◽

Finite Length ◽

Leading Edge ◽

Low Density ◽

Cold Wall ◽

Trailing Edge ◽

Flow Past ◽

Density Flow ◽

Recent Method

An experimental study of the flow past a thin finite length plate in a supersonic low density stream is reported. The paper discusses the corrections that are necessary for surface pressures measured under rarefied conditions. It is shown that the recent method of ‘orifice’ corrections due to Harbour & Bienkowski is versatile and reliable to use for both cold wall and insulated wall measurements. For the conditions of the experiment, the flow over the plate was found to be dominated by both leading-edge and trailing-edge interactions.

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