Thermal Conductivity of High-Strength Polyethylene Fiber and Applications for Cryogenic Use

Abstract

The local temperature rise of the tape is one of instabilities of the conduction-cooled high temperature superconducting (HTS) coils. To prevent the HTS tape from locally raising a temperature, high thermal conductive fiber reinforced plastic was applied to coil bobbin or spacer for heat drain from HTS tape. The thermal conductivity of ramie fibers increases by increasing orientation of molecular chains with drawing in water, and decreases by chain scission with γ-rays irradiation or by bridge points in molecular chains with vapor-phase-formaldehyde treatments. Thermal conductivity of high strength ultra-high-molecular-weight (UHMW) polyethylene (PE) fiber increases lineally in proportion to tensile modulus and decreases by molecular chain scissions with γ-rays irradiation. This result suggested the contribution of the long extended molecular chains due to high molecular weight on the high thermal conductivity of high strength UHMW PE fiber. Thermal conductivity of high strength UHMW PE fiber reinforced plastics in parallel to fiber direction is proportional to the cross sectional ratio of reinforcement oriented in the conduction direction. Heat drain effect of high strength UHMW PE fiber reinforced plastic from HTS tape is higher than that of glass fiber reinforced plastic (GFRP) and lower than that of aluminum nitride (AlN). In the case of HTS coil, the thermal stability wound on coil bobbin made of high strength UHMW PE fiber reinforced plastic is good as that of AlN, and better than that of GFRP.

Crystalline polymer nanofibers with ultra-high strength and thermal conductivity

“…Both SAED and micro Raman analyses clearly verify the high crystallinity and molecular alignment. Values of k ( T ) from 20 K to 320 K are reported, where k reaches up to 90 W m −1 K −1 at 130 K. This suggests that PENF can be used as an efficient heat transfer material for cryogenic purposes particularly where an electrically insulating material is concurrently desired 46 . At low temperatures, k increases as ~ T 1 , which stems from the one dimensionality of phonon transport and extrinsic scattering (e.g., defects, boundary).…”

Thermal conductivity of highly crystallized polyethylene

“…Knowledge of thermal conductivity is essential for, e.g., technological applications and processing of polymers [11]. Several studies of PE [12][13][14] have concerned the changes in κ of samples modified by uniaxial stretching. This produces PE fibers with highly oriented chains, and κ may increase from ~1 to as much as ~100 W m -1 K -1 because of increased crystallinity and alignment of the polymer chains along the drawing direction [13].…”

Crystalline Polyethylene Nanofibers with the Theoretical Limit of Young's Modulus

“…This small deviation confi rms that the nanofi bers are tightly fi xed at both ends and that they don't slide, lift off from the substrate, or plastically deform. Therefore, the adhesion from the glue and the Van der Waals force between the PE nanofi ber and the silicon substrate validate the fi xed ends approximation made in Equation (2) . In addition, as mentioned in previous reports, the ratio between the suspended length of the nanofi ber and its outer diameter should be at least 16 in order to eliminate the shear deformation of the nanofi bers during the FDS test.…”