Journal of the Textile Machinery Society of Japan

The motion of a slender body falling in still liquid is theoretically analyzed as the simplest model of a fiber in textile technology. Then, the numerically calculated results are compared with the experimental results. The obtained results are as follows:
(1) A slender body, which begins to fall vertically, rotates slowly to have a horizontal posture. It accelerates the horizontal velocity until it inclines to θ=40°-50°. Thereafter, a slender body decelerates its horizontal velocity, and finally approaches to a horizontal posture asymptotically. It does not move horizontally, and falls vertically at the constant speed.
(2) A slender body accelerates its angular velocity until it inclines to θ=10°-20° for calculated results (about 30° for experimental results). However it decelerates its angular velocity thereafter.
(3) The tendency of the falling behaviors of the slender body obtained by the numerical calculation agrees well with experimental results.

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The effective thermal conductivity of a undirectionally oriented fiber assembly heated from a lower surface is measured by an experimental apparatus based on the steady comparative method, and the free convective heat transfer generating in a fiber assembly is estimated experimentally. The following results are obtained:
(1) The effective thermal conductivity of a fiber assembly heated from a lower surface is higher than that heated from a upper surface in the region of the lower volumetric ratio.
(2) The critical modified Rayleigh's number to generate the free convetion is about 0.18 for polyester fibers and 0.19 for cotton fibers. The free convective heat transfer is given by (i) for polyester fibers; N_u; ^*=1.21 R_a; ^*0.113 (R_a; ^*>0.18) N_u; ^*=1 (R_a; ^*≤0.18) (ii) for cotton fibers; N_u*; =1.20 R_a*; 0.112 (R_a*; >0.19) N_u*; =1 (R_a*; ≤0.19) where, N_u*; and R_a*; are the modified Nusselt's number and the modified Rayleigh's number, respectively.

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