In an industrial-scale acetylator the gas-admitting side of a rayon staple fiber mat tends to be acetylated sooner than the other sides. To illustrate the mechanism of acetylation, a differential equation has been formulated by considering supply and consumption of a reacting material in the fiber mat. By numerical calculation, we have obtained the following relation between gas velocity G [Kg/m² min], the fiber mat thickness w [Kg/m²] and the difference in acetylated mole fraction by the distance from the gas-admitting sideΔM. ΔM=0.415ρg(w/G)^1.36 where ρ_g is the density of the reactant gas.
Further, by considering the removal of reaction heat from the fiber mat by reactant gas during acetylation, another equation has been deduced, with the following solution: C_f(t_f-t_g)/AK_m(C_pG/C_fw)^m=∑<∞><n=1>(-1)ⁿΓ(m)u^m+n/Γ(m+n+1)=τ_m(μ) where u: C_pGθ/C_sw C_f: Specific heat of fiber mat [Kcal/Kg°C] A: Reactant heat of completely acetylated fiber per Kg cellulose [Kcal/Kg]
K, m, Experimental constant which permits reaction rate R to be expressed in R=Kmθ^m-1 C_p: Specific heat of reactant gas t_f-t_g: Temperature difference between fiber mat and reactant gas [Kcal/Kg°C]
By analyzing this relation from experimental data, we obtained the relation between the real temperature difference (t_f-t_g) and that shown by a thermometer (t_f-t_g)T. The relation is (t_f-t_g)=1.50 (t_f-t_g)^T1.08
Also the relation between the mass velocity of reactant gas theoretically calculated by the real temperature difference, Gth, and the actual mass velocity, G, has been obtained, as follows: Gth/w=0.035 (G/w)^1.36 if it is the removal of the reaction heat; or Gth/w=0.013 (G/w)^1.36 if it is the difference in acetylated mole fraction. Consequently, the relation between the maximum temperature difference of the fiber mat, (t_f-t_g)_M, and G/w is (t_f-t_g)_M =561 (w/G)^1.22

View full abstract

The influence which several factors relating to the make-up of a fiber assembly have on sound absorption characteristics was investigated by measuring the normal incident absorption coefficients of fiber assemblies from 250 to 2, 000c/s at intervals of 1/3 octaves. The results obtained are:
(1) There are two other types of absorption characteristics besides the well-known viscosity resistance type (I). One is a fibrous resonance type (II), of which the absorption characteristics show resonance absorption at low frequency but which, in a high frequency range, belongs to type (1). The other is an intermediate type (III), which is between (I) and (II).
(2) The absorption characteristics of a fiber assembly belong to type (I) if the fibers are arranged parallel to the direction of the propagation of the sound wave. The air in the fiber assembly plays a part in the absorbing action. If the fibers are arranged so as to divide the air space in the assembly into small sections, the value of its absorption coefficient is high.
(3) It is experimentally estabished that the absorbing mechanism of a fiber assembly comes mainly from the frictional action between the surface of fibers and the air in the assembly. Fiber assemblies are equal to one another in their absorption characteristics if the fibers are the same in total surface area, even it they differ in length or fineness.
(4) To increase the absorption coefficient of a fiber assembly in a low frequency range, it is better to increase its thickness than to reduce its porosity. The thickness of a fiber assembly has an effective value which increases the absorption coefficient to a maximum for a certain frequency and a certain porosity degree.
(5) The relation between a certain frequency (f) and a certain effective porosity (P_e), which porosity increases the absorption coefficient at that frequency to a maximum value, is shown as follows: f=K(100-P_e)^-1.3 where K is a constant which is decided by the kind of fiber material, its fineness, the fiber orientation and the thickness of the fiber assembly. If K is obtained experimentally at a certain frequency, the value of P_e for every frequency is calculable by the above equation. There is the most effective porosity (P_me) giving the greatest value among the maximum absorption coefficients in P_e of all frequencies.The larger the total surface area is, the greater P_me is and the lower the frequency is.

View full abstract

The mechanisms of the opening action in the nose part around the lickerin and the action of removing trash and fibers from the lickerin were analyzed, and the effects of the factors affecting these actions were examined.
With a wide nose-lickerin setting, a high lap-feeding rate, a slow lickerin speed or a large tooth angle of the garnet wire, the above-mentioned opening action was low. The lickerin speed varied the centrifugal force and affected the action of removing trash and fibers from the lickerin. Therefore, raising lickerin speed improved the cleaning action, rather than reducing the lap-feeding rate. The tooth angle of the garnet wire, too, had a bearing on the above-mentioned removing action; it is not advisable to increase the tooth angle.

View full abstract

The mode of water absorption by fabrics has been investigated in order to study their absorbency. The influence of the texture and density of fabrics, the degree of the twisting of threads and the blending percentage of synthetic fibers upon the water absorbency of fabrics has been clarified.
1) The relationship between the amount of absorption P and the centrifugal acceleration E is given experimentally by: P=Ae^-lE+Be^-mE+Ce^-nE where A is the amount of absorption in the crevices of weave intersections; B, the amount of absorption in the capillary spaces between individual fibers within a yarn; C, the amount of absorption within fibers themselves when centrifugal acceleration is 0; l, m, n are the the coefficients of easiness of squeezing.
2) The texture and porosity of fabrics influence water absorbency by fabrics.
3) Water absorbency by fabrics decreases with an increase in density.
4) The degree of thread-twisting influenced absorption only slightly within the range of this experiment.
5) Water absorption by fabrics showed a definite tendency to increase with an increase in the blending percentage of synthetic fibers within the range of our experiment.

View full abstract

The influence of the flow resistance of fabrics on their absorption characteristics has been investigated by measuring the flow resistance and the absorption characteristics. To deal with this subject from the point of view of the design and density of fabrics, we wove 13 different kinds of cotton fabrics as samples. The results obtained are as follows:
(1) The relation between flow resistance R_f of fabrics and flow speed V can be given as follows: R_f=A_i+B_iV where A_i and B_i are constants fixed by the design and density of a fabric. In a range of small densities, the value of B_i is nearly zero, while A_i and B_i increase together in value as the density of a fabric increases.
(2) There are two types of absorbing mechanisms, the viscosity resistance type and the resonance type depending on the kinds of fabrics. A fabric is of the viscosity resistance type if its flow resistance depends only on air viscosity in a small range of flow speeds, namely, R_f=A_i.
(3) A fabric is of the viscosity resistance type if it has an air space behind it, provided the relation among frequency f₀, which shows the maximum absorption coefficient, depth d of the air space, and R_f can be given as follows: f₀=(c/4-aR_f)d^-1 where c is the speed of a sound wave and a is a constant fixed by the design of the fabric. This empirical formula means that a fabric has the maximum absorption coefficient when it is placed at a shorter distance than the place where the particle velocity is a maximum.
(4) The relation between maximum absorption coefficient α_∞ and of R_f fabrics woven with the same design is: α_∞=a'+a“ R_f where a' and a” are constants fixed by the design of the fabrics.

View full abstract