Possibility of Remarkable Enhancement of Separation Factor by “Cryogenic-Wall” Thermal Diffusion Column

Abstract

From a view point that the maximum separation factor (αβ)max attainable in total reflux operation of thermal diffusion column depends on temperature difference ΔT between hot Th and cold Tc surfaces in the form of ΔT/T c as where δ (≡r h/r c) is the ratio of hot wire to cold-wall radii, αT the thermal diffusion factor and Z* (≡Z/r c) the normalized column height, remarkable enhancement of separation factor is expected through an adoption of “Cryogenic-Wall” (ex. 77.35K) instead of “Ordinary Cold- wall” (ex. T c = 288.15K). The effect of “Cryogenic-Wall” was analyzed on the basis of approximate formulae involving explicitly design parameters for the column constants. In the case where r c=1.5 cm, Z=150 cm and ΔT=1,000 K, (αβ)max for H2-HT through “Ordinary Cold-wall” TD column is 63.4, while that through “Cryogenic-Wall” TD column is 885, for which ΔT= 2,430K is required in the “Ordinary Cold-wall” TD column and it is impossible for the hot-wire to be at so high temperature because of its melting. The magnitude of enhancement is, however, smaller than that expected from the ratio of ΔT/T c because (1) the value of αT decreases in lower temperature region, and (2) the argument of the exponential function for (αβ)max is not proportional directly to αT·ΔT/T c but to αT·ΔT/[Tbar], where [Tbar] is the reference mean temperature higher than T c. The optimum pressure of “Cryogenic-Wall” TD column is considerably smaller (0.024 MPa for the case above) than that of “Ordinary Cold-wall” TD column (0.103 MPa).