喷射染色设备上影响染料吸收因素的分析.docxVIP

Analysis of the factors influencing dye uptakeon jet dyeing equipment Introduction An important objective of sample colorations in a textile dyehouse laboratory is to simulate production-scale conditions. While typical laboratory equipment, e.g. a rotating beaker-type machine, is useful for colour matching purposes, a more detailed process analysis in the laboratory might require machines that operate more closely like those in bulk production. One important question in this context is if pilot-scale machines can be used to accurately predict the dye exhaustion of bulk dyeing machines. The influence of the liquor flow rate on the exhaustion rate, initially established on package dyeing machines, has been known for a long time and has been confirmed several times since then, also for other types of dyeing equipment . There are at least three possible factors, which alone or in combination, can explain this sensitivity of the dye-uptake rate. All three factors contribute to a reduced dye supply at the fibre surface, thereby possibly leading to a process in which the ratedetermining step is no longer the diffusion of the dye inside the fibre (film diffusion-controlled process) but the diffusion of the dye from the dyebath to the fibre surface (liquid-diffusion limited). All three factors also gain in importance as the fluid velocity drops. In the first case, it is known that as the fluid velocity drops, a diffusional boundary layer of increasing thickness develops at the substrate surface which reduces masstransfer to the individual fibre. In the second case, the primary cause is a much diminished fluid velocity near the fibre surface compared with the macroscopic average dyebath flow rate. This is caused by flow resistance in the fibre assembly (microscopic depletion) . The resistance can occur, for example, in the intra-yarn pores or at the intersection of yarns in assemblies. This phenomenon is not to be confused with boundary layer effects which, when flow direc