Numerical simulation and experiment of pressure and temperature field for jet impinging ramie fiber separation and degumming

In order to research and develop a new technology of ramie fiber splitting and residual gum removal, ramie fibers treated by alkali scouring with 10.8% residual gum content were selected as the research object. A hydraulic dynamic device was trial-manufactured for investigating the ramie fiber splitting and residual gum removal. According to the trial results, an equipment with a high temperature (373 K) water-jet function was designed and manufactured. Firstly, without consideration of interaction among factors, orthogonal experiments with 3 factors and 3 levels were carried out using the equipment with single nozzle to inspect the influence of jet distance, inlet pressure, and treating time on the residual gum content. The results showed that the optimal combination was 30 mm jet distance, 1.2 MPa inlet pressure, and 16 min treating time, and the jet distance was the primary factor. Under the optimal conditions, residual gum rate was 3.1%. Secondly, under the conditions of the inlet pressure of 1.2 MPa, the outlet diameter of 2.0 mm, and the temperature of 373 K, the distribution of both temperature field and pressure field, and the effective area on ramie fiber surface by the treatment of water-jet impact with single nozzle were simulated using the FLUENT software, with different jet distance of 20, 30, 40 and 50 mm. The numerical simulation results indicated that with 30 mm jet distance, the pressure field on ramie fiber surface was in a range from 0.16 to 0.30 MPa, which was consistent with the outcomes of hydraulic dynamic impact experiment as well as the orthogonal experiments. Thus, it hinted that the jet distance at 30 mm was the most effective condition for the ramie fiber splitting and residual gum removal. Meanwhile, the inlet pressure at 1.2 MPa, the outlet diameter of 2.0 mm, the temperature at 373 K, the jet distance at 30 mm, and the internal space between nozzles ranging from 20, 30 to 40 mm were set to simulate the effective area on ramie fiber surface by the treatment of water-jet impact with double nozzles. The numerical simulation results suggested that the optimal internal space between nozzles was 30 mm, and the pressure field and temperature field on ramie fiber surface were from 0.2 to 0.3 MPa and from 320 to 334 K respectively. Under the optimal conditions, it had a better overlap area and a maximum coverage of pressure field. Eventually, the residual gum content and fiber breaking force were applied to assess the fiber quality after treatment. Based on the single nozzle trial results and the data analyses, jet distance was the most impactful factor. According to the optimal internal space between nozzles of 30 mm, multi tests were carried out with jet distance of 20, 30, 40 and 50 mm and treating time of 12, 14, 16 and 18 min. The results stated that the optimal internal space was 30 mm and the optimal treating time was 16 min, which acquired 3.1% residual gum content and 51.71 cN singe-fiber breaking force. According to the results of numerical simulation and equipment practices, it suggested that the fiber splitting and residual gum removal of the pre-degumming ramie fiber were satisfactorily achieved at one time, without fiber damage ascribed to the flexible property of water within a certain pressure extent. This technology not only can combine the stages of fiber splitting, bleaching, and rinsing in the existing process, but also provides a novel technology for researching and developing equipment for ramie fiber splitting and gum removal.