Numerical simulation of gas-liquid two-phase jet flow in air-bubble generator

Air-bubble generator is the key part of the self-inspiration type swirl flotation machines,whose flow field structure has a great effect on flotation.The multiphase volume of fluid(VOF),standard k-ε turbulent model and the SIMPLE method were chosen to simulate the present model;the first order upwind difference scheme was utilized to perform a discrete solution for momentum equation.The distributing law of the velocity,pressure,turbulent kinetic energy of every section along the flow direction of air-bubble generator was analyzed.The results indicate that the bubbles are heavily broken up in the middle cross section of throat sect and the entrance of diffuser sect along the flow direction,and the turbulent kinetic energy of diffuser sect is larger than the entrance of throat sect and mixing chamber.

Evaluation of Fractionation of Softwood Pulp in a Cylindrical Hydrocyclone

Pulp fiber length characterization is addressed in this article. It is .suggested that the proposed separation index H（L） is a viable index to the fiber fractionation performance for evaluating hydrocyclones. Fractionation of softwood （coniferous wood） bleached chemithermomechanical pulp （BCTMP） fiber was carried out with a cylindrical hydrocyclone. Pulp fiber length characteristics in different streams were examined using the fiber quality analyzer （FQA）, and the cumulative fiber length fraction, the fiber length fraction density function and the separation index H（L） for different streams were obtained. It is found that H（L） is very useful for characterizing the fiber fractionation performance by indicating the separation capacity of hydrocyclone for individual subgroup of fibers in different streams under different operation conditions. Results of H（L） show that there exists a critical fiber length. A higher proportion of fibers longer than the critical fiber length is in the overflow stream, and a higher proportion of fibers shorter than the critical fiber length in the undertow stream. The data obtained from FQA suggest that the split ratio is the most significant parameter for fiber fractionation performance, which is the best when the split ratio is in the range between 0.14 and 0.2. The effect of feed rate on fiber fractionation performance is weak.

Experimental detection of bubble-wall interactions in a vertical gas–liquid flow

Bubble motions and bubble-wall interactions in stagnant liquid were experimentally investigated by high-speed CCD and PIV technique with the main feature parameters such as E?tv?s numbers Eo = 0.98–1.10, Morton number Mo = 3.21 × 10^(-9)and Reynolds numbers Re = 180 ~ 190. The effect of bubble injecting frequency and the distance S between the gas injection nozzle and the wall on the statistical trajectory of bubbles, average velocity distribution of flow field and Reynolds shear stress were studied in detail. It was shown that the combination of bubble injecting frequency and the distance S caused different bubble motion forms and hydrodynamic characteristics.When the normalized initial distance was very little, like S*≈ 1.2(here S*= 2S/d_e, and deis the bubble equivalent diameter), bubbles ascended in a zigzag trajectory with alternant structure of high and low speed flow field around the bubbles, and the distribution of positive and negative Reynolds shear stress looked like a blob. With the increase of distance S*, bubbles' trajectory would tend to be smooth and straight from the zigzag curve. Meanwhile, with the increase of bubble injecting frequency, the camber of bubble trajectory at 20<y<60 mm had a slight increase due to the inhibitory effect from the vertical wall. Under larger spacing, such as S*≈ 3.6, the low-frequency bubbles gradually moved away from the vertical plane wall in a straight trajectory and the high-frequency bubbles gradually moved close to the vertical wall in a similar straight trajectory after an unstable camber motion. Under the circumstances, high-speed fluid was mainly distributed in the region between the wall and the bubbles, while the relative large Reynolds shear stress mainly existed in the region far away from the wall.

Evaluation of Fractionation of Softwood Pulp in a Cylindrical Hydrocyclone

Pulp fiber length characterization is addressed in this article. It is suggested that the proposed separation index H(L) is a viable index to the fiber fractionation performance for evaluating hydrocyclones. Fractionation of softwood (coniferous wood) bleached chemithermomechanical pulp (BCTMP) fiber was carried out with a cylin- drical hydrocyclone. Pulp fiber length characteristics in different streams were examined using the fiber quality analyzer (FQA), and the cumulative fiber length fraction, the fiber length fraction density function and the separa- tion index H(L) for different streams were obtained. It is found that H(L) is very useful for characterizing the fiber fractionation performance by indicating the separation capacity of hydrocyclone for individual subgroup of fibers in different streams under different operation conditions. Results of H(L) show that there exists a critical fiber length. A higher proportion of fibers longer than the critical fiber length is in the overflow stream, and a higher proportion of fibers shorter than the critical fiber length in the underflow stream. The data obtained from FQA suggest that the split ratio is the most significant parameter for fiber fractionation performance, which is the best when the split ratio is in the range between 0.14 and 0.2. The effect of feed rate on fiber fractionation performance is weak.

Highly efficient degradation of emerging contaminants by magnetic CuO@Fe_(x)O_(y) derived from natural mackinawite(FeS) in the presence of peroxymonosulfate

In this study,natural mackinawite (Fe S),a chalcophilic mineral,was utilized to prepare iron/copper bimetallic oxides (Cu^(O)@Fe_(x)O_(y)) by displacement plating and calcination process.Various characterization methods prove that Cu;is successfully coated on the surface of Fe S,which were further oxidized to Cu^(O),Fe_(3)O_(4)and/or Fe_(2)O_(3)during calcination process,respectively.Cu^(O)@Fe_(x)O_(y)performed highly efficient capacity to activate PMS for the degradation of various emerging pollutants including sulfamethoxazole(SMX),carbamazepine (CBZ),bisphenol A (BPA),2,4-dichlorophenol (2,4-DCP) and diclofenac (DCF) in aqueous solution.Complete removal of the above pollutants was observed after 8 min of Cu^(O)@Fe_(x)O_(y)/PMS treatment.Taking SMX as an example,the key parameters including Cu^(O)@Fe_(x)O_(y)dosage,PMS dosage and initial p H were optimized.The results show that the catalytic system can be worked in a wide p H range (3.0-9.0).The quenching experiments and electron spin resonance (ESR) test demonstrated that the main reactive oxygen species in Cu^(O)@Fe_(x)O_(y)/PMS system were hydroxyl radicals (^(·)OH) and sulfate radicals(SO_(4)^(·ˉ)),and SO_(4)^(·ˉ)was the primary reactive species.Besides,the influence of coexisting anions (i.e.,Cl^(ˉ),NO_(3)^(ˉ),HCO_(3)^(ˉ)and H_(2)PO_(4)^(ˉ)) for the degradation of SMX was explored.Cu^(O)@Fe_(x)O_(y)/PMS system can maintain good catalytic activity and reusability in different water bodies and long-term running.This work provided a green strategy to fabricate the efficient catalyst in PMS-based advanced oxidation processes.