This study explored the feasibility of improving the hydraulic headbox of papermaking machines by studying the flow of wood-pulp suspensions behind a flat plate inserted in a convergent channel. Pulp fiber concentrations of the wake downstream of the plate were investigated by flow visualization and optical measurements. Changes in the time-average and fluctuation of the fiber concentration along the flow direction were examined under typical flow velocity conditions. In addition, the control of the flow characteristics was investigated. The behaviors of the pulp fibers and the wake flow were found to be strongly related to the flow states in the upstream passages partitioned by the plate. The distribution of the fiber concentration was complex because of the formation of a thin water layer on the plate and the generation of Karman’s vortices at the trailing edge of the plate. Compared with the flow in a parallel channel, fluctuations in the fiber concentration decreased in the convergent channel. However, at low flow velocities, the convergent channel has a weak effect on equilibrating the time-averaged fiber concentration.

This paper proposes a novel imaging method using near infrared light of single wavelength to visualize the concentration distribution of salt generated by neutralization reaction of aqueous solutions of acid and alkali in a microfluidic channel. This method is based on the absorption characteristics of the aqueous solutions at the wavelength of 1520 nm in the ν₁+ν₃ absorption band of water. The wavelength of 1520 nm is an isosbestic point for the aqueous solutions of the acid and alkali with respect to their concentrations while the absorbances of the salt solutions at 1520 nm vary with their salt concentrations. To verify the proposed single-wavelength imaging method, the concentration images of sodium chloride (NaCl) were obtained and analyzed in two cases of the combinations of two liquids flowing into a T-shaped microchannel: (i) water and aqueous solution of NaCl, and (ii) hydrochloric acid and sodium hydroxide. The measured concentrations of NaCl agreed well with the expected distributions of the concentrations and verified the proposed method.

Dragonflies generate three-dimensional flow to gain aerodynamic forces. However, three-dimensional flow in free-flight of dragonfly is not clarified experimentally. In this study, experimental visualization and particle image velocimetry (PIV) analysis using tomography is carried out to clarify experimentally the three-dimensional flow. The flap simulator mimicking flapping motion of dragonfly is used for visualization because reproducible measurement is important for tomography. The flow is visualized with tomography from front and lateral side of the flap simulator. As a result, straight flight of dragonfly generates swift flow in a posterior direction in the center on the direction of wingspan. Moreover, it is confirmed that the flow is drawn to base-side of wings. It is suspected that the flow pulled by the flow in a posterior direction. Therefore, straight flight of dragonfly does not generate the extra flow in the direction of wingspan and generates the swift flow in a posterior direction.