Experimental assessment on the performance of hot wire anemometry in and around a permeable medium by comparison with Particle Image Velocimetry

The air flow through a test section partially obstructed by a permeable array of wires was measured simultaneously by Hot Wire Anemometry (HWA) and Particle Image Velocimetry. The objective of the study was the assessment of the suitability of HWA for the measurement of flow velocities amid and adjacent to groups of small obstacles. In the present case the obstacles are set in a regular array configuring a highly permeable structure. The probe was placed at three characteristic positions: in the free flow close to the wire array, inside the permeable medium, and at the interface between the permeable structure and the free flow. The measurements were performed with the hot wire operating under natural convection and mixed convection heat transfer, and operating the hot wire at different overheat ratios. Natural convection plumes extending over several permeable volume elements were detected when the hot wire was under natural convection, in some cases reaching velocities up to 60 mm/s downstream from the hot wire position. For low velocity flows, natural convection can be regarded as a flow velocity offset, which becomes negligible at local velocities higher than 0.03 m/s. For higher velocities, in the mixed convection regime, the intrusivity of the HWA probe becomes relevant. Furthermore, the flow in the test section used in the study presents a linear instability that produces velocity fluctuations. Availing ourselves of this phenomenon we verified the dynamic response of the HWA at the lowest velocity where the flow shows periodic fluctuations; for a local mean velocity of (0.131 ± 0.012) m/s the HWA showed a satisfactory dynamic response up to 20 Hz.     

E. coli O157:H7 Desorption by Rhamnolipid Biosurfactant in Water-Unsaturated Porous Media

Animal waste is a valuable resource, which can add organic matter, nitrogen, phosphorous and potassium as well as other nutrients needed for plant growth when it is used in the agricultural field. When applied to an agricultural field, infectious agents or pathogenic organisms in the animal waste are usually retained in the soil. At the same time, surfactants are popularly utilized in pesticide applications to aid pesticide solubility and mobility. Consequently, the retained pathogenic strains might be flushed out of the soil matrices with a possibility of contaminating the groundwater. In this research, we investigated desorption of E. coli O157:H7 pre-deposited in silica sand and its subsequent release and transport in the presence of rhamnolipid biosurfactant in unsaturated laboratory columns. Based on the experimental observations, it was discovered that retained E. coli O157:H7 was released during flushing with rhamnolipid biosurfactant solutions. E. coli O157:H7 release rate coefficient increased both with the increase of rhamnolipid biosurfactant concentration and the increase of water saturation. With the increase of rhamnolipid biosurfactant concentration, the air–water surface tension decreased. With the increase of water saturation, the air–water interfacial area decreased. Both the decreased air–water surface tension and air–water interfacial area favored E. coli O157:H7 release. Increase of E. coli O157:H7 release rate coefficient with the decrease of air–water surface tension was more pronounced for low air–water interfacial area (i.e., high water saturation). Similarly, increase of E. coli O157:H7 release rate coefficient with the decrease of air–water interfacial area was more pronounced for low air–water surface tension (i.e., high rhamnolipid biosurfactant concentration). E. coli O157:H7 retention in unsaturated systems was found to be controlled by the capillary force, which was greatly impacted by water saturation and air–water surface tension. Increase of water saturation and rhamnolipid biosurfactant concentration both contributed to the decrease of the capillary force, resulting in increased E. coli O157:H7 release rate.     

Proposal of a SkilMate Hand and its component technologies for extravehicular activity gloves

In this study, we propose a SkilMate Hand for space extravehicular activity gloves which is equipped with devices of both a power assist and a tactile media. The paper focuses on development of component technologies for constructing a SkilMate Hand, which is proposed for recovering deteriorated haptic sensation in human hands. First, we manufacture a power assist device which compensates the bending moment exerted at a human finger joint utilizing a standing-wave-type ultrasonic motor. We plot the examined characteristics, propose a control policy of the actuators and show some control perforce in Bode plots. Second, we produce a tactile media device which is composed of a vibrotactile sensor element on the outer side and a vibrotactile display element on the inner side at the fingertips of the SkilMate Hand. Piezo-rubber is chosen to be used as a vibrotactile sensing transducer whose sensing performance is examined in the extremely high/low-temperature regions. We locate SkilMate in a wider framework of wearable intelligent machines which assist in affording such working surroundings that they can exhibit their skills in spite of their necessity for wearing special suits typical in hazardous environments. A proposal of a wearable intelligent machine such as that of a SkilMate with its concept has not been made before.