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SUMMARYThe effect of periodic rectangular wall roughness on planar nanochannel flow is investigated by dissipative particle dynamics simulation. The wall protrusion length is varied, and its effect on the flow is examined. Analysis of particle trajectories and average residence time reveals temporary trapping of fluid particles inside the rectangular cavities for a considerable amount of time. This trapping affects the density, velocity, pressure, and temperature distribution inside and close to the cavities. Inside the cavities, low-velocity regions and regions of high density related to high pressure and high temperature are observed. When compared with that of the channel with flat walls case, lower flow velocities, temperatures, and pressures are observed for grooved channels. The reduction of the above quantities is more pronounced as the protrusion length, that is, the roughness characteristic length, decreases. Finally, the relation of friction factor, f , with the flow Reynolds number is discussed. The model predicts fRe D constant in the range 206 Re 6 100. The results of this work are of direct relevance to the design of nanofluidic devices.

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Human fetal thermoregulation, maternal-fetal heat exchange, and the role of the umbilical cord in these processes are not well understood. Ethical and technical limitations have restricted current knowledge to animal studies, that do not reflect human morphology. Here, we present the first 3-dimensional computational model of the human umbilical cord with finite element analysis, aiming to compute the maternal-fetal heat exchange. By modelling both the umbilical vein and the two umbilical arteries, we found that the coiled geometry of the umbilical artery, in comparison with the primarily straight umbilical vein, affects blood flow parameters such as velocity, pressure, temperature, shear strain rate and static entropy. Specifically, by enhancing the heat transfer coefficient, we have shown that the helical structure of the umbilical arteries plays a vital role in the temperature drop of the blood, along the arterial length from the fetal end to the placental end. This suggests the importance of the umbilical cord structure in maternal-fetal heat exchange and fetal heat loss, opening the way for future research with modified models and scenarios, as the basis for early detection of potential heat-transfer related complications, and/or assurance of fetal wellbeing.

Abstract. The current research work presents experiments of an essentially incompressible fluid flow in pipes. The experimental equipment consists of a horizontal pipe including a gate valve, a Venturi meter, a wide angle diffuser, an orifice plate, a 90-degree elbow and pressure tappings. An elbow connects the pipe to a rotameter with further pressure tappings. All pressure tappings connected to manometers held on a vertical panel behind the pipe work and show pressure at various points. The effect of the pipe geometry in the flow pattern is presented. Furthermore head losses are estimated, at specific stream-wise cross-sections, for mass flow rate numbered from 0.056 to 0.411 l/s. The manometers measure and clearly show pressure distribution against a calibrated scale. The diagrams of mass flow rate and head losses are presented in specific crosssections, where geometry changes. All measurements were calibrated and validated in a maximum standard deviation difference of 5%. The head losses decrease as the mass flow rate decreases, for all pipe geometries. In the future the experimental results can be used to verify numerical simulation results.