Riassunto analitico
Due to the convection of the charge distribution that is present at any solid liquid interface - Electrical Double Layer (EDL) - the flow of liquids within conduits can generate currents and voltages, named Streaming Current and Streaming Potential, respectively. This phenomenon, also called Streaming Electrification, is recognized to potentially give raise to severe consequences in manu fields.
As an example, in petroleum industry the flow of fuels through pipes can lead to explosions of the industrial plant.
Even when working with powders, like in flour industries, the effect of flow electrification of the flour flowing through pipelines can lead to hard explosions. Despite the manu critical consequences of Streaming Electrification, the phenomenon is stil little understood and only few rudimental theoretical models are available. Indeed, the phenomenon seems to be properly taken into account only once the consequences are critical. However, the movement of fluids - flow - is the basis of almost all human activities.
As an example, every day many people are subjected to extracorporeal circulation treatments all around the world, meaning that their blood is circulated in polymeric tubing and no studies have been done yet on the streaming electrifications that these applications imply. In addition, people undergoing such treatments may be subject to a phenomenon whose appearance isn't predictable to date: the Systemic Inflammatory Response Syndrome (SIRS). It is opinion of the writer that a better understanding of the phenomena of streaming current and potential in this kind of environment may, in part, concour in explaining the appearance of SIRS. The aim of the present work is to design and characterize a measuring system and a method able to analyze such quantities.
To this purpose I designed and realized a feedback ammeter for the current measurement in conductive liquids and an ad-hoc instrumentation amplifier able to compensate for the common mode voltage to measure the streaming potential generated by the pulsatile flow of liquid, set by a peristaltic pump - the kind of pump used in extracorporeal circulation.
According to the parameters that characterize the different extracorporeal circulation treatments, parameters investigated during the measures were the liquid velocity, modified by means of the pump, and the pump segment's material, PVC and Silicone have been used.
Results show that both a current and a voltage, up to 70nA and 20mV respectively, can be generated and measured with good repeatability by the measuring system and method proposed.
Moreover, it is possible to notice that both the measured currents and voltages are linearly dependent on the liquid flow velocity and that the analysis conducted on the materials dependence may open the door to a type of classification of materials having the ability to reduce the impact of the streaming electrification in biomedical applications.
Other important parameters like liquid conductivity have been neglected in this first study, as it is supposed that in a biomedical application the blood's conductivity is constant, and are left as future work.
|
