Clogging Phenomena Research Articles

Soil clogging phenomena in constructed wetlands with subsurface flow

The paper presents a short description of soil clogging processes during sewage infiltration as well as a simple theoretical model of sand clogging by suspended solids. The Kozeny-Carman equation was used to investigate the influence of the decreasing porosity due to clogging on the sand permeability. A comparison of the results obtained using the derived theoretical relationships with empirical data showed an acceptable agreement.

Properties of electric arc plasma for metal cutting

The properties of plasmas generated for the air plasma cutting process have been investigated in this study. The plasma arc cutting process employs a plasma torch with a very narrow bore to produce a transferred arc to the workpiece at an average current density of within the bore of the torch. The energy and momentum of the high-velocity plasma jet generated by the plasma torch melts, vaporizes and removes the metal from the region of impingement of the jet. Measurements have been made of the total arc voltage, nozzle voltage, air flow rate and nozzle pressure over a range of arc currents of 40 - 160 A for a nozzle with a bore of 1.5 mm. Using high-resolution digital photography, the radius of the arc at the nozzle exit has been measured over the current range. Photographic observations indicate that an underexpanded supersonic plasma jet emanates from the nozzle. An approximate two-zone arc model has been developed to estimate the arc radius, voltage and pressure of the arc at the nozzle exit as a function of current and the predicted results have been compared with experiments. The study reveals that the nozzle of the plasma torch is heavily clogged because of the presence of an electric arc with a very high current density in the nozzle. The nozzle clogging effect increases the pressure in the chamber upstream of the nozzle as the arc current is increased for a constant mass flow rate of air. The nozzle clogging phenomenon is crucial to generate a plasma jet with the high momentum required to remove material from the molten workpiece and to maintain plasma stability.

Soil clogging phenomena in constructed wetlands with subsurface flow

The paper presents a short description of soil clogging processes during sewage infiltration as well as a simple theoretical model of sand clogging by suspended solids. The Kozeny-Carman equation was used to investigate the influence of the decreasing porosity due to clogging on the sand permeability. A comparison of the results obtained using the derived theoretical relationships with empirical data showed an acceptable agreement.

Non-ideal phenomena in osmotic flow through selective membranes

Several models that account for deviations from ideality of osmotic flow have been developed. These correspond to the boundary layer, cavitation and partial clogging effects with an effectively semi-permeable membrane. The osmotic boundary layer effect is analyzed separately for a low and a high range of osmotic pressures, to cover situations where the Van 't Hoff law does not hold. Predictions of the models are compared to available experimental data of osmotic flow vs. bulk osmotic pressure with good agreement, indicating that the models are feasible. The importance of the osmotic boundary layer effect, independent of the nature of the membrane, and the relevance of cavitation and partial clogging phenomena to the internal structure of real membranes are discussed.

SLF Innterruption by a Gas Circuit Breaker Without Puffer Action

A full size model gas circuit breaker without puffer has been built and tested based on a new arc quenching principle of self-flow generation. The breaker generates the flow around current zero due to the pressure rise in the cylinder by positive utilization of nozzle clogging phenomenon. The test was carried out on BTF and SLF conditions prescribed in IEC standards. The breaker successfully interrupted 40 kA for BTF and SLF respectively at 84 kV. Based on the test results and the theoretical analysis of the self-flow generating behavior, it is remarked that the new arc quenching principle is more effective to get higher fault clearing capability compared with the puffer principle.