Vent Section Research Articles

A finite element analysis of thermoelastic damping in vented MEMS beam resonators

The effect of geometry on thermoelastic damping in micro-beam resonators is evaluated using an eigenvalue formulation and a customized finite element method. The vented clamped–clamped (CC) and clamped-free (CF) beams with square-shaped vents along their centerlines, are both analyzed by the finite element method. The quality factor and the resonant frequency are obtained as functions of various geometrical parameters including the location, number and size of the vents. The numerical results reveal that the addition of vent sections in the clamped end region can significantly increase the quality factor. The maximum improved quality factor as high as 3801 and 2257 times those of the CC and CF solid beams are realized. The methodology presented in this work provides a useful tool in design optimization of micro beam resonators against thermoelastic damping.

Predicting backdrafting and spillage for natural-draft gas combustion appliances: A validation of VENT-II

VENT-II is a computer program designed to provide detailed analysis of natural-draft and induced-draft combustion appliance vent systems (i.e., furnace or water heater). This program is capable of predicting house depressurization thresholds that lead to backdrafting and spillage of combustion appliances; however, validation reports of the program being applied for this purpose are not readily available. The purpose of this article is to assess VENT-II's ability to predict combustion gas spillage events due to house depressurization by comparing VENT-II simulated results with experimental data for four appliance configurations. The results show that VENT-II correctly predicts depressurizations resulting in spillage for natural draft appliances operating in cold and mild outdoor conditions but not for hot conditions. In the latter case, the predicted depressurizations depend on whether the vent section is defined as part of the vent connector or the common vent when setting up the model. Overall, the VENT-II solver requires further investigation before it can be used reliably to predict spillage caused by depressurization over a full year of weather conditions, especially where hot conditions occur.

Diameter effect in the initiation process of combustion in a ram accelerator in subdetonative mode

A large variety of initiation results in a ram accelerator have shown that a series of interactive parameters play a key role, such as the design of the facility, tube diameter, shape of both the projectile and sabot and the choice of the reactive propellant mixture. Two different ram accelerators were used at ISL for this study, namely a 30-mm and a 90-mm-caliber. In addition to the diameter effect, it was observed that the dimension of the sabot must be adapted not only to the caliber of the tube but also to both the launching device and vent section that are located before the ram accelerator tube. For instance, a sensitive mixture yielded a superdetonative mode in the larger tube diameter facility at ISL. Comparative experiments were conducted in these two caliber ram accelerators at ISL. Important transient effects were observed as the projectile enters the tube which could explain the discrepancies between the data derived from similar devices. The aim of the present paper is to provide a series of data that show the effect of the tube diameter on the initiation process of the propellant mixtures that are currently used in this facility. The design of the sabot is also discussed.

Theoretical analysis of the devolatilizing performance of an intermeshing co‐rotating twin‐screw extruder with a type of square‐channel flighted element

AbstractThe local film interfaces in the long vent section of an intermeshing, co‐rotating twin‐screw extruder (ICoTSE) with square‐channel flights (SFs) and the exposure time to the vapor phase were analyzed. A theoretical overall film‐interface geometry factor (OFIGFcal) was calculated from a new devolatilization (DV) model proposed previously by the authors, and the predictions were compared to the experimental results (OFIGFexp) for polystyrene/ethylbenzene (PS/EB). The OFIGF represents a measure of the devolatilization performance of the long vent section. The ratio of the experimental to the predicted apparent film interface areas was 5.5, which demonstrates the enhancing effect of the roughness and bubble‐forming behavior of the film interfaces on DV. The predicted concentrations of EB in the PS melt at the exit of the long vent section agreed well with experimental results.

Modeling of Polymer Devolatilization in a Multi-vent Screw Extruder

Abstract A model for representing polymer devolatilization behavior in a screw extruder with multi-vent sections has been proposed. In this model, an overall film-interface geometry factor (OFIGF) comprised of several local film-interface geometry factors (LFIGF) is used as a measure for the devolatilizing performance of a screw extruder. Moreover, the OFIGF is related to screw geometries and open angles of open areas in vent sections, and dependent on the degree of filling or the flowrate of the fluid and the screw speed. An intermeshing co-rotation twin-screw extruder popularly used was taken as an example to discuss the effect of the OFIGF on its devolatilizing performance. For this purpose, a solution of how to calculate the local film-interface areas and their exposure time in a venthole unfitted zone (VUfZ) and a venthole fitted zone (VFZ) with an open area was presented. Furthermore, several interesting results about how the OFIGF is affected by flowrate, screw speed, lead, and number of tips were predicted and discussed. The results suggested that the devolatilizing performance of the VFZ is lower than that of the VUfZ due to decrease in the surface renewal effect there, and a plot of ln {(wout – w*)/(win – w*)} against (N1/2/Q) in generally used flowrate and screw speed ranges for a given screw geometry does not strictly satisfy a linear relationship due to the filling-degree dependence of the OFIGF.

An Experimental Study on Devolatilizing Performance of a Long Vent Section in a Twin-screw Extruder

The devolatilizing performance of a long vent section in an intermeshing co-rotation twin-screw extruder manufactured by The Japan Steel Works was measured by using an ethylbezene/polystyrene mixture. The experimental data were fitted by using the previous devolatilization models and a new model proposed by the authors. As a result, a plot of ln {(wout-w*)/(win-w*)} against N1/2/Q based on the previous models shows the flow rate dependence. In contrast, a plot of ln {(wout-w*)/(win-w*)}/(LabN1/2/Q) against N based on the new model can be approximated by a linear relationship. This suggests that the effect of the changes in degree of filling, length of filled zone in a vent section as well as the change in viscosity of fluid induced by shear heating on the devolatilizing performance should be taken into account. Hence, the new model is more applicable for analyzing the devolatilizing performance of a twin-screw extruder.

A Devolatilization Model for a Screw Extruder with Multi-vent Sections

A devolatilization model for polymer melt in a multi-vent screw extruder has been proposed. In this model an overall film-interface geometry factor (OFIGF) comprised of local film-interface geometry factors (LFIGFs) is used as a measure of devloatilizing performance of a screw extruder. Moreover, the OFIGF is related to screw geometry, and opening angles of the open areas in vent sections and dependent on degree of filling or flowrate and screw speed. A solution was given how to calculate the film-interface areas and their exposure time in a venthole unfitted zone (VUfZ) without an open area and a venthole fitted zone (VFZ) with an open area for intermeshing co-rotation twin-screw extruders, and the OFIGFs for the two cases mentioned above were predicted under the conditions found in screw geometry and the opening angle of open area. The results suggested that devolatilizing performance of VFZ is lower than that of VUfZ due to the decrease in surface renewal effect, and a plot of ln{(wout-w*)/(win-w*)} against N1/2/Q does not strictly satisfy with a linear relationship in the general range of flowrate and screw speed owing to the dependencies of the OFIGF on them and those dependencies should be further considered for predicting the devolatilizing performance, and designing and scaling-up screw extruders.

Some remarks on volcanic vent evolution during plinian eruptions

The magma mass discharge rate governs the eruption magnitude of plinian eruptions, and depends strongly on conduit geometry. The presence of lithic clasts in pumice deposits results largely from conduit erosion, and the magma discharge rate and the lithic abundance in the resulting deposit are parameters linked by the overall vent widening rate. Many pumice fall deposits have lithic-enriched basal and top sections; pumice flow deposits tend to carry more lithics than the preceding fall layer. Theoretical models of vent evolution for a cylindrical conduit with radius R indicate an R 4 dependency of the magma discharge rate, which would lead to rapidly decreasing lithic abundances from bottom to top in plinian fall deposits, and from fall to flow deposits, contrary to observations. To simulate observed lithic abundance patterns, a model of conduit evolution with a stepped geometry was developed, in which the lower conduit section remains at approximately constant radius, while the upper conduit section widens. The mass discharge rate during an eruption then increases with R 2 top , and predicted lithic abundance patterns agree qualitatively with field data. Field evidence for conduit widening in the upper conduit section only is presented from plinian pumice beds from Nisyros, Greece. The change in eruption style from plinian fall to surge and ash flow is sometimes accompanied by a dramatic change in lithic abundance and lithic type. In these cases, this transition in deposition style is not the result of a gradual increase in mass discharge rate because of overall vent widening, but is caused by catastrophic rupture of the lower vent section during incipient caldera collapse, with resulting changes in magma discharge rates, lithic abundance and possibly water/magma interaction.