Silicone tube humidity generator

We describe the model and construction of a two-flow (or divided-flow) humidity generator, developed at LNE-CNAM, that uses mass flow controllers to mix a stream of dry gas with a stream of humid gas saturated at 28 °C. It can generate a wide range of humidity, with mole fractions in the range 0.7 × 10−6 < x < 9000 × 10−6, without using low temperature or high pressure. This range is suitable for calibrating balloon-borne instruments that measure humidity in the stratosphere, where x ~5 × 10−6. The generator’s novel feature is a saturator that comprises 5 m of silicone tubing immersed in water. Water enters the humid gas stream by diffusing through the wall of the tubing until the gas stream flowing through the tubing is saturated. This design provides a simple, low-cost humidity generator with an accuracy that is acceptable for many applications. The key requirement is that the tubing be long enough to ensure saturation, so that the saturator’s output is independent of the dimensions and permeability of the tube. A length of only a few meters was sufficient because the tube was made of silicone; other common polymers have permeabilities that are 1000 times smaller. We verified the model of the transition from unsaturated flow to saturated flow by measuring the humidity while using three tube lengths, two of which were too short for saturation. As a more complete test, we used the generator as a primary device after correcting the calibrations of the mass flow controllers that determined the mixing ratio. At mole fractions 50 × 10−6 < x < 5000 × 10−6, the generator’s output mole fraction xgen agreed to within 1 % with the value xcm measured by a calibrated chilled-mirror hygrometer; in other words, their ratio fell in the range xgen/xcm = 1.00 ± 0.01. At smaller mole fractions, their differences fell in range xgen − xcm = ±1 × 10−6.

Hydrodynamics of Pulsed Fluidized Bed of Ultrafine Powder: Fully Collapsing Fluidized Bed

The processing of fine and ultrafine particles using a fluidized bed is challenging in view of their unpredictable hydrodynamic behavior due to interparticle forces. The use of assisted fluidization techniques in such cases can be effective in improving the bed hydrodynamics. This work investigates the dynamics of pulsed fluidized bed of ultrafine nanosilica subjected to square-wave flow pulsations. The pulse duration used in this study is sufficient to allow the complete collapse of the pulsed fluidized bed between two consecutive flow pulsations. The proposed pulsation strategy is carefully implemented using electronic mass flow controllers with the help of analog output signals from data acquisition system. Given that the different regions of the fluidized bed exhibit varying dynamics, which together contribute to overall bed dynamics, the bed transients in the upper, central, and lower regions of the fluidized bed are monitored using several sensitive pressure transducers located along the height of the bed. The effect of the flow pulsation on the hydrodynamics of the fluidized bed is rigorously characterized. A significant reduction in the minimum fluidization velocity was obtained and an increase in the bed homogeneity was observed due to flow pulsations. The frequency domain analysis of the signals clearly delineated the frequency of the various events occurring during the fluidization.

Investigation of Optimal Dilution Ratio from a Dilution Tunnel Using in Particulate Matter Measurement

Combustion of fuels leads to the formation of gaseous and particulate matter pollutants that have an impact on air quality and the environment. Comparison to the gaseous emissions from stack, measuring of particulate matter (PM) needs extra attention because particles do not behave as a continuum. Dilution tunnels are used with the PM measuring instruments to dilute the hot exhaust gases leaving from the stack. The main focus of this study was to investigate the dilution ratio results obtained from a partial flow dilution tunnel. The partial flow dilution system consists of a porous tube diluter, an ejector diluter and an air heater. The dilution air flow settings into the porous tube diluter and ejector diluter are selected for a wide range of dilution ratios. Two mass flow controllers were used to regulate the flow of dilution air into the diluters. The experiments were conducted at the Renewable Energy Laboratory of the Vrije Universiteit Brussel (VUB).There were a total of fifteen experiments with four flow settings conducted. Dilution ratio (DR) is evaluated based on the ratio of the CO2 (dry) concentration in the raw sample to the diluted sample. The results obtained from the experiments with the partial flow diluters are limited between 34 and 110. The experimental results are also compared with other works and found quite similar

Vapor Delivery Systems for the Study of the Effects of Reformate Gas Impurities in HT-PEM Fuel Cells

The reforming of methanol can be an alternative source of hydrogen for fuel cells because it has many practical advantages over hydrogen, mainly due to the technological limitations related to the storage, supply, and distribution of the latter. However, despite the ease of methanol handling, impurities in the reformate gas produced from methanol steam reforming can affect the performance and durability of fuel cells. In this paper different vapor delivery systems, intended to assist in the study of the effects of some of the impurities, are described and compared with each other. A system based on a pump and electrically heated evaporator was found to be more suitable for the typical flow rates involved in the anode feed of an H3PO4/PBI based HT-PEMFC unit cell assembly. Test stations composed of vapor delivery systems and mass flow controllers for testing the effects of methanol slip, water vapor, CO, and CO2 are also illustrated.

Vapor Delivery Systems for the Study of the Effects of Reformate Gas Impurities in HT-PEM Fuel Cells

The reforming of methanol can be an alternative source of hydrogen for fuel cells, since it has many practical advantages over hydrogen, mainly due to the technological limitations related to the storage, supply and distribution of the latter. However, despite the ease of methanol handling, impurities in the reformate gas, produced from methanol steam reforming can affect the performance and durability of fuel cells. In this paper different vapor delivery systems, intended to assist in the study of the effects of some of the impurities, are described and compared with each other. A system based on a pump and electrically heated evaporator was found to be more suitable for the typical flow rates involved in the anode feed of a H3PO4/PBI-based HT-PEMFC unit cell assembly. Test stations composed of vapor delivery system and mass flow controllers for testing the effects of methanol slip, water vapor, CO and CO2 are also illustrated.