Laboratory-Scale Solids Metering Device

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  • LaboratoryScale Solids Metering DeviceJames E. Knap Citation: Review of Scientific Instruments 28, 837 (1957); doi: 10.1063/1.1715740 View online: http://dx.doi.org/10.1063/1.1715740 View Table of Contents: http://scitation.aip.org/content/aip/journal/rsi/28/10?ver=pdfcov Published by the AIP Publishing Articles you may be interested in An automated thermophoretic soot sampling device for laboratory-scale high-pressure flames Rev. Sci. Instrum. 85, 045103 (2014); 10.1063/1.4868970 Pressure measurements in laboratory-scale blast wave flow fields Rev. Sci. Instrum. 78, 125106 (2007); 10.1063/1.2818807 Laboratoryscale setup for anionic polymerization under inert atmosphere Rev. Sci. Instrum. 66, 1090 (1995); 10.1063/1.1146052 Deoxidation of Stainless Steel by Carbon in Laboratory-Scale Vacuum Induction Melting J. Vac. Sci. Technol. 7, S144 (1970); 10.1116/1.1315903 Measuring the Coordinates of a Number of Points in a Complex LaboratoryScale Model Rev. Sci. Instrum. 36, 1156 (1965); 10.1063/1.1719825

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  • NOTES 837

    heater adjusted to hold the sample at 20C, the nitrogen boils away in about an hour.

    This apparatus has advantages of simplicity and ease of changing samples. It will hold samples in a magnet with a gap of only 1t in., the outside diameter of the upper Dewar flask. It is easy to rotate samples in a magnetic field. Good temperature control is readily achieved. If temperature gradients are likely to be created because of Joule heating, Peltier effect, or other effects, they can be reduced by mounting the sample in good thermal contact with a copper block or by filling the sample chamber with a liquid such as isopentane.

    Laboratory-Scale Solids Metering Device JAMES E. KNAP

    Development Department, Union Carbide Chemicals Company, South Charleston, West Virginia

    (Received June 28, 1957)

    TH~ metering of solids into reactions or formula-tIOns on a laboratory scale presents a consider-

    able problem. Several devices have been reportedl- 3 for batch or continuous injection of solids into glass equip-ment. Figures 1 and 2 show construction and assembly of an improved screw type meter developed in this Laboratory.

    This device has several advantages over previous small solids feeders: (a) either continuous or intermit-tent operation is possible; (b) attachment to the reac-tior: vessel is accomplished with spherical glass fittings whIch do not require meticulous aligning as do standard-taper joints; (c) strength and smoothness of operation are obtained with a metal screw and two bearings. This equipment has been effectively used with solids of widely different properties, e.g., sulfur, aluminum chloride, sodium bromide.

    The metering equipment was made from a !-in. wood auger and standard Pyrex glassware (Fig. 1). The cutoff auger was extended by welding on quarter-inch rods to allow bearings to be used at each end of the equipment.

    FIG. 2. Manual metering of solids to a chemical reaction.

    The bearings were made of glass tubing inserted in bored rubber stoppers which in turn were fitted into 19/38-standard-taper ground glass joints. The bearing at the drive-feed end of the conveyor was sealed to the shaft by a sleeve of rubber tubing while the bearing at the delivery end was a sealed glass tube. The seals prevented leakage of the purge gas and entry of moist air into the system. The auger was slightly oversize for 1S-mm Pyrex tubing, but the two pieces were ground into fit by turning the auger in the tube in the presence of carborundum grinding compound and water. The feed and delivery fittings are one-inch Pyrex tubing which adapt to the feed hopper and reaction vessel via 3S/25-spherical ground glass joints.

    The equipment is shown in operation in Fig. 2. The conveyor may be driven manually or by a friction or low-tension pulley drive. The feed hopper was made from a one-liter dropping funnel: a 35/2S-spherical ground-glass joint was attached to connect it to the

    rr-----n y 35/ 25 Spherical joint

    FIG. 1. Solids me-tering device for lab-oratory use.

    Rubber stopper with gloss

    bearing

    Sealed glass beoflng

    ----- 35/25 Spherical jOint

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  • 838 NOTES

    conveyor and the top was cut off to facilitate charging the hopper. An inlet for inert gas was installed on the top of the hopper by inserting a glass tee through a rubber stopper.

    1 A. Stock and O. Guttmann, Rer. deut. chern. Ges. 37, 885 (1904).

    2 E. Swift, Jr. and J. H. Billman, Ind. Eng. Chern. Anal. Ed. 17, 600 (1945).

    3 S. H. Webster and L. M. Dennis, J. Am. Chern. Soc. 55, 3234 (1933).

    Precision Pressure Controller for High-Pressure Systems

    A. GREENVILLE WHITTAKER

    Chemistry Division, Research Department, U. S. Naval Ordnance Test Station, China Lake, California

    (Received November 19, 1956; and in final form, June 24, 1957)

    PRECISE pressure control on a high-pressure com-bustion bomb has been a problem for quite some time. Various methods of attempting to minimize or control pressure buildup during the combustion of small amounts of material were tried. Among these were surge tanks, pop-off valves, solenoid valves actuated by Bourdon tubes equipped with limit switches, and relief valves coupled with high-pressure regulators to prevent pressure undershoot. All these methods have some merit, but in general, they were not sensitive enough and their controlling range was too broad. These shortcomings have been overcome by using a sensitive transducer to sense the pressure changes and amplifying the signal from the transducer so as to operate a solenoid valve. In principle, the electronic part of the apparatus consisted of an oscillator that generated a 2S00-cy carrier voltage that was applied to a transducer. The ac unbalance voltage from the transducer was put through a carrier amplifier, a mixer, a demodulator, and an output amplifier. The amplified unbalance signal was fed to a zero center dc milliammeter. This meter was modified to act as a variable capacitor whose capaci-tance was related to the unbalance signal from the transducer. It was coupled to a capacity-sensitive circuit in such a way that the deflection of the meter pointer actuated the capacity-sensitive circuit; this circuit in turn operated the solenoid attached to the exhaust line of a high pressure system. l The transducer used was a resistance bridge type. However, with slight modifications, other types of resistance transducer or differential transformers can be used as the pressure sensitive element.

    The solenoid valve used had Kel-F seats, was rather small in size, and could be operated at pressures up to 3000 psi. This valve, manufactured by Skinner Electric Valve Division, Norwalk, Connecticut, (Model No. VSO-100) was found to operate very well under all control conditions that were investigated. Because the

    HEX BRASS NUT

    .ALUMINUM

    SLEEVE

    "O"RING NO.1

    COARSE FRlTTEO

    FIG. 1. Orifice and holder.

    valve had a i-in. port, it was necessary to throttle it with suitable size orifice. The construction of the orifice and holder is shown in Fig. 1. The capillary was made from glass capillary tubing 0.6 mm i.d. The tubing was drawn at one end to give an opening of about 0.2 mm i.d., and the other end was flared so that it could be supported on O-ring No.3. This capillary can be made of metal if large orifice openings are necessary.

    Matching the leak rate of the orifice to the system to be controlled was the most important feature for the successful operation of the controller. The matching was achieved empirically by operating the controller with various sized orifices in place. If the orifice was too large or too small the controller would not operate properly. In practice, it was not difficult to find the proper orifice size. Orifices can be calibrated according to their leak rate in psi per sec at a given pressure. Thus an orifice that gave a leak rate of 3 psi/sec at 200 psig was found satisfactory for a rate of gas production of 0.33 I (STP) per second in a system whose volume was about 11. This orifice was found to be usable over the pressure range 200 to 1000 psig when the rate of gas production was approximately proportional to the first power of the pressure. In a region where the rate of gas production was proportional to about the fourth power of the pressure, a given orifice could be used over a pressure range in the neighborhood of only 300 psi.

    In combustion studies there is an unavoidable pres-sure surge associated with ignition. Under such circum-stances the system was pressurized a few pounds below the desired control pressure. The system automatically goes into control at the selected pressure one to 2 sec after the event was started. During the control period the pressure was constant to O.2% for a system in which the rate of gas production was proportional to the first power of the pressure. The on-off cycling period of the solenoid was about 1 sec. Only situations dealing with increasing pressure change have been considered. Systems showing decreasing pressure can be treated in the same way, except that the solenoid and orifice should be placed in the pressurizing line instead of the

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